PRECIPITATION OF ASPHALTENES,

QUANTIFICATION OF MALTENES, UV AND FTIR

SPECTROSCOPIC STUDIES OF C7 AND

C5 + C7 ASPHALTENES FROM 350OC ATMOSPHERIC

RESIDUUM CRUDES.

BY

ANIGBOGU, IFEOMA VERONICA

PG/M.Sc/08/49193

DEPARTMENT OF PURE AND INDUSTRIAL

CHEMISTRY,

FACULTY OF PHYSICAL SCIENCES

UNIVERSITY OF NIGERIA, NSUKKA.

NOVEMBER, 2011

i

PRECIPITATION OF ASPHALTENES, QUANTIFICATION OF

MALTENES, UV AND FTIR SPECTROSCOPIC STUDIES OF C7 AND

C5 + C7 ASPHALTENES FROM 350

OC ATMOSPHERIC RESIDUUM

CRUDES.

BY

ANIGBOGU, IFEOMA VERONICA

PG/M.Sc/08/49193

DEPARTMENT OF PURE AND INDUSTRIAL CHEMISTRY,

FACULTY OF PHYSICAL SCIENCES

UNIVERSITY OF NIGERIA, NSUKKA.

NOVEMBER, 2011.

ii

CERTIFICATION

Anigbogu, Ifeoma V. a postgraduate student of the Department of Pure and

Industrial Chemistry with registration number, PG/M.Sc/08/49193 has

satisfactorily completed the requirements for the course and research work for

the award of the degree of Master of Sciecne (M.Sc) in Fossil Fuel (Petroleum

and Coal) Chemistry. This research project has been approved for the

Department of Pure and Industrial Chemistry, Faculty of Physical Sciences,

University of Nigeria, Nsukka.

By

____________________ ____________________

Prof. C.A. Nwadinigwe Dr. P.A. Obuasi

Project Supervisor Head of Department

iii

DEDICATION

I dedicate this work firstly, to the saviour of my life, Jesus Christ, whom by His

grace, favour and help kept me alive after the terrible sickness that befell me,

and helped me to be able to complete this programme. Even when the going was

tough, he encouraged me and taught me that only the tough gets going.

Secondly, I dedicate this work to my beloved husband Mr. Emmanuel

Anigbogu, who has always been a source of great support and inspiration all

through the cause of this programme.

iv

ACKNOWLEDGEMENTS

I wish to acknowledge the assistance of some individuals who have contributed

to the success of this work. First and foremost, my appreciation goes to my

project supervior Prof. C.A. Nwadinigwe whose advice and helpful suggestion

and support have directed the progress of this programme especially this project

work from its insception to the conclusion. His instructions, criticisms and

contributions greatly improved this work both in scope and in quality. My

appreciation also goes to my Head of Department Dr. P.A. Obuasi.

I will ever remain grateful to my beloved husband, who is God’s gift to me. God

will not disappoint us in Jesus name. I appreaciate my father Mwogeoffery

Ugwu (Rtd), my sliblings, Obinna Ugwu, Mrs. Ngene Chizoba, Mr. Valentime

Ugwu and Ejike for their prayers.

My special thanks go to the senior laboratory technician Mr. Cliford Ezeugwu

(Food Chemistry Department), Mr. Uba and Mr. Menakaya (Laboratory

Attendants), Dr. Parka E. Joshua (Biochemistry Department), who were

instrumental to the success of this work. Also to my special friends. Mrs. Ngozi

Alumona, Obiageli Egbu, Amara Chukwuneke, Mr. Emmanuel Okon, Mr. Alifa

David, Ikenna, Adika, C.C., Madam Gloria, Mr. Oformater, Mrs. Vivian

Okonkwo and others. I say thank you. I have learnt so much from you all

collectively and individually.

I will not forget Jesus Reigns Catholic Charismatic Renewal UNN, a place

where I encountered God as God. I express my thanks to the members of the

singing ministry. I express my gratitude to all my roommates in 330 Odili (PG)

Hall, You all have been like sisters to me.

Lastly my special appreaciation goes to my Darling friend and sister Dr. to be

Miss Phidelia Waziri who with perseverance carefully typed my work.

ANIGBOGU IFEOMA VERONICA

v

TABLE OF CONTENTS

Approval page - - - - - - - - - - i

Certification - - - - - - - - - - ii

Dedication - - - - - - - - - - iii

Acknowledgements - - - - - - - - - iv

Abstract - - - - - - - - - - v

Table of contents - - - - - - - - - vi

List of figures - - - - - - - - - - x

List of tables - - - - - - - - - - xi

Chapter one

1.0 Introduction - - - - - - - - - 1

1.1 Background of the study - - - - - - - 1

1.1.1 Types of crude oil - - - - - - - - 1

1.1.2 Fractions of crude oil - - - - - - - - 2

1.2 Origin of asphaltene from petroleum/crude oil - - - - 5

1.3 Statement of the Asphaltenes/Resins problem - - - - - 8

1.4 Aims and objectives - - - - - - - - 10

1.5 Scope of the study - - - - - - - - 12

CHAPTER TWO

2.0 Literature review - - - - - - - - 13

2.1 Occurrence and nature of asphaltenes and resins - - - - 15

vi

2.2 Composition of asphaltenes and resins - - - - - 17

2.3 Structure and chemistry of asphaltenes and other heavy organic deposits - 22

2.4 Asphaltene chemical structure under pyrolysis condition - - - 26

2.5 Molecular weight of asphaltene particles - - - - - 29

2.6 Influence of resins constituents on asphaltene constituent - - - 33

2.7 Causes of asphaltene problem, asphaltene self-association

and micelle / colloid concept. - - - - - - - 36

2.8 Economic effect and relevance / significance of asphaltene precipitation - 42

2.9 Prevention and remedies of asphaltene precipitation - - - - 43

CHAPTER THREE

3.0 Materials and Methods (Methodology) - - - - - 47

3.1 Experimental Methods - - - - - - - 47

3.2 Materials and Methods - - - - - - - 47

3.3 Distillation of Each of the Three Crudes - - - - - 49

3.4 Precipitation of Asphaltene, Purification of Asphaltenes and Various Analysis Carried

out on the Pure Asphaltenes Precipitate - - - - - 50

3.4.1 Precipitation of Asphaltenes - - - - - - - 50

3.4.2 Purification of Extracted Asphaltenes - - - - - 51

3.5 Fractionation of Maltenes - - - - - - - 53

3.5.1 Activation of the Silica Gel - - - - - - - 53

3.5.2 Chromatography Procesure - - - - - - - 53

vii

3.5.3 Extraction of Each of the Saturates, Aromatics and Resins (Maltene) from

their various Effluents - - - - - - - - 55

3.6 Physical Methods for Analysing the Asphaltene Fraction - - - 56

3.6.1 Infrared Spectra Analysis - - - - - - - 56

3.6.2 The Ultraviolet Visible Spectra Analysis - - - - - 56

3.6.3 UV – Specroscopic Procedure - - - - - - 57

3.6.4 Melting Point Analysis - - - - - - - 57

CHAPTER FOUR

4.0 Results and Discussions - - - - - - - 60

4.1 Results of Bonny Export, Bodo and Mogho Crude oils before and after Distillation at

350OC - - - - - - - - - 60

4.2 Results from Asphaltene Precipitation - - - - - 62

4.3 Comparism of the weight of the Precipitated Asphaltene with Time Using N-heptane

and n-pentane + n- heptanes Mixed Solvent - - - - - 71

4.4 Summary of the results of FTIR Spectrophotometric analysis - - 74

4.5 Summary of the results of UV/Visible Spectrophotometric Analysis- - 76

4.6 Results of the chemical physical properties - - - - - 78

4.7 Result of the effect of resins on asphaltene precipitation - - - 81

viii

CHAPTER FIVE

Conclusion - - - - - - - - - - 83

New knowledge arising from this work - - - - - - 85

Literature Citied - - - - - - - - - 86

Appendix - - - - - - - - - - 96

ix

LIST OF TABLES

2.2a Elemental Composition of Asphaltenes from World Sources [23] - 19

2.2b Elemental Composition of Various Asphaltenes[23] - - - 20

2.2c Elemental Composition of Petroleum Resins[10] - - - 21

2.5a Total nC5, nC7, nC9 Asphaltene Content of Crude oil [75] - - 32

2.9 Optimizing Asphaltene – Dispersant Dosage in the Adiatic Sea.[8] - 46

4.1 Physical properties of Bonny Export, Bodo and Mogho crude oils before and after

distillation at 350OC - - - - - - - 60

4.2a Composition of Asphaltenes in Bonny Export Crude- - - 62

4.2b Physical Properties of Maltenes (filtrate) from Bonny Export Crude- 63

4.3a Composition of the Asphaltenes from Bodo Crude - - - 65

4.3b Physical Properties of Maltenes from Bodo Crude - - - 66

4.4a Composition of the Asphaltenes in Mogho Crude - - - 68

4.4b Physical properties of Maltenes from Mogho Crude - - - 69

4.5a Summary of the results of IR Analysis of Asphaltenes from Single Solvent

System (Sample A) - - - - - - - 74

4.5a Summary of the results of IR Analysis of Asphaltenes from Mixed Solvent

System (Sample B) - - - - - - - 75

4.6 UV Spectra of the Asphaltene Fractions of Crude Oil - - 76

x

4.7 Chemical and Physical Properties of Crude oils as obtained

from n-heptane single solvent (80mins) - - - - - 78

4.8 Effect of resins on asphaltene precipitation - - - - - 81

xi

LIST OF FIGURES

1: Classification Procedure for Heavy Crude oil Fractions

(>350° boiling Fraction) [3,8,13] - - - - - 3

1.2a: Examples of Some organic Compounds in Petroleum (organic origin of

Petroleum)[26] - - - - - - - - 5

1.2b: Continued Buried of Sediment and Rock layers in Subsiding Basin - 7

1.3a: Asphaltene Precipitation and Deposition in Subsec Flowing, near Wellbore

Region, Seperators e.t.c.[8] - - - - - - 9

1.3b Deposition and plugging of petroleum flow conduits due to streaming

potential generated and sticking of asphaltene particules to the walls [34] 10

2.0(a) Simplified Petroleum Fractionation Method[9] - - - 13

2.0b Continum of Aromatics, Resins and Asphaltenes in Petroleum[37] - 14

2.3a Molecular Structure of Asphaltene Proposed for Maya crude (Mexico) by Altamirano, et al IMP Bulletin.[46] - - - - 23

2.3b Molecular Struture of Asphaltene Proposed for 510c Residue of venezuelian

Crude by Carbognani[46] - - - - - - 24

2.3c Resin fraction with two subgroups (i,ii) - - - - 26

2.4a Proposed Asphaltene Struture Model: Condensed Aromatic

Cluster Model[47 - - - - - - - 27

2.4b Proposed Asphaltene Struture based on Bridged Aromatic Model[47] - 28

2.5a The Molecular Weight of this Asphaltene[45] - - - - - 30

xii

2.5b “Long Diagram shows that the Asphaltene include the Crude Oil

Material Highest in Molecular Weight, Polarity, and/or Aromaticity[13] 31

2.6 Schematic Illustration of Archipelago Model of Asphaltene Monomers,

Asphaltene Aggregate in absence of Resins, and Asphaltemic Aggregate in

presence of Resins[64] - - - - - - - 34

2.7a: Formation of Asphaltene Micelles in the Presence of Excess Amounts of

Aromatic Solvent [34] - - - - - - - 40

2.7b: Asphaltene Flocculation due to Excess Amount of Paraffins

in the Solution[34] - - - - - - - 41

2.7c: Steric-colloid Formation of Flocculated Asphaltene with Resins[34] - 42

3.4 Flow chart of the separation scheme of the atmospheric residuum - 52

3.5: Flow Chart of the Seperation Scheme of Maltenes - - - 55

4.2a % Weight of Asphaltenes from Bonny Export Crude (Single Solvent)

with stirring time - - - - - - - 64

4.2b: % Weight of Asphaltenes from Bonny Export Crude (mixed Solvent)

with stirring time - - - - - - - 64

4.3a: % Weight of Asphaltenes from Bodo Crude (Single Solvent)

with stirring time - - - - - - - 67

xiii

4.3b: % Weight of Asphaltenes from Bodo Crude (mixed Solvent system)

with stirring time - - - - - - - 67

4.4a: % Weight of Asphaltenes from Mogho Crude (Single Solvent)

with stirring time - - - - - - - 70

4.4b: % Weight of Asphaltenes from Mogho Crude (mixed Solvent)

with stirring time - - - - - - - 70

4.5: Effect of n – heptane Single Solvent with stirring time for Bonny, Bodo

and Mogho Crudes (mixed graph) - - - - - - 72

4.6: Effect of n – pentane + n - heptane mixed Solvents with stirring time for

Bonny, Bodo and Mogho Crudes (mixed graph)- - - - 73

Bodo and Mogho Crudes (mixed graph) - - - - 80

4.9: Barchart of the Weight of Heavy Fractions of each of the Three Crude Oils

Studied and their Asphaltene content. - - - - 80

4.10: Effects of Resin on Asphaltenes Stabilization. - - - 82

xiv

LIST OF PICTURES

3.1 Weighing balance(Model:Adventurers) - - - - - 49

3.4 Magnetic stirrer - - - - - - - - 50

3.5 Centrifuging apparatus - - - - - - - 50

3.6 Oven/Incubator (Model – mini/50 Genlab limited - - - - 51

3.7 Fractionation setup (column chromatography) - - - - 54

3.8 Water bath with resin + dichloromethane + methanol effluent during evaporation of

Bonny Export maltenes - - - - - - - 56

3.9 UV/Visible Spectrophotometer - - - - - - 57

3.10 Melting point analyser - - - - - - - 57

xv

ABSTRACT

Asphaltenes behave like blood cholesterol in that they deposit on the inner walls of crude oil

transportation pipes thereby narrowing the internal diameters. This poses great dangers,

including pipe bursts. This work aims at removing asphaltenes from light crudes by solvent

precipitation. Three different Nigerian crude oils sourced from Bonny Export and Mogho in

Rivers State and Bodo in Delta State were studied. The crude oils were first distilled at 350OC

to remove the lighter fractions leaving behind a dead crude known as 350OC atmospheric

residuum which consist mainly of high molecular weight saturates, aromatics, resins and

asphaltenes. Asphaltenes were precipitated from each of these atmospheric distillation

residues at different stirring time intervals using n-heptane (single solvent) and n-pentane +

n-heptane (mixed solvent system). The corresponding yields of asphaltenes were determined

for each time duration. It was found that asphaltene precipitation was more in Mogho crude

oil for both n-hepane single solvent and n-pentane + n-heptane mixed solvent system and

least in Bonny Export crude oil. Physical parameters such as FTIR (Fourier transform infra-

red spectroscopy), uv-vis spectroscopy and melting point analysis were used to characterize

the precipitated asphaltenes while the maltenes (i.e. crude oil minus the asphaltenes:

saturates, aromatics, and resins) were fractionated in other to quantify the ratio of aromatics

to saturates and resins to asphaltenes as parameters that control the stability of asphaltenes in

crude oils. From the results, the FTIR data revealled that the asphaltene fraction of crude oils

was made up of both saturated (cyclic aliphatic hydrocarbons etc.) and unsaturated (e.g.

substituted aromatic hydrocarbon etc) parts as supported by our uv/vis spectra on the

asphaltene precipitates. Also the ratio of aromatics to saturates and resins to asphaltenes was

higher in Bonny Export crude and lower in Mogho crude. This indicated that Bonny Export

crude has the lowest asphaltene precipitation risk while Mogho crude had the highest

asphaltene precipitation risk. Addition of resins (extracted from each of the crudes) to a

mixture of 1ml crude + 40ml n-heptane brought about a reduction in asphaltene precipitate

for all the crudes. This indicated that resins solubilize asphaltenes in crude oil. On the basis of

these findings: it was shown that asphaltenes precipitated more using the mixed solvent

system. These findings also showed that asphaltenes precipitate in crude oil, but other

constituents of crude oil especially the resins, influence asphaltene precipitation.

1

CHAPTER ONE

3.0 INTRODUCTION

1.1 BACKGROUND OF THE STUDY

Crude oil is a complex mixture of hydrocarbons and other compounds of varying

molecular weight and polarity. [1] [2] Alternatively crude oil can be said to be a collective term

used to described a hydrocarbon rich mixture of compounds that is usually found as a

subterranean deposit that accumulated over millions of years. The physical and chemical

characteristics of crude oil vary widely from one production field to another and even within the

same field.[3]

1.1.1 TYPES OF CRUDE OILS

(i) LIGHT CRUDE AND VERY LIGHT CRUDE OIL: This is liquid petroleum that has low

density and that flows freely at room temperature. It has low viscosity, low specific gravity

and high API gravity (34 – 39OAPI) due to the presence of a high proportion of light

hydrocarbon fractions. It generally has a low wax content. [4a] very light crude is defined with

API gravity above 40OAPI.[4b]

(ii) MEDIUM CRUDE OIL: This is any liquid petroleum with an API gravity between 22 –

33OAPI.[4b]

(iii) HEAVY CRUDE OIL AND EXTRA HEAVY CRUDE OIL: is any type of crude oil

which does not flow easily. It is refered to as “heavy” because its density or specific gravity

is higher than that of light crude oil. Heavy crude oil is defined as any petroleum with an API

gravity less than 20° [5] Heavy oil is asphaltic and contains asphaltenes and resins. It is

“heavy” (dense and viscous) due to the high ratio of aromatics and napthenes to paraffins and

2

high amounts of NSO’s (Nitrogen, Sulfur, Oxygen and heavy metals). Heavy oil has a higher

percentage of compounds with over 60 carbon atoms and hence a high boiling point and

molecular weight.[5] Heavy oil typically contains very little paraffin and may or may not

contain high levels of asphaltenes. Extra heavy crude oil is defined with API gravity below

10.0° API (i.e. with density greater than 1000kg/m3 or, equivalently, a specific gravity

greater than 1), with a specific gravity of greater than one, extra heavy crude oil is present as

a dense non-aqueous phase liquid when spilled in the environment. [6]

1.1.2 FRACTIONS OF CRUDE OIL

LIGHTER FRACTIONS: The compound and compound classes present in the lighter fractions

of crude, which is typically the fraction that can be recovered by atmospheric distillation, can be

identified by chromatographic and spectroscopic techniques. [7]

HEAVY FRACTION OF CRUDE OIL: This fraction is classified based on solubility, [7] with

maltenes (i.e. saturates, resins and aromatics) being soluble in n-alkanes such as n-heptane [8] and

asphaltenes being soluble in benzene/toluene and insoluble in n-alkanes such as n-heptane or n-

pentane. [8] This heavy fraction is non-distillable and remain in the residue fuels as the distillable

fractions (lighter fractions) are removed.[9]

The addition of a low boiling point alkanes example n-pentane, n-heptane or other

alkanes to crude oils originates the selective precipitation of the most aromatic and highest

molecular weight compounds present in the crude oils.[10][11] The crude oil fractions that

precipitates under such conditions is known as asphaltenes. Being a complex mixture of a wide

array of different molecular types.[12] The amount and characteristics of the asphaltene

constituents in crude oil depends to a greater or lesser extent on the source of the crude oil. [9]

3

Asphaltenes Resins Aromatics Saturate

s

The asphaltene content of crude oil varies from 0.1% to more than 20% depending on the

production field.

A convenient laboratory method has been developed to quantify the asphaltene fraction.

This technique separates “dead” oil that has lost its gaseous components, into saturates,

aromatics, resins and asphaltenes (SARA) depending on their solubility and polarity, (figure 1.)

[8]

Atmospheric residue

Extract with n – heptanes (C7: oil = 30:1)

Maltenes

Adsorbed on silica, elute with Precipitation

n-alkane Toluene Toluene/methanol

Figure 1: Classification procedure for heavy crude oil fractions (>360°C boiling fraction)

[3],[8],[13]

This SARA method is a reasonable first step for categorizing dead oil, it is also a simple

procedure that can be performed in many laboratory because of its simplicity, SARA analysis

has become a widespread means for comparing oils. However, SARA analysis has several

disadvantages that becomes apparent when it is used for purpose beyond its original intent. [8] In

addition laboratory methods varies greatly and the yield of asphaltenes varies with the type of n-

4

alkane (i.e. precipitant) used, liquid precipitant to oil volume ratio, contact time, pressure and

temperature. [8,14,15,16]

A single oil could have two or more SARA results depending on precipitant used. [8] A

commonly accepted view in petroleum industry is that asphaltenes form micelles which are

stabilized by adsorbed resins kept in solution by aromatics. Two key parameters that control the

stability of asphaltene micelles in a crude oil are the ratio of aromatics to saturates and that of

resins to asphaltenes. When these ratios decrease, asphaltene – micelles will flocculate and form

larger aggregates. [17][18] This fraction is well known for its tendency to precipitate during

production and refining operations causing significant losses to the oil industry every year.[19-20]

The asphaltene precipitation depends mainly on the stability of the asphaltenes and

stability depends not only on the properties of the asphaltenes fraction but on how good a solvent

the rest of the oil is for its asphaltene. As recognized by de Boer et al. (1995), light oils with

small amounts of asphaltenes are more likely to cause problems during production than heavy oil

with larger amounts of material in the asphaltene fraction. The heavier oil also contains plenty of

intermediate components that are good asphaltene solvents whereas the light oil may consist

largely of paraffinic materials in which, by definition, asphaltenes have very limited solubility.

Asphaltenes in heavier oils can also cause problems if they are destabilized by mixing with

another crude oil during transportation or by other steps in oil processing.[12,13]

In particular, the characteristics of the disperse phase and the peptizing power of the

resins [18,19] are considered fundamental factors for stabilization of asphaltenes in crude oil.[12]

Crude oil can be classified by chemical compositon, density, viscosity and distillation

characteristics to name a few. [23] The classification system based on composition refers to only

5

the hydrocarbon nature of oils namely paraffin (alkanes) naphthenic or cycloalkanes and

aromatic hydrocarbons namely Sulphur containing compounds, Nitrogen containing compounds,

organomettallic compounds, oxygen containing compounds. [24][25]

1.2 Origin of asphaltene from petroleum/crude oil

Crude oil is a naturally occurring substance consisting of organic compounds in the form

of gas, liquid, or semisolid. The simplest of these compounds is methane.

Figure 1.2(a) Examples of some organic compounds in petroleum

Figure 1.2(a) shows some examples of organic compounds in petroleum, from the

simplest (methane) to the most complex (asphaltene). Asphaltenes are the most complex and

most polar fractions found in crude oil, with more than 36 carbon atoms bound to more than 167

hydrogen atoms, three nitrogen atoms, two oxygen atoms, and two sulphur atoms. [26][27]

Semisolid petroleum is tar, which is dominated by larger complex hydrocarbons and

asphaltenes (Figure 1.2a).[25] Petroleum formation takes place in sedimentary basins, which are

6

areas where the earth crust subsides and sediments accumulate within the resulting depression.

Throughout geologic time, the world oceans have expanded and receded over the earth’s land

surfaces and contributed sediment layers to subsiding sedimentary basins. [26] Development of

stagnant water conditions in some of the expanded oceans caused the bottom waters to be

depleted in oxygen (anoxic), which allowed portion of the decaying plankton to be preserved as

a sediment layer enriched in organic matter. Methane producing microorganisms referred to as

methanogens may thrive under certain favorable condition within the organic rich sediment layer

during its early burial. There microorganisms consume portions of the organic matter as food

source and generate methane as a byproduct. This methane, which is typically the main

hydrocarbon in natural gas, has a distinct neutron deficiency in its carbon nuclei which allows

microbial natural gas to be readily distinguished from methane generated by thermal processes

later in the basin’s subsidence history. The microbial methane may bubble up into the overlying

sediment layers and escape into the ocean waters or atmosphere. If impermeable sediment layers,

called seals, hinder the upward migration of microbial gas, the gas may collect in underlying

porous sediments, called reservoirs.

Burial of the organic-rich rock layer may continue in some subsiding basins to depths of

6,000 to 18,000 feet, exposing the rocks to temperatures of 150 to 350°F (66 to 177°C) for a few

million to tens of billions of years. The organic matter within the organic rich rock layer begins

to cook during this period of heating and portions of it thermally decompose into crude oil and

natural gas. If the original source of the organic matter is plankton (i.e. algae, bacteria e.t.c)

crude oil will be the dorminant petroleum generated with lesser amounts of natural gas

generation.

7

Petroleum has a lower density, than the water that occupies pores, voids and cracks in the

source rock and the overlying rock and sediment layers. This density difference forces the

generated petroleum to migrate upwards by buoyancy until sealed reservoirs in the proper

configurations serve as traps that concentrate and collect the petroleum Figure 1.2(b).

Figure 1.2(b): Continued buried of sediment and rock layers in subsiding basin.

In some basins, petroleum may not encounter a trap and continue migrating upwards into

overlying water or atmosphere as petroleum seeps. Crude oil that migrates to or near the surface

of a basin will lose a considerable amount of its hydrocarbons to evaporation, water washing,

and microbial degradation leaving a residual tar enriched in large complex hydrocarbons and

asphaltenes.[25]

Asphaltene is an important constituents in crude oils. While it is also a major factor that

causes difficulties in oil recovery.[28][29] During the evolution and migration of oil reservoirs, the

8

asphaltenes may be flocculated or precipitated out from crude oils due to the changes of pressure,

temperature and/or the composition of reservoir fluid. [30]

Owing to the alteration of ambient conditions, asphaltenes are liable to be precipitated out

during oil recovery, transportation and post-processing. It can make oil production more arduous

and costly because of the partially plugging in oil well- and pipeline by asphaltenes. It may

further decrease recovery efficiency or even stop oil production due to the shutoff of oil pore

throat or even of the whole oil well. [30]

1.3 STATEMENT OF THE ASPHALTENES/RESINS PROBLEMS

Asphaltenes are best known for the problems they cause as solid deposit that obstruct

flow in the production system.[31] In asphaltene self associate and/or precipitate, the self

association and precipitation is mediated by other solubility fractions particularly the resins.[32]

Hence asphaltenes and their related compounds resins have often been lumped together as

residue in crude oil [8] causing reduction in crude oil production as they can block the pores of

reservoir rocks and can also plug the wellbore tubing, flowlines, separators, pumps, tanks and

other equipment and as a result, causing barrier to the flow of oil as shown schematically below:

[33][34]

9

Figure 1.3(a): Asphaltene precipitation and deposition in subsea flowlines, near wellbore region,

Seperators. e.t.c. [8]

Not only do asphaltenes increase fluid viscosity and density, they also have the potentials

to derail upstream activities, and can also cause downstream disruptions, such as adhering to hot

surfaces in refineries. [8] As mentioned earlier asphaltene precipitation can make oil production

more arduous and costly because of the partially plugging in oil well and pipeline by asphaltene.

It may further decrease recovery efficiency or even stop oil production due to the shut off of oil

pore throat or even of the whole oil well. [30]

At reservoir conditions, the adsorption of asphaltene to mineral surfaces causes a reversal

in wettability of the reservoir from water wet to oil wet and also results in insitu permeability

reductions. Both factors also reduce oil production. Apart from the production loss, the cost of

removing precipitated asphaltene from equipment and flowlines can be very expensive and

significantly alter the economics of a project. Examples of this cases have been reported in the

prinos field, Greece, Hansimessaoud field, Algeria, Ventura Avenue field, California, and other

places throughout the world.[35][33]

10

Furthermore, flocculation of asphaltene was found to reduce the effectiveness of wax

inhibitors, due to the formation of complex asphaltene paraffin solid aggregate. [36] Asphaltene

precipitation can cause major problems during the transportation of bitumen and heavy oil. The

flow of paraffin diluted bitumen through transportation pipelines and processing equipment can

result in deposition of precipitated asphaltenes. This deposition causes higher pumping rates and

can lead to a build up of internal pipeline pressure.[37] as shown in figure 1.3b below.

Figure 1.3b: Deposition and plugging of petroleum flow conduits due to streaming potentail generated and sticking of asphaltene particles to the walls.[34]

Some other examples of problems that arise due to asphaltene flocculation and/or

sedimentation are: Destabilization of asphaltene constituent as a result of the change in medium

during fuel oil-heavy crude oil blending. Ignition delay and poor combustion (often caused by

high content of asphaltene constituent (≥6%) in crude oil) leading to boiler fouling, diminished

heat transfer, stack (particulate) emissions, and corrosion.[9] e.t.c. Thus, with all these and other

problems – that arise as a result of asphaltene precipitation, it can be seen that there is need for

predicting the conditions for asphaltene precipitation.

1.4 AIMS AND OBJECTIVES

The definition of the non-volatile constituents of petroleum (i.e., the asphaltene

constituents, the resin constituents and to some extent, part of the oils fraction, insofar as

11

nonvolatile oils occur in residue and other heavy feed stocks) is an operational aid. It is difficult

to base such separations on chemical or structural features. This is particularly true for the

asphaltene constituents and the resin constituents, for which the separation procedure not only

dictates the yield but can also dictate the quality of the fraction. The technique employed also

dictates whether or not the asphaltene contains coprecipitated resins. This is based on the general

definition that asphaltene constituents are insoluble in n-pentane (or in n-heptane) but resins are

soluble in n-pentane (or n-heptane). To date, little or no effort has been made to study asphaltene

precipitation from crude oil using mixed n-pentane/n-heptane solvent system. Since the use of

different hydrocarbon liquids influences the yield of asphaltenes as well as resins fraction,

The objectives of this present work are as follows:

� To investigate the effect of the pure solvent i.e., n-heptane and also the mixed n-

pentane/n-heptane solvent systems, on asphaltene precipitation.

� To investigate the effect of stirring time on asphaltene precipitate.

� To fractionate the resulting maltenes obtained – after precipitation of asphaltenes and

compare their ratios (i.e. of aromatics to saturates and resins to asphaltenes) with the

extent of precipitation of asphaltene.

� Determine the melting point of the asphaltene precipitate obtained.

� To ascertain the functional group properties (i.e., using IR and UV) of each asphaltene

precipitate, in other to elucidate if the compound is truly asphaltene.

� To determine the role resins play, if any, in asphaltene stability which may help chemists

develop better methods for preventing and remediating asphaltene problems.

12

1.5 Scope of the Study

� Three different crude oil samples will be used for this work.

� The samples will be collected and distilled at 350°C to strip off lighter fractions.

� For each oil sample (3500C atmospheric residuum), asphaltene precipitation reaction will

be carried out, keeping crude oil/solvent constant, varying stirring time and also weighing

asphaltene yield in each case.

� Functional group properties of each asphaltene precipitation will be ascertained (IR and

UV). Also melting point analysis will be carried out on the asphaltenes precipitated.

� To fractionate the resulting maltenes obtained after precipitation of asphaltenes and

compare their ratios (i.e. aromatics to saturates and resins to asphaltenes ) with the extent

of asphaltenes obtained.

13

CHAPTER TWO

2.0 Literature Review

Crude oils can be fractionated and classified in a number of ways. Standard laboratory

methods have been defined for the fractionation of petroleum. The older ASTM D – 2006

method and ASTM D-2007 method are no longer in official use but may still find use in private

laboratories. Indeed, these methods found such wide use that many modifications have been

proposed that are still in use.[32] The overall product of these fractionation methods, which with

the ensuing sub-fractionation, provides the representation of petroleum a composite of the four

fractions (saturates, aromatics, resins and asphaltenes).[9][2] Fig 2.0(a) below:

Figure 2.0 (a): Simplified petroleum fractionation method [9]

Feedstock

n - heptane

Asphaltenes

(insoluble)

Deasphalted oil

percolate through alumina

Asphaltenes

(soluble in toluene)

Resins (pyridine wash)

Aromatic (Toluene wash)

Saturates (n – heptanes

wash)

Carbenes / carboids (insoluble in toluene)

Carbenes

soluble in CS2

Carboids

insoluble in CS2

14

Figure 2.0(a) above shows the four major solubility fractions (i.e. Asphaltenes, resins,

aromatics and saturates). However, the heavier components, asphaltenes and their related

compounds resins have often been lumped together as residue and deemed unworthy of or too

challenging for further examination.[8] Details of the methods used to separate them are markedly

different from the other three fractions as they mainly contain paraffins and naphthene therefore,

are termed non polar. While, aromatics, resins and asphaltenes form a continuum with increasing

polarity, molar mass and heteroatom content (Figure 2.0(b) below.

Figure 2.0(b): Continuum of Aromatics, Resins and Asphaltenes in Petroleum[37]

15

Asphaltenes are the heaviest and most complex fraction in a crude oil sample, which

appears as brown or black solid particles precipitated from a crude oil by using a low boiling –

point alkane e.g. n-pentane or n-heptane. The asphaltene yield decreases as the carbon number of

an alkane increases, while it increases monotonically and finally reaches a plateau if the liquid

precipitant –to – oil volume ratio increases up to 20-40 for n-pentane and n-heptane,

respectively. Some would argue that the n-C7 asphaltenes are the “real” asphaltenes, whereas the

n-C5 material is a mixture of asphaltenes and resins [13]. Resins are primarily good arphaltene

solvents, and are not known to deposit on their own, but they deposit with asphaltenes. [34],[39]

The reasons for the asphaltene deposition (precipitation) can be many factors including

variations of temperature, pressure, composition, flow regime, and wall and electrokinetic

effect.[34] The precipitation is mediated by other solubility fractions. Therefore it is evident that

petroleum is a delicately balanced physical system where the asphaltenes depend on the other

fractions for complete mobility and phase stability. [9]

Considering that the major barrier in a profitable deposition – free oil production scheme

is the presence of asphaltene, this literature review focuses on what follows the role of other

solubility fractions such as aromatics, saturates and resins in crude oil and most expecially the

role resins play if any in solubilizing asphaltene in petroleum fluids.

2.1 Occurrence and Nature of Asphaltenes and Resins

Asphaltenes are molecular substances that are found in crude oil, along with resins,

aromatic hydrocarbons and alkanes (i.e., saturated hydrocarbons). [40],[41]

Asphaltenes are today widely recognised as soluble chemically altered fragments, of

kerogen which migrated out of the source rock for the oil, during oil catagenesis. Asphaltenes

16

had been taught to be held in solution in oil by resins (similar structure and chemistry, but

smaller).[42] but this (i.e. the role that the resin fraction plays in stabilizing asphaltene) has been a

major topic of debate. A contrary view holds that specific interactions between asphaltenes and

resins are not required to explain asphaltene stability,[43] that resins are primarily good solvents

for asphaltenes and that non – vanderwalls forces are primarily responsible for flocculation of

asphaltenes. [44] Another reference [45] state that there is no implied genetic relationship between

asphaltenes and resins, that resins may polymerize to form asphaltenes and asphaltenes may

break down into resins. However, no matter how resins are defined, they still include species that

contribute to the overall solvent quality of the oil with respect to its asphaltenes. [13]

Asphaltenes appear as brown or black solid particles precipitated from crude by using a

low boiling point alkane.[4] The colour of dissolved asphaltene is deep red at very low

concentration in benzene as 0.003% makes the solution distinctly yellowish. The colour of crude

oils and residues is due to the combined effect of neutral resins and asphalteness. [46]. Heavier,

black oil crudes will typically have higher asphaltene content. The black colour of some crude

oils, and residues is related to the presence of asphaltenes which are not properly peptized [46],[47]

In nature, asphaltenes are hypothesized to be formed as a result of oxidation of neutral

resins. On the contrary, the hydrogenation of asphaltic compound – products containing neutral

resins and asphaltene produces heavy hydrocarbon oils, i.e. neutral resins and asphaltenes are

hydrogenated into polycyclic aromatic or hydroaromatic hydrocarbons. They differ, however,

from polycyclic aromatic hydrocarbons by presence of oxygen and sulfur in varied amounts.

On heating above 300-400oc, asphaltenes are not melted but decompose leaving a

carbonaceous residue [9] (or carbon and volatile products).[46] While the resin fraction becomes

17

quite fluid on heating but often show pronounced brittleness when cold. Being a polar molecule,

asphaltenes adsorb to formation surfaces, especially clay. They can oil wet formations, which

will increase water flow. With their aromatic ring structure, asphaltenes are not soluble in

straight chain alkanes (hexane, heptanes, pentane). They are soluble in aromatic solvents like

xylene and toluene. [47]

Heavy oils, tar sands and biodegraded oils (as bacteria cannot assimilate asphaltenes, but

readily consume saturated hydrocarbons and certain aromatic hydrocarbon isomers –

enzymatically controlled) contain much higher proportions of asphaltenes than do medium API

oils or light oils. Condensate are virtually devoid of asphaltenes.[42]

2.2 Composition of asphaltenes and resins.

Asphaltenes constitutents isolated from different sources are remarkably constant in

terms of ultimate composition, although careful inspections of the date shows extreme ranges for

the composition. Asphaltene constitutents from different sources have never before been

compared with any degree of consistency. The composition of the resins fraction can vary

considerably and is dependent on the kind of precipitating liquid and on the temperature of the

liquid system.[9]

Asphaltene and resins consist primarily of carbon, hydrogen, Nitrogen, oxygen, sulphur

as well as trace amounts of vanadium and nickel, including condensed polynuclear aromatics and

other metallic elements. [10],[42,[47]

There are indication which shows that the condensed aromatic nuclei carry alkyl, and

alicyclic systems with heteroatoms (that is N, O, and S) scattered throughout in various, aliphatic

18

and heterocyclic locations. With the increasing molar mass of the asphaltene fractions, both

aromaticity and proportion of the heteroelement increases.[18]

The elemental composition of asphaltene constituents isolated by use of excess (greater

than 40) volumes of n-pentane as the precipitating medium show that the amounts of carbon and

hydrogen usually vary over only a narrow range. These values corresponds to a hydrogen-to-

carbon atomic ratio of 1.15+ 0.5% (as shown in figure 5 below)[32], although values outside this

range are sometimes found.[9] Furthermore, it is still believed that asphaltene constituents, are

precipitated from petroleum by hydrocarbons solvents because of this composition, not only

because of solubility properties.[9]

19

Table 2.2a Elemental composition of asphaltenes from world sources (Speight, 1999)

Source Composition (wt %) Atomic ratios

C H N O S H/C N/C O/C S/C

Canada 79.0 8.0 1.0 3.9 8.1 1.21 0.011 0.037 0.038

Iran 83.7 7.8 1.7 1.0 5.8 1.19 0.017 0.009 0.026

Iraq 80.6 7.7 0.8 0.3 9.7 1.15 0.009 0.003 0.045

Kuwait 82.2 8.0 1.7 0.6 7.6 1.17 0.017 0.005 0.035

Mexico 81.4 8.0 0.6 1.7 8.3 1.18 0.006 0.016 0.038

Sicily 81.7 8.8 1.5 1.8 6.3 1.29 0.016 0.017 0.029

USA 84.5 7.4 0.8 1.7 5.6 1.05 0.008 0.015 0.025

Venezuela 84.2 7.9 2.0 1.6 4.5 1.13 0.020 0.014 0.020

In contrast to the carbon and hydrogen contents of asphaltenes, notably variations occur in the

proportions of the hetero elements, in particular in the propotions of oxygen and sulfur. Oxygen

contents vary from 0.3 to 10.3%. On the otherhand, the nitrogen content of the asphaltenes has a

somewhat lesser degree of variation (0.6-3.3%).[37]

The use of n-heptane as the precipitating medium yields a product that is substantially

different from the n-pentane insoluble material as shown below [32]

20

Table 2.2b Elemental composition of various asphaltenes

Source Solvent

medium

Composition (wt %) Atomic ratios

C H N O S H/C N/C O/C S/C

Canada n-pentane 79.5 8.0 1.2 3.8 7.5 1.21 0.013 0.036 0.035

n-heptane 78.4 7.6 1.4 4.6 8.0 1.16 0.015 0.044 0.038

Iran n-pentane 83.8 7.5 1.4 2.3 5.0 1.07 0.014 0.021 0.022

n-heptane 84.2 7.0 1.6 1.4 5.8 1.00 0.016 0.012 0.026

Iraq n-pentane 81.7 7.9 0.8 1.1 8.5 1.16 0.008 0.010 0.039

n-heptane 80.7 7.1 0.9 1.5 9.8 1.06 0.010 0.014 0.046

Kuwait n-pentane 82.4 7.9 0.9 1.4 7.4 1.14 0.009 0.014 0.034

n-heptane 82.0 7.3 1.0 1.9 7.8 1.07 0.010 0.017 0.036

For example, the hydrogen-to-carbon atomic ratio of the n-heptane precipitate is lower

than that of the n-pentane precipitate. This indicates a higher degree of aromaticity in the n-

heptane precipitate. Nitrogen - to – carbon, oxygen – to – carbon, and sulfur - to – carbon ratios

are usually higher in the n-heptane precipitate, indicating higher proportions of the hetero

elements in this material. [32][37]

Elemental constituents of a suite of petroleum resins isolated by the same procedure, and

therefore comparable,[32] show that the proportions of carbon and hydrogen, like those of the

asphaltenes, vary over a narrow range: 85± 3% carbon and 10.5 ± 1% hydrogen. The proportions

21

of nitrogen (0.5 ± 0.15%) and oxygen (1.0 ± 0.2%) also appear to vary over a narrow range, but

the amount of sulfur (0.4 to 5.1%) varies over a much wider range. [9][32]

There are notable increases in the H/C ratios of the resins relative to those of the

asphaltenes. Indeed, where as the asphaltenes may have in excess of 50% of the total carbon as

aromatic carbon, in the resins the proportion of the total carbon occurring as aromatic carbon is

significantly lower.[18][48] Presumably this indicates that aromatization is less advanced in the

resins than in the asphaltenes. There is also a tendency to decreased proportions of nitrogen,

oxygen, and sulfur in the resins relative to the asphaltenes. [37]

Table 2.2(c) Elemental composition of petroleum resins [10]

Source Composition (wt%) Atomic ratios

C H O N S H/C O/C N/C S/C

Canada 86.1 11.9 1.1 0.5 0.4 1.66 0.009 0.005 0.002

Iraq 77.5 9.0 3.1 0.3 10.1 1.39 0.03 0.003 0.048

Italy 79.8 9.7 7.2 Trace 3.3 1.46 0.067 - 0.016

Kuwait 83.1 10.2 0.6 0.5 5.6 1.47 0.005 0.005 0.025

USA 85.1 9.0 0.7 0.2 5.0 1.27 0.006 0.002 0.022

Venezuela 76.6 9.6 -- 4.5-- 6.3 1.45 - - 0.030

22

2.3 STRUCTURE AND CHEMISTRY OF ASPHALTENES AND OTHER HEAVY

ORGANIC DEPOSITS.

Asphaltenes and resins are two of the several, but important, heavy organics present in

petroleum fluids. There exact molecular structure are not generally known in a particular oil field

and they could vary from well to well.[34][46] The molecular nature of the asphaltene fractions of

petroleum and bitumens has been subject to numerous investigations. However, determining the

actual structure of the constituents of the asphaltene fractions has proven to be difficult because

they are a mixture of many thousands of molecular species.[37]

Asphaltenes are lyophilic with respect to aromatics, in which they form highly scattered

colloidal solutions. Specifically asphaltenes of low molecular weight are lyophobic with respect

to paraffins like pentanes and petroleum crudes. There have been considerable efforts by analytic

chemists to characterize the asphaltenes in terms of chemical structure and elemental analysis as

well as by the carbonaceous sources.[46]

Attempts have been made to describe the total structure of asphaltenes, resins and other

heavy fractions based on physical and chemical methods. [34][37][46] Physical methods include IR,

NMR, ESR, mass spectrometry, x-ray, ultracentrifugation, electron microscopy, VPO, GPC,

e.t.c. Chemical methods involves oxidation, hydrogenation, elemental and pyrolysis GC – FID –

GC – MS. The chemical structures of asphaltenes, are difficult to ascertain due to the complex

nature of the asphaltenes.[34][42][46] Nevertheless, the various investigations have brought to light

some significant facts about asphaltene structure.[37]

It is undisputed that the asphaltenes are composed mainly of polyaromatic carbon i.e.,

polycondensed aromatic benzene units with oxygen, nitrogen and sulfur, (NSO) compound

23

combined with minor amounts of a series of heavy metals, particularly vanadium and nickel

which occur in porphyrin structures. Further more, asphaltene rotational diffusion measurements

show that small PAH (polycyclic aromatic hydrocarbon), chromophores (blue fluoreseing) are in

small asphaltene molecules while big PAH chromophores (red fluoreseing) are in big molecules.

This implies that there is only one fused polycyclic aromatic hydrocarbon (PAH) ring system per

molecule. [42]

The various figures below shows some of the representative structures of asphaltenes:

Figure 2.3a: molecular structure of asphaltene proposed for Maya crude (Mexico) by

Altamirano, et al IMP Bulletin, 1986 [46]

24

Figure 2.3b: Molecular structure of asphaltene proposed for 510c residue of Venezuelan crude

by carbognani [INTEVEP S.A Tech. Rept., 1992) [46]

Petroleum asphaltene have a varied distribution of heteroatom (N, O, S) functionality.

Nitrogen exist as varied heterocyclic types but the more conventional primary, secondary and

tertiary aromatic amines have not been established as being present in petroleum asphaltenes.[50]

There are also reports in which the organic nitrogen has been defined in terms of basic and

nonbasic types. [37] Spectroscopic investigations suggest that carbazoles occur in asphaltenes,

which supports, earlier mass spectroscopic evidence for the occurrence of carbazole nitrogen in

asphaltenes. [37] The application of x-ray absorption near-edge structures (XANES) spectroscopy

to the study of asphaltenes has led to the conclusion that a large portion of the nitrogen is present

in aromatic systems, but in pyrrolic rather than pyridinic form.[51] Other studies have brought to

light the occurrence of four – ring aromatic nitrogen species in petroleum.

Evidence for the presence and nature of oxygen functions in asphaltenes has been derived

from infrared spectroscopic examination of the products after interaction of the asphaltenes with

25

acetic anhydride. Thus, when asphaltenes are, heated with acetic anhydride in the presence of

pyridine, the infrared spectrum of the product exhibits prominent absorptions at 1680, 1730, and

1760cm-1. These observations suggest acetylation of free and hysdro-bonded phenolic hydroxyl

groups present in asphaltenes.[50][52] Oxygen has been identified in carboxylic, phenolic and

ketonic locations but is not usually regarded as being located primarily in heteroaromatic ring

systems.[37]

Sulfur occurs as benzothiophenes. More highly condensed thiophene – types may also

exist but are precluded from identification by low volatility. Other forms of sulfur that occur in

asphaltenes include the alkyl – alkyl sulfides, alkyl – aryl sulfides and aryl – aryl sulpfides.[37]

Nickel and vanadium occur as porphyrins but whether or not these are an integral part of

asphaltene structure is not known. Some of the porphyrins can be isolated as a separate stream

from petroleum.

In accordance with the Nuclear Magnetic Resonance (NMR) data and results of chemical

analysis, attempts have been made to describe the total structure of asphaltenes.[37] Strausz et al

identified a host of structural units in Alberta asphaltenes from detailed chemical and

degradation studies. He also showed that the extent of aromatic condensation is low and that

highly condensed pericyclic aromatic structures are present in very low concentrations. From his

work he concluded that petroleum asphaltenes were mainly derived through the catalytic

cyclization, aromatization and condensation of n – alkanoic (probably fatty acids) precursors.

He came up with a hypothetical asphaltene molecule consisting of large aromatic clusters.[54]

It must be remembered that asphaltene constituents are a solubility class and, as such may

be an accumulation of life (literally) thousands of structural entities. Hence caution is advised

26

against combining a range of identified products into one (albeit – hypothetical) structure. An

often ignored but extremely important aspect of asphaltene chemistry and physics, is the micelle

structure, which represents the means by which asphaltene constituents exists in crude oil.

The large variety of functional groups and heteroatom content in the asphaltenes indicates

that asphaltene molecules have the potential to form links with other similar molecules in a

number of ways. Their links may be formed through acid-base interactions, aromatics (П-П)

stacking, hydrogen bonding, dipole – dipole interactions or even weak van – der waals

interactions. However, П-П bonding is considered the prevalent theory.[55]

Investigations have shown that a variety of hydrocarbon types and functional types occur

in resin fractions.[18][32][56][57] In addition, the resin constituents contain a variety of functional

groups, including thiophene, benzothiophene and dibenzothiophene systems, hydrogen – bonded

hydroxyl groups, pyrrole (and indole) N – H functions, ester functions, acid functions, carbonyl

(ketone or quinine) functions, and sulfur – oxygen functions. [9][52] Figure 2.3c below shows a

representation of a resin structure.

Figure 2.3c: Resin fraction with two subgroups (i, ii)

27

2.4 Asphaltene chemical structure under pyrolysis condition

Here, two different views of the asphaltene structure have been proposed. The first,

following Yen, T,F [47] who assumes extensive condensation of the aromatic rings into large

sheets. These sheets are assumed to be soluble, because of the saturated rings and side chains

around the molecular periphery as shown in figure 2.4a below

Figure 2.4a: Proposed asphaltene structural model: condensed aromatic cluster model[47]

This type of structure, with lower molecular weight, has been proposed by groenzin and

Mullins,[58] on the basis of spectroscopic studies. In a complex mixture, structure such as this

cannot be left out, particularly when the fraction of aromatic carbon approaches 70%, however,

such a chemical structure cannot account for the average amount of volatile product evolution

under the pyrolysis conditions from a range of asphaltenes.

28

A very different structural organization, illustrated in figure 2.4b below was proposed by

Speight and by Strausz and co–workers (e.g. Murgich et al) on the basis of pyrolytic and

selective oxidation studies to determine the building blocks of asphaltenes.

Figure 2.4b Proposed asphaltene structure based on bridged aromatic model [47]

A structure of the type in figure 2.4a cannot give significant mass yields of volatile

products in a pyrolysis experiment. The side chains would crack off readily, and the naphthenic

rings then would undergo a combination of dehydrogenation (to form aromatics) and cracking

29

(to give mainly light ends). On the contrary, a structure of the type in figure 2.4b can give a wide

range of product sizes, from methane to toluene – insoluble carbon residue, depending on the

balance between cracking, product release, and molecular rearrangements.

Data on the nature of product from the cracking of asphaltenes give further support to the

diversity of asphaltenes from different crude oils and indicate that the chemical structures in

asphaltenes must be consistent with the evolution of a significant yield of volatile products

during pyrolysis.[59] Chemical characterization of the products from the pyrolysis of asphaltenes

depends strongly on the analytical methods selected and, possibly on the chemistry of the

asphaltene selected. When the cracked products are analysed by gas chromatography (GC), the

dominant components in the cracked products are n–alkanes and n- alkenes for a wide range of

asphaltenes. For example, Arkok et al.[33] used curic – point pyrolysis to analyse products from

asphaltenes from an Arabian crude. Paraffins, Olefins, and aromatics were identified by gas

chromatography – mass spectroscopy (GC-MS), but only up to C21. In this range, n– alkane and

n – alkene products dominated.[60][47]

2.5 MOLECULAR WEIGHT OF ASPHALTENE AND RESIN PARTICLES

The physical and physico-chemical properties of asphaltenes are different from those of

neutral resins. The reported molecular weight of asphaltenes varies considerably depending upon

the method and conditions of measurement. These methods include ultracentrifuge, vapour

pressure Osmometry (VPO), electron microscope, solution viscometry, cryoscopic methods,

e.t.c. Reported molecular weight from ultracentrifuge and electron microscope studies are high.

To the contrary, those from solution viscometry and cryoscopic methods are low. The prevalent

method for determining asphaltene molecular weights has become vapour pressure 0smometry

30

(VPO). However, the value of the molecular weight from VPO must be weighed carefully, since

in general, the measured value of the molecular weight is a function of temperature, the solvent

molecular properties.

Asphaltene particles can assume various forms when mixed with other molecules

depending on the relative sizes and polarities of the particles present. The molecules of

asphaltene constituents span a wide range from a few hundred to several million leading to

speculation about self-association.[9][34][46]

Figure 2.5a: The molecular weight of this asphaltene is 7819 [45]

Asphaltene molecular weights are variable because of the tendency of the asphaltene constituents

to associate even in dilute solution in nonpolar solvents. However, data obtained using highly

polar solvents indicate that the molecular weights, in solvents that prevent association, usually

fall in the range 2000 ± 500.[9][55] It should be noted that although the results with asphaltene

constituents available from several crude oils suggest that molecular weight varies with the

dielectric constant of the solvent, there may be other factors which may in part also be

responsible for this phenomenon. The final phenomenon that influences the molecular weight of

31

n-C5 asphaltene

Polarity = N,S,O

Aromaticity =

n-C7 asphaltene

Mo

lecu

lar

wei

gh

t

Polarity and aromaticity

the asphaltene is the relative polarity of the solvent used in the precipitation technique. Figure

2.5b below.

Figure 2.5b: Long diagram shows that the asphaltenes include the crude oil

material highest in molecular weight, polarity and/or aromaticity.[13]

Both polarity and molecular weight of aspahltene constituents in a solvent define the

solubility boundaries and explains conceptually how asphaltene constituents are precipitated

from the mixture in crude oils that can be considered a type of continuum of molecular weight

and polarities.

Also, Auflem 2002 observed that the molecular weight, polarity and aromaticity of

precipitated asphaltene generally decrease with increasing carbon number of n-alkane

precipitant. He compared the wt % of Asphaltene precipitates of the n-C5, n-C7 and nC9 fractions

of crude oil.

32

Table 2.5a: Total nC5, nC7, nC9 asphaltene content of crude oil [75]

Paraffin solvent Wt % Asphaltene

n-pentane (C5) 1.0833 ± 0.0050

n- heptane (C7) 0.5167 ± 0.0059

n-nonane (C9) 0.3982

This is an additional confirmation that asphaltene precipitation decreases with increase in

carbon chain length of precipitating solvent.

The molecular weights of resin fractions in benzene are substantially lower than the

molecular weights of the corresponding asphaltenes in benzene. Compared to the molecular

weights of the asphaltenes, the molecular weight of the resins do not vary, except for the limits

of experimental error, with the nature of the solvent or the temperature of the determination

indicating that there is no association in non polar solvents such as benzene.

The molecular weights of resin fractions, as determined by various methods, are true

molecular weights and that forces that result in intermolecular association contribute very little,

if anything to their magnitude. [9]

One area of investigation that has shed some light on the behaviour of resins during

refining is the construction of molecular weight and polarity maps based on gel permeation

chromatographic data.[61]

33

2.6 INFLUENCE OF RESIN CONSTITUENTS ON ASPHALTENE CONSTITUENTS

The behaviour of asphaltene in petroleum has been complicated by another solubility

class called the resins [9] which have similar structure and chemistry like asphaltene.[42] There is

evidence that the structural aspects of the constituents of the resin fraction may differ very little

from those of the corresponding asphaltene fraction, the main difference being the proportion of

aromatic carbon within each fraction.[18][32][62] It has also been postulated that resin constituents

and asphaltene constituents are small fragments of kerogen [63] or atleast have the same origins as

the kerogen and therefore, a relationship might be anticipated. The analogy is to lock and key

mechanism in which the asphaltene constituent and resin constituents with similar structural

features form a bonding union.[9]][42] As mentioned earlier, resins are structurally very similar to

asphaltenes but have a higher hydrocarbon ratio and lower heteroatom content, polarity and

molar mass. Hence, the number of links they can form through hydrogen bonding, aromatic

stacking or acid – base interactions is lower than those formed by asphaltenes.[37] It has been

suggested that resins contributes to the enhanced solubility of asphaltenes in crude oil by

solvating the polar and aromatic portions of the asphaltenic molecules and aggregates. The

solubility of asphaltenes in crude oil is mediated largely by resin salvation and these resins play a

critical role in precipitation, and emulsion stabilization phenomena[64]

Asphaltenes may be dispersed in the crude oils by the action of resins. The polar resin

molecules may form micelles with asphaltene molecules as the nucleus. Figure 2.6

34

Figure 2.6: Schematic illustration of archipelago model of asphaltene monomers, asphaltene

aggregate in absence of resins, and asphaltenic aggregate in presence of resins.[64]

(a) In a resin poor environment micelles may form from multiple asphaltene molecules.

(b) As a result of these physico-chemical shifts the chemistry of asphaltenes is extremely

difficult to establish as it changes with the composition of the crude oil.[45] In addition

when resins and asphaltenes are present together, resin-asphaltene interactions appear to

be preferred over asphaltene – asphaltene interactions, resin – resins interactions appear

to be inconsequential in petroleum.

Numerous analytical techniques have been employed to work on asphaltene and oil

fraction of the crude oil, while only few studies to determine the role resins play in

asphaltene stability has only been briefly documented in the literature. For instance, Chang

and Fogler [65] studied the interactions between asphaltenes and resins. In their study, two

types of oil soluble polymers, dodecylphenolic resin and poly (octadecene maleic anhydride)

35

were synthesized and used to prevent asphaltenes from flocculating in heptanes media

through the acid-base interactions with asphaltenes. The results indicated that there polymers

could associate with asphaltenes to either inhibit or delay the growth of asphaltene

aggregates in alkane media. However, multiple polar groups on a polymer molecule make it

possible to associate with more than one asphaltene molecule, resulting in hetero –

coagulation between asphaltenes and polymers. It was found that the size of the asphaltene-

polymer aggregates was strongly affected by the polymer-to-asphaltene weight ratio. At low

polymer-to-asphaltene weight ratios, asphaltenes were found to flocculate among themselves

and with polymers until the flocs precipitated out of solution. On the other hand, at high

polymer-to-asphaltene weight ratios, small asphaltene polymer aggregates formed that

remained fairly stable in solution.

Moschopedia and Speight showed that dilute solutions (0.01 -0.5% w/w) of Athabasca

asphaltenes in a variety of non-polar organic solvents exhibit the free hydroxyl absorption

band (c. 3585cm-1) in the infrared. At higher concentration (> 1% w/w) this band becomes

less distinquishable, with concurrent onset of the hydrogen–bonded hydroxyl absorption (c.

3200 – 3450cm-1). Upon addition of a dilute solution (0.1 – 1%) of the corresponding resins

to the asphaltene solutions, the free hydroxyl absorption was reduced markedly or

disappeared, indicating the occurrence of intermolecular hydrogen bonding between the

asphaltenes and resins. Therefore, hydrogen bonding may be one of the mechanism by which

resin-asphaltene interactions are achieved. Also resin – asphaltene interactions appear to be

stronger than asphaltene – asphaltene interactions. Thus, in petroleums and bitumen’s it is

believed that asphaltenes exist not as agglomerations but as single entities–that are dispersed

by resins.[50]

36

In a recent work by Murgich et al (1999), the conformation of lowest energy of an

asphaltene molecule of the Athabasca sand oil was calculated through molecular mechanics.

Molecular aggregates formed from the asphaltene with nine resins from the same oil, in an n-

octane and toluene medium were studied. The resins showed higher affinities for the

asphaltene than toluene and n-octane and also exhibited a noticeable selectivity for some of

the external sites of the asphaltene. This showed that this selectivity depended on the

structural fit between the resins and the site of the asphaltene. The selectivity explains why

resins of one oil may not solubilize asphaltenes from other crudes.[66]

2.7 Causes of asphaltene problem, asphaltene self-association and micelle/colloid

concept

The mere presence of asphaltenes in crude oil does not portend asphaltene-related

production problems. [8] As mentioned earlier, what is important is the stability of those

asphaltene and stability depends not only on the properties of the asphaltene fraction, but on how

good a solvent the rest of the oil is for its asphaltenes. As recognized by de Boer et al (1995),

light oils with small amounts of asphaltenes are more likely to cause problems during production

than heavy oil with large amount of material in the asphaltene fraction. [8][9][13] The heavier oils

also contains plenty of intermediate components that are good asphaltene solvents whereas the

light oil may consist largely of paraffin materials in which, by definition, asphaltene have very

limited solubility. Asphaltenes in heavier oil can also cause problems if they are destabilized by

mixing with another crude oil during transportation or by other steps in oil processing.[13] The

problem appears to be that asphaltene self associate and form aggregates.[37]

37

Measurement of asphaltene molar mass was the first indication of asphaltene self –

association –[37] Leon et al performed surface tension and stability measurements to study the

self – association behaviour of two different association samples, one from a stable crude oil

(non-precipitation) and the other from an unstable crude oil were characterized by high

aromaticity. Low hydrogen content, and high condensation of the aromatic rings. Asphaltenes

from stable crude oils showed low aromaticity, high hydrogen content, and low condensation of

their aromatic rings. They showed that these structural and compositional characteristics of the

asphaltenes strongly influence their self-association behaviour. They found that asphaltenes from

unstable oil begin to aggregate at lower concentrations than asphaltenes from stable oils. Self

association appears to be related to a high content of condensed aromatics, which supports a П –

П bonding mechanism. However, the role of heteroatoms in asphaltene self – association was not

investigated by this group of researchers.[67]

As mentioned earlier, asphaltene self-associate and other constituents especially resins,

influence the association. The associated asphaltenes can be considered as micelles, colloidal

particles and / or macromolecules. [37]

An early hypothesis of the physical structure of petroleum indicated that asphaltenes are

the centre of micelles or colloids formed by association or possibly adsorption of part of the

maltenes (i.e., resins) onto the surfaces or into the interiors of the asphaltene aggregates.[68]

It is widely accepted that at low concentrations asphaltene appear as non associated

molecules (monomers), but with changes in temperature, pressure, or concentration, monomers

associate to form aggregates or micelles. At higher concentrations, asphaltenes aggregate and

38

form non dissolved larger particles that at a later stage agglomerate and precipitate, forming the

undesirable deposits.[17]

The term “micelle”, “colloid” and “aggregate” are often used interchangeably in the

literature. A micelle is an aggregate that remains constant in size and aggregation number for a

given set of environmental constraints. The concentration at which asphaltene molecules start to

aggregate is called the critical micelle concentration (CMC).

In the micellar view of asphaltenes, asphaltene-monomers form micelles above a CMC.

Researchers have focused on identifying a CMC with interfacial tension measurements[69][70]

However, Yarranton et al (2000) demonstrated that asphaltene self-association occurs in the

absence of any evidence of micelle formation.[71] Recent work by Alboundoware et al (2001)

suggested that apparent asphaltene CMC’s may result simply from a change in asphaltene molar

mass, without involving the micelle model. Hence, the micelle model is not supported by strong

experimental evidence.[72]

A better supported model of asphaltene structure is the colloidal model. According to the

colloidal view (Leontaritis and Mansoori, 1998), a crude oil is composed of asphaltene

molecules (colloids with their surface covered by resin molecules) suspended in the crude oil.

Figure 2.6 above. The adsorbed resins prevent aggregates and disperse the asphaltene. The

colloids can aggregate upon a change in the system temperature, pressure, concentration and

composition that causes resins to desorb from the asphaltenes. The colloidal view is consistent

with small–angle neutron scattering (SANS) and small–angle X-ray scattering (SAXS) evidence

of asphaltene aggregate in the nanometer size range. The colloidal model is the prevalent view of

asphaltenes in crude oils.[64][73]

39

According to this alternative school of thought, asphaltenes exist as free molecules in a

non-ideal solution (Hirschberg et al,). Hirschberg et al assumed that “pure” asphaltenes

aggregate by a linear “polymerization” process. The asphaltene monomer they considered

corresponded to asphaltene sheet defined by Yen. They proposed that in crude oil the

“polymerization” is blocked (reduced) by the association of asphaltenes with similar but less

polar hetero-components, the resins.[74]

The greatest difference between the polymer/macromoleculer view and micelle/colloidal

view of asphaltene is the fact that the latter considers asphaltene aggregates to be solid particles.

There is no convincing evidence to explain which if any of the views correctly describes the

nature of the asphaltenes.[37]

The different views of an asphaltene aggregate have led to two types of asphaltene

solubility models: the continous thermodynamic models and colloidal models [37]

(i) The continous thermodynamic models: this is based on the assumption that

asphaltene precipitation process is thermodynamically reversible. This may happen

since it is assumed that the asphaltene particles can be dispersed and stabilized in the

oil. The complete dissolution of asphaltenes in some organic solvents such as toluene

supports this assumption.

(ii) Thermodynamic colloidal model: this approach is based on the assumption that

asphaltenes are solid particles colloidally suspended in crude oil. Asphaltene

particles may undergo aggregation to form larger flocculation under Vander waals

attraction forces. This concept is based mainly on titration experiments,, which

demonstrate that once the adsorption equilibrium of resins between solid (asphaltene)

40

and liquid phases is disturbed by adding paraffin solvents, the asphaltene particles

flocculate irreversibly.[75]

(iii) Reversibility of asphaltene aggregation: Hirseberg et al assumed that aggregation was

reversible, but probably very slow, Joshi et al found the precipitation from a live

crude oil to be reversible in a matter of minutes, except for a subtle irreversibility

observed for the first depressurization of crude oil.

Hammani et al also found that the aggregation was generally reversible, but that the

kinetics of the reticulation varied significantly depending on the physical state of the system.

Peramary et al reported differences in the reversibility of solvent and temperature induced

aggregation.[75]

Finally, whether the asphaltene particles are dissolved in crude oil, in steric colloidal state

or in micellar form, depends to a large extent, on the presence of the other particles (parafins,

aromatics, resins e.t.c) in the crude oil.[34]

Various investigators, have established the existence of asphaltene micelles when an

excess of aromatic hydrocarbons is present in a crude oil as shown below

+ +

Figure 2.7a: formation of asphaltene micelles in the presence of excess amounts of aromatic

solvents.[34]

41

The figure above shows three forms of asphaltene micelle and this indicates the fact that

in the presence of excess amounts of aromatic hydrocarbon, asphaltene particles cannot

flocculate but self associate, and form micelle.[34]

In a petroleum fluid, due to excess amounts of paraffins in the solution, small asphaltene

particles can be dissolved while relatively large particles of asphaltene may flocculate out of the

solution and then form steric colloids. Flocculation of asphaltene in paraffinic crude oil are

known to be irreversible, because of their large size and their adsorption affinity to solid

surfaces.

Asphaltene and its flocculates are said to be surface active agents. However, if there is enough

resin in the solution so that they can cover the surface of the asphaltene particles by adsorption,

asphaltene steric colloids are formed. Figure 2.7c below.

Figure 2.7b : Asphaltene flocculation due to excess amount of

paraffins in the solution.[34]

42

Figure 2.7c: Steric – colloid formation of flocculated asphaltenes with resins.[34]

2.8 ECONOMIC EFFECT AND RELEVANCE / SIGNIFICANCE OF ASPHALTENE

PRECIPITATION

Heavy organic deposition during oil production and processing is a very serious problems

in many areas including Venezuela, the Persian Gulf, the Adriatic Sea and the Gulf of Mexico

and other areas throughout the world;[8][34] causing several undersea pipeline plugging with

substantial economic loss to the oil production operation.[76] In one example from eastern

Venezuala, severe asphaltene deposition problems caused a high volume production well to plug

within seven months of treatment.[77] Several cleaning methods has been attempted, including

physically scraping the wellbore and injecting xylene down the tubing. Each cleaning event cost

approximately US $50,000 and two days of shut-in production. After squeeze treatment (2.9)

with activator and inhibitor, the oil production rate increased and frequency of well cleaning

decreased to every eight months. The combination of increased production and less frequent

cleaning generated an annualized gain of 60,882 barrels (9,674m3), and a return on investment of

more than 3,000%.[8] Also in the prinos field in North Aegean Sea, there were wells that,

especially at the start of production, would completely cease flowing in a matter of few days

after an initial production rate of up to 3,000 BPD.[34] Heavy organic deposition in the North Sea

43

and in the Gulf of Mexico oil fields, in recent years have caused several under – sea pipeline

plugging with substantial economic loss to oil production, operation.[76]

The economic implications of this problems were tremendous considering the fact that a

problem well workover cost could get as high as a quarter of a million dollars.[32]

Although asphaltenes are a major concern in production operations, because of their role in

emulsion stabilization and fouling, this fraction of crude oil is also important [47] in the following

ways:

• The conversion of vacuum residues by processes such as coking, catalytic cracking and

hydrogenation.[32]

• Asphaltene in the form of distillation products from oil refineries are used as “tar – mats”

on roads.[42]

• Asphaltene materials – are used for water proofing and roofing.[42]

2.9 Prevention and remedies of asphaltene precipitation

Asphaltenes can deposit anywhere in the production system, but perhaps the most

damaging place is in the near – wellbore region where asphaltene – blocked pores are difficult to

access for remediation.[8]

Flocculation and deposition of asphaltenes can be controlled through better knowledge of

the mechanisms that cause its flocculation in the first place.[34] It can also be controlled using

various methods such as:

44

1. Production techniques

2. Chemical treating techniques.

1. Production techniques includes:

i. Reduction of shear

ii. Elimination of incompatible materials from asphaltic crude streams

iii. Minimization of pressure – drops in the production facility and

iv. Minimization of mixing of lean feed stock liquids into asphaltic crude streams

2. Chemical treating techniques

i. Solvents

ii. Dispersants/solvents

iii. Oil/dispersant/solvents

The dispersant/solvent approach is used for removing asphaltenes from formation

minerals. Continuous treating may be required to inhibit asphaltene deposition in the tubing.

Batch treatments are common for dehydration equipment and tank bottoms. There are also

asphaltenes precipitation inhibitors that can be used by continuous treatment or squeeze

treatments.[34][42] Conventional asphaltene flocculation inhibitor treatments involve either

periodic intervention with solvent soaks or continuous injection of chemicals into wellbore.

These methods are effective at presenting agglomeration and deposition of asphaltenes in

flowlines and tubular, but they do not protect the producing formation, because the chemicals

interact with the oil after it has left the formation, potentially leaving asphaltenes behind.

An improved method developed by Nalco Energy Services adds chemicals to the crude

oil while it is still in the formation.[78] The method entails squeezing as asphaltene deposition

inhibitor into the formation to stabilize the asphaltenes before flocculation occurs. However,

45

tests have shown that squeezing inhibitors alone does not, produce long-term benefits;

formations do not absorb inhibitors adequately, allowing inhibitors to be quickly released from

the formation as oil is produced. Pretreating the formation with an activator chemical enhances

absorbtion of the inhibitor into the formation without changing formation wettablity.

The general squeeze procedure includes cleaning out and flowing back the well, pumping

in activator, a spacer of crude oil, inhibitor, and then more crude oil, and shutting in the well for

12 to 24 hours before resuming production. [77]

The activator prepares the formation and reacts with the inhibitor to make a complex that

remains in place for a prolonged period as the well produces oil.[8]

Asphaltene – dispersants are substitutes for the natural resins and works much in the

same way as resins. That is, dispersants will keep the asphaltenes well dispersed (peptized) to

prevent their flocculation / aggregation. Dispersants will also clean up sludge in the fuel system

and they have the ability to adhere to surface of materials that are insoluble in the oil and convert

them into stable colloidal suspensions. [27]

Laboratory analysis of fluid samples indicated that asphaltene deposition could be

controlled only by continuous downhole injection of asphaltene dispersant. The appropriate

treatment program was designed and initiated with the desired results.

Once a successful treatment program was underway, additional laboratory work on

samples collected as part of a monitoring program helped the operator optimize dispersant

dosage. It was clear from surface – samples analysis that as dosage increased, the volume of

46

stable asphaltene dispersed in the crude increased. This indicated that fewer asphaltenes were

available to deposit in the well.

Asphaltene deposition Condition of crude

0 to 1% Crude strongly stabilized; dosage reduction

indicated

1 to 2% Crude well – stabilized; treatment adequate;

no dosage change indicated.

2 to 3.5% Crude not perfectly stabilized; small increase

in dosage indicated

> 3.5% Crude not stabilized; insufficient dosage

Table 2.9: Optimizing asphaltene – dispersant dosage in the Adriatic Sea. [8]

The volume of asphaltene deposition decreased as dispersant dosage increased.

However, over treatment with dispersant increases cost. Optimization requires a compromise that

allows a tolerable level that allowed deposition of only 1% to 2% of the asphaltene volume

enabled the wells to operate for several years without asphaltene deposition problems.[77]

A treatment level that optimized cost and sufficiently stabilized the asphaltene was shown

to provide a protection level that was 98% to 100% effective. Continuous treatment at this level

has enabled the wells to operate for several years without any plugging problems.[8]

Cleaning the pipeline of asphaltene required a technique that would be environmentally

acceptable, cost effective and successful in the complex pipeline geometry. [79]

47

CHAPTER THREE

MATERIALS AND METHOD (METHODOLOGY)

3.0 Sample Collection

In this present work, a total of three Nigerian crude oils were studied. The crude oils were

sourced from Bodo in Delta State, Bonny Export and Mogho (Port Harcourt) in Rivers State as

shown in the map in appendix 1.

3.1 Sample Treatment

The three crude oils were employed for precipitation of asphaltenes using pure n-heptane

solvent and n-pentane + n-heptane mixed solvent with respect to stirring time, in a solvent to oil

volume ratio of 40:1 and also for fractionation of maltenes. Detailed results of this work are

provided in chapter four.

3.2 Materials and reagents

All the analysis in this work was performed using high purity solvents and

chemicals that were of analytical reagent grade. For distillation of crude oil at

350°c an appropriately calibrated thermometer(3600 c), a heating mantle (that heats

more than360°c) with thermal regulator, cotton wool to lag exposed portion of

flask, a round bottom flask (250ml), antibumping chip (porcelane chips) to avoid

spilling of the crude, distillation chamber, water for cooling the distillation

chamber, analytical balance (weighing with an accuracy of 0.001g and of maximum

capacity 310g), reagent bottle (for storing crude oil before distillation and

atmospheric residuum after distillation), conical flask, a stopper.

48

For asphaltene precipitation and Fractionation of the maltenes, reagent grade solvents and

materials used were n-pentane (95% purity, sigma Aldrich laborchemical), n-heptane (99.5%

FSA Laboratory supplies meadow road, Lough – borough, LEII ORG, England), Toluene

(99.96% purity BDH laboratory supplies, chemical Ltd poole BH15 17D, England), methanol

(99% purity Fisher Chemicals), Silica gel (99.5% purity, BDH Laboratory supplies, chemical ltd

poole BH-1517D England). Dichloromethane (99% purity, BDH Laboratory supplies), Magnetic

Stirrer (constant temperature magnetic stirrer 78 HW - 1). Spatula, weighing balance (capable of

weighing with an accuracy of 0.001g and a maximum capacity of 310g), filter paper (Whatman

number 2 with pore size of 2µm), graduated cylinders, Centrifuge (model no. 80-2B with

maximum speed 4000rpm serviced and maintained by Finlab Nig. Limited), beakers, petridish,

oven (model-mini/50 Genlab Limited), 50ml standard laboratory burrette with a glass stopper.

For melting point analysis, the material and apparatus used were capillary tubes and the

melting point analyser (electrothermal melting point analyser, melts with a maximum capacity of

400-4500c). For UV/vis spectrophotometer the reagent grade solvent and apparatus used were

Toluene and UV spectrophotometer (Jenway England, model 6405 UV/vis spectrometer), and

printer. For Ir the apparatus used was FTIR Spectrophotometer.

49

Picture 3.1: Weighing balance (Ohaous; Model: Advanturers)

3.3 DISTILLATION OF EACH OF THE THREE CRUDES

The simple distillation process was conducted at the Department of Food Science and

Technology, Post - Graduate laboratory, University of Nigeria Nsukka. For each distillation

process that took place, the set up was first made.Then 200mls of the particular crude to be

distilled was poured into a 250ml round bottom flask containing porcelain chip and corked with

a stopper to prevent bubbling off of the crude. The heating mantle was then plugged to the source

of electricity and set at 3500c, with a thermometer inserted to the stopper. As the temperature

rises, the lighter fractions of the crude oil distilled off and was collected in the receiver (conical

flask with cotton wool to lag off exposed portion of the flask). At 350°C the lighter fractions of

the crude had been distilled off leaving a heavy organic rich residue known as the dead crude oil

(Atmospheric residuum). The whole system was allowed to cool, and the dead crude was stored

in the reagent bottle. The process was repeated until a reasonable quantity for each of the crude

oil was obtained. The results of this process are shown in chapter four.

50

3.4 PRECIPITATION OF ASPHALTENES, PURIFICATION OF ASPHALTENES

AND VARIOUS ANALYSIS CARRIED OUT ON THE PURE ASPHALTENES

PRECIPITATE.

3.4.1 PRECIPITATION OF ASPHALTENES

The precipitation of asphaltenes was conducted at the Energy Commission Research Centre,

University of Nigeria Nsukka. In this present work 40mls of n-heptane single solvent was mixed

with 1ml of each of the crudes also 40mls of n-pentane + n-heptane (mixed solvents in the ratio

20:20) was added to 1ml of each of the crudes. The mixture of dead oil (i.e. atmospheric

residium) and the n-heptane solvent and also the mixture of

the dead crude and the n-pentane + n-heptane mixed solvent

was agitated by using a magnetic stirrer for 20mins, 40mins,

60mins and 80mins respectively and allowed to equilibrate for

48hrs. The stirring time was varied with same quantity of

liquid precipitant to oil volume ratio for the n-heptanes

solvent and the n-pentane+n-heptane solvent in other to study

the stirring time effect on the asphaltene yield.

Picture 3.4: Magnetic Stirrer (Constant temperature magnetic stirrer 78 HW-1)

After 48hrs equilibration, the mixture was centrifuged for 30mins at 2000rpm using a

centrifuging apparatus. After this procedure the

supernatant (maltene) was decanted and kept

separately while the solid residue, which was

mainly composed of precipitated asphaltenes, was

kept rinsing with the liquid precipitant (about

40mls) until a clear solvent was observed.

51

Picture 3.5: Centrifuging apparatus (model no. 80-2B with maximum speed 4000rpm)

The precipitated asphaltenes were slowly dried in a vacuum oven at about 80°c (as shown

below) until no change in weight was observed.

Picture 3.6: Oven/incubator (model – mini/50 Genlab Limited)

These asphaltenes are refered to as C7 asphaltenes since n-heptane was used for the

precipitation and C5+C7 asphaltenes since C5+C7 mixed solvent system (i.e. in the ratio 20:20)

was used for the precipitation.

3.4.2 PURIFICATION OF EXTRACTED ASPHALTENES

The dried C7 and C5+C7 asphaltenes were purified to remove any non asphaltenic solids

(i.e clay, sand, some adsorbed hydrocarbons e.t.c.) that co-precipitated along with the

asphaltenes. To remove these solids, each of the asphaltenes were dissolved in 10mls of toluene

in which asphaltene is soluble, this mixture was filtered and to the filterate (composed mainly of

asphaltenes) 20mls of n-alkanes was added to reprecipitate asphaltenes. The fractions of the C7

and C5+C7 asphaltenes that did not desolve in toluene were discarded (i.e. non asphaltenic

52

solids). Finally, the reprecipitated asphaltenes were dried for 80mins in an oven, the dried

asphaltene from the oven was washed and dried until no change in weight was observed. The

melting point, ultraviolet and infrared analyses were carried out. The UV and IR spectroscopy

were used for final assessment of the precipitated asphaltenes as shown in subsequent sub topics

below.

The maltenes were further separated into saturates, aromatics and resins (by a process

termed SAR method) by first exposing the maltenes at room temperature to evaporate the n-

alkane that was used to precipitate asphaltene, the volume, weight and density of the maltenes

were obtained and the results are as shown in chapter 4.

Figure 3.4: below shows the flow chart of the separation of the atmospheric residuum from Bonny Export, Bodo and Mogho crudes.

Figure 3.4: Classification procedure for the various heavy crude oil fractions (350OC

boiling fraction)

This is refered to as NAMAL method for the separation of atmospheric residuum into

asphaltenes and maltenes.

Non aspaltenic solids

Atomospheric residuum

Extract with C5 and C7

C7: oil = 40:1 & C5 + C7: oil = 40:1

Malteness

Soluble Insoluble

Extract with pentane

Insoluble Soluble

Asphaltenes

53

3.5 FRACTIONATION OF MALTENES

The fractionation of maltenes was conducted at the department of Pure and Industrial

Chemistry. The maltenes obtained from the n-heptane single solvent (ie 80mins only for each of

the crudes) were fractionated into saturates, aromatics and resins.

The separation into these petroleum fractions was performed using chromatographic

method. This technique is described in detail below.

3.5.1 ACTIVATION OF THE SILICA GEL

Approximately 200g of silica (granulated) gel was spread evenly on a tray and dried in an

oven for 24hrs at a temperature of 105°C. Aproximately 40.34g of the dried silica gel was

packed in a 50ml standard laboratory burette and used to carry out the column chromatography

and 50mls of dichloromethane was added gradually in other to prepare the slurry and also to

wash off any trace of impurity in the silica gel. After this procedure, the silica gel was ready for

use in chromatography.

3.5.2 CHROMATOGRAPHY PROCEDURE

5ml of maltene sample was added to the top of the activated silica gel (granulated) in the

standard laboratory burette with the help of a funnel and allowed to percolate as shown below.

54

Picture 3.7: Fractionation setup (Column chromatography)

After the entire sample has entered the gel, 30mls of n-heptane was added to maintain a

liquid level well above the silica gel until saturates were washed off from the adsorbent.

Approximately 30mls of heptane effluent (i.e. n-heptane + saturates) was collected from the

column. After the collection, the flask was replaced with another flask for the collection of

aromatics.

Immediately after all the heptane effluent has eluted toluene in the amount of 200mls (for

aromatics from Mogho crude) and 150mls (for aromatics from Bodo Crude) and 130mls (for

aromatics from Bonny crude) was added to the column through a separatory funnel. The column

was allowed to drain and approximately 200mls, 150mls and 130mls of toluene effluent was

collected for Mogho aromatics, Bonny export aromatics and Bodo aromatics respectively. At this

point, resins have adsorbed on the gel.

To recover the resins, a solvent mixture of dichloromethane and methanol (in the ratio

50:50) in the amount of 100ml was charged slowly to the top of the gel column. At this point

approximately 100ml of dichloromethane + methanol effluent (r

After each effluent has been collected for a particular crude, the

replaced with a fresh activated s

three crudes studied.

Figure 3.5: below shows the flow chart of the separation

and resins

This is referred to as SAR methodthree crude oil studied.

Figure 3.5: Flow chart of the separation scheme

3.5.3 EXTRACTION OF EACH OF THE SATURATES, AROMATICS AND RESINS

(MALTENE) FROM THEIR VARIOUS EFFLUENTS

The drying of the various affluents were c

of Nigeria Nsukka. The n-heptane effluent

romethane + methanol effluent (resin + solvent) was collected.

collected for a particular crude, the silica gel was removed and

th a fresh activated silica gel. This procedure was carried out for the maltenes in

: below shows the flow chart of the separation of maltenes into saturates,

R method for the recovery of the components of the maltenes in the

Flow chart of the separation scheme

EXTRACTION OF EACH OF THE SATURATES, AROMATICS AND RESINS

(MALTENE) FROM THEIR VARIOUS EFFLUENTS

us affluents were conducted at the department of Biochemistry University

heptane effluent (saturates + n heptane) was evaporated at room

55

esin + solvent) was collected.

ilica gel was removed and

the maltenes in the

saturates, aromatics

mponents of the maltenes in the

EXTRACTION OF EACH OF THE SATURATES, AROMATICS AND RESINS

epartment of Biochemistry University

was evaporated at room

56

temperature, while the dichloromethane + methanol effluent (resin + dichloromethane +

methanol) and the tolune effluents (aromatic + toluene)were evaporated at 65°c in a water bath

as shown below. After solvent evaporation each fraction was weighed until no change in

weighed was observed.

.

Picture 3.8: Water bath (Model DK) with resin + dichloromethane + methanol effluent during

evaporation of Bonny Export crude

3.6 PHYSICAL METHODS FOR ANALYSING THE ASPHALTENE FRACTION

3.6.1 INFRARED SPECTRA ANALYSIS: The FTIR analysis was conducted at the National

Research Institute for Chemical Technology (NARICT), Federal Institute for Science and

Technology, Zaria. The infrared spectra analysis of asphaltenes (from 80mins stirring time) were

obtained by carrying out the analysis without interacting the asphalting with any solvent (termed

neat). The procedure was carried out using an FTIR Spectrophotometer. Specify the model of the

Spec.

3.6.2 THE ULTRAVIOLET VISIBLE SPECTRA ANALYSIS: This analysis was conducted

at the department of Pure and Industrial Chemistry. The ultraviolet visible Spectra analysis of the

57

precipitated asphaltene fractions were recorded on a Jenway England, model 6405 UV/Vis as

shown in picture 3.9 below.

3.6.3 UV – SPECTROSCOPIC PROCEDURE

0.01g of each of the precipitates from Bonny Export, Bodo and Mogho crude (ie 80mins

only for both n-heptane and n-pentane+n-heptane mixed solvent ) was dissolved in 3mls of

toluene and poured into a cuvet then placed in the sample compartment of the UV/vis

spectrophotometer as shown below. The sample was then scanned in the UV region. Details of

this report is shown in chapter 4.

Picture 3.9: UV Visible spectrophotometer (Jenway England, model 6405 UV/vis spectrometer)

3.6.4 MELTING POINT ANALYSIS: This analysis was carried out in Pharma-chem

laboratory (U.N.N). It was done by putting a pinch of the asphaltene precipitate in a capillary

tube and dropped in one of the three compartments in the melting point analyser (electrothermal

melting point analyser, which heats up to the range of 350-450°C) as shown in picture 3.10

below

58

Picture 3.10: Melting point analyser (Electrothermal melting point analyser) Cat no.: 1A6304,

For all these analysis, the samples decomposed between the range of 350-410OC to a darker

material (carbonaceous material).

EXPERIMENTAL PROCEDURE TO DETERMINE THE ROLE OF RESINS IN

STABILISING (SOLUBILISING) ASPHALTENES IN CRUDE OIL USING n-HEPTANE

SINGLE SOLVENT ONLY.

To 1ml of each of Bonny Export, Bodo and Mogho crudes (atmospheric residium) 40mls

of n- heptane was added and to this mixture, the same quantity of resins extracted from the

fractionation of n-heptane maltenes (that was obtained from 80mins asphaltenes

precipitation)from Bonny Export, Bodo, and Mogho crudes respectively were added to the same

crude from which they were extracted and stirred with a magnetic stirrer for 80minutes and the

mixtures (resins+1ml of crudes + 40mls of n-heptane) were allowed to age (ie equilibrate) for 2

days (48hours).

After 48hours equilibration (aging) the mixture was Centrifuged for 30minutes at

2000rpm using a Centrifuging apparatus (model no: 80 – 2B). after this procedure the

Supernatant (maltenes) was decanted and kept seperately while the solid residue composed

59

mainly of asphaltenes was kept rinsing with the liquid precipitant (about 40mls) until a clear

solvent was observed. The precipitated asphaltenes were slowly dried in a vacuum

oven/incubator (model; mini/50) at about 80°C until no change in weight was observed .Details

of this result is as shown in chapter 4.

PURIFICATION OF PRECIPITATED C7 – ASPHALTENES WHEN RESINS

WAS ADDED TO THE CRUDE OIL: The dried C7 – asphaltenes were purified to remove any

non asphaltic materia that co-precipitated along with the asphaltenes. To remove this solids the

asphaltenes were dissolved in 10ml of toluene and filtered to remove any solid particles, the

fraction of the C7 – asphaltenes that did not desolve in toluene (non aspaltenic) was discarded.

To the soluble part (composed of asphaltenes) 20ml of n-heptane was added, and then dried in a

vacuum oven at 80°C until no change in weight was observed. Detailed result of this experiment

is shown in chapter 4.

60

CHAPTER FOUR

4.0: RESULTS AND DISCUSSIONS

Asphaltenes has been precipitated from Bonny, Bodo and Mogho (Porth Harcourt) crudes

using n-heptane and n-pentane+n-heptane mixed solvent at various reaction time (20mins,

40mins, 60mins and 80mins). The results of the distillation and composition of the asphaltenes

and maltenes in each of the three different crudes and the role resins play in solubilising

asphaltenes in crude oils are shown in table 4.1, 4.2a, 4.2b.

4.1 RESULTS OF THE PHYSICAL PROPERTIES OF BONNY EXPORT, BODO

AND MOGHO CRUDE OILS BEFORE AND AFTER DISTILLATION AT 350O

C

Table 4.1: PHYSICAL PROPERTIES OF BONNY EXPORT, BODO AND MOGHO

CRUDE OILS BEFORE AND AFTER DISTILLATION

Source of the crude oils Bonny Export Bodo Mogho

Weight of crude used (g) 528.5 632.7 415.8

Weight of atmospheric residuum (g)

182.02 211.7 126.17

Volume of crude (ml) 675 750 500

Volume of atmospheric residuum (ml)

224 250 140

Density of crude (g/ml) 0.78 0.84 0.83

Density of atmospheric residuum (g/ml)

0.81 0.85 0.90

API gravity of crude 49.91 o 36.95 o 38.89 o

API gravity of atmospheric residuum

45.3 o 34.97 o 25.72 o

61

COMMENTS

As accepted generally, there are various types of crudes, the extra heavy crude oil, the heavy

crude oil, the medium crude oil, the light crude oil and the very light crude oil.

� Extra heavy crude oil is any liquid petroleum with an API gravity less than 10°API.

� Heavy crude oil is defined as any liquid petroleum with an API gravity less than 20°API.

� Medium crude oil is any liquid petroleum with an API gravity between 22 - 33° API.

� Light crude oil is any liquid petroleum with an API gravity between 34 - 39°API.

� Very light crude oil is defined as any liquid petroleum with an API gravity above

40°API.

This shows that from the results obtained for API gravity in table 4.1 above Bonny Export is

a very light crude i.e. with an API gravity of 49.91°, Bodo crude is a light crude because its API

gravity is 36.95°API also Mogho crude is a light crude because its API gravity is 38.98° API.

However, after distillation when all the lighter fractions of the various crudes has been

removed, Bonny Export (atmospheric residuum) still behaved like a very light crude but its

density became slightly higher than normal. Bodo (atmospheric residuum) behaved like a light

crude with a slightly raised density compared to its original density but in the case of Mogho

crude though a light crude but after distillation it behaved more like a medium crude and its

density increased greatly compared to its original density. This shows that the heavy organics in

Mogho crude oil will be more compared to that in Bonny Export and Bodo crudes, indicating the

presence of a very high paraffinic material which light crude oils are known for meaning that

Mogho crude may probably have the highest asphaltene content compared to Bodo and Bonny

Export crude, because asphaltene have very limited solubility in paraffinic materials

62

It is a well known fact that density measurement is the simplest way to estimate the

cohesive forces and, therefore, the interaction energies of a particular material. The density is

also a measurement of the molecular parking of the solid, and in the case of aromatic

compounds, this parking strongly depends on the structural molecular topology of the molecules.

This indicates that Mogho crude and Bodo crude with higher densities are likely to have higher

aromaticity, therefore higher asphaltene precipitates and more complex structures than Bonny

Export crude.[80]

4.2: RESULTS FROM ASPHALTENE PRECIPITATION

Detailed result of the compositions of asphaltene and the physical properties of the

maltenes from each of the three crude oils are as shown in the tables below.

Table 4.2a: Composition of Asphaltenes in Bonny Export crude for both n-heptane single

solvent and n-pentane + n-heptane mixed solvent.

Stirring Time

(solvent+ crude)

Solvent Weight of

asphaltenes after

drying (g)

% weight of

asphaltenes (%)

20mins n-heptane 0.001 0.69

40mins n-heptane 0.006 1.33

60mins n-heptane 0.007 1.67

80mins n-heptane 0.009 2.14

20mins n-pentane + n-heptane 0.003 0.88

40mins n-pentane + n-heptane 0.007 1.60

60mins n-pentane + n-heptane 0.008 2.05

80mins n-pentane + n-heptane 0.010 2.90

Table 4.2(a): Shows clearly that the weight / weight 0/0 of asphaltenes increased with increase in stirring time for both single n-heptane solvent and the mixed n-pentane + n-heptane solvents. This is also shown in figure 4.2a and b.

63

FILTRATE (MALTENES) FROM BONNY EXPORT CRUDE AS SHOWN BELOW:

Table 4.2b: Physical Properties of maltenes (filtrate) from Bonny Export crude

Stirring Time

(solvent+ crude)

Solvent Weight of

maltenes

Volume of

maltenes

Density of

maltenes (g/ml)

20mins n-heptane 5.962 9.00 0.662

40mins n-heptane 6.559 9.40 0.698

60mins n-heptane 6.706 9.60 0.699

80mins n-heptane 7.248 10.2 0.711

20mins n-pentane + n-heptane 4.564 7.60 0.6005

40mins n-pentane + n-heptane 4.907 7.20 0.6815

60mins n-pentane + n-heptane 5.066 7.20 0.7036

80mins n-pentane + n-heptane 3.917 5.40 0.7254

Table 4.2 (b): Shows that the densities of the maltenes from Bonny Export crude increased with

increase in asphaltene yield.

Fig. 4.2a(i): % weight of asphaltens for bonny Export Crude (n

Fig. 4.2a(ii): % weight of asphaltenes from Bonny Export Crude (n

solvent system) versus time

0

0.69

0

0.5

1

1.5

2

2.5

3

3.5

0 20mins 40mins

0

0.88

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 20mins 40mins

weight of asphaltens for bonny Export Crude (n-heptane solvent) with time

% weight of asphaltenes from Bonny Export Crude (n-pentane + n

1.33

2.08

3.2

40mins 60mins 80mins

% weight of asphaltene vs

time

1.71

2.9

3.85

40mins 60mins 80mins

% weight of asphaltenes vs

time

64

heptane solvent) with time

pentane + n-heptane

% weight of asphaltene vs

% weight of asphaltenes vs

65

Table 4.3a: Composition of the asphaltenes from Bodo Crude for both n-heptane single

solvent and n-pentane + n-heptane mixed solvent.

Stirring Time

(solvent+ crude)

Solvent weight of

asphaltene

after drying (g)

% weight of

asphaltene

(0/0)

20mins n-heptane 0.012 5.850

40mins n-heptane 0.013 6.191

60mins n-heptane 0.040 7.390

80mins n-heptane 0.039 6.500

20mins n-pentane + n-heptane 0.014 6.830

40mins n-pentane + n-heptane 0.030 7.850

60mins n-pentane + n-heptane 0.043 8.600

80mins n-pentane + n-heptane 0.041 7.523

Table 4.3 (a) : shows that the weight / weight 0/0 of the asphaltenes increased from 20mins to 60

mins but decreased slightly at 80mins stirring time for both the single n-heptane solvent and

mixed n-pentane + n-heptane solvent system. This is also shown in Figure 4.3 a and b.

66

FILTRATE (MALTENES) FROM BODO CRUDE AS SHOWN BELOW:

Table 4.3b: Physical Properties of maltenes (Filtrate) from Bodo Crude for both n-heptane

single solvent and n-pentane + n-heptane mixed solvent.

Stirring Time

(solvent+ crude)

Solvent Weight of

maltenes

Volume of

maltenes

Density of

maltenes (g/ml)

20mins n-heptane 0.838 6.800 0.120

40mins n-heptane 0.837 5.800 0.144

60mins n-heptane 0.811 4.840 0.169

80mins n-heptane 0.820 7.900 0.104

20mins n-pentane + n-heptane 0.836 8.400 0.100

40mins n-pentane + n-heptane 0.818 7.200 0.114

60mins n-pentane + n-heptane 0.820 3.600 0.228

80mins n-pentane + n-hepta ne 0.817 5.000 0.163

Table 4.3(b), shows clearly that the densities of the maltenes from Bodo crude increased

with its resulting asphaltenes (Table 4.3a).

Fig. 4.3a(i) % weight of asphaltenes from Bodo Crudes (n

Fig. 4.3a(ii) % weight of asphaltenes from Bodo Crudes (n

solvent)

0

5.8546.191

0

1

2

3

4

5

6

7

8

0mins 20mins 40mins

0

6.829

7.850

0

1

2

3

4

5

6

7

8

9

10

0mins 20mins 40mins

% weight of asphaltenes from Bodo Crudes (n-heptane single solvent)

% weight of asphaltenes from Bodo Crudes (n-pentane + n

6.191

7.390

6.500

60mins 80mins

% weight of

asphaltene vs time

7.850

8.600

7.520

60mins 80mins

% weight of

asphaltene vs time

67

heptane single solvent)

pentane + n-heptane mixed

68

Table 4.4a: Composition of the asphaltenes in Mogho crude for both n-heptane single

solvent and n-pentane + n-heptane mixed solvent.

Stirring Time Solvent Weight of

asphaltene after

drying (g)

% weight of

asphaltene

20mins n-heptane 0.029 10.623

40mins n-heptane 0.027 10.189

60mins n-heptane 0.018 6.590

80mins n-heptane 0.024 9.877

20mins n-pentane + n-heptane 0.036 11.688

40mins n-pentane + n-heptane 0.029 10.546

60mins n-pentane + n-heptane 0.024 6.838

80mins n-pentane + n-heptane 0.025 10.081

Table 4.4(a), shows clearly that the weight / weight 0/0 of the asphaltenes decreased from

20mins to 60mins but increased slightly with 80mins stirring time giving a precipitate slightly

higher than the precipitate obtained from 60mins stirring time for the n-heptane single solvent

and the n-pentane + n-heptane mixed solvent. This is also shown in Figure 4.4 a and b.

69

FILTRATE (MALTENES) FROM MOGHO CRUDE AS SHOWN BELOW:

Table 4.4b: physical properties of maltenes from Mogho crude for both n-heptane single

solvent and n-pentane + n-heptane mixed solvent.

Stirring Time Solvent Weight of

maltenes

Volume of

maltenes

Density of

maltenes (g/ml)

20mins n-heptane 0.871 10.20 0.085

40mins n-heptane 0.873 10.60 0.082

60mins n-heptane 0.876 12.00 0.073

80mins n-heptane 0.882 11.20 0.0788

20mins n-pentane + n-heptane 0.864 4.80 0.180

40mins n-pentane + n-heptane 0.876 5.00 0.175

60mins n-pentane + n-heptane 0.871 6.00 0.145

80mins n-pentane + n-heptane 0.875 6.20 0.14

Table 4.4b, shows clearly that the densities of the maltenes increased along side with

their corresponding asphaltenes, but decreased at 60mins stirring time for n-heptane single

solvent and also decreased at 80mins stirring time for n-pentane + n-heptane mixed solvent.

Fig. 4.4a(i) % weight of asphaltenes from Mogho Crude (n

Fig. 4.4(ii) % weight of asphaltenes from Mogho Crude

vs time

00

2

4

6

8

10

12

0mins 20mins

00

2

4

6

8

10

12

14

0mins 20mins

% weight of asphaltenes from Mogho Crude (n-heptane single solvent) vs time

% weight of asphaltenes from Mogho Crude (n-heptane + n-pentane mixed solvent)

10.62310.189

6.59

9.877

20mins 40mins 60mins 80mins

% weight of

asphaltenes vs time

11.688

10.546

6.838

10.081

20mins 40mins 60mins 80mins

% weight of

asphaltenes vs time

70

heptane single solvent) vs time

pentane mixed solvent)

asphaltenes vs time

asphaltenes vs time

71

4.3 COMPARISM OF THE WEIGHT OF THE PRECIPITATED ASPHALTENE

WITH STIRRING TIME USING N-HEPTANE SINGLE SOLVENT AND N-

PENTANE + N-HEPTANE MIXED SOLVENT.

It is generally accepted that asphaltene precipitation depends mainly on the stability of

the asphaltenes and stability depends not only on the properties of the asphaltene fraction but on

how good a solvent the rest of the oil is for its asphaltenes.

In comparism of the weight of the asphaltene precipitated using n– heptane single solvent

and n–pentane + n-heptane mixed solvent with respect to stirring time for Bonny Export, Bodo

and Mogho crudes:

Table 4.2 (a-b), table 4.3 (a-b), and table 4.4 (a-b) shows the percentage weight of

asphaltenes precipitated from Bonny Export, Bodo and Mogho crudes and their resulting

maltenes using n-heptane single solvent and n-pentane + n-heptane mixed solvent for 20, 40, 60

and 80 minutes stirring time for each of the crudes.

Table 4.2 (a-b) from Bonny Export crude shows that the weight of asphaltenes precipitate

increased with increase in stirring time, for both the C7 – asphaltene and the C5 + C7 –

asphaltenes (Figure 4.2 a - b), also the densities of their maltenes increased with increase in

stirring time.

In the case of Bodo crude (Table 4.3 a-b) and Mogho crude (Table 4.4 a-b), their

asphaltene precipitate do not follow the same trend as in Bonny Export crude (Figure 4.3 a-b and

Figure 4.4 a-b), but the densities of their maltenes increased alonge with their corresponding

asphaltene precipitate. According to these results, it is possible to suppose that asphaltene

precipitation depends on stirring time but due to the presence of other solubility fractions (i.e. the

saturates, aromatics and resins) which may not be present in the right ratios, Bodo and Mogho

crudes did not depend on stirring time. It may also be because the other solubility fractions

as saturates, aromatics and resins)

asphaltenes, therefore making their asphaltenes unstable and so prec

were more and did not depend on stirring time.

It was also noticed that Mogho crude (though a light crude) precipitated more asphaltenes

followed by Bodo crude and then Bonny Export crude for both single and mixed solvent system

(Figure 4.5 and 4.6 below). This indicates that the amount and characteristics of the asphaltene

constituents in crude oil depends to a greater

MIXED GRAPH OF ASPHALTENE PRECIPITATE FROM BONNY

AND MOGHO CRUDES USING N

TO TIME.

Figure 4.5: Effect of n-heptane single solvent with

and Mogho Crudes

0

2

4

6

8

10

12

20mins 40mins

0.691.33

5.856.191

10.62310.189

not depend on stirring time. It may also be because the other solubility fractions

as saturates, aromatics and resins) in Bodo and Mogho crude oils are not good solvents for their

asphaltenes, therefore making their asphaltenes unstable and so precipitation in these crudes

not depend on stirring time.

Mogho crude (though a light crude) precipitated more asphaltenes

followed by Bodo crude and then Bonny Export crude for both single and mixed solvent system

. This indicates that the amount and characteristics of the asphaltene

l depends to a greater extent on the source of the crude.[9]

HALTENE PRECIPITATE FROM BONNY EXPORT, BODO

CRUDES USING N-HEPTANE SINGLE SOLVENT WITH RESPECT

heptane single solvent with stirring time on Bonny

Crudes

40mins 60mins 80mins

2.08

3.2

6.191

7.390

6.5

10.189

6.59

9.877

% weight of asphaltenes

for Bonny Export crude

using single solvent

% weight of asphaltenes

for Bodo crude using

single solvent

% weight of asphaltenes

for Mogho crude using

single solvent

72

not depend on stirring time. It may also be because the other solubility fractions (such

not good solvents for their

ipitation in these crudes

Mogho crude (though a light crude) precipitated more asphaltenes

followed by Bodo crude and then Bonny Export crude for both single and mixed solvent system

. This indicates that the amount and characteristics of the asphaltene

[9]

EXPORT, BODO

SOLVENT WITH RESPECT

Bonny Export, Bodo

% weight of asphaltenes

for Bonny Export crude

% weight of asphaltenes

for Bodo crude using

% weight of asphaltenes

for Mogho crude using

MIXED GRAPH OF ASPHALTENE PRECIPITATE FROM BONNY

AND MOGHO CRUDES USING N

WITH RESPECT TO STIRRING

Figure 4.6: Effect of n-heptane

Bodo and Mogho Crudes

COMMENT

For both Bonny Export, Bodo and Mogho crudes as shown in

mixed solvent precipitant (n-pentane + n

solvent (n-heptane) precipitant. This is due to the addition of n

made up the mixed solvent system as

asphaltene precipitation increases with decrease in the carbon chain

solvent. [75] This increase in asphaltene yield for precipitation using mixed solvent system is also

indicative of the fact that for a given crude oil sample, the yield and properties of the precipitated

20mins

0.88

6.82911.688

% weight of asphaltenes for Bonny Export Crude using mixed solvent

% weight of asphaltenes for Bodo Crude using mixed solvent

% weight of asphaltenes for Mogho Crude using mixed solvent

ALTENE PRECIPITATE FROM BONNY EXPORT, BODO

USING N-PENTANE + N-HEPTANE MIXED SOLVENTS

STIRRING TIME.

heptane + n-pentane mixed solvent precipitant on

Bodo and Mogho Crudes

, Bodo and Mogho crudes as shown in figures 4.5 and 4.6 above, the

pentane + n-heptane) precipitated more asphaltenes than single

This is due to the addition of n – pentane to n

made up the mixed solvent system as in agreement with the generally accepted fact that

asphaltene precipitation increases with decrease in the carbon chain – length of the precipitating

This increase in asphaltene yield for precipitation using mixed solvent system is also

cative of the fact that for a given crude oil sample, the yield and properties of the precipitated

40mins 60mins 80mins

1.71

2.93.85

7.8508.600

7.52310.546

6.838

10.081

% weight of asphaltenes for Bonny Export Crude using mixed solvent

% weight of asphaltenes for Bodo Crude using mixed solvent

% weight of asphaltenes for Mogho Crude using mixed solvent

73

EXPORT, BODO

MIXED SOLVENTS

on Bonny Export,

figures 4.5 and 4.6 above, the

heptane) precipitated more asphaltenes than single

pentane to n – heptane which

in agreement with the generally accepted fact that

length of the precipitating

This increase in asphaltene yield for precipitation using mixed solvent system is also

cative of the fact that for a given crude oil sample, the yield and properties of the precipitated

74

asphaltenes strongly depend on the specific precipitation method and precipitant used. This

means that a single oil could have two or more results depending on the precipitant used.[8]

4.4 SUMMARY OF THE RESULT OF FTIR SPECTROPHOTOMETRIC

ANALYSIS

Table 4.5a: RESULT OF IR ANALYSIS OF ASPHALTENES OBTAINED USING

SINGLE N-HEPTANE SOLVENT

Samples (A)

Asphaltenes Precipitation

using Single Solvent (n-

heptane)

Approximate

characteristic

frequencies (cm-1

)

Bonds

Bonny Export Crude

733.94

1264.38

3056.31

Substituted aromatic hydrocarbon.

C – H bending.

C – H of aromatics.

Mogho (Port Harcourt) Crude

734.90

1265.35

1441.84

2930.9

3080.

Substituted aromatic hydrocarbon.

C – H bending.

C – H bending.

Cyclic aliphatic hydrocarbon.

C-H of aromatics.

Bodo Crude

734.9

971.19

1271.13

1373.36

1456.30

1601.93

1718.63

2933.83

3060

Substituted aromatics hydrocarbon

C = C – H bending out of plane.

C–H bending.

C-H bending.

C – H bending.

C = C of aromatic

C = O (acid, aldehydes, ketones and esters

Cyclic aliphatic hydrocarbon. C-H of aromatics.

75

TABLE 4.5b: RESULTS OF IR ANALYSIS OF ASPHALTENES OBTAINED USING N-

PENTANE + N-HEPTANE MIXED SOLVENT SYSTEM.

Samples B

Asphaltenes Precipitated

using mixed Solvent (n-

pentane+n-heptane)

characteristic

frequencies (cm-1

)

Bonds

Bonny Export Crude at

733.94

1264.38

2932.86

Substituted aromatic hydrocarbon

C – H bending

Cyclic aliphatic hydrocarbon.

Mogho (Port Harcourt) Crude

736.83

1266.31

1450.52

2931.9

Substituted aromatic hydrocarbon.

C – H bending.

C – H bending.

Cyclic aliphatic hydrocarbon.

Bodo Crude 734.90

1276.92

1459.2

1726.35

2929.97

Substituted aromatic hydrocarbon.

C – H bending.

C – H bending.

C = O (acid, aldehydes, ketones and esters

Cyclic aliphatic hydrocarbon.

IR INTERPRETATION

Data from IR as shown in figure I-VI in the appendice is summarized in table 4.5a and b,

obtained from Bonny Export, Bodo and Mogho crudes shows characteristic frequencies at

3056.31,3060,3080 that are due to C-H stretch for aromatic hydrocarbon. This is supported by

the absorptions at 733.94, 734.90, 736.83 that are due to substituted aromatic hydrocarbon. This

confirms the same class of crude oil composition, this class of crude oil composition consist of

the unsaturated part of asphaltenes, that is that part of asphaltenes that consist of fused benzene

rings. However, absorption frequencies at 2933.83, 2930.93, 2932.86, 2929.97 and 2931.9 are

76

due to cyclic aliphatic hydrocarbon. This is supported by the absorptions at 1264.34, 1271.17,

1265.35, 1276.92, 1266.31 that are due to C-H bending. These suggest the same class of crude

oil composition. These classes of crude oil consist of the saturated part of asphaltenes structure.

The IR reveals that asphaltenes fraction of crude oil is made up of both saturated and unsaturated

part as supported by our UV spectra on the asphaltene precipitates.

4.5 RESULTS OF UV/VISIBLE SPECTROPHOTOMETRIC ANALYSIS.

Table 4.6: UV Spectra of the Asphaltene Fractions of Crude Oil.

Samples UV Spectra Data

Asphaltenes precipitated using single solvent

(n-heptane) for 80 minutes

λ (nm) A λ (nm) A

Bonny Export Crude (C7 asphaltenes) 389.8 1.935 418.2 1.366

Bodo Crudes (C7 asphaltenes) 388.9 2.389 509.6 2.906

Mogho Crude (C7 asphaltenes) 389.8 2.303 510.0 2.888

Asphaltenes precipitated using mixed solvent

(n-pentane+n-heptane) for 80 minutes

Bonny Export Crude (C5 + C7 asphaltenes) 388 2.149 449.4 2.389

Bodo Crudes (C5 + C7 asphaltenes) 387.2 2.833 482.6 2.791

Mogho Crude (C5 + C7 asphaltenes) 388.6 2.977 432.8 2.193

UV/VISIBLE INTERPRETATION

Table 4.6 shows the summary of the UV-visible spectra data of asphaltene fractions from

Bonny Export, Bodo and Mogho crudes using n-heptane single solvent and n-pentane + n-

heptane mixed solvent system for 80mins stirring time as shown in figure vii - xii (Appendix 14

– 19). Each of the asphaltene fractions shows absortion maxima in the visible region of the

77

electromagnetic spectrum, indicating that the C7 and C5 + C7 asphaltenes are largely unsaturated

as supported by the asphaltene structure in figures 2.3a, 2.3b, 2.4a and 2.4b.

Similar absoptions at the following wavelengths: 389.8, 388.9, 387.2 and 388.6nm which

are supported by absorptions at 418.2, 509.6, 510.0, 449.4, 482.6 and 432.8nm suggest the same

class(es) of crude oil composition which is the presence of fused benzene rings or polynuclear

aromatics in asphaltenes which indicate unsaturated and highly conjugated systems. These are

similar to the absorptions found in the literature. The range of the absorption bands for both the

C7 and C5 + C7 asphaltenes are about 400 – 500nm which corresponds to benzenoide band for

highly polynuclear aromatics. This is in agreement with the asphaltene structure. In addition the

uv visible absorption bands are similar to those shown else where (Evdokimov and Losev).[81]

This range (400-500) of absorption band for all the asphaltene precipitates obtained from

Bonny Export, Bodo, and Mogho crudes, which corresponds to the benzenoid bands for

polynuclear aromatics, implies the existence of chromophores in the asphaltenes. These

asphaltenes as a consequence are coloured the chromophores very likely available in these

asphaltenes are: conjugated double bonds involving aromatic hydrocarbons as supported by the

infrared spectra on the asphaltenes from Bonny Export,Bodo and Mogho crudes.

From molecular orbital theory, the allowed possible transitions are: σ →σ*, n→σ*,

П→П*, and n→П* where n= non bonding, σ = sigma, П = pie and those with asterisk are anti-

bonding. The wavelength absorption range is consistent with fundamental molecular orbital

theoretical assumption or specification. This assumptions is that the energy difference ∆E =

HOMO – LUMO is small, and also the longer the wavelength of absorption, the smaller the

energy of irradiation. Thus, exposure of these compounds with small ∆E values and long

78

wavelengths of absorptions to high irradiation energies will destroy these compounds. Hence,

under these conditions, they can decompose.

Our UV and IR spectra are consistent and reveal the presence of some Island and

Archipelago architectures (Sabbah et al, 2011)[82]: 2,3,7,8,12,13,17,18 – octaethyl - 21H, 23H –

porphine; 5,10,15,20 – Tetra – p- tolyl – 21H, 23H-porphine; 5,10,15,20 – Tetrakis (4-

methoxyphenyl) -21H, 23H – porphines; 5,10,15,20 – Tetrakis [4 – (allyloxy) phenyl] – 21H,

23H – porphine; phenanthrene; 1,3,6,8 – tetradecyl pyrene; 2,7 –Bis (2-pyren-1-yl-ethyl) -9, 9 –

diethyl – 9H – fluorene; 1,4 –Bis (2-pyren-1-yl-ethyl) – benzene; 1,4 –dipyren – 1 yl- butane.

4.6 RESULT OF THE CHEMICAL AND PHYSICAL PROPERTIES OF CRUDE OILS

OBTAINED FROM N-HEPTANCE MALTENES

Table 4.7: Chemical and Physical Properties of Crude oils as obtained from

n-heptane maltenes ( 80minutes).

Source

of crude

API

gravity

of crude

Density of

atmospheric

residuum

Wt of

saturates

Wt of

aromatics

Ratio of

aromatics

to

saturates

Wt

of

resin

s (g)

Wt of

asphalt

enes

Ratio of resins

to asphaltenes

Bonny

Export 49.91 0.81 0.364 0.114 0.313 0.121 0.01 12.1

Bodo

crude 36.95 0.85 0.574 0.159 0.277 0.085 0.039 2.180

Mogho

crude 38.98 0.90 0.643 0.17 0.264 0.100 0.050 2.000

Table 4.7 shows the physical and chemical properties of the studied crudes. As

mentioned earlier, it is generally accepted that a high ratio of resins to asphaltenes and aromatics

to saturates is indicative of low asphaltene precipitation risk.[2] As recognized by De Boer et al,

79

the heavier oil also contains plenty of intermediate component that are good asphaltene solvents

whereas the light oil may consist largely of paraffinic materials in which, by definition,

asphaltenes have very limited solubility.[13]

In this present study, the composition factor mentioned were examined and shown in

Table 4.7. The three crudes shows very high values of saturates, indicating the presence of

paraffinic material. Also, according to these results, it is possible to suppose that the crude oils

with higher densities also show the higher cohesive energies and, therefore, the lower solubility

in the crude oil generating unstable crude oils. This result also shows that the density and

aromaticity of the crudes increases simultaneously as the asphaltene precipitates increases from

Bonny Export, Bodo and Mogho crudes. This shows that crude oil with higher aromaticity,

higher saturates and higher density like in Bodo and Mogho crude oils precipitate more

asphaltenes, and are likely to be problematic, most times such crudes are termed unstable crudes.

Infact, it was observed that the ratio of saturates to aromatics and the ratio of resins to

asphaltenes decreases as the asphaltene precipitate increases. This can be shown in the chart

below (figure 4.9).

Figure 4.9: Weight of heavy fractions of each of the three crude oils

studied and their various asphaltene content.

Figure 4.9 shows a bar chart which can be interpreted in terms of asphaltene stability and

stabilization properties of the maltenes.

From the bar chart above Mogho crude has the highest precipitation of asphaltenes

because of the presence of saturate which indicates high paraffinic material in which by

definition asphaltenes has limited solubility also the weigh

crude indicating higher asphaltene precipitation than in Bonny Export and Bodo crudes. Also as

mentioned earlier the ratio of saturates to aromatics and resins to asphaltenes is highest for

Bonny Export crude indicating t

lowest for Mogho crude, indicating the highest asphaltene precipitation risk. All these shows

that Mogho crude is likely to be more problematic followed by Bodo crude.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Bonny Export

0.364

0.114

0.121

0.01

eight of heavy fractions of each of the three crude oils

studied and their various asphaltene content.

Figure 4.9 shows a bar chart which can be interpreted in terms of asphaltene stability and

erties of the maltenes.

From the bar chart above Mogho crude has the highest precipitation of asphaltenes

because of the presence of saturate which indicates high paraffinic material in which by

definition asphaltenes has limited solubility also the weight of aromatics is higher in Mogho

crude indicating higher asphaltene precipitation than in Bonny Export and Bodo crudes. Also as

mentioned earlier the ratio of saturates to aromatics and resins to asphaltenes is highest for

Bonny Export crude indicating the lowest asphaltene precipitation risk and these ratios are

lowest for Mogho crude, indicating the highest asphaltene precipitation risk. All these shows

that Mogho crude is likely to be more problematic followed by Bodo crude.

Bodo Crude Mogho Crude

0.574

0.643

0.159 0.17

0.085 0.1

0.039 0.05

wt of saturates (g)

wt of aromatics (g)

wt of resins (g)

wt of asphaltenes (g)

80

eight of heavy fractions of each of the three crude oils

Figure 4.9 shows a bar chart which can be interpreted in terms of asphaltene stability and

From the bar chart above Mogho crude has the highest precipitation of asphaltenes

because of the presence of saturate which indicates high paraffinic material in which by

t of aromatics is higher in Mogho

crude indicating higher asphaltene precipitation than in Bonny Export and Bodo crudes. Also as

mentioned earlier the ratio of saturates to aromatics and resins to asphaltenes is highest for

he lowest asphaltene precipitation risk and these ratios are

lowest for Mogho crude, indicating the highest asphaltene precipitation risk. All these shows

wt of saturates (g)

wt of aromatics (g)

wt of resins (g)

wt of asphaltenes (g)

81

4.7 RESULT OF THE EFFECT OF RESINS ON ASPHALTENE PRECIPITATION

Addition of resins to crude oil reduced the precipitation of asphaltenes in the crude oil as

shown in Table 4.8 below.

Table 4.8: Effect of Resins on Asphaltene Precipitation.

Weight % of asphaltenes without resins Weight % of asphaltenes with

resins

Source of

crude

Final weight

of asphaltenes

Weight % of

asphaltenes

Final weight

of asphaltenes

after

purification

Weight % of

asphaltenes

Bonny Export 0.013 3.2 0.008 1.663

Bodo crude 0.039 6.5 0.018 3.035

Mogho Crude 0.050 9.877 0.023 5.425

In the experiment reported in table 4.8 Above, resins separated from Bonny Export crude

oil were added to the n – heptanes solution (i.e. 1ml crude + 40ml of n – heptane) of Bonny

Export crude oil, also the resins separated from Bodo crude and Mogho crudes were added to

their various n-heptane solutions (ie 1ml crude + 40ml n –heptane). From table 4.8 shown

above, 3.2% of asphaltene was precipitated from Bonny Export crude, 6.5% from Bodo crude

and 9.877% from Mogho crude before addition of the resins extracted from each of the crudes

but after the addition of resins to these crude oils, asphaltene precipitation in Bonny Export

crude, Bodo crude and Mogho crude reduced to 1.663%, 3.035% and 5.425% respectively

indicating that resins stabilize (solubilize) asphaltenes in crude oil.

Figure 4.10 shows the effectiveness of

To estimate the relative contribution of the resins to the stability of the crude oil, a plot of

the effectiveness of the resins and the asphaltene precipitation reduction as a function of the

stability of the crude oils is shown in Figure 4.10 above.

Figure 4.10 shows that the percentage weight of asphaltenes in Mogho, Bodo and Bonny

Export crudes (when resins extracted from the crude was added) reduced from 9.877

and 3.20/ 0 respectively to 5.425

Bonny Export). Indicating that resins stabilize (solubilize) asphaltenes in crude oil.

0 2

Bonny Export

Bodo crude

Mogho Crude

.10 shows the effectiveness of resins to stabilize their corresponding asphaltenes.

To estimate the relative contribution of the resins to the stability of the crude oil, a plot of

effectiveness of the resins and the asphaltene precipitation reduction as a function of the

stability of the crude oils is shown in Figure 4.10 above.

Figure 4.10 shows that the percentage weight of asphaltenes in Mogho, Bodo and Bonny

resins extracted from the crude was added) reduced from 9.877

to 5.4250/0( for Mogho crude), 3.0350/0( for Bodo), and 1.663

Bonny Export). Indicating that resins stabilize (solubilize) asphaltenes in crude oil.

2 4 6 8 10

3.2

6.5

9.877

1.663

3.035

5.425

Weight % of asphaltenes

with resins

Weight % of asphaltenes

without resins

82

resins to stabilize their corresponding asphaltenes.

To estimate the relative contribution of the resins to the stability of the crude oil, a plot of

effectiveness of the resins and the asphaltene precipitation reduction as a function of the

Figure 4.10 shows that the percentage weight of asphaltenes in Mogho, Bodo and Bonny

resins extracted from the crude was added) reduced from 9.8770/0, 6.50/0

( for Bodo), and 1.6630/0(for

Bonny Export). Indicating that resins stabilize (solubilize) asphaltenes in crude oil.

Weight % of asphaltenes

Weight % of asphaltenes

83

CHAPTER FIVE

Conclusion

Asphaltene precipitation with stirring time using n–heptane single solvent and n-pentane

+ n-heptane mixed solvent from 350OC atmospheric residuum (dead crude oils) is a useful

method to study the stability of crude oils. It was also found to be an important technique for the

study of the chemical factors that affect asphaltene precipitation.

As said earlier De Boer et al, recognized that light crude oils may consist largely of

paraffinic material in which by definition asphaltenes has very limited solubility.[13] This

indicates why the weight of saturates (composed mainly of paraffinic material) obtained from

these studied crude oils were very high compared to the weights of their aromatics, resins and

asphaltenes.

In this present study, it was also found that the density and the aromaticity of the

atmospheric residium increases simultaneousely with increase in asphaltenes from Bonny

Export, Bodo to Mogho crudes. There was a noticeable decrease in the ratio of aromatics to

saturates and resins to asphaltenes with Bonny Export having the highest ratio and Mogho the

least, there was also a noticeable increase in the ratio of asphaltenes to maltenes with Bonny

Export having the least ratio and Mogho the higest ratio. This shows that Mogho crude has the

highest asphaltene precipitate and Bonny Export the least. Therefore, Mogho crude with the

highest amount of density, saturate, aromaticity and asphaltenes is likely to be more problematic.

Further more, the drastic reduction of asphaltene precipitate in Bonny Export, Bodo and

Mogho crudes with additional resins extracted from the same crudes showed that resins from one

crude oil solubilise asphaltenes from the same crude oil.

84

This study also shows generally that the maltenes from Bonny Export crude oil exhibits higher

asphaltene stabilization effectiveness compared to the maltenes from Bodo and Mogho crude oils

indicating that Bonny Export crude is a more stable crude compared to Bodo and Mogho crudes

(unstable crudes).

Finally, this study shows clearly that asphaltene precipitation occurs in crude oil but other

constituents of crude oil especially resins, influence this precipitation. Thus resins play a critical

role in asphaltene precipitation.

85

NEW KNOWLEDGE ARISING FROM THIS RESEARCH WORK

For the first time precipitation of asphaltenes from 3500C atmospheric residuum (dead crude oil)

using mixed solvent system is reported.

This research work confirmed that the length of stirring time affect the yield of asphaltenes. This

has not been reported before.

Apart from the generally accepted fact that high ratio of aromatic to saturates and resins to

asphaltenes is indicative of low asphaltene precipitation risk. It was found from this work that

high ratio of asphaltenes to maltenes is indicative of high asphaltene precipitation risk.

This work showed that NAMAL method was an effective method for the separation of

atmospheric residuum into asphaltenes and maltenes.

This work showed that SAR method was an effective and cheap method for the separation of

maltenes into saturates, aromatics, and resins.

It was found that increasing resin content of one crude oil solubilizes the asphaltenes from the

same crude oil.

86

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96

APPENDIX 1

MAP OF THE SOURCE OF BONNY EXPORT, BODO AND MOGHO CRUDE OILS

▼

◄

►

97

APPENDIX 2

DENSITY OF CRUDE OIL IN g/ml

Bonny Export Bodo Mogho

0.78 0.84 0.83

Density of crude (g/ml) = ������ � �� �(�)

������ � �� �(��)

Bonny Export crude = ���.�

���= 0.78�/�

Bodo crude = �!�.�

��"= 0.84�/�

Mogho crude = $%�.�

�""= 0.83�/�

DENSITY OF ATOMPHERIC RESIDUUM

Bonny Export Bodo Mogho

0.81 0.85 0.90

Density of atmospheric residuum in g/ml = ������ � '���()���� ��(� ���(�)

������ � '���()����(��)

Bonny export = %��."�

��$= 0.81�/�

Bodo = �%%.�

��"= 0.85�/�

Mogho = %��.%�

%$"= 0.90�/�

98

APPENDIX 3

API GRAVITY OF THE CRUDE OILS

Bonny Export Bodo Mogho

49.91O 36.95O 38.89O

OAPI gravity = %$%.�

-)��� ��'���. − 131.5

Bonny Export = %$%.�

".�� − 131.5 = 49. 910

Bodo = %$%.�

".�$ − 131.5 = 36.950

Mogho = %$%.�

".�! − 131.5 = 38.890

API GRAVITY OF ATMOSPHERIC RESIDUUM

Bonny Export Bodo Mogho

45.3O 34.97O 25.72O

OAPI gravity = %$%.�

-)��� ��'���. − 131.5

Bonny Export = %$%.�

".�% − 131.5 = 45.300

Bodo = %$%.�

".�� − 131.5 = 34.972

Mogho = %$%.�

".3" − 131.5 = 25.720

99

APPENDIX 4

PERCENTAGE WEIGHT OF ASPHALTENES FROM BONNY EXPORT

ATMOSPHERIC RESIDUUM

Stirring time Solvent Weight of asphaltenes before drying (g)

Weight of asphaletenes after drying (g)

Percentage weight of asphaltenes (%)

20mins n-heptane 0.144 0.001 0.69%

40mins n-heptane 0.450 0.006 1.33%

60mins n-heptane 0.385 0.008 2.08%

80mins n-heptane 0.312 0.010 3.20%

20mins n-pentane + n-heptane 0.343 0.003 0.88

40mins n-pentane + n-heptane 0.410 0.007 1.71

60mins n-pentane + n-heptane 0.345 0.010 2.90

80mins n-pentane + n-heptane 0.312 0.012 3.85

Percentage weight of Bonny export asphaltenes = 56789: 2; <=>9<?:6@6= <;:6A BAC7@8

������ � '()�'���D�( E���� �.�D� × 100

Density of Bonny Export maltenes = ������ �'���D�( (�)

G����� � �'���D�( (��)

100

APPENDIX 5

PERCENTAGE WEIGHT OF ASPHALTENES FROM BODO ATMOSPHERIC

RESIDUUM

Stirring time Solvent Weight of asphaltenes before drying (g)

Weight of asphaletenes after drying (g)

Percentage weight of asphaltenes (%)

20mins n-heptane 0.205 0.012 5.850

40mins n-heptane 0.210 0.013 6.190

60mins n-heptane 0.541 0.040 7.390

80mins n-heptane 0.600 0.039 6.500

20mins n-pentane + n-heptane 0.205 0.014 6.830

40mins n-pentane + n-heptane 0.382 0.030 7.850

60mins n-pentane + n-heptane 0.500 0.043 8.600

80mins n-pentane + n-heptane 0.545 0.041 7.523

Percentage weight of Bodo asphaltenes = 56789: 2; <=>9<?:6@6= <;:6A BAC7@8

������ � '()�'���D�( E���� �.�D� × 100

Density of Bodo maltenes = ������ �'���D�( (�)

G����� � �'���D�( (��)

101

APPENDIX 6

PERCENTAGE WEIGHT OF ASPHALTENES FROM MOGHO ATMOSPHERIC

RESIDUUM

Stirring time Solvent Weight of asphaltenes before drying (g)

Weight of asphaletenes after drying (g)

Percentage weight of asphaltenes (%)

20mins n-heptane 0.273 0.029 10.623

40mins n-heptane 0.265 0.027 10.189

60mins n-heptane 0.273 0.018 6.590

80mins n-heptane 0.243 0.024 9.877

20mins n-pentane + n-heptane 0.308 0.036 11.688

40mins n-pentane + n-heptane 0.275 0.029 10.546

60mins n-pentane + n-heptane 0.351 0.024 6.838

80mins n-pentane + n-heptane 0.248 0.025 10.081

Percentage weight of Mogho asphaltenes = 56789: 2; <=>9<?:6@6= <;:6A BAC7@8

������ � '()�'���D�( E���� �.�D� × 100

Density of Mogho maltenes = ������ �'���D�( (�)

G����� � �'���D�( (��)

102

APPENDIX 7

WEIGHT OF MALTENES AND RATIO OF ASHALTENES TO MALTENES

Source of crudes

Weight of

saturate (g)

Weight of

aromatics (g)

Weight of

resins (g)

Weight of

asphaltenes

(g)

Weight of

maltenes (g)

Ratio of

asphaltenes

to maltenes

Bonny Export

0.364 0.114 0.121 0.010 0.599 0.017

Bodo 0.574 0.159 0.085 0.039 0.818 0.048

Mogho 0.643 0.170 0.100 0.050 0.913 0.055

Weight of maltenes (g) = wt of saturates + wt of aromatics + wt of resins

Ratio of asphaltenes to maltenes = 56789: 2; <=>9<?:6@6=

������ � �'���D�(

PERCENTAGE WEIGHT OF ASPHALTENE FROM 350O

C ATMOSPHERIC

RESIDUUM WITH ADDITIONAL RESINS EXTRACTED FROM EACH OF THE

CRUDES

Source of crudes Solvent Initial weight of

asphaltenes before

drying (g)

Final weight of

asphaltenes after

drying (g)

Percentage weight

of asphaltenes

(%)

Bonny Export n-heptane 0.481 0.008 1.663

Bodo n-heptane 0.018 0.593 3.035

Mogho n-heptane 0.023 0.424 5.425

Percentage of weight of asphaltenes when resins was added to the atmospheric residuum =

HD���'� ������ � '()�'���D�( E���� �.�D� (�)

I�D'� ������ � '()�'���D� '��� �.�D� × 100

103

APPENDIX 8

Figure 1: C7 asphaltene from Bonny Export Crude

104

APPENDIX 9

Figure II: C7 asphaltene from Bodo Crude

ANIGBOGU IFEOMA V.

105

APPENDIX 10

Figure III: C7 asphaltene from Mogho Crude

106

APPENDIX 11

Figure IV: C5 + C7 asphaltene from Bonny Export Crude

107

APPENDIX 12

Figure V: C5 + C7 asphaltene from Bodo Crude

ANIGBOGU IFEOMA V.

108

APPENDIX 13

Figure VI: C5 + C7 asphaltene from Mogho Crude

109

APPENDIX 14

Figure VII: C7 asphaltene from Bonny Export Crude (UV)

110

APPENDIX 15

Figure VIII: C7 asphaltene from Bodo Crude (UV)

111

APPENDIX 16

Figure IX: C7 asphaltene from Mogho Crude (UV)

112

APPENDIX 17

Figure X: C5 + C7 asphaltene from Bonny Crude (UV)

113

APPENDIX 18

Figure XI: C5 + C7 asphaltene from Bodo Crude (UV)

114

APPENDIX 19

Figure XII: C5 + C7 asphaltene from Mogho Crude (UV)