Asphaltene and Naphthenate Mechanisms of Emulsion ... · Asphaltene and Naphthenate Mechanisms of Emulsion Stabilization in water-in-crude oil Emulsions Marit-Helen Ese, Keith L

Trondheim Emulsions 6-23-03 1

Asphaltene and Naphthenate Mechanisms of EmulsionStabilization in water-in-crude oil Emulsions

Marit-Helen Ese, Keith L. Gawrys andPeter K. Kilpatrick

(919) 515-7121; (919) 515-3465 (fax)[email protected]

Symposium Honoring Dr. Jan Czarnecki on theOccasion of his 65th Birthday

4th International Conference on Petroleum Phase Behavior5th International Symposium on the Chemistry and Physics of

Petroleum-Water EmulsionsTrondheim, Norway, June 23-26, 2003


MotivationProcessing naphthenic acid-based crudes involves:

Emulsion problems - severe separation and transport problems - bad oil quality

Foam problems during transportPrecipitation of metal salts based on naphthenic acids(naphthenates)

- separation problemsCorrosion problems during refining and transportCatalyst problems

- refining problemEnvironmental problems (bad water quality)


OutlineRecent Observations on PetroleumEmulsions

Naphthenate Molecular Structures

Emulsion Stabilization Results

Optical Polarizing Microscopy

Neutron Scattering of Emulsions: TheCore-Shell Model

Conclusions and Acknowledgements


CEF Design and Measurement Principles• CEF is a measure of the electric field

strength required to induce the flow ofcurrent through a w/o emulsion

• Surface-active crude components form abarrier to current flow until electromotiveforce causes film rupture and watercoalescence

0

0.005

0.01

0.015

0.02

0.025

0.03

0 0.4 0.8 1.2 1.6

Cur

rent

(mA

)

Electric Field (kV/cm)cef

+

- V

V

V

+

-

+

-critical electric field - water bridges

electrodes, conductivity jumps

+

- droplet chains lengthen and bridge

entire gap

0 kV/cm droplets form short chains parallel to electric field

+

-


Water-in-Crude Oil Emulsion Stability:Asphaltenic vs Naphthenate Mechanism

0

0.5

1

1.5

2

2.5

3

0 2 4 6 8 10

water

= 0.30, T=60oC, Salinity = 1% NaCl

AHHOB4B6CSABANSTHSJVAlbaSMSCSAfricac.e.f.

y = 0.34582 + 0.27709x R= 0.96401

Cri

tical

Ele

ctri

c Fi

eld

(kV

/cm

)

Asphaltene x Delta H/C

Block 17 Africa Crude – High TAN #

Strong Correlation for Asphaltenic Crudes


Dalia (Block 17 West Africa) W/O Emulsion Stability:Goldszal et al., TotalFinaElf, Paper 56f, Spring AIChE Meeting (2002)

0

10

20

30

40

50

60

70

80

90

100

4 5 6 7 8 9 10 11 12 13 14final pH

0

0.1

0.2

0.3

0.4

0.5

0.6stability (% non decanted water at 48 h)

surface tension (mJ/m²)

surface tension

stability

TANc

TANc

Sudden Transitions in W/OEmulsion Stability w pH


Emulsion Stabilization Mechanisms

Solvation Shell

Electrostatic Steric Gibbs-Marangoni 3rd Phase Film

Convective Flow dueto Film Drainage

Surfactant Diffusion dueto Interfacial Tension Gradient

Molecular Aggregate


Mechanism of Adsorption of AsphaltenesTo O/W Interfaces and Film Formation

bulk asphaltenes (cA)

Fickian diffusion

near-interface asphaltenes

cAs = 2cA(Dt/ )1/2

adsorption (rate constant = ka)

adsorbed, unconsolidated asphaltenes ( 1)

adsorbed, consolidated asphaltenes ( )

consolidation (rate constant = kc)

(CA)

kA

ΓA

kc) ΓC


Naphthenate’s ability to organize intolamellar structures (LLC)

Illustrated as

β-Cholanic Acid (CA)

Acid/Soap Ratio ca. 4-6


Experimental Procedure: Emulsion Type Studies

Oil-phase

Water-phase

Equilibrate for about 24 hbefore EMULSIFICATION(15,000 rpm for 3 min)

Centrifugation

Emulsion

Characterization:Water- or Oil continuous

Watercontinuous

Oilcontinuous

Oilcontinuous

Watercontinuous

Pure water Pure oil


0

0.5

1

1.5

2

2.5

3

3.5

8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13

Initial pH in Aqueous phase

Tran

sitio

n C

once

ntra

tion

(wt%

CA-

mat

eria

l in

emul

sion

)

Water

Brine (3.5 wt% NaCl)

CA-concentrations where oil continuous emulsions first appear Studied as a function of initial pH in the aqueous phase

A/S~35A/S~15

A/S~4

A/S~8A/S~2

A/S~3

A/S~320

A/S~80

A/S~1330

A/S~0.4

A/S~0.15

A/S~910

A/S~8770

A/S~54400

W/O Emulsions

O/W Emulsions


Polarizing Micrograph: 1.5 % (w/w) CA; pH 11.5 W/O Emulsion

30 µm


Emulsion Studies of Asphaltenic Filmswith Added Cholanic Acid/Soap

0.5 % (w/w) HO asphaltenes in 50:50 (v/v)heptane: tolueneIncreasing amounts of β-cholanic acid(0.025 – 1.5 %, w/w)Varying pH (9-13) of aqueous phase; 50:50(v/v) water:oil in emulsion


Emulsion StabilityCA and Asphaltene stabilized emulsions at varying pH

(centrifuged at 10 000 rpm for 30 min)

(oil/water = 50%/50%)

Emulsion Stability - CA+Asph in Brine at varying pH

0

10

20

30

40

50

60

70

80

90

100

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

wt% CA-material in the emulsion

wt%

Brin

e re

cove

red

pH = 13.2pH = 12.5pH = 12.0pH = 11.5pH = 10.8pH = 10.0

E4

E1

E2E5

E6

Unstable


Experimental Design: SANS

Deuteratedwater with

Hydrogenated CA-soap andHydrogenated

HO Asphaltenes

DeuteratedHepTol

Equilibrate for about 24 hbefore EMULSIFICATION(15,000 rpm for 3 min)


SANS of Emulsions Stabilized by Different Mechanisms

0.01 0.10.01

0.1

1

10

100

1000

10000

Q (Å-1)

I(Q

) (cm

-1)

E1 - A E2 - A+0.025% CA E3 - A+0.05% CA E5 - A+1% CA E6 - A+1.4% CA E7 - 1% CA E8 - 1.5% CA E9 - 2% CA

E4 was destabilized,making SANS-measurement of this emulsion impossible

Jump in Intensity E3 to E5; morethan order of magnitude


Emulsionsstabilized by

0.5 wt%asphaltene in the

oil phase andincreasing amountof CA added to the

aqueous phase(brine at pH = 12)

The emulsions were diluted in mineraloil (1:3) before the

pictures were taken

35.7µm

E40.1% CA + Asph

E51% CA + Asph

E61.4% CA + Asph

E81.5% CA

E30.05% CA + Asph

E10.5% Asph


Drop Size Distribution data obtained for Emulsion E6 total CA-concentration in the emulsion is 1 wt%

Aqueous phase: brine at pH = 12Oil phase: 0.5wt% Asphaltenes in 45/55 Heptane/Toluene

E6

0

20

40

60

80

100

120

140

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 1010.5 11

Droplet Diameter (µm)

Dro

plet

Fre

quen

cy

Mean: 3.71 Median: 3.67Min: 0.69Max: 10.59

d32 = 5.01

skewness0 = 83

35.7µm


Emulsion Stability & Sauter Mean Droplet Diameters (d32)(water phase: brine at pH = 12)

44915.2701.5E8

461135.6001.0E7

43835.010.51.4E6

702567.520.51.0E5

92155520.10.50.10E4

891276.910.50.050E3

571656.490.50.025E2

292468.160.50E1

% waterresolved

Skewnessabout origin

d32 (µm)wt% asphin the oil phase

wt% CAin the emulsion

Sample


Transition from Asphaltene- to Liquid Crystal Stabilized Emulsions

E40.1% CA + Asph

E51% CA + Asph

E61.4% CA + Asph

E71% CA

35.7 µm


The Core-Shell Model

rcore

ρcore

t

ρshell

ρoil

d-Water(Brine)

d-HepTol(45/55)

Fixed parameters:ρoil ρcore rcore

Varying parameters:ρshell t

Hydrogenated Surfactant Film, w/ or w/o Entrained d-Solvent


Polydisperse Core-Shell Model Fits

0.01

0.1

1

10

100

1000

Inte

nsity

(cm

-1)

3 4 5 6 7 8 90.01

2 3 4 5 6 7 8 9

Q (Angstrom-1)

E7 (1% wt CA emulsion)

avg core rad (A) = 28000 (fixed)avg shell thickness (A) = 115.37 ± 0.126overall polydispersity (0,1) = 0.44 (fixed)

SLD core (A-2) = 5.89e-06 (fixed)SLD shell (A-1) = 4.1193e-06 ± 1.18e-09

SLD solvent (A-2) = 6.08e-06 (fixed)bkg scattering (cm-1) = 0.001 (fixed)

E6 (1.5% wt CA + 0.5% wt HOA emulsion)

avg core rad (A) = 25100 (fixed)avg shell thickness (A) = 116.57 ± 0.137overall polydispersity (0,1) = 0.44 (fixed)

SLD core (A-2) = 5.89e-06 (fixed)SLD shell (A-2) = 1.0558e-06 ± 3.51e-09

SLD solvent (A-2) = 6.08e-06 (fixed)bkg scattering (cm-1) = 0.001 (fixed)

Water drivenfrom interface

Consistent with~2-5 % CA inlamellar film


Emulsion StabilityCA and Asphaltene stabilized emulsions at varying pH

(centrifuged at 10 000 rpm for 30 min)

(oil/water = 50%/50%)

Emulsion Stability - CA+Asph in Brine at varying pH

0

10

20

30

40

50

60

70

80

90

100

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

wt% CA-material in the emulsion

wt%

Brin

e re

cove

red

pH = 13.2pH = 12.5pH = 12.0pH = 11.5pH = 10.8pH = 10.0

E4

E1

E2E5

E6

Unstable


Effect of blending B6 and Africa crude oilon emulsion stability

0.0 0.2 0.4 0.6 0.8 1.00

20

40

60

80

Africa StockB6 Stock

% W

ater

res

olve

d

ΦAfrica

Destabilization of asphaltene-stabilizedemulsions by acidicresins

Napthenic acidand naphthenate-stabilizedemulsions


ConclusionsMixtures of naphthenates and naphthenic acids formextremely stable emulsions of water-in-oil stabilized by a“third phase” liquid cyrstalline film mechanism

The concentration and pH range over which this occurs ismodest and very sensitive to details of molecular architec-ture, consistent with simple molecular packing arguments

Naphthenates dramatically destabilize asphaltenic filmemulsions in a window of composition and pH, suggestingjudicious blending of crudes and petroleum fluids tominimize emulsion formation


Conclusions (con’t)Small Angle Neutron Scattering (SANS) of Deuteratedwater in Deuterated oil emulsions, but stabilized byHydrogenated films of surfactants with or without entrainedDeuterated solvents, provides a very effective means ofcontrast variation to elucidate film structure andcomposition

Our results on very simple model systems are consistentwith obervations on crude oil systems of great currentinterest


NSF Grant CTS-981727

Shell, ChevronTexaco, ExxonMobil, Ondeo-Nalco, Champion Technologies

NIST and ExxonMobil – Eric Sirota, Min Lin

Argonne National Lab -- Papannan Thiyagajaran, Dennis Wozniak

Acknowledgements

Documents

Asphaltene and Naphthenate Mechanisms of Emulsion ... · Asphaltene and Naphthenate Mechanisms of Emulsion Stabilization in water-in-crude oil Emulsions Marit-Helen Ese, Keith L