Demirbas- Producing Bio-Oil From Olive Cake

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Energy Sources, Part A: Recovery, Utilization, andEnvironmental Effects

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Producing Bio-oil from Olive Cake by Fast PyrolysisA. Demirbas

a

aSila Science, Trabzon, Turkey

Availabl e online: 29 Feb 2008

To cite this art icle: A. Demi rbas (2007): Producin g Bio-oil fr om Olive Cake by Fast Pyrolysis, Energy Sources, Part A: RecovUti l i zat ion, and Environment al Eff ects, 30:1, 38-44

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Energy So urces, Part A, 30:3844, 2008

Copyright Taylor & Francis Group, LLC

ISSN: 1556-7036 print/1556-7230 online

DOI: 10.1080/00908310600626747

Producing Bio-oil from Olive Cakeby Fast Pyrolysis

A. DEMIRBAS1

1Sila Science, Trabzon, Turkey

Abstract This article reports on physico-chemical properties of olive cakes to eval-uate them as a raw material in energy production through thermo-chemical pyrolysisconversionprocess. The present study focuses on the actions related to the possibilitiesto utilize in particularly olive cake as an agricultural residue. Olive cake is a very

promising material for the production of bio-oil. Liquid, solid, and gaseous products

were obtained from olive cake by pyrolysis. If the purpose were to maximize the yieldof liquid products resulting from biomass pyrolysis, a low temperature, high heatingrate, and short gas residence time process would be required. Flash pyrolysis gives

high oil yields. The heating was carried out from 298 K to 1,050 K in the absence ofoxygen. The yields of liquid products were obtained from the olive cake by pyrolysis

for the runs of different heating rates: 10 K/s, 20 K/s, and 40 K/s. The highest bio-oilyields from the olive cakes were 31.0% at 700 K, 36.0% at 700 K, and 41.0% at 700 Kobtained from 10 K/s, 20 K/s, and 40 K/s heating rate runs, respectively. The highestbio-oil yields olive stone shells were 27.0% at 700 K, 31.0% at 700 K, and 34.5% at750 K obtained from 10 K/s, 20 K/s, and 40 K/s heating rate runs, respectively.

Keywords bio-oil, fast pyrolysis, fuels, olive cake, olive kernel

Introduction

Agricultural residues such as olive kernels, fruit stones and nut shells, are very good

precursors for the production of bio-oil, bio-char and bio-gas fuels (Demirbas, 2000a;

Aygun et al., 2003). Energy in agriculture is important in terms of crop production and

agroprocessing for value adding (Ozkan et al., 2004). Direct combustion is the old way

of using biomass. Biomass thermo-chemical conversion technologies such as pyrolysis

and gasification are certainly not the most important options at present; combustion

is responsible for over 97% of the worlds bio-energy production (Demirbas, 2004a).

Amongst thermochemical transformations, pyrolysis has received much attention since

the process conditions can be optimized to produce liquids, which may be upgraded

to fuels and solid (Zabaniotou et al., 2000). Use for energy recovery is mainly by

combustion, while pyrolysis and gasification are being investigated at laboratory and

plot scales (Di Blasi et al., 1997).

Beside forest residues, a variety of organic materials has been pyrolized successfullyin the current pilot plant, such as hazelnut shell, palm residues, rice husks, olive kernels,

wheat straw, plastic wastes, automotive shredder residues, dried sludge, and switch grass

(Demirbas, 2004b). Olive kernels have been used traditionally for combustion.

Address correspondence to Professor Ayhan Demirbas, P.K. 216, TR-61035 Trabzon, Turkey.E-mail: [email protected]

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Bio-oil from Olive Cake 39

Pyrolysis of biomass generates three different energy products in different quantities:

coke, oils, and gases. Liquid, solid, and gaseous products were obtained from olive cake

by pyrolysis. These included oil, water-soluble products, char, permanent gases, and

C1C4 hydrocarbon gases. The liquid fraction of the pyrolysis products consists of two

phases: an aqueous phase and a non-aqueous phase. The non-aqueous phase is called aspyrolysis oil or bio-oil, and is the product of greatest interest. Because of its size and

composition, olive kernel is a very promising material for the production of bio-oil.

Depending on the operating conditions, the pyrolysis process can be divided into

three subclasses: conventional slow pyrolysis, fast pyrolysis, and flash pyrolysis (Maschio

et al., 1992). Fast pyrolysis for production of liquids has developed considerably since

the first experiments in the late 1970s (Bridgwater and Peacocke, 2002). If the purpose

were to maximize the yield of liquid products resulting from biomass pyrolysis, a low

temperature, high heating rate, short gas residence time process would be required. For a

high char production, a low temperature, low heating rate process would be chosen.

If the purpose were to maximize the yield of fuel gas resulting from pyrolysis, a

high temperature, low heating rate, long gas residence time process would be preferred

(Demirbas and Arin, 2002).

The chemical composition and calorific value of olive husks have been studied in

detail by Demirbas (1998; 2000b; 2002a; 2002b). Table 1 shows the results of structural,

proximate and elemental analyses of olive husk samples given in several articles. From

Table 1, the higher heating value (HHV) of fresh olive husks (23.2 MJ/kg) is higher

than the HHV of processed husks (20.6 MJ/kg). The difference can be explained by the

absence of the extracted olive oil, which has estimated HHV of 39.6 MJ/kg.

Table 2 shows the average ash composition from olive husk samples. Table 3 shows

the elementary analysis results and ash contents of chars from the olive husk samples.

Table 1

Structural, proximate, and elemental analyses of olive husk samples

Fresh olive husk

(wt% dry basis)

Processed olive husk

(wt% dry and ash free basis)

Structural analysis

Hemicelluloses 22.3 24.3

Cellulose 23.5 25.6

Lignin 44.9 50.1

Extractives 9.3

Proximate analysis

Ash 3.2

Fixed carbon 32.8 33.8

Volatile matter 64.0 66.1

Elemental analysis

C 52.2 52.8

H 6.5 6.7

O 40.5 39.8

N 0.8 0.7

Higher heating value (MJ/kg) 23.2 20.6

Source: Demirbas, 1998, 2000, 2002a, 2002b.


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40 A. Demirbas

Table 2

Average ash composition from olive husk samples (wt% dry basis)

SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O SO3 P2O5 Others

29.4 8.4 6.3 14.5 4.2 26.2 4.3 0.6 2.5 3.6

Source: Demirbas, 2002b.

The char produced from the olive husk sample contained 91.3% carbon where the

carbonization temperature was 1,150 K.

This article reports on physico-chemical properties of olive cakes to evaluate them

as a raw material in energy production through thermo-chemical pyrolysis conversion

process.

Experimental

The physico-chemical characteristics of olive fruit constituents and olive cakes were ana-

lyzed according to standard methods. Moisture and total solid contents were determined

by heating the sample at 378 K for 24 h.

The olive stone shell and olive cakes were utilized for thermo-chemical conversion

process for liquid bio-oil production in pyrolysis unit as per the procedure followed by

Demirbas et al. (1996). The main element of this device was a horizontal cylindrical re-

actor of stainless-steel, 127.0 mm height, 17.0 mm inner diameter, and 25.0 mm outer di-

ameter inserted vertically into an electrically heated tubular furnace and provided with an

electrical heating system power source, with changing heating rates. Air dried sample was

weight for run 1.00 g and pyrolyzed in the horizontal tube reactor. Heat to tube was sup-

plied from external heater and the power was adjusted to give an appropriate heat up time.

The simple thermocouple (NiCrConstantan) was placed directly in the pyrolysis medium.

For each run, the heater was started at 298 K and terminated when the desiredtemperature. The heating was carried out from 298 K to 1,050 K in the absence of

oxygen. The pyrolysis products were collected as condensable liquids products, tarry

materials, non-condensable gaseous products, and solid residue (char). The experiments

were carried out to determine the effect of the pyrolysis temperature and the heating rate

Table 3

Elementary analysis results, ash contents and higher heating values (HHVs)

of chars from the olive husk samples

550 K 650 K 750 K 850 K 950 K 1,050 K 1,150 K

C 71.2 78.0 86.4 89.0 89.6 90.6 91.3

H 6.0 4.2 3.0 2.4 2.0 1.8 1.4

O 16.0 11.1 3.9 1.9 1.5 0.9 0.6

N 1.0 0.8 0.6 0.4 0.5 0.3 0.2

Ash 5.8 5.9 6.1 6.3 6.4 6.5 6.7

HHV, MJ/kg 29.1 30.1 32.3 32.5 32.7 32.8 32.8

Source: Demirbas, 2001.


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on pyrolysis yields. The temperature was maintained at 550 K, 600 K, 650 K, 700 K,

750 K, 800 K, 850 K, 900 K, 950 K, 1,000 K, and 1,050 K, while the heating rates were

10 K/s, 20 K/s, and 40 K/s.

Following pyrolysis, the liquid products were collected in a series of traps maintained

at about 273 K. These liquid products contained an aqueous and a non-aqueous phase,which were separated and weighed. After pyrolysis, the solid char was removed and

weighed. The soluble part of the liquid phase which dissolved in dichloromethane was

extracted in a rotary evaporator and the quantity of bio-oil was established. Then, the

gaseous phase was calculated from the material balance.

Results and Discussion

Crude olive cake contains the olive stone shell crushed into fragments, stone kernel, the

skin and the crushed pulp, about 25% water and a remaining quantity of oil making

them subject to rapid spoilage. Processed olive cake differs from crude olive cake mainly

by lower oil content and smaller water content because it has been dehydrated during

the oil extraction process. The quantity extracted oil gained from the fresh olive kernels

depends on the extraction method, extraction fluid, and the history of the fresh kernels.

The quantity and chemical composition of the bio-oil gained from the olive cake depends

on the history of the fresh cake, heating rate, pyrolysis temperature, resistant time, and

particle size.

The main components of ripe olive fruit are given in Table 4. The average dry matter

content of olive is 3348% by weight. A ripe olive composes of four parts: epicarp, edible

mesocarp, endocarp (stone shell), and olive stone kernel. The olive fruit is ovoid shape

and weighs from 315 g. The epicarp (or skin) is covered with wax and turns from light

green to black as the fruit ripens. The mesocarp (or flesh) has low sugar content (25%)

and high oil content (1332%) that varies according to the variety and ripeness of the

fruit. The endocarp (or stone) of the olive is hard and made of fibrous lignin. It is ovoid

shape and it encloses a seed (olive kernel) that accounts for 23% of fruit weight and

contains 24% oil.The olive stone shell is particularly rich in lignin and poor in cell content. The crude

fiber content in stone shell is high. The cell wall constituents of olive stone shell can be

compared to that of cereal straws having an apparently high degree of lignification.

Table 5 shows the yields of condensed liquid, tar, char and gas from the olive cake

samples for 10 K/s heating rate at different pyrolysis temperatures. The yields of total bio-

oils (condensed liquidC tar) are 34.4% and 31.8% at 650 K and 750 K, respectively. The

most interesting temperature range for the production of the pyrolysis products is between

Table 4

Main components of ripe olive fruit

ComponentFresh olive,

wt%Processed olive,

wt%Processed olive,

wt% basis on dry matter

Epicarp 0.51 0.51 12

Mesocarp 8488 7885 2644

Endocarp (Olive stone) 1216 1522 5674

Olive stone shell 914 1319 4768

Olive stone kernel 23 23 69


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42 A. Demirbas

Table 5

Yields of condensed liquid, tar, char and gas from the olive cake samples

at different pyrolysis temperatures (wt%). Heating rate: 10 K/s

550 K 650 K 750 K 850 K 950 K 1,050 K

Condensed liquid 25.4 26.5 25.1 20.6 14.9 14.5

Tar 8.7 7.9 6.7 5.7 3.3 1.9

Char 45.5 39.5 36.6 33.3 31.8 31.6

Gas 20.4 26.1 31.6 40.4 50.0 51.8

625 and 725 K. The char yield decreases as the temperature increases. The production of

the liquid products has a maximum at temperatures between 625 and 725 K. At higher

temperatures, the rather large molecules present in the liquid and residual solid are broken

down to produce smaller molecules which enrich the gaseous fraction (Maschio et al.,

1992).Pyrolysis actually begins between 535 and 775 K. The reactions are exothermic,

and unless heat is dissipated, the temperature will rise rapidly. The primary products are

beginning to react with each other before they can escape the reaction zone (Goldstein,

1991). If the temperature continues to rise above 775 K, a layer of char will be formed

that is the site of vigorous secondary reactions. Pyrolysis is completed at temperatures

of 675 to 925 K (Chum, 1991).

Figure 1 shows the plots of the yields of liquid products from the olive cake by

pyrolysis for the runs of different heating rates: 10 K/s, 20 K/s, and 40 K/s. From Figure

1, the highest bio-oil yields were 28.9% at 700 K, 32.9% at 700 K, and 36.8% at 750 K

obtained from 10 K/s, 20 K/s, and 40 K/s heating rate runs, respectively.

Figure 2 shows the plots of the yields of liquid products from the olive stone shell

by pyrolysis. From Figure 2, the highest bio-oil yields were 31.0% at 700 K, 36.0% at

Figure 1. Plots of the yields of liquid products from the olive cake by pyrolysis.


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Figure 2. Plots of the yields of liquid products from the olive stone shell by pyrolysis.

Figure 3. Plots of the yields of liquid products from mesocarp of the olive fruit by pyrolysis. The

oil extracted by diethyl ether from the sample before the pyrolysis.

700 K, and 41.0% at 700 K obtained from 10 K/s, 20 K/s, and 40 K/s heating rate runs,

respectively.

Figure 3 shows the plots of the yields of liquid products from the olive fruit mesocarp

(edible outer part of olive fruit) by pyrolysis. The oil extracted by diethyl ether from the

sample before the pyrolysis. From Figure 3, the highest bio-oil yields were 27.0% at

700 K, 31.0% at 700 K, and 34.5% at 750 K obtained from 10 K/s, 20 K/s, and 40 K/sheating rate runs, respectively.

Conclusion

Fast pyrolysis is a technology that can be used to convert diverse wood based and

agricultural residues into a liquid called pyrolysis-oil or bio-oil. Liquid (tar), solid (char)


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44 A. Demirbas

and gaseous products were obtained from olive cake by pyrolysis. Flash pyrolysis gives

high oil yields.

The liquid fraction of the pyrolysis products consists of two phases: an aqueous phase

containing a wide variety of organo-oxygen compounds of low molecular weight and a

non-aqueous phase containing insoluble organics (mainly aromatics) of high molecularweight. This phase is called as bio-oil or tar and is the product of greatest interest. The

ratios of acetic acid, methanol, and acetone of aqueous phase were higher than those of

non-aqueous phase.

If the purpose were to maximize the yield of liquid products resulting from biomass

pyrolysis, a low temperature, high heating rate, short gas residence time process would

be required. For a high char production, a low temperature, low heating rate process

would be chosen. If the purpose were to maximize the yield of fuel gas resulting from

pyrolysis, a high temperature, low heating rate, long gas residence time process would

be preferred.

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Demirbas- Producing Bio-Oil From Olive Cake