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Biocrude from biomass: pyrolysis of cottonseed cake
Renewable Energy 24 (2001) 615–625 www.elsevier.nl/locate/renene
Biocrude from biomass: pyrolysis of cottonseed cake ¨ zbay b, A.E. Pu¨tu¨n a, B.B. Uzun a, E. Pu¨tu¨n N. O a
a,*
Department of Chemical Engineering, Faculty of Engineering and Architecture, Iki Eylu¨l Campus, Anadolu University, 26470 Eskis¸ehir, Turkey b Bozu¨yu¨k Vocational School, Anadolu University, Bozu¨yu¨k/Bilecik, Turkey
Abstract Fixed-bed pyrolysis experiments have been conducted on a sample of cottonseed cake to determine the possibility of being a potential source of renewable fuels and chemicals feedstocks, in two different reactors, namely a tubular and a Heinze retort. Pyrolysis atmosphere and pyrolysis temperature effects on the pyrolysis product yields and chemical composition have been investigated. The maximumm oil yield of 29.68% was obtained in N2 atmosphere at a pyrolysis temperature of 550°C with a heating rate of 7°C min⫺1 in a tubular reactor. 2001 Elsevier Science Ltd. All rights reserved. Keywords: Cottonseed cake; Pyrolysis; Bio-Oil; Biomass
1. Introduction With the depletion of fossil fuels and concerns over CO2 emissions, renewable biomass is now being considered as an important energy resource all over the world. Indeed there are a number of biomass sources being considered as potential sources of fuels and chemical feedstocks. The interest in using biomass and its products as a fuel arose during the 1970s due to the increase in conventional fossil energy prices [1–3]. Due to this fact, pyrolysis has attracted considerable attention all over the world and pyrolytic oil is of particular interest also. For this reason intensive research activities for developing an alternative renewable source of liquid hydrocarbons is attracting a great deal of attention for future energy
* Corresponding author. Tel.: +90-222-335-0580/6301; fax: +90-222-323-9501. E-mail address: [email protected] (E. Pu¨tu¨n). 0960-1481/01/$ - see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 0 - 1 4 8 1 ( 0 1 ) 0 0 0 4 8 - 9
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¨ zbay et al. / Renewable Energy 24 (2001) 615–625 N. O
systems. Biomass, for one, has a great potential by offering annually renewable sources to replace the liquid hydrocarbons used mainly for transportation [4–7]. Thus both the developing world and the industrialized nations require new technologies which efficiently utilize the biomass resource. Thermochemical processes are thought to have great promise as a means for efficiently and economically converting biomass into higher value fuels. Pyrolysis lies at the heart of all thermochemical fuel conversion processes [8,9]. The pyrolytic oil is of particular interest since it may be stored and transported, and hence does not have to be used at or near the process plant. The oil may be used directly as a liquid fuel, added to petroleum refinery feedstocks or catalytically upgraded to transport grade fuels. From this point of view, there are a number of waste and biomass sources being considered as potential sources of fuels most favourable for (i) plants which grow abundantly and require little cultivation in arid lands, and (ii) wastes, available in relatively large quantities, from agricultural plants such as sunflowers, hazelnuts and cotton. Cotton is one of Turkey’s most important agricultural crops since Turkey is one of the eight countries that are producing 85% of the world’s cotton crop. Today the cotton area is about 600,000 hectares and gradually will increase to about 900,000 hectares by 2002 with the completion of the GAP (Southeastern Anatolian Project) [10]. Although cotton is being cultivated mainly for its lint which is universally used as a textile raw material, cottonseed is an important source of vegetable oil. Consequently the cottonseed oil industry generates cottonseed cake and a residue like ginnery waste, and both of them can be considered as feedstocks for a future thermochemical demonstration unit together with sunflower oil industry wastes and latex producing plants [11,12].
2. Experimental 2.1. Pyrolysis The cottonseed cake sample investigated in this study has been taken from some cottonseed oil factories around Adana located in Southern Anatolia. The pyrolysis experiments were performed in two different reactors, namely a Heinze retort and a well-swept tubular reactor, in static and nitrogen atmospheres. The 316 stainless steel Heinze retort used previously [13,14] has a volume of 400 cm3 (70 mm i.d.) and is externally heated by an electric furnace in which the temperature is measured by a thermocouple inside the bed. The connecting pipe between the reactor and the trapping system was heated to 400°C to avoid condensation of tar vapour. The second reactor [15] was a 316 stainless steel tubular reactor (72.5×3.64 cm i.d.) which was externally heated by an electric furnace (61.9×9.5 cm i.d.) with the temperature being controlled by 3 thermocouples inside the bed. The experiments performed in the Heinze reactor were carried out in two groups. In the first, to determine the effect of the pyrolysis temperature and the heating rate on the cottonseed cake pyrolysis yields. 40 g of air-dried cake was placed in the reactor and the temperature was raised at 7°C min⫺1 to a final temperature of either
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300, 400, 450, 500, 550, or 700°C and held for either a minimum of 30 min or until no further significant release of gas was observed. The flow of the gas released was measured using a soap film for the duration of the experiments. The liquid phase was collected in a glass liner located in a cold trap maintained at about 0°C. The liquid phase consisted of aqueous and oil phases which were separated and weighed. After pyrolysis, the solid char was removed and weighed, then the gas yield was calculated by the difference. The second group of experiments were also performed in the Heinze reactor in order to establish the effect of sweep gas velocity on the pyrolysis yields, under a nitrogen atmosphere. The experiments were conducted at sweep gas flow rates of either 50, 100, 200, or 400 cm3 min⫺1. For all these experiments, the heating rate and the final pyrolysis temperature were 7°C min⫺1 and 550°C, respectively, based on the results of the first group of experiments. The third group of experiments were performed in the well-swept tubular reactor to determine the effect of the pyrolysis temperature and sweeping gas flow rates on the pyrolysis yields. 10 g of sample was placed in the reactor and sweep gas was controlled and measured by a rotameter. The experiments were carried out with a temperature increment of 7°C min⫺1 to the final temperature of either 400, 450, 500, 550, or 700°C under nitrogen atmosphere. The sweep gas flow rates were 50, 100, 200, 400 cm3 min⫺1. 2.2. Characterization Proximate and elemental analyses (Carlo Erba, EA 1108) were carried out on the cottonseed cake (Tables 1 and 2). The oils analysed in this study have been obtained under experimental conditions that gives maximum oil yield. The elemental compositions and calorific values of the pyrolysis oils were determined. The 1H NMR of the same oils were obtained at a H frequency of 90 MHz using a Jeol EX 90A instrument. The sample was dissolved in chloroform-d. The IR spectra of the oils were recorded using a Jasco FT-IR Infrared Spectrophotometer. Chemical class composition of the oils were determined by liquid column chromatographic fractionation. The columns used were packed with silica-gel 70–230 mesh, pretreated at 105°C for 2 h prior to use. The column was eluated successively with pentane, toluene, ether and methanol to produce aliphatic, aromatic, ester and polar
Table 1 Proximate analysis of cottonseed cake Percentage (as received) Volatiles Fixed carbon Ash Moisture
78.7 10.3 4.9 6.1
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Table 2 The elemental composition of cottonseed cake and bio-oils Component
Cottonseed cake
Oila
Oilb
Oilc
C H N O H/C O/C
52.0 5.9 1.3 40.8 1.36 0.59
65.9 8.5 5.7 19.9 1.54 0.23
65.0 8.4 5.8 20.8 1.55 0.24
68.46 9.36 6.06 16.12 1.64 0.18
a b c
Obtained at 550°C, 7°C min⫺1. Obtained at 550°C, 7°C min⫺1, nitrogen flow rate of 100 cm3 min⫺1. Obtained, at 550°C, 7°C min⫺1, nitrogen flow rate of 200 cm3 min⫺1.
fractions, respectively. Each fraction was dried and weighed and then subjected to elemental and IR analyses. The pyrolysis oil was fractionated by distillation according to ASTM D 285-62 in the ranges of ⬍140°C, 140–240°C, 240–350°C, ⬎350°C for simulated distillation of the resultant fractions by GC (HP 5890 Series II) according to ASTM D 288784 in order to compare the distillation curves of the pyrolysis product distillates to those of conventional transport fuels [14]. 3. Results and discussion 3.1. Product yields Figure 1 shows the product yields for the pyrolysis of cottonseed cake in relation to final temperature of pyrolysis at heating rates of 7°C min⫺1. The yield of conver-
Fig. 1.
The yields of the pyrolysis products.
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sion increased from 69% to 76% while the final pyrolysis temperature was increased from 300°C to 700°C. While the oil yield was 21% at pyrolysis temperature of 300°C, it appeared to go through a maximum of 24% at the final temperature of 500–550°C. Then, at the final pyrolysis temperature of 700°C, the oil yield decreased to 21%. The product yields of pyrolysis in relation to the rate of nitrogen is given Fig. 2 for the heating rate of 7°C min⫺1. The oil yield increased 11.16% when reaching a nitrogen flow rate of 100 cm3 min⫺1 and there was no obvious influence on the yield increase. Indeed, the highest yield of 27% was obtained at a final pyrolysis temperature of 550°C with a heating rate of 7°C min⫺1 and nitrogeen flow rate of 100 cm3 min⫺1. Figures 3, 4, 5 and 6 show the yields and conversion obtained in the well-swept fixed-bed tubular reactor in relation to the final temperature of pyrolysis of either 400, 450, 500, 550, or 700°C at a heating rate of 7°C min⫺1 with nitrogen flow rates of either 50, 100, 200, or 400 cm3 min⫺1. The product yields of pyrolysis in relation to the rate of nitrogen is given in Fig. 7. The pyrolysis conversions were increased for all sweeping gas rates as the pyrolysis temperature increased. The maximum pyrolysis conversion was achieved at the pyrolysis temperature of 700°C with a sweeping gas rate of 72.39%, while an increment of total conversion was detected by increasing the pyrolysis temperature. The maximum oil yield of 29.68% was obtained at a pyrolysis temperature of 550°C with a sweeping gas flow rate of 200 cm3 min⫺1. When comparing the oil yields of sweep-gas experiments it can be seen that the oil yield of the tubular reactor was 9.12% higher than the Heinze reactor at the pyrolysis temperature of 550°C with the sweeping gas rates of 200 cm3 min⫺1 and 100 cm3 min⫺1, respectively. This difference is probably attributable to the
Fig. 2. Effect of sweep gas flow rate on the product yields of Heinze oil (sweep gas flow rate of 100 cm3 min⫺1).
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Fig. 3. Effect of pyrolysis temperature on the product yields of the tubular reactor (sweep gas flow rate of 50 cm3 min⫺1).
Fig. 4. Effect of pyrolysis temperature on the product yields of the tubular reactor (sweep gas flow rate of 100 cm3 min⫺1).
geometry of the tubular reactor due to the possibility of rapid removal of pyrolysis products from the hot zone to minimize the secondary reactions such as thermal cracking, repolymerization and recondensation to maximize the liquid yield. These results suggest that mass transfer restrictions to volatile evolution are much less marked for cottonseed cake compared to coals and oil shales where oil yields are generally increased significantly as the carrier gas flow rate decreases [16–18]. This major difference is probably attributable to the low bulk density and high oxygen content of cottonseed cake.
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Fig. 5. Effect of pyrolysis temperature on the product yields of the tubular reactor (sweep gas flow rate of 200 cm3 min⫺1).
Fig. 6. Effect of pyrolysis temperature on the product yields of the tubular reactor (sweep gas flow rate of 400 cm3 min⫺1).
3.2. Chemical composition The elemental composition of the cottonseed cake and the oils characterized are listed in Table 2 and the calorific values of the bagasse and the oils are listed in Table 3. The average chemical composition of the Heinze oil tubular reactor oils analyzed were CH1.5495N0.0748O0.2267 and CH1.6410N0.0758O0.1765. Heinze retort product oil is characterized by high oxygen content with a higher H/C ratio than the tubular reactor
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Fig. 7. Effect of sweep gas flow rate on the bio-oil yields of the tubular reactor (sweep gas flow rate of 200 cm3 min⫺1, pyrolysis temperature of 550°C).
Table 3 Calorific values of cottonseend cake, Heinze retort oils and well-swept tubular reactor oil Material
Calorific values (kcal/kg)
Cottonseed cake Heinze oila Heinze oilb Tubular oilc
4300 7400 7250 8061
a b c
Obtained at 550°C, 7°C min⫺1. Obtained at 550°C, 7°C min⫺1, nitrogen flow rate of 100 cm3 min⫺1. Obtained at 550°C, 7°C min⫺1, nitrogen flow rate of 200 cm3 min ⫺1.
oil and the original cake. Further comparison of H/C ratios with conventional fuels indicates that the H/C ratios of the oils obtained in this study lie between those of light and heavy petroleum products. Also, calorific values indicate that the energy contents of the oils are very close to that of petroleum. The IR spectrum of the Heinze oil is given in Fig. 8. The O–H stretching vibrations between 3200 and 3400 cm⫺1 indicate the presence of phenols, alcohols. The C–H stretching vibrations between 2800 and 3000 cm⫺1 and C–H deformation vibrations between 1350–1475 cm⫺1 indicate the presence of alkanes. The CBO stretching vibrations with absorbance between 1650–1750 cm⫺1 indicate the presence of ketones or aldehydes. The absorbance peaks between 1575 and 1675 cm⫺1 represent CBC stretching vibrations indicative of alkenes and aromatics. The results of the adsorption chromatography of the oils showed that the pyrolysis oil consists of 65% n-pentane solubles. The aliphatic, aromatic, ester and polar frac-
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Fig. 8. IR spectra of the fractions separated from the bio-oil (Heinze oil). (a) Bio-oil, (b) pentane (c) toluene subfraction.
tions of the oil are 11%, 23%, 40% and 26%, respectively. There is an indicative increase of 5% in the aliphatic fraction of the oil obtained under a sweep gas regime due to the restrictions to repolymerization and recondensation. The fractions of this oil are 16%, 20%, 39% and 25%, respectively. The 1H NMR spectrum of the Heinze oil investigated, shown in Fig. 9, indicates that an unimportant amount of the aliphatic carbon is bound to oxygen (peaks in 3.5–4.5 ppm chemical shift range) compared to sunflower bagasse Heinze oil [9]. As is known, most of the aromatic hydrogen intensity occurring in the 6.5–7.5 ppm range indicates that the aromatic species are largely phenolic. In addition to phenols, IR spectroscopy has indicated that carboxylic acids and ketones/aldehydes are also major oxygen functions present in the polar fractions. The alkanes and alkyl groups present in the spectrum are probably derived from lipids and residual oil in the cake. The hydrogen distributions and estimated carbon aromaticity are given in Table 4. The carbon aromaticity has been calculated assuming that the aliphatic H/C ratio lies in the range of 2.0–2.2. To further assess the compatibility of the oil with currently utilized transport fuels, simulated distillation curves of the Heinze retort oil were obtained. Yields of 8%, 36%, 30% and 26% were obtained for fractions boiling under 140°C, 140–240°C,
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Fig. 9.
1
H-NMR spectra of the bio-oil (Heinze oil).
Table 4 1H-NMR results of the oils Hydrogen environment
Mole % (% of total hydrogen) Heinze retort oil
Aromatic/alkene (inc. peak at 5.5 ppm) Aliphatic adjacent to oxygen (3.3–4.5 ppm) Aliphatic adjacent to aromatic/alkene group (3.3–4.5 ppm) Other aliphatic (bonded to aliphatic only 0.4–1.8 ppm) Carbon aromaticity
4.7 1.3 19.7 74.3 0.28
240–350°C and above 350°C, respectively. The fractions boiling at 140–240°C and 240–350°C were compared with kerosene and diesel fuel (Fig. 10). The simulated distillation curves showed that the whole 140–240°C fraction was similar to kerosene and the 240–350°C fraction was similar to diesel fuel.
4. Conclusion The oil yields of the experiments conducted in the tubular reactor were higher than the oil of the fixed bed Heinze retort. The oil yield reached a maximum of 29% with the tubular reactor under nitrogen atmosphere. The higher yield of The tubular reactor is attributable to the reactor geometry. Sweeping gas removed the pyrolysis products from the hot zone to minimize the secondary reactions such as thermal cracking, repolymerization and recondensation, to maximize the liquid yield. The 1H NMR spectrum indicated that the aromaticity of the oil is very low.
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Fig. 10. Comparison of the simulated distillation curves.
The H/C ratios and simulated distillation curves of the fractions obtained from the pyrolysis oil has shown that the fractions are quite similar to the currently utilized transport fuels.
References [1] Safer SS, Zabosk SR. Biomass Energy Conversion Processes for Energy and Fuels, 1981. [2] Bridgwater AV, Kuester JL. Proceedings of the Conference on Research in Thermochemical Biomass Conversion. 1988. [3] Bridgwater AV, Double JM. Int. J. Enrgy. Res. 1999:118-179. [4] Calvin M. Die Naturwissenschaften 1980;67:525–33. [5] Elliott DC, Schiefelbein GF. ACS Fuel Chem Preprints 1989;34(4):1160–6. [6] Bridgwater AV, Cottam M. Energy and Fuels 1992;6(2):113–20. [7] Soltes J. In: Soltes EJ, Milne TA, editor. ACS Symposium Series 376, 1988. [8] Antal MJ. Advances in Solar Energy 1983;1:61–109. ¨ M, Yorgun S, Gerc¸ el HF, Andresen J, Snape CE, Pu¨ tu¨ n E. Fuel Process Technol [9] Pu¨ tu¨ n AE, Koc¸ kar O 1996;46(1):49–63. [10] Eisa MH, Barghouti S, Gillham F, Al-Saffty MT. World Bank Technical Paper No. 231. 1994:112. ¨ M, Gerc¸ el F, Andresen J, Brown S, McRae C, Snape CE. World Renewable [11] Pu¨ tu¨ n E, Koc¸ kar O Energy Congress, 1999. ¨ zbay N, Koc¸ kar O ¨ M, Pu¨ tu¨ n E. Energy Source 1997;19:905–17. [12] Pu¨ tu¨ n AE, O [13] Heinze R. Oel u Kohle 1943;39:973. [14] Pu¨ tu¨ n E, Akar A, Ekinci E, Bartle KD. Fuel 1988;67:1106–10. ¨ zcan A, Pu¨ tu¨ n E. JAAP 1999;52:33–49. [15] Pu¨ tu¨ n AE, O [16] Bolton C, Snape CE, O’Brien RJ, Kandiyoti R. Fuel 1987;66:1413–7. [17] Ekinci E, Pu¨ tu¨ n AE, C¸ itiroglu M, Love GD, Lafferty CJ, Snape CE. ICCS, Newcastle-upon-Tyne, 1991:520-523. [18] Ekinci E, Citiroglu M, Pu¨ tu¨ n E, Love GD, Lafferty CJ, Snape CE. Fuel 1992;71:1511–4.
Biocrude from biomass: pyrolysis of cottonseed cake ¨ zbay b, A.E. Pu¨tu¨n a, B.B. Uzun a, E. Pu¨tu¨n N. O a
a,*
Department of Chemical Engineering, Faculty of Engineering and Architecture, Iki Eylu¨l Campus, Anadolu University, 26470 Eskis¸ehir, Turkey b Bozu¨yu¨k Vocational School, Anadolu University, Bozu¨yu¨k/Bilecik, Turkey
Abstract Fixed-bed pyrolysis experiments have been conducted on a sample of cottonseed cake to determine the possibility of being a potential source of renewable fuels and chemicals feedstocks, in two different reactors, namely a tubular and a Heinze retort. Pyrolysis atmosphere and pyrolysis temperature effects on the pyrolysis product yields and chemical composition have been investigated. The maximumm oil yield of 29.68% was obtained in N2 atmosphere at a pyrolysis temperature of 550°C with a heating rate of 7°C min⫺1 in a tubular reactor. 2001 Elsevier Science Ltd. All rights reserved. Keywords: Cottonseed cake; Pyrolysis; Bio-Oil; Biomass
1. Introduction With the depletion of fossil fuels and concerns over CO2 emissions, renewable biomass is now being considered as an important energy resource all over the world. Indeed there are a number of biomass sources being considered as potential sources of fuels and chemical feedstocks. The interest in using biomass and its products as a fuel arose during the 1970s due to the increase in conventional fossil energy prices [1–3]. Due to this fact, pyrolysis has attracted considerable attention all over the world and pyrolytic oil is of particular interest also. For this reason intensive research activities for developing an alternative renewable source of liquid hydrocarbons is attracting a great deal of attention for future energy
* Corresponding author. Tel.: +90-222-335-0580/6301; fax: +90-222-323-9501. E-mail address: [email protected] (E. Pu¨tu¨n). 0960-1481/01/$ - see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 0 - 1 4 8 1 ( 0 1 ) 0 0 0 4 8 - 9
616
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systems. Biomass, for one, has a great potential by offering annually renewable sources to replace the liquid hydrocarbons used mainly for transportation [4–7]. Thus both the developing world and the industrialized nations require new technologies which efficiently utilize the biomass resource. Thermochemical processes are thought to have great promise as a means for efficiently and economically converting biomass into higher value fuels. Pyrolysis lies at the heart of all thermochemical fuel conversion processes [8,9]. The pyrolytic oil is of particular interest since it may be stored and transported, and hence does not have to be used at or near the process plant. The oil may be used directly as a liquid fuel, added to petroleum refinery feedstocks or catalytically upgraded to transport grade fuels. From this point of view, there are a number of waste and biomass sources being considered as potential sources of fuels most favourable for (i) plants which grow abundantly and require little cultivation in arid lands, and (ii) wastes, available in relatively large quantities, from agricultural plants such as sunflowers, hazelnuts and cotton. Cotton is one of Turkey’s most important agricultural crops since Turkey is one of the eight countries that are producing 85% of the world’s cotton crop. Today the cotton area is about 600,000 hectares and gradually will increase to about 900,000 hectares by 2002 with the completion of the GAP (Southeastern Anatolian Project) [10]. Although cotton is being cultivated mainly for its lint which is universally used as a textile raw material, cottonseed is an important source of vegetable oil. Consequently the cottonseed oil industry generates cottonseed cake and a residue like ginnery waste, and both of them can be considered as feedstocks for a future thermochemical demonstration unit together with sunflower oil industry wastes and latex producing plants [11,12].
2. Experimental 2.1. Pyrolysis The cottonseed cake sample investigated in this study has been taken from some cottonseed oil factories around Adana located in Southern Anatolia. The pyrolysis experiments were performed in two different reactors, namely a Heinze retort and a well-swept tubular reactor, in static and nitrogen atmospheres. The 316 stainless steel Heinze retort used previously [13,14] has a volume of 400 cm3 (70 mm i.d.) and is externally heated by an electric furnace in which the temperature is measured by a thermocouple inside the bed. The connecting pipe between the reactor and the trapping system was heated to 400°C to avoid condensation of tar vapour. The second reactor [15] was a 316 stainless steel tubular reactor (72.5×3.64 cm i.d.) which was externally heated by an electric furnace (61.9×9.5 cm i.d.) with the temperature being controlled by 3 thermocouples inside the bed. The experiments performed in the Heinze reactor were carried out in two groups. In the first, to determine the effect of the pyrolysis temperature and the heating rate on the cottonseed cake pyrolysis yields. 40 g of air-dried cake was placed in the reactor and the temperature was raised at 7°C min⫺1 to a final temperature of either
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300, 400, 450, 500, 550, or 700°C and held for either a minimum of 30 min or until no further significant release of gas was observed. The flow of the gas released was measured using a soap film for the duration of the experiments. The liquid phase was collected in a glass liner located in a cold trap maintained at about 0°C. The liquid phase consisted of aqueous and oil phases which were separated and weighed. After pyrolysis, the solid char was removed and weighed, then the gas yield was calculated by the difference. The second group of experiments were also performed in the Heinze reactor in order to establish the effect of sweep gas velocity on the pyrolysis yields, under a nitrogen atmosphere. The experiments were conducted at sweep gas flow rates of either 50, 100, 200, or 400 cm3 min⫺1. For all these experiments, the heating rate and the final pyrolysis temperature were 7°C min⫺1 and 550°C, respectively, based on the results of the first group of experiments. The third group of experiments were performed in the well-swept tubular reactor to determine the effect of the pyrolysis temperature and sweeping gas flow rates on the pyrolysis yields. 10 g of sample was placed in the reactor and sweep gas was controlled and measured by a rotameter. The experiments were carried out with a temperature increment of 7°C min⫺1 to the final temperature of either 400, 450, 500, 550, or 700°C under nitrogen atmosphere. The sweep gas flow rates were 50, 100, 200, 400 cm3 min⫺1. 2.2. Characterization Proximate and elemental analyses (Carlo Erba, EA 1108) were carried out on the cottonseed cake (Tables 1 and 2). The oils analysed in this study have been obtained under experimental conditions that gives maximum oil yield. The elemental compositions and calorific values of the pyrolysis oils were determined. The 1H NMR of the same oils were obtained at a H frequency of 90 MHz using a Jeol EX 90A instrument. The sample was dissolved in chloroform-d. The IR spectra of the oils were recorded using a Jasco FT-IR Infrared Spectrophotometer. Chemical class composition of the oils were determined by liquid column chromatographic fractionation. The columns used were packed with silica-gel 70–230 mesh, pretreated at 105°C for 2 h prior to use. The column was eluated successively with pentane, toluene, ether and methanol to produce aliphatic, aromatic, ester and polar
Table 1 Proximate analysis of cottonseed cake Percentage (as received) Volatiles Fixed carbon Ash Moisture
78.7 10.3 4.9 6.1
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Table 2 The elemental composition of cottonseed cake and bio-oils Component
Cottonseed cake
Oila
Oilb
Oilc
C H N O H/C O/C
52.0 5.9 1.3 40.8 1.36 0.59
65.9 8.5 5.7 19.9 1.54 0.23
65.0 8.4 5.8 20.8 1.55 0.24
68.46 9.36 6.06 16.12 1.64 0.18
a b c
Obtained at 550°C, 7°C min⫺1. Obtained at 550°C, 7°C min⫺1, nitrogen flow rate of 100 cm3 min⫺1. Obtained, at 550°C, 7°C min⫺1, nitrogen flow rate of 200 cm3 min⫺1.
fractions, respectively. Each fraction was dried and weighed and then subjected to elemental and IR analyses. The pyrolysis oil was fractionated by distillation according to ASTM D 285-62 in the ranges of ⬍140°C, 140–240°C, 240–350°C, ⬎350°C for simulated distillation of the resultant fractions by GC (HP 5890 Series II) according to ASTM D 288784 in order to compare the distillation curves of the pyrolysis product distillates to those of conventional transport fuels [14]. 3. Results and discussion 3.1. Product yields Figure 1 shows the product yields for the pyrolysis of cottonseed cake in relation to final temperature of pyrolysis at heating rates of 7°C min⫺1. The yield of conver-
Fig. 1.
The yields of the pyrolysis products.
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sion increased from 69% to 76% while the final pyrolysis temperature was increased from 300°C to 700°C. While the oil yield was 21% at pyrolysis temperature of 300°C, it appeared to go through a maximum of 24% at the final temperature of 500–550°C. Then, at the final pyrolysis temperature of 700°C, the oil yield decreased to 21%. The product yields of pyrolysis in relation to the rate of nitrogen is given Fig. 2 for the heating rate of 7°C min⫺1. The oil yield increased 11.16% when reaching a nitrogen flow rate of 100 cm3 min⫺1 and there was no obvious influence on the yield increase. Indeed, the highest yield of 27% was obtained at a final pyrolysis temperature of 550°C with a heating rate of 7°C min⫺1 and nitrogeen flow rate of 100 cm3 min⫺1. Figures 3, 4, 5 and 6 show the yields and conversion obtained in the well-swept fixed-bed tubular reactor in relation to the final temperature of pyrolysis of either 400, 450, 500, 550, or 700°C at a heating rate of 7°C min⫺1 with nitrogen flow rates of either 50, 100, 200, or 400 cm3 min⫺1. The product yields of pyrolysis in relation to the rate of nitrogen is given in Fig. 7. The pyrolysis conversions were increased for all sweeping gas rates as the pyrolysis temperature increased. The maximum pyrolysis conversion was achieved at the pyrolysis temperature of 700°C with a sweeping gas rate of 72.39%, while an increment of total conversion was detected by increasing the pyrolysis temperature. The maximum oil yield of 29.68% was obtained at a pyrolysis temperature of 550°C with a sweeping gas flow rate of 200 cm3 min⫺1. When comparing the oil yields of sweep-gas experiments it can be seen that the oil yield of the tubular reactor was 9.12% higher than the Heinze reactor at the pyrolysis temperature of 550°C with the sweeping gas rates of 200 cm3 min⫺1 and 100 cm3 min⫺1, respectively. This difference is probably attributable to the
Fig. 2. Effect of sweep gas flow rate on the product yields of Heinze oil (sweep gas flow rate of 100 cm3 min⫺1).
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Fig. 3. Effect of pyrolysis temperature on the product yields of the tubular reactor (sweep gas flow rate of 50 cm3 min⫺1).
Fig. 4. Effect of pyrolysis temperature on the product yields of the tubular reactor (sweep gas flow rate of 100 cm3 min⫺1).
geometry of the tubular reactor due to the possibility of rapid removal of pyrolysis products from the hot zone to minimize the secondary reactions such as thermal cracking, repolymerization and recondensation to maximize the liquid yield. These results suggest that mass transfer restrictions to volatile evolution are much less marked for cottonseed cake compared to coals and oil shales where oil yields are generally increased significantly as the carrier gas flow rate decreases [16–18]. This major difference is probably attributable to the low bulk density and high oxygen content of cottonseed cake.
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Fig. 5. Effect of pyrolysis temperature on the product yields of the tubular reactor (sweep gas flow rate of 200 cm3 min⫺1).
Fig. 6. Effect of pyrolysis temperature on the product yields of the tubular reactor (sweep gas flow rate of 400 cm3 min⫺1).
3.2. Chemical composition The elemental composition of the cottonseed cake and the oils characterized are listed in Table 2 and the calorific values of the bagasse and the oils are listed in Table 3. The average chemical composition of the Heinze oil tubular reactor oils analyzed were CH1.5495N0.0748O0.2267 and CH1.6410N0.0758O0.1765. Heinze retort product oil is characterized by high oxygen content with a higher H/C ratio than the tubular reactor
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Fig. 7. Effect of sweep gas flow rate on the bio-oil yields of the tubular reactor (sweep gas flow rate of 200 cm3 min⫺1, pyrolysis temperature of 550°C).
Table 3 Calorific values of cottonseend cake, Heinze retort oils and well-swept tubular reactor oil Material
Calorific values (kcal/kg)
Cottonseed cake Heinze oila Heinze oilb Tubular oilc
4300 7400 7250 8061
a b c
Obtained at 550°C, 7°C min⫺1. Obtained at 550°C, 7°C min⫺1, nitrogen flow rate of 100 cm3 min⫺1. Obtained at 550°C, 7°C min⫺1, nitrogen flow rate of 200 cm3 min ⫺1.
oil and the original cake. Further comparison of H/C ratios with conventional fuels indicates that the H/C ratios of the oils obtained in this study lie between those of light and heavy petroleum products. Also, calorific values indicate that the energy contents of the oils are very close to that of petroleum. The IR spectrum of the Heinze oil is given in Fig. 8. The O–H stretching vibrations between 3200 and 3400 cm⫺1 indicate the presence of phenols, alcohols. The C–H stretching vibrations between 2800 and 3000 cm⫺1 and C–H deformation vibrations between 1350–1475 cm⫺1 indicate the presence of alkanes. The CBO stretching vibrations with absorbance between 1650–1750 cm⫺1 indicate the presence of ketones or aldehydes. The absorbance peaks between 1575 and 1675 cm⫺1 represent CBC stretching vibrations indicative of alkenes and aromatics. The results of the adsorption chromatography of the oils showed that the pyrolysis oil consists of 65% n-pentane solubles. The aliphatic, aromatic, ester and polar frac-
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Fig. 8. IR spectra of the fractions separated from the bio-oil (Heinze oil). (a) Bio-oil, (b) pentane (c) toluene subfraction.
tions of the oil are 11%, 23%, 40% and 26%, respectively. There is an indicative increase of 5% in the aliphatic fraction of the oil obtained under a sweep gas regime due to the restrictions to repolymerization and recondensation. The fractions of this oil are 16%, 20%, 39% and 25%, respectively. The 1H NMR spectrum of the Heinze oil investigated, shown in Fig. 9, indicates that an unimportant amount of the aliphatic carbon is bound to oxygen (peaks in 3.5–4.5 ppm chemical shift range) compared to sunflower bagasse Heinze oil [9]. As is known, most of the aromatic hydrogen intensity occurring in the 6.5–7.5 ppm range indicates that the aromatic species are largely phenolic. In addition to phenols, IR spectroscopy has indicated that carboxylic acids and ketones/aldehydes are also major oxygen functions present in the polar fractions. The alkanes and alkyl groups present in the spectrum are probably derived from lipids and residual oil in the cake. The hydrogen distributions and estimated carbon aromaticity are given in Table 4. The carbon aromaticity has been calculated assuming that the aliphatic H/C ratio lies in the range of 2.0–2.2. To further assess the compatibility of the oil with currently utilized transport fuels, simulated distillation curves of the Heinze retort oil were obtained. Yields of 8%, 36%, 30% and 26% were obtained for fractions boiling under 140°C, 140–240°C,
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Fig. 9.
1
H-NMR spectra of the bio-oil (Heinze oil).
Table 4 1H-NMR results of the oils Hydrogen environment
Mole % (% of total hydrogen) Heinze retort oil
Aromatic/alkene (inc. peak at 5.5 ppm) Aliphatic adjacent to oxygen (3.3–4.5 ppm) Aliphatic adjacent to aromatic/alkene group (3.3–4.5 ppm) Other aliphatic (bonded to aliphatic only 0.4–1.8 ppm) Carbon aromaticity
4.7 1.3 19.7 74.3 0.28
240–350°C and above 350°C, respectively. The fractions boiling at 140–240°C and 240–350°C were compared with kerosene and diesel fuel (Fig. 10). The simulated distillation curves showed that the whole 140–240°C fraction was similar to kerosene and the 240–350°C fraction was similar to diesel fuel.
4. Conclusion The oil yields of the experiments conducted in the tubular reactor were higher than the oil of the fixed bed Heinze retort. The oil yield reached a maximum of 29% with the tubular reactor under nitrogen atmosphere. The higher yield of The tubular reactor is attributable to the reactor geometry. Sweeping gas removed the pyrolysis products from the hot zone to minimize the secondary reactions such as thermal cracking, repolymerization and recondensation, to maximize the liquid yield. The 1H NMR spectrum indicated that the aromaticity of the oil is very low.
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Fig. 10. Comparison of the simulated distillation curves.
The H/C ratios and simulated distillation curves of the fractions obtained from the pyrolysis oil has shown that the fractions are quite similar to the currently utilized transport fuels.
References [1] Safer SS, Zabosk SR. Biomass Energy Conversion Processes for Energy and Fuels, 1981. [2] Bridgwater AV, Kuester JL. Proceedings of the Conference on Research in Thermochemical Biomass Conversion. 1988. [3] Bridgwater AV, Double JM. Int. J. Enrgy. Res. 1999:118-179. [4] Calvin M. Die Naturwissenschaften 1980;67:525–33. [5] Elliott DC, Schiefelbein GF. ACS Fuel Chem Preprints 1989;34(4):1160–6. [6] Bridgwater AV, Cottam M. Energy and Fuels 1992;6(2):113–20. [7] Soltes J. In: Soltes EJ, Milne TA, editor. ACS Symposium Series 376, 1988. [8] Antal MJ. Advances in Solar Energy 1983;1:61–109. ¨ M, Yorgun S, Gerc¸ el HF, Andresen J, Snape CE, Pu¨ tu¨ n E. Fuel Process Technol [9] Pu¨ tu¨ n AE, Koc¸ kar O 1996;46(1):49–63. [10] Eisa MH, Barghouti S, Gillham F, Al-Saffty MT. World Bank Technical Paper No. 231. 1994:112. ¨ M, Gerc¸ el F, Andresen J, Brown S, McRae C, Snape CE. World Renewable [11] Pu¨ tu¨ n E, Koc¸ kar O Energy Congress, 1999. ¨ zbay N, Koc¸ kar O ¨ M, Pu¨ tu¨ n E. Energy Source 1997;19:905–17. [12] Pu¨ tu¨ n AE, O [13] Heinze R. Oel u Kohle 1943;39:973. [14] Pu¨ tu¨ n E, Akar A, Ekinci E, Bartle KD. Fuel 1988;67:1106–10. ¨ zcan A, Pu¨ tu¨ n E. JAAP 1999;52:33–49. [15] Pu¨ tu¨ n AE, O [16] Bolton C, Snape CE, O’Brien RJ, Kandiyoti R. Fuel 1987;66:1413–7. [17] Ekinci E, Pu¨ tu¨ n AE, C¸ itiroglu M, Love GD, Lafferty CJ, Snape CE. ICCS, Newcastle-upon-Tyne, 1991:520-523. [18] Ekinci E, Citiroglu M, Pu¨ tu¨ n E, Love GD, Lafferty CJ, Snape CE. Fuel 1992;71:1511–4.