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Liquid products from Verbascum stalk by supercritical fluid extraction
Energy Conversion & Management 42 (2001) 125±130
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Liquid products from Verbascum stalk by supercritical ¯uid extraction Mustafa Cemek, Mehmet M. KuÈc° uÈk* Education Faculty, Yuzuncu Yil University, 65080-Van, Turkey Received 25 January 2000; accepted 14 March 2000
Abstract Verbascum stalk mill was converted to liquid products by using organic solvents, such as methanol, ethanol and acetone, with catalysts (10% NaOH or ZnCl2) and without catalyst in an autoclave at temperatures of 533, 553 and 573 K. The liquid products were extracted by liquid±liquid extraction using benzene and diethyl ether. The yields from supercritical methanol, ethanol and acetone extractions were 44.4, 43.3 and 60.5 wt%, respectively, at 573 K. In the catalytic runs with methanol and ethanol, the extracts were 52.4 and 44.8% using 10% NaOH and 55.5 and 60.6% using ZnCl2, respectively, at 573 K. The yields from supercritical methanol increased from 38.2 to 52.4% as the temperature was increased from 533 to 573 K in the catalytic run. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Supercritical ¯uid extraction; Verbascum stalk; Thermochemical process; Biomass liquefaction
1. Introduction Worldwide, biomass ranks fourth as an energy resource, providing approximately 14% of the world's energy needs: biomass is the largest source of energy in developing nations, providing 035% of their energy, particularly in rural areas where it is often the only accessible and aordable source of energy [1±3]. Since the oil crisis of the early 1970s, declining reserves and ¯uctuating prices of fossil fuels have intensi®ed the search for an alternate renewable raw material to replace petroleum all * Corresponding author. E-mail address: [email protected] (M.M. KuÈc° uÈk). 0196-8904/01/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 1 9 6 - 8 9 0 4 ( 0 0 ) 0 0 0 4 9 - 2
126
M. Cemek, M.M. KuÈc° uÈk / Energy Conversion & Management 42 (2001) 125±130
over the world. There are two general approaches to the use of biomass as a starting material for the production of oils or chemicals. The ®rst of these approaches consists of complete conversion of the biomass to product oils and other soluble components. This type of process, known as liquefaction, aims at maximizing the yields of soluble products derived from the biomass feedstock and is, therefore, not concerned with retaining the integrity of the cellulose polymer. The oils may have an interest as transportable and stockable liquid fuel for direct combustion or co-generation uses as well as feedstock for upgrading to chemicals [2]. Recently, biomass and its derivatives have been investigated as alternative feedstocks for fuels and organic chemicals. There are many advantages in using biomass as a source of energy and chemicals: (1) biomass has negligible sulfur, nitrogen and metal content and is a renewable source which could assure a diversi®ed and continuous supply of energy to regions not possessing fossil fuel reserves and at times when petroleum supplies become scarce due to political or other factors, and (2) usage of biomass maintains the balance of carbon dioxide in the atmosphere and may also help minimize environmental problems. Several approaches have been proposed for production of fuels from biomass; pyrolysis, ethyl alcohol and biogas production and direct and indirect liquefaction [2,3]. The liquefaction of biomass depends on the chemical composition of the main components (cellulose, lignin and hemicelluloses) and re¯ects their responses to temperature, solvent and catalyst. Biomass liquefaction processes have been based on the earlier work of Appell et al. [4]. They reported that a variety of lignocellulosic materials could be converted partially into a fuel oil by reaction with carbon monoxide and water at an elevated temperature in the presence of sodium carbonate acting as a catalyst. Many investigators [5±8] have studied the development of liquefaction techniques for conversion of biomass to oil. This work deals with liquefaction of biomass in order to obtain synthetic liquid fuels. The liquefaction of wood has been investigated in the presence of solutions of alkalis and glycerin [9,10]. In the presence of glycerin, the wood is completely converted to liquid and gaseous products within the temperature range of 520±600 K. In the presence of alkali, the polymers and polyglyceride are formed on low-heating and the glycerin is spent entirely [10]. Various agricultural residues, such as hazelnut shell, grain dust, sun¯ower stalk and Pragmites australis and Verbascum stalks are available in Turkey as the source of biomass energy and chemicals. The present study is based on conversion to products of Verbascum stalk at an elevated temperature and pressure with and without catalysts by using dierent organic solvents in an autoclave. The conversion products obtained from the liquefaction were fractionated into benzene fractions and diethyl ether fraction constituents by liquid±liquid extractions.
2. Experimental Verbascum stalk samples were supplied from the Van province in Turkey. Air dried samples were ground in a Thomas±Wiley mill to pass through a screen of 1.0 mm aperture and extracted with petroleum ether (bp 40±608C). All the runs were performed in a 100 ml cylindrical autoclave made of 316 stainless steel.
M. Cemek, M.M. KuÈc° uÈk / Energy Conversion & Management 42 (2001) 125±130
127
The sample was loaded from the bolt hole into the autoclave, and then the hole was plugged with a screw bolt in each run. In a typical run, the autoclave was loaded with the sample (10.0 g) and a solvent (75 ml) or solution containing the desired quantities of catalyst. Methanol, ethanol or acetone as solvents and NaOH and ZnCl2 as catalysts were used in the supercritical extractions. An external heater heated the autoclave, and the power was adjusted to give a heating time of approximately 90 min. The temperature of the autoclave was measured with a simple thermocouple (NiCr±constantan) and controlled at 533, 553 and 573 2 5 K for 75 min. Supercritical ¯uid liquefaction of Verbascum stalk was performed at three conversion temperatures: 533, 553 and 573 K. After each run, the gas was vented and the autoclave contents were poured into a vessel. All the residual oil and solids were removed from the autoclave by washing with the solvents used. After evaporating the solvent, the liquefaction mixture was added to water (200 ml) and extracted with benzene (4 50 ml) and then with diethyl ether (4 50 ml) in a separating funnel. Upon removal of the solvents, the yields of the products were determined. 3. Results and discussion The conversion scheme of biomass to liquid products is given in a previous study [11]. The results from the chemical analysis of the Verbascum stalk are shown in Table 1. The yields from the non-catalytic and catalytic supercritical ¯uid extractions are given in Table 2. Supercritical ¯uid extraction was performed in the autoclave above the critical temperature and pressure of the solvent. Table 2 shows that as the temperature increases, the yield of the extract increases. Above the critical temperature of the solvent, pressure increases as a function of the temperature. Thus, the yields of supercritical ¯uid extraction increase with increasing pressure in agreement with the theory of gas extraction [12,13]. The yields of supercritical ¯uid liquefaction with methanol, ethanol and acetone were 28.7, 21.4 and 29.4% at 533 K; 40.6, 29.8 and 42.4% at 553 K; and 44.4, 43.3 and 60.5% at 573 K, respectively. The yields of conversion increased with the temperature increase from 533 to 573 K, as listed in Table 2, and temperature appears to have a signi®cant eect on liquefaction yield. Table 2 shows that there is a signi®cant dierence in the percentage of liquefaction yields from the methanol and catalytic methanol runs. The methanol solubles increased from 28.7 to Table 1 Results from chemical analysis of Verbascum stalk Structural analysisa Lignin Hemicelluloses Cellulose a
Proximate analysis 31.4 17.6 50.3
wt % of dry and ashless material.
Ash Moisture Soxhelet extractives with petroleum ethera
2.4 5.3 0.7
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M. Cemek, M.M. KuÈc° uÈk / Energy Conversion & Management 42 (2001) 125±130
Table 2 Yields from supercritical ¯uid extractions of Verbascum stalk (as percent of dry and ashless sample used) Conversion yield at (K):
Solvent (75 ml): Methanol Tcritic 513:1 K) Ethanol Tcritic 516:1 K) Methanol Tcritic 508:0 K) Water Tcritic 647:8 K)
Catalytic conversion at (K):
533
553
573
Catalytic conversion at (K): 533
553
573
28.7 21.4 29.4 ±
40.6 29.8 42.4 ±
44.4 43.3 60.5 17.1
Methanol + 10% NaOH Ethanol + 10% NaOH Methanol + 10% ZnCl2 Ethanol + 10% ZnCl2 Water + 10% NaOH
44.0 36.6 ± ± ±
52.4 44.8 55.6 60.6 49.5
38.2 31.2 ± ± ±
38.2% at 533 K, from 40.6 to 44.0% at 553 K and from 44.4 to 52.4% by using NaOH (10.0% of the sample weight) as a catalyst. The liquefaction yields also increased in the ethanolic runs with the same catalyst. NaOH appeared to have a positive eect on the percentage yields, as seen in the catalytic runs. Table 2 shows that ZnCl2 (10.0% of the sample weight) as catalyst was more eective than NaOH, but its solubilities in benzene and ethyl ether are low. The fractionation of the products obtained from the supercritical ¯uid extractions is given in Tables 3±5. The fractionation was performed by liquid±liquid extraction, with benzene, diethyl ether and water used as solvents in the fractionations. Insolubles in these solvents were called tarry materials. In the liquid±liquid extraction, the benzene and diethyl ether solubles increased with increasing temperature, but at the same time, both tarry materials and water solubles also increased. The tarry materials and water solubles were very high, particularly in the ZnCl2 catalytic runs (Table 5). In the liquefaction process, the micellar-like broken down fragments produced by hydrolysis are degraded to smaller compounds by dehydration, dehydrogenation, deoxygenation and decarboxylation. These compounds, once produced, rearrange through condensation, cyclization and polymerization, leading to new compounds [14]. When wood or biomass is heated, there is an attack on the glycosidic linkages, which then leads to dehydration, decarboxylation and decarbonylation and cleavage of the molecules into smaller fragments which are soluble, and ®nally, gaseous compounds are formed. Lignin degradation reactions Table 3 Yields of fractions from supercritical ¯uid extracts of Verbascum stalk at 533 K (as percent of dry and ashless sample used)
Ethanol Methanol Acetone Ethanol + 10% NaOH Methanol + 10% NaOH
Benzene-solubles
Diethyl ether-solubles
Tarry material
Water-solubles
1.1 3.3 5.6 3.6 5.9
0.4 1.2 1.1 1.6 2.8
5.1 5.6 8.5 7.3 10.4
14.6 18.7 14.2 18.7 19.2
M. Cemek, M.M. KuÈc° uÈk / Energy Conversion & Management 42 (2001) 125±130
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Table 4 Yields from supercritical ¯uid extractions of Verbascum stalk at 553 K(as percent of dry and ashless sample used)
Ethanol Methanol Acetone Ethanol + 10% NaOH Methanol + 10% NaOH
Benzene-solubles
Diethyl ether-solubles
Tarry material
Water-solubles
2.3 5.6 9.2 5.0 5.9
1.5 2.4 2.6 2.7 2.9
9.1 13.6 12.3 9.4 14.1
17.0 19.3 18.3 19.6 21.2
Table 5 Yields from supercritical ¯uid extractions of Verbascum stalk at 573 K (as percent of dry and ashless sample used)
Ethanol Methanol Acetone Water Ethanol + 10% NaOH Methanol + 10% NaOH Water + 10% NaOH Ethanol + 10% ZnCl2 Methanol + 10% ZnCl2
Benzene-solubles
Diethyl ether-solubles
Tarry material
Water-solubles
5.6 6.7 16.7 1.3 6.8 9.1 1.5 4.5 4.6
2.6 2.8 7.2 1.2 3.4 4.9 1.2 2.2 2.6
15.6 14.4 15.6 ± 13.6 15.6 ± 29.5 18.6
17.4 19.3 18.8 ± 21.1 22.8 ± 24.4 29.7
include fragmentation of a- and b-ether linkages and carbon±carbon bond cleavage, leading to the formation of soluble and gaseous products [14]. Assuming that hemicelluloses decompose early in the temperature pro®le of the reaction with wood, the lignin initially associated with the hemicellulose fraction will ®nd itself in a free state. Structural rearrangements will then take place and the elevated temperature will lead to an increase in the mobility of the free lignin. Upon increasing the temperature of the degradation reactions, condensation is enhanced and thermal decomposition leads to volatiles. The free radicals formed during decomposition of cellulose and lignin at the higher temperature have a random tendency to form condensed macromolecules, leading to an acetone-insoluble fraction. In most cases, hydrogen gas is used in a biomass liquefaction process to stabilize the free radicals and to avoid these condensation reactions.
4. Conclusion Conversion by supercritical ¯uid extraction of biomass to liquids has been demonstrated with the use of a number of processing con®gurations. These dierent processing techniques tend to emphasize dierent mechanism subsets within the large group of potential chemical
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mechanisms by which biomass is converted to primary products and, thereafter, further converted by varying degrees to ®nal products. The relative abundance of identi®ed low molecular weight phenolic compounds decreases from lignin to wood to cellulose in the liquefaction product [15]. This is in agreement with the known phenolic nature of lignin. Verbascum stalk samples were converted to liquid products by using organic solvents such as methanol, ethanol and acetone with catalysts (10% NaOH or ZnCl2) and without catalyst in an autoclave at temperatures of 533, 553 and 573 K. The liquid products were extracted by liquid±liquid extraction using benzene and diethyl ether. The yield from the supercritical extractions with acetone was 60.5% at 573 K. In the catalytic runs with methanol and ethanol, the extracts were 52.4 and 44.8% using 10% NaOH and 55.6 and 60.6% using ZnCl2, respectively, at 573 K. The yields from supercritical methanol were increased from 38.2 to 52.4% as the temperature was increased from 533 to 573 K in the catalytic run. Acknowledgements Yuzuncu Yil University Research Fund supported this work, and the authors are grateful to the Yuzuncu Yil University Research Fund for the ®nancial support of this study. References [1] KuÈc° uÈk MM. Recent advances in biomass technology. Fuel Science & Technology Int'l 1994;12(6):845±71. [2] KuÈc° uÈk MM, Demirbas° A. Biomass conversion processes. Energy Convers Mgmt 1997;38:151±65. [3] KuÈc° uÈk MM, Tunc° M. Supercritical ¯uid extraction of biomass. Energy Education Science & Technol 1999;2:1± 6. [4] Appell HR, Fu YC, Friedman S, Yavorsky PM, Wender I. Converting organic wastes to oil. US Bureau of Mines Report of Investigation, No. 7560, 1971. [5] Eager RL, Mathews JF, Pepper MJ, Zohdy H. Studies on the products resulting from the conversion aspen poplar to an oil. Can J Chem 1981;59:2191±7. [6] Erzengin M, KuÈc° uÈk MM. Liquefaction of sun¯ower stalk by using supercritical gas extraction. Energy Convers Mgmt 1998;39:1203±6. [7] KuÈc° uÈk MM, AgÆirtas° S. Liquefaction of Pragmites australis by supercritical gas extraction. Bioresource Technology 1999;69:141±3. [8] Akdeniz F, KuÈc° uÈk MM, Demirbas° A. Liquids from olive husk by using supercritical ¯uid extraction and thermochemical methods. Energy Education Science & Technol 1998;2:17±22. [9] Rustamov VR, Abdullayev KM, Samedov EA. Biomass conversion to liquid fuel by two-stage thermochemical cycle. Energy Convers Mgmt 1998;39:869±75. [10] Demirbas A. A new method on wood liquefaction. Chimica Acta Turcica 1985;13:363±8. [11] KuÈc° uÈk MM. Liquefaction of hazelnut seed coat by supercritical gas extraction. Energy Convers Mgmt 1994;36:145±8. [12] Paul PFM, Wise WS. The principle of gas extraction. London: Mills and Boon, 1971. [13] Hawthorne SB. Analytical-scale supercritical ¯uid extraction. Anal Chem 1990;62:633A±42A. [14] Demirbas A. Mechanisms of liquefaction and pyrolysis reactions of biomass. Energy Convers Mgmt 2000;41:633±46. [15] Eager RL, Pepper JM, Roy JC. Chemical studies on oils derived from aspen poplar wood, cellulose, and isolated aspen poplar lignin. Can J Chem 1983;61:2010±5.
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Liquid products from Verbascum stalk by supercritical ¯uid extraction Mustafa Cemek, Mehmet M. KuÈc° uÈk* Education Faculty, Yuzuncu Yil University, 65080-Van, Turkey Received 25 January 2000; accepted 14 March 2000
Abstract Verbascum stalk mill was converted to liquid products by using organic solvents, such as methanol, ethanol and acetone, with catalysts (10% NaOH or ZnCl2) and without catalyst in an autoclave at temperatures of 533, 553 and 573 K. The liquid products were extracted by liquid±liquid extraction using benzene and diethyl ether. The yields from supercritical methanol, ethanol and acetone extractions were 44.4, 43.3 and 60.5 wt%, respectively, at 573 K. In the catalytic runs with methanol and ethanol, the extracts were 52.4 and 44.8% using 10% NaOH and 55.5 and 60.6% using ZnCl2, respectively, at 573 K. The yields from supercritical methanol increased from 38.2 to 52.4% as the temperature was increased from 533 to 573 K in the catalytic run. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Supercritical ¯uid extraction; Verbascum stalk; Thermochemical process; Biomass liquefaction
1. Introduction Worldwide, biomass ranks fourth as an energy resource, providing approximately 14% of the world's energy needs: biomass is the largest source of energy in developing nations, providing 035% of their energy, particularly in rural areas where it is often the only accessible and aordable source of energy [1±3]. Since the oil crisis of the early 1970s, declining reserves and ¯uctuating prices of fossil fuels have intensi®ed the search for an alternate renewable raw material to replace petroleum all * Corresponding author. E-mail address: [email protected] (M.M. KuÈc° uÈk). 0196-8904/01/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 1 9 6 - 8 9 0 4 ( 0 0 ) 0 0 0 4 9 - 2
126
M. Cemek, M.M. KuÈc° uÈk / Energy Conversion & Management 42 (2001) 125±130
over the world. There are two general approaches to the use of biomass as a starting material for the production of oils or chemicals. The ®rst of these approaches consists of complete conversion of the biomass to product oils and other soluble components. This type of process, known as liquefaction, aims at maximizing the yields of soluble products derived from the biomass feedstock and is, therefore, not concerned with retaining the integrity of the cellulose polymer. The oils may have an interest as transportable and stockable liquid fuel for direct combustion or co-generation uses as well as feedstock for upgrading to chemicals [2]. Recently, biomass and its derivatives have been investigated as alternative feedstocks for fuels and organic chemicals. There are many advantages in using biomass as a source of energy and chemicals: (1) biomass has negligible sulfur, nitrogen and metal content and is a renewable source which could assure a diversi®ed and continuous supply of energy to regions not possessing fossil fuel reserves and at times when petroleum supplies become scarce due to political or other factors, and (2) usage of biomass maintains the balance of carbon dioxide in the atmosphere and may also help minimize environmental problems. Several approaches have been proposed for production of fuels from biomass; pyrolysis, ethyl alcohol and biogas production and direct and indirect liquefaction [2,3]. The liquefaction of biomass depends on the chemical composition of the main components (cellulose, lignin and hemicelluloses) and re¯ects their responses to temperature, solvent and catalyst. Biomass liquefaction processes have been based on the earlier work of Appell et al. [4]. They reported that a variety of lignocellulosic materials could be converted partially into a fuel oil by reaction with carbon monoxide and water at an elevated temperature in the presence of sodium carbonate acting as a catalyst. Many investigators [5±8] have studied the development of liquefaction techniques for conversion of biomass to oil. This work deals with liquefaction of biomass in order to obtain synthetic liquid fuels. The liquefaction of wood has been investigated in the presence of solutions of alkalis and glycerin [9,10]. In the presence of glycerin, the wood is completely converted to liquid and gaseous products within the temperature range of 520±600 K. In the presence of alkali, the polymers and polyglyceride are formed on low-heating and the glycerin is spent entirely [10]. Various agricultural residues, such as hazelnut shell, grain dust, sun¯ower stalk and Pragmites australis and Verbascum stalks are available in Turkey as the source of biomass energy and chemicals. The present study is based on conversion to products of Verbascum stalk at an elevated temperature and pressure with and without catalysts by using dierent organic solvents in an autoclave. The conversion products obtained from the liquefaction were fractionated into benzene fractions and diethyl ether fraction constituents by liquid±liquid extractions.
2. Experimental Verbascum stalk samples were supplied from the Van province in Turkey. Air dried samples were ground in a Thomas±Wiley mill to pass through a screen of 1.0 mm aperture and extracted with petroleum ether (bp 40±608C). All the runs were performed in a 100 ml cylindrical autoclave made of 316 stainless steel.
M. Cemek, M.M. KuÈc° uÈk / Energy Conversion & Management 42 (2001) 125±130
127
The sample was loaded from the bolt hole into the autoclave, and then the hole was plugged with a screw bolt in each run. In a typical run, the autoclave was loaded with the sample (10.0 g) and a solvent (75 ml) or solution containing the desired quantities of catalyst. Methanol, ethanol or acetone as solvents and NaOH and ZnCl2 as catalysts were used in the supercritical extractions. An external heater heated the autoclave, and the power was adjusted to give a heating time of approximately 90 min. The temperature of the autoclave was measured with a simple thermocouple (NiCr±constantan) and controlled at 533, 553 and 573 2 5 K for 75 min. Supercritical ¯uid liquefaction of Verbascum stalk was performed at three conversion temperatures: 533, 553 and 573 K. After each run, the gas was vented and the autoclave contents were poured into a vessel. All the residual oil and solids were removed from the autoclave by washing with the solvents used. After evaporating the solvent, the liquefaction mixture was added to water (200 ml) and extracted with benzene (4 50 ml) and then with diethyl ether (4 50 ml) in a separating funnel. Upon removal of the solvents, the yields of the products were determined. 3. Results and discussion The conversion scheme of biomass to liquid products is given in a previous study [11]. The results from the chemical analysis of the Verbascum stalk are shown in Table 1. The yields from the non-catalytic and catalytic supercritical ¯uid extractions are given in Table 2. Supercritical ¯uid extraction was performed in the autoclave above the critical temperature and pressure of the solvent. Table 2 shows that as the temperature increases, the yield of the extract increases. Above the critical temperature of the solvent, pressure increases as a function of the temperature. Thus, the yields of supercritical ¯uid extraction increase with increasing pressure in agreement with the theory of gas extraction [12,13]. The yields of supercritical ¯uid liquefaction with methanol, ethanol and acetone were 28.7, 21.4 and 29.4% at 533 K; 40.6, 29.8 and 42.4% at 553 K; and 44.4, 43.3 and 60.5% at 573 K, respectively. The yields of conversion increased with the temperature increase from 533 to 573 K, as listed in Table 2, and temperature appears to have a signi®cant eect on liquefaction yield. Table 2 shows that there is a signi®cant dierence in the percentage of liquefaction yields from the methanol and catalytic methanol runs. The methanol solubles increased from 28.7 to Table 1 Results from chemical analysis of Verbascum stalk Structural analysisa Lignin Hemicelluloses Cellulose a
Proximate analysis 31.4 17.6 50.3
wt % of dry and ashless material.
Ash Moisture Soxhelet extractives with petroleum ethera
2.4 5.3 0.7
128
M. Cemek, M.M. KuÈc° uÈk / Energy Conversion & Management 42 (2001) 125±130
Table 2 Yields from supercritical ¯uid extractions of Verbascum stalk (as percent of dry and ashless sample used) Conversion yield at (K):
Solvent (75 ml): Methanol Tcritic 513:1 K) Ethanol Tcritic 516:1 K) Methanol Tcritic 508:0 K) Water Tcritic 647:8 K)
Catalytic conversion at (K):
533
553
573
Catalytic conversion at (K): 533
553
573
28.7 21.4 29.4 ±
40.6 29.8 42.4 ±
44.4 43.3 60.5 17.1
Methanol + 10% NaOH Ethanol + 10% NaOH Methanol + 10% ZnCl2 Ethanol + 10% ZnCl2 Water + 10% NaOH
44.0 36.6 ± ± ±
52.4 44.8 55.6 60.6 49.5
38.2 31.2 ± ± ±
38.2% at 533 K, from 40.6 to 44.0% at 553 K and from 44.4 to 52.4% by using NaOH (10.0% of the sample weight) as a catalyst. The liquefaction yields also increased in the ethanolic runs with the same catalyst. NaOH appeared to have a positive eect on the percentage yields, as seen in the catalytic runs. Table 2 shows that ZnCl2 (10.0% of the sample weight) as catalyst was more eective than NaOH, but its solubilities in benzene and ethyl ether are low. The fractionation of the products obtained from the supercritical ¯uid extractions is given in Tables 3±5. The fractionation was performed by liquid±liquid extraction, with benzene, diethyl ether and water used as solvents in the fractionations. Insolubles in these solvents were called tarry materials. In the liquid±liquid extraction, the benzene and diethyl ether solubles increased with increasing temperature, but at the same time, both tarry materials and water solubles also increased. The tarry materials and water solubles were very high, particularly in the ZnCl2 catalytic runs (Table 5). In the liquefaction process, the micellar-like broken down fragments produced by hydrolysis are degraded to smaller compounds by dehydration, dehydrogenation, deoxygenation and decarboxylation. These compounds, once produced, rearrange through condensation, cyclization and polymerization, leading to new compounds [14]. When wood or biomass is heated, there is an attack on the glycosidic linkages, which then leads to dehydration, decarboxylation and decarbonylation and cleavage of the molecules into smaller fragments which are soluble, and ®nally, gaseous compounds are formed. Lignin degradation reactions Table 3 Yields of fractions from supercritical ¯uid extracts of Verbascum stalk at 533 K (as percent of dry and ashless sample used)
Ethanol Methanol Acetone Ethanol + 10% NaOH Methanol + 10% NaOH
Benzene-solubles
Diethyl ether-solubles
Tarry material
Water-solubles
1.1 3.3 5.6 3.6 5.9
0.4 1.2 1.1 1.6 2.8
5.1 5.6 8.5 7.3 10.4
14.6 18.7 14.2 18.7 19.2
M. Cemek, M.M. KuÈc° uÈk / Energy Conversion & Management 42 (2001) 125±130
129
Table 4 Yields from supercritical ¯uid extractions of Verbascum stalk at 553 K(as percent of dry and ashless sample used)
Ethanol Methanol Acetone Ethanol + 10% NaOH Methanol + 10% NaOH
Benzene-solubles
Diethyl ether-solubles
Tarry material
Water-solubles
2.3 5.6 9.2 5.0 5.9
1.5 2.4 2.6 2.7 2.9
9.1 13.6 12.3 9.4 14.1
17.0 19.3 18.3 19.6 21.2
Table 5 Yields from supercritical ¯uid extractions of Verbascum stalk at 573 K (as percent of dry and ashless sample used)
Ethanol Methanol Acetone Water Ethanol + 10% NaOH Methanol + 10% NaOH Water + 10% NaOH Ethanol + 10% ZnCl2 Methanol + 10% ZnCl2
Benzene-solubles
Diethyl ether-solubles
Tarry material
Water-solubles
5.6 6.7 16.7 1.3 6.8 9.1 1.5 4.5 4.6
2.6 2.8 7.2 1.2 3.4 4.9 1.2 2.2 2.6
15.6 14.4 15.6 ± 13.6 15.6 ± 29.5 18.6
17.4 19.3 18.8 ± 21.1 22.8 ± 24.4 29.7
include fragmentation of a- and b-ether linkages and carbon±carbon bond cleavage, leading to the formation of soluble and gaseous products [14]. Assuming that hemicelluloses decompose early in the temperature pro®le of the reaction with wood, the lignin initially associated with the hemicellulose fraction will ®nd itself in a free state. Structural rearrangements will then take place and the elevated temperature will lead to an increase in the mobility of the free lignin. Upon increasing the temperature of the degradation reactions, condensation is enhanced and thermal decomposition leads to volatiles. The free radicals formed during decomposition of cellulose and lignin at the higher temperature have a random tendency to form condensed macromolecules, leading to an acetone-insoluble fraction. In most cases, hydrogen gas is used in a biomass liquefaction process to stabilize the free radicals and to avoid these condensation reactions.
4. Conclusion Conversion by supercritical ¯uid extraction of biomass to liquids has been demonstrated with the use of a number of processing con®gurations. These dierent processing techniques tend to emphasize dierent mechanism subsets within the large group of potential chemical
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mechanisms by which biomass is converted to primary products and, thereafter, further converted by varying degrees to ®nal products. The relative abundance of identi®ed low molecular weight phenolic compounds decreases from lignin to wood to cellulose in the liquefaction product [15]. This is in agreement with the known phenolic nature of lignin. Verbascum stalk samples were converted to liquid products by using organic solvents such as methanol, ethanol and acetone with catalysts (10% NaOH or ZnCl2) and without catalyst in an autoclave at temperatures of 533, 553 and 573 K. The liquid products were extracted by liquid±liquid extraction using benzene and diethyl ether. The yield from the supercritical extractions with acetone was 60.5% at 573 K. In the catalytic runs with methanol and ethanol, the extracts were 52.4 and 44.8% using 10% NaOH and 55.6 and 60.6% using ZnCl2, respectively, at 573 K. The yields from supercritical methanol were increased from 38.2 to 52.4% as the temperature was increased from 533 to 573 K in the catalytic run. Acknowledgements Yuzuncu Yil University Research Fund supported this work, and the authors are grateful to the Yuzuncu Yil University Research Fund for the ®nancial support of this study. References [1] KuÈc° uÈk MM. Recent advances in biomass technology. Fuel Science & Technology Int'l 1994;12(6):845±71. [2] KuÈc° uÈk MM, Demirbas° A. Biomass conversion processes. Energy Convers Mgmt 1997;38:151±65. [3] KuÈc° uÈk MM, Tunc° M. Supercritical ¯uid extraction of biomass. Energy Education Science & Technol 1999;2:1± 6. [4] Appell HR, Fu YC, Friedman S, Yavorsky PM, Wender I. Converting organic wastes to oil. US Bureau of Mines Report of Investigation, No. 7560, 1971. [5] Eager RL, Mathews JF, Pepper MJ, Zohdy H. Studies on the products resulting from the conversion aspen poplar to an oil. Can J Chem 1981;59:2191±7. [6] Erzengin M, KuÈc° uÈk MM. Liquefaction of sun¯ower stalk by using supercritical gas extraction. Energy Convers Mgmt 1998;39:1203±6. [7] KuÈc° uÈk MM, AgÆirtas° S. Liquefaction of Pragmites australis by supercritical gas extraction. Bioresource Technology 1999;69:141±3. [8] Akdeniz F, KuÈc° uÈk MM, Demirbas° A. Liquids from olive husk by using supercritical ¯uid extraction and thermochemical methods. Energy Education Science & Technol 1998;2:17±22. [9] Rustamov VR, Abdullayev KM, Samedov EA. Biomass conversion to liquid fuel by two-stage thermochemical cycle. Energy Convers Mgmt 1998;39:869±75. [10] Demirbas A. A new method on wood liquefaction. Chimica Acta Turcica 1985;13:363±8. [11] KuÈc° uÈk MM. Liquefaction of hazelnut seed coat by supercritical gas extraction. Energy Convers Mgmt 1994;36:145±8. [12] Paul PFM, Wise WS. The principle of gas extraction. London: Mills and Boon, 1971. [13] Hawthorne SB. Analytical-scale supercritical ¯uid extraction. Anal Chem 1990;62:633A±42A. [14] Demirbas A. Mechanisms of liquefaction and pyrolysis reactions of biomass. Energy Convers Mgmt 2000;41:633±46. [15] Eager RL, Pepper JM, Roy JC. Chemical studies on oils derived from aspen poplar wood, cellulose, and isolated aspen poplar lignin. Can J Chem 1983;61:2010±5.