Energy Fuels 2010, 24, 136–144 Published on Web 10/06/2009
: DOI:10.1021/ef900521k
Preparation and Property Measurement of Liquid Fuel from Supercritical Ethanolysis of Wheat Stalk† Wei Zhao,*,‡ Wen-Juan Xu,‡ Xiao-Jing Lu,‡,§ Chen Sheng,‡ Shi-Teng Zhong,‡ Shi-Rong Tang,‡ Zhi-Min Zong,‡ and Xian-Yong Wei*,‡ ‡
Key Laboratory of Coal Processing and Efficient Utilization (Ministry of Education), China University of Mining and Technology, Xuzhou 221008, Jiangsu, China, and §Datang International Power Generation Company, Limited, Xilinhaote 026000, Inner Mongolia, China Received May 25, 2009. Revised Manuscript Received September 8, 2009
Optimum conditions for preparing liquid fuel (LF) by supercritical ethanolysis (SCE) of wheat stalk powder (WSP) were determined by orthogonal experiment. Fuel properties, including pH, density, viscosity, flash and ignition temperatures, heating value, water content, and distillation range, of the LF obtained under the optimum conditions were measured. Subsequent treatments, including dehydration and distillation, were conducted upon the LF. The LFs before and after the treatments were analyzed with gas chromatography/ mass spectrometry (GC/MS). SCE of model substances cellulose and lignin was also examined for understanding the formation pathways of typical organic compounds in the LF. The results show that the optimum conditions for preparing LF are 300 °C (reaction temperature), 10 min (reaction time), and 1:24 (WSP/ ethanol ratio). After treatments, fuel properties of the LF are eligible for practical use. The main components in the LF include shorter chain carboxylic acids and their ethyl esters, furan derivatives, cyclopentanones, phenol derivatives, benzene derivatives, aromatic acid derivatives, longer chain carboxylic ethyl esters, and sterides.
the liquid/vapor products, and the ability to dissolve materials not being normally soluble in either the liquid or gaseous phase of the solvent. It can provide a single-phase environment for reactions that would otherwise occur in a multiphase system under conventional conditions.11 Therefore, it can promote the gasification/liquefaction reactions and is a candidate for biomass liquefaction. Water is considered an environmentally friendly supercritical solvent for biomass.7,8,12-14 However, the critical temperature of water is higher, and separating the liquid fuel (LF) from the reaction mixture costs more energy. As a commonly used organic solvent, ethanol has much better solvency for biomass and a much lower critical temperature and pressure than water.9,15 Recently, Cemek and Kucuk16 reported the oil yields of 44.4, 43.3, and 60.5 wt % obtained from catalytic liquefaction of Verbascum stalk with supercritical methanol, ethanol, and acetone, respectively, at 300 °C, but the report did not mention the oil composition. Supercritical methanolysis of wood was reported to afford oil in the yield up to 90% under the conditions of 350 °C/43 MPa, and related mechanisms were investigated using model compounds related to cellulose, hemicellulose, and lignin.17-20 Xu and Etcheverry15 investigated catalytic
1. Introduction Because the major conventional energy resources, such as coal, petroleum, and natural gas, are at the verge of becoming extinct, biomass, including agricultural residues (wheat/rice straws and corn waste), wood, woodwaste, and forestry residues, etc., with its great abundance and high energy potential, can be considered as one of the promising environmentally friendly renewable energy options. There are several ways to make use of the energy contained in the biomass from old direct burning to pyrolysis, gasification, and liquefaction.1-6 In comparison to gasification and pyrolysis, the reaction conditions of direct liquefaction are mild, and thereby more and more attention is being paid to related investigations.7-10 Supercritical fluid has unique transport properties (gas-like diffusivity and liquid-like density), complete miscibility with † Presented at the 2009 Sino-Australian Symposium on Advanced Coal and Biomass Utilisation Technologies. *To whom correspondence should be addressed. Telephone: þ86-(516)-83995916. E-mail:
[email protected] (W.Z.); Telephone: þ86-(516)-83884399. E-mail:
[email protected] (X.-Y.W.). (1) Sheng, C.; Azevedo, J. L. T. Biomass Bioenergy 2005, 28 (5), 499– 507. (2) Onay, O.; Kockar, O. M. Fuel 2006, 85 (12-13), 1921–1928. (3) Luo, Z.; Wang, S.; Liao, Y.; Zhou, J. Biomass Bioenergy 2004, 26 (5), 455–462. (4) Song, C. C.; Hu, H. Q.; Zhu, S. W.; Wang, G.; Chen, H. Energy Fuels 2004, 18 (1), 90–96. (5) Yokoyama, S.; Ogi, T.; Koguchi, K.; Nakamura, E. Liq. Fuels Technol. 1984, 2 (2), 155–163. (6) Minowa, T.; Kondo, T.; Sudirjo, S. T. Biomass Bioenergy 1998, 14 (5-6), 517–524. (7) Qu, Y. X.; Wei, X. M.; Zhong, C. L. Energy 2003, 28 (7), 597–606. (8) Qian, Y. J.; Zuo, C. J.; Tan, J.; He, J. H. Energy 2007, 32 (3), 196– 202. (9) Yamazaki, J.; Minami, E.; Saka, S. J. Wood Sci. 2006, 52 (6), 527– 532. (10) Yamada, T.; Ono, H. Bioresour. Technol. 1999, 70 (1), 61–67.
r 2009 American Chemical Society
(11) Savage, P. E. Chem. Rev. 1999, 99 (2), 603–622. (12) Williams, P. T. Energy Fuels 2006, 20 (3), 1259–1265. (13) D’Jesus, P.; Boukis, N.; Kraushaar-Czarnetzki, B.; Dinjus, E. Fuel 2006, 85 (7-8), 1032–1038. (14) Matsumura, Y.; Sasaki, M.; Okuda, K.; Takami, S.; Ohara, S.; Umetsu, M.; Adschiri, T. Combust. Sci. Technol. 2006, 178 (1-3), 509– 536. (15) Xu, C. B; Etcheverry, T. Fuel 2008, 87 (3), 335–345. (16) Cemek, M.; Kucuk, M. M. Energy Convers. Manage. 2001, 42 (2), 125–130. (17) Ishikawa, Y.; Saka, S. Cellulose 2001, 8 (3), 189–195. (18) Tsujino, J.; Kawamoto, H.; Saka, S. Wood Sci. Technol. 2003, 37 (3-4), 299–307. (19) Minami, E.; Kawamoto, H.; Saka, S. J. Wood Sci. 2003, 49 (2), 158–165. (20) Minami, E.; Saka, S. J. Wood Sci. 2003, 49 (1), 73–78.
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Energy Fuels 2010, 24, 136–144
: DOI:10.1021/ef900521k
Zhao et al.
hydroliquefaction of woody biomass in sub- and supercritical ethanol. However, the use of H2 and catalyst could make the process unpractical and lead to potential pollution. Preparing LF is the main target of biomass liquefaction up to now. The values of pH, density, viscosity, flash and ignition temperatures, water content, and distillation range are known to be typical key properties for combustion applications in boilers, furnaces, and engines. The fuel property of pyrolysis liquid from biomass was measuered.21-23 However, few fuel property measurements of liquid from biomass liquefaction were carried out. In this work, we use ethanol as the solvent and investigate the effects of reaction temperature, reaction time, and wheat stalk powder (WSP)/ethanol ratio on the yield of LF from supercritical ethanolysis (SCE) of the WSP without H2 or catalyst for optimizing the reaction conditions. Fuel properties and composition were emphatically examined.
Table 1. Proximate, Ultimate, and Chemical Analyses (m %) of WSP proximate analysis
ultimate analysis
chemical analysis (dry base)
Mad Aad Vdaf Cdaf Hdaf Ndaf Odaf St,d cellulose hemicellulose lignin 9.6
7.5 70.2 42.2 5.3
0.4 34.8 0.2
44.9
36.6
20.0
Table 2. Metal Contents (m %) in Ash from the WSP Na
Mg
Al
K
Ca
Fe
Mn
Cu
Zn
Ni
1.2
1.5
0.3
2.1
1.9
0.1
0.004
0.002
0.009
0.001
Table 3. Measurement Methods for Fuel Property
2. Experimental Section 2.1. Materials. Wheat stalks were collected from the field in the vicinity of Xuzhou City, Jiangsu, China. They were washed with water and then dried in sunlight, chopped into small pieces, and pulverized to pass through an 80-mesh sieve (100 °C). This is due to a high amount of low boiling volatile compounds in LF. A low flash temperature also indicates a high vapor pressure. The fire temperature of LF is 108 °C, higher than that of diesel and lower than that of gasoline and biodiesel. The combustion heat of fuel is the amount of heat produced when the fuel is burned completely. The results of the heating values for the LFs are given in Table 7. The gross heating value of LF is 38.7 MJ kg-1, higher than that of stalk and near that of bio-oil and diesel. The water content of LF from SCE of WSP is 20.5 m %. Usually, the water contents of oil from biomass pyrolysis are in the range of 5-40%.25-27 After dehydration with anhydrous CaCl2, the water content was reduced to 1.17 m %, which does not fit the fuel standard (
