Energy Fuels 2010, 24, 2071–2077 Published on Web 02/24/2010
: DOI:10.1021/ef901241e
Bio-Oil from Hydro-Liquefaction of Bagasse in Supercritical Ethanol Jade Chumpoo† and Pattarapan Prasassarakich*,†,‡ †
Department of Chemical Technology, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand, and ‡Center for Petroleum, Petrochemicals, and Advanced Materials, Chulalongkorn University, Bangkok, 10330, Thailand Received October 29, 2009. Revised Manuscript Received February 1, 2010
The liquefaction of sugar cane bagasse in supercritical ethanol, with or without various proportions of water as a proton donor, was conducted in a batch reactor to evaluate the optimal conditions for bio-oil production. The following variables were studied: temperature, initial H2 pressure, and catalyst type (FeS, Fe2S3/AC, and FeSO4). For noncatalytic liquefaction using ∼100% (v/v) ethanol, a high oil yield of 59.6% (daf) and biomass conversion of 89.8% were obtained at 330 °C under initial H2 pressure of 4.93 MPa. For catalytic liquefaction in the presence of FeSO4 under the same conditions, the oil yield increased to 73.8% (daf) and the biomass conversion reached 99.9%. The bio-oil obtained had a 1.81-fold higher heating value (26.8 MJ/kg) than the original starting sugar cane bagasse (14.8 MJ/kg). From gas chromatography/mass spectrometry (GC/MS) analysis, the dominant components of the liquefaction oil were found to be phenolic compounds, aldehydes, and esters, such as phenol, phenol derivatives, and furan derivatives.
biomass conversion process into liquid products is pyrolysis with rapid heating at high temperature (400-600 °C).3-5 The pyrolysis oil contains water and organic compounds with high oxygen content resulting in a low heating value, and the pyrolysis oil needs to be upgraded using catalysts.6-8 Several studies have been carried out to investigate the conversion of biomass into high-energy and high-density liquids (as opposed to gases) via liquefaction.9-19 The aim
Introduction Recently, the energy utilization from biomass resources has received considerable attention due to the worldwide increasing energy demands yet dwindling levels of nonrenewable petroleum based sources with, consequentially, increasing and unstable oil prices and the challenge of energy security. Therefore, the demand for bioenergy (biomass-derived energy) has grown very fast in recent decades. Biomass is considered carbon neutral and renewable, thus the use of biomass as a alternative fuel for fossil fuels can significantly reduce the net CO2 emission.1 Potentially suitable biomass materials include renewable resources that do not compete directly with human or livestock food including wood, wood waste (sawdust and wood fiber-based sludge from pulp/paper mills), forestry residues (limbs, bark, tree tops), and nonconsumed agricultural residues (wheat/rice straws, palm oil shell, and corn waste). In particular, natural materials that are renewable and available in large quantities, or certain wastes from agricultural operations, may have potential to be used as low-cost ethical and sustainably renewable raw materials, as they represent the unused resources, are widely available, and are environmental friendly. Biomass currently contributes about 10-14% of the world’s primary energy supply and supplies more than 30% of the energy in some developing countries.2 However, biomass is not suitable to be used directly for energy generation due to its high moisture content and low calorific value. The typical
(5) Salehi, E.; Abedi, J.; Harding, T. Bio-oil from sawdust: Pyrolysis of sawdust in a fixed-bed system. Energy Fuels 2009, 23, 3767–3772. (6) Czernik, S.; Bridgwater, A. V. Overview of applications of biomass fast pyrolysis oil. Energy Fuels 2004, 18, 590–598. (7) Zhang, Q.; Chang, J.; Wang, T. J.; Xu, Y. Upgrading bio-oil over different solid catalysts. Energy Fuels 2006, 20, 2717–2720. (8) Peng, J.; Chen, P.; Lou, H.; Zheng, X. Upgrading of bio-oil over aluminum silicate in supercritical ethanol. Energy Fuels 2008, 22, 3489– 3492. (9) Yamazaki, J.; Minami, E.; Saka, S. Liquefaction of beech wood in various supercritical alcohols. J. Wood Sci. 2006, 52, 527–532. (10) Qu, Y.; Wei, X.; Zhong, C. Experimental study on the direct liquefaction of Cunninghamia lanceolata in water. Energy 2003, 28, 597– 606. (11) Qian, Y.; Zuo, C.; Tan, J.; He, J. Structural analysis of bio-oils from sub- and supercritical water liquefaction of woody biomass. Energy 2007, 32, 196–202. (12) Zhong, C.; Wei, X. A comparative experimental study on the liquefaction of wood. Energy 2004, 29, 1731–1741. (13) Xu, C.; Lad, N. Production of heavy oils with high calorific values by direct liquefaction of woody biomass in sub/near-critical water. Energy Fuels 2008, 22, 635–642. (14) Matsumura, Y.; Nonaka, H.; Yokura, H.; Tsutsumi, A.; Yoshida, K. Co-liquefaction of coal and cellulose in supercritical water. Fuel 1999, 78, 1049–1056. (15) Xu, C.; Etcheverry, T. Hydroliquefaction of woody biomass in sub- and super-critical ethanol with iron-based catalysts. Fuel 2008, 87, 335–345. (16) Liu, Z.; Zhang, F. S. Effect of various solvents on the liquefaction of biomass to produce fuels and chemical feedstocks. Energy Convers. Manage. 2008, 49, 3498–3504. (17) Yuan, X. Z.; Li, H.; Zeng, G. M.; Tong, J. Y.; Xie, W. Sub- and supercritical liquefaction of rice straw in the presence of ethanol-water and 2-propanol-water mixture. Energy 2007, 32, 2081–2088. €k, M. M. Liquid products from Verbascum (18) Cemek, M.; K€ uc-u stalk by supercritical fluid extraction. Energy Convers. Manage. 2001, 42, 125–130. (19) Wang, G.; Li, W.; Chen, H.; Li, B. Direct liquefaction of sawdust in Tetralin. Energy Sources 2007, 29, 1221–1231.
*To whom correspondence should be addressed. Telephone: 662-2187517. Fax: 662-255-5831. E-mail:
[email protected]. (1) University of Illinois at Urbana-Champaign, Center for Advanced BioEnergy Research. The Bioenergy Cycle (Online) http://www. bioenergy.uiuc.edu/about/bioenergy.html, September 16, 2009. (2) Kucuk, M.; Demirbas, A. Biomass conversion processes. Energy Convers. Manage. 1997, 38, 151–165. (3) Ingram, L.; Mohan, D.; Bricka, M.; Steele, P.; Strobel, D.; Crocker, D.; Mitchell, B.; Pittman, C. U., Jr. Pyrolysis of wood and bark in an auger reactor: Physical properties and chemical analysis of the produced bio-oils. Energy Fuels 2008, 22, 614–625. (4) Mullen, C. A.; Boateng, A. A. Chemical composition of bio-oils produced by fast pyrolysis of two energy crops. Energy Fuels 2008, 22, 2104–2109. r 2010 American Chemical Society
2071
pubs.acs.org/EF
Energy Fuels 2010, 24, 2071–2077
: DOI:10.1021/ef901241e
Chumpoo and Prasassarakich
the addition of FeS and FeSO4 as catalysts enhanced both the oil yield and biomass conversion and altered the oil composition, as revealed by GC/MS analysis.15 From the plant residues, the liquefaction of rice straw in ethanol-water and 2-propanol-water solvent mixtures at different temperatures and solvent mixture (v/v) ratios revealed that the solvent mixture could inhibit residue formation and promote bioconversion.17 Indeed, a marked reduction in the oxygen content of the obtained bio-oil was noted with an increasing (v/v) ratio of solvent mixture, and this contributed to the increase in the heating value of the bio-oil. Cemek et al.18 studied the liquefaction of Verbascum stalks in methanol, ethanol, and acetone, with 10% (w/v) NaOH or ZnCl2 as a catalyst, and found that the oil yield was dependent upon the temperature, solvent type, and catalyst used. Among all the supercritical organic solvents, ethanol may be the most promising one for biomass liquefaction because it is not only effective for liquefaction but also can itself be derived as a renewable resource when produced from the bioconversion of lignocellulosic materials. For direct liquefaction of biomass, the factors which are important in determining the quality and quantity of the obtained liquid fuel are the type of biomass, catalyst, solvent, ratio of solvent/biomass, and of course, the temperature and pressure of the reactor. Catalysts have been widely employed in biomass direct-liquefaction processes to suppress the formation of char and to enhance the yield of liquid product. To enhance liquid yields and to obtain liquid products with lower oxygen contents, a supply of hydrogen during the liquefaction has been shown to be effective.15 About 50 million tons of sugar cane are produced annually in Thailand; therefore, a tremendous amount of sugar cane bagasse are available as biomass resource for energy generation.22 Bagasse is utilized in the industrial sector and a significant amount of about 2.2-3.5 million tons annually are being unused and lost. This unused bagasse has a high potential to convert to liquid fuel or chemical feedstock. However, few research works focused on the liquefaction of sugar cane bagasse aiming to find the optimum conditions while the bio-oil composition had never been reported.23-25 In this research reported here, sugar cane bagasse was liquefied in supercritical solvent (ethanol, ethanol/water). The objective of this work was to investigate the effects of the catalyst on the oil yield and composition.
of biomass liquefaction is to produce liquid fuels and chemicals from the biomass. The macromolecule compounds in the biomass are decomposed into fragments of lighter molecules, of which the reactive fragments repolymerize into oily compounds (bio-oil). More recently, the liquefaction/extraction process of coal, cellulose, and used rubber tires with supercritical water or organic solvents, such as alcohols and acetone, has gained attention.20 This increasing interest in supercritical fluid extraction is because of the low viscosity and controllable solvent power of the supercritical fluid.21 Supercritical fluid extraction (SCFE) has the advantage of a high mass transfer rate which allows the easy separation of the extract (oil and solvent) from the solid residue, without the major problem of the conventional liquefaction process. Supercritical fluids have previously been reported as good media for the extraction of biomass.9-19 Extensive research work has been reported on the direct liquefaction of biomass in sub/near- or supercritical water. For example, the direct liquefaction of woody material in water revealed that the oil yield was dependent on the reaction time, temperature, and feedstock ratio (biomass/water),10 even if the use of Na2CO3 as the catalyst, the oil yield, and characteristics were dependent on the conditions, with a complex heavy oil compound containing hydrocarbons, aldehydes, ketones, hydroxybenzene, and esters being obtained.11 Further studies on the liquefaction oil obtained from four woody materials in water revealed that the heavy oil yield was dependent on the lignin content and that K2CO3 as a catalyst was necessary to obtain high oil (30%) and low residue (10%) yields.12 For the liquefaction of sawdust in water, Ca(OH)2, Ba(OH)2, and FeSO4 were found to be effective catalysts for enhancing the oil yield and biomass conversion, with a higher heating value for the obtained heavy oil.13 From the gas chromatography/mass spectrometry (GC/MS) analysis of the heavy oil obtained, carboxylic acids, phenolic compounds, and their derivatives and long chain alkanes were found to be the major compounds identified. Using water as a reaction medium instead of organic solvents is advantageous from the environmental and economical points of view but also is more importantly disadvantageous due to its high critical point. The drawbacks of utilizing water as the solvent for liquefaction of biomass, however, include lower yields of the water-insoluble products, which typically have a higher heating value compared with the water-soluble products with a lower heating value, and a higher oxygen content in the liquid products, resulting in low heating values for the obtained liquid products.14 To enhance the yields of liquid products with lower oxygen contents, and thus higher heating values, organic solvents, such as ethanol, 2-propanol, acetone, and tetralin, have been utilized instead of water.9,15-19 The hydro-liquefaction of a woody biomass in ethanol revealed that the oil yield still depended on the reaction temperature, time, and initial hydrogen pressure.15 Likewise, for the liquefaction of pinewood in water, acetone, and ethanol as solvents, the oil yield and composition were greatly affected by the solvent type, with the most prevalent compounds being phenol derivatives and hydrocarbons, with many methyl- or ethyl-esters being found when ethanol was employed as the solvent.16 Moreover,
Experimental Section Materials. The sample of sugar cane bagasse used in this study was obtained from the Suphanburi province, Thailand, and was ground and sieved to a particle size of
