Fast Pyrolysis of Rice Husk_ Product Yields and Compositions

Bioresource Technology 98 (2007) 22–28

Fast pyrolysis of rice husk: Product yields and compositions W.T. Tsai a

a,¤

, M.K. Lee b, Y.M. Chang

a

Department of Environmental Engineering and Science, Chia Nan University of Pharmacy and Science, Tainan 717, Taiwan b Department of Occupational Safety and Health, Chia Nan University of Pharmacy and Science, Tainan 717, Taiwan Received 7 August 2004; received in revised form 29 November 2005; accepted 2 December 2005 Available online 19 January 2006

Abstract A series of pyrolysis oils and chars were prepared from agricultural by-product rice husk by the lab-scale fast pyrolysis system using induction heating. The eVect of process parameters such as pyrolysis temperature, heating rate, holding time, nitrogen gas Xow rate, condensation temperature and particle size on the pyrolysis product yields and their chemical compositions was examined. The maximum oil yield of over 40% was obtained at the proper pyrolysis conditions. The chemical characterization by elemental, caloriWc, spectroscopic and chromatographic studies showed that the pyrolysis oils derived from the fast pyrolysis of rice husk contained considerable amounts of carbonyl groups and/or oxygen content, resulting in low pH and low heating values. © 2005 Elsevier Ltd. All rights reserved. Keywords: Biomass; Rice husk; Fast pyrolysis; Yield; Chemical composition

1. Introduction Since the energy crisis in the 1970s, the energy utilization from biomass resources (called biomass energy) has received much attention. The energy obtained from agricultural wastes or agricultural residues is a form of renewable energy and, in principle, utilizing this energy does not add carbon dioxide, which is a greenhouse gas, to the atmospheric environment, in contrast to fossil fuels (McKendry, 2002a). Due to the lower contents of sulfur and nitrogen in the biomass waste, its energy utilization also creates less environmental pollution and health risk than fossil fuel combustion. Because of the warm climate and wide cultivation, rice has been used as a main food for 100 years in Taiwan. In recent years, the annual production of rice had a decreasing trend; there was still ca. 1.7 millions in 2002 (COA, 2002). It meant that the rice husk, which is a major by-product of the rice-milling industries, was abundantly generated at the annual production of over 300,000 metric tons. However, only small fraction of the agrowaste generated in Taiwan

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was used for poultry feed or as Wlter materials. Most of it was arbitrarily dumped into Welds, disposed of landWlls, reused as fuel for household cooking and paving materials in the animal husbandry in response to the environmental regulations of solid waste management (Tsai et al., 2004). Like other biomass wastes, rice husk contains a high amount of organic constituents (i.e., cellulose, hemicellulose and lignin) and possesses a high-energy content (Ebeling and Jenkins, 1985; Mansaray and Ghaly, 1997, 1998). Therefore, it could be recognized as a potential source of renewable energy based on both beneWts of energy recovery and environmental protection. With respect to the conversion technologies for energy use, pyrolysis has been widely used for converting biomasses into liquids and solids among the thermo-chemical technologies (Klass, 1998; Demirbas, 2001; McKendry, 2002b; Gross et al., 2003). Pyrolysis is generally described as the thermal decomposition of the organic components in biomass waste in the absence of oxygen at mediate temperature, to yield tar (pyrolysis oil), char (charcoal) and gaseous fractions (fuel gases). For convenience, there are two approaches for the conversion technology. One, called as conventional or traditional pyrolysis, is to maximum the yield of fuel gas at the preferred conditions of high temperature, low heating rate

W.T. Tsai et al. / Bioresource Technology 98 (2007) 22–28

and long gas resistance time, or to enhance the char production at the low temperature and low heating rate. Another, called as Xash or fast pyrolysis, is to maximize the yield of liquid product at the processing conditions of (1) very high heating rate (>100 °C/min) and heat transfer rate, (2) Wnely ground biomass feed (