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Rice in your gas tank: Boosting biofuel production from rice straw
By Synopsis: MTS -Chem Matters Research Paper: Xiujin Li, Ph.D. of the Beijing University of Chemical Technology
May 25, 2008, 17:16 PST
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Researchers in China are reporting a discovery that could turn rice straw into an inexpensive new renewable source of biofuel. Their new study, scheduled for the July 16 issue of ACS' bimonthly journal Energy & Fuels, describes a way to boost production of biofuel from rice straw by almost 65 percent.
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Scientists report the production of biofuels from rice straw (above), which is a leftover from harvesting the grain.
Courtesy of Wikimedia Commons
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In the new study, Xiujin Li and colleagues point out that China is the world's largest rice producer, a crop that leaves behind about 230 million tons of rice straw each year. Rice straw is the stem and leaves left behind after harvesting the grains. Scientists, however, have not tapped rice straw for production of biogas because bacteria cannot easily break down its cellulose due to the complex physical and chemical structures of lignocellulosic biomass.
The researchers treated rice straw with sodium hydroxide before allowing bacteria to ferment it into a biogas. That so-called pretreatment increased biogas production by making more cellulose and other compositions in straw available for digestion by the bacteria. Three prototype facilities have been built in China using this technology.
Physicochemical Characterization of Rice Straw Pretreated with Sodium Hydroxide in the Solid State for Enhancing Biogas Production
Department of Environmental Science and Engineering, and Center for Resources and Environmental Research, Beijing University of Chemical Technology, Beijing, People's Republic of China, 100029
Abstract:
The biogas yield of rice straw during anaerobic digestion can be substantially increased through solid-state sodium hydroxide (NaOH) pretreatment. This study was conducted to explore the mechanisms of biogas yield enhancement. The chemical compositions of the pretreated rice straw were first analyzed.
Fourier transform infrared (FTIR), hydrogen-1 nuclear magnetic resonance spectroscopy (1H NMR), X-ray diffraction (XRD), and gas permeation chromatography (GPC) were then used to investigate the changes of chemical structures and physical characteristics of lignin, hemicellulose, and cellulose. The results showed that the biogas yield of 6% NaOH-treated rice straw was increased by 27.3−64.5%. The enhancement of the biogas yield was attributed to the improvement of biodegradability of the rice straw through NaOH pretreatment. Degradation of 16.4% cellulose, 36.8% hemicellulose, and 28.4% lignin was observed, while water-soluble substances were increased by 122.5%. The ester bond of lignin−carbohydrate complexes (LCCs) was destroyed through the hydrolysis reaction, releasing more cellulose for biogas production.
The linkages of interunits and the functional groups of lignin, cellulose, and hemicellulose were either broken down or destroyed, leading to significant changes of chemical structures. The original lignin with a large molecular weight and three-dimensional network structure became one with a small molecular weight and linear structure after NaOH pretreatment. The cellulosic crystal style was not obviously changed, but the crystallinity of cellulose increased. The changes of chemical compositions, chemical structures, and physical characteristics made rice straw become more available and biodegradable and thus were responsible for the enhancement of the biogas yield.
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Source:ACS Publications
Copyright © 2008 American Chemical Society
© Copyright 2008 by Classbrain.com
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