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Thermogravimetric Analysis on The Pyrolysis

Two varieties of Philippine rice hulls, R-302 and R-19 were pyrolyzed at three heating rates of 10, 20 and 50 K/min using a dynamic thermogravimetric analyzer (TGA) in a nitrogen environment. Results show that the decomposition of hemicellulose starts at lower temperature than cellulose. Lignin decomposes at higher temperature than hemicellulose and cellulose. An abrupt weight loss can be noticed at second peak of active pyrolysis. As the heating rate is increased, there is a shift to higher temperature and total percentage weight loss showed a very slight change. Likewise, the rates of degradation of the two varieties are practically similar. Kinetic parameters were obtained using Arrhenius law and global mass loss kinetic models. Results show that the major components of the rice hulls have the following order of activation energy: cellulose>hemicellulose> lignin.
Key words: rice hulls, thermogravimetric analysis, pyrolysis
Rice hull or husk is the thin but tough outer sac of the rice grain. It accounts for about 20% by weight of the whole rice (Grist, 1975; Beagle, 1978). It is considered a major agricultural waste in rice producing countries like the Philippines. An estimated 150 thousand metric tons of rice hulls are available for utilization. This estimate is based on a projected 7.28 million metric tons of rice produced in the Philippines for this year up to year 2000 (Manila Star, July, 1999).
At present, uses of rice hulls in the Philippines are in minor applications such as insulating materials; extenders for construction materials and as landfill. Direct combustion is also practiced mainly for domestic source of heat for cooking in special stoves. Commercial applications of rice hull are limited too. It is used as a source of heat for drying corn, palay, tobacco and handicrafts. Burning of rice hulls is not encouraged anymore with the passing of the Philippine Clean Air Act in 1999. Hence, many are left to rot and …

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