Rice straw is a renewable, cheap, and abundant waste in tropical countries. The pentose content of rice straw can be used as a substrate for many types of value-added products such as xylitol and biofuel. Dilute acid hydrolysis mainly releases pentose from rice straw. The objective of the study was to determine the effect of H2SO4 concentration and reaction time on the xylose production. The variation of the main product xylose with the reaction time was described by a kinetic model and kinetic parameters were calculated to describe the variation of the xylose production with time. The optimum yield (19.35？g/L) was obtained at 0.24？mol/L H2SO4 and 30 minutes. 1. Introduction Rice straw is one of the most abundant agricultural wastes. For instance, approximately 731 million tons per year rice straw is produced globally (Africa: 20.9 million tons, Asia: 667.6 million tons, Europe: 3.9 million tons, America: 37.2 million tons 61, and Oceania: 1.7 million tons) [1]. Nearly 600 million tons of agricultural residues are produced by India annually; out of which, approximately 300 million tons of it remain unused. The options for the disposal of rice straw are limited by the great bulk of material, slow degradation in the soil, harboring of rice stem diseases, and high mineral content. Though rice straw is used as animal feed and soil fertilizer, the utilization ratio remains low compared to other straws. Rice straw has low digestibility value as animal feed. Although rice straws contain materials for social benefit, their apparent value is less than the cost of collection, transportation, and processing for beneficial use. Open-field burning is a major practice for rice straw disposal. It causes air pollution, a threat to human health [2]. Rice straw contains 19–27% of hemicellulose, a heteropolymer composed mainly of xylose followed by arabinose [3, 4]. The hemicellulosic and cellulosic contents of rice straw can be hydrolyzed chemically or enzymatically. Chemical hydrolysis includes dilute sulfuric acid hydrolysis that can be used for either the pretreatment before enzymatic hydrolysis or the conversion of hemicellulose to pentose [5] remaining cellulose and lignin fractions being almost unaltered. Lignocellulosic structure as well as hydrolysis reactions of sugar polymers in a dilute acid medium is very complicated. The substrate is in the solid phase and the catalyst in the liquid phase. Various factors (particle size, liquid to solid ratio, type and concentration of acid used, temperature, and reaction time) influence monomer yield [6]. In the present
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