| Summary: | 碩士 === 國立臺北科技大學 === 有機高分子研究所 === 97 === Lignocellulosic materials, such as agricultural residues and energy plants, are the most abundant renewable biomass on earth. They are potential feed stock for the manufacturing of biofuels and chemicals. However, the effective utilization of lignocellulosic materials is limited by the close association of the three main components-cellulose, hemicellulose and lignin. Adequate pretreatment processes are therefore needed to fractionate the biomass, so that a more complete utilization of the biomass can be achieved.
In this study, rice hulls were subjected to wet oxidative (WO) steam explosion , followed by an alkaline peroxide (AP) treatment (1% H2O2, pH 11.5, 80 ℃, 45 min, solid to liquid ratio 8% w/w). The effects of WO steam explosion residence time and oxygen content on xylan and lignin removal and enzymatic saccharification were studied using experimental design. The WO steam explosion experiments were performed at 190℃, with residence time ranging from 5 min to 20 min and oxygen content from 0% to 60%. The results indicate that the main effect of WO steam explosion was the solubilisation of hemicellulose, which alone was not sufficient to achieve a high enzymatic digestibility. An additional AP treatment was necessary to remove most lignin and ash from the WO steam exploded rice hulls, and to significantly improve the enzymatic digestibility. With the combination of WO steam explosion and AP treatment, > 95% of the ash was removed under all the WO steam explosion conditions. The removal of lignin, on the other hand, increased with increasing severity of WO steam explosion, and the effect of oxygen concentration was especially significant. The lignin removal reached 85% when the WO steam explosion was performed with 60% oxygen. The enzymatic digestibility also increased with increasing severity of WO steam explosion, reaching a maximum of about 96 % when a 20 min residence time and 60% oxygen were used. However, under this WO steam explosion condition, the yield of xylooligosaccharides was low (about 50%), as a large portion of xylan was converted to xylose. When xylooligosaccharides are considered as a co-product, a milder WO steam explosion condition should be used. In the present study, the highest yield of xylooligosaccharides (71%) was obtained at the WO steam explosion condition of 190℃, 12.5 min with 30% oxygen.
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