Dissolution And Degradation Of Rice Straw Cellulose For Preparing Reducing Sugar By Ionic Liquids

The utilization of renewable biomass for energy production has obtained extensive concern, due to the limited reserves of fossil fuel. Rice straw cellulose is the most abundant natural biodegradable materials on earth. One of its hydrolysis products is fermentable reducing sugar, which can be further transformed into some important sources of energy such as ethanol. But with its high crystalline structure and presence of mass hydrogen bonds intra- and inter-molecular, effective hydrolysis of cellulose remains a major challenge; therefore it requires pre-processing before hydrolysis to improve the efficiency of cellulose degradation.The synthesises of ionic liquids 1-Butyl-3-methylimidazolium chloride [BMIM]Cl and 1-Allyl-3-methylimidazolium chloride [AMIM]Cl were carried out, which were identified by FT-IR and 1~H-NMR. Rice straw was dissolved under ordinary heating and microwave heating when [BMIM]Cl and [AMIM]Cl were respectively used as solvent. The result showed that [BMIM]Cl and [AMIM]Cl were both effective pretreatment agents, the yields of reducing sugar were sharply higher than that of untreated cellulose(30.9%). When [BMIM]Cl was used as solvent, the reducing sugar yields of rice straw was 86.44% under the traditional heating, and 86.95% under microwave heating; when [AMIM]Cl was used as solvent, the reducing sugar yields of rice straw were 94.55% under the traditional heating, and 96.21% under microwave heating. Rice straw cellulose was dissolved in ionic liquids under the condition of traditional and microwave heating. The optimum solution process was determined.The regenerated rice straw cellulose, solution, hydrolysate and so on were studied by FT-IR, X-ray diffraction (XRD), scanning electron microscopy (SEM) and high performance liquid chromatography (HPLC). The results showed that microwave heating can promote enzymolysis. Compared to original cellulose, derivatization reactions of regenerated rice straw didn't occur during the dissolution. Crystal forms of rice straws before and after dissolution were not changed, which are Crystal StructureⅠ. XRD showed that the crystallinity of cellulose decreased due to the effects of ionic liquids. SEM images revealed that the surface morphologies of regenerated cellulose became rough and the dense regular structure of the original was spoiled. With the assist of microwave, the crystallization degree of regenerated straw decreased and amorphous region increased more obviously. HPLC analysis of saccharification products revealed that, glucose and xylose were major components in hydrolysate solution. The preliminary mechanism of dissolution methods was also discussed.The used ionic liquids were recovered and reused. It showed that the recovery rates of [BMIM]Cl and [AMIM]Cl were 82.5% and 85.82% respectively. And their puritis were both more than 90%. The structure of recovered [BMIM]Cl and [AMIM]Cl were unchanged. So they kept their original dissolution capital and they could be repeatly used.