| The bio-ethanol has become the hotspot of the develop and research in many countries, because of the board source and renewable capability of lignocellulose materials and the cleanability and harmlessness of bio-ethanol. The technology bottleneck of preparing fuel ethanol from lignocellulose is the pretreatment. So far, many kinds of treatment measures have been adopted by researchers, but achieved a little. Supercritical water, organic solvent system lithium chloride/N, N-dimethyl acetamide (LiCl/DMAc), and ionic liquids 1-Butyl-3-methylimidazolium chloride [BMIM]Cl and 1-Allyl-3-methylimidazolium chloride [AMIM]Cl, which are green solvent, were used as solvents in this article. Rice straw, microcrystalline cellulose, and cotton were separately hydrolyzed or dissolved, and the mechanisms of various methods were discussed. Using the yield of reducing sugar to judge the effect of pretreatment measures. The most rational pretreatment method of lignocellulose was determined by analyzing and comparing.The supercritical hydrolysis of rice straw in the batch reactor was investigated first. The maximum conversion was 18.10%; and the by-product of hydrolysis was 5-hydroxymethylfurfural and glyceraldehyde. The hydrolysis of microcrystalline cellulose and cotton was studied, and the maximum conversions were 25.10% and 36.02% respectively; the laws of glucogenesis and reasons of the discrimination of various raw materials under supercritical hydrolysis were analyzed and stated.The synthesises of [BMIM]Cl and [AMIM]Cl were carried out, which were identified by FT-IR and 1H-NMR. The purity of [BMIM]Cl was 90.93%, while the purity of [AMIM]Cl being 85.82%.Secondly, rice straw, microcrystalline cellulose, and cotton were dissolved under ordinary heating and microwave heating when [BMIM]Cl, [AMIM]Cl and LiCl/DMAc were respectively used as solvent. The optimum treating conditions were determined and the saccharification experiments of enzyme were implemented. The result showed that [BMIM]Cl,[AMIM]Cl,LiCl/DMAc were all effective pretreatment agents, the yields of reducing sugar were sharply higher than that of untreated cellulose. When LiCl/DMAc was used as solvent, the yields of reducing sugar of rice straw, microcrystalline cellulose, and cotton were 98.06%, 95.05% and 80.18% under the traditional heating respectively, and 98.67%, 96.4% and 83.51% under microwave heating; when [BMIM]Cl was used as solvent, the reducing sugar yields of rice straw, microcrystalline cellulose, and cotton were 86.44%, 87.67% and 83.15% under the traditional heating, and 86.95%, 87.94% and 84.03% under microwave heating; when [AMIM]Cl was used as solvent, the reducing sugar yields of rice straw, microcrystalline cellulose, and cotton were 94.55%, 89.27% and 83.67% under the traditional heating, and 96.21%, 92.31% and 85.09% under microwave heating. All of the yields were higher than that of before pretreatment (30.9%, 56.62%, and 53.7%). The order of dissolving ability was [BMIM]Cl < [AMIM]Cl < LiCl/DMAc. Microwave heating can promote enzymolysis.The dissolution process and dissolution mechanism of cellulose concerned with LiCl/DMAc, [BMIM]Cl, [AMIM]Cl were studied by FT-IR, XRD and SEM. The test results of FT-IR showed that for various kinds of cellulose[BMIM]Cl, [AMIM]Cl and LiCl/DMAc acted on which illustrated that derivatization reactions of all kinds of cellulose didn't occur during the dissolution. The XRD results indicated that crystal forms of rice straws before and after dissolution were not changed, which are Crystal Structureâ… . However, the crystallinity of microcrystalline cellulose almost disappeared, and the structure of cotton were changed from Crystal Structureâ… to Crystal Structureâ…¡. For all of cellulose, the crystallization degree decreased and amorphous region increased after dissolving, even there were all amorphous regions. SEM images showed that the dissolution and swelling of cellulose treated in three kinds of solvents were good. All of the surface morphologies of cellulose changed a lot. The dissolving mechanism of lignocellulose of LiCl/DMAc, [BMIM]Cl and [AMIM]Cl were discussed.This thesis also introduced the recovery of ionic liquids after pretreatment. It showed that the recovery rate and purity of [BMIM]Cl were 82.5% and 97.46%, and the reducing sugar yield of rice straw was 84.52%; the recovery rate and purity of [AMIM]Cl were 85.82% and 93.56%, and the reducing sugar yield of rice straw was 92.48%. Therefore, ionic liquids could be successfully recovered and completely recycled used. Due to comprehensive consideration, [AMIM]Cl is the recommended treating agent.
|
PDF Full Text Request