| Biomass based materials such like crop residues are abundant renewable resources in the world. Converting biomass materials into alternative petrochemical will release the dependence on fossile oils of the human society as well as to reduce the environment pollution. The purpose of this study was to investigate the liquefaction process for converting crop residues into biopolyols to develop a new approach to the reasonable and high efficient utilization of crop residues.Four kinds of crop residues, including corn stover, rice straw, wheat straw and corn cob, were selected as materials. A series of experiments were conducted with various operational parameters under different conditions of liquefaction. The yield of liquefaction, the physical and chemical properties of biopolyols and the re-circulated liquefaction of crop residues were analyzed. The kinetic liquefaction model of crop residues was established based on the liquefying mechanism and the reacting kinetics analyses and on the experimental data. The optimized model of liquefaction process was also established.The results showed that it was efficient to liquefy corn stover with ethylene carbonate or EC/EG blended solvents as a liquefying solvent and 98% sulfur acid as a catalyst. The suitable temperature and the reaction time were among 130-180℃ and 60-90 min, respectively. The optimum ratio of material/solvent and the catalyst/solvent were among 20%-40% and 2.5%-4.5%, respectively.The experiments of liquefaction of crop residues with EC and EC/EG blended solvents indicated that the liquefying results with the two solvents were similar. It was easier to liquefy the mono-component than the crop residues and the lignin than the cellulose with the two solvents. The changes of viscosity were inverse correlative with liquefaction yield. The higher the liquefaction yield was, the lower the viscosity, vice versa. There was positive correlation between the liquefaction yield and the hydroxyl numbers. The acid numbers decreased or kept in the same value with the increase of liquefaction yield.A lot of C=O bond formed and the pyranoid ring disappeared during the liquefaction of cellulose according to the analysis of FTIR. The syringic ring disappeared, however, the aromatic ring could be detected during the liquefaction of lignin. When the corn stover was liquefied with EC as liquefying solvent, it was easier to break for the components of cellulose and lignin than that of hemicellulose. The degree of cleavage for lignin was more significant.The regression model of liquefaction was obtained from the quadratic orthogonal experimental data. With the regression equation, the liquefaction yield reached 92.06% at optimum conditions of 170℃ for 95 min with the ratio of material/solvent and catalyst/solvent were 20% and 3.70%, respectively.In the re-circulated liquefaction, the optimized condition of the first liquefaction with fresh liquefying solvent was 170℃, 60 min, and the ratio of the material/solvent and the catalyst/solvent were 25%and 4%. respectively. For the second and the third liquefaction with biopolyols as the solvent, the condition was 160℃ and 170℃, 45 min and 60 min, the material/solvent ratio of 20% and 25%, and the catalyst/solvent ratio of 4% and 3.5%, respectively.The experimental results indicate that both the liquefaction of cellulose and crop residues at the early stage follow the pseudo-first-order reaction. The kinetic model is -(dC_m)/(dt)= k·Cm To cellulose, the reaction activation faction is k = 3.09×10~8e The reaction activation energy of cellulose is 79.20 kJ/mol, which suggests the cellulose is easier to be liquefied.
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