【作者】 梁凌云；

【导师】 毛志怀；

【作者基本信息】 中国农业大学 ， 农产品加工及贮藏工程， 2005， 博士

【摘要】 热化学液化是一种高效的生物质转化技术,能够将木质纤维素类材料转化为液体。将农业废弃物——农作物秸秆,通过热化学液化转化成为工业原料,替代石化产品,能够减轻农业废弃物对环境的污染,减少人类对石化资源的消耗与依赖,同时使大量农作物秸秆被增值转化,为农业生产开拓一个新的发展领域,将有利于生态环境的改善和农业的可持续发展。 本课题以农作物秸秆(玉米秸、麦秸、稻草、玉米芯)作为主要原料,以不同液化条件的选择、液化规律的探索以及液化工艺参数的优化为主要研究过程,分析了液化产物的得率及各质量参数,研究了秸秆循环液化、液化机理以及液化反应动力学,对液化工艺进行了优化,并建立秸秆液化反应动力学模型,以期为秸秆液化的工业化生产提供理论依据。 试验了不同的液化剂和催化剂对液化效果的影响,研究表明:EC和EC/EG混合溶剂是高效的液化剂,浓硫酸是一种高效的催化剂。在此基础上,进行了各参数的单因素试验,根据各液化条件与液化得率之间的关系,确定了秸秆液化的较适宜工艺参数范围:液化温度130～180℃、物料量20%～40%、催化剂量2.5%～4.5%以及液化时间60～90 min。秸秆在EC以及EC/EG混合溶剂中的液化趋势基本相同;单一组分较全秸秆容易液化,且其中木质素较纤维素容易液化。液化产物粘度的变化与液化得率基本上呈负相关性。在液化过程中,酸值和羟值在试验中变化范围较小。随着液化得率提高,羟值会相应增加,而酸值在试验过程中则相应减少或保持不变。 利用FTIR对纤维素、木质素以及玉米秸的液化产物及残渣进行分析,结果如下:纤维素在液化过程中有大量酯键生成,并且吡喃环消失;木质素在液化过程中紫丁香环消失,芳香环减少但仍然存在;玉米秸在液化的过程中,其中的纤维素和木质素先于半纤维素被液化,并且木质素变化程度较大。 以液化得率为试验指标,安排了二次回归正交旋转组合设计试验,得出试验指标和各参数之间的回归数学模型,并以此为基础对液化工艺进行了优化,得到优化工艺条件为:反应温度170℃,反应时间95 min,物料量20%,催化剂量3.70%,此时液化得率为92.06%。 为了节省液化剂并为秸秆连续液化生产提供依据,对秸秆循环液化进行研究,得到各循环次数下的最优组合条件:第一次液化,反应温度170℃,反应时间60 min,物料量25%,催化剂量4%;第二次液化,反应温度160℃,反应时间45 min,物料量20%,催化剂量4%;第三次液化,反应温度170℃,反应时间60 min,物料量25%,催化剂量3.5%。 纤维素以及不同秸秆液化的化学动力学研究结果显示,秸秆在液化反应初期(约12 min)符合伪一级反应,液化的化学反应动力学方程为-dC_m/dt=k·C_m,反应速率常数因物料的不同而不同。纤维素在液化初期阶段符合伪一级反应,液化反应动力学模型为-dC_m/dt=k·C_m,反应活化能公式为K=3.09×10~8e 79.20/RT,活化能为79.20 kJ/mol,属于容易进行的反应。更多还原

【Abstract】 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.更多还原