【作者】 郭萍梅；

【导师】 黄凤洪；

【作者基本信息】 中国农业科学院 ， 农产品质量与食物安全， 2009， 博士

【摘要】 目前生物柴油生产技术主要采用的是液体碱催化酯交换转化技术,该技术存在对设备腐蚀性强、催化剂不能回收、污染环境等问题。而固体催化转化技术是有效解决途径之一,但存在催化剂与产物分离困难、催化剂活性不高等问题。磁性纳米固体催化剂实现了将优异性能的磁性材料与活性物质的组装,具有催化活性高、可重复使用、回收快速简便等优点,近年来成为催化领域研究热点之一。本文针对生物柴油绿色催化转化中存在的关键技术问题,设计制备了磁性纳米固体碱催化剂Na₂O SiO₂/Fe₃O₄,采用多种手段对其进行了表征,结果表明其催化性能优于目前国内外报道的同类催化剂;研究建立了磁性纳米固体碱催化油脂酯交换反应动力学模型,并探讨其催化机理;首次将磁性纳米固体碱催化剂应用于磁稳定床中制备生物柴油,通过与现行工艺对比,结果证明磁稳定床可显著提高催化剂的使用效率,降低催化剂的消耗。具体研究结果如下:1、优化确定了共沉淀法制备纳米磁性物质Fe₃O₄的工艺条件,并制备出具有较好磁性和顺磁性的Fe₃O₄纳米粒子。2、筛选优化确定模数为1的硅酸钠溶液为最合适的固体碱活性物质前体,并采用热分析、X射线衍射、红外表征后得出其碱活性位点为Si-O-Na键。3、研究确定了催化剂的最佳制备方法并对其工艺参数进行了优化,采用多种手段对其结构和性能进行表征,制备得到平均粒径87.6nm、比表面积为107.9m²/g的磁性纳米固体碱催化剂Na₂O SiO₂/Fe₃O₄。4、优化了在釜式搅拌反应器中磁性纳米固体催化剂催化棉籽油酯交换制备生物柴油的工艺条件,首次转化率98%以上,催化剂反复使用11次后,催化活性90%以上;优化并确定了催化剂最佳再生工艺参数,再生催化剂首次转化率98%以上,重复使用8次后,活性90%以上,催化剂的回收率为88.3%,磁回收率为86.4%。与国内外相关研究对比,本文研制的催化剂活性高、使用周期长、反应条件温和,反应时间短。5、以棉籽油为原料的酯交换生成反应动力学研究结果表明,主要产物的生成反应分为初始阶段、增长阶段和平衡阶段。酯交换反应速率对棉籽油浓度由初始阶段的拟0.5级反应,逐步转变为增长阶段的拟2级反应,最终转化为平衡阶段的零级反应。初始阶段十六酸甲酯、十八酸甲酯和二十酸甲酯反应活化能分别为103.4kJ/mol、154.4kJ/mol、102.6kJ/mol;增长阶段分别为50.4kJ/mol、52.2kJ/mol、43.2kJ/mol。探讨了磁性纳米固体碱Na₂O SiO₂/Fe₃O₄催化棉籽油与甲醇的酯交换反应机理。6、研究了将磁性纳米固体碱催化剂应用于磁稳定床中催化酯交换制备生物柴油,结果表明,在优化的操作条件下,催化剂连续使用210h后,催化活性90%以上。更多还原

【Abstract】 Currently, liquid bases are the primary catalysts used in biodiesel industry, which may bring about problems such as equipment corrosion, catalyst non recyclability, environmental pollution and complex processing. At the same time, nano scale magnetic solid base catalysts, assembled from magnetic materials and living matter, have become one of the research focuses in recent years, due to its high catalytic activity, recyclability, and rapid recycling, etc.In this study, nano scale magnetic solid catalyst Na₂O·SiO₃/Fe₃O₄ was produced which aimed to these problems in key technical environmentally friendly for biodiesel production, and the structure and properties of the catalyst were analyzed by various technologies. The result showed that its catalytic performance is better than the same catalysts reported at home and broad. The transesterification reaction kinetics models were established and the mechanism of transesterification reaction was speculated.The nano scale magnetic solid base catalyst was applied for the first time in the magnetically stabilized bed reactor for biodiesel production. Compared with the existing reaction mode, transesterification technics employing magnetically stabilized bed reactor enhanced reaction efficiency of nano scale magnetic catalyst, and reduced the loss of catalyst. The main results are as follows:1. Nano scale Fe₃O₄ was prepared by coprecipitation method and the process was optimized. The nano scale Fe₃O₄ particle from our lab has good specific saturation magnetization and paramagnetism.2. The catalytic activity of sodium silicate was the best when SiO₂ and Na₂O modulus was one through filtrating and optimizing. The results from thermogravimetric analysis, X Ray Diffraction and Infrared spectra indicated that the active site was Na O Si.3. The best preparing method and process of the catalyst were confirmed and optimized, the structure and properties of the catalyst were analyzed by various technologies. The nano scale catalysts with mean diameter of 87.63 nm and BET of 107.9 m2/g were prepared.4. Process conditions of making biodiesel via the transestrification from cottonseed oil and methanol were investigated in the autoclave stirred reactor. The first transesterification rate exceeded 98% and the catalytic activity exceeded 90% after eleven batches under the optimized conditions. The first catalytic activity of the regenerated catalyst exceeded 98%. The recycle technic of catalyst was optimized, and the catalytic activity of regenerated catalyst exceeded 90% after eight batches, with a mass recycle rate of 88.27% and a magnetism recycle rate of 86.44%. Compared with the results in relevant research, the transesterification reaction conditions using Na₂O·SiO₃/Fe₃O₄ as catalyst were moderate, the catalytic activity of the catalyst was high, and the reaction time was short.5. The transesterification reaction kinetics results from cottonseed oil and methanol showed that the reaction can be divided into the initial, growing and equilibrium stages. The reaction orders in the different stages were 0.5, 2.0 and 0 respectively. In the initial stage, the activation energies of C16 methyl esters, C18 methyl esters and C20 methyl esters were 103.41kJ/mol, 154.39kJ/mol and 102.58kJ/mol respectively. In the growing stage, the activation energies were 50.41kJ/mol, 52.17kJ/mol and 43.16kJ/mol respectively. Based on these results, the mechanism of transesterification reaction was speculated.6. Biodiesel was prepared with transesterification from cottonseed oil and methanol in the magnetically stabilized bed reactor. The results showed that the catalytic activity of the catalyst exceeded 90% after 210 hours.更多还原