木质纤维素水解液合成的碳基磁性催化剂活性基团构建及催化机理分析

The purpose of this work is using lignocellulosic hydrolyzates as the source of organic carbon, and study the formation mechanism of controllable prepared carbon-based magnetic material under supercritical hydrothermal conditions, analyze the effects of the formation of active groups on the surface of carbon-based magnetic catalyst, followed by verification of its catalytic mechanism of the esterification and transesterification of Jatropha oil with high acid value. Firstly, Jatropha hulls are used as the starting lignocellulosic material, which is hydrolyzed to water-soluble hydrolyzates in a hydrolysis reactor. The optimum conditions of hydrolysis and composition of the hydrolyzates are studied. Secondly, the carbon-based magnetic materials with embedded magnetic core and loaded active groups are synthesized under supercritical hydrothermal conditions. The generation, transformation and abscission of active groups on surface of catalyst are visually studied with a diamond micro reactor coupled with online Infrared and Raman microscopies. Lastly, biodiesel from Jatropha oil with high acid value is successfully produced via the synthesized carbon-based magnetic catalysts. The reusability of the catalyst is studied after its separation by a magnetic field. Meanwhile, the catalytic performance, life time and stabilization are investigated with many characterization techniques. This work will explain the effects of supercritical water on the formation of active groups on catalyst surface and catalytic activities as well as to synthesize novel carbon-based magnetic catalysts for biodiesel production from low-qualified oils with high high acid value.

本项目以木质纤维素水解液作碳源，探索其在超临界水热条件下,可控制备碳基磁性材料的形成机理和催化剂表面活性基团构建方式，并利用高酸值小桐子油酯化及转酯化反应对催化剂催化性能进行检测为研究任务。首先，利用小桐子果壳作为木质纤维素实验原料，结合本组自制的水解装置将其转化为可溶性水解液，并进行水解条件优化及水解液成分分析；其次，通过超临界水热制碳、包埋磁核、负载活性基团等方式快速合成碳基磁性催化材料，并利用微型可视钻石反应器，结合全反射红外和透射拉曼在线表征技术，考察催化材料表面的活性基团生成、转变和脱落过程；最后，利用合成的催化剂用于高酸值小桐子油制备生物柴油，通过外磁场分离回收该催化剂并再次利用，考察催化剂催化性能、使用寿命及稳定性能。通过本项目的支持，阐明超临界水对木质纤维素水解液合成的碳基磁性催化剂活性基团构建及催化性能的影响，并建立适用于高酸值小桐子油制备生物柴油的新型催化剂合成方案。

生物柴油作为一种近似碳中性、清洁、可再生且可供内燃机直接使用的生物燃料，有望成为石化柴油的最佳替代品之一。但是如何在生物柴油生产过程中，所用催化剂实现低能耗分离、多次利用和减少排放废弃物，一直是国内外研究的热点与难点问题。本项目以木质纤维素水解液作碳源，探索其在超临界水热条件下,可控制备碳基磁性材料的形成机理和催化剂表面活性基团构建方式，并利用高酸值小桐子油酯化及转酯化反应对催化剂催化性能进行检测为研究任务。通过本项目的支持，阐明超临界水对木质纤维素水解液合成的碳基磁性催化剂活性基团构建及催化性能的影响，并建立适用于高酸值小桐子油制备生物柴油的新型催化剂合成方案。选取小桐子果壳为碳源，通过木质纤维素水解技术将其转化为小桐子果壳水解液和小桐子果壳水解残渣两部分。利用小桐子果壳水解液为碳源，在180 ºC条件下两次水热沉淀及在600 ºC条件下高温热解，然后再利用H2SO4在150 ºC条件下磺化的新方法，合成了一种新型的果壳碳磁性固体酸（AC-600-SO3H@Fe/JHC）催化剂。利用小桐子果壳水解残渣为碳载体，与硝酸镍和尿素水溶液在高温水热条件下生成沉淀，并通过高温还原、包埋硅酸钠和活化等方法，合成了一种新型的果壳碳基磁性固体碱（Na2SiO3@Ni/JRC）催化剂。并且AC-600-SO3H@Fe/JHC和Na2SiO3@Ni/JRC催化剂两步法循环3次催化高酸值小桐子油合成生物柴油，生物柴油得率仍在96.5%以上。本项目利用制备的可磁场分离的新型碳基磁性固体酸/碱催化剂成功循环用于高酸值油脂合成高得率生物柴油，然后失活的碳基镍固体碱可催化副产物甘油水热转化合成氢气，最后利用设计组建的连续流动釜式反应装置（50 mL和5 L）协同催化剂可实现连续高效清洁合成生物柴油，以此实现了合成生物柴油的绿色工艺研究。