一步法合成SO_4^(2-)/TiO_2酸位结构及酯化机理研究

Structure and catalysis for esterification mechanism of sulfated titania prepared by one-step

利用高酸值麻疯树油中游离脂肪酸与甲醇酯化反应作为目标反应,通过直接煅烧工业原料偏钛酸,制得高酯化活性的ST(SO42-/TiO2)固体酸.FTIR研究表明:ST固体酸具有焦硫酸结构酸位,含有高键级高共价特性S=O.S=O强烈的诱导效应提高了与之相连的配位不饱和钛原子的路易斯酸性,吸水后产生质子酸.随着硫含量增加,质子酸性增加.ST固体酸制备过程中,硫酸根与二氧化钛发生固相反应,硫酸根强键合在二氧化钛表面,同时部分硫酸根分解产生三氧化硫并原位吸附,从而形成固体酸位.ST固体酸通过质子化羧酸、甲醇亲核加成、脱水脱质子机理催化酯化反应.对于麻疯树油中游离脂肪酸与甲醇的酯化反应,酸强度H0介于-12.70与-8.2之间的酸中心具有较好的催化活性.

For esterification of free fatty acid in high acid value Jatropha curccas L. seed oil with methanol, ST（SO^2-4/TiO2） solid acid prepared by directly calcining cheap industrial metatitanic acid has high activity. FTIR studies suggested that ST solid acid possessed pyrosulfate structure with high bond order and high covalent S=O. The intensive inductive effect of S=O made the neighboring unsaturated coordinated titanium atom to have strong Lewis acidity, which converted protonic acidic sites when the catalyst absorbed water. The protonic acidity increased with the S content increasing. During preparing ST solid acid, the sulfate was effectively binded to the titania surface through the solid phase reaction of sulfate with titania. At the same time, SO3 generated by decomposition of partial sulfate was absorbed ill situ and formed solid acid structure. The strong acid site increased and the weak acid site decreased with the calcination temperature increasing. Since the surface sulfate decomposed at higher calcination temperature, the amount and strength of acid site deceased sharply, which induced the decreasing of the esterification activity of the ST solid acid. For the esterification of free fatty acid in high acid value Jatropha curccas L. oil with methanol, the acid site in H0 between - 12.70 and -8.2 has better catalytic activity. The ST solid acid catalysed esterification proceeds through a reaction routine of protonating fatty acid, which conducts nucleophilic addition with methanol and then deprotonating.