酸性离子液体催化乙酰丙酸自缩合制备生物燃料前体

CATALYTIC PERFORMANCE OF ACIDIC IONIC LIQUIDS FOR LEVULINIC ACID ALDOL SELF-CONDENSATION TO BIOFUEL PRECURSORS

制备了两种磺酸功能化离子液体和两种羧酸功能化离子液体用于催化乙酰丙酸羟醛自缩合反应。利用红外光谱、酸碱滴定及Hammett指示剂与紫外-可见吸收光谱联用技术,对其结构、酸量及酸强度进行了分析,并评价了其催化性能。结果表明,离子液体的酸强度与乙酰丙酸转化率呈正相关,与航空煤油前体C9~C16收率呈负相关;羧酸功能化离子液体N,N,N-三乙基-N-羧甲基四氟硼酸铵([c-m-N(Et)3]BF4)有利于C9~C16产物的生成。以[c-m-N(Et)3]BF4为催化剂,考察了溶剂种类和反应条件对乙酰丙酸羟醛自缩合反应的影响。在乙酰丙酸3 g、溶剂乙醚用量27 mL、催化剂用量10%、反应温度130℃和反应时间6 h的条件下,乙酰丙酸转化率为49.1%,产物C5~C8、C9~C16和C17~C21的收率分别为7.4%、16.8%和24.7%。[c-m-N(Et)3]BF4重复使用4次,其结构和催化性能基本不变。

Levulinic acid(LA)is one of important biomass-derived platform compounds which can be used to prepare biofuel precursors by aldol self-condensation reaction.Two kinds of sulfonic acid functionalized ionic liquids and two kinds of carboxylic acid functionalized ionic liquids were prepared for levulinic acid(LA)self-condensation.Their structures,acid amount and acid strength were analyzed by means of IR spectrum analysis,acid-base titration,Hammett method combined with UV-vis spectroscopy analysis,respectively.Then the catalytic performance of the prepared ionic liquids for LA self-condensation was evaluated.The results show that the acid strength of ionic liquids had positive correlation with LA conversion and had negative correlation with the yield of C9C16 products.The carboxylic acid functionalized ionic liquid[c-m-N(Et)3]BF4 exhibited a better catalytic performance for the formation of C9C16 products.The effects of different solvents and reaction conditions on LA self-condensation catalyzed by[c-m-N(Et)3]BF4 were investigated.The suitable reaction conditions were determined as follows:LA of 3 g,diethyl ether solvent amount of 27 mL,a catalyst amount of 10%,a reaction temperature of 130℃and a reaction time of 6 h.Under these conditions,the conversion of LA was 49.1%,and the yields of C5C8,C9C16 and C17C21 products were 7.4%,16.8%and 24.7%,respectively.Furthermore,[c-m-N(Et)3]BF4 could be reused at least four times without a significant change in its structure and catalytic performance.