双核碱性离子液体催化棉籽油酯交换制备生物柴油

采用两步法制备了五种新型咪唑类碱性双核功能化离子液体化合物,并考察了对棉籽油酯交换制备生物柴油的催化性能。结果表明,咪唑类碱性双核功能化离子液体具有很好的催化活性,其催化活性与阳离子中碳链长度有关。其中,双-(3-甲基-1-咪唑)亚乙基双氢氧化物离子液体的催化活性最好。催化剂量、反应时间、反应温度及醇油比对生物柴油中脂肪酸甲酯含量及选择性影响的研究发现,在催化剂用量为0.4%(质量分数),醇油摩尔比为12,反应温度为55℃,反应时间为4 h时,脂肪酸甲酯的含量和选择性分别达98.5%和99.9%。催化剂7次循环后,产物中脂肪酸甲酯含量仍达到96.2%,单甘酯和双甘酯的含量很少,表明该催化剂重复使用良好。

Preparation of biodiesel by transesterification from cottonseed oil using the basic dication ionic liquids as catalysts

Novel five basic binuclear functional ionic liquids with an imidazolium structure were synthesized via a two step method and used as the catalyst in the preparation of biodiesel through transesterification from cottonseed oil. The ionic liquids exhibit good catalytic performances in the transesterification; among them, bis-(3-methyl-1-imidazolium-)-ethlyene dihydroxide performs best. Their catalytic activity is related to the lengths of the carbon chain in the cations. The influences of the catalyst dosage, reaction time and temperature, and the molar ratio of methanol to cottonseed oil on the transesterificaion were investigated. The fraction and selectivity of fatty acid methyl ester in the biodiesel product reach 98.5% and 99.9%, respectively, at 55℃ for 4h with a bis-(3-methyl-1-imidazolium-)-ethlyene dihydroxide catalyst dosage of 0.4% and methanol to cottonseed oil molar ratio of 12. The fraction of fatty acid methyl ester can be maintained at 96.2% with only little monoglycerides and diglycerides in the product after the catalyst is repeatedly used for 7 times, which implies that these bication ionic liquids with an imidazolium structure are suitable catalysts for the synthesis of biodiesel through transesterification.