氮杂环卡宾二氧化碳加合物催化转酯反应制备生物柴油

N-Heterocyclic carbene carboxylate catalysts for biodiesel production by transesterification

为了开发一种无金属有机催化剂用于生物柴油的制备,合成了一系列咪唑(啉)类氮杂环卡宾的二氧化碳加合物(N-heterocyclic carbenes CO2adducts,NHC-CO2),通过加热使其释放游离卡宾,并催化转酯反应制备生物柴油。为了比较催化活性,不同结构的NHC—CO2被用于大豆油的转酯反应中。结果发现:当使用咪唑类催化剂时,产物中甲酯含量大于90%,而当使用咪唑啉型催化剂,甲酯含量不足20%,这说明咪唑类催化剂更适合本研究中的转酯反应。催化剂最佳用量为大豆油的2%(摩尔百分比),最佳醇油比为12∶1。本研究中催化剂前体释放游离卡宾进入反应介质,反应迅速,产品分离简单,是制备生物柴油的有效绿色方法。

To develop a metal-free organic catalyst for biodiesel production,a series of N-heterocyclic carbene CO2 adducts（NHC-CO2） were designed and synthesized,whose thermolysis could generate free carbene that catalyzes the transesterification of soybean oil to biodiesel.NHC-CO2 adducts with different structures were used to compare the catalysis in the transesterification of soybean oil.When imidazole catalysts were used,a final product was obtained with methyl esters content higher than 90%,whereas imidazoline catalysts generated a final product with methyl esters content less than 20%.This indicates that imidazole catalysts are suitable for the transesterification reaction.The optimum amount of catalyst was 2%（molar ratio） of soybean with a best yield at 12 ∶ 1 alcohol to oil ratio.In this research,precatalyst releases free NHC into the reaction media,which is a green method for the preparation of biodiesel with rapid response and simple separation.