双功能分子筛催化生物质糖直接醇解制备乙酰丙酸酯研究

Alkyl levulinate is an important platform molecule for production of liquid fuels and chemicals from biomass, which is widely used in flavor, paint, and pharmaceutical industries. One-pot production of alkyl levulinates from direct alcoholysis of biomass derived C6-carbohydrates is a simple operating process compared to the other reaction routes. Nowadays, production of alkyl levulinates in high yield from cheap and abundant glucose-based carbohydrates is still challenging. Therefore, based on the mechanism of C6-carbohydrate conversion to alkyl levulinate, the project will design bifunctional zeolite catalysts combined Brønsted (B) and Lewis (L) acidities for the conversion of glucose-based carbohydrates to alkyl levulinate. In alcohol medium, glucose is first isomerized to fructose over L acid sites of the bifunctional zeolite catalyst, and then fructose is dehydrated and alcoholyzed to alkyl levulinate over B acid sites. In addition, mesopores will be created in zeolite to improve the diffusion of reactants and products and enhance the reaction efficiency. The studies of the project will focus on the fine-tuning of L and B acidities of the bifunctional zeolite, and explore the effects of L/B acidities and pore structure of the bifunctional zeolite on the selectivity of alkyl levulinate. Through the study of the project, the structure-performance relationship between the bifunctional zeolite catalyst and the conversion of carbohydrates to alkyl levulinates will be established, and an efficient catalytic system for the transformation of biomass derived carbohydrates to alkyl levulinates will be developed.

乙酰丙酸酯是由生物质制备液体燃料及化学品的重要平台化合物，在香料、涂料、医药等工业具有广泛用途。由C6生物质糖直接醇解，“一锅”制备乙酰丙酸酯，具有操作流程简单的优点。目前，以廉价、丰富的葡萄糖基生物质糖为原料，高收率地获得乙酰丙酸酯依然面临挑战。本项目根据糖转化制备乙酰丙酸酯的反应机理，提出用具有Brønsted (B)酸性和Lewis (L)酸性的双功能沸石催化葡萄糖基生物质糖转化制备乙酰丙酸酯。葡萄糖首先在双功能催化剂L酸位上异构为果糖，然后B酸位再催化果糖经脱水、醇解转化为乙酰丙酸酯；并在沸石分子筛上引入介孔，促进反应物和产物扩散，提高反应效率。本项目重点研究双功能沸石L酸和B酸酸性的精细调控，探索沸石的L酸/B酸酸性和孔结构对乙酰丙酸酯选择性的影响。通过本项目的研究，建立双功能沸石催化剂与糖转化制备乙酰丙酸酯反应之间的构效关系，开发高效的生物质糖催化转化制备乙酰丙酸酯反应体系。

乙酰丙酸酯是由生物质制备液体燃料及化学品的重要平台化合物，在香料、涂料、医药等工业具有广泛用途。由C6生物质糖直接醇解制备乙酰丙酸酯，具有操作流程简单的优点。本项目采用具有B酸和L酸酸性的双功能催化剂催化糖转化为乙酰丙酸酯，考察了B酸位和L酸位在糖转化为乙酰丙酸酯中的作用，建立了双功能催化剂与糖转化为乙酰丙酸酯反应之间的构效关系。发现B酸位在糖转化为乙酰丙酸酯时是必不可少的，且强B酸位更有利于乙酰丙酸酯生成；L酸位主要是催化葡萄糖异构为果糖，从而促进乙酰丙酸酯生成。催化剂的介孔结构有利于反应的扩散传质，有利于乙酰丙酸酯生成。通过研究，建立了糖高效转化为乙酰丙酸酯的催化体系。在Sn-Beta分子筛和SO42-/ZrO2组成的二元固体酸催化剂体系上，葡萄糖在170 oC反应24 h，得到62%的乙酰丙酸甲酯收率，且该二元固体催化剂易于回收和再生。对于多聚糖纤维素的转化，在Sn-Beta分子筛和硅钨酸组成的催化剂上，在160 oC反应10 h，分别从α-纤维素和微晶纤维素获得55%和62%的乙酰丙酸甲酯收率。本项目的系统研究，加深了对糖转化为乙酰丙酸酯反应的认识，为设计性能更加优异的催化剂提供了依据。