木质纤维素制乙酰丙酸甲酯的双功能催化剂设计及可控合成

Levulinic acid is an important platform chemicals derived from biomass. Harsh reaction conditions, easy aggregation and extremely high cost for product separation with the homogeneous acid-catalyzed production process technology have lead to low product yield and high cost. So the study on the production process technology for high yield of levulinic acid at low temperature using cheap lignocellulose as raw material is of great importance. This project combines the advantages of an inorganic acid and a solid acid catalyst system for a more efficient one. A bifunctional catalyst consisting of metal salt and quaternary ammonium salt is designed for catalytic production of methyl levulinate directly from cellulose using methanol as solvent. This process technology can reduce product aggregation thus has easy product separation with high yield. Three major parts of the work will be carried out in the project. First, we will select an appropriate metal salt as the catalyst precursor based on common melting point properties and catalytic performance. Secondly, a superior composite catalyst based on metal salt and quaternary ammonium salt will be synthesized, focusing on the effects of quaternary ammonium cations and anions and the length of alkyl chain on the properties of the composite catalyst. Finally, we will reveal the interaction between quaternary ammonium salt and metal salt and the catalytic mechanism of the obtained catalyst, providing theoretical guidance to efficient synthesis of bifunctional catalysts and achieving high yield of methyl levulinate. This study will provide new insights for more efficient utilization of lignocellulose.

乙酰丙酸是一种来源于生物质的重要平台化合物。目前由于其生产过程中采用了反应条件苛刻、产物易聚合、分离成本极高的均相酸催化工艺，导致产物收率低、成本高。因此研究以廉价木质纤维素为原料，能在较低温度下实现乙酰丙酸高收率的工艺具有重要意义。本项目结合无机酸和固体酸两种催化体系的优势，构建高效催化系统，设计一种由金属盐和季铵盐组成的双功能催化剂，以甲醇作溶剂，用纤维素直接生成乙酰丙酸甲酯。该工艺不仅能减少产物聚合，而且产物易分离、收率高。本项目主要开展三方面工作：首先依据共熔点和催化特性，探寻适宜的金属盐做主催化剂；其次构筑性能优越的金属盐与季铵盐复合催化剂，重点研究季铵盐阳离子种类、取代基烷基链长度及阴离子种类对复合催化剂性能的影响；最后通过表征手段揭示季铵盐和金属盐相互作用及催化机理，理论指导双功能催化剂的高效合成，实现乙酰丙酸甲酯的高收率，为木质纤维素的高效利用提供科学基础。

以木质纤维素为原料可制备的化学品种类较多，但由于工艺上存在诸多的技术瓶颈，导致木质纤维素的利用率较低。而在众多的下游产品当中，乙酰丙酸甲酯是一类重要的化学中间体和新能源化学品，具有广泛的工业应用价值，但要实现木质纤维素的高效转化，关键还是高性能催化剂的开发研究。本课题从易到难的研究思路分别在以蔗糖、淀粉、纤维素及木质纤维素为原料的反应体系，研究金属盐、离子液体、两者复盐、金属盐复盐的催化特性，找出最佳催化剂组合。在本项目实施过程中，主要进行四方面工作：首先，在蔗糖反应体系，离子液体与金属盐具有协同作用，乙酰丙酸甲酯的收率超过70%；其次，在淀粉反应体系，离子液体[DMIM]HSO4 协同Al2(SO4)3•18H2O具有较为显著的催化性能，乙酰丙酸甲酯收率也达到51.6%；第三，在纤维素反应体系，SnCl2.2H2O/ ZnCl2双金属氯盐的催化效果最佳，而离子液体并不能有效的促进纤维素转化为乳酸甲酯和乙酰丙酸甲酯，有的离子液体还起到严重的阻碍作用；第四，在木质纤维素(甘蔗渣)反应体系，SnCl2.2H2O/ZnCl2双金属盐催化剂经过反应条件的优化，乳酸甲酯最高收率为22.8%，特殊反应条件下，乙酰丙酸甲酯收率可达到14.8%。这些研究成果为今后木质纤维素的大规模应用奠定良好的基础。