锡硅分子筛催化糖类制备乳酸及乳酸甲酯研究进展

Research Progress on Transformation of Sugar to Lactic Acid and Methyl Lactate Catalyzed by Stannosilicate Zeolites

综述了制备乳酸(LA)及乳酸甲酯(ML)的工艺路线,对比分析了各路线的优缺点。着重介绍了锡硅分子筛非均相催化糖类制备乳酸及其乳酸甲酯的清洁新工艺,从活性中心性质和扩散性能等角度,在分子尺度上介绍了该反应过程的机理,并讨论了锡硅分子筛的稳定性及其影响因素。研究表明,锡硅分子筛的锡活性中心与糖类反应物的羰基基团配位,造成羰基氧原子的电子向锡中心偏移,使糖类分子获得活化而发生反应,制备乳酸或乳酸甲酯。此反应过程主要包括:(1)葡萄糖异构化生成果糖;(2)果糖反羟醛缩合制得二羟基丙酮;(3)二羟基丙酮脱水生成丙酮醛;(4)丙酮醛与水或醇加成生成半缩醛。该反应工艺从源头上克服了传统发酵路线毒性高、污染重的诸多弊端。

Different technological processes for preparing lactic acid(LA)and methyl lactate(ML)were reviewed.In addition,both advantages and disadvantages of each process were compared and discussed.Especially,heterogeneous transformation of carbohydrate to LA and ML by using stannosilicate zeolite was discussed in detail.Based on reaction activity and diffusion property of stannosilicate zeolite,reaction mechanism is summarized.Meanwhile,influential factors to the stability of stannosilicate zeolites are also discussed.It has been found that tin active sites of stannosilicate zeolites can coordinate with carbonyl groups of sugars,and result in the electron of carbonyl oxygen atoms shifting to tin centers.Due to the above mechanism,carbohydrate is activated and produces LA and ML.There are four fundamental steps during the process:(1)Glucose isomerization to fructose;(2)Conversion of fructose to dihydroxyacetone through Retro-Aldol reaction;(3)Dehydration of dihydroxyacetone to pyruvaldehyde;(4)Addition reaction of pyruvaldehyde with water or alcohol to form hemiacetal,then hemiacetal isomerization to LA and ML.The above reaction process can eliminate several drawbacks of traditional fermentation process,such as high toxicity and serious pollution.