金属离子催化葡萄糖异构化和脱水反应特性研究

Catalytic Characteristics of Metal Ions for Glucose Isomerization and Dehydration

以金属氯化物为催化剂,研究金属离子对葡萄糖异构化和脱水反应的催化特性。考察金属离子种类、用量和温度对反应过程的影响,用动力学模型拟合实验数据,定量分析金属离子的催化规律。葡萄糖脱水制备HMF的反应是一个串联反应,基于此机理构建的动力学模型能准确描述各组分浓度随时间的变化。Ni^(2+)、Cr^(3+)和Sn^(4+)具有良好的催化活性,但3种金属离子呈现不同的催化特性。Sn^(4+)的葡萄糖转化速率最快,Ni^(2+)最慢,但Sn^(4+)的副反应速率常数是Ni^(2+)的约20倍。实验范围内,增加Ni^(2+)用量,葡萄糖异构化和副反应速率加快,但对果糖脱水过程没有催化活性。增加Cr^(3+)用量能显著提升葡萄糖异构化速率,对其它反应影响不大。随着Sn^(4+)用量的增大,各步反应速率均加快,但整个反应过程中的副反应的严重程度有所降低。反应速率常数随温度的变化规律遵循Arrhenius模型,对Ni^(2+)而言,升高温度更能促进果糖副反应的发生;金属离子为Cr^(3+)时,升高温度有利于果糖脱水生成HMF;而对于Sn^(4+),升高温度则更有利于葡萄糖的异构化。

The catalytic characteristics of metal ions for glucose isomerization and dehydration were investigated with metal chloride as catalyst.The influences of metal ion category,content and temperature on reaction process were studied.The reaction kinetic model was applied to correlate experimental data to analyze catalytic characteristics quantitatively.The process of glucose to HMF was a tandem reaction,and the kinetic model based on this mechanism could simulate the reaction accurately.Ni^(2+),Cr^(3+) and Sn^(4+) possessed good catalytic activity for glucose conversion,among which the catalyst activity of Sn^(4+) was the highest,and that of Ni^(2+) was the lowest.The kinetic constant of side reaction of Sn^(4+) was about 20 times of that of Ni^(2+).For Ni^(2+),reaction rate of glucose isomerization and side reaction increased,yet the catalytic activity for fructose dehydration to HMF was negligible with the increasing of Ni^(2+) content.Increasing of Cr^(3+) could enhance reaction rate of glucose isomerization significantly,and almost had no effect on other reactions.With the increasing of Sn^(4+) content,reaction rate of all steps increased,yet the intensity of side reaction would decrease.The influence of temperature on reaction constants followed the Arrhenius model.Higher temperature was beneficial to the side reaction,fructose dehydration and glucose isomerization respectively,when Ni^(2+),Cr^(3+) and Sn^(4+) were used,respectively.