Abstract:

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. Ni²⁺, Cr³⁺ and Sn⁴⁺ possessed good catalytic activity for glucose conversion, among which the catalyst activity of Sn⁴⁺ was the highest, and that of Ni²⁺ was the lowest. The kinetic constant of side reaction of Sn⁴⁺ was about 20 times of that of Ni²⁺. For Ni²⁺, reaction rate of glucose isomerization and side reaction increased, yet the catalytic activity for fructose dehydration to HMF was negligible with the increasing of Ni²⁺ content. Increasing of Cr³⁺ could enhance reaction rate of glucose isomerization significantly, and almost had no effect on other reactions. With the increasing of Sn⁴⁺ 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 Ni²⁺, Cr³⁺ and Sn⁴⁺ were used, respectively.

Key words: metal ion, glucose, isomerization, fructose, 5-hydroxymethylfurfural