Effect of maleic acid on the selectivity of glucose and fructose dehydration and degradation.

摘要

5-Hydroxymethyfurfural (HMF), a platform chemical can upgrade to a variety of fuels and polymers, can be manufactured from lignocellulose. This study focuses on the Lewis and Bronsted acid effect on hexose dehydration for HMF production. We report the positive effect of maleic acid, a dicarboxylic acid used as Bronsted acid, on the selectivity of hexose dehydration to 5-hydroxymethyfurfural (HMF), and subsequent hydrolysis to levulinic and formic acids. We also describe the kinetic analysis of a Lewis acid (AlCl 3) alone and in combination with HCl or maleic acid to catalyze the isomerization of glucose to fructose, dehydration of fructose to HMF, hydration of HMF to levulinic and formic acids, and degradation of these compounds to humins. Results show that AlCl3 significantly enhances the rate of glucose conversion to HMF and levulinic acid in the presence of both maleic acid and HCl. In addition, the degradation of HMF to humins, rather than levulinic and formic acids, is reduced by 50% in the presence of maleic acid and AlCl 3 compared to hydrochloric acid combined with AlCl3. The results suggest a different reaction mechanism for the dehydration of glucose and rehydration of HMF between maleic acid and HCl.;Further elevated temperature (140-180 °C) experiment demonstrate the maleic acid alone behaves like Lewis acid to isomerization glucose to fructose. Maleic acid also found facilitating glucose ring open reaction. Compared to HCl combined with AlCl3, calculated activation energy justifies maleic acid can lower the isomerization step activation energy when combined with AlCl3.