Maleic acid (MA) and AlCl 3 self-assemble into catalytic complexes (Al-(MA) 2 -(OH) 2 (aq)) with improved selectivity for converting glucose to HMF, and levulinic acid. The calculated activation energy (E a ) of the MA-aluminum catalyzed glucose-to-fructose isomerization is 95 kJ·mol -1 compared to 149 kJ·mol -1 for HCl and AlCl 3 alone. Furthermore, conversion of fructose to HMF is enhanced. The catalytic conversion of fructose to HMF by MA and AlCl 3 at 180 o C is 1.7× faster
We report the positive effect of maleic acid, a dicarboxylic acid, on the selectivity of hexose dehydration to 5hydroxymethyfurfural (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. The results show that AlCl 3 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 HCl combined with AlCl 3 . The results suggest different reaction mechanisms for the dehydration of glucose and rehydration of HMF between maleic acid and HCl.
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