Experimental and kinetic study of glucose conversion to levulinic acid in aqueous medium over Cr/HZSM-5 catalyst

Abstract

In this study, a series of Cr modified HZSM-5 catalysts were synthesized, characterized, and tested for the conversion of glucose to levulinic acid (LA). The results showed that the catalyst with larger surface area, high acid density, and appropriate ratio of Lewis acid to Brønsted acid seemed beneficial for LA production from glucose. The highest LA yield of 64.4 mol% was obtained from 100 mol% glucose conversion at 180 °C for 180 min with 0.75 g 8%Cr/HZSM-5 catalyst. Furthermore, a simplified kinetic analysis which based on the pseudo first-order model was also developed to describe the behavior of glucose conversion to LA, and the results showed that the conversion of glucose to LA was a sequential reaction which consisted of glucose dehydration and HMF rehydration. The activation energy for glucose dehydration and HMF rehydration over 8%Cr/HZSM-5 catalyst were 69.1 and 54.0 kJ/mol, respectively, significantly lower than those over HZSM-5, which would be attributed to the impregnation of Cr into HZSM-5 enhancing the catalyst Lewis acid, and thus finally accelerated the glucose conversion through glucose-fructose isomerization, however, excessive Lewis acid also resulted the glucose into byproducts. Finally, the recycling experiments indicated that the Cr/HZSM-5 catalyst can be reused for at least four times with the activity loss less than 13.1%. It can be concluded that the Cr/HZSM-5 catalyst is an efficient and stable catalyst for LA production from glucose in aqueous media.