Investigation of hydrothermal conversion reactions of glucose to lactic acid

Biomass is one of the environmentally friendly resources for human society, transportation fuels and chemicals. Glucose from biomass is widely used to be converted into high value-added platform molecules such as sorbitol, 5-hydroxymethylfurfural, levulinic acid and lactic acid. In our study, sol-gel catalysts and zeolite catalysts were prepared for the hydrothermal conversion of glucose to lactic acid and their activities were investigated. Catalysts containing different metal structures supported by ZrO2 and SiO2 were synthesized by sol-gel method. Beta H zeolite and USY H zeolites and also Sn-USY zeolite and Zn-USY zeolites were prepared and used as zeolite catalysts. The studies were carried out in a high temperature and pressure reactor under different pressure (2.5-3.5MPa), glucose amount (0.45-0.6g), catalyst amount (0.25-0.35g), temperature (170-190 °C) and time (1-3h) conditions and the reaction products were determined by a High Pressure Liquid Chromatography device. X-Ray Diffraction (XRD), BET surface analysis and Scanning electron microscope (SEM-EDS) analyses were performed to characterize the highly active Zn/SiO2 and USY zeolite catalysts. As a result of the reactions carried out at 180°C for 2 hours with 0.3 g catalyst amount under 3MPa N2 pressure, the highest lactic acid yield of 13.2% was obtained with Cr/ZrO2 among ZrO2 supported sol-gel catalysts and the highest lactic acid yield of 34.8% was obtained with Zn/SiO2 catalyst among SiO2 supported sol-gel catalysts. The highest lactic acid yields among zeolite catalysts were obtained with USY H zeolite and Zn-USY zeolite catalysts as 48.3% and 43.8%, respectively.