Hydrolysis of biomass to levulinic acid over hy-zeolite supported ionic liquid catalyst

Abstract

Levulinic acid has received significant attention as a platform chemical for synthesizing a broad range of bio-based fuels. In this study, a series of hydrogen form of Y zeolite (HY-zeolite) supported ionic liquid (HY-IL) catalysts: HY-IL-1. HY-IL-2 and HY-IL-3 were synthesized, characterized and explored for catalytic conversion of glucose to levulinic acid. The synthesized ionic liquid, 1,4-methylsulfonic acid imidazolium tetrachloroaluminate was characterized using elemental analysis. Meanwhile, the HY-IL catalysts and the parent HY zeolite were characterized using x-ray diffraction, field emission scanning electron microscopy, nitrogen physisorption, Fourier-transform infrared, thermogravimetric analysis, ammonia temperature-programmed desorption and infrared pyridine to determine the catalyst properties. The experimental result revealed that HY-IL-2 exhibited the highest catalytic performance with 62.2 % of levulinic acid yield from reaction conducted at 180 °C for 6 h using 0.4 g of catalyst and 0.5 wt% of glucose concentration. High surface area, high concentration of acid sites and low Brønsted to Lewis acid ratio of HY-IL-2 were the reason for the high levulinic acid production from glucose. The optimization study of levulinic acid production from glucose and cellulose was conducted using response surface methodology with Box-Behnken design. At optimum condition, 60.6% and 27.2% of levulinic acid yields were obtained from glucose and cellulose, respectively. Meanwhile, when the testing was done on the biomass, oil palm frond (OPF) and empty fruit bunch (EFB), 21.0% and 22.4% of levulinic acid yield were obtained respectively at reaction temperature of 170 °C, reaction time of 4 h, 0.6 g of HY-IL-2 and 0.4 wt% of feedstock concentration. The process efficiency for OPF and EFB for levulinic acid production was 65.4% and 77.0%, respectively. Kinetic study of glucose conversion to levulinic acid was derived using the first-order model pseudo-homogeneous. The study was done at various temperature and time ranges of 120–200 °C and 1–6 h, respectively. The kinetic model consists of 4 key steps: 1) glucose dehydration to 5-hydroxymethylfurfural (5-HMF), 2) glucose degradation to produce humin, 3) 5-HMF rehydration to produce levulinic acid, and 4) 5-HMF degradation to form humin. The kinetic study revealed that the reaction rate for every step increased with the increase of the temperature. The activation energy for glucose conversion to 5-HMF and 5-HMF conversion to levulinic acid was 36.1 and 26.1 kJ/mol, respectively. The activation energy obtained was lower and comparable with the previous catalysts employed for glucose conversion to levulinic acid. The finding of this study demonstrated the potential of zeolite-supported ionic liquid as a catalyst for biomass transformation to platform chemicals under mild process conditions.