Zeolite immobilized ionic liquid as an effective catalyst for conversion of biomass derivatives to levulinic acid

Levulinic acid (LA) has received significant attention as a platform chemical for synthesizing a broad range of bio-based fuels. In this study, a series of HY zeolite immobilized ionic liquid (HY-IL) catalysts have been explored for catalytic conversion of glucose to LA. The catalysts were prepared by immobilizing 1,4 methyl sulfonic acid imidazolium tetrachloroaluminate ([MSIM][AlCl₄]) acidic ionic liquid into HY zeolite with various ionic liquid to zeolite weight ratio (0.4, 0.5, 0.6). The synthesized [MSIM][AlCl₄] was characterized using CHNS elemental analysis and ¹H and ¹³C NMR. Meanwhile, HY-ILs and parent HY zeolite catalyst were characterized using XRD, FESEM, N₂ physisorption, FTIR, TGA, NH₃-TPD and pyridine adsorption to determine the catalyst properties. BET surface area and NH₃-TPD revealed the surface area of HY-IL decreased, while the acidity of HY-IL increased after the addition of ionic liquid into HY zeolite. Meanwhile, pyridine adsorption revealed addition of ionic liquid increased Lewis acid sites in HY zeolite compared to Brønsted acid sites. Among the catalysts tested, HY-IL-2 exhibited the highest catalytic performance with 62.2% of LA yield from reaction conducted at 180 °C for 6 h using 0.4 g of catalyst and 0.5 wt% of glucose. Utilization of other biomass derivatives (sucrose, maltose, cellulose) under optimum condition demonstrated that LA yield obtained were in the order of glucose > sucrose > maltose > cellulose while oil palm frond (OPF) and empty fruit bunch (EFB) showed comparable LA yield. This study emphasized the potential of zeolite immobilized ionic liquid as catalyst for biomass conversion to LA under mild process condition.