Renewable levulinic acid production catalyzed by iron modified by zeolite and functionalized ionic liquid

Abstract

Levulinic acid is a versatile platform chemical that can be derived from biomass as an alternative to fossil fuel resources. In this study, a series of heterogeneous iron modified HY zeolites (Fe/HY zeolite): 5% Fe/HY, 10% Fe/HY, 15% Fe/HY, and homogeneous functionalized ionic liquids (FIL): 1-butyl-3-methylimidazolium tetrachloroferrate ([BMIM][FeCl4]), 1-sulfonic acid-3-methylimidazolium chloride ([SMIM][Cl]), 1-sulfonic acid-3-methylimidazolium tetrachloroferrate ([SMIM][FeCl4]), were synthesized, characterized, and tested as a catalyst for glucose conversion to levulinic acid. The properties of Fe/HY zeolite were characterized using x-ray diffraction (XRD), field emission scanning electron microscopy - energy dispersive x-ray (FESEM-EDX), x-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), nitrogen (N2) physisorption, thermal gravimetric analysis (TGA), temperature programmed desorption of ammonia (NH3-TPD), and pyridine-FTIR. The synthesized FIL were characterized using carbon, hydrogen, nitrogen, and sulfur (CHNS) elemental analysis and carbon-13 and proton nuclear magnetic resonance (13C and 1H NMR). The acidic properties of FIL were examined using pyridine-FTIR, Hammett function, and acid-base titration. Experimental results indicated that the selective Fe/HY zeolite and FIL for levulinic acid production from glucose were 10% Fe/HY and [SMIM][FeCl4], with 62% yield at 180 °C for 3 h, and 68% yield at 150 °C for 4 h, respectively. For Fe/HY zeolite, catalyst with large surface area, high concentration of acid sites and appropriate ratio of Brønsted to Lewis acids seemed suitable for levulinic acid production. It was also discovered FIL which contained both Brønsted and Lewis acid sites, offered a good catalytic performance. Optimization of levulinic acid yield from glucose and oil palm fronds (OPF) were conducted using the response surface methodology (RSM). At optimum conditions, 61.8% and 19.6% of levulinic acid yields were attained from glucose and OPF, respectively, over 10% Fe/HY zeolite. Meanwhile, by using [SMIM][FeCl4] 69.2% and 24.8% of levulinic acid yields were produced from glucose and OPF, respectively. Both catalysts can be reused without significant loss of catalytic activity. Kinetic studies of glucose conversion to levulinic acid were performed using both 10% Fe/HY zeolite and [SMIM][FeCl4]. The kinetic parameters obtained were lower and comparable with previous catalysts employed in glucose conversion to levulinic acid. This study demonstrated the potential of proposed catalysts to be used in a biorefinery for processing renewable feedstocks at mild process conditions.