EFFECT OF ANION VARIATION OF IMIDAZOLIUM-BASED IONIC LIQUIDS ON HYDROGENATION OF LEVULINIC ACID TO Y-VALEROLACTONE AND PENTANOIC ACID OVER RU/C CATALYST

摘要

A new, efficient, and reusable combination of imidazolium-based Bronsted acidic ionic liquids (ILs) as a co-catalyst with 5% Ru/C was employed for selective aqueous phase hydrogenation of levulinic acid (LA). Activity and selectivity performance in the hydrogenation of levulinic acid were found to be a function of acidities of ionic liquids. A combination of 5% Ru/C and strong acidic IL ([Hmim][HSO_4]) showed 100% LA conversion with 99% selectivity to gamma-valerolactone (GVL). Although a combination of 5% Ru/C and relatively weak acidic IL ([Hmim][HCOO]) has shown 56% selectivity to pentanoic acid with 80% conversion of LA. IL and Ru/C, both are easily separable by means of simple filtration and can be reused up to several cycles with consistent results. Bronsted acidities of ionic liquids were measured by the Hammet acidity function and UV-visible spectroscopy, and 5% Ru/C catalyst was characterized by X-ray diffraction, high-resolution transmission electron microscopy, and energy dispersive X-ray spectroscopy techniques. The effect of concentrations of ionic liquid and catalyst on LA conversion and GVL selectivity was also studied.