Microwave Irradiation-Enhanced Catalytic Transfer Hydrogenation of Levulinic Acid to γ-Valerolactone Using Ruthenium: A Comparative Study with Conventional Heating Processes

Conversion of biomass-derived levulinic acid to gamma-valerolactone (GVL) via catalytic transfer hydrogenation (CTH) using conventional oven heating (COH) is associated with issues, such as long reaction time, and low yield. Microwave irradiation (MWI) appears to be a solution to address these issues as MWI can shorten reaction times and enhance yields. To explore effectiveness of MWI for LA conversion, MWI and COH are compared for LA conversion via CTH catalyzed by a model catalyst, Ru/C. Through investigating the effects of temperature and reaction time, MWI is validated to shorten the reaction time and enhance LA conversion efficiencies in comparison with COH. The optimal condition for the full LA conversion to GVL by Ru/C using MWI is 160 degrees C for 30 min with 10 mg (Ru/C)/mL (2-PrOH). MWI is also validated to improve conversion of several common levulinate esters (LAEs) to GVL. The regenerated Ru/C can also exhibit almost the same catalytic activity as the pristine Ru/C for LA conversion using MWI. These results indicate that Ru/C is a highly-effective catalyst for LA conversion and MWI can further enhance LA conversion by Ru/C by shortening reaction time and increasing yield of GVL. Thus, MWI is a promising process for enhancing biomass conversion. [GRAPHICS] .