Experimental and modeling studies on the Ru/C catalyzed levulinic acid hydrogenation to γ-valerolactone in packed bed microreactors

Abstract

The hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) was performed in perfluoroalkoxy alkane capillary microreactors packed with a carbon-supported ruthenium (Ru/C) catalyst with an average particle diameter of 0.3 or 0.45 mm. The reaction was executed under an upstream gas–liquid slug flow with 1,4-dioxane as the solvent and H2 as the hydrogen donor in the gas phase. Operating conditions (i.e., flow rate and gas to liquid flow ratio, pressure, temperature and catalyst particle size) were varied in the microreactor to determine the influence of mass transfer and kinetic characteristics on the reaction performance. At 130 °C, 12 bar H2 and a weight hourly space velocity of the liquid feed (WHSV) of 3.0 gfeed/(gcat·h), 100% LA conversion and 84% GVL yield were obtained. Under the conditions tested (70–130 °C and 9–15 bar) the reaction rate was affected by mass transfer, given the notable effect of the mixture flow rate and catalyst particle size on the LA conversion and GVL yield at a certain WHSV. A microreactor model was developed by considering gas–liquid–solid mass transfer therein and the reaction kinetics estimated from the literature correlations and data. This model well describes the measured LA conversion for varying operating conditions, provided that the internal diffusion and kinetic rates were not considered rate limiting. Liquid–solid mass transfer of hydrogen towards the external catalyst surface was thus found dominant in most experiments. The developed model can aid in the further optimization of the Ru/C catalyzed levulinic acid hydrogenation in packed bed microreactors.