(393c) Solvent Effects in the Catalytic Conversion of Fructose to Lactic Acid

Lactic acid (LA) is an industrial bulk chemical that is catalogued as a platform molecule from which green solvents, biodegradable polymers and others products may be manufactured. The catalytic production of LA from fructose in water is limited by low LA selectivity and low catalyst activity. Dumesic and coworkers [1] found that polar aprotic organic solvents such as g-valerolactone (GVL) cause significant increases in reaction rates compared to water in addition to increased product selectivity for Brønsted acid-catalyzed reactions of biomass derived feedstocks. Inspired by Dumesicâ??s work, here we report a similar effect for the Lewis acid-catalyzed conversion of fructose to lactic acid. We demonstrate that the combination of a Sn-Beta zeolite with mainly Lewis acidity prepared using a post-synthetic procedure and a solution of GVL and water as solvent is an effective catalytic process for the production of lactic acid from fructose. We also show that the incorporation of trace amounts of K₂CO₃ in the GVL and water solvent causes an additional improvement on the LA selectivity and yield. The effect of the solvent, tin content, and reaction temperature on the catalytic performance was assessed for the conversion of fructose to LA. Our results demonstrate that using GVL and water as a reaction solvent significantly increases the fructose conversion turnover frequency and LA production rate while decreasing the formation of degradation products as compared to the results obtained when only water is employed as solvent. The catalysts were characterized using nitrogen adsorption, X-ray Diffraction, X-ray Photoelectron Spectroscopy, Fourier Transform Infrared Spectroscopy and Inductively Coupled Plasma Atomic Emission Spectroscopy. Characterization of the modified materials shows that a highly crystalline Sn-Beta zeolite catalyst was synthesized with a surface area similar to that of the parent material. The Al content was as low as 236 ppm and the Sn content was varied from 0.4 to 4.1%.

1. Mellmer, M. A., Sener, C., Gallo, J. M. R., Luterbacher, J. S., Alonso, D. M., and Dumesic, J. A. Angew. Chem. Int. Ed. 53, 11872 (2014).