Conversion of xylose into D-xylitol using catalytic transfer hydrogenation with formic acid as H-donor

Abstract

d-Xylitol, a biomass-derived sweetener, is increasingly used in cosmetics and pharmaceutical products. The raw material for d-xylitol production, d-xylose, is easily accessible from dissolving pulp production. d-xylitol production involves the heterogeneously catalyzed hydrogenation of d-xylose; this process is energy intensive, as the use of H2 requires high pressure and temperature. This work examined catalytic transfer hydrogenation for xylose conversion into xylitol. Formic acid (FA) was used to replace H2 as the H-donor, as it is easily available, inexpensive, may be obtained from renewable sources, and it avoids the risks associated with the use of high-pressure inflammable gas. A variety of commercially available catalysts were screened to reveal the one enabling the highest yield. The experiments were performed at 40, 80, and 140 °C, with pure xylose as a model compound. Triethylamine (Et3N) was added to ensure sufficient conversion rates. Based on the preliminary studies an experimental design was created (Design Expert®), including the two best performing catalysts Ru/Al2O3 and Ru/C, to investigate the influence of temperature and H-donor and base concentration on xylitol yield. Ru/C resulted in maximum d-xylitol yield of 73.2 % at 100 °C, FA to d-xylose ratio 5:1 and Et3N to FA ratio 0.4.