Sequential Conversion of D-Xylose to Furfuryl Alcohol by Bet:FA:MA–Water Dehydration and EutG–GDH Whole-Cell Bioreduction

A sequential two-stage chemo-biocatalytic process was investigated for the conversion of D-xylose to furfuryl alcohol (FOL), an important furan derivative widely used in the manufacture of resins, polymers, fuels, and other value-added products. In the first stage, D-xylose was dehydrated to furfural (FAL) in a ternary Betaine:Formic acid:Malonic acid–water (Bet:FA:MA–H2O) reaction medium. Under the selected conditions, a FAL yield of 65.8% was obtained from 22.5 g/L D-xylose using 15 wt% Bet:FA:MA at 170 °C for 30 min. For the subsequent bioreduction stage, a recombinant Escherichia coli strain co-expressing the aldehyde reductase EutG and glucose dehydrogenase (GDH) was constructed. Using glucose as a co-substrate, EutG–GDH whole cells were able to reduce commercial FAL at concentrations up to 150 mM under the selected conditions of 40 °C and pH 7.5. For the sequential process using the D-xylose-derived dehydration liquor, the acidic reaction mixture was adjusted to pH 7.5 and diluted from 98.7 to 30.0 mM FAL before whole-cell bioreduction. The conditioned 30.0 mM FAL feed was essentially completely converted to FOL within 24 h. These results demonstrate the laboratory-scale feasibility of sequentially combining Bet:FA:MA–H2O-mediated D-xylose dehydration with EutG–GDH whole-cell FAL reduction after interstage pH adjustment and dilution.