Covalent Immobilization of Yeast Alcohol Dehydrogenase on an Amine-Functionalized Polymeric Resin Enhances Stability for Furfural Hydrogenation to Furfuryl Alcohol Using Ethanol as the Terminal Reductant

Biocatalytic processes could be highly beneficial for valorizing biomass-derived chemicals to support a circular bioeconomy. Intrinsic stability-related challenges with enzymes have often been remediated using enzyme immobilization techniques that enhance the enzymes' stability by reducing inhibition and facilitating recycling and reuse. A covalent bonding strategy using glutaraldehyde as a cross-linker on a primary amine-functionalized polymeric resin was utilized in this study for immobilizing yeast alcohol dehydrogenase (YADH) for coupled ethanol oxidation and furfural reduction. It was demonstrated that the capping of residual amine moieties on the support was critical to avoiding yield loss during the reaction, and furfural is a competent capping reagent. Fourier transform infrared spectroscopy, thermogravimetric analysis, nitrogen physisorption, and scanning electron microscopy studies confirmed the successful functionalization of the resin and the YADH immobilization. A residual activity study demonstrated 94% activity retention after 20 cycles. Fed-batch and repeated-batch experiments over 48 h demonstrated excellent reusability, three times higher longevity, and four times higher substrate consumption for the immobilized YADH toward catalysis of ethanol-dependent furfural reduction to furfuryl alcohol compared to soluble YADH. The effects of internal and external mass transport limitations on the immobilized-enzyme-catalyzed reaction were also investigated and mitigated through process design.