Biomass conversion to valuable chemicals has gained huge traction to reduce dependence on petroleum sources which in turn, would help remediate the adverse effects of rapid climate change. The utilization of environmentally beneficial techniques, like biocatalysis, is appealing in processes involving biomass valorization. Enzymes offer excellent product selectivity, operate at room temperature and pressure, and have negligible activation energy barriers. Furfural (FF) is an important lignocellulosic biomass-derivative that is primarily produced from corn cob. Almost 80% of all the furfural produced globally is used to produce furfuryl alcohol (FFA). The annual global market for FFA is expected to reach $1.5 billion by 2028 at a compound annual growth rate of 6%. FFA finds major applications in the production of foundry resins, farm chemicals, fibers, and adhesives among others. FFA can be produced by direct hydrogenation of FF using transition metal-based catalysts which suffer from drawbacks like high-temperature requirement (&gt;130°C), low selectivity, catalyst deactivation, and metal toxicity. Prior studies suggest that yeast alcohol dehydrogenase (YADH), a commonly used redox enzyme, can be used to catalyze FF reduction to FFA in an aqueous medium under room temperature and pressure. However, YADH requires an expensive cofactor, nicotinamide adenine dinucleotide (NADH), for its catalytic activity is therefore required to be regenerated continuously for the viability of the process. The cofactor regeneration can be achieved by simultaneous oxidation of a suitable substrate which is also catalyzed by YADH, an approach known as substrate coupled cascade reaction. In this study, we have demonstrated that ethanol could be used as a reductant in the substrate coupled enzymatic cascade synthesis of FFA from FF using YADH. Batch reaction studies have been done to optimize crucial parameters like pH, enzyme and cofactor concentrations, the ratio of initial ethanol/FF concentration, residence time, and maximum furfural concentration that could be used without inhibiting the enzyme significantly. Initial results suggest that FFA production is maximum at pH 8, with about 14% and 60% ethanol and FF conversion respectively, along with 100% product selectivity. Hence, it could be a promising approach for the valorization of biomass using green technology.

Biocatalytic furfuryl alcohol production from furfural using ethanol as the reductant at high titer

ACS Spring 2022

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