(614b) Biocatalytic Production of Biomass-Based Chemical Derivatives

The conversion of biomass into valuable chemicals has been attracting increased attention to counter the adverse effects of rapid climate change by reducing dependence on petroleum resources. Emphasis on environmentally beneficial techniques, like biocatalysis, for biomass valorization is growing as enzymes can achieve ~100% product selectivity and may be more sustainable as they can operate at ambient temperature and pressure, and use of water as the reaction medium instead of organic solvents, all of which are atypical of traditional chemocatalysis. Important biomass-derived chemicals, like ethanol (EtOH), need to be converted into higher value chemicals, considering the fluctuating ethanol market arising from mismatched production and demand. Evidently, commercially valuable enzymes like yeast alcohol dehydrogenase (YADH) can catalyze ethanol dehydrogenation to produce acetaldehyde (AcA) which is used as a feedstock for several industries like polymers, paints, solvents and preservatives. One of the challenges towards commercialization of such a technology is the regeneration of the expensive nicotinamide (NAD) cofactors required by these oxidoreductase enzymes like YADH. It is therefore pertinent to couple YADH catalyzed by EtOH oxidation with a reductive counterpart, which could be catalyzed either by the same or a different NAD dependent redox enzyme using a co-substrate which acts as the terminal oxidant. In this study, several renewable feedstocks like D-fructose, butyraldehyde (BuA), and furfural (FAL) have been studied as potential co-substrates for YADH catalyzed EtOH oxidation. Batch reactions have been studied to determine optimum reaction parameters and, in some cases, technoeconomic feasibility has been assessed using process simulations. Comparison of yield of AcA and different coproducts have been provided and evaluation of enzyme stability at relatively high substrate concentrations have been done to determine the challenges to scalability. Based on the data so far, BuA coupled process has the highest co-product yield of ~85% and can be operated at up to 1M EtOH concentration but seems to be economically discouraging based on the relatively lower price of the product n-butanol. D-fructose coupled process has proven to be thermodynamically infeasible with about only ~18% co-substrate conversion. FAL coupled EtOH oxidation seems to be thermodynamically feasible with ~74% furfuryl alcohol (FOL) yield within a wide range of pH. Enzyme stability is challenging at high FAL concentrations and is currently under investigation to improve the scalability of the process. It is expected that the distinct relative volatilites of AcA (b.p.= 21 °C), ethanol (b.p.= 78 °C) and FOL (b.p.=170 °C) will facilitate separations. Hence, the current approach used in this study could be a promising alternative for the valorization of biomass using sustainable technology.