Biorefinery of galacturonic acid using a biofuel cell as a reactor

Abstract

A reactor based on an enzymatic biofuel cell (an EBFC reactor) was constructed to simultaneously generate electricity and chemical products from biomass. Biomass has previously been used either as a raw material for chemical products or as an energy source. To obtain energy and product materials at the same time, we performed an enzymatic reaction in which pyrroloquinoline-quinone-dependent glucose dehydrogenase (PQQ-GDH) oxidizes galacturonic acid (the main component of pectin, a biomass) to galactaric acid. In this EBFC reactor, the anode consisted of PQQ–GDH physically adsorbed on carbon felt (CF) coated with poly-methylene green and the cathode consisted of bilirubin oxidase (BOD) physisorbed onto bare CF. First, the enzymatic reaction was confirmed to proceed at the PQQ–GDH-modified electrode by keeping the anode potential constant by a potentiostat, where galactaric acid was obtained in a 93% yield without byproducts in 24 hours. Second, the bioanode was combined with a BOD-modified biocathode to build an EBFC reactor. The open-circuit voltage was 0.58 ± 0.07 V, and the maximum power was 90 ± 7 μW cm⁻³ for a load resistance of 4 kΩ. The conversion yield of EBFC was 3.1%. Thus, it was demonstrated that the EBFC, which has been recognized as a system for obtaining energy, can also be used as a biorefinery reactor.