Biological CO2 Fixation for the Production of Formic Acid Powered by Sugars

Formic acid (FA, CH2O2) is the simplest carboxylic acid. It is mainly used as a preservative and antibacterial agent in livestock feed. A significant fraction of FA is used in the leather-processing, textile and rubber industries and a small fraction of formic acid is used as a cleaning agent replacing mineral acids. Aqueous FA is a promising liquid hydrogen-storage carrier with a hydrogen storage density of 4.3% H2 weight. On industrial scales, most formic acid is produced through carbonylation of methanol, which is produced from fossil fuels. Since carbohydrate (CH2O), the most abundant renewable chemical energy, has low costs (e.g., $~0.30/kg), we propose to fix CO2 to formic acid powered by sugars through a novel synthetic enzyme pathway comprising 13 enzymes. The overall stoichiometric reaction is 6 CO2 + 7 H2O + C6H10O5 (starch, Phase I; cellulose, Phase II) -7 12 CH2O2. Cell-free biosystems are in vitro assembly of numerous enzymes and/or cofactors for implementing complicated biological reactions that microbes and chemical catalysts cannot do, for example, 12 mol of dihydrogen generated from per glucose, enzymatic conversion of cellulose to starch. In this project, we (Gate Fuels Inc. and Virginia Tech) will validate the technological feasibility of enzymatic conversion of 6 CO2 and starch to 12 formic acid by putting 13 enzymes together under modest reaction conditions (e.g., ~30-40 oC and ~1 atm) and will use a biomimetic cofactor replacing a costly and unstable cofactor NAD. The production of formic acid from high-concentration CO2 released by power stations and renewable sugars would bring numerous benefits: (i) utilize CO2 for the production of a value-added chemical, which is produced from fossil fuels, (ii) decrease net CO2 emissions, (iii) create high-paying biomanufacturing jobs and promote rural economy, (iv) utilize abundant domestic renewable resources, (v) enhance national energy security, and (vi) enhance technology export in the future. Cell-free systems would become a disruptive biomanufacturing platform, compared to living entities.