University of Hawaii at Manoa,
Keywords: CO2 fixation, renewable energy, bioplastic, drop-in fuels, green chemicals
Summary:With rapid technology progress and cost reduction, more electrical power is generated from renewable solar radiation and wind. Because of the intrinsic intermittency, however, the renewable power posts a great challenge to grid stability, and many times has to be restricted or wasted. A green technology is developed to use the renewable power and produce a bioplastic and drop-in liquid fuels from CO2. Through the green process, the intermittent electricity is first used to split water into hydrogen and oxygen via electrolysis. The clean hydrogen, as a stable energy carrier, is then used by a hydrogen-oxidizing bacterium to fix CO2. Under autotrophic growth conditions, CO2 was reduced to biomass at 0.8 g L-1 hr-1, about 10 times faster than that of a typical oil-producing microalga (Neochloris Oleoabundans). More importantly, a large portion of the reduced carbon is stored in polyhydroxybutyrate (PHB), accounting for 60% of dry cell mass. The productivity of the biopolyester (5.3 g L-1 d-1) is much higher than that of microalgal oil (0.13 g L-1 d-1). PHB is a biodegradable thermoplastic that can find a variety of environmentally friendly applications. Under a solid acid catalysis, the biopolyester can also be reformed into a hydrocarbon oil (C6-C18) from which a gasoline-grade fuel (77 wt% oil) and a biodiesel-grade fuel (23 wt% oil) are obtained. Aromatics and alkenes are the major compounds of the oil, depending on the catalyst and reaction conditions. This work demonstrates that drop-in transportation fuels can be directly produced from carbon dioxide, water and renewable energy.