Flue-to-Fuel: Biomediated carbon capture and utilization of dilute CO2 gas streams to biomethane

Abstract

Capturing anthropogenic carbon dioxide (CO2) and utilizing it as a feedstock for chemical production has been identified as an essential step towards mitigating climate change. The most dominant CO2 emissions originate from flue gases that contain diluted concentrations of CO2 emitted from combustion and industrial processes. Conventional capture technologies such as amine scrubbing are impeded by their high energy demand due to the thermodynamically low driving force for desorbing CO2. A new concept is here presented that exploits the robustness of microbial catalysts to simultaneously desorb the CO2 from an amine-based absorbent and convert the captured CO2 to biomethane (CH4) in a single step by the use of renewable hydrogen. The concept combines carbon capture with that of power-to-methane, to hereby abate CO2 emissions and use the captured CO2 as a resource. Experimental results of the conceptual design in batch reactors demonstrated high microbial biocompatibility with amine methyl diethanolamine (MDEA). The biocompatibility was examined in the range of 0 – 500 mM MDEA, and the system demonstrated almost full bioavailability of the absorbed CO2 until 120 mM of MDEA. Within this range, the CH4 productivity ranged from 40.7 - 63.6 NmLCH4 L-1culture h-1 from synthetically absorbed CO2 with a maximum conversion 1.77 times higher than traditional biomethanation with gaseous CO2. Conversion of raw flue gas from a biogas engine resulted in only a slight decrease in conversion efficiency compared to that of pure gasses, which demonstrated that the concept has high robustness to the impurities and oxygen present in raw flue gas.