Performance of carbon capture by a weakly alkaline absorbent and bio-regeneration of the CO2-rich solution
It is expected that integrated carbon capture and conversion(iCCC)will reduce the overall cost of carbon capture & conversion by leveraging the CO2 conversion process to simultaneously regenerate CO2-rich solutions.To assess the feasibility of coupling biomethana-tion and carbon capture,the absorption performance of a slightly alkaline absorbent(pH=10)prepared with 4.2 g/L NaHCO3,6 g/L Na2CO3 and a microbial nutrient solution for CO2 in simulated flue gas in a packed column was investigated.Second,the CO2-rich solu-tion was subjected to a five-cycle regeneration experiment using the biomethanation process in anaerobic bottles.The results show that in the flow-through mode,when the gas flow rate of packed column is≤1.0 L/min,with the increase of liquid flow rate,CO2 removal rates of all experimental groups gradually increase and can be stabilized above 80％,and the liquid flow rate of this packed column is suitable to be≤0.9 L/min.Overall volumetric mass transfer coefficients of the packed column at different gas flow rates(0.4-1.2 L/min)are gen-erally stable between 17-19 mol/(h·kPa·m3).As a result of CO2 absorption,NaHCO3 in the absorption solution increases and Na2 CO3 decreases,with a ratio between 1.2 and 1.9.Under the condition that the CO2 removal rate is greater than 80％,the slightly alka-line absorbent can be recycled 6 times at a gas flow rate of 0.6 L/min and liquid flow rate of 0.7 L/min.The utilization rate of the ac-tive component CO2-3 reaches 89.5％,and the total inorganic carbon(TIC)of the formed CO2-rich solution is 0.127 mol/L at a pH of 8.82,creating an environment conducive to the growth of biomethanation microorganisms.The results of the cyclic experiments on the bio-regeneration of the CO2-rich solution reveal that the absorbed CO2 of the absorbent is basically stable in the range of 69.6-78.6 mmol/L after each regeneration and the CH4 production is reproducible during the regeneration process.As a result of the regeneration experiment,alkali-resistant bacteria at the phylum level,such as Firmicutes and Actinobacteriota,are somewhat enriched.Approximately 99％of ar-chaeal genera are dominated by hydrogenotrophic methanogens before and after regeneration,but the slightly alkaline environment during regeneration results in a 19.5％ decrease in the relative abundance of Methanobrevibacter and a 18.7％ increase in the relative abundance of unclassified f Methanobacteriaceae,respectively.In conclusion,the above experimental results indicate the feasibility of biomethana-tion combined with carbon capture.
integrated carbon capture and conversion(iCCC)absorbentCO2-rich solutionbio-regenerationbiomethanation
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