弱碱性吸收剂碳捕集及CO_(2)富液生物再生性能

Performance of carbon capture by a weakly alkaline absorbent and bio-regeneration of the CO_(2)-rich solution

碳捕集转化一体化工艺能利用CO_(2)转化过程同步实现CO_(2)富液再生,有望降低碳捕集转化整体成本。为评价生物甲烷化与碳捕集耦合的可行性,首先,在填料塔中考察了以4.2 g/L NaHCO_(3)、6 g/L Na_(2)CO_(3)、微生物营养液配制的弱碱性吸收剂(pH=10)对模拟烟气中CO_(2)的吸收性能;其次,在厌氧瓶内利用生物甲烷化过程对CO_(2)富液开展5个周期的循环再生试验。结果表明,填料塔气体流量≤1.0 L/min时,随液体流量增加,所有试验组CO_(2)去除率逐渐上升并能稳定在80%以上,该填料塔液体流量宜≤0.9 L/min;不同气体流量(0.4~1.2 L/min)下填料塔体积总传质系数基本稳定在17~19 mol/(h·kPa·m^(3));CO_(2)吸收导致吸收液中NaHCO_(3)增加、Na_(2)CO_(3)减少,二者变量比值在1.2~1.9。气体流量为0.6 L/min、液体流量为0.7 L/min时,在维持80%以上CO_(2)去除率的前提下,该弱碱性吸收剂可循环使用6次,此时活性组分CO_(3)^(2-)利用率达89.5%,形成的CO_(2)富液中总无机碳量为0.127 mol/L,pH为8.82,能为生物甲烷化微生物提供适宜的生长环境。CO_(2)富液循环生物再生试验表明,每次再生后的吸收剂CO_(2)吸收量基本稳定在69.6~78.6 mmol/L,且再生期间CH 4产生过程具有良好的重复性;再生试验后,Firmicutes、Actinobacteriota等耐碱性门水平细菌得到一定富集;氢营养型产甲烷菌在再生前后古菌属中占比均接近99%,但再生试验期间弱碱性环境导致Methanobrevibacter相对丰度降低了19.5%,unclassified_f_Methanobacteriaceae增加了18.7%。初步证实了碳捕集耦合生物甲烷化工艺的可行性。

It is expected that integrated carbon capture and conversion(iCCC)will reduce the overall cost of carbon capture&conversion by leveraging the CO_(2)conversion process to simultaneously regenerate CO_(2)-rich solutions.To assess the feasibility of coupling biomethanation and carbon capture,the absorption performance of a slightly alkaline absorbent(pH=10)prepared with 4.2 g/L NaHCO_(3),6 g/L Na_(2)CO_(3)and a microbial nutrient solution for CO_(2)in simulated flue gas in a packed column was investigated.Second,the CO_(2)-rich solution 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,CO_(2)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 generally stable between 17-19 mol/(h·kPa·m^(3)).As a result of CO_(2)absorption,NaHCO_(3)in the absorption solution increases and Na_(2)CO_(3)decreases,with a ratio between 1.2 and 1.9.Under the condition that the CO_(2)removal rate is greater than 80%,the slightly alkaline 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 active component CO_(3)^(2-) reaches 89.5%,and the total inorganic carbon(TIC)of the formed CO_(2)-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 CO_(2)-rich solution reveal that the absorbed CO_(2)of the absorbent is basically stable in the range of 69.6-78.6 mmol/L after each regeneration and the CH_(4) 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 archaeal 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 biomethanation combined with carbon capture.