Study On Mechanism And Kinetics Of CO₂ Absorption Into Alcohol Amine Catalyzed By Carbonic Anhydrase

Excessive emission of carbon dioxide(CO2)from coal-fired pilot plants,the iron and steel manufacturing industries,as well as other industrial sources,causes many environmental problems such as leading to global climate change.Fossil fuel-fired power generation has been considered to be the largest contributor to anthropogenic CO2 emission.Carbon capture and storage(CCS)is regarded as an effective method to remove large quantities of CO2 and combat global mean temperature change.Post-combustion CO2 capture by amine absorption,as a leading contender for application in CCS,has a big potential for large-scale implementation in the retrofitting existing power plants.However,amine-based CO2 capture suffers from high regeneration energy consumption and other undesirable problems such as amine degradation and equipment corrosion.Therefore,how to develop effective process configurations solvents that can be applied in industry is one of research hotspots of CO2 capture.Based on the research significance above,the content of this work can be summaried as following:(1)Reaction kinetics of the absorption of carbon dioxide(CO2)in aqueous solutions of sterically hindered secondary alkanolamines using the stopped-flow techniques.In this section,pseudo first-order reaction rate constants(k0)of CO2 reaction with sterically hindered secondary amines at temperatures of 293-313 K and various amine concentrations was studied using the rapid-mixing stopped-flow technique.It was found that the values of k0 increased as the concentration of aqueous solution of amines and solution temperature were increased.Both the base-catalyzed hydration mechanism and the termolecular mechanism used to fit the experimental data showed that the predicted CO2 absorption rates of MAE and EAE using the termolecular mechanism presented an absolute average deviation(AAD)of 2.81%and 14.96%from the experimental date,respectively.However,in case of the hindered amine,IPAE and TBAE,the base-catalyzed hydration mechanism could give a more precise prediction of CO2 absorption rates with AAD of 7.97%and 5.15%.(2)The development of kinetics model for CO2 absorption into tertiary amines containing carbonic anhydrase.CO2 absorption into aqueous solutions of two tertiary alkanolamines,namely,MDEA and DMEA with and without carbonic anhydrase(CA)was investigated with the use of the stopped-flow technique at temperatures in the range of 293-313 K,CA concentration varying from 0-100 g/m3 in aqueous MDEA solution with the amine concentration ranging from 0.1-0.5 kmol/m3,and CA concentration varying from 0-40 g/m3 in aqueous DMEA solution with the amine concentration ranging from 0.05-0.25 kmol/m3.The results show that the pseudo first-order reaction rate(k0,amine;s-1)is significantly enhanced in the presence of CA as compared with that without CA.The enhanced values of the kinetic constant in the presence of CA has been calculated and a new kinetics model for reaction of CO2 absorption into aqueous tertiary alkanolamine solutions catalyzed by CA has been established and used to make comparisons of experimental and calculated pseudo first-order reaction rate constant(k0,with CA)in CO2-MDEA-H2O and CO2-DMEA-H2O solutions.The AADs were 15.21%and 15.17%respectively.The effect of pKa on the CA activities has also been studied by comparison of CA activities in different tertiary amine solutions,namely,TEA,MDEA,DMEA and DEEA.The pKa trend for amines were:DEEA>DMEA>MDEA>TEA.In contrast the catalyst enhancement in amines was in the order:TEA>MDEA>DMEA>DEEA.Therefore,it can be seen that the catalyst enhancement in the amines decreased with their increasing pKa values.(3)Dissolved carbonic anhydrase for enhancing carbon dioxide absorption into high CO2-loaded,aqueous monoethanolamine solutions.The possible benefit of the addition of carbonic anhydrase(CA)to the solutions of aqueous CO2-loaded monoethanolamine(MEA)to enhance the kinetics of the reaction between carbon dioxide and high CO2-loaded MEA solutions was investigated in a stirred cell apparatus.The absorption experiments have been performed at temperatures of 293-313 K and CO2 loading from 0-0.5 mol/mol in the stirring cell apparatus.The results show that the absorption rate of CO2 in a high CO2-loaded MEA solution can be enhanced after the dissolution of enzyme(CA)in the solution.It’s also the first time to monitor the performance of enzyme in CO2-loaded amine solutions.The results were interpreted by use of both linear model and a Langmuir-Hinshelwood-like model.The results show that the Langmuir-Hinshelwood-like model shows an accurate fitting result.