Kinetics Of CO₂ Absorption Into Aqueous Potassium Carbonate Promoted By Basic Amino Acid Salts

Effect of carbon dioxide emissions on global climate change has become more intensive and the effective way is to reduce the carbon emissions from fossil fuel-fired power plant.Chemical absorption method is one of the most feasible methods for carbon capture.Due to the advantages such as low absorption heat,low cost,resistance to degradation,aqueous potassium carbonate solutions have being paid widespread attention and applied in several capture systems with high temperature and pressures.However,a key limitation is slow reaction rate of absorption under conditions for post combustion CO₂ capture.Rate promoters have been intensively studied to improve the absorption rate.Compared with available promoters,amino acid salts?AAS?with basic side chain,e.g.potassium lysinate?LysK?,have potential use as alternative promoters because of having high reactive amine group,negligible volatility,resistance to oxidative degradation.However,very limited information on their properties and kinetics is available in the literature.The study on CO₂ absorption using amino acid salt and promoted carbonate solutions will have important theoretical and practical significance.This thesis compared the absorption rate of CO₂ among LysK,potassium argininate?ArgK?and potassium histidinate?HisK?promoted 35wt% potassium carbonate solutions and 5.0 M monoethanolamine?MEA?solution.The physicochemical properties of three AAS were determined under various conditions using density and viscosity meters.Solubilities of CO₂ and N₂O in aqueous AAS solutions were obtained by analogy method.The vapor-liquid equilibrium data were determined over 1.0-2.5 M LysK and temperature of 313-343 K by nitrogen cycling method.The mass transfer and kinetics of CO₂ absorption into aqueous LysK solutions were investigated using a wetted-wall column at concentrations ranging from 0.25 M to 2.00 M and temperatures from 298 K to 333 K.Reaction rate constants were derived based on the zwitterion and termoecular mechanisms.The performance of CO₂ absorption by LysK promoted carbonate solutions was also studied.Screening results showed that the basic AAS investigated are the promising promoters.CO₂ absorption rates into promoted carbonate solutions can improve about three times than those into unpromoted solutions.LysK and ArgK have comparable kinetics towards CO₂ with MEA.The product species in the CO₂-loaded AAS solutions were identified as carbamate and bicarbonate by 13 C nuclear magnetic resonance?NMR?spectra.Density and viscosity of aqueous potassium salts of lysine,histidine and arginine were measured.Experimental results were correlated well with empirical correlations.Physical solubility of CO₂ in these solutions are in sequence as ArgK < LysK < HisK.The ion specific parameters(h_<sub>AA-),based on the Weisenberger and Schumpe model,were fitted using the solubility data of N₂O in the aforementioned AAS systems.It was also found that h_<sub>AA-decreases with the increasing temperature.The equilibrium partial pressures of CO₂ increase with the increasing temperature and CO₂ loading of solutions.However,the equilibrium partial pressures of CO₂ will be below 0.1 kPa when the CO₂ loadings are not higher than 0.5.The kinetics of CO₂ into unloaded aqueous solutions of LysK showed that its reaction rate constants increase considerably with concentration and temperature.Lys K shows higher chemical reactivity toward CO₂ than the industrial standard MEA.The reaction order is found to be an average value of 0.96 with respect to LysK.The activation energy is obtained as 27.79 kJ/mol.Under the conditions investigated,LysK promoted carbonate solutions showed faster absorption rates than unpromoted solutions.The absorption rates of CO₂?NCO₂?increased significantly with the increasing LysK concentration and temperature.NCO₂ can reach 0.55-1.0×10^-2mol m^-2s^-1,about ten-time enhancement,with the addition of 1.0 M LysK.But the value is still lower than that of industrial standard 5.0M MEA.