Coupled CO₂ Capture And Mineralization With Low-concentrations Amine Solutions

The massive emission of greenhouse gases such as CO₂ has led to global warming,sea-level rise,desertification,extreme weather and other problems.At present,among all kinds of carbon emission sources in China,the CO₂emission of thermal power industry accounts for 40%of the national total emission.Therefore,major CO₂ emission sources such as coal-fired power plants are the key objects of CO₂ emission reduction at this stage.Among carbon emission reduction methods,carbon capture,utilization and storage technology（CCUS）is the most widely used method.However,the high cost of CCUS limits its further industrial application.In this paper,the slurry containing Ca（OH）₂ and amine is used to absorb CO₂,integrate the absorption and mineralization process,and mineralize CO₂ into calcium carbonate at room temperature and pressure.In the first part,monoethanolamine（MEA）,N-methyldiethanolamine（MDEA）,2-amino-2-methyl-propanol（AMP）and piperazine（PZ）were selected as CO₂ transfer media in the integrated reaction.The effects of different ethanolamine concentrations,reaction temperatures and Ca（OH）₂ concentrations on the integrated reaction were studied.Moreover,the kinetics of integrated reaction was studied via the surface coverage model.The optimum reaction conditions for the integrated reaction mediated by MEA,MDEA and PZ were as follows:the concentration of amine was 0.05 mol/L,the reaction temperature was 20℃,the concentration of Ca（OH）₂ was 1.00 mol/L,and the extent of mineralization were 98.19%,98.00%and 86.50%,respectively.The optimum reaction conditions for the integrated reaction with AMP as the medium were amine concentration of 0.03 mol/L,reaction temperature of 20℃,Ca（OH）₂ concentration of 1.00 mol/L and extent of mineralization reached 87.42%.When the concentration of amine is properly increased,the extent of mineralization of the integrated reaction with four amines increased,but when the concentration of amine is too high,the extent of mineralization decreased to a certain extent.With the increase of reaction temperature,the extent of mineralization of integrated reaction with MEA,MDEA and AMP decreased first and then increased,and were lower than that at20℃.The extent of mineralization integrated reaction with PZ decreased from 86.00%to75.04%with the increase of temperature.When the concentration of Ca（OH）₂ increased from0.50 mol/L to 1.00 mol/L,the extent of mineralization of the integrated reaction with four amines increased.When the concentration of Ca（OH）₂ exceeded 1.00 mol/L,decreases in the extent of mineralizations of the integrated reaction of four amines were observed.After determining the optimal reaction conditions,the recycling performance of four absorption solutions is studied through five cycle experiments under the optimal conditions.After the fifth cycle experiments,the extent of mineralizations of the integrated reaction with MEA,MDEA,AMP and PZ were stable at 80.04%,85.88%,75.56%and 83.16%,respectively.In addition,the composition of the precipitate and the crystal phase of calcium carbonate in the integration reaction with MEA and MDEA were analyzed by X-ray diffraction（XRD）and scanning electron microscope（SEM）.The crystal forms of Ca CO₃ in the two integrated reactions were calcite.However,the morphology of Ca CO₃ in the integration reaction with MEA was chain,and the morphology of Ca CO₃ in the integration reaction with MDEA was spindle.Moreover,the integrated reaction kinetics were studied by surface coverage model.According to the description of the surface coverage model,Ca CO₃ will deposit on the unreacted Ca（OH）₂ surface,which is not conducive to mineralization.The k_s value and k_pvalue in the model can reflect the degree of Ca CO₃ covering Ca（OH）₂ in the process.The surface coverage model was used to fit the extent of mineralization under different amine concentration and temperature.The results show that in the integrated reaction mediated by MEA,appropriate increasing in the concentration of amine can improve the overall reaction rate of the integrated reaction and reduce the surface coverage at low MEA concentration（0.01-0.05 mol/L）.Heating will reduce the overall reaction rate of the integrated reaction and increase the surface coverage.In the integrated reaction with MDEA,appropriate increasing in the MDEA concentration will increase the total reaction rate and reduce the surface coverage.Heating will cause the decrease of assembly reaction rate and lead to a certain increase of surface coverage.In the integrated reaction mediated with AMP,increasing the concentration of AMP is conducive to the reaction rate,but also increases the surface coverage;Heating is not conducive to the integrated reaction rate and will increase the surface coverage.