| Because of the reversible chemical reaction between CO2and the carrier, theCO2tranport in the facilitated transport membrane is accelerated remarkably. Hence,the facilitated transport membrane, especially fixed carrier membrane, has excellentseparation performance and great application potential. Currently, the mass transportmechanism of the facilitated transport membrane is still not quite clear and theapplication study of the facilitated transport membrane is not systematic. In this paper,the mechanism of reaction and mass transport in facilitated transport membranes hasbeen investigated. Various CO2separation membrane processes have been simulatedand the application potential of the fixed carrier membranes developed by ourresearch group has been evaluated. The results can offer guidance for furtherdevelopment and application of CO2separation membranes.PVAm-PIP/PS flat sheet membrane and PVAm-PVA/PVC hollow fibermembrane as well as hollow fiber membrane module were prepared. Theexperimental data offered foundation for the researches about mechanism of reactionand mass transport and simulation of separation process.According to different reversible reaction equations, three expressions for CO2permeance were derived for facilitated transport membranes containing amine groups.These expressions were evaluated by fitting experimental data and comparingprediction results with experimental data. It is proved that for common immolizedliquid membranes containing primary or secondary amines, the reaction equation is assame as the reaction equation of CO2and amines without water and the expressionderived from this equation is feasible for calculation of CO2permeance. For fixedcarrier membranes containing primary or secondary amines, the reaction betweenamines and CO2is complex, the expression derived from the most simple reactionequation is feasible for the calculation of CO2permeance.A detailed analysis was carried out for the two-stage system for CO2capturefrom post-combustion gas and industrial waste gas, which confirms that permeate sidevacuum is feasible. The target for post-combustion CO2capture proposed by U.S.department of energy can be achieved by two-stage system with permeate sidevacuum when separation performance of the membrane is as high as that of the DDT membrane developed by our research group. High selectivity of the membrane is notrequired for the two-stage system with permeate side vacuum. Improving the CO2permeance, increasing the pressure ratio and reducing the cost of membranes andmodules are effective methods to reduce the process cost. Moreover, reducingseparation performance of the second-stage membrane in a certain range has littleeffect on product CO2purity, CO2recovery and total unit cost. As the feed CO2concentration increases, product CO2purity and CO2recovery will increase and totalunit cost will decrease.The characteristics of the one-stage and one-step system, the two-stage sysemand the two-step system were analyzed for the processes of CO2removal from thebiogas and the hydrogen-rich gas. For the process of CO2removal from the biogas,both two-stage system and two-step system were proved to be feasible. The two-stepsystem is suggested for the situation that high CH4recovery is required, while thetwo-step system is suggested for the situation that high CH4recovery is not required,or simple process is required. For the process of CO2removal from the hydrogen-richgas, using CO2permselective membrane can achieve high product H2purity andrecovery. When CO2/H2selectivity is sufficiently high under high feed pressure, theone-stage and one-step system and the two-stage system are economical systems toproduce high purity H2. |
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