Study On Preparation Of Supported Ionic Liquid Membrane And CO₂ Separation Performance

The environmental problems caused by the greenhouse effect are increasingly evident.While CO2 capture and storage technology(CCS) only focuses on point sources of CO2 emission, which are centralized, stationary and account for 50% of total CO2 emissions, the technology of atomspheric CO2 capture focuses on non-point sources of CO2 emission, which are dispersed, moible and account for the remaining 50% of total CO2 emissions. This technology has become a new means to reduce greenhouse effect, however, faces the challenge of extremely low atomspheric CO2 concentration. Compared to the alkali absorption method, with the disadvantages of high energy consumption, high cost, strong causticity and strong pollution, etc, supported ionic liquid membrane(SILM) is a new green separation technology, which combines the advantages of membrane technology and ionic liquid. Membrane stability and gas separation performance of SILM are significantly affected by supporting membrane structure. In this paper, we adopte both asymmetric and symmetric supporting membrane to prepare SILM, study membrane stability and CO2 separation performance of SILM and try to capture atmospheric CO2 with SILM.The main contents include the following aspects:Combined with various characterization methods, the preparation of SILM and the impact of different membrane structure on membrane performance of SILM are studied. Results show that (1) There is a maximum capacity for IL fixed by supporting membrane, which is larger for asymmetric membrane than symmetric one. (2) In the process of SILM preparation, membrane transparency increases contiuously, while the transparency difference between asymmetric supporting membrane and symmetric SILM is larger than that of asymmetric one. (3) Gas passes through supporting membrane depending on the interation of diffusion and Knudsen diffusion, while gas passes through SILM depending on solution-diffusion mechanism. (4) Asymmetric SILM possesses better stability and mechanical properties than symmetric one and can stand operating pressure as high as 0.6MPa, while the operating pressure for symmetric SILM can't exceed 0.25MPa.Gas permeability and selectivity of single gas and dual gas are tested, then we further attempted to separate low-concentration CO2 gas with SILM. Results show that (1)QCO2>QAir>QN2> and SCO2/Air<SCO2/N2>SCO2/N2. The gas permeability of asymmetric SILM is 1-2 orders of magnitude higher than that of symmetric one. The CO2/N2 ideal selectivity of asymmetric SILM is less 1.6, but for symmetric one, it can reach 17.9, which can be improved by filtering IL. (2) Both dual and single gas separation performances were at the same level, which meant SILM having the potential application of selective CO2 removal and recovery. (3) For low-concentration CO2 gas, low concentration of CO2 and the form of mixture produced little effect on gas separation performance of both SILMs, so it is promising to achieve better low-concentration CO2 gas separation performance by optimizing SILM.In summary, different supporting membrane structures have significant effect on SILM performance.The asymmetric SILM is more stable, while the symmetric one has better gas separation performance. Preparation of optimized SILM with high stability and well separation performance is a new research direction for future applications of SILM in gas separation and enrichment, with the prospect of commercial applications, and provides a new idea and methods for the industrialization of atmospheric CO2 capture.