Preparation And Performance Of Fluorinated/Copolymerized Rubbery Polymer Gas Separation Membrane

Gas membrane separation process has been used successfully in the environment pretection and energy conservation because of many advantages.As the core of the membrane separation process,the rubbery material was one of the key factors in the preparation of gas separation composite membranes.Polydimethylsiloxane?PDMS?,as a typical rubbery polymetric material with high permeability,was used to be the selective layer of composite membrane.However,PDMS,like the most rubbery polymer,had a tendency to be swollen and lead to selectivity loss in volatile organic compounds?VOCs?separation and CO₂ capture processes.In order to solve the problem of poor swelling resistance,composite membrane was prepared by using polytrifluoropropylmethylsiloxane?PTFPMS?,a rubbery polymer with C-F bonds and an asymmetric structure in the molecule,as the selective layer materials.The solvent resistance performance of PTFPMS composite membrane in typical petroleum solutions was discussed.In addition,for the low selectivity of the present rubbery polymer,mixed matrix membranes?MMMs?were composed of imidazole functionalized graphene oxide?ImGO?,a CO₂-philic nano-sheet inorganic material,and poly?ether-b-amide??PEBAX?for CO₂ capture.The effects of the preparation conditions and operating conditions on the membrane gas separation performance were investigated.Based on backpropagation neural network-genetic algorithm?BPNN-GA?hybrid model,the relative importance of input parameters,such as air gap length,injection rate and temperature of dope solution,injection rate,temperature and composition of bore liquid,were investigated.The most important preparation parameter had been investigated to obtain the excellent gas separation performance of PDMS/PEI hollow fiber composite membrane.The analysis of relative importance indicated that the air gap length had the greatest influence on the permeation rate of O₂ and N₂ in PDMS/PEI hollow fiber composite membrane,which is 29.10 and 30.88%respectively.With the increase of air gap length,the O₂ permeation rate of PDMS/PEI hollow fiber composite membrane decreased from 102 GPU to 57 GPU,and the selectivity increased slightly.The mechanical property of PEI membrane was excellent over the range of air gap length,so it can be used in high pressure membrane separation processes.In order to solve the problem of poor swelling resistance of PDMS in the separation of VOCs,PTFPMS with C-F bond in the main chain as the membrane material was prepared.The PTFPMS homogeneous membrane was prepared by solution casting method.The permeation behaviors of swell gases and high global warming potentials gases in PTFPMS dense membrane had been investigated.The permeability,solubility and diffusivity of the gases in PTFPMS were discussed.The relationship between the gas critical properties and the permeability coefficient,the solubility coefficient and the diffusion coefficient was studied.The permeabilities coefficient of PFCs were lower than those of permanent gases and alkanes with the same number of carbon atoms.With the increase of pressure,the permeability coefficients of CO₂,C₃H₆ and C₃F₈ were increasing.According to Henry's law and Flory-Huggins theory,the theoretical values of the gas solubility coefficients agreed well with the experimental values for the low-dissolved gas except H₂.But for the high-dissolved gases,the theoretical values were the same with experimental values when the pressure is low.In order to improve the feasibility of PTFPMS used in industrial process,PTFPMS/PEI hollow fiber composite membrane was prepared by using PEI hollow fiber asymmetric membrane as the support layer and PTFPMS with good swelling resistance as the selective layer.The composite membranes were applied to C₃H₆/N₂ and CO₂/N₂ and other gases separation processes.With the increase of PTFPMS concentration,the gas permeation rate decreased,the selectivity of H₂/N₂ decreased and the selectivity of CO₂/N₂increased.The permeation rates of CO₂ and C₃H₆ were the highest in the range of PTFPMS coating solution concentration.The apparent activation energy of the gas permeating through the PTFPMS/PEI hollow fiber composite membrane indicated that the operating temperature had the greatest effect on the N₂ permeation,and at the lower temperature.With the increase of operating pressure,the permeation rate of C₃H₆ increases fastest.The PTFPMS/PEI hollow fiber composite membrane reveals better solvent resistance performance than the PDMS/PEI composite membrane.The selectivity decrease ratio of PTFPMS/PEI hollow fiber composite membranes varies in the range of 1.56 to 10.70%,lower than those of PDMS/PEI membranes of 8.02 to 21.34%.After 30 days of durability test,the permeability and selectivity of the composite membrane did not change significantly.Therefore,PTFPMS/PEI hollow fiber composite membrane indicated promising applications in gas separation of petrochemical industry and VOCs recovery.A new type of rubbery polymer,PEBAX,was chosen as the matrix,which contained imidazolyl functionalized graphite oxide?ImGO?,which contained a hydrophilic group of carbonyl groups,in order to improve the CO₂ separation performance of siloxane-based rubbery polymer materials such as PDMS and PTFPMS.ImGO/PEBAX mixed matrix membranes?MMMs?with high CO₂ permeability and selectivity were prepared by using ImGO as filler.The effects of the addition amount of ImGO and the operating conditions on the membrane properties were discussed.The results showed that the addition of ImGO enhanced the CO₂ separation performance of PEBAX membrane.Compared with pure PEBAX membrane,the selectivity of CO₂/N₂ was improved by 46.0%.When the ImGO loading was 0.8wt.%,the CO₂ membrane separation performance of MMMs was the best,which of the CO₂ permeability coefficient was 76,2 Barrer,combined with the CO₂/N₂ selectivity was 105.5.The addition of ImGO improved the mechanical properties of the MMMs.When the ImGO loading was 0.8wt.%,the tensile strength and elongation at break of the MMMs were 13.63 MPa and 460.24%,respectively.The increase of mechanical properties ensured the service life of ImGO/PEBAX MMMs and widened the applications.