Study on CO2/N2 separation performance of polyethyleneimine-modified polyamide thin-film composite reverse osmosis membrane
Traditional carbon dioxide(CO2)separation membranes are subject to the"Trade-off"effect,which makes it difficult to realize the simultaneous improvement of permeability and separation selectivity.In this study,polyethyleneimine(PEI)was selected as amine-based carrier molecules and loaded onto the surface of commercial polyamide(PA)composite reverse osmosis membrane by electrostatic deposition to prepare composite PEI-PA membrane for the facilitated transport of CO2.The influences of membrane fabrication and separation process conditions on the CO2/N2 separation performance of the obtained PEI-PA membrane were systematically investigated.The study of membrane preparation showed that the CO2 permeability of the composite membrane increased with the concentration of PEI in a certain range.And the amine groups in the PEI modified layer had ideal transport activity of CO2 at the neutral pH.Under the optimal modification conditions(2.0％mass fraction of PEI with molecular mass of 1 800 g/mol,pH=7),the CO2 permeability and CO2/N2 selectivity of the composite membrane could reach 96.9 GPU and 90.0,which were 37.8％and 22.4％higher than unmodified membranes,respectively.Separation performance test showed that the CO2 permeation increased with the pressure in a certain range.But it would approach saturation and become lower in growth proportion than N2,resulting in attenuation of the CO2 permeation ratio and CO2/N2 selectivity.Besides,the increase of gas temperature and flow rate significantly increased N2 permeation,resulting in selectivity decline.Above results verify the feasibility of transforming reverse osmosis membranes into CO2 separation membranes,which provides a reliable basis for industrial scale-up practice.
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