Preparation Of Polyionic Liquid Crosslinked Membranes And Their Gas Permeation Properties

The growing atmospheric concentration of greenhouse gases?such as CO₂?is a matter of widespread public concern due to the resulting significant environmental problems,which are largely associated with global warming and unpredictable climate changes.Ionic liquids proved have good solution selectivity for CO₂.The simplest approach is the use of supported ionic liquid membranes?SILMs?,SILMs showed good gas permeability,but poor mechanical properties.If the pressure differential across the membrane is high enough to push out the IL phase from the pores of the support.PILs have the same chemical structures with ionic liquids,even though PILs afforded solid membranes,their major drawback is the substantial drop in both gas permeability and diffusivity compared with SILMs.Therefore,the preparation of gas separation membrane with high CO₂ permeability is of great significance.In this paper,we synthesised ami no-terminated imidazole-based polyionic liquid PIL using Poly-Radziszewski one-step reaction to fabricate PIL gas separation membrane.There are two methods for the membrane fabrication.Of the first method,thin layer composite membrane is prepared by means of interfacial polymerization.By reducing the thickness of the separation layer,the diffusion path of gas in the membrane is shorten and the permeation of the membrane is increased.Of the second method,glycidyl ethers was used as crosslinking agent to prepare PIL cross-linked membrane.By introducing a large number of ether bond within the membrane,increase the the CO₂ solubility of membrane,improve the gas permeability of PIL separation membrane.The PIL thin layer composite membrane was prepared by interfacial polymerization reaction of PIL and 1,3,5-Benzenetricarbonyl Trichloride?TMC?on the surface of the polysulfone membrane.Membrane structure and morphology are determined by FTIR and SEM.There are defects on the membrane surface.And the PIL thin layer composite membrane shows poor CO₂/N2 separation property.Trimethylolpropane triglycidyl ether?TMPGE?and Polyoxyethylene bis?glycidyl ether??PEG,Mw=526 g/mol?were used as crosslinking agents to react with amino of the PIL by thermal crosslinking and rubbery PIL cross-linked membranes was obtained.In order to improve the gas permeability of the membrane,the non-reactive ionic liquid 1-ethyl-3-methylimidazolium bistrifluorosulfonylimide?[emim][Tf2N]?wasaddedinto the PIL cross-linked membrane.The gas transport property was tested and the influence of molecular weight of PIL and IL concentration was studied.Thestructure if membrane has been determined by Fourier Transform Infrared Spectroscopy,X-ray diffraction and differential scanning calorimetry?DSC?,amorphous structure at room-temperature of cross-linked PIL membranes was confirmed.The CO₂ permeability of LPIL-PEG?LP?1:2??is 170 Barrer?35 ?,2 atm?while the CO₂/N2 selectivity is 36.The CO₂ permeability of HPIL-PEG?HP?1:2??is 167 Barrer?35 ?,2 atm?while the C02/N2 selectivity is 18.Both of them showed good gas permeability that are close to 2008 Robeson Upper Bound.For PIL-IL composite membranes,with the increasing of the IL contents,the gas permeability are gradually increased with the highest CO₂ permeability of 395 Barrer.