Preparation Of Supported Ionic Liquid Membranes And Its Gas Separation Performance

In order to slow down the climate warming,alternative technologies of chemical absorption for CO₂ capture are urgently needed to be developed.Ionic liquids?ILs?with several excellent features,like non-volatility,high CO₂ dissolving capacity and tunable physical properties,have attracted wide attention and are considered as a new generation of green solvents in the field of CO₂ capture.Supported ionic liquid membranes?SILM?,gained by immobilizing IL into porous supports,is one of the new membrane materials for CO₂ gas separation.It overcomes the liquid-phase-loss defect of supported liquid membranes,and has gained renewed interest over the last two decades.Comparing to traditional preparation method for SILM,impregnation and coating,the newly-proposed supercritical fluid deposition?SCFD?is able to promote the CO₂ permeation by reducing the thickness of the liquid filled up layer,while maintaining the gas separation selectivity.SCFD method is worth for futher investigation to improve the CO₂ sepration performance of SILM.In this work,three-layered alumina supports were prepared by hot coating,and two kinds of ILs,[Emim][BF₄]and[Emim][Tf₂N],was confined into three-layered tubular Al₂O₃ supports to prepare SILMs using SCFD method.Influences of several preparation parameters on gas separation parameters of prepared SILMs?IL loading,CO₂ permeance,N₂ permeance and CO₂/N₂selectivity?was investigated,and the optimum preparation parameters was determined.?1?Considering both the CO₂ permeance and the CO₂/N₂ selectivity,it was found that pressure and temperature had limited influence on SILM performance,while the deposition time,IL amount and co-solvent amount were the most crucial factors in SILM preparation using SCFD.?2?The optimum preparation parameters for[Emim][BF₄]-SILMs were:1 h of deposition time,1.875 mg/mL of IL amount and 11.25vol%of ethanol amount,under which the[Emim][BF₄]-SILMs presented an IL loading of 2.6 mg/g,CO₂ and N₂ permeance of 6.4 GPU and 0.14 GPU and CO₂/N₂ selectivity of 45.3,and reached the Rebeson upper bound.?3?The optimum preparation parameters for[Emim][Tf₂N]-SILMs were:6 h of deposition time,2.5 mg/mL of IL amount and 3.75vol%of ethanol amount.under which the[Emim][Tf₂N]-SILMs presented an IL loading of 2.3 mg/g,CO₂ and N₂ permeance of 22.6GPU and 0.83 GPU and CO₂/N₂ selectivity of 27.1,and was close to the Robeson upper bound.?4?The influences of physical properties of ILs on preparation of SILMs were discussed,it was found that[Emim][BF₄]of higher surface tension led to a higher preparation efficiency,while[Emim][Tf₂N]of lower surface tension firstly filled up the small pores of the top layer of support,and then the larger pores of the intermediate layer,making it possible to obtain a thinner liquid filled up layer.Besides,it was found that IL with smaller molar volumn had lower solubility parameter,and was more mixable with scCO₂-ethanol system,which was conductive to IL deposition,meanwhile ILs with lower solubility parameter also had greater CO₂ dissolving capacity but the CO₂/N₂ dissolving selectivity was lower.In addition,IL with lower viscosity were beneficial to improve the CO₂ permeance of SILM.