PDMS/PEI Composite Membranes Filled With Cu₃（BTC）₂for Gas Separation

At present， in many polymer membrane materials for gasseparation, there is very few material with good permeability andseparation performance. Cu₃（BTC）₂, one of the metal organic frameworkcompounds（MOFs）, has large BET surface area, controlled porosity andaffinity towards CO₂. Self-synthesized composite membrane is blendingmodified by adding this material, which aims to improve thecomprehensive performance of composite membrane.In this study, a kind of PDMS/PEI composite membrane wassynthesized and the effect of different synthesizing conditions on thepermeation properties has been investigated. Experimental resultsindicate that the separation factors increases with the increase of PEIconcentration, while, the permeability declines. In addition, compositemembrane with silicon polymer C as selective layer has higher separationfactors. With the increase of PDMS in casting solution or castingrevolution, the permeability of membrane decreases; while, separationfactors reduce.Self-synthesized PDMS/PEI composite membrane was modified by adding Cu₃（BTC）₂, which is a kind of MOFs, to the based membrane（PEI）and casting layer （PDMS）. In the experiment about the modification ofbased membrane, the influences of the amount of Cu₃（BTC）₂and theconcentration and temperature of casting solution were studied.According to the experimental results, composite membrane with3%Cu₃（BTC）₂filled in based membrane has the best permeation properties.Compared to the unmodified membrane, the separation factors ofmodified membrane for O₂/N₂, CO₂/N₂, CO₂/CH₄increase from2.02,11.16,3.51to3.24,13.97,6.59, respectively. Composite membrane with20%PDMS casting on based membrane has the best separation factors.What’s more, high temperature has a good effect on the increase ofpermeability; on the contrary, the separation factors have benefit fromlow temperature.Additionally, the impacts of the amount of Cu₃（BTC）₂, the feedingpressure and temperature were investigated in the experiment aboutmodifying composite membrane by filling Cu₃（BTC）₂into the castinglayer. Experimental results show that the composite membrane with25%filling Cu₃（BTC）₂exhibits the best separation performance; Thepermeance of modified membrane for CO₂, O₂, N₂and CH₄are2.28,1.92,2.48and1.51times as the permeance of the unmodified membrane.Compared to the unmodified membrane, the separation factors ofmodified membrane for O₂/N₂, CO₂/N₂, CO₂/CH₄increase from2.40, 13.93,6.13to2.84,17.98,10.05, respectively. Moreover, highertemperature is good for the improving of the permeation and separationproperties of modified membrane. In addition, higher feeding pressure isadvantage to the increase of permeability, but disadvantage to the risingof separation factors.At last, the influence of different operation conditions （such asfeeding temperature, feeding pressure, feeding composition and residualvelocity） in the process of CH₄-CO₂permeating through modifiedPDMS/PEI composite membrane with25%Cu₃（BTC）₂filled into castinglayer has been investigated. The experimental consequences indicates thatthe increase of feeding pressure, residual velocity and feeding molefriction of CO₂, the reducing of feeding temperature can all enhance thegas separation efficient of CH₄-CO₂mixture.