Effect Of Support Layer On Oxygen Enrichment Performance Of PDMS Composite Membrane

Energy-saving and environmental protection are the main topics in current energy field worldwide.It has become an attracting problem to develop the oxygen resource in atmosphere as a new power properly.Compared with traditional cryogenic condensation and PSA method, membrane technology on oxygen enrichment is generally applied in chemical engineering, medicine,and metallurgy owing to the advantages of its simple process,easy operation,low energy consumption,and so on.Many polymeric materials have been reported to be good candidates of the membranes for oxygen enrichment.Polydimethylsiloxane(PDMS)is of special interest owing to its high intrinsic permeation rate and acceptable selectivity.But for its poor mechanical and film forming abilities,PDMS composite membrane is commonly utilized,in which PDMS as the active skin layer is coated on a porous polymeric support.The performance of composite membrane are determined by the selective layer,support membrane materials,and membrane morphology.It plays a crucial role to choose the suitable materials as support membranes for preparing high performance oxygen-enriched composite membranes.The objective of this work is to prepare PDMS composite membranes with polycarbonate(PC),polyetherimide(PEI)and polysulfone(PSF)as support layer respectively and investigate the gas permeation performance affected by support layer materials and membrane morphology.The effects of H₂O on the behavior of phase separation of PC,PEI,and PSF three kinds of casting solution at 25℃were studied according to the linerized cloud point(LCP)correlation respectly.It could be seen that NSA coagulation ability was stronger when the intercept |a| was larger for the condition of the same slope of the simulated LCP line.The sequence of H₂O coagulation ability for the three polymers was as follows:PC＞PEI＞PSF.The effects of nonsolventγ-butyrolactone(γ-GBL)on the behavior of phase separation of PC casting solution were studied at different operating temperature according to the LCP correlation.It was found that the phase separation behavior of PC/NMP/γ-GBL also exhibited well agreement with the LCP correlation.Therefore,the maximum content ofγ-GBL in casting solution could be obtained according to the binodal line of the system,which provided scientific basis for the composition of casting solution.Support membranes were prepared by the dry/wet phase inversion method with PC,PEI, and PSF as membrane materials respectively.The effects of polymer concentration and the γ-GBL content of casting solution were studied.The membrane morphology was characterized with SEM and the gas permeation performance was carried out with pure O₂,N₂. The separation factor of the support membranes prepared showed were about 0.9,and the highest oxygen permeation rate was 25700 GPU under the operating parameters of 0.5MPa and 25℃.The composite membrane were prepared using PDMS as coating material with the dip-coating method.The influences of polymer concentration,additive content,and PDMS contents were systemically studied.The oxygen permeation rates of PDMS composite membranes with PC,PEI,and PSF as support membranes were 233,224 and 266 GPU respectly.Finally,the resistance model of composite membrane was employed to reserch the influences of support membrane on PDMS composite.The oxygen permeation rate of composite membrane increased as the pore size and porosity of support membrane increasing, and decreased as the filter ratio increasing.