Preparation Of PVSA/PVAm Blend Composite Membranes And Their Performances For CO₂ Separation

Fixed carrier membranes for CO2 separation are promising membranes, whichhave the advantages of both stability and good permselectivity. Polymer blending is auseful method which can result in a new product with properties not found in singlepolymers. Poly(N-vinyl-γ-sodium aminobutyrate)(PVSA) and polyvinyamine(PVAm)are two fixed carrier membrane materials developed by our research group. In thiswork, fixed carrier blend materials—PVSA/PVAm were prepared by using PVSA andPVAm successfully. Composite membranes were developed with the blend materialPVSA/PVAm as active layers and polyethersulfone ultrafiltration membrane assupport. Tensile elongation measurement was used to test the mechanics of blendmaterials. FTIR(Fourier Transform Infrared Spectroscopy), XRD(X-ray diffractions)and ESEM (Environmental Scanning Electron Microscope) were employed tocharacterize the structure of PVSA and blend materials PVSA/PVAm and themorphology of the PVSA/PVAm blend composite membranes. The results show thatthe mechanical properties of the blend polymer are better than that of the two singlepolymers, the active layers of the composite membranes are smooth and dense. The permselectivities of the blend composite membranes were measured withpure CO2 and CH4 gas as well as binary mixture of CO2 and CH4. The effects of manykinds of factors such as "coupling effects", PVSA/PVAm ratio, cross-linking andcasting temperature and relative humidity on performances of the PVSA/PVAm blendcomposite membranes were discussed in detail. The permselectivity of the blendmembranes for CO2/N2 and CO2/O2 were also measured. The PVSA/PVAm blendcomposite membranes present excellent comprehensive performances, which arebetter than single PVSA and PVAm composite membranes. For pure feed gases, atpressure of 1.04 atm,PVSA wt%=33.3%, the PVSA/PVAm blend compositemembrane displays a CO2 permeation rate of 6.48×10-6 cm3 (STP)cm-2 s-1 cmHg-1 andCO2/CH4 ideal separation factor of 217. For mixed feed gas composed of 50% CO2and 50% CH4, at CO2 partial pressure of 0.518 atm,PVSA wt%=33.3%, thePVSA/PVAm blend composite membrane displays a CO2 permeation rate of5.56×10-6 cm3 (STP)cm-2 s-1 cmHg-1 and CO2/CH4 ideal separation factor of 49.7. Thepermeation rate sequence of different gases is CO2＞O2＞CH4＞N2, and the idealselectivity sequence of different gas systems is α CO2/N2＞αCO2/CH4＞αCO2/O2. IICopolymer poly( maleic acid sodium-co-acrylamide) (MAS-Am) wassynthesized by using maleic anhydride and acrylamide. The composite membraneMAS-Am/PES were developed with this material as active layer and polyethersulfoneultrafiltration membrane as support. And the permselectivities of the compositemembrane were also measured with pure CO2 and CH4 gas as well as binary mixtureof CO2 and CH4. For pure feed gases, at pressure of 1.04 atm,MAS-Am compositemembrane displays a CO2 permeation rate of 1.05×10-6 cm3 (STP)cm-2 s-1 cmHg-1 andCO2/CH4 ideal separation factor of 66. For mixed feed gas composed of 50% CO2 and50% CH4, at CO2 partial pressure of 0.56 atm, the MAS-Am composite membranedisplays a CO2 permeation rate of 5.58×10-7 cm3 (STP)cm-2 s-1 cmHg-1 and CO2/CH4ideal separation factor of 43.6.