Preparation Of PDMS - PSf Composite Membrane And Its Oxygen Separation Performance

Poly(dimethylsiloxane)(PDMS), as the most widely used material in the separation of oxygen and nitrogen, has an intrinsic oxygen/nitrogen selectivity of 2.2 and high gas permeation rate. However, its membrane mechanical performance is too poor to be used directly. Usually, PDMS is coated as the selective layer on the porous polymeric support membrane to form oxygen-enrichment composite membranes in the real applications. Moreover, not only the membrane material but also the structure of the substrate have been studied deeply to improve the performance of the composite membrane. However, during coating time, the property of coating solution like the viscosity and the molecular weight is also the key to the composite membrane with excellent performance. Different type of silicone rubber leads to the different performance of the composite membrane. PDMS has high molecular weight is easier coated than low high molecular weight. In this dissertation, the experiments mainly inspect the preparation of support membranes with stable performance and suitable structure, the relationships between the membrane formation and its permeability, and the coating solution viscosity as well as the PDMS molecular weight, the effect of blow zero coating on performance of composite membranes.The composite membranes were prepared by coating PDMS on the surface of porous support membranes, which are prepared via phase inversion process using polysulfone(PSf) as the substrates material. To prepare the PSf substrate with pore size and porosity, which is helpful to form a thin defect-free PDMS dense membrane coated on the substrate surface, the concentration of PSf and the organic additive of y-butyrolactone(GBL) were investigated to control the structure of the substrate. In the result, the support membrane has stable performance of 27000GPU permeability and no selectivity between oxygen and nitrogen.PDMS/PSf composite membranes for oxygen/nitrogen separation were fabricated by the wet-coating method. The effects of PDMS concentration in the coating solution, solvent type and the pre-crosslinking time on the resultant PDMS/PSf membrane performance were systematically investigated. The relationships between the membrane formation and its permeability, and the coating solution viscosity as well as the PDMS molecular weight were further explored. The experimental results indicate that the viscosity of the coating solution and the viscosity-average molecular weight of PDMS should be higher than certain value to form compact selectivity layers, the coating solution with low viscosity at low coating rate can maximize the permeability of the composite membrane. The oxygen permeance of the resultant PDMS/PSf composite membrane fabricated under the optimal critical conditions reached as high as 2197 GPU (pure gas) with the O2/N2 separation factor of 2.05 which is much higher than the reported values in literatures.PDMS/PSf composite flat membranes were fabricated by low temperature coating method. The effect of blow zero coating on performance of composite membranes was investigated, the comparison was made for composite membranes performance between low temperature coating with homoeothermy coating in the view of PDMS concentration and coating speed, furthermore, the organic solvent and high pressure resistance of composite membranes prepared by low temperature coating was tested. The results indicate that, compared with homoeothermy coating, composite membranes coated by low temperature coating appeared higher O2 permeability under the premise of intrinsic separation factor between oxygen and nitrogen; complete and thin dense layer was prepared easier by low temperature coating under conditions of low PDMS concentration and low coating speed. In this study, the permeability of composite membranes coated in-20 ℃ temperature reached 1300GPU in the case of intrinsic separation factor between oxygen and nitrogen, moreover, the organic solvent and high pressure resistance of composite membranes showed a relative high stability to guarantee industrial life.