| Membrane technology is widely used in the field of oxygen-enrichment for combustion-supporting and medical care because of its characteristics of flexibility, simple equipments and safety. Enriched oxygen can be used to help fuel combustion. It will reduce the energy consumption and the exhaust emission, which is to the great interest of energy-saving and emission-reduction strategy in our country. An oxygen concentration of 25%to 35%is required to help fuel combustion, which means the selectivity of oxygen/nitrogen should be about 2.0 and the gas permeation rate should be comparablely high.Poly (dimethylsiloxane) (PDMS), as the most widely used material in the separation of oxygen and nitrogen, has an intrinsic oxygen/nitrogen selecity of 2.2 and high gas permeation rate. However, its membrane mechanical peformance 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. As a result, support membranes with appropriate pore diameter and excellent mechanical performance play an important role in the performance of the composite membranes. Composite membranes prepared with polyacrylonitrile(PAN) as support membrane can get a practical selectivity of 2.0 for oxygen and nitrogen and very high gas permeation rate. However, the mechanical performance of PAN is also not good enough for gas separation application. As a result, there is little research on PAN material for the gas separation application. Cellulose acetate(CA) has comparable good mechanical performance and good compatibility with PAN. To combine the advantages of these two materials, we blend them to investigate an excellent composite membrane with better mechanical performance, selectivity and gas permeation rate.The composite membranes are prepared by coating PDMS on the surface of porous support membranes, which are prepared via phase inversion process using PAN and CA as the substrates material, N,N-Dimethylacetamide (DMAc) as the solvent and water as the coagulant. To prepare the PAN/CA support membrane with excellent mechanical performance and appropriate pore size and porosity, the blend ratio of PAN/CA, the total polymer concentration and PEG600 additive concentration are investigated to control the structure of the support membranes. SEM, DSC, light transmittance and mechanical strength tests are used to show the structure and dynamic formation process of membranes. The oxygen permeation rates of the composite membranes are also measured.Firstly, the blend ratio of CA to PAN is investigated. It is shown that the appropriate blend ratio is 0.10 and the tensile breaking stress of blend membrane can be enhanced from 1.74MPa to 2.08MPa. The composite membrane coated with 8%PDMS can get a selectivity of 2.08 for oxygen to nitrogen and oxygen permeation rate of 100.5GPU(1GPU=10-6cm3 (STP)/cm2·s·cmHg).Secondly, the total polymer concentration is investigated. It is shown that the appropriate total polymer concentration is 20%and the tensile breaking stress of blend membrane can be enhanced linearly with the increasing of total polymer concentration. The composite membrane coated with 6%PDMS can get a selectivity of 2.05 for oxygen to nitrogen and oxygen permeation rate of 151.9GPU.Finally, the effect of PEG600 additive concentration is investigated. It is shown that the appropriate PEG600 additive concentration is 4%and the corresponding tensile breaking stress of blend membrane is 2.47MPa. The appropriate PDMS concentration is 6%. The corresponding composite membrane can get a selectivity of 2.01 for oxygen to nitrogen and oxygen permeation rate of 221.9GPU, which meets the requirement of oxygen-enrichment membranes.
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