Cellulose nitrate-based multilayer composite membranes for gas separation

Cellulose nitrate (CN)-based composite hollow fiber membranes are prepared for gas separation. The membrane performance is studied in terms of the concentration of CN coating solution, polysulfone (PS) substrate, pre-wetting treatment, solvent used in CN solution, and the various substrate materials. In order to fabricate a useful multilayer composite membrane, the surface porosity of composite hollow fiber has to be reduced to a certain degree, before silicone rubber coating, by adjusting the CN coated layer and the PS substrate structure. The effect of pre-wetting treatment on the membrane performance is found to be minor, which may be due to the coating technique and the relatively highly permeable substrate used in this study. The solvent used in dissolving CN also affects the gas permselective property of the multilayer composite membranes and this effect may be attributed to the formation of different membrane morphology of CN layer caused by the different physical properties of solvents. The selection of substrate materials is important and this work suggests that a permeable material is more suitable to serve as the substrate. Besides, the substructure resistance in the substrate should be kept as low as possible in order not to deteriorate membrane performance of the resultant multilayer composite hollow fiber membranes.