ANALYSIS OF GAS PERMEATION THROUGH COMPOSITE MEMBRANES

The properties of membranes have to be adjusted to the separation problems. In gas separation solution-diffusion type membranes are usually used. These membranes can be made from polymeric materials such as rubber polymers which have moderate permeabilities and low selectivities or from rigid glassy polymers with low permeabilities and moderate selectivities. Combinations of both types of materials allow a membrane's properties to be tailored to specific separation problems. Such membranes were prepared as composite structures with poly(ethersulfone) for the substructure and poly(dimethylsiloxane) or poly(butadien-styrene) copolymer for the coating layer. Their properties in gas separation were measured with oxygen-nitrogen and carbon dioxide-methane mixtures. The results were correlated with the preparation techniques. Three types of composite membranes could be identified which are referred to as pore-flux-type, mixed-flux-type, and nonpore-flux-type composite membranes. Using three simple models, the results obtained from gas separation tests can be explained and the theoretical thickness of the substructure can be estimated.