Continuous separation of oxygen from air has received a wide range of attention owing to its potential applications in various combustion devices.
The permeabilities and selectivities of $O_2$ and $N_2$ were tested using silicone rubber, polyurethane and cellulose acetate membranes in order to see whether the separation of oxygen from air by the membranes is feasible or not.
Under the steady state experimental condition using silicone rubber membrane, the fluxes of oxygen and nitrogen increased linearly with the increase of pressure difference. The permeabilities of these two gases were independent of pressure difference and membrane thickness. The diffusivities remained constant and Henry's law was applicable to Polymer-gases relation. Also the diffusivities did not depend on hardening temperature and pressure. The separation ability of this membrane did not change under high pressure of 40Kg/㎠. The fluxes were quite steady during 24-hour operation.
The polyurethane membrane was prepared by casting $CH_2 Cl_2$ after complete polymerization of PUR 725 A+B system and then hardened in a vacuum oven. The permeabilities of $O_2$ and $N_2$ were better in this membrane than in those prepared otherwise. The polyurethane membrane has lower permeability but higher selectivity than silicone rubber membrane.
In freeze-dried cellulose acetate membrane, the fluxes of $O_2$ and $N_2$ was proportional to pressure difference. Thus the freeze-drying technique used to evaporate the water in the membrane enables the microporous structure of the skinlayer in the surface of membrane to remain without deterioration. But the cellulose acetate membrane can not be used for oxygen-nitrogen separation process since the permeability of oxygen is the same as that of nitrogen.
As to the silicone rubber membrane the flux in the permeated air increased but the concentration of $O_2$ in permeate reached its saturation point as pressure difference increased. And there existed the maximum gas concentration obtainable through the permeation for each specific membrane thickness. This phenomenon was explained by the Local Elasto-Plastic Deflection model proposed in our laboratory.
