OXYGEN NITROGEN SEPARATION BY POLYCARBONATE/CO(SALPR) COMPLEX MEMBRANES/

An oxygen carrier, cobalt di-(salicylal)-3,3'-diimino-di-n-propylamine (Co(SalPr)), was added into a polycarbonate membrane for improving it s oxygen/nitrogen selectivity. Both the oxygen permeability and oxygen /nitrogen selectivity increased when only 3 wt% of Co(SalPr) was added . The permeability kept increasing but the selectivity decreased when more than 3 wt% of Co(SalPr) was added. The oxygen to nitrogen solubil ity ratio decreased when 3 wt% of Co(SalPr) was added. Further increas e in Co(SalPr) content led to an increase in oxygen/nitrogen solubilit y ratio. It was astonishing to know that the effect of Co(SalPr) conte nt on the oxygen/nitrogen solubility ratio was totally opposite to tha t on the oxygen/nitrogen selectivity. A membrane gas transport model w hich combines the dual mobility model with pore model was adopted to e xplain the above phenomenon. The specific volume measurement implied t hat the pore diffusion was responsible for this behavior. The contribu tion of sorption-diffusion type transport was also investigated by exa mining the transport behavior of the 3 wt% Co(SalPr) containing membra ne through which the pore diffusion is relatively low. The effect of u pstream pressure on the oxygen permeability and solubility implied tha t the diffusivity of Henry's mode was much higher than that of Langmui r's mode. It was also found that the effects of upstream pressure and operating temperature on the oxygen/nitrogen selectivity were both in accordance with those on the Henry's mode solubility ratio. The above information suggested that in addition to the pore diffusion the ratio of Henry's mode diffusion dominated the O-2/N-2 separation instead of the overall O-2 to N-2 solubility ratio.