Effects of shear rate on O2/N2 gas separation performance of Mindel S-1000

Mindel S-1000, a commercial blend of Polysulfone and Acrylonitrile- Butadiene-Styrene (ABS), was chosen in this study as a membrane material for oxygen/nitrogen separation system. N-methyl-2-pyrrolidone (NMP) and tetrahydrofuran (THF) were used as a solvent to prepare 21 wt% polymer dope solution. The membrane was fabricated using pneumatically-controlled flat sheet membrane casting system with dry/wet phase inversion method. The optimum casting shear rate for Mindel S-1000 membrane preparation was found to be in the range between 220.13 s-1 to 440.27 s-1 with a constant evaporation time of 15 seconds. As the membrane was cast at low shear rate, thicker skin layer and large pore radius tend to form. As the shear rate increased the support layer tend to be non-compact that caused increased in permeability but this does not thinning the skin layer significantly. Thus, the membranes prepared at higher shear rate enhanced the molecular orientation in the skin layer in which not only improving the selectivity of the membrane, the gas fluxes also increased. On the other hand, shear rate above the optimum value reduced the membrane thickness severely and this reduced it gas separation performance. At the optimum shear, oxygen/nitrogen selectivity for this membrane was found to be 4.86 with the oxygen and nitrogen pressure-normalized fluxes were 10.5 GPU and 2.2 GPU, respectively. This shows that Mindel S-1000 has great potential as membrane material for gas separation process