Charged Surface of Polyacrylonitrile Colloid and Its Application to N₂/CO₂ Separation

Nano-sized polyacrylonitrile (PAN) colloidal dispersions of 44.6 +/- 8.3 nm prepared by the modified emulsion polymerization method are utilized for gas separation. The emulsion (o/w) polymerization using organic solvent instead of precipitation polymerization is utilized, and both the size of the colloidal particle and the zeta potential could be controlled by the content of the material constituting emulsion. Thus, the solubility of CO2 is dependent on the zeta potential on the surface of colloids, resulting in that the degree of absorption of CO2 is controllable. Then, N-2/CO2 separation experiment is carried out by applying the synthesized PAN colloidal dispersions into a polymer composite. The composite membranes are prepared by adding PAN colloidal dispersions based on poly(vinyl pyrrolidone) (PVP). It is observed that the neat PVP membrane has no separation performance, while the PVP/PAN colloidal composite film shows the improved N-2/CO2 selectivity of 17. This improved separation performance is due to the fact that the solubility of CO2 decreased by absorption to specific functional groups, resulting in the enhancement of N-2 separation.