Recent Works on the CMSM Precursors

Attempts are still being made to improve the performance of CMSMs. Several uniqne works were selected from the recent literature to be described more in detail as below. 

Polyaciylonitrile hollow fibers were spun by the diy/wet phase inversion process by David and Ismail [31], Thermostabilization was performed by oxidative stabilization process at 250°C for 30 min under pure oxygen or compressed air. The carbonization was done at 500°C under nitrogen for a certain amount of time, which is called soak time . 

Combination of cross-linking and carbonization was applied to fabricate novel PI membrane to achieve high gas separation performance and better phy sical/chem-ical stability [61]. This was done by preparing PI from 4,4 -diaminodiphenylacety-lene (p-intA) and 2,2 -bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA). In order to avoid excessive cross-linking a co-PI containing 2,3,5,6-tetra- 

The poly merblends of PI and polyvinylpyrrolidone (PVP) was used as precursor, assuming that the partially intermingled PVP phase in the continuous PI matrix will produce porous carbon structures by the decomposition of PVP during pyrolysis [62], PI was synthesized from benzophenone tetracarboxylic dianhydride (BTDA) and 4,4 -oxydianiline (ODA). Membranes were prepared by casting the polymer dope, either PI or PI/PVP blend, on a glass plate. The east polymer film was im-idized by stepwise heating up to 250°C and then carbonized at either 550 or 700°C. 

For the fabrication of CMS membranes from commercially available relatively inexpensive polymeric material, Centeno and Fuertes chose poly(vinylidene chloride-co-vinyl chloride) (PVDC-co-PVC) copolymer commercially available imder the trade name of Saran [63]. The polymer solution was spin-coated on a finely polished surface of porous carbon support. In some cases the polymer film was preoxidized in air at 150 or 200°C. The carbonization was carried out at either 500 or 1,000°C. 

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