PREPARATION OF POLYIMIDE COMPOSITE MEMBRANE BY CHEMICAL-VAPOR-DEPOSITION AND POLYMERIZATION TECHNIQUE (CVDP)

A dry process of chemical vapor deposition and polymerization (CVDP) w as employed to prepare a polyimide composite membrane for water-ethano l separation, using an apparatus newly developed for this investigatio n. The characteristics of the apparatus were studied by depositing pyr omellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (P,P-oxydi aniline, ODA) in a vacuum of 10(-6) Torr. Deposited layers were conver ted to a thin polyimide film by heating at 200-degrees-C for 3 h in a vacuum. The composite membranes were prepared by forming a polyimide l ayer of 0.2 mum thickness on the surface of asymmetric supporting memb ranes made by the phase-inversion process. The polyimide composite mem brane prepared under the best conditions exhibited a separation factor alpha (H2O/EtOH) of over 140 for 95 vol % aqueous ethanol solution wi th flux of 0.1 kg/M2 h at 25-degrees-C in pervaporation mode. Also, it was demonstrated that this new technique of chemical vapor deposition and polymerization (CVDP) was very useful for the preparation of a so lvent-resistant composite membrane in a completely dry process.