Separation performance of polyimide composite membrane prepared by dip coating process

The effects of the preparation conditions in a dip coating process on polyimide composite membranes have been investigated. Polyimide precursor obtained from pyromellitic dianhidride (PMDA) and 4,4'-oxydianiline (ODA) was mixed with triethylamine and poly(amic acid)tri-ethylamine salt (PAA salt) was made. An asymmetric polyimide membrane (PI-2080) as a supporting membrane was dipped in a PAA salt (concentration 0-5 wt.%) methanol solution. The coating layers of PAA salt were converted to these of polyimide by annealing at 200 degreesC for 3 h in an ordinary vacuum oven. The performance of the polyimide composite membrane was evaluated by gas permeation (N-2, O-2, CO2, at 1 kg/cm(2)) and pervaporation (feed: a 95 vol.% ethanol aqueous solution at 30-60 degreesC). The composite membranes prepared using a coating solution of 5 wt.% PAA salt showed the CO2/N-2 selectivity of over 25 on gas permeation, and separation factor alpha (H-2 O/EtOH) of over 800 with a total flux of 0.21 kg/m(2) h on pervaporation. (C) 2001 Elsevier Science B.V. All nights reserved.