Development of polyimide membranes for the separation of water vapor from organic compounds

Attempts were made to develop solvent-resistant polyimide capillary membranes with integrally skinned asymmetric structure to be used for the treatment of wood dryer emissions or vacuum pyrolysis aqueous effluents. Model mixtures of 1-propanol (1-PrOH)/H2O and acetic acid (AA)/H2O, with concentrations of 10-90 wt % of organic components, were used as vaporous feeds. Solvent-resistant membranes with good mechanical and excellent vapor separation properties were prepared from polyimides based on PMDA and BPDA by the dry/wet phase-inversion technique. Molecular structure largely influences membrane properties. For the asymmetric polyimide membranes studied, a tendency similar to that of homogeneous dense membrane was found. Membranes prepared from polyimides with diamine and dianhydride moieties, both containing rigid backbone and aromatic rings, displayed higher permeability and selectivity. Test conditions exhibited influences on membrane separation performance. Membranes prepared from copolyimide BPDA-50DDS/500DA and PMDA-50DDS/500DA exhibited the best mechanical and chemical properties as well as water vapor separation properties, which are considered to be of practical usefulness for applications of these membranes in the removal of water from water/organic mixtures. (C) 2002 Wiley Periodicals.