Water vapor permeation properties of aromatic polyimides

Water vapor permeation and separation behavior in solvent-resistant polyimide dense membranes was investigated. Model mixtures of 1-propanol (1-PrOH)/H2O, and acetic acid (AA)/H2O with concentration of 10 wt.% of organic compounds, as well as a pyrolysis aqueous phase containing 11 wt.% organic compounds were used as vapor feeds. Solvent-resistant polyimide membranes with good mechanical and excellent water vapor separation properties could be prepared from PMDA- and BPDA-based membrane materials. The polyimide molecular structure had a strong effect on the mechanical, chemical and water vapor separation performance of the membranes prepared. Test conditions exhibited influence on membrane separation behavior. It was found that decreasing temperature favored the separation of water vapor from organics in the polyimide membranes. Membranes prepared from copolyimide BPDA–50DDS/50ODA and PMDA–50DDS/50ODA exhibited the best mechanical and chemical properties along with excellent water vapor separation performance. These membranes are particularly useful in the removal of water from water/organic mixtures.