SEPARATION OF SMALL MOLECULES USING NOVEL ROLLTRUDED MEMBRANES .19 APPARATUS AND PRELIMINARY-RESULTS

A novel membrane production technique, rolltrusion, has been developed for the preparation of permselective polymeric membranes for both gas and vapor separations and pervaporation applications. Pinhole-free thin films with a regulated three-dimensional morphology comprising crystalline and amorphous regions have been produced with improved mechanical properties in three dimensions. Because rolltrusion is a solid-state processing technique, it is not restricted by solubility constraints inherent in the common solvent-based thin-film production techniques. Consequently it can be extended to include commercially available engineering plastics that have not been used as membranes previously because of their limited solvent solubility. These polymers are interesting because of their applicability to temperatures in excess of 200 to 300-degrees-C in harsh chemical environments, compared with the ca. 150-degrees-C ceiling usually encountered in the most rugged of solvent-cast polymers. In the first part of this series we detail an automated experimental permeation apparatus that permits testing of both single-component and multicomponent gases and vapors over a temperature range of -73 to 273-degrees-C. Currently, modifications to the permeation cell are underway to permit pervaporation studies in the apparatus. To illustrate the operation of the apparatus, and to some degree the effect of rolltrusion processing, experimental permeability, diffusivity, solubility, and actual gas separation factors (via gas chromatography) are detailed for several light gases in rolltruded isotactic poly (propylene) (iPP) and in the thermally and chemically resistant thermoplastic, poly (ether ether ketone) (PEEK). Permeation temperatures to at least 225-degrees-C have been studied using PEEK, representing the first published experimental permeability and gas-separation results for such engineering polymers at temperatures above 200-degrees-C.