SURFACE FLUORINATION OF POLY(PHENYLENE OXIDE) COMPOSITE MEMBRANES .1.TRANSPORT-PROPERTIES

The effect of surface fluorination on the ps transport properties of c omposite membranes, comprising an inert porous ceramic support and a s elective layer consisting of poly (phenylene oxide), was examined. A s mall reactor volume permitted the treatment time and the fluorine feed concentration to be investigated independently. The gas transport pro perties of the treated membranes were evaluated for six gases (N2, O2, CH4, H-2, He and CO2), in terms of permeance (P/l or pressure-normali zed flux) and the ideal selectivity for eight pairs of these gases. It was generally found that fluorination at different fluorine feed conc entrations and reaction times reduced the permeance of all of the gase s. The permeance of the lighter gases (He and H-2) was reduced by a sm aller factor than that of the heavier gases (N2 and CH4). Fluorination increased the selectivity of He and H-2 relative to N2 or CH4 by a sm all factor, but reduced the selectivity of O2 and CO2 relative to N2 o r CH4. When the membranes were coated with a layer of poly(dimethylsil oxane) (PDMS) subsequent to fluorination, the permeance decreased, con siderably more for N2 and CH4 than for the other gases. Surface coatin g also substantially increased the selectivities of all the gas pairs. The largest gains in selectivity after fluorination and coating were found at the higher concentration (0.1% F2) and intermediate treatment times of 3 to 5 min. Based on these results, surface coating with PDM S is recommended as a post-treatment step in the fluorination process.