Specifics of highly selective ammonia transport through gas-separating membranes based on perfluorinated copolymer in the form of hollow fibers

Facilitated transport of ammonia through perfluorosulfonic acid polymer-based hollow-fiber membranes in Co2+, NH4+ and H+ ionic forms was investigated. Hollow-fiber membranes were prepared from a copolymer of tetrafluoroethylene with perfluoro-3,6-dioxa-5-methyl-1-octene-8-sulfonyl fluoride by molding from the melt, followed by hydrolysis of the sulfonyl fluoride copolymer in NaOH and ionic exchange in HCl or CoSO4 solutions or by direct hydrolysis in morpholine. Experimental data on permeability and diffusion coefficients and solubilities of ammonia in these membranes, measured independently, are presented. The investigated membranes in a moist state exhibited fairly high coefficients PNH3 of permeability for NH3 and separation factors α [(PNH3 7.8 X 10 −7 cm3 (STP).cm/cm2 sec-cmHg; α1 = PH3/PH2 ≥ (102-103)] compared with those of other polymeric membranes. A qualitative analysis is presented of the possible mechanisms of transport involved in the reaction of reversible bonding of NH3 molecules to membrane functional groups. For these purposes, IR and radiospectroscopy were also employed to confirm the proposed mechanisms of complexing and trans-membrane gas transport. Transport properties of perfluorosulfonic acid polymer-based membrane are compared with other data available in the literature, and are discussed in terms of a complex phase structure of the ionomeric material.