Facilitated transport of molecular oxygen in cobalt-chelated copolymer membranes prepared by soap-free emulsion polymerization

Abstract

Selectivity sorption and permeation of molecular oxygen are described for 2-methylacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester cobalt(II) coordinated with rubbery copolymer membranes. Rubbery copolymers with different highly chelating group contents are prepared by using soap-free emulsion copolymerization. Amounts of cobalt(II) ion adsorbed by the rubbery copolymer membranes are in the range of 0.7–2.0 wt.%, in other words, cobalt(II)-complex contents in membranes are up to ca. 12 wt.%. The cobalt(II)-complex in membranes is a kind of highly oxygen-affinity material as well as rapid and reversible oxygen adsorption/desorption behavior showing. IR results of the oxygen-binding cobalt(II)-complexes show evidence for formation of mononuclear superoxo complexes. Sorption isotherms of oxygen for the membranes are analyzed with a dual-mode sorption model to give C C′ (the saturated amount of oxygen reversibly bound to the cobalt(II) sorption site) and K (the oxygen-affinity constant of cobalt(II)-complex). The oxygen permeability of the membrane containing cobalt(II)-complex increased with decreasing upstream oxygen pressure, which is in accordance with a dual-mode transport model. Moreover, the oxygen permeability/selectivity combinations are above and to the right of the “upper bound” line as the cobalt(II) contained as much as 1.7 wt.% (cobalt(II)-complex 12.3 wt.%) in membrane under high upstream oxygen pressure ( P u≤2 atm), however, the best oxygen permeability and selectivity combinations in this study are as high as 11.2/10.3 under P u=0.5 atm, respectively.