Poly(ethylene glycol) and poly(dimethyl siloxane): Combining their advantages into efficient CO 2 gas separation membranes

Abstract

Polymer blending is a versatile tool to combine the beneficial properties of two or more components in one single material. Here, we present the preparation, thermal- and mass transport properties of a series of blend membranes made from the commercially available PEBAX ® MH 1657 and a poly(ethylene glycol) (PEG) based additive. The additive (PDMS–PEG) consists for 80 wt.% of PEG and the remaining 20 wt.% is poly(dimethyl siloxane) (PDMS), which is highly flexible and permeable. As such, we combine the high selectivity of PEG for CO 2 with the high permeability of PDMS. We extensively study the gas transport properties, and in particular the CO 2/light gas separation performance, using pure and mixed gases. The pure gas CO 2 permeability in the PEBAX ®1657/PDMS–PEG blend membranes increased by a factor 5 to approximately 530 Barrer at 50 wt.% PDMS–PEG loading. CO 2 sorption measurements revealed only a 50% increase in CO 2 solubility and the increase in permeability could be mainly attributed to an increase in diffusivity. Remarkably, the CO 2/H 2 selectivity is enhanced (∼10%) at 50 wt.% loading, while the CO 2/N 2 and CO 2/CH 4 selectivity only slightly decreases. Mixed gas CO 2/H 2 and CO 2/CH 4 permeation measurements up to CO 2 partial pressures of 25 bar reveal that the CO 2 permeability is slightly reduced when gas mixtures are used. The CO 2/H 2 selectivity was found to be independent of the PDMS–PEG loading and feed pressure at a value of approximately 9–10. CO 2/CH 4 mixed gas selectivity decreased slightly with PDMS–PEG loading and pressure, but always remained above 10.