Journal of Membrane Science 251 (2005) 51–57 Tunable CO 2 transport through mixed polyether membranes Nikunj P. Patel a , Marcus A. Hunt c , Sheng Lin-Gibson d , Sidi Bencherif d , Richard J. Spontak a, b, ∗ a Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695, USA b Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695, USA c Fiber and Polymer Science Program, North Carolina State University, Raleigh, NC 27695, USA d Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA Received 23 September 2004; received in revised form 31 October 2004; accepted 5 November 2004 Abstract Gas-separation membranes composed of polyethers such as poly(ethylene glycol)diacrylate (PEGda) or poly(propylene glycol)diacrylate (PPGda) exhibit high CO 2 solubility selectivity, which makes them attractive for use in H 2 and air purification. In this work, we investigate the factors governing CO 2 and H 2 transport in mixed polyether matrices. Addition of semicrystalline poly(ethylene oxide)s to amorphous PEGda lowers the net CO 2 permeability and CO 2 /H 2 selectivity due to crystal formation. Gas permeation through the amorphous fraction, however, remains unaffected, confirming the existence of a molecular weight limit below which the entire membrane participates in gas transport. The permeabilities of CO 2 and H 2 , as well as their activation energy of permeation, in miscible PEGda/PPGda blends follow the linear rule of mixtures over the temperature range explored. Incorporation of amine moieties employed in liquid membranes into either the PEGda matrix during crosslinking or the PEG backbone generally reduces CO 2 /H 2 selectivity but occasionally improves CO 2 permeability. © 2004 Elsevier B.V. All rights reserved. Keywords: Polyether; Gas-separation membrane; Reverse selectivity 1. Introduction The increasing interest in H 2 as the next-generation fuel expected to replace dwindling petroleum reserves [1–3] con- tinues to drive the development of purification strategies by which to separate H 2 from other light gases. Since most of the worldwide H 2 supply derives directly from synthetic gas (“syngas”) via the two-stage water-gas shift reaction [4], removal of CO 2 from H 2 is of paramount importance. Such separation can be achieved by exposing a high-pressure CO 2 /H 2 gas stream to a glassy polymer membrane, which permits more rapid permeation of H 2 molecules (due to their smaller size and, hence, higher diffusivity) than CO 2 molecules through the rigid, size-sieving polymer matrix [5]. In this scenario, however, requisite post-repressurization of ∗ Corresponding author. Tel.: +1 919 515 4200; fax: +1 919 515 3465/7724. E-mail address: rich spontak@ncsu.edu (R.J. Spontak). the H 2 permeate is economically prohibitive. Alternatively, the mixed CO 2 /H 2 stream can be subjected to liquid amine- based membranes [6] or zeolitic adsorbents [7] designed to remove CO 2 as the permeate, thereby yielding a puri- fied, high-pressure H 2 retentate. While these technologies are currently employed for H 2 , as well as air, purification, they suffer from inherent drawbacks that can promote equip- ment corrosion, system fouling, energy consumption and environmental contamination. Development of comparable polymer membranes capable of removing CO 2 from mixed CO 2 /H 2 streams requires a high CO 2 solubility (S) selectiv- ity (α S = S CO 2 /S H 2 > 1), since the corresponding diffusiv- ity (D) selectivity (α D = D CO 2 /D H 2 ) is less than unity and the net membrane selectivity (α CO 2 /H 2 ) required for design and assessment purposes, given by α S α D in the context of solution-diffusion molecular transport [8], must be greater than unity. Initial gas-transport studies [9–11] of commercial poly (ether-b-amide) multiblock copolymers have established that 0376-7388/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2004.11.003