Solvent‐Templated Block Ionomers for Base‐ and Acid‐Gas Separations: Effect of Humidity on Ammonia and Carbon Dioxide Permeation

Abstract

Abstract As energy needs continue to drive the development of biogas and fossil‐fuel technologies, methods by which to selectively remove basic (NH 3 ) and acidic (CO 2 ) gases are becoming increasingly important, especially in light of global climate change. Block copolymers are considered as suitable membrane candidates in gas separations due to the ability of such copolymers to microphase‐separate and spontaneously form nanoscale morphologies that exhibit spatially modulated chemical specificity. Incorporation of charged moieties along the midblock of a thermoplastic elastomeric multiblock copolymer yields an amphiphilic block ionomer possessing a flexible molecular network stabilized by rigid endblocks. The presence of hydrophilic microdomains introduces an important consideration regulating molecular transport: humidity. In this study, solvent‐templating paradigms are employed to control the morphologies of midblock‐sulfonated pentablock ionomers, as discerned by electron microscopy and X‐ray scattering. The effect of humidity on the permeation of NH 3 , CO 2 , and N 2 is then investigated through the resulting membranes. As expected, NH 3 permeates significantly faster than N 2 , especially under humid conditions. Although not as pronounced, similar behavior is observed for CO 2 , thereby establishing that this block ionomer is generally selective to humidified polar gases.