Advances in high permeability polymeric membrane materials for CO2 separations

Abstract

Global CO₂ emissions have increased steadily in tandem with the use of fossil fuels. A paradigm shift is needed in developing new ways by which energy is supplied and utilized, together with the mitigation of climate change through CO₂ reduction technologies. There is an almost universal acceptance of the link between rising anthropogenic CO₂ levels due to fossil fuel combustion and global warming accompanied by unpredictable climate change. Therefore, renewable energy, non-fossil fuels and CO₂ capture and storage (CCS) must be deployed on a massive scale. CCS technologies provide a means for reducing greenhouse gas emissions, in addition to the current strategies of improving energy efficiency. Coal-fired power plants are among the main large-scale CO₂ emitters, and capture of the CO₂ emissions can be achieved with conventional technologies such as amine absorption. However, this energy-consuming process, calculated at approximately 30% of the power plant capacity, would result in unacceptable increases in power generation costs. Membrane processes offer a potentially viable energy-saving alternative for CO₂ capture because they do not involve any phase transformation. However, typical gas separation membranes that are currently available have insufficiently high permeability to be able to process the massive volumes of flue gas, which would result in a high CO₂ capture. Polymer membranes highly permeable to CO₂ and having good selectivity should be developed for the membrane process to be viable. This perspective review summarizes recent noteworthy advances in polymeric materials having very high CO₂ permeability and good CO₂/N₂ selectivity that largely surpass the separation performance of conventional polymer materials. Five important classes of polymer membrane materials are highlighted: polyimides, thermally rearranged polymers (TRs), substituted polyacetylenes, polymers with intrinsic microporosity (PIM) and polyethers, which provide insights into polymer designs suitable for CO₂ separation from, for example, the post-combustion flue gases in coal-fired power plants.