Advances in high permeability polymeric membrane materials for CO_2 separations

摘要

Global CO_2 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 CO_2 reduction technologies. There is an almost universal acceptance of the link between rising anthropogenic CO_2 levels due to fossil fuel combustion and global warming accompanied by unpredictable climate change. Therefore, renewable energy, non-fossil fuels and CO_2 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 CO_2 emitters, and capture of the CO_2 emissions can be achieved with conventional technologies such as amine absorption. However, this energyconsuming 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 CO_2 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 CO_2 capture. Polymer membranes highly permeable to CO_2 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 CO_2 permeability and good CO_2/N_2 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 CO_2 separation from, for example, the post-combustion flue gases in coal-fired power plants.