Energy has been proposed as a feed of the long-term development. Fossil fuel burning serves the main part of energy needs. The projections of world energy consumption by all the energy sources up to the mid-21stcentury introduce natural gas stays on ahead of the others. It involves with the simultaneous challenges of CO2 separation from natural/bio gas (acid gas removal) as well as subsequent capture of CO2 emitted from power plants (in order to mitigating the global warming accompanied by CO2 emission). Membrane gas separation has crucial advantages among all other CO2 separation technologies such as absorption, adsorption, and cryogenic distillation. One of the main purposes of research in membrane gas separation is fabrication of membranes with superior permeability and selectivity. Although polymeric membranes possess many advantages such as the ability for easy fabrication of large membrane areas at low cost, they suffer from problems associated with the trade-off relationship between permeability and selectivity. Therefore, they traditionally undergo an upper bound limitation. Although there are many opportunities for polymeric-based membrane for gas separation applications, but most of the existing membrane materials cannot economically utilize in these opportunities. Therefore, even today, many progresses are made in alternative emerging materials in order to develop the CO2 separation performances. There are various methods have been examined to improve current levels of membrane performance such asgrafting, blending, crosslinking, ion-exchange treatment, mixing with suitable dense/molecular sieve fillers and etc. This chapter is especially devoted to explain challenging issues affect the CO2 separation properties of conventional polymeric membranes. Moreover, advanced classes of highly CO2 separation performance polymeric membranes are summarized.
