CO2 separation by mixed matrix membranes incorporated with carbon nanotubes: a review of morphological, mechanical, thermal and transport properties

Membrane-based technology is a low-cost alternative for gas purification processes due to its easy implementation and low energy consumption. However, the participation of membrane systems in the CO2 separation technologies market for natural gas sweetening is only 10% due to the trade-off between permeability and selectivity and poor stability of the polymeric materials available. Therefore, to expand current operating conditions or meet adverse requirement in new applications, such as low pressure and high flue gas temperatures, new membrane materials need to be developed. Mixed matrix membranes (MMMs) formed by the incorporation of inorganic fillers in polymeric matrices can overcome the high cost of inorganic membranes and reduce polymeric membrane limitations. The main challenge is the development of MMMs with a defect-free interfacial morphology. In this sense, the type of load is one of the most important factors. Among the inorganic fillers, carbon nanotubes (CNTs) have great potential for chemical adaptation, as well as high mechanical and thermal properties, which can result in high performance MMMs. This review was prepared to summarize the advances achieved with polymeric matrices incorporated with CNTs (CNTs-MMMs) and contribute to their development by showing the possibilities of combining CNTs with different polymers and their respective properties. It has been observed that CNTs can increase the mechanical, thermal and transport properties of polymeric membranes. Furthermore, Robeson's upper bound revealed that some CNTs-MMMs were suitable for industrial use because of their excellent performances and with greatest application potential for CO2/N2 separation.