Since the second industrial revolution, the use of fossil fuels has been powering the advance of human society. However, the surge in carbon dioxide (CO₂) emissions has raised unsettling concerns about global warming and its consequences. Membrane separation technologies have emerged as one of the major carbon reduction approaches because they are less energy-intensive and more environmentally friendly compared to other separation techniques. Compared to pure polymeric membranes, mixed matrix membranes (MMMs) that encompass both a polymeric matrix and molecular sieving fillers have received tremendous attention, as they have the potential to combine the advantages of both polymers and molecular sieves, while cancelling out each other’s drawbacks. In this review, we will discuss recent advances in the development of MMMs for CO₂ separation. We will discuss general mechanisms of CO₂ separation in an MMM, and then compare the performances of MMMs that are based on zeolite, MOF, metal oxide nanoparticles and nanocarbons, with an emphasis on the materials’ preparation methods and their chemistries. As the field is advancing fast, we will particularly focus on examples from the last 5 years, in order to provide the most up-to-date overview in this area.

Membrane‐based gas separation provides an energy‐efficient approach for the simultaneous CO ₂ and H ₂ S removal from sour natural gas. The fluorinated polyimide (PI) membranes exhibited a promising balance between permeability and permselectivity for sour natural gas separation. To further improve the separation efficiency of fluorinated PI membranes, a melamine‐copolymerization synthetic approach is devised that aims to incorporate melamine motifs with high sour gas affinity into the structure of the PI membranes. The fluorinated copolyimide membranes that are structurally engineered exhibited excellent solution‐processability and enhanced sweet‐mixed gas selectivity compared to their original PI membranes. Additionally, under a five‐component sour mixed‐gas feed, these melamine‐copolymerized fluorinated PI membranes provided superior combined H ₂ S and CO ₂ removal efficiency in comparison to conventional glassy polymer membranes. The melamine‐copolymerization strategy provides an easily operable and generally effective approach to developing performance‐enhancing PI membranes for sour natural gas separation.

Natural gas can contain significant amounts of impurifies, including CO2, H2S, N2, He, and C3+ hydrocarbons. These C3+ hydrocarbons are valuable chemical feedstocks and can be used as a liquid fuel for power generation. Membrane-based separation technologies have recently emerged as an economically favorable alternative due to reduced capital and operating cost. Polymeric membranes for the separation and removal of C3+ hydrocarbons from natural gas have been practiced in chemical and petrochemical industries. Therefore, these industries can benefit from membranes with improved C3+ hydrocarbon separation. This chapter overviews the different gas processing technologies for C3+ hydrocarbon separation and recovery from natural gas, highlighting the advantages, research and industrial needs, and challenges in developing highly efficient polymer-based membranes. More specifically, this chapter summarizes the removal of C3H8 and C4H10 from CH4 by prospective polymer architectures based on reverse-selective glassy polymers, rubbery polymers, and its hybrid mixed matrix membranes. In addition, the effect of testing conditions and gas compositions on the membrane permeation properties (permeability and selectivity) is reviewed.