Polyimide-based thermal rearranged (TR) membrane for highly efficient natural gas separation: A review

Abstract

The burgeoning demand for cleaner energy sources has accentuated natural gas as a pivotal resource, necessitating advancements in separation technologies to enhance its purity and efficiency. Thermal rearranged (TR) polymers exhibit exceptional gas separation performance due to their ability to form a rigid polybenzoxazole (PBO) structure during the TR process, coupled with the creation of ultra-micropores structure facilitated by the removal of CO₂. However, one of the primary obstacles impeding the industrial development of TR polymers is the elevated permeability of TR membranes, which unfortunately compromises selectivity significantly. In this review, the formation mechanism, functional group structure and position within TR polymers is first examined. Subsequently, a comprehensive analysis of various modifications applied to TR membranes, including the integration of nano-fillers to create TR mixed matrix membranes (MMM), engineering of monomer structures, and the development of carbon molecular sieve (CMS) membranes. An in-depth structure–property relationship of TR membranes, assessing how various filler structures, copolymerization techniques, crosslinking segments, and monomer engineering techniques impact their performance is also discussed. Furthermore, the utilization of TR membranes as precursors to fabricate CMS membranes was investigated. Based on thedetailed analysis of their CO₂ separation performance, the challenges of various modification strategies for TR membranes are identified. Finally, this review concludes with strategic recommendations for future research, emphasizing the need for long-term stability studies, scale-up endeavors and the exploration of hybrid membrane systems. Our review of the current state of polyimide-based TR membrane technology provides a roadmap for advancing the field towards sustainable and efficient natural gas processing.