Fabrication and Performance of Asymmetric Polyetherimide Air Separation Membranes Using N‐Butyl Pyrrolidinone as a Greener Solvent

Membrane‐based gas separation has emerged as an energy‐efficient and scalable alternative to conventional separation technologies. However, the fabrication of defect‐free polymeric membranes using environmentally benign solvents remains a major challenge. In recent years, studies have explored the use of green solvents as sustainable replacements for conventional toxic solvents in membrane preparation. In this study, selective polyetherimide flat sheet membranes were successfully fabricated using N‐butyl pyrrolidone as a green solvent for the first time. The effect of the N‐butyl pyrrolidone/tetrahydrofuran ratio on the resulting membrane morphology, gas permeation properties, and O 2 /N 2 selectivity was systematically investigated. The optimized membrane demonstrated competitive gas separation performance, exhibiting 2.54 GPU permeance and 4.47 selectivity of O 2 /N 2 values comparable to those obtained from conventional solvent systems. He/N 2 selectivity was also investigated to clarify the membrane mechanism. NBP is demonstrated to be an effective and sustainable alternative to traditional solvents for the fabrication of asymmetric, selective polyetherimide membranes, representing a significant step toward greener and safer membrane production for gas separation applications.