Pyrolysis temperature-regulated gas transport and aging properties in 6FDA-DAM polyimide-derived carbon molecular sieve membranes

Carbon molecular sieve (CMS) membranes with exceptional separation performance and scalable processing are promising for precise gas separation. However, their broad applicability is hampered owing to stability issues, mainly resulting from physical aging. Herein, we manipulate the pyrolysis temperature (550 degrees C, 650 degrees C and 750 degrees C) to regulate the gas transport properties and control the physical aging of CMS membranes derived from 6FDA-DAM polyimide. The morphology, chemical composition and pore size of the membranes were charac-terized using SEM, IR, XPS and XRD. Results demonstrated that the pore structure of CMS membranes shows densification with increasing the pyrolysis temperature, affording enhanced separation efficiency for gas pairs: H2/N2, H2/CH4, and CO2/CH4 pairs based on the size-sieving effect. Moreover, the effect of aging is more considerable for membranes pyrolyzed at a higher temperature. In addition, the membrane subjected to pre-aging treatment via vacuum storage exhibit better, stable gas separation performance beyond the upper-bond for polymeric membranes. The separation mechanism of the CMS membranes reveals that gas permeation behavior is dominated by diffusion. Tailoring gas permeation and physical aging can provide an alternative approach to tune the gas transport properties of CMS membranes.

Automated summary

Carbon molecular sieve (CMS) membranes derived from 6FDA-DAM polyimide exhibit improved gas separation efficiency with increasing pyrolysis temperature, leading to densification of the pore structure and enhanced size-sieving effect. Membranes pyrolyzed at higher temperatures are more susceptible to physical aging, but pre-aging treatment can improve and stabilize gas separation performance beyond the upper limit of polymeric membranes. The gas permeation behavior of CMS membranes is dominated by diffusion, making tailoring of gas permeation and physical aging a viable approach to tune their gas transport properties.