Experimental and computational analysis of carbon molecular sieve membrane formation upon polyetherimide pyrolysis

Carbon molecular sieve membranes (CM) are typically synthesized through pyrolysis of polymers, and are suitable for gas separation under high pressure conditions due to their high selectivity and mechanical strength. There is a lack of knowledge of the mechanisms of membrane formation during pyrolysis, which would be of fundamental importance to a better understanding and precise control of the process. In this work, we investigate the process of CM formation upon pyrolysis of polyetherimide. A carbon membrane was synthesized on a ceramic support and characterized by different techniques, demonstrating the conversion of the polymeric precursor into a porous and predominantly amorphous carbon structure, containing embedded graphitic domains. The membrane showed effective molecular sieve performance as demonstrated in gas permeation tests. Reactive molecular dynamics simulations were carried out to explore the mechanisms of the polymer→CM transformation at the atomistic level. The simulations show that the continuous reaction among the reactive radicals formed upon polymer pyrolysis along with atomic rearrangements spontaneously led to the formation of a nanoporous amorphous carbon matrix, containing interconnected graphitic domains throughout the structure, as observed in the experiments. These results are expected to be of great help to the development of techniques for controllable synthesis of CMs.

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