Envisioned role of slit bypass pores in physical aging of carbon molecular sieve membranes

Abstract

Carbon molecular sieve (CMS) hollow fibers are a special class of rigid, molecular sieving membranes with unique scalability and excellent separation properties for challenging gas-pairs. These high-performing membranes are subject to moderate productivity losses and selectivity gains over time via a phenomenon typically referred to as physical aging. This article considers the role of slit bypass pores in physical aging as sensed by membrane property changes of CMS derived from aromatic polyimide precursors. Such pores are believed to be edge imperfections between adjacent ultramicroporous plates that may tighten over time, causing a reduction in penetrant diffusion coefficients. The envisioned mechanism leading to such slit bypass pores and their effects on penetrant transport are considered here from a fundamental perspective. Importantly, these slit bypass pores can be manipulated to suppress physical aging in CMS hollow fiber membranes, therefore enabling attractive long-term separation properties for multiple challenging applications.