Functional semiladder polymers for gas separation

Assessing feasibility within an integrated catalytic-membrane system

Abstract

Global warming poses a growing threat towards all living beings and their ecosystems, driving the need for more efficient and sustainable industrial processes. Gas separation is a process that is indispensable for purification, storage, and utilization of gases produced in industry. Traditional methods like cryogenic distillation and absorption are effective but energy-intensive and complex, whereas membrane-based separations offer a more energy-efficient, simpler, and modular alternative. The effectiveness of membrane is primarily determined by the type of material used in its fabrication and by its properties (thermal, chemical, etc.). In this work, attention is focused on semi-ladder aromatic multifunctional polymers incorporating xanthene units in their main chain, synthesized via a robust, one-step, metal-free polycondensation of isatin derivatives with bisphenols. The resulting materials exhibit high chemical and thermal stability, making them well-suited for challenging separation applications. Gas transport studies demonstrate that membranes based on bisphenol AF exhibit superior permeability compared to those derived from 4,4?-biphenol. In particular, fluorinated semi-ladder polymers incorporating N-propyl isatin show an enhanced permeability–selectivity balance across multiple gas pairs. These results underscore the strong potential of semi-ladder polymer membranes as energy-efficient materials for advanced gas separation technologies. Although semi-ladder polymer membranes have been tested with ultra-high-purity gases, evaluating their performance with real gas mixtures is crucial for practical applications. To address this, the membrane system will be integrated with a catalytic reactor to supply representative gas mixtures, enabling a more realistic assessment of transport properties.