The Perfluoropolymer Upper Bound


Albert Wu


Albert Wu, James Drayton, Zachary Smith

Author Affiliation: 

Department of Chemical Engineering, Massachusetts Institute of Technology


Perfluoropolymers have fundamentally distinct thermodynamic partitioning properties compared to those of their hydrocarbon counterparts. However, current upper bound theory assumes hydrocarbon solubility behavior for all polymers, regardless of their chemical composition. Herein, the fundamental presupposition of invariance in solubility behavior to upper bound performance is critically assessed for perfluoropolymers and hydrocarbon-based polymers. By modifying solubility relationships, theoretical perfluoropolymer upper bounds are established, showing a positive shift of the upper bound front as a result of beneficial solubility selectivities for certain gas pairs, including N2/CH4, He/H2, He/N2, He/CH4, and He/CO2. Predictions are compared to currently available experimental data. Within the framework of the solution-diffusion model, an additional analysis is presented to compare two independent approaches often pursued in efforts to surpass the polymer upper bound: (1) achieving solubility selectivity through the use of perfluoropolymers and (2) improving diffusion selectivity through the use of rigid hydrocarbon-based polymers. This analysis demonstrates the significant benefit that can be achieved by considering both the chemical and morphological features of solid-state macromolecules when designing membrane materials. Finally, promising future applications for perfluoropolymers are discussed.