Gas‐separation polymer membranes display a characteristic permeability–selectivity trade‐off that has limited their industrial use. The most comprehensive approach to improving performance is to devise strategies that simultaneously increase fractional free volume, narrow free volume distribution, and enhance sorption selectivity, but generalizable methods for such approaches are exceedingly rare. Here, we present an in situ crosslinking and solid‐state deprotection method to access previously inaccessible sorption and diffusion characteristics in amine‐functionalized polymers of intrinsic microporosity. Free volume element (FVE) size can be increased while preserving a narrow FVE distribution, enabling below‐upper bound polymers to surpass the H2/N2, H2/CH4, and O2/N2upper bounds and improving CO2‐based selectivities by 200 %. This approach can transform polymers into chemical analogues with improved performance, thereby overcoming traditional permeability–selectivity trade‐offs.
Gas‐separation polymer membranes display a characteristic permeability–selectivity trade‐off that has limited their industrial use. The most comprehensive approach to improving performance is to devise strategies that simultaneously increase fractional free volume, narrow free volume distribution, and enhance sorption selectivity, but generalizable methods for such approaches are exceedingly rare. Here, we present an in situ crosslinking and solid‐state deprotection method to access previously inaccessible sorption and diffusion characteristics in amine‐functionalized polymers of intrinsic microporosity. Free volume element (FVE) size can be increased while preserving a narrow FVE distribution, enabling below‐upper bound polymers to surpass the H2/N2, H2/CH4, and O2/N2upper bounds and improving CO2‐based selectivities by 200 %. This approach can transform polymers into chemical analogues with improved performance, thereby overcoming traditional permeability–selectivity trade‐offs.
more » « less- PAR ID:
- 10236616
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie
- Volume:
- 133
- Issue:
- 12
- ISSN:
- 0044-8249
- Page Range / eLocation ID:
- p. 6667-6673
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract Mixed matrix membranes (MMMs) comprising size‐sieving fillers dispersed in polymers exhibit diffusivity selectivity and may surpass the upper bound for gas separation, but their performance is limited by defects at the polymer/filler interface. Herein, a fundamentally different approach employing a highly sorptive filler that is inherently less sensitive to interfacial defects is reported. Palladium nanoparticles with extremely high H2sorption are dispersed in polybenzimidazole at loadings near the percolation threshold, which increases both H2permeability and H2/CO2selectivity. Performance of these MMMs surpasses the state‐of‐the‐art upper bound for H2/CO2separation with polymer‐based membranes. The success of these sorption‐enhanced MMMs for H2/CO2separation may launch a new research paradigm that taps the enormous knowledge of affinities between gases and nanomaterials to design MMMs for a wide variety of gas separations.
-
more » « less
Abstract 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. Herein, the fundamental presupposition of invariance in solubility behavior to upper bound performance is critically assessed for perfluoropolymers and hydrocarbon 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. Within the framework of the solution–diffusion model, an analysis is presented to compare two independent approaches often pursued in efforts to surpass the polymer upper bound: (a) achieving solubility selectivity via perfluoropolymers and (b) improving diffusion selectivity via rigid hydrocarbon polymers. This analysis demonstrates the significant benefit that can be achieved by considering both the chemical composition and morphology of solid‐state macromolecules when designing membrane materials.
-
more » « less
Polymers of intrinsic microporosity (PIMs) have shown promise in pushing the limits of gas separation membranes, recently redefining upper bounds for a variety of gas pair separations. However, many of these membranes still suffer from reductions in permeability over time, removing the primary advantage of this class of polymer. In this work, a series of pentiptycene-based PIMs incorporated into copolymers with PIM-1 are examined to identify fundamental structure–property relationships between the configuration of the pentiptycene backbone and its accompanying linear or branched substituent group. The incorporation of pentiptycene provides a route to instill a more permanent, configuration-based free volume, resistant to physical aging via traditional collapse of conformation-based free volume. PPIM-ip-C and PPIM-np-S, copolymers with C- and S-shape backbones and branched isopropoxy and linear
n -propoxy substituent groups, respectively, each exhibited initial separation performance enhancements relative to PIM-1. Additionally, aging-enhanced gas permeabilities were observed, a stark departure from the typical permeability losses pure PIM-1 experiences with aging. Mixed-gas separation data showed enhanced CO2/CH4selectivity relative to the pure-gas permeation results, with only ∼20% decreases in selectivity when moving from a CO2partial pressure of ∼2.4 to ∼7.1 atm (atmospheric pressure) when utilizing a mixed-gas CO2/CH4feed stream. These results highlight the potential of pentiptycene’s intrinsic, configurational free volume for simultaneously delivering size-sieving above the 2008 upper bound, along with exceptional resistance to physical aging that often plagues high free volume PIMs. -
more » « less
Abstract Graphene oxide (GO) nanosheets stacked in parallel with subnanometer channels can exhibit an excellent size‐sieving ability for membrane‐based gas separation. However, gas molecules have to diffuse through the tortuous nanochannels, leading to low permeability. Herein we demonstrate two versatile approaches to modify the GO (before membrane fabrication by vacuum‐filtration) to collectively increase gas permeability, etching using hydrogen peroxide to generate in‐plane nanopores and acidifying using hydrochloric acid. For example, a membrane prepared at a pH of 5.0 using the 4‐h‐etched GO (HGO‐4h) shows He permeability of 5.3 Barrer and He/CH4selectivity of 800, which are 5 times and 1.5 times those of the GO membranes, respectively. Decreasing the pH from 5.0 to 2.0 for HGO‐4h enhances He permeability to 57 Barrer and He/CH4selectivity to 1,800. The HGO‐4h prepared at the pH of 2.0 exhibits separation properties of H2/CO2, H2/N2, He/N2, and He/CH4surpassing their corresponding upper bounds.
