The influence of pore aperture, volume and functionality of isoreticular gmelinite zeolitic imidazolate frameworks on the mixed gas CO2/N2 and CO2/CH4 separation performance in mixed matrix membranes

Machiel Van Essen,Luuk Van Den Akker,Raymond Thür,Menno Houben,Ivo F.J Vankelecom,Zandrie Borneman,Kitty Nijmeijer

doi:10.1016/j.seppur.2020.118103

Machiel Van Essen, Luuk Van Den Akker + Show 5 more

Open Access

https://doi.org/10.1016/j.seppur.2020.118103

Copy DOI

Abstract

Zeolitic imidazolate frameworks (ZIFs), a subclass of metal–organic frameworks (MOFs), have been widely investigated as additive in mixed matrix membranes (MMMs), but systematic studies to identify critical intrinsic ZIF-type parameters that determine the MMM performance are lacking. Therefore, three isoreticular gmelinite (GME) ZIFs, i.e., ZIF-68, 69 and 78 that are distinct by their partial different imidazolate linkers, were incorporated in Matrimid matrices to systematically elucidate the effects of the varying pore aperture, pore diameter, pore volume and functionality of the ZIFs on the CO2/N2 and CO2/CH4 MMM mixed gas permeability. The incorporation of the ZIFs in Matrimid increases the CO2 permeability for all MMMs for both CO2/N2 and CO2/CH4 feed mixtures without compromising the selectivity. The highest increase in CO2 permeability is observed for the 20 wt% ZIF-68 MMM, with an increase in CO2 permeability of 116% for CO2/N2 feed and 122% for CO2/CH4 feed relative to Matrimid was achieved and surpassed the permeability of conventional ZIF-8/Matrimid MMMs. Regarding the isoreticular ZIF series, the results showed that for a higher permeability a larger pore aperture, diameter and volume of the ZIFs in the MMMs are more beneficial than a more polar functionality with smaller pore size, aperture and volume.

Highlights

The inevitable transition towards renewable energy sources and the necessary reduction of the effects of greenhouse gases make the field of gas separation highly relevant [1]
Three isoreticular gmelinite (GME) Zeolitic imidazolate frameworks (ZIFs), i.e., ZIF-68, 69 and 78 that are distinct by their partial different imidazolate linkers, were incor porated in Matrimid matrices to systematically elucidate the effects of the varying pore aperture, pore diameter, pore volume and functionality of the ZIFs on the CO2/N2 and CO2/CH4 matrix membranes (MMMs) mixed gas permeability
Regarding the isoreticular ZIF series, the results showed that for a higher permeability a larger pore aperture, diameter and volume of the ZIFs in the MMMs are more beneficial than a more polar functionality with smaller pore size, aperture and volume

Summary

Introduction

The inevitable transition towards renewable energy sources and the necessary reduction of the effects of greenhouse gases make the field of gas separation (e.g., separation and purification of CO2 and CH4) highly relevant [1]. A promising way to overcome this trade-off is the incorporation of additives (e.g., zeolites, carbon nanotubes and metal–organic frameworks (MOFs)) into polymer matrices, forming mixed matrix membranes (MMMs) [5]. One of these additive examples, MOFs, are microporous crystalline materials, which consist out of metal cations linked by organic anions [1]. These micro porous networks generally exhibit high surface areas and gas uptake and are capable of molecular sieving, due to well-defined pore sizes and apertures [6]. The presence of organic linkers enables various strategies to fine tune pore size and aperture as well as the pore polarity of ZIFs [9,10,11]

Methods

Results

Conclusion