Investigation of ZIF‐78 Morphology and Feed Composition on the Mixed Gas CO₂/N₂ Separation Performance in Mixed Matrix Membranes

Abstract

organic linkers. The obtained ordered organic-inorganic networks exhibit high surface areas and their pore size, aperture and functionality is highly tunable, due to the variability in available organic linkers. [1] For example, a series of iron(III) carboxylate MOFs shows varying framework flexibility, pore size, pore aperture, and 3D structure by varying the carboxylate linker type. [2-6] These properties make MOFs very attractive materials in the field of gas storage and separation, since gas sorption and diffusion are tunable by linker variation. [7,8] Despite these promising characteristics, MOFs often lack chemical and thermal stability, which limits their practical application. Nonetheless, the number of stable MOFs has been increasing over the years. [9] One subclass of thermally and chemically stable MOFs are zeolitic imidazolate frameworks (ZIFs), which consist out of zinc or cobalt cations and a variety of imidazolate linkers. Since the first reported ZIFs, many new ZIF structures and topologies have been unraveled. [10] Due to their versatility, stability, and microporous nature (i.e., high gas uptake), multiple ZIF containing membrane structures have been investigated for gas separation purposes. [11,12] By the use of high-throughput synthesis, ZIF structures analogous to the zeolite gmelinite (GME) topology were found, which exhibited extraordinary high CO 2 uptake. [13] These hexagonal anisotropic GME ZIF crystals have two 1D channel types (one pore exists out of KNO cages, with pore apertures ranging from 4.5 to 8 Å, the other out of alternating GME and HPR cages, with pore apertures ranging from 3.6 to 4.3 Å) that are oriented parallel along the c-axis of the crystal structure (Figure 1). [14,15] GME ZIFs are constructed by linking Zn 2+ with 2-nitroimidazolate (nIm) and another imidazolate linker, where the other imidazolate linker determines the pore size, aperture, and polarity. [13,14] Controlling size and shape of the mixed linker ZIFs is rather difficult, since the difference in pK a values between the variable imidazoles and 2-nitroimidazole (nIm) causes different degrees of deprotonation in the reaction mixture. [16] Nonetheless, for ZIF-69 and 78 (both with GME topology) it was shown that their size and aspect ratio could be controlled by using specific zinc salts and deprotonating agents and adapting the ratio between zinc and the imidazoles. [17-19] In this work, the influence of the zeolitic imidazolate framework 78 (ZIF-78) morphology, with 1D pores, on the mixed matrix membrane (MMM) CO 2 /N 2 mixed gas separation performance is investigated as well as the influence of the feed composition and pressure. Low aspect ratio and a high aspect ratio ZIF-78 particles are synthesized and incorporated in Matrimid with 10 and 20 wt% additive content. High pressure CO 2 and N 2 sorption measurements show that both the low and high aspect ratio ZIF-78 metal-organic frameworks (MOFs) exhibit similar sorption behavior. The incorporation of ZIF-78 into Matrimid results in improved CO 2 permeabilit...

Aqueous One-Step Modulation for Synthesizing Monodispersed ZIF-8 Nanocrystals for Mixed-Matrix Membrane

“…The polyimide Matrimid 5218, which is a widely used commercial membrane material with good intrinsic gas separation performance, is adopted as the polymer matrix in this work. 26 ZIF-8-DA/Matrimid composites exhibited higher gas selectivity and permeability than the pristine Matrimid and ZIF-8/Matrimid films, indicating an excellent interfacial adhesion between the newly synthesized ZIF-8-DA and Matrimid. This DA-modulated ZIF-8 synthesis protocol provides a simple but effective way to yield monodispersed ZIF-8 nanoparticles with improved interfacial compatibility with a polymer matrix for gas separations.…”

“…We further investigated the dispersion of the synthesized ZIF-8-DA nanoparticles in a polyimide matrix, Matrimid. The polyimide Matrimid 5218, which is a widely used commercial membrane material with good intrinsic gas separation performance, is adopted as the polymer matrix in this work . ZIF-8-DA/Matrimid composites exhibited higher gas selectivity and permeability than the pristine Matrimid and ZIF-8/Matrimid films, indicating an excellent interfacial adhesion between the newly synthesized ZIF-8-DA and Matrimid.…”

A Review on Removal of Carbon Dioxide (CO2) using Zeolitic Imidazolate Frameworks: Adsorption and Conversion via Catalysis

“…Polymer enhances the adsorption capacity and selectivity and can also be used as a binder to strengthen the adhesion between ZIFs and the substrate. ZIF-78 improved CO2 permeability's up to 39% in the Matrimid ® membrane without a significant decrease in the selectivity of pure Matrimid ® membranes [162] . Notes: barrer, 10 −10 cm 3 (STP) cm cm −2 s −1 cmHg −1 .…”

“…The morphology of ZIF materials exhibits an insignificant effect on CO2 adsorption [162] . The low and high aspect ratio ZIF-78 showed similar CO2 adsorption behavior [162] . However, leaf-like ZIF (ZIF-L) with 2D morphology exhibited high CO2 adsorption.…”

“…Several polymers and their blend were reported, including polyether-block-amide (PEBA2533) polymer [159] , Pebax-1657 [160] , Pebax ® 2533 [161] , Matrimid ® [162] , polysulfone [163] , and Matrimid ® /polysulfone blend [164] . Polymer and inorganic supports were also reported for poly(vinyl chloride)-poly(oxyethylene methacrylate) (PVC-POEM)/alumina [165] .…”