Functionalized filler/synthesized 6FDA-Durene high performance mixed matrix membrane for CO2 separation

https://doi.org/10.1016/j.jiec.2020.10.033Get rights and content

Highlights

  • Surface modification of the filler via the aminosilane coupling agent was considered.

  • Zeolite 13X particles were functionalized by 3-aminopropyl(diethoxy)methylsilane.

  • Functionalized filler was embedded into the synthesized 6FDA-Durene polyimide (PI).

  • CO2 permeability of 887 Barrer and CO2/N2 selectivity of 25.3 were achieved.

  • The mechanical properties of MMMs were improved after filler modification.

Abstract

Modifying the polymer-filler interface is an efficient strategy to enhance the gas separation performance of zeolite-filled mixed matrix membranes (MMMs) by overcoming the interfacial defects. In this study, zeolite 13X particles were modified with 3-aminopropyl(diethoxy)methylsilane (APDEMS) and subsequently embedded into the synthesized 6FDA-Durene polyimide (PI) to prepare MMMs. The characteristic properties of modified zeolite particles and fabricated MMMs were investigated via FTIR, XRD, BET, DLS and SEM analyses. Moreover, the separation performance of resultant membranes was studied for CO2/N2 separation considering filler content (0–20 wt.%) at different feed pressure in the range of 0.2 to 1 MPa. The best separation performance was obtained by embedding 15 wt.% of aminosilanized zeolite 13X (ASZX) into the PI membrane that exhibits the excellent CO2 permeability of 887 Barrer and CO2/N2 selectivity of 25.3 at the feed pressure of 0.2 MPa. These values increased by about 95% and 81%, respectively compared to those for pure PI membrane. In addition, the thermomechanical properties of MMMs were improved after aminosilane modification of zeolite particles. Surface modification of the zeolite particles via the aminosilane coupling agents can be considered as a suitable strategy to improve filler/polymer interfacial adhesion which consequently increases the CO2 adsorption through the CO2-amine interactions.

Introduction

The emission of carbon dioxide (CO2) greenhouse gas is one of the most important challenges of today’s environmental concerns [1]. Membrane gas separation technology has grown rapidly during the recent decades because of many noteworthy advantages over conventional carbon capture technologies such as higher separation performance, simplicity of scale-up, lower costs and fewer environmental challenges [2], [3]. Mixed matrix membranes (MMMs) comprised of an inorganic (dispersed filler) phase dispersed into a polymeric (continuous matrix) phase, demonstrate superior separation properties. MMMs are benefited from both the constituent advantages; acceptable mechanical properties and low fabrication cost of polymeric materials together with excellent gas separation characteristics of inorganic materials make the MMMs to be distinguished as great potentials for gas separation applications [4], [5], [6].

Glassy polyimides (PIs) are one of the most attractive materials for MMMs preparation due to their excellent permeability, chemical and thermal stability and acceptable mechanical properties. Polar imide functional groups have high affinity with electrons of polar components which provides a suitable situation for the separation of polar components from a mixture [7], [8], [9]. Aromatic PIs consisting of a rigid backbone with bulky structure exhibit very high permeability with moderate selectivity for gas separation applications [10]. Among them, highly permeable 4,4 -(hexafluoroisopropylidene) diphthalic anhydride (6FDA)-based PIs offer excellent gas separation properties including high thermal and mechanical properties [11]. Until now, various microporous materials have been employed to enhance the separation performance of PI based MMMs [4]. Liu et al. [12] incorporated zeolite-like MOF nanocrystals as a filler into different 6FDA-based PI membranes and found the porous and CO2-philic framework of zeolite-like MOFs could remarkably enhance the separation performance of 6FDA-based MMMs. Japip et al. [13] reported an increase up to 3-fold in CO2 permeability of the 6FDA-Durene membrane by embedding 20 wt.% of ZIF-71 nanoparticles, while Nafisi et al. [14] reported an increase of 38% for ZIF-8 filled MMMs at the same filler loading. Both studies revealed that embedding of ZIF particles decreased the CO2/N2 selectivity of MMMs compared to pure 6FDA-Durene PI membrane.

Zeolite molecular sieves are one of the most commonly used inorganic fillers owing to their suitable properties such as high chemical and thermal stability, high mechanical strength and well-defined porous microstructure that results in higher diffusivity compared to polymeric materials [15], [16], [17], [18]. Zeolites with larger pore sizes such as zeolite 13X could facilitate gas molecule transport through membranes and increase the permeability [19]. McEwen et al. [20] investigated the adsorption isotherms of CO2, CH4 and N2 in ZIF-8, zeolite 13X and BPL activated carbon. They found that zeolite 13X has a higher gas adsorption capacity compared to BPL and ZIF-8, and also, a higher selectivity for CO2 over CH4 and N2. This is motivated us to use zeolite 13X as a dispersed phase to fabricate 6FDA-Durene PI MMMs.

Despite of favorable properties of MMMs, their performance suffers from poor filler-polymer adhesion because of different characteristics of inorganic and polymeric phases [21]. In this regard, different techniques such as annealing [22], priming [23], the addition of low molecular weight organic compounds [24], [25], [26], utilization of copolymers [27], [28] and treating with silane coupling agents [29], [30] have been employed to improve the zeolite-polymer adhesion and eliminate the unselective gaps [31]. Silane coupling agents are silicon containing materials that are comprised of both organic and inorganic groups, which are capable to modify the interfacial region through bridging between zeolite and polymeric matrix [32]. Aminosilane agents make hydrogen bonds with the hydroxyl group of zeolite structure. In addition, aminosilanes have amine reactive end groups that are proper choices for CO2 separation applications due to the CO2-favored characteristic of amine units [33].

This work aims to enhance the CO2/N2 separation performance of synthesized 6FDA-Durene based MMMs through surface modification of zeolite particles. To the best of our knowledge, this is the first report of employing aminosilanized zeolite 13X for improving the separation properties of 6FDA-Durene based MMMs. The structure of this manuscript is organized as follows; in the experimental section, the procedures of PI synthesis, zeolite 13X modification and the MMMs fabrication were described. The characterization methods and gas permeation experiments were explained. In the results and discussion section, the physical and chemical properties of modified zeolite particles were evaluated by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), dynamic light scattering (DLS), and scanning electron microscope (SEM). Subsequently, the modified particles were incorporated (from 0 to 20 wt.%) to 6FDA-Durene polyimide and the fabricated MMMs were characterized by FTIR spectroscopy, XRD, differential Scanning Calorimetry (DSC) and SEM. In addition, gas separation performances of MMMs were examined for CO2/N2 separation considering the filler content as well as operating pressure (0.2-1 MPa). Moreover, the mechanical properties of prepared MMMs were determined. Lastly, in the conclusion section, the results are briefly summarized and the main conclusion of this research was expressed.

Section snippets

Materials

4,4̕-(Hexafluoroisopropylidene) diphthalic anhydride (6FDA), 2,3,5,6-tetramethyl-p-phenylenediamine (Durene diamine), 3-Aminopropyl (diethoxy) methylsilane (97%, APDEMS), acetic anhydride (≥99%), acetylacetone (≥99.3%), triethylamine (TEA, ≥99.5%) and molecular sieve 13X (2 μm average particle size) were purchased from Sigma-Aldrich Co. N,N-dimethylacetamid (DMAc), methanol, ethanol and chloroform were HPLC grade and acquired from Daejung Chemicals and Metals Co. (South Korea). Carbon dioxide

Characterization of Zeolite Particles

The FTIR spectra of pure APDEMS agent, zeolite 13X and ASZX are shown in Fig. 2(A). Characteristic bands of APDEMS are located at 1075, 1100 and 1165 cm−1 (Sisingle bondOsingle bondC2H5 stretching), 1258 cm−1 (Sisingle bondCH2 stretching, alkoxy Csingle bondCsingle bondO stretching), 1297 cm−1 (Sisingle bondCH3 stretching), 3485 cm−1 (N-H stretching), 1575 cm−1 (Nsingle bondH bending) and 750 to 950 cm−1 (Csingle bondO stretching), 2879, 2926 and 2973 cm-1 (asymmetric stretching of single bondCH, single bondCH2 and single bondCH3), 1390 and 1482 cm−1 (single bondCH3 and single bondCH2 bending) [35]. Spectrum (b) shows the characteristic bands

Conclusions

The effect of aminosilane modification of 13X zeolite particles on membrane characteristic and gas separation properties of 6FDA-Durene polyimide based mixed matrix membranes (MMMs), filled with pure 13X zeolite and the aminosilane modified ones (ASZX), were investigated. The FTIR, XRD, DLS and SEM analyses were performed on zeolite particles and fabricated MMMs to characterize them after modification. The analysis results confirmed the proper silane modification reaction of zeolite particles.

Conflict of interests

The authors declare that they have no known Conflict of Interest.

Declaration of Competing Interest

The authors report no declarations of interest.

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