Key Takeaways & Executive Findings
- •• Covalent integration of ZIF-8-NH2 with Kapton polyamide acid eliminates filler aggregation, enabling high filler loading (45% mass) without compromising membrane integrity. • The optimized MMM achieves H2 permeability of 297 barrer and H2/N2 and H2/CH4 selectivities of 43.9 and 62.2, respectively, surpassing the Robeson 2008 upper bound. • The covalent bridging between filler and polymer matrix creates a defect-free interface, significantly improving gas separation performance. • This work provides a novel strategy for fabricating high-performance MMMs for hydrogen purification and other gas separation applications.
Abstract
Zeolitic imidazolate framework-8 (ZIF-8) is a typical filler used to fabricate mixed matrix membranes (MMMs) on account of its attractive advantage of high selective permeability for gas separation. However, the performance is usually affected by filler aggregation due to strong interactions among fillers and weak interactions between the polymer and fillers, which will lead to a decrease of selectivity and the performance of gas separation will be strongly influenced. Herein, we modified ZIF-8 with 3-amino-1,2,4-triazole to obtain ZIF-8-NH2, Kapton polyamide acid was selected as the polymer matrix. Results showed that the ZIF-8-NH2/Kapton MMMs has a good compatibility interface between ZIF-8 and Kapton because of the covalent bridging, even the filler loading up to 45% (mass). The 45% (mass) of ZIF-8-NH2/Kapton membrane showed 297 barrer (1 barrer = 10^-10 cm3·cm·cm^-2·s^-1·cmHg^-1, 1 cmHg = 1333.22 Pa, standard temperature and pressure) of the permeability of H2 and 43.9 and 62.2 of selectivities for H2/N2 and for H2/CH4, respectively, which are beyond the upper limit of Robeson 2008.
1. Introduction
At present, the global warming due to the excessive emission of CO2 is becoming more and more serious. Searching for a clean energy source is highly attractive for addressing the growing environmental problems [1]. H2, a green energy source, has a higher energy density than conventional fuels, and typically requires a further purification through a series of separation technologies to meet usage towards high purity [2]. In comparison to the conventional adsorption and distillation, membrane technology offers distinct advantages e.g. low energy consumption, simple operation, easy scalability, and a smaller footprint [3].
Membrane material dominates the whole process economy for gas purification, and especially, polymeric membranes are widely used due to a great processability and low price [4]. The organic microporous materials play an important role in mass transfer due to their unique properties, such as the gas permeability and Brunauer-Emmett-Teller (BET) surface area [5]. Li et al. [6] fabricated a polydimethylsiloxane healed BTDA-TDI/MDI (P84) membranes with selectivities for H2/CH4 and H2/N2 3.4 and 3.7 times of P84 without being healed, respectively. Li et al. [7] synthesized the hyper cross-linked polyimide modified with -NH2 to improve CO2 separation, which reached a permeability of 77.56 barrer (1 barrer = 10^-10 cm3·cm·cm^-2·s^-1·cmHg^-1, 1 cmHg = 1333.22 Pa, standard temperature and pressure (STP)) for CO2. Generally, more complex multistep operations are necessary for a lower selectivity, while the membrane productivity is correlated with the permeability, and thus the required number of modules and the membrane area are determined [4,8]. Unfortunately, a “trade-off” effect limits the separation performance of polymeric membranes, namely membrane with a high permeability usually results in a low selectivity and vice versa [9-11]. This theory was described as Robeson upper bound plot for gas separation described in polymeric membranes [12].
Mixed matrix membranes (MMMs) are developed by doping specific nano/micron-sized particles in the polymeric matrix, where the conspicuous processability of polymer and the permeability of fillers are combined. Metal-organic frameworks (MOFs) membranes generally exhibit higher gas permeability and selectivity than the conventional polymeric membranes, owing to their uniform channel structure, appropriate pore size for the transfer of gases. For instance, Jheng et al. [13] blended zirconium 1,4-dicarboxybenzene MOF into immiscible 4,4’-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) polyimide and when the loading reached 35% (mass) of the filler, the permeability towards CO2 attained 104.7 barrer and the selectivities of CO2/CH4 and CO2/N2 are 31.7 ± 5.8, 16.5 ± 1.5 respectively. Ehsani and Pakizeh [14] used the MOF micron particles of zeolitic imidazolate framework-11 as the filler and Pebax as the polymer matrix to fabric MMM, they found the performance of gas separation of H2
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Guozhen Li, Shiqi Ling, Yuhui Cui, Shilong Dong, Tianyin Liu, Ting Li, Siyu Pang, Peiyong Qin (2024). A covalently integrated ZIF-8/polyamide acid mixed matrix membrane with superior gas separation performance. Chinese Journal of Chemical Engineering. https://doi.org/10.1016/j_cjche_144878629
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Frequently Asked Questions
What is the main innovation of this paper?
The main innovation is the covalent integration of ZIF-8-NH2 with Kapton polyamide acid, which eliminates filler aggregation and creates a defect-free interface, enabling high filler loading (45% mass) and superior gas separation performance.
What gas separation performance was achieved?
The optimized membrane achieved H2 permeability of 297 barrer and H2/N2 and H2/CH4 selectivities of 43.9 and 62.2, respectively, surpassing the Robeson 2008 upper bound.
Why is ZIF-8 modified with 3-amino-1,2,4-triazole?
Modification introduces amino groups that covalently bond with the polyamide acid matrix, improving interfacial compatibility and preventing filler aggregation.
What is the significance of surpassing the Robeson upper bound?
Surpassing the Robeson upper bound indicates that the membrane achieves a better trade-off between permeability and selectivity than most polymeric membranes, making it promising for industrial gas separation applications.
What are the potential applications of this membrane?
The membrane is particularly suitable for hydrogen purification from gas mixtures (e.g., H2/N2 and H2/CH4), which is relevant to clean energy production and petrochemical processes.
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