Modification of covalent organic frameworks with dual functions ionic liquids for membrane-based biogas upgrading
Graphical abstract
Introduction
Biogas is an alternative renewable and clean energy source that can alleviate the problem of depletion of fossil energy resources and environmental pollution [1]. Among the various upgrading technologies, membrane separation has attracted much attention for its relatively low energy consumption and small footprint. High-performance membrane materials are urgently demanded for efficient membrane-based biogas upgrading [2]. Covalent organic frameworks (COFs) are a kind of burgeoning crystalline material with permanent porosity, which are constructed from pure organic building blocks through strong covalent bonds by light elements [3]. COFs have drawn immense attention in recent years for gas storage and separation because of their unique properties such as ordered and adjustable pore structure, large surface area and facilely tailorable functionality [4]. Schiff-based COFs, formed by Schiff-base reaction, is a major type of COFs with outstanding thermal and chemical stability such as COF-300 and CTF-1 [[5], [6], [7]]. These merits make COFs suitable for applications under harsh conditions and excellent candidates for fabrication of highly efficient gas separation membranes. Gascon et al. introduced an azine-linked COF (ACOF-1) into Matrimid® 5218 to prepare MMMs for CO2/CH4 separation [8]. Compared to the pristine membrane, the ACOF-1/Matrimid® 5218 membrane showed a one-fold increase in CO2 permeability because of fast transport of gases through the filler pores, coupled with a slightly increased CO2/CH4 selectivity owing to the CO2-philic properties of these porous fillers. However, further improving separation performance of COFs-based MMMs is a challenge due to the limited functional groups on the frameworks and relatively larger pore size (0.6–4.8 nm) [9] than gas molecules (0.26–0.5 nm). The appropriate modification of COFs aiming towards target separation mixtures is considered as an effective strategy, which could remedy the shortages of the individual materials and generate new properties that can never be reached through the single component.
Taken both the diffusivity and solubility of gas molecules into consideration, modification of the pore walls of COFs with appropriate species or functional groups offers a promising alternative. Jiang et al. demonstrated a strategy to enhance the CO2 adsorption on COF by converting the hydroxyl groups in COF ([HO]100%-H2P-COF) into carboxylic acid groups ([HO2C]100%-H2P-COF) [10]. The pore size was reduced from 2.5 nm to 1.4 nm after conversion, and the stronger affinity of carboxylic acid groups towards CO2 led to a 5-fold dramatic increase of adsorption capacity. The [HO2C]100%-H2P-COF showed a high CO2/N2 selectivity of 77, whereas [HO]100%-H2P-COF exhibited a selectivity of only 8 at 100 kPa. Although this chemical conversion/modification is effective, it might lead to transformation of crystal structure and dissolution of parent materials during the bond breaking-forming process [11]. Therefore, modification of COFs with a simple and effective method to regulate physiochemical microenvironment of COFs is highly desired.
Ionic liquids (ILs) are organic salts which consist of cations and anions in liquid phase [12]. ILs have become promising candidates in CO2 capture and separation, owing to their unique properties such as high CO2 solubility and nonvolatility [13]. The solubility of CO2 in some imidazolium-based ILs can exceed 1 mol/mol ILs, more than three orders of magnitude higher than that in water (only 0.0007 mol/mol water) at 20 °C, 1 bar [12], due to a weak anion Lewis acid/base complexation between CO2 and IL [14]. Compared with the conventional methyldiethanolamine (MDEA) absorption technology, the IL-based CO2 capture process could reduce the total energy by 66%, including electricity and thermal energy [15]. Besides direct application as absorbent, combination of membranes and ILs are expected to play a leading role in cost-effective, energy efficient and simple CO2 separation technology. Jonathan Albo et al. [14,[16], [17], [18]] have extensively studied various ILs with different supports for CO2 separation, which exhibited high permeation and selectivity towards CO2 and good long-term stability. ILs have also been incorporated into porous materials as cavity occupants or binding agents to improve the physicochemical property and gas affinity [19]. Ban et al. [20] and Li et al. [21] reported a strategy to synchronously improve CO2 permeability and selectivity through combining ILs with MOF cages. The design of modification in fillers has been demonstrated to be an effective method in enhancing the MMMs separation performance. However, as far as we know, there is no previous report about COFs with ILs to form COF composites to enable the fabrication of high-performance MMMs.
Herein, we envisage that COFs modified with ILs will afford a superior separation performance for the CO2-based gas mixture based on the dual functions of narrowing pore size and elevating CO2 solubility. Modification of the porous COF-300 with an IL, 1-butyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl)imide ([bmim][Tf2N]), via a post-impregnation method is demonstrated. The [bmim][Tf2N] is featured by its intrinsic high CO2 solubility. The resultant IL@COF-300 composite particles are incorporated into Pebax matrix to prepare MMMs for CO2/CH4 separation from biogas, which is an important process for sustainable and energy-saving biofuel manufacturing in order to replace fossil fuels [22]. These membranes show high performance for CO2/CH4 mixture separation and a good long-term operating stability.
Section snippets
Materials
Terephthaldehyde and tetra-(4-anilyl)-methane are purchased from Changchun Sanbang Co., Ltd (China). Anhydrous dioxane, acetic acid and anhydrous tetrahydrofuran are bought from Beijing Bailingwei Co., Ltd (China). 1-butyl-3-methylimidazolum bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]) is obtained from Aladdin Industrial Co. (China). Pebax® MH 1657 consisted of polyamide 6 (PA6, 40 wt%) and polyethylene oxide (PEO, 60 wt%) is offered by Tianjin Kelaite Co., Ltd. (China). Methanol and
Modification of COF-300 with [bmim][Tf2N]
The IL@COF-300 particles are synthesized by post-impregnation method. Notably, [bmim][Tf2N] is diluted by methanol before impregnation in order to decrease their viscosity and to facilitate gases diffusion [19]. As shown in Fig. 1, the morphology of the COF-300 and IL@COF-300 particles is characterized by SEM and TEM. The COF-300 particles reveal an oblong shape and the average size of particles is in the range of 1–2 μm approximately, as confirmed by Fig. 1 (a) and Fig. 1 (b). The IL@COF-300
Conclusion
We propose a strategy of modifying COF-300 by utilizing IL with high CO2 solubility through post-impregnation to fabricate the IL@COF-300/Pebax membranes. The pore size of COF-300 decreases from 1.28 nm to 1.09 nm after IL modification, which restricts the diffusion of the larger CH4 molecules more than CO2 molecules, and thus increasing the diffusion difference between CO2 and CH4. In addition, the IL has strong interaction with CO2 on the COF pore walls and thus remarkably elevating the CO2
CRediT authorship contribution statement
Rui Zhao: Conceptualization, Methodology, Software, Investigation, Writing - original draft. Hong Wu: Supervision. Leixin Yang: Formal analysis. Yanxiong Ren: Formal analysis. Yutao Liu: Visualization. Zihan Qu: Data curation. Yingzhen Wu: Data curation. Li Cao: Validation. Zan Chen: Validation. Zhongyi Jiang: Writing - review & editing, Project administration.
Declaration of competing interest
The authors declare no conflict of interest.
Acknowledgements
Greatly acknowledge the financial support of National Natural Science Foundation of China (21878215, 21621004), National Key R & D Program of China (2017YFB0603400), National Key Laboratory of United Laboratory for Chemical Engineering (SKL-ChE-17B01) and State Key Laboratory of Organic–Inorganic Composites (oic-201701004).
References (51)
- et al.
Techno-economic analysis and performance comparison of aqueous deep eutectic solvent and other physical absorbents for biogas upgrading
Appl. Energy
(2018) - et al.
A new degassing membrane coupled upflow anaerobic sludge blanket (UASB) reactor to achieve in-situ biogas upgrading and recovery of dissolved CH4 from the anaerobic effluent
Appl. Energy
(2014) - et al.
Porous Al2O3/TiO2 tubes in combination with 1-ethyl-3-methylimidazolium acetate ionic liquid for CO2/N2 separation
Separ. Purif. Technol.
(2014) - et al.
Acetate based supported ionic liquid membranes (SILMs) for CO2 separation: influence of the temperature
J. Membr. Sci.
(2014) - et al.
Separation performance of CO2 through supported magnetic ionic liquid membranes (SMILMs)
Separ. Purif. Technol.
(2012) - et al.
Simultaneous enhancement of mechanical properties and CO2 selectivity of ZIF-8 mixed matrix membranes: interfacial toughening effect of ionic liquid
J. Membr. Sci.
(2016) - et al.
Application of interfacially polymerized polyamide composite membranes to isopropanol dehydration: effect of membrane pre-treatment and temperature
J. Membr. Sci.
(2014) - et al.
Gas transport properties of interfacially polymerized polyamide composite membranes under different pre-treatments and temperatures
J. Membr. Sci.
(2014) - et al.
Synergistic effect of combining carbon nanotubes and graphene oxide in mixed matrix membranes for efficient CO2 separation
J. Membr. Sci.
(2015) - et al.
The effects of polymer chain rigidification, zeolite pore size and pore blockage on polyethersulfone (PES)-zeolite A mixed matrix membranes
J. Membr. Sci.
(2005)
Nanoporous ZIF-67 embedded polymers of intrinsic microporosity membranes with enhanced gas separation performance
J. Membr. Sci.
Janus composite nanoparticle-incorporated mixed matrix membranes for CO2 separation
J. Membr. Sci.
A study of gas transport through interfacially formed poly(N,N-dimethylaminoethyl methacrylate) membranes
Chem. Eng. J.
Porous, crystalline, covalent organic frameworks
Science
A 2D mesoporous imine-linked covalent organic framework for high pressure gas storage applications
Chem. Eur J.
A GO-assisted method for the preparation of ultrathin covalent organic framework membranes for gas separation
J. Mater. Chem. A.
A crystalline imine-linked 3D porous covalent organic framework
J. Am. Chem. Soc.
The atom, the molecule, and the covalent organic framework
Science
Azine-linked covalent organic framework (COF)-based mixed-matrix membranes for CO2/CH4 separation
Chem. Eur J.
Harnessing filler materials for enhancing biogas separation membranes
Chem. Rev.
Two-dimensional covalent organic frameworks for carbon dioxide capture through channel-wall functionalization
Angew. Chem. Int. Ed.
Covalent organic frameworks as a platform for multidimensional polymerization
ACS Cent. Sci.
Ionic-liquid-based CO2 capture systems: structure, interaction and process
Chem. Rev.
Carbon capture with ionic liquids: overview and progress
Energy Environ. Sci.
Ionic liquid design and process simulation for decarbonization of shale gas
Ind. Eng. Chem. Res.
Cited by (54)
Research progress of covalent organic framework-base membranes in the last five years
2024, Coordination Chemistry ReviewsMOFs/COFs hybrids as next-generation materials for electrocatalytic CO<inf>2</inf> reduction reaction
2024, Chemical Engineering JournalPIM-based mixed matrix membranes containing covalent organic frameworks/ionic liquid composite materials for effective CO<inf>2</inf>/N<inf>2</inf> separation
2024, Separation and Purification Technology