Shaped composites of citric acid based mofs and their applications

Abstract

The invention relates to a shaped, extruded, MOF composite article comprising the MOF of formula K2(M1xM21-x)3(Cit)2, where Cit is fully dehydrogenated citrate anion, M1 and M2 are metal cations, x is from 0 to 1.0, and a water-insoluble polymer. The shaped MOF composite article may have the shape of a fiber, sheet, bead or pellet.

Description

[0001] Shaped composites of citric acid based MOFs and their applications

[0002] Technical Field

[0003] The invention relates to a shaped MOF composite article, a method of making same, and a process for removing an acid gas from a fluid stream using the shaped MOF composite article.

[0004] Technical background

[0005] Carbon capture, utilization and storage (CCLIS) generally refers to various technologies believed to play an important role in meeting global energy and climate goals. For instance, these technologies are considered by many as essential in keeping global temperature increases below 1 .5 °C.

[0006] CCLIS involves capturing CO2 from diluted gas streams, such as flue gas, air, etc. In the case of flue gas, the CO2 concentration is in the range of 8 to 14 volume %; in the case of ambient atmospheric air, the CO2 concentration is about 450 ppm. Currently, the upfront cost for CO2 capture from a variety of streams is more than 80% of the total CCUS costs. In the case of direct air capture, the upfront cost for CO2 capture is almost 99% of the total CCUS cost.

[0007] The primary method for CO2 capture involves aqueous amine based solvent systems. However, these amine-based systems suffer from high energy loss from regenerating the solvent (due to boiling and condensing 70% of water). Another significant energy penalty is the energy consumed for pumping a large amount of viscous solvents during solvent circulation. Furthermore, solvent based systems suffer from water loss and solvent loss and large amount of water and solvent-have to be replenished. Also, the solvent loss itself contributes to global emissions and is a potential health hazard. A discussion of disadvantages associated with these techniques can be found in review articles such as: “Water- lean solvents for postcombustion CO2 capture: fundamentals, uncertainties, opportunities, and outlook”, D. J. Heldebrant et al Chem. Rev., 2017, 117, 14 , 9594-9624; and “Ionic liquid based CO2 capture systems: structure, interaction and process”, S. Zeng et al. Chem. Rev., 2017, 117, 14,9625-9673.

[0008] Solid adsorbents, such as metal organic frameworks (MOFs), diamine- appended MOFs, covalent organic frameworks (COFs), zeolites, porous silicas or porous polymeric powders have attracted significant attention, as they can potentially achieve a high adsorption efficiency with much less energy consumption.

[0009] UTSA-16 traditionally referred to a MOF derived from citric acid and cobalt. In this application, UTSA-16 is utilized as a general term to refer all MOF materials derived from citric acid, and the term UTSA-16(Co) is used to refer to the MOF derived from citric acid and cobalt. UTSA-16(Co) is a solid adsorbent for CO2 capture owning to its isotherm features, mechanism of adsorption, and stability:

[0010] - “Micro porous metal-organic framework with potential for carbon dioxide capture at ambient conditions”, S. Xiang et al., Nature Comm., 2012, 3, 954;

[0011] - “CO2 Adsorption Sites in UTSA-16: Multitechnique Approach”, A. Masala et al., J. Chem. Phy. C, 2016, 120, 22,12068-12074;

[0012] - “CO2 capture in dry and wet conditions in UTSA-16 metal organic framework’, A. Masala et al., ACS Appl. Mater. Interfaces, 2017, 9, 1 455- 463.

[0013] This material exhibits a higher selectivity toward CO2 adsorption, even in the presence of water. UTSA-16 retains 70% of its CO2 separation potential in the presence of moisture. The chemical structure of UTSA-16(Co) has been confirmed to be “[K2Co3(Cit)2]”, see “New insights into UTSA-16", by A. Masala et al., Phys. Chem. Chem. Phys., 2016, 18, 220-227. More recently, the MOF UTSA-16(Zn) and bimetallic MOF UTSA-16 (Zn / Co) have been found to exhibit a similar CO2 separation performance to that of the original UTSA-16(Co):

[0014] - “Novel metal-organic framework of UTSA-16 (Zn) synthesized by a microwave method: Outstanding performance for CO2 capture with improved stability to acid gases", by S. Gaikwad et al., J. Ind. Eng. Chem., 2020, 87, 250-263;

[0015] - “Bimetallic UTSA-16 (Zn, X; X = Mg, Mn, Cu) metal organic framework developed by a microwave method with improved CO2 capture performances", R. Gaikwad et al., J. Ind. Eng. Chem., 2022, 111 , 346-355;

[0016] - Patent application US 20230191365.

[0017] Most recently, novel scalable green methods with high atomic efficiency for the synthesis of UTSA-16 MOFs based on citric acid have been developed. The MOFs have a general formula of K2(M1xM2i-x)3(Cit)2, where Cit is fully dehydrogenated citrate anion, M1 and M2 are metal cations of Zn, Co, Cu, Mg, Ni, Ca, Mn, Cr, Zr, and Fe. The method includes reacting 1 molar equivalent of citric acid with 0 to 1 .0 molar equivalent of metal carbonate and / or metal oxide and 1.5 to 0.5 molar equivalent of a basic potassium compound (e.g., potassium carbonate, potassium bicarbonate and / or potassium hydroxide), where the total molar equivalent of the metal carbonate and potassium carbonate is 1 .5. This step is followed by reacting with a metal salt aqueous solution. The total molar equivalent of the metal carbonate and / or metal oxide and metal acetate is 1 to 1.5. The solvent used is deionized (DI) water. All reaction steps are conducted at a temperature below 100 °C and at ambient pressure.

[0018] Typically, however, powder solid adsorbents such as MOFs cannot be easily utilized in industrial applications. In fact, it has been reported that MOF powders can decrease the pressure within a pipeline, reducing, or even completely blocking the flow. Their use can also lead to abrasions due to powder blowing. A significant reduction of the pure MOF component also has been reported for powder application, along with other issues such as dustiness, clogging, and transfer and handling impediments. A discussion of the above mentioned issues can be found in “Binding materials for MOF monolith shaping processes: A review towards real life application”, \f. Ntouros, et al., Energies, 2022, 15(4), 1489.

[0019] To overcome such problems, solid adsorbent powders can be shaped into beads or pellets, typically from 1 to 6 mm in diameter. Several techniques have been used to shape MOFs, for example:

[0020] - extrusion: “Shaping of ultrahigh-loading MOF pellet with a strongly anti-tearing binder for gas separation and storage", J. Zheng et al., Chem. Eng. J., 2018, 354, 1075-1082,

[0021] - granulation: “A more efficient way to shape metal-organic framework (MOF) powder materials for hydrogen storage applications", J. Ren, et al., Int. J. Hydrogen Energy, 2015, 40, 4617-4622,

[0022] - casting: “Shaping of MOFs via freeze-casting method with hydrophilic polymers and their effect on textural properties", E. Hastiirk et al., Microporous Mesoporous Mat., 2020, 295, 109907.,

[0023] - spray drying: “Aqueous-system-enabled spray-drying technique for the synthesis of hollow polycrystalline ZIF-8 MOF Particles", S. Tanaka and R. Miyashita, ACS Omega, 2017, 2, 10, 6437-6445,

[0024] - phase inversion: “Metal-organic framework-polyacrylonitrile composite beads for Xenon capture”, B. J. Riley et al., ACS Appl. Mater. Interfaces, 2020, 12, 40, 45342-45350, - and 3D printing : “3D printing of cellulose / leaf-like zeolitic imidazolate frameworks (CelloZIF-L) for adsorption of carbon dioxide (CO2) and heavy metal ions", H. N. Abdelhamid, et al., Dalton Trans., 2023, 52, 2988-2998.

[0025] A comprehensive review of these techniques can be found in “Recent advances in the shaping of metal-organic frameworks", X.-M. Liu et al., Inorg. Chem. Front., 2020, 7, 2840-2866.

[0026] Specifically for UTSA-16, three techniques, namely deposition and in-situ growth, 3D printing, and extrusion, have been explored to shape UTSA-16 composites.

[0027] To use the deposition and in-situ growth techniques, a preformed porous support has to be utilized and the MOF loading tends to be low:

[0028] - “Carbon hollow fiber-supported metal-organic framework composites for gas adsorption" S. Lawson et al., Energy Technol. 2018, 6, 4, 694-701 ;

[0029] - “MOF-74 and UTSA-16 film growth on monolithic structures and their CO2 adsorption performance" F. Rezaei etal., Chem. Eng. J., 2017, 313, 1346-1353; and

[0030] - “Electrospun fiber mats with multistep seeded growth of UTSA-16 metal organic frameworks by microwave reaction with excellent CO2 capture performance" R. Gaikwad et al., Microporous Mesoporous Mat. 2021 , 323, 111233.

[0031] UTSA-16 composites shaped by 3D printing techniques using PVA and hydroxypropyl cellulose along with boehmite caused significant CO2 adsorption capacity losses:

[0032] - “Multiscale investigation of adsorption properties of novel 3D printed UTSA-16 structures" C. A. Grande et al., Chem. Eng. J., 2020, 402, 126166; and

[0033] - “3D-printed metal-organic framework monoliths for gas adsorption processes” H. Thakkar et al., ACS Appl. Mater. Interfaces 2017 , 9, 41 , 35908-35916.

[0034] UTSA-16 shaping by extrusion using a water-soluble binder is difficult since a high and constant alcohol-water ratio has to be kept in the pastes to avoid the MOF degradation, and carefully controlling this parameter is challenging:

[0035] - “An efficient recipe for formulation of metal-organic frameworks" C. A. Grande, et al., Chem Eng. Sci., 2015, 124, 154-158; and

[0036] - “Adsorption and diffusion ofl-h, N2, CO, CH4 and CO2 in UTSA-16 metal-organic framework extrudates" V. I. Agueda, et al., Chem Eng. Sci., 2015, 124, 156-159. The shaping procedure using extrusion affects the adsorption properties of the

[0037] MOF crystals due to the interactions with the binder and plasticizers which reduces the surface area of UTSA-16 MOF. The preparation of composite MOF material was recently reported in patent application US 2024 / 0082815 where zirconium-based MOF (MOF 808-gly) was combined with a binder material (either aminopropylsilesquioxane or PVA and PAA) for the capture of gas or fluids.

[0038] The patent application US 2022 / 0370984 relates to a composite MOF material shaped as hollow fibers formed by extrusion from a dope solution. The material comprises magnesium or manganese-based MOF with polymers.

[0039] The preparation of ePS and PPO aerogel composites with UTSA-16(Co) and their applications for CO2 / CH4 separation was recently reported: “Tailoring novel polymer / UTSA-16 hybrid aerogels for efficient CH4 / CO2 separation" C. Atzori et al. Microporous Mesoporous Mat. 2022, 341 , 112106. However, the preparation utilizes chloroform, a highly toxic solvent, the resulting composites lose significant amount of the CO2 adsorption capacity, and the process is difficult to scale for industrial application.

[0040] Shaping MOF composites by a phase inversion process has been explored in the literature as well. The process relies on the use of polar solvents to give uniform sorbent dispersion via sonication, which is ultimately followed by a water quench in the spinning process. These harsh conditions often induce a variety of MOF degradation problems. So far, only MIL-101 (Cr) and UiO-66 have been reported to survive such a shaping procedure while maintaining nearly 90% of the MOF-based capacities “Scalable formation of diamine-appended metal-organic framework hollow fiber sorbents for postcombustion CO2 Capture” W. Quan et al., JACS Au., 2022, 2, 6,1350- 1358.

[0041] Within this context, there is a need for a MOF composite material having a high acid gas adsorption capacity, having a shape suitable for use in various devices such as pipes, and which can be manufactured in a straightforward and reliable manner.

[0042] Summary of the invention

[0043] It is a first object of the invention to provide a shaped, extruded, MOF composite article comprising the MOF of formula K2(M1xM2i-x)3(Cit)2, where Cit is fully dehydrogenated citrate anion, M1 and M2 are metal cations, x is from 0 to 1.0, and a water-insoluble polymer.

[0044] In some variations, the shaped MOF composite article has the shape of a fiber, sheet, bead or pellet. In some variations, M1 and M2 are metal cations belonging to the group of Zn, Co, Cu, Mg, Ni, Ca, Mn, Cr, Zr, and Fe.

[0045] In some variations, the water insoluble polymer is selected from the group consisting of: polysulfone, polyimide, cellulose, polyacrylonitrile, polyvinyl difluoride, polyvinylchloride, and mixtures thereof.

[0046] In some variations, the shaped MOF composite article is a fiber with an outer diameter between 0.5 mm and 10 mm.

[0047] In some variations, the shaped MOF composite article is a flat sheet with a thickness between 0.5 mm and 10 mm.

[0048] In some variations, the shaped MOF composite article is a pellet with an outer diameter between 0.5 mm and 10 mm.

[0049] In some variations, the said MOF is UTSA-16(Zn).

[0050] In some variations, the said MOF is UTSA-16(Co).

[0051] The invention further relates to a method of making a shaped MOF composite article as defined above, comprising forming a dope solution containing the said MOF, the water insoluble polymer, a solvent, and extruding the said dope solution.

[0052] In some variations, the said dope solution is extruded into a water bath.

[0053] In some variations, the method further comprises exchanging the water bath with an alcohol.

[0054] In some variations, the alcohol comprises (or is selected from) methanol, ethanol and / or isopropanol.

[0055] In some variations, said alcohol contains 1 to 50% by weight of water.

[0056] In some variations, the method further comprises drying the shaped MOF composite article, preferably in ambient air.

[0057] In some variations, the solvent is a polar solvent, preferably selected from the group consisting of: DMF, DMAc, NMP, DMSO, THF, and mixtures thereof.

[0058] In some variations, the dope solution further comprises a pore former.

[0059] The invention further relates to the shaped MOF composite article which is obtainable by the above method.

[0060] The invention further relates to a process for removing an acid gas from a fluid stream containing the acid gas, the process comprising contacting the fluid stream with the shaped MOF composite article as defined above, whereby at least a portion of the acid gas is adsorbed by the shaped MOF composite article to produce a purified fluid stream.

[0061] In some variations, the acid gas is CO2, SO2, H2S or mixtures thereof. In some variations, the fluid stream is a flue gas.

[0062] In some variations, the fluid stream is an atmospheric air.

[0063] The invention makes it possible to address the needs expressed above.

[0064] In particular, the invention provides a MOF composite material having a high acid gas adsorption capacity, having a shape suitable for use in various devices such as pipes, and which can be manufactured in a straightforward and reliable manner.

[0065] Advantageously, the MOF composite material is water-stable.

[0066] Advantageously, the MOF composite material contains a relatively high amount of MOF.

[0067] Advantageously, the MOF composite material is in the fiber shape which can be packed into a structured contactor device that exhibits low pressure drop, high mass transfer and heat transfer rates.

[0068] Brief description of the drawings

[0069] Figure 1 illustrates the procedure for the preparation of shaped UTSA-16 MOF composite articles according to some embodiments.

[0070] Figure 2 is a photograph of the cross section of a fiber containing 75% by weight of UTSA-16(Zn) and polyacrylonitrile prepared according to the present invention.

[0071] Figure 3 shows the pure CO2 adsorption profiles for UTSA-16(Zn) powder, a UTSA-16(Zn) / PAN fiber containing 75%w of UTSA-16(Zn) dried from water and a UTSA-16(Zn) / PAN fiber containing 75%w of UTSA-16(Zn).

[0072] Detailed description

[0073] The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0074] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. Also, all conjunctions used are to be understood in the most inclusive sense possible. Thus, the word "or" should be understood as having the definition of a logical "or" rather than that of a logical "exclusive or" unless the context clearly necessitates otherwise. Further, the singular forms and the articles "a", "an" and "the" are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms: includes, comprises, including and / or comprising, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It will be further understood that the term consists and / or consisting, when used in this specification, specifies the presence of stated features, integers, steps, operations, elements, and / or components, and do preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0075] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0076] It is specified that the expressions “from... to...” and “between... and...” used in this description must be understood as including each of the mentioned limits.

[0077] The shaped MOF composite article of the invention is an extruded article, i.e. is obtained by an extrusion process.

[0078] Preferably, the extrusion process includes a phase inversion utilizing water as a coagulation medium.

[0079] The MOF in the shaped MOF composite article has the general formula of K2(M1xM2i-x)3(Cit)2 where Cit is fully dehydrogenated citrate anion, x is a number from 0 to 1.0, and each of M1 and M2 is a metal cation, preferably a metal cation of Zn, Co, Cu, Mg, Ni, Ca, Mn, Cr, Zr, or Fe.

[0080] The MOF is preferred to be manufactured by the methods disclosed in the US patent provisional filing No. 63 / 593,627, filed on October 27, 2023, having the title Synthesis and application of citric acid based MOFs, incorporated herein by reference in their entirety. The methods utilize water as the solvent and the reactions are carried out at atmospheric pressure with temperature below 100 °C. The methods may comprise:

[0081] (a) reacting 1 molar equivalent of citric acid with i molar equivalent of a metal carbonate component and with j molar equivalent of a basic potassium compound; (b) reacting the product of (a) with k molar equivalent of a metal salt component, wherein the method is conducted in a solvent consisting of water at ambient pressure and at a temperature no greater than 100 °C.

[0082] The MOF may be present in the shaped MOF composite article in the form of solid MOF particles.

[0083] The solid MOF particles may have a particle size of less than or equal to 1000 pm, typically less than or equal to 500 pm, and sometimes even less than or equal to 10 pm. MOF particles may have a particle size from 0.01 to 0.1 pm, from 0.1 to 1 pm, from 1 to 10 pm, from 10 to 25 pm, from 25 to 50, from 50 to 75 pm, from 75 to 100 pm, from 100 to 200 pm, or from 200 to 500 pm.

[0084] By “particle size" is herein meant the dimension of a particle, in particular the Feret diameter, measured by an analytical method, such as SEM (Scanning Electron Microscopy), microscopy, and sieving.

[0085] The amount of MOF particles in the composite article may vary from 25 to 95 % by weight, typically from 30 to 95 % by weight. The amount of MOF particles may vary from 25 to 35 % by weight, from 35 to 45 % by weight, from 45 to 55 % by weight, from 55 to 65 % by weight, from 65 to 75 % by weight, from 75 to 85 % by weight or from 85 to 95 % by weight.

[0086] The shaped MOF composite article further comprises a water-insoluble polymer.

[0087] The term "water-insoluble" as used herein means that the polymer has a solubility in water at pH 7 and at 25°C of less than 5 wt.%, preferably less than 2 wt.%, more preferably less than 1 wt.%. Solubility is assessed by placing different amounts of polymer in a volume of water at 25°C under stirring. The polymer is preferably dried beforehand (such as at 105°C for 2 hours). An amount of polymer can be considered as being fully dissolved when the solution is homogeneous.

[0088] Water-insoluble polymers can be natural or synthetic. For example, natural polymers include but are not limited to: lignin, cellulose and its derivatives comprising esters of cellulose. For examples, synthetic polymers include but are not limited to polyacrylonitrile, poly(methyl methacrylate), polystyrene, poly(ethylene terephthalate), aromatic polyamides, aliphatic polyamides, polyimides, polyesters, polyetherketones, polyethersulfones, polyetheresters, polysulfones, polyvinyl fluoride, polyvinyl difluoride, polyvinylchloride, polybenzimidazoles, polybenzoxazoles, polyazoaraomatics, poly(2,6-dimethylphenylene oxide), polyphenylene oxides, polyureas, polyurethanes, polyhydrazides, polyazomethines, polyacetals, polyquinoxaline, polyamideesters, polyacetylenes, polymer with intrinsic porosities (PIMs), any combinations (blends) or copolymers thereof.

[0089] The use of polyacrylonitrile is preferred. Polyacrylonitrile (PAN) is a polymer with good chemical resistance, low price, and excellent processability for fabricating MOF composites. PAN can be a homopolymer, copolymer, and / or terpolymer of acrylonitrile. The PAN copolymers include poly(acrylonitrile-co-itaconic acid), poly(acrylonitrile-co- acrylic acid) and poly(acrylonitrile-co-methacrylic acid), poly(acrylonitrile-co-methyl methyl acrylate), poly(acrylonitrile-co-methyl acrylate). The PAN terpolymers include poly(acrylonitrile-methyl acrylate-itaconic acid), poly(acrylonitrile-methyl methacrylateitaconic acid) and poly(acrylonitrile-methyl acrylate-acrylic acid).

[0090] The weight-average molecular weight (Mw) of the PAN can preferably range from 10,000 to 2,000,000 Dalton, preferably ranging from 60,000 to 500,000 Dalton.

[0091] The polymer in the shaped MOF composite article may be in the form of a porous matrix. By “porous matrix” is meant a solid material that contains a network of interconnected pores or voids throughout its structure. These pores can vary in size, shape, and distribution, creating a material that has a high surface area and can allow fluids or gases to pass through it.

[0092] The amount of polymer in the shaped MOF composite article may vary from 5 to 75 % by weight, typically from 5 to 50 % by weight. The amount of polymer may notably vary from 5 to 15 % by weight, from 15 to 25 % by weight, from 25 to 35 % by weight, from 35 to 45 % by weight, from 45 to 55 % by weight, from 55 to 65 % by weight or from 65 to 75 % by weight.

[0093] The shaped MOF composite article can be prepared by forming a dope solution containing the MOF (preferably in the form of a powder of solid MOF particles), the water insoluble polymer and a solvent and extruding the dope solution.

[0094] The solvents used for making the dope solution may include non-polar solvents, polar protic solvents as well as polar aprotic solvents.

[0095] A single solvent compound or mixtures of solvent compounds may be used as “the solvent”.

[0096] By “polar” is meant a molecule that has a dipole moment equal to or higher than 1.5 D at 25°C, and preferably equal to or higher than 3 D, or 4 D, or 4.5 D, or 5 D at 25°C. The dipole moment can be measured by using a dipole meter and by interpretation of the results using the Debye Huckel equation. A “non-polar” solvent is a solvent which is not “polar”. By “apolar” is meant a molecule that has a dipole moment equal to or inferior than 2 D, or 1 .5 D, or 1 D or 0.5 D at 25 °C. The dipole moment can be measured by using a dipole meter and by interpretation of the results using the Debye Huckel equation.

[0097] By “aprotic” is meant a molecule which does not contain any acidic hydrogen and thus does not act as a hydrogen bond donor. In particular, the aprotic molecule is free of -OH, -NH, -SH, and -PH groups.

[0098] By “protic” is meant a molecule which does contain an acidic hydrogen and thus does act as a hydrogen bond donor.

[0099] Among the compounds which can be present in the solvent, mentioned may be made of water and aliphatic alcohols, particularly polyhydric alcohols such as ethylene glycol and glycerin.

[0100] The use of a polar solvent is preferred, since the polar solvent can be conveniently removed by using water.

[0101] Preferred solvents are N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethylsufoxide (DMSO), tetrahydrofurane (THF) and combinations thereof. The use of NMP and DMSO is particularly preferred.

[0102] The dope solution may also include one or more additives. The additives may be liquid or solid and may be selected to serve any number of functions: viscosity modifications, imparting porosity and / or other properties to the shaped MOF composite article, or for other purposes. Preferably, a pore former is present as an additive. A pore former refers to a substance that may promote the formation of open connected pores in the final product after completely or partially removing the said substance. A viscosity modifying additive may advantageously facilitate the spinning process.

[0103] Examples of additives that can be employed include but are not limited to polyethylene oxides and polypropylene oxides, polyvinylalcohol, polyvinylpyrrolidone, surfactants such as alkylaryl polyether alcohols, alkyl sulfates, alkylarylsulfates, triethylphosphate, formamide, and salts such as lithium chloride. Combinations of such additives also can be used. The nature and amount of the additives can depend on desired product properties, process and / or equipment parameters or other factors. The amount of additives can be within a range of from about 0% to about 30% based on the weight of the dope solution. The amount of additives in the dope solution may for example vary from 0 to 5 % by weight, from 5 to 10 % by weight, from 10 to 15 % by weight, from 15 to 20 % by weight, from 20 to 25 % by weight or from 25 to 30 % by weight. The amount of solvent in the dope solution may vary from 20 to 30 % by weight, from 30 to 40 % by weight, from 40 to 50 % by weight, from 50 to 60 % by weight, from 60 to 70 % by weight or from 70 to 80 % by weight.

[0104] The amount of MOF particles in the dope solution may vary from 5 to 15 % by weight, from 15 to 25 % by weight, from 25 to 35 % by weight, from 35 to 45 % by weight, from 45 to 55 % by weight or from 55 to 65 % by weight.

[0105] The amount of polymer in the dope solution may vary from 1 to 5 % by weight, from 5 to 15 % by weight, from 15 to 25 % by weight, from 25 to 35 % by weight, from 35 to 45 % by weight, from 45 to 55 % by weight or from 55 to 65 % by weight.

[0106] For example, the dope solution may comprise:

[0107] - from 20 to 40 % by weight of MOF particles;

[0108] - from 5 to 15 % by weight of polymer;

[0109] - from 50 to 70 % by weight of solvent;

[0110] - from 0 to 10 % by weight of additives.

[0111] The shaped MOF composite article may be extruded from the dope solution by way of a dry-jet wet-quench spinning process (to achieve non-solvent induced phase separation or NIPS).

[0112] The dope solution may be formed by dissolving the polymer in the solvent, thereby obtaining a polymer solution. The MOF in powder form may be added to the solution (preferably after dissolving the polymer). Optional additives, such as CaCl2, LiCI, polyethylene oxide, etc., may be added together with the MOF powder or at another stage of the preparation of the dope solution. The dope solution may be degassed under heat and / or vacuum prior to extrusion.

[0113] Extrusion may be carried out through a die or spinneret.

[0114] The shape of the MOF composite is determined by the die or spinneret utilized. For a flat sheet MOF composite, a film extrusion die is utilized. For a fiber MOF composite, a spinneret is utilized. For MOF composite pellets, a pelletizer can be utilized after the spinneret. The fiber MOF composite may be a hollow fiber or a nonhollow fiber. A hollow fiber can be formed by injecting a non-solvent, or an air stream as an internal coagulant through the inner tube of the spinneret used for fabrication of hollow fibers by the dry / wet spinning.

[0115] The nascent composite emerging from the die or spinneret is preferably put in contact with water, such as in a water bath. The extrusion can directly take place in the water bath. Alternatively, the nascent composite emerging from the die or spinneret can be allowed to pass through a cooling medium such as an air gap before being collected in a water bath. The nascent composite solidifies in the water bath, which acts as a coagulation medium. Solidified composite may be pulled from the coagulation bath (water bath) onto and around a rotating barrel, then directed into a washing medium. The washing medium may comprise water, one or more alcohols, and mixtures thereof. Pulling and piddling (a technique described, for example in patent US 8,753,741 ) into a washing barrel also can be employed.

[0116] The water in the water bath may be for instance deionized water. Alternatively, said water may also be an aqueous solution.

[0117] Instead of (or in addition to) water, another nonsolvent can be used, a linear and / or branched C1-C6 alcohol can be used, for example: methanol, ethanol or isopropanol. Using water in the water bath may be the easiest way to proceed.

[0118] After extrusion, the composite may remain soaked in the water bath, for example for a duration of 1 hour to 72 hours, such as from 5 to 48 hours, or for approximately 24 hours, in order to remove the solvent from the dope solution.

[0119] In case a hollow fiber is prepared, use can be made of spinneret having a tubein-orifice structure. A bore fluid may be pumped as an internal coagulant through the inner tube of the spinneret. A bore fluid can be water, or a water alcohol mixture as described above. A bore fluid can further be a gas stream, for example an air stream.

[0120] Obtaining MOF composites of desired morphologies or properties may depend on factors such as spinneret design, dope and bore fluid (if any) flow rates and / or physical properties, air gap dimensions, bath conditions, shear forces within the spinneret, ratios of dope to bore fluid volumetric flow rates, draw ratios and so forth. Patent US 5,181 ,940, the entire contents of which are incorporated herein by reference, provides details on the manufacture of hollow fiber membranes that may be found applicable.

[0121] In some cases, heat treatment (in a suitable oven or a in suitable fluid, such as a water bath or a steam chamber, for instance) can be undertaken, e.g., to impart desired mechanical properties to the MOF composites. Stepwise heating, followed by plateau temperature maintenance, optionally interspersed with one or more cooling and reheating periods, can be employed in some cases. Temperatures typically are above room temperature (20 °C) and are often at least 10 °C below the glass transition temperature of the water insoluble polymer. In some variations, the heat treatment may be carried out by directly extruding into a heated water bath.

[0122] Preferably, the water bath is exchanged with an alcohol prior to drying. This may involve withdrawing the MOF composite from the water bath and immersing it into an alcohol bath - or alternatively, gradually modifying the composition of the water bath to turn it into an alcohol bath. In some variations, the heat treatment mentioned in the previous paragraph may be carried out after this exchange.

[0123] The alcohol bath may comprise one more or more alcohol compounds and optionally water, for example in a total amount of 1 to 50 wt.%. When water is present in the alcohol bath, the exchange may simply consist in the addition of one or more alcohol compounds to the water bath. The alcohol compounds preferably comprise or consist of C1 to C6 alcohol compounds, more preferably C1 to C4 alcohol compounds. The alcohol compounds are most preferably selected from methanol, ethanol, isopropanol and mixtures thereof.

[0124] Figure 1 schematically shows a preferred succession of steps of the method for making a shaped MOF composite article according to the invention (before the drying step).

[0125] It was found that the MOF composites exhibit significantly lower CO2 adsorption capacity if the MOF composites are dried directly from the water bath. For example, a 75% weight of UTSA-16Zn / PAN composite fiber dried directly from water exhibits a CO2 adsorption capacity of only 6.94 % weight at 30 °C under atmospheric pressure of CO2, which is significantly below the projected adsorption capacity of 11 .23 % weight based on the proportional dry weight of the MOF inside the fiber. The total CO2 adsorption capacity loss is 38%. Unexpectedly, it was further found that the CO2 adsorption capacity loss is well below 10% if the fibers are dried from an alcohol solvent. For example, a 75 % weight of UTSA-16Zn / PAN composite fiber dried from isopropanol (I PA) exhibits a CO2 adsorption capacity of 10.87 % weight at 30 °C under atmospheric pressure of CO2, which is very close to the projected adsorption capacity of 11 .23 % weight based on the proportional dry weight of the MOF inside the fiber. The total CO2 adsorption capacity loss is only 3%.

[0126] Drying, for example, can be conducted under ambient conditions or by supplying heat, e.g., in an oven or any drying means known by the skilled person, at temperatures such as from 50 °C to 150 °C.

[0127] The obtained shaped MOF composite article can be in particular in the shape of a fiber, sheet, bead or pellet. Herein, it is understood that beads may display a substantially spherical shape and pellets may display a substantially cylindrical shape.

[0128] The MOF composite pellets and fibers can be prepared in any desired diameters. In one example, the composite MOF fiber or pellet or bead may have a diameter (outer diameter) within a range of from about 0.1 mm to about 10 mm, preferably from 0.5 to 6 mm. In the case where the MOF composite is a bead, the diameter may correspond to the diameter of the sphere. In the case where the MOF composite is a pellet, the diameter may correspond to the dimension along the longitudinal axis of the cylinder. The MOF composite flat sheet can be prepared in any desired thickness. In one example, the composite MOF flat sheet may have a thickness within a range of from about 0.1 mm to about 10 mm, preferably from 0.5 to 6 mm. In case there are any variations in diameter or thickness in an article, these values refer to the average diameter or thickness.

[0129] The shaped MOF composite article described herein can have a density within a range of from about 0.2 g / cm3to about 1 g / cm3, preferably from about 0.3 g / cm3to about 0.8 g / cm3.

[0130] Many of the properties characterizing the shaped MOF composite article can be obtained by selecting or adjusting the equipment design, the process conditions or other factors. Porosity attributes, for instance, can be tailored by solvent concentration, pore former, other additive or by other approaches.

[0131] Many of the MOF composite articles according to the invention can be best described as having an open-cell or interconnected structure. Specifically, the polymer matrix encapsulates the active adsorbents (MOF particles) in an open-cell arrangement, without blocking the active adsorbents, thus promoting good mass transport.

[0132] Total porosity amounts can be within a range of from about 20% to about 80% by volume relative to the volume of shaped MOF composite article, preferably from about 30% to about 70% by volume by volume relative to the volume of shaped MOF composite article. The total porosity of a shaped MOF composite can be measured from the difference in its weight when dry and when saturated with a liquid, such as water and / or isopropanol. Pore size can vary and the MOF composite article described herein can include macroporosity, microporosity and / or nanoporosity.

[0133] The shaped MOF composite article can be characterized by analytical techniques such as nitrogen BET (Brunauer-Emmett-Teller), scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectrometry (FTIR), or others, as currently known in the art or developed in the future. Standard methods or protocols (e.g., thermal gravity analysis, adsorption column) can be employed to assess the properties of the shaped MOF composite article.

[0134] Advantageously, methods described herein can produce shaped MOF composite articles that are self-supporting (also referred to as “free-standing”), a property describing a material or an article that does not require an external supporting structure to prevent it from collapsing or crumbling.

[0135] The MOF composite pellets described in this application can be utilized in a standard equipment, such as packed beds or columns.

[0136] The MOF composite flat sheets can be packed into a device in a configuration known as plate and frame, spiral wound.

[0137] For many applications, the (preferably non-hollow) MOF fibers described herein are packaged into modular adsorption devices. An illustrative adsorption device (also referred to herein as a “cartridge”) includes multiple (a plurality of, i.e., two or more) fibers that are laid parallel to or wound, e.g., helically, around a center tube. One or more cartridges can be assembled into a module. In illustrative examples, a module for purifying a raw fluid (an acid gas, for instance) includes at least two modular adsorption devices that are installed in a vessel in series or in parallel. Operations can be conducted in an axial or cross flow arrangement. Either shell side or bore side feeding can be employed. In some implementations, a module is provided with one or more heating elements that can be used to release adsorbed contaminant, regenerating the reinforced sorbent fibers. Various cartridge and / or module configurations that can be employed are described, for instance, in patent application US 2023 / 0008877.

[0138] The shaped MOF composite article described herein, assembled into a cartridge and / or module, for example, can be used to remove an acid gas from a fluid stream, e.g., a flue gas stream. The flue gas stream may originate from a point of source. For example, a fluid stream containing an acid gas (CO2, for instance) is brought into contact with the shaped MOF composite article. As at least a portion of the acid gas (e.g., CO2) becomes adsorbed by the shaped MOF composite article, the fluid stream is depleted in the acid gas (e.g., CO2), generating a stream that is purified relative to the acid gas.

[0139] The shaped MOF composite article containing a contaminant such as an acid gas (e.g., CO2) can be regenerated for reuse or for environmentally safe disposal. Various methods can be employed, using heat, vacuum, lower pressure, or any combination thereof. If the regeneration technique relies on heat, the desorption process can be a temperature swing adsorption (TSA) method, while many processes based on lowered pressures are known as pressure swing adsorptions (PSA). Another useful technique that can be employed to release adsorbed species from the reinforced sorbent fibers involves both heating and vacuum, the process being known as temperature-vacuum swing adsorption or TVSA. These techniques are well known in the art (see, e.g., patent US 9,457,340, and US 8,974,577, the entire contents of both being incorporated herein by this reference).

[0140] In some embodiments, steam can be directed to the shaped MOF composite article directly to regenerate the shaped MOF composite article.

[0141] The shaped MOF composite articles such as described herein also can find applications in the direct removal of an acid gas from an ambient atmosphere. Some approaches that can be employed to capture carbon dioxide from the atmosphere typically rely on a blower to circulate the air through the articles acting as adsorbents, included in an adsorbent device. As carbon dioxide is adsorbed, clean air is released. Once the adsorbents are saturated with carbon dioxide, the air circulation is directed to another adsorbent device, and the current adsorbent device is regenerated by heat, or vacuum, or a combination of both. The heat source can be from renewable energy sources, such as solar or wind energy.

[0142] The carbon dioxide released from the articles described herein can be utilized for enhanced oil recovery, to prepare synthetic fuels, such as methanol, methane, jet fuels, etc. In some embodiments, the carbon dioxide is injected for storage.

[0143] Other acid gases which may be adsorbed instead of, or together with, CO2, include SO2 and / or H2S.

[0144] The invention is further illustrated in the following non-limiting exemplification section.

[0145] Examples

[0146] Example 1

[0147] A dope solution was prepared first by dissolving 7.0 g of polyacrylonitrile in 36.0 g of NMP, followed by mixing 21 .0 g of UTSA-16(Zn) powder. After degassing, the dope solution was transferred into a fiber spinning apparatus equipped with a spinneret. The dope solution was extruded from a spinneret to form a nascent fiber and the nascent fiber was delivered into deionized water. The fiber was further soaked in water for 24 hours (to remove the NMP solvent), after which it was air dried.

[0148] A section of the fiber was tested with a thermogravimetric instrument for its CO2 adsorption property. The fiber was first heated to 110 °C and held at 110 °C for 30 min to activate the fiber under nitrogen. This was followed by cooling the activated fiber to 30 °C under nitrogen. The fiber was then exposed to a dry CO2 gas stream for 30 min. The weight gain of the fiber after the CO2 exposure was 6.94% by weight. Example 2

[0149] A dope solution was prepared first by dissolving 7.0 g of polyacrylonitrile in 36.0 g of NMP, followed by mixing 21 .0 g of UTSA-16(Zn) powder. After degassing, the dope solution was transferred into a fiber spinning apparatus equipped with a spinneret. The dope solution was extruded from a spinneret to form a nascent fiber and the nascent fiber was delivered into a deionized water. The fiber was further soaked in water for 24 hours (to remove the NMP solvent), then the fiber was placed in IPA for 2 hours, after which it was air dried.

[0150] A section of the fiber was tested with a thermogravimetric instrument for its CO2 adsorption property. The fiber was first heated to 110 °C and held at 110 °C for 30 min to activate the fiber under nitrogen. This was followed by cooling the activated fiber to 30 °C under nitrogen. The fiber was then exposed to a dry CO2 gas stream for 30 min. The weight gain of the fiber after the CO2 exposure was 10.87% by weight.

[0151] A photograph of the cross section of the fiber of example 2 is shown in Figure 2. Figure 3 shows the comparison for the CO2 adsorption capacity among UTSA-

[0152] 16Zn powder, and UTSA-16Zn / PAN fibers dried from water and IPA, respectively (examples 1 and 2).

Claims

Claims1. A shaped, extruded, MOF composite article comprising the MOF of formula K2(M1xM2i-x)3(Cit)2, where Cit is fully dehydrogenated citrate anion, M1 and M2 are metal cations, x is from 0 to 1.0, and a water-insoluble polymer.

2. The shaped MOF composite article according to claim 1 having the shape of a fiber, sheet, bead or pellet.

3. The shaped MOF composite article according to any one of claims 1 to 2, wherein M1 and M2 are metal cations belonging to the group of Zn, Co, Cu, Mg, Ni, Ca, Mn, Cr, Zr, and Fe.

4. The shaped MOF composite article according to any one of claims 1 to 3, wherein the water insoluble polymer is selected from the group consisting of: polysulfone, polyimide, cellulose, polyacrylonitrile, polyvinyl difluoride, polyvinylchloride, and mixtures thereof.

5. The shaped MOF composite article according to any one of claims 1 to 4, which is a fiber with an outer diameter between 0.5 mm and 10 mm.

6. The shaped MOF composite article according to any one of claims 1 to 4, which is a flat sheet with a thickness between 0.5 mm and 10 mm.

7. The shaped MOF composite article according to any one of claims 1 to 4, which is a pellet with an outer diameter between 0.5 mm and 10 mm.

8. The shaped MOF composite article according to any one of claims 1 to 7, wherein the said MOF is UTSA-16(Zn).

9. The shaped MOF composite article according to any one of claims 1 to 8, wherein the said MOF is UTSA-16(Co).

10. A method of making the shaped MOF composite article according to any one of claims 1 to 9, comprising forming a dope solution containing the said MOF, the water insoluble polymer, a solvent, and extruding the said dope solution.

11. The method according to claim 10, wherein the said dope solution is extruded into a water bath.

12. The method according to claim 10 or 11 , further comprising exchanging the water bath with an alcohol.

13. The method according to claim 12, wherein the alcohol comprises, or is selected from methanol, ethanol or isopropanol.

14. The method according to claim 12 or 13, wherein said alcohol contains 1 to 50% by weight of water.

15. The method according to any one of claims 10 to 14, further comprising drying the shaped MOF composite article, preferably in ambient air.

16. The method according to any one of claims 10 to 15, wherein the solvent is a polar solvent, preferably selected from the group consisting of: DMF, DMAc, NMP, DMSO, THF, and mixtures thereof.

17. The method according to any one of claims 10 to 16, wherein the dope solution further comprises a pore former.

18. The shaped MOF composite article which is obtainable by the method of any one of claims 10 to 17.

19. A process for removing an acid gas from a fluid stream containing the acid gas, the process comprising contacting the fluid stream with the shaped MOF composite article according to any one of claims 1 to 9 or 18, whereby at least a portion of the acid gas is adsorbed by the shaped MOF composite article to produce a purified fluid stream.

20. The process according to claim 19, wherein the acid gas is CO2, SO2, H2S or mixtures thereof.

21. The process according to any one of claims 19 to 20, wherein the fluid stream is a flue gas.

22. The process according to any one of claims 19 to 20, wherein the fluid stream is an atmospheric air.

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