Method for synthesizing zinc metal-organic framework materials

Abstract

Embodiments of the present invention relate generally to a method for preparing metal organic frameworks (MOFs), specifically zinc MOFs having the formula Zn2Ht2Ox. The method generally involves contacting at least one cycloazocarbyl compound, such as an N-heterocyclic compound, with an oxalate (or dicarboxylic acid or dithio compound) and a zinc cation in liquid suspension at a temperature of up to 100°C and a pressure of about 1 atmosphere.

Description

[Technical field]

[0001] The present invention relates generally to methods for the synthesis of metal-organic frameworks, and more particularly to methods for the synthesis of zinc-containing metal-organic frameworks. [Background technology]

[0002] Metal-organic frameworks (herein referred to as "MOFs") and porous coordination polymers (herein referred to as "PCPs") are a class of network solids composed of organic spacers linking metal ions or metal ion clusters. These materials are useful due to their high surface area and the properties of complex metals, including an ordered (crystalline) structure permeated with pores. The order of these materials makes them amenable to structural characterization by X-ray diffraction techniques. This property is particularly interesting for the rapid adsorption of gases. This class of materials has been proposed for the adsorption and separation of gases, such as carbon dioxide (herein referred to as "CO2") from industrial emissions, e.g., to replace amine scrubbing of CO2.

[0003] Water stability has been shown to be a weak point for many MOFs, as even small amounts of atmospheric moisture can damage order and porosity. Identifying materials that combine high CO2 capture capacity with high stability in the presence of moisture or steam is a challenge. Industrial flue gases contain both molecules, and removing moisture from flue gases prior to CO2 capture not only carries a significant energy cost penalty, but also unnecessarily increases the capital cost of the capture system.

[0004] U.S. Patent No. 9,782,745, entitled "METAL ORGANIC FRAMEWORK, PRODUCTION AND USE THEREOF," issued on October 10, 2017, discloses that certain Zn MOFs exhibit high CO2 adsorption capacity with high adsorption selectivity for CO2 compared to nitrogen, as well as good thermal and water stability. The MOFs therein had complete reversibility and could be subjected to multiple cycles of adsorption and desorption.

[0005] PCT Publication WO 2019 / 204934, entitled “SYNTHESIS OF ZINC MOF MATERIALS,” teaches improvements to the synthesis techniques for preparing Zn MOFs disclosed in U.S. Pat. No. 9,782,745.

[0006] Both U.S. Patent No. 9,782,745 and PCT Publication WO 2019 / 204934 disclose metal-organic frameworks (MOFs) having pores, the frameworks comprising zinc ions, oxalates, and cycloazocarbyl compounds. The cycloazocarbonyl compounds of the MOFs therein are described as at least bidentate with 2, 3, or 4 nitrogen atoms, typically as part of a 5-membered ring. Examples of cycloazocarbyl compounds therein are imidazolates, triazolates, and tetrazolates, more specifically 1,2,4-triazolate, 1H-1,2,4-triazolate-1-carboxamidine, 3-amino-1,2,4-triazolate, imidazolate, 4-fluoroimidazolate, 2-methyl-imidazolate, and 1,2,3,4-tetrazolate. Of particular interest is a Zn(II) material called CALF-20, which has the chemical formula Zn2Tz20x, where Tz = 1,2,4-triazolate and Ox = oxalate.

[0007] US Patent No. 9,782,745 illustrates the synthesis of a particular example within this family of Zn MOFs, identified as CALF-20, which is carried out as a batch process solvothermally in a sealed autoclave at pressures above ambient pressure. In this procedure, Zn(II) oxalate and a stoichiometric excess of 1,2,4-triazole relative to both Zn and oxalate were added to water and methanol in a polytetrafluoroethylene (PTFE)-lined autoclave. The mixture was then heated (i.e., at high pressure) to 180°C for 48 hours in the sealed autoclave and washed with water. The space-time yield of this process is relatively low, on the order of about 40 kg / m3 / h, making the cost of synthesis a significant limiting factor for CALF-20 and related MOFs. The reaction can also be carried out in pure methanol or ethanol. Subsequently, it has been found that CALF-20 prepared by the autoclave method may contain zinc oxide impurities, as assessed by PXRD (powder X-ray diffraction), which are completely removed by an annealing process that involves two steps of heating to 200°C for 24 hours, with cooling and washing steps between each step. However, this purification step adds additional time and cost to the synthesis of CALF-20.

[0008] WO 2019 / 204934 discloses an improved synthesis technique for preparing CALF-20 at reduced temperature and pressure. The method relies on forming a compound of a cycloazocarbyl with an oxalate, or an oxalate mixed with an additional chelating ligand, prior to adding a zinc salt to the reaction medium. The disclosure also illustrates the use of a mixture of low alcohol and water as the sole solvent.

[0009] Barriers to the commercial application of Zn MOFs such as CALF-20 in gas separation applications include the complex synthesis process and the high synthesis cost using conventional synthesis processes. Specific drawbacks of synthesis processes known in the art include, for example, low space-time yields, the use of hazardous solvents, and / or the formation of impurities that are difficult to separate. The use of solvents during synthesis poses challenges, including the need for appropriate equipment and processes for safe handling and handling. Novel PCP and MOF synthesis techniques that overcome one or more of these barriers are desirable. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 9,782,745 [Patent Document 2] International Publication No. 2019 / 204934 Summary of the Invention

[0011] In a broad aspect of the present invention, a method for preparing a Zn MOF of composition of formula Zn2Ht2Ox comprises the steps of: Ht is a first N-heterocyclic compound selected from 1,2,4-triazolates, or a combination of 1,2,4-triazolates and at least a second N-heterocyclic compound, where the first N-heterocyclic compound is different from the second N-heterocyclic compound; ·Ox is an oxalate, the dianionic form of the diacid oxalic acid or a dicarboxylic or dithio compound; Zn is the zinc cation The method includes contacting a first N-heterocyclic compound and optionally a second N-heterocyclic compound, an oxalate or a dicarboxylic acid or a dithio compound, and a solvent comprising water in a liquid suspension at a temperature of 100°C or less and a pressure of 0.9 to 1.1 atmospheres to form crystals of the Zn MOF.

[0012] In another broad aspect of the invention, a method for preparing a Zn MOF of composition of formula Zn2Ht2Ox is provided, comprising the steps of: Ht is a first N-heterocyclic compound selected from 1,2,4-triazolates or a combination of a 1,2,4-triazolate and a second N-heterocyclic compound; wherein the first N-heterocyclic compound is different from the second N-heterocyclic compound; ·Ox is an oxalate, the dianionic form of the diacid oxalic acid or a dicarboxylate or dithio compound; Zn is the zinc cation The method includes contacting a first N-heterocyclic compound, optionally a second N-heterocyclic compound, an oxalate or dicarboxylic acid or dithio compound, and a solvent consisting solely of water in a liquid suspension at a temperature of 100°C or less and a pressure of 0.9 to 1.1 atmospheres to form crystals of the Zn MOF.

[0013] In a further embodiment of the invention, the method for preparing a zinc-containing MOF or Zn MOF of formula: Zn2Ht2Ox, wherein Ht is 1,2,4-triazolate; ·Ox is oxalate, the dianionic form of the diacid oxalic acid; Zn is the zinc cation, The method includes contacting 1,2,4 triazole, an oxalate salt, and a zinc salt or zinc oxide with a solvent comprising water in a liquid suspension at a temperature of not more than 100°C and a pressure of not more than 0.9-1.1 atmospheres.

[0014] In yet a further embodiment of the present invention, the method for preparing a zinc-containing MOF or Zn MOF of formula: Zn2Ht2Ox, wherein Ht is 1,2,4-triazolate; ·Ox is oxalate, the dianionic form of the diacid oxalic acid; Zn is the zinc cation, The process involves contacting 1,2,4 triazole, an oxalate salt, and a zinc salt or zinc oxide in a liquid suspension at a temperature below 100°C and at a pressure within 0.9 to 1.1 atmospheres with a solvent consisting solely of water. [Brief description of the drawings]

[0015] [Figure 1] The powder X-ray diffraction (PXRD) of CALF-20 Zn MOF produced as described in WO 2019 / 204934 is compared to Zn MOFs produced as described in Examples 3 and 4. The diffraction peaks for X-ray diffraction lines 1, 2, and 3 are substantially the same, indicating that the Zn MOFs prepared by these methods have substantially the same structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Definition: The term alkyl refers to a monovalent saturated hydrocarbon radical (C1-C 12 The term "alkyl" refers to a C1-C3 alkyl group. The alkyl group can be linear or branched. The alkyl group can be substituted. In certain embodiments, the alkyl is a C1-C3 alkyl.

[0017] The term aminoalkyl refers to a monovalent radical —NHR, where R is an alkyl group as defined above.

[0018] The term dialkylamino refers to a -N(R)2 monovalent radical, where each R is an alkyl group as defined above. In certain embodiments, R is a C1-C3 alkyl.

[0019] The term amino refers to the group -NH2.

[0020] The term cycloalkyl refers to an alkyl radical having a 3- to 8-membered carbon ring. Cycloalkyl groups may be optionally substituted.

[0021] The term alkenyl refers to a monovalent hydrocarbon radical (C-C) that may contain 2 to 12 carbon atoms containing one or more double bonds. 12 Alkenyl groups may be straight chain or branched. Alkenyl groups may be optionally substituted.

[0022] The term cycloalkenyl refers to an alkenyl radical having a 3-8 membered carbon ring. One or more double bonds are within the carbon ring. The cycloalkyl group may be optionally substituted. In one embodiment, the cycloalkenyl group contains one or more double bonds.

[0023] The term alkynyl refers to a monovalent hydrocarbon radical (C-C) that may contain 2 to 12 carbon atoms containing one or more triple bonds. 12 alkynyl).

[0024] The term N-heterocyclic refers to a chemical species containing a 5- to 8-membered ring, the ring containing at least one nitrogen. The other ring members may be carbon, one or more additional nitrogens, or one or more oxygen or sulfur. The ring may contain one or more double bonds or may be aromatic.

[0025] The term lower alcohol refers to an alkyl alcohol having 1 to 4 carbon atoms, including all isomers thereof. This term includes mixtures of lower alcohols. In a particular embodiment, the lower alcohol is ethanol.

[0026] Aqueous alcohol refers to a mixture containing water and an alcohol, preferably a lower alcohol. Aqueous alcohol may contain a mixture of two or more alcohols, preferably a mixture of two or more lower alcohols.

[0027] Stoichiometric excess refers to the relative amount of a reagent or compound in excess of the stoichiometric amount defined by the formula Zn2Ht2Ox, where the number represents the relative molar content of the compound in the product.

[0028] Solvent refers to a liquid medium used to suspend or dissolve reagents or compounds.

[0029] Room temperature is a temperature in the range of about 15°C to about 30°C.

[0030] The term atmosphere refers to the surrounding environment in which people and / or processes operate. Standard atmospheric pressure is 101 kilopascals at sea level.

[0031] The term zinc compound refers to two or more zinc-containing materials as liquids or solids.

[0032] WO 2019 / 204934 discloses a synthetic method for producing Zn MOFs using a specific addition sequence with a solvent other than water (non-aqueous solvent).

[0033] The present synthesis method produces Zn MOFs, including, for example, CALF-20, of porous crystalline structure with desirable properties, such as selective adsorption of one or more gas species and good thermal and steam exposure stability. The present method not only provides more economical conditions of synthesis and solvents while reducing the formation of impurities that are difficult to separate, but also eliminates the use of pressure vessels during synthesis. The present method can also eliminate the use of light alcohols as synthesis solvents and / or eliminate reagent addition steps, compared to the method disclosed in WO 2019 / 204934. Furthermore, the present method includes a change in the order of reagent addition disclosed in WO 2019 / 204934, thereby significantly shortening the reaction time for forming the desired Zn MOF structure while providing high yields and high purity.

[0034] The method of the present invention not only significantly impacts the type of equipment used, making it possible to adapt the synthesis method of the present invention relatively easily in existing chemical industry plants, but also eliminates or reduces the amount of waste containing hazardous chemicals during the synthesis. Furthermore, the method of the present invention allows for a higher synthesis space-time yield compared to the method disclosed in WO 2019 / 204934 due to a significant reduction in reaction time and the omission of several washing or purification steps.

[0035] The use of zinc oxide as the zinc reagent has also been demonstrated, which deviates from the teachings of WO 2019 / 204934. 2+ We demonstrate that ZnO dissolution driven by the formation of the containing MOF allows for relatively rapid formation of the product via dissolution and reprecipitation, leaving little unreacted ZnO.

[0036] The present invention relates to a method for preparing a zinc-containing MOF or a Zn MOF of formula: Zn2Ht2Ox, wherein ·Ht is a first N-heterocyclic compound selected from 1,2,4-triazolates, or a combination of an N-heterocyclic compound (1,2,4-triazolate) and a second N-heterocyclic compound, where the first N-heterocyclic compound is different from the second N-heterocyclic compound; ·Ox is oxalate, the dianionic form of the diacid oxalic acid; ·Zn is the zinc cation.

[0037] In one embodiment, the present invention provides a Zn of formula: The present invention provides a method for producing a MOF, wherein Zn is a zinc cation; Ht is a first N-heterocyclic compound, particularly a first cycloazocarbyl compound, or more particularly a 1,2,4-triazolate; or a combination of a first N-heterocyclic compound, particularly a first cycloazocarbyl compound, or more particularly a 1,2,4-triazolate, with at least a second N-heterocyclic compound, particularly a second cycloazocarbyl compound, where the first N-heterocyclic compound and the first cycloazocarbyl compound are different from the second N-heterocyclic compound and the second cycloazocarbyl compound; Ox is an oxalate, or a combination of oxalate and one or more chelating ligands other than oxalate; the method comprises contacting, in liquid suspension at a temperature of 100° C. or less, the 1,2,4-triazole, an oxalate salt, and optionally a zinc salt or zinc oxide, with a solvent composed mostly or entirely of water.

[0038] In an embodiment, the present invention may further relate to a Zn MOF of formula Zn2Ht2CLx containing oxalate and 1,2,4-triazolate, where Zn is a zinc cation, Ht is a combination of a first N-heterocyclic compound, in particular a first cycloazocarbyl compound, more particularly a 1,2,4-triazolate, with at least a second N-heterocyclic compound, in particular a second cycloazocarbyl compound, where the first N-heterocyclic compound is different from the second N-heterocyclic compound, and LC is a combination of an oxalate with one or more chelating ligands other than oxalate. In particular, the embodiment may relate to a Zn MOF in which the second cycloazocarbyl compound is an imidazolate, a 1,2,4-triazolate, a pyrazolate or a tetrazolate, and / or the other chelating ligand is a squarate (squaric acid) or a rubeanate (rubeanic acid).

[0039] The use of zinc oxide as the zinc reagent for zinc is also disclosed. Low solubility of Zn 2+The dissolution of ZnO driven by the formation of the containing MOF allows for a relatively rapid formation of the product via dissolution and reprecipitation, which can leave little unreacted ZnO at the end of the synthesis process.

[0040] A typical Zn MOF product has the stoichiometry Zn2Ht2Ox, where Ht is a cycloazocarbyl and Ox is an oxalate or a combination of oxalate with any other ligand.

[0041] The particular product CALF-20 has the stoichiometry Zn2Tz2Ox, where Tz is a 1,2,4-triazolate and Ox is an oxalate. It is currently believed that the reaction to form Zn MOFs, particularly CALF-20, can be carried out with up to a 5% stoichiometric excess of any one component.

[0042] In one embodiment, the synthesis of zinc-containing MOFs or Zn MOFs of formula: Zn2Ht2Ox, wherein Ht is a first N-heterocyclic compound selected from 1,2,4-triazolates, or a combination of a first N-heterocyclic compound (1,2,4 triazolate) and a second N-heterocyclic compound, where the first N-heterocyclic compound is different from the second N-heterocyclic compound; ·Ox is an oxalate, the dianionic form of the diacid oxalic acid or a dicarboxylic or dithio compound; Zn is the zinc cation The method can include a method comprising contacting a first N-heterocyclic compound and optionally a second N-heterocyclic compound, an oxalate or dicarboxylic acid or dithio compound, and optionally a zinc salt or zinc oxide, in a liquid suspension at a temperature of about 100° C. or less and a pressure of 0.9-1.1 atmospheres or less, with a solvent comprising water. The synthetic method can result in a formulation of Zn MOF crystals.

[0043] The embodiment may further comprise adding a zinc salt or zinc oxide as a zinc reagent to the solution or liquid suspension during a first step, adding an oxalate salt to the solution or liquid suspension during a second step, and adding a first N-heterocyclic compound, and optionally a second N-heterocyclic compound, as a cycloazocarbyl compound, in particular a second cycloazocarbyl compound, to the solution or liquid suspension during a third step, the third step being after the second step and the second step being after the first step.

[0044] The embodiment may further comprise mixing a zinc salt or zinc oxide as the zinc reagent, a first N-heterocyclic compound, and optionally a cycloazocarbyl compound, particularly a second N-heterocyclic compound as the second cycloazocarbyl compound, and an oxalate salt to form a mixture, followed by adding a solvent to the mixture.

[0045] In another embodiment, the synthesis of zinc-containing MOFs or Zn MOFs of formula: Zn2Ht2Ox, wherein Ht is a first N-heterocyclic compound selected from 1,2,4-triazolates, or a combination of a first N-heterocyclic compound (1,2,4 triazolate) and a second N-heterocyclic compound, where the first N-heterocyclic compound is different from the second N-heterocyclic compound; ·Ox is an oxalate, the dianionic form of the diacid oxalic acid or a dicarboxylic or dithio compound; Zn is the zinc cation The method can include contacting a first N-heterocyclic compound and optionally a second N-heterocyclic compound, an oxalate or a dicarboxylic acid or a dithio compound in a liquid suspension at a temperature of about 100° C. or less and a pressure of 0.9 to 1.1 atmospheres or less with a solvent consisting solely of water.

[0046] In embodiments, the first N-heterocyclic compound can be a first cycloazocarbyl compound and the optional second N-heterocyclic compound is an optional second cycloazocarbyl compound, the first cycloazocarbyl compound and the optional second cycloazocarbyl compound contain a 5- or 6-membered ring, the first cycloazocarbyl compound and the optional second cycloazocarbyl compound are at least bidentate, the ring contains 2, 3 or 4 nitrogens, and the ring is optionally substituted with non-hydrogen substituents selected from -NH2, C1-C3 alkylamino, C1-C3 dialkylamino, C1-C3 alkyl, C2-C3 alkenyl, or C2-C3 alkynyl.

[0047] In other embodiments, the first N-heterocyclic compound can be a first cycloazocarbyl compound, the optional second N-heterocyclic compound can be a second cycloazocarbyl compound, and the first cycloazocarbyl compound and the optional second cycloazocarbyl compound can be bidentate.

[0048] In yet further embodiments, the first N-heterocyclic compound can be a first cycloazocarbyl compound and the optional second N-heterocyclic compound can be a second cycloazocarbyl compound, and the first cycloazocarbyl compound and the optional second cycloazocarbyl compound contain a 5- or 6-membered ring.

[0049] In other embodiments, the first N-heterocyclic compound can be a first cycloazocarbyl compound, the optional second N-heterocyclic compound can be a second cycloazocarbyl compound, and the first cycloazocarbyl compound and the optional second cycloazocarbyl compound can be unsubstituted.

[0050] In embodiments, the first N-heterocyclic compound may be a first cycloazocarbyl compound, the optional second N-heterocyclic compound may be a second cycloazocarbyl compound, and the first cycloazocarbyl compound and the optional second cycloazocarbyl compound may be bidentate and unsubstituted.

[0051] In embodiments, the first N-heterocyclic compound can be a first cycloazocarbyl compound, the optional second N-heterocyclic compound can be a second cycloazocarbyl compound, and the first cycloazocarbyl compound and the optional second cycloazocarbyl compound can be an unsubstituted 1,2,4-triazolate, an unsubstituted 1,2,3-triazolate, an unsubstituted tetrazolate, an unsubstituted imidazolate, or an unsubstituted pyrazolate.

[0052] In embodiments, the first N-heterocyclic compound can be a first cycloazocarbyl compound, the optional second N-heterocyclic compound can be any second cycloazocarbyl compound, and the first cycloazocarbyl compound and the optional second cycloazocarbyl compound can be an imidazolate, triazolate, 1.2.4-triazolate, 1,2,3-triazolate, pyrazolate, or tetrazolate.

[0053] In other embodiments, the first N-heterocyclic compound can be a first cycloazocarbyl compound, the optional second N-heterocyclic compound can be an optional second cycloazocarbyl compound, and the first cycloazocarbyl compound and the optional second cycloazocarbyl compound can be a chelating ligand, which is 1.2.4-triazolium oxalate.

[0054] Additionally, in other embodiments, the first N-heterocyclic compound can be a first cycloazocarbyl compound and the optional second N-heterocyclic compound can be a second cycloazocarbyl compound, and the first cycloazocarbyl compound and the optional second cycloazocarbyl compound can be selected from the group consisting of 1H-1,2,4-triazolate-1-carboxamidine, 3-amino-1,2,4-triazolate, imidazolate, 4-fluoroimidazolate, 2-methyl-imidazolate, and 1,2,3,4-tetrazolate.

[0055] In embodiments, the first N-heterocyclic compound can be a first cycloazocarbyl compound, and the optional second N-heterocyclic compound can be any second cycloazocarbyl compound.

[0056] In embodiments, the first N-heterocyclic compound can be a first cycloazocarbyl compound, the optional second N-heterocyclic compound can be a second cycloazocarbyl compound, and the first cycloazocarbyl compound and the optional second cycloazocarbyl compound can be unsubstituted 1,2,4-triazolates.

[0057] In an embodiment, a portion of the first N-heterocyclic compound and optional second N-heterocyclic compound can be substituted for the 1.2.4-triazole as a reactant to form a Zn MOF with a mixture of cycloazocarbyl ligands with 1.2.4-triazolates.

[0058] In embodiments, the second cycloazocarbyl compound may be an imidazolate, 1,2,4-triazolate, pyrazolate or tetrazolate, and / or the other chelating ligand is a squarate (from squaric acid) or rubeanate (from rubeanic acid).

[0059] In embodiments, the molar ratio of 1,2,4-triazole to the second cycloazocarbyl compound added to the reaction ranges from 1:1 (50 mole % each) to 100:1.

[0060] In embodiments, the molar ratio of 1,2,4-triazole to second cycloazocarbyl compound added to the reaction may be 5:1 or greater.

[0061] In embodiments, the molar ratio of 1,2,4-triazole to second cycloazocarbyl compound added to the reaction may be 10:1 or greater.

[0062] It will be understood that multiple cycloazocarbyl compounds in addition to the 1,2,4-triazole can be used in the reactions herein. In such cases, the molar ratio of the 1,2,4-triazole to the total mixture of other cycloazocarbyl compounds (e.g., the other cycloazocarbyl compound can have a second cycloazocarbyl compound and a third cycloazocarbyl compound) can be calculated from the above ratios, e.g., a 1:1 molar ratio is 50 mole % equivalents of each. The hydrate of oxalic acid can be oxalic acid dihydrate.

[0063] In embodiments, the diacid may be squaric acid.

[0064] In embodiments, the dithio compound may be rubeanic acid, in which case the dithio compound may be an alternative chelating agent.

[0065] In embodiments, the molar ratio of the first ligand, eg, oxalate, to the second ligand added to the reaction ranges from 1:1 (50 mole percent each) to 100:1.

[0066] In embodiments, the molar ratio of the first ligand, eg, oxalate, to the second ligand added to the reaction is 5:1 or greater.

[0067] In embodiments, the molar ratio of the first ligand, eg, oxalate, to the second ligand added to the reaction is 10:1 or greater.

[0068] It will be understood that the reactions herein may use more than one chelating ligand in addition to the oxalate, and in such cases the molar ratio of the oxalate to the total mixture of other chelating ligands, e.g., secondary and tertiary ligands, may be calculated from the ratios above.

[0069] In an embodiment, the synthesis of zinc-containing MOFs or Zn MOFs of formula: Zn2Ht2Ox, wherein Ht is 1,2,4-triazolate; ·Ox is oxalate, the dianionic form of the diacid oxalic acid; Zn is the zinc cation, This may involve contacting the 1,2,4 triazole, the oxalate reagent, and a zinc salt or zinc oxide with a solvent comprising water in a liquid suspension at a temperature of about 100° C. or less and at a pressure within the range of 0.9 to 1.1 atmospheres.

[0070] In an embodiment, the synthesis of zinc-containing MOFs or Zn MOFs of formula: Zn2Ht2Ox, wherein Ht is 1,2,4-triazolate; ·Ox is oxalate, the dianionic form of the diacid oxalic acid; Zn is the zinc cation, The process involves contacting 1,2,4 triazole, an oxalate reagent, and a zinc salt or zinc oxide with a solvent consisting solely of water in a liquid suspension at a temperature below about 100°C and at a pressure within the range of 0.9 to 1.1 atmospheres.

[0071] In some embodiments, the reaction to form the Zn MOF can be carried out with a 5% or less stoichiometric excess of any one component, for example, the Ht component, the Ox component and / or the Zn component.

[0072] In embodiments, the reaction to form the Zn MOF can be carried out with a stoichiometric excess of triazole in the range of 10% to 100%.

[0073] In embodiments, the zinc salt may be a zinc reagent consisting of zinc carbonate, zinc acetate dehydrate, zinc chloride, or zinc nitrate.

[0074] In embodiments, zinc oxide may be the zinc reagent.

[0075] In embodiments, the oxalate reagent is lithium oxalate, sodium oxalate, potassium oxalate, or oxalic acid, or any combination thereof.

[0076] In an embodiment, an aqueous alcohol containing one lower alcohol can be added. The aqueous alcohol can be used as a solvent and / or dispersant.

[0077] In embodiments, the aqueous alcohol may be aqueous ethanol or aqueous methanol.

[0078] In embodiments, the aqueous alcoholic solution may contain 10% or more by volume of one or more alcohols, particularly 10% or more by volume of one or more lower alcohols.

[0079] In embodiments, the aqueous alcoholic solution may contain 25% or more by volume of one or more alcohols, particularly 25% or more by volume of one or more lower alcohols.

[0080] In embodiments, the aqueous alcoholic solution may contain 50% or more by volume of one or more alcohols, particularly 50% or more by volume of one or more lower alcohols.

[0081] In an embodiment, the aqueous alcohol may contain 40 to 60% by volume of one or more alcohols, particularly 40 to 60% by volume of one or more lower alcohols.

[0082] The separate liquid solutions or liquid suspensions can contain the desired stoichiometric amounts of zinc salt or zinc oxide relative to oxalic acid and cycloazocarbyl compound, respectively, which can be a molar ratio of zinc cation to oxalic acid to total cycloazocarbyl compound of 2:1:2. For example, a first cycloazocarbyl compound, or a first and a second cycloazocarbyl compound can be used in the reaction.

[0083] Preferably, in embodiments, the three components, zinc cation, oxalate and one or more cycloazocarbyl compounds, can be combined in a stoichiometric (molar) excess or deficiency of up to 5% with any of the three components to maximize product yield and / or minimize the formation of co-precipitates that are difficult to wash off.

[0084] In an embodiment, the order of addition of the liquid solutions or liquid suspensions may be as follows: in a first step, the first cycloazocarbyl, optionally the second cycloazocarbyl and the oxalate are added, followed by a second step of adding the zinc compound; in a first step, the zinc compound is added together with the first cycloazocarbyl and optionally the second cycloazocarbyl, followed by a second step of finally adding the oxalate; in a first step, the zinc compound is added together with the oxalate, followed by a subsequent step of finally adding the first cycloazocarbyl and optionally the second cycloazocarbyl; or in a first step, all solid components, for example the first cycloazocarbyl, optionally the second cycloazocarbyl, the oxalate and the zinc compound are mixed, followed by a second step of finally adding the solvent. The first N-heterocyclic compound can be a first cycloazocarbyl and the optional second N-heterocyclic compound can be a second cycloazocarbyl compound. The first N-heterocyclic compound is different from the second N-heterocyclic compound.

[0085] As will be appreciated by those skilled in the art, unintended deviations from the desired stoichiometry may occur if the starting materials used contain impurities. Starting materials of the necessary purity to achieve the desired stoichiometry are commercially available or can be prepared by methods well known in the art.

[0086] The resulting mixture can then be stirred until formation of the Zn MOF is complete.

[0087] The reaction can be carried out at ambient room temperature, for example, from about 15° C. to about 30° C., or optionally at a temperature up to about 100° C. The reagent suspension can optionally be heated above room temperature before mixing.

[0088] In an embodiment, the reagents, suspensions and / or solutions are heated and / or controlled to a temperature above ambient temperature, for example about 15°C, preferably at a temperature from about ambient to about 60°C, more preferably at a temperature from about ambient to about 30°C, prior to mixing.

[0089] In other embodiments, the reagents, suspensions and / or solutions are heated and / or controlled to a temperature above ambient temperature, for example about 15°C, preferably at a temperature from about ambient to about 90°C, more preferably at a temperature from about ambient to about 60°C, prior to mixing.

[0090] Additionally, in other embodiments, the reagents, suspensions and / or solutions are heated and / or controlled to a temperature above ambient temperature, for example about 15°C, preferably at a temperature from about ambient to about 100°C, more preferably at a temperature from about ambient to about 90°C, prior to mixing.

[0091] In embodiments, after addition of the last reagent or reagent suspension, the reaction mixture can be heated to reflux under atmospheric pressure, using a suitable condenser or related known apparatus to avoid solvent loss, the reflux temperature being dependent on the solvent or solvent mixture used.

[0092] It is discovered that heating the reaction mixture increases the rate of formation of the Zn MOFs.

[0093] The Zn MOF of the above process can be recovered from the suspension by any suitable filtration method and washed with a suitable solvent, water, a lower alcohol or a miscible mixture thereof. The washing solvent can be the same as or different from that used in the reaction. The washing solvent is preferably the same as that used in the reaction.

[0094] The completeness of the reaction and the purity of the product can be assessed by PXRD (powder X-ray diffraction), or by testing the powder surface area using Brunauer-Emmett-Teller (BET) surface area analysis, or by measuring the specific gas adsorption properties.

[0095] In embodiments, the Zn MOF prepared by the methods herein has a powder X-ray diffraction pattern with a highest intensity diffraction peak in the range 10°<20<15° using Cu Kα radiation.

[0096] In embodiments, the Zn MOF prepared by the methods herein is in the form of a powder and has a nitrogen sorption of 450 m, as determined according to the Langmuir sorption model applied to a nitrogen sorption isotherm at 77° K, as known in the art. 2 / g or more.

[0097] The Zn MOF prepared by the method herein has pores. In one embodiment, the Zn MOF has pores in a single domain crystal, and the pores in the single domain crystal have a pore size in the range of 0.3 to 2 nm. Preferred Zn MOFs prepared by the method herein can have a pore size in nm ranging from 0.4 to 1.9, 0.5 to 1.8, 0.6 to 1.7, or 0.7 to 1. In certain embodiments, the Zn MOF prepared by the method herein can have a pore size in nm or about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, about 0.9, about 1.0, about 1.1, about 1.2, about 1.3, about 1.4, about 1.5, about 1.6, about 1.7, about 1.8, about 1.9, or about 2.0.

[0098] The Zn MOFs prepared as described herein can be used in a method for the sorptive separation of a first component, e.g., an acid gas component or carbon dioxide, from a gas mixture containing the first component, acid gas or carbon dioxide, the separation method comprising the steps of: (a) contacting the gas mixture with at least one sorbent comprising a Zn MOF; (b) sorbing the first component in and / or on the Zn MOF and recovering a first product gas stream depleted in the first component compared to the gas mixture; and (c) selectively adsorbing or desorbing the first component from the Zn MOF by at least one of a pressure swing, a temperature swing, a partial pressure swing and a moisture swing and recovering a second product gas stream enriched in the first component compared to the gas mixture.

[0099] Zn MOFs can be formed into sorbent sheets of 100-1000 micrometer thickness, which are further assembled into contactors, parallel flow contactors, or contactor beds for the purpose of separation of gas components, particularly carbon dioxide and its removal from industrial flue gases. EXAMPLES

[0100] The following reactions are conducted at ambient room temperature and pressure without heating any components unless otherwise noted.

[0101] Thermogravimetric analysis is a simple tool to assess the degree of CO2 adsorption on selected powder samples at set temperatures and concentrations of CO2. In the following examples, CO2 adsorption capacity at 50°C under 15% CO2 in nitrogen is used to verify the quality of products formed by various exemplary synthetic processes disclosed.

[0102] [Example 1] First, Zn was added to the aqueous solvent in which the MOF crystals were formed under atmospheric reflux conditions (100 °C) to prepare Zn MOFs without any additional steps. A 5-liter, three-necked round-bottom flask equipped with an overhead stirrer, thermocouple, condenser, and heating mantle was charged with 336 g (3 mol) of basic zinc carbonate and 600 ml of DIH2O was added under slow stirring at 50 rpm. 190.6 g (1.507 mol) of oxalic acid dihydrate powder was added under stirring at 100 rpm in 8 min, during which CO2 was released. After charging, the slurry was stirred at 150 rpm for 30 min to release CO2. 208.9 g (3 mol) of 1,2,4-triazole dissolved in 400 ml of DIH2O was added to the flask in 5 min, followed by further stirring for about 30 min, during which CO2 was further released. The aqueous suspension was heated to reflux temperature with stirring at 250 rpm and held at approximately 100°C for 1 hour. The temperature was then quenched by adding cold distilled water to the slurry product before the suspension was collected and transferred to a Buchner funnel for filtration. The cake formed was then rinsed with distilled water until the filtrate conductivity was less than 100 microsiemens / cm. After drying the powder at 110°C under air for approximately 20 hours, 529 g of powder was obtained (99% of theoretical weight). The powder CO2 capacity at 50°C with 15% CO2 in nitrogen was measured at 46.2.0 cc / g.

[0103] [Example 2] A 500 ml three-neck round bottom flask equipped with an overhead stirrer, thermocouple, condenser and heating mantle was used. The flask was charged with 33.6 g (0.3 mol) basic zinc carbonate, 19.06 g (0.15 mol) oxalic acid dihydrate and 20.89 g (0.3 mol) 1,2,4-triazole. With stirring, 110 ml distilled water was added in 30 min. After the water was added, the slurry was stirred at 250 rpm for another 20 min to complete the reaction and release CO2, after which it was heated to reflux (~100 °C) for 1 h under stirring at 350 rpm. Distilled water was added to the slurry product and suction filtered in a Buchner funnel, followed by flushing the cake with distilled water until the conductivity of the filtrate was less than 100 microsiemens / cm. After drying the powder at 110° C. for about 20 hours, 53.3 g of powder was obtained (almost 100% of theoretical weight). The CO2 capacity of the dried powder at 50° C. and 15% CO2 in nitrogen was 34.9 cc / g.

[0104] [Example 3] In a 500 ml jacketed beaker, zinc acetate dehydrate powder (44 g, 0.2 mol) was dissolved in 120 ml of distilled water already warmed at 50 °C. After the salt was completely dissolved, oxalic acid dehydrate powder (12.6 g, 0.1 mol) was slowly added to the solution while mixing the solution. After 30 minutes, 1,2,4-triazole (21 g or 0.3 mol) was slowly added and the solution was mixed at 50 °C overnight. The solid content of the slurry was calculated to be about 39.3 wt%. After the reaction was completed, the precipitated product was suction filtered in a Buchner funnel, followed by washing the cake with distilled water until the conductivity of the filtrate was less than 100 microsiemens / cm. After drying the powder at 110 °C for about 20 hours, 30 g of powder was obtained. The CO2 capacity of the dry powder at 50 °C and 15% CO2 in nitrogen was 42.4 cc / g.

[0105] [Example 4] In a 500 ml jacketed beaker, zinc acetate dehydrate powder (44 g, 0.2 mol) was dissolved in 80 ml of DIH2O already warmed at 50°C. After the zinc salt was completely dissolved, oxalic acid dehydrate powder (12.6 g, 0.1 mol) was slowly added to the solution with mixing. After 30 minutes, 1,2,4-triazole (21 g, 0.3 mol) was slowly added and the solution was mixed at 50°C overnight. The solids content of the slurry increased to 49.2 wt% compared to Example 3. After drying the powder at 110°C for about 20 hours, 30 g of powder was obtained. The CO2 capacity of the dry powder at 50°C and 15% CO2 in nitrogen was 42.6 cc / g.

[0106] [Example 5] In a 500 ml jacketed beaker, zinc acetate dehydrate powder (44 g, 0.2 mol) was dissolved in 120 ml of DIH2O water already warmed at 50 °C. After the zinc salt was completely dissolved, oxalic acid dehydrate powder (12.6 g, 0.1 mol) was slowly added to the solution with mixing. After 30 minutes, 1,2,4-triazole (28 g, 0.4 mol) was slowly added and the solution was mixed at 50 °C overnight. The solid content of the slurry was calculated to be about 41.0 wt%. After the reaction was completed, the precipitated product was suction filtered in a Buchner funnel, followed by flushing the cake with distilled water until the conductivity of the filtrate was less than 100 microsiemens / cm. After drying the powder at 110 °C for about 20 hours, 28 g of powder was obtained. The CO2 capacity of the dry powder at 50 °C and 15% CO2 in nitrogen was 41.0 cc / g.

[0107] [Example 6] FIG. 1 shows and compares the X-ray diffraction patterns of the materials prepared in Example 3, Example 4, and the materials prepared according to the method described in WO 2019 / 204934. In FIG. 1, the x-axis is 2θ degrees and the y-axis is intensity. X-ray diffraction line 1 relates to the material prepared by the method disclosed in WO 2019 / 204934. X-ray diffraction line 2 relates to the material prepared in Example 3, and X-ray diffraction line 3 relates to the material prepared in Example 4. The diffraction peaks of X-ray diffraction lines 1, 2, and 3 are substantially the same, indicating that the materials prepared by these methods have substantially the same structure.

[0108] [Example 7] A 1 liter beaker equipped with a high shear mixer was charged with 150 ml MeOH (ACS grade) and 150 ml RO HO (reverse osmosis water). Under stirring at 350 rpm, 77.2 g oxalic acid dihydrate (98%, 0.6 mol) and 84.4 g 1,2,4-triazole (99%, 1.21 mol) were added sequentially. The mixture was stirred for 1.5 hours for compound formation, during which the viscosity increased, and the stirring speed was adjusted to 1245 rpm to provide sufficient stirring. 135.3 g basic zinc carbonate (58% Zn, 1.2 mol) was added in small portions for 5 hours, during which the stirring speed was adjusted from 1245 rpm to 3277 rpm. 80 ml of additional solvent (MeOH / H2O=1 / in vol) was added to dilute the slurry which appeared too dry. Stirred overnight (16 hours) and then 82 ml of MeOH / H2O (1 / 1 vol) was added to wet the slurry and stirred at 4397 rpm for up to 18 hours. A sample was taken, dried in an oven at 90°C, and tested by TGA for CO2 capacity at 15% CO2 / 50°C. After 21 hours of stirring, the reaction was stopped and after workup and drying the capacity was 44.1 cc / g for CO2 under 15% CO2 in nitrogen at 50°C.

[0109] [Example 8] A 1-liter beaker equipped with an anchor-shaped blade and a non-visible overhead stirrer was charged with 100 ml MeOH (ACS grade) and 100 ml RO HO. Under non-splash stirring, 112.75 g basic zinc carbonate (58% Zn, 1.0 mol) was added. 69.78 g 1,2,4-triazole (99%, 1.0 mol) was added in one portion. The mixture was stirred for 20 min, during which time solids adhering to the walls of the beaker were pushed into the slurry with a spatula. 64.33 g oxalic acid dihydrate (98%, 0.5 mol) was added in portions over 1.25 h, during which time 50 ml MeOH / hhO (1 / 1 vol) was added. The mixture was stirred for a total of 40.5 h until the third day, when 100 ml of mixed solvent was added as the product was dry. The as-synthesized powder capacity is 39.8 cc / g CO2 under 15% CO2 in nitrogen at 50° C. After washing with H2O and drying, the capacity was 44.5 cc / g CO2 under 15% CO2 in nitrogen at 50° C.

[0110] [Example 9] A 500 ml 3-neck round bottom flask equipped with an overhead stirrer, thermocouple, condenser and heating mantle was charged with 19.05 g (0.15 mol) of oxalic acid dihydrate and 50 ml of distilled water (DIH2O). 24.54 g (0.3 mol) of zinc oxide was added with stirring at 250 rpm for 22 minutes and 20 ml of DIH2O was used to flush the powder from the flask neck into the flask. After stirring for an additional 40 minutes, a solution of 20.89 g (0.3 mol) of 1,2,4-triazole dissolved in 30 ml of DIH2O was fed to the flask followed by rinsing the beaker and flask neck with 20 ml of DIH2O. After stirring at 350 rpm for 30 minutes, the reaction slurry was heated above 90°C and maintained for 3.75 hours. DIH2O was added to the slurry and filtered through a Büchner funnel with suction, followed by flushing the cake with DIH2O until the conductivity of the filtrate was less than 100 microsiemens / cm. After drying the powder at 110°C for approximately 20 hours, 52.6 g of powder was obtained. The CO2 capacity at 50°C and 15% CO2 in nitrogen was 40.4 cc / g.

[0111] Table 1: Comparison of synthesis parameters and powder test results for Example 7 and Example 8. CALF-20 was successfully prepared in Example 7 and Example 8. [Table 1]

Claims

1. Formula Zn ２ Ht ２ A method for preparing a Zn MOF of composition Ox, wherein Ht is a first N-heterocyclic compound, either a 1,2,4-triazolate or a combination of a 1,2,4-triazolate and at least a second N-heterocyclic compound, said second N-heterocyclic compound being different from said first N-heterocyclic compound; Ox is an oxalate, a dianionic form of the diacid oxalic acid, a dicarboxylic acid or a dithio compound; Zn is a zinc cation; contacting said first N-heterocyclic compound, said Ox, and a solvent comprising water in a liquid suspension at a temperature of 100° C. or less and a pressure of 0.9 to 1.1 atmospheres; forming crystals of the Zn MOF.

2. 2. The method of claim 1, wherein the step of contacting the first N-heterocyclic compound, the Ox, and the solvent comprising water further comprises contacting the second N-heterocyclic compound with the first N-heterocyclic compound, the Ox, and the solvent.

3. During the first step, a zinc salt or zinc oxide is added as a zinc reagent to the solution or liquid suspension, During a second step, an oxalate is added to the solution or liquid suspension, and 2. The method of claim 1, further comprising adding said first N-heterocyclic compound as a first cycloazocarbyl compound to said solution or said liquid suspension during a third step.

4. The method of any one of claims 1 to 3, wherein the solvent further comprises only water.

5. 4. The method of claim 3, wherein the zinc reagent further comprises one of zinc oxide, zinc acetate, zinc salts, zinc carbonate, zinc acetate dehydrate, zinc chloride, or zinc nitrate.

6. The method of claim 1, wherein the temperature of the liquid suspension is in the range of 15°C to 100°C.

7. Formula Zn ２ Ht ２ A method for preparing a zinc-containing MOF or Zn MOF of formula Ox, wherein Ht is 1,2,4-triazolate, Ox is oxalate, the dianionic form of the diacid oxalic acid, and Zn is a zinc cation; The method includes contacting in a liquid suspension at a temperature below 100° C. and a pressure within 0.9 to 1.1 atmospheres 1,2,4 triazole, an oxalate salt, and a zinc salt or zinc oxide, and a solvent comprising water.

8. The method of claim 7 , wherein the solvent further comprises only water.

9. 8. The method of claim 7 carried out with no more than 5% stoichiometric excess of any one component.

10. The process of claim 7, carried out with a stoichiometric excess of triazole in the range of 10% to 100%.

11. 8. The method of claim 7 further comprising adding a zinc reagent in the first step.

12. The method of claim 7, further comprising adding an oxalate which is one of lithium oxalate, sodium oxalate, potassium oxalate or oxalic acid, or any combination thereof.

13. 8. The method of claim 7 further comprising adding an aqueous alcohol.

14. 8. The method of claim 7, further comprising carrying out the reaction at a temperature within the temperature range of 15°C to 30°C.

15. 8. The method of claim 7, further comprising controlling the temperature of one or more reagents and / or the liquid suspension to a temperature between 15°C and 100°C prior to mixing.

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