WO2019162344A1

WO2019162344A1 - Process for preparing a mof with gamma-valerolactone

Info

Publication number: WO2019162344A1
Application number: PCT/EP2019/054244
Authority: WO
Inventors: Karl Petter Lillerud; Sachin CHAVIN
Original assignee: Profmof As
Priority date: 2018-02-20
Filing date: 2019-02-20
Publication date: 2019-08-29
Also published as: GB201802710D0

Abstract

There is provided a process for preparing a metal organic framework (MOF), comprising the steps (i) preparing a reaction mixture comprising a metal salt and at least one organic linker compound in gamma-valerolactone (GVL)solvent; and(ii) heating the reaction mixture from step (i).

Description

PROCESS FOR PREPARING A MOF WITH GAMMA-VALEROLACTONE

Field of the Invention

The present invention relates to a process for preparing metal organic frameworks (MOFs), in particular to a process for preparing Zr-MOFs. Specifically, the process employs gamma- Valero lactone (GVL) as a solvent. The invention also relates to MOFs produced by such processes.

Background

MOFs or "metal organic frameworks" are compounds having a lattice structure having vertices or "cornerstones" which are metal-based inorganic groups, for example metal oxides, linked together by organic linkers. The linkers are usually at least bidentate ligands which coordinate to the metal-based inorganic groups via functional groups such as carboxylate and/or amine. The porous nature of MOFs renders them promising materials for many applications such as gas storage and catalyst materials.

Perhaps the best known MOF is MOF-5 in which each Z114O cornerstone is coordinated by six bis-carboxylate organic linkers. Other MOFs in which the inorganic cornerstone is for example chromium, copper, vanadium, cadmium or iron are also known.

Numerous processes are known in the prior art for the production of MOFs. The most commonly used techniques involve the reaction of a metal salt with the desired organic linker in a suitable solvent, usually organic, such as

dimethylformamide (DMF). High pressures and temperatures are commonly required to facilitate the reaction. Typical methods are disclosed in, for example, WO 2009/133366, WO 2007/023134, W02007/090809 and WO 2007/118841.

The use of elevated temperatures and pressures not only increases the cost of the process but also means that scale-up to an industrial level poses many

challenges. Apparatus suitable for withstanding the severe reaction conditions is often only compatible with small scale batch synthesis, rather than the continuous processes favoured for large scale production. Employing high pressures also carries with it safety concerns, particularly when combined with the use of corrosive liquids. Moreover, the use of organic solvents as the reaction medium is undesirable as such solvents are harmful to the environment and are expensive.

As a result of these drawbacks, replacement of the organic solvent with an aqueous medium has been investigated and is reported in, for example, US 7411081 and US 8524932. However, many MOFs are still being prepared in organic solvents because of the very low solubility of many organic linkers in aqueous media. This necessitates the use of solvents which are expensive and harmful to the environment.

Synthesis methods using Dimethylformamide (DMF), Dimethyl sulfoxide (DMSO), and Dimethylamide (DMA) are reported in the literature. DMF and DMA are toxic and their high exposure is considered to be dangerous to life or health. DMSO is a non-toxic solvent but it can be easily decomposed by acids at lower than boiling point temperature, possibly leading to an explosion. Moreover, DMSO upon decomposition will produce dimethyl sulfide, which is highly flammable. Therefore, high volume industrial production using solvents like DMF, DMSO, and DMA is unfeasible and of high health and environmental concern.

As MOFs become increasingly employed as alternatives to, for example, zeolites, polymers and activated carbons there is a need for the development of novel processes for their production which are applicable to use on an industrial scale. The process should ideally be one which is“green” and thus considered environmentally friendly. It should preferably provide high volume MOF production per volume of solvent used. It would also be advantageous to have a process with easier waste management by biodegradation, incineration etc. Ideally, a process which offers improvement in more than one of the above aspects would be developed.

The present inventors have surprisingly found that MOFs may be prepared in a straightforward process utilising gamma- valero lactone (GVF) as a solvent. The procedure is applicable to use on an industrial scale and offers an environmentally friendly and cheap route to these valuable materials.

Gamma- Valero lactone (GVF - structure shown in figure 1) is a colourless organic liquid and has been identified as a potential green solvent. It is readily obtained from cellulosic biomass. It can be produced at a price between 1-2 US$/L. GVL boils at 207 °C and has a flash point of 96 °C which are both higher than for DMF (B.P. 150 °C and flash point 67 °C ) thereby rendering it easier to operate at high temperature. GVL is chemically and thermally more stable than the organic solvents (such as DMF, DMA and DMSO) usually employed in MOF synthesis. The higher stability of GVL may allow for solvent recycling in MOF production processes.

GVL is also considered as a potential fuel, therefore the solvent waste may be used as a fuel to produce energy thus making the overall processes more economical. GVL upon burning will produce C0₂ while DMF and DMSO will produce toxic nitrogen and sulfur-containing compounds. Alternatively, because of the high solubility of GVL in water, biodegradation could be pursued to manage the waste.

Summary of the Invention

Thus, in a first aspect, the invention provides a process for preparing a metal organic framework (MOF), comprising the steps:

(i) preparing a reaction mixture comprising a metal salt and at least one organic linker compound in gamma- valero lactone (GVL) solvent; and

(ii) heating the reaction mixture from step (i).

In a particularly preferable embodiment, the metal organic framework is a zirconium-based metal organic framework (Zr-MOF).

In a further aspect, the invention provides a metal organic framework (MOF) produced or formable by the processes as herein described.

Detailed Description

The present invention describes a process for the preparation of a metal organic framework (MOF), such as a zirconium-based metal organic framework (Zr-MOF). The process involves preparing a reaction mixture comprising a metal salt and at least one organic linker compound in gamma- valerolactone (GVL) solvent and heating the reaction mixture. The process typically involves

subsequently isolating the MOF. MOF

As used herein, the term“MOF” is intended to cover any metal organic framework. MOFs typically comprise at least one metal ion or cluster of metal ions and at least one organic linker compound.

The metal ion or cluster of metal ions may be any suitable metal selected from Groups 1 to 16 of the Periodic Table. The metal ion may have any valence appropriate for the specific metal. Non-limiting metal ions are those from chemical elements in the following groups: alkali metals (Li, Na, K, Rb, Cs, Fr), alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra), transition metals (Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, lr, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg) and post-transition metals (Al, Ga, In, Tl, Sn, Pb, Bi), as well as metalloids (B, Si, Ge, As, Sb, Te, Po), lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) and actinides (Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No,

Lr). Unusual metals not mentioned above or newly discovered could be also used in the method of the invention. In one embodiment the metal ion is selected from the group consisting of Zn, Cu, Ni, Co, Fe, Mn, Cr, Cd, Mg, Ca, Al, Zr, Gd, Eu, Tb, Ce, Y, Hf, and mixtures thereof.

In a particularly preferable embodiment, the metal ion is selected from the group consisting of, zirconium, magnesium, zinc, aluminium, iron, cerium, hafnium and yttrium. Most preferably, the metal ion is zirconium.

Whilst it is possible for a mixture of metal ions to be used, it is preferable if the MOF contains only a single type of metal ion.

In a particularly preferred embodiment, the process of the invention is used to prepare zirconium-based metal organic frameworks (Zr-MOFs). As used herein, the term“Zr-MOF” is intended to cover any metal organic frameworks (MOFs) which comprise at least one zirconium metal ion. The Zr-MOFs of the invention have“cornerstones” which are zirconium inorganic groups. Typical zirconium inorganic groups include zirconium ions connected by bridging oxygen or hydroxide groups. These inorganic groups are further coordinated to at least one organic linker compound. In some cases, the inorganic groups may be further connected to non bridging modulator species, complexing reagents or ligands (e.g. sulfates or carboxylates such as formate, benzoate or acetate) and/or solvent molecules. The zirconium oxide unit is usually based on an idealized octahedron of Zr-ions which are p3-bridged by O² and/or OH ions via the faces of the octahedron and further saturated by coordinating moieties containing O-atoms like carboxylate groups. The idealised Zr oxide cluster is considered to be a Zr₆0₃₂-cluster which comprises between 6 and 12 (preferentially as close as possible to 12) carboxylate groups. However, in practice, there is a degree of flexibility in the structure of the cluster. The cluster may be represented by the formula Zr₆O_x(OH)_8-x wherein x is in the range 0 to 8. For example, the cluster may be represented by the formula

Zr₆(0)₄(0H)₄,

Whilst it not outside the bounds of the present invention for the Zr-MOF to comprise additional metal ions other than zirconium, such as hafnium, titanium, or cerium, zirconium may be the only metal ion present. If additional metal ions are present these may be present in an amount of up 50 wt% relative to total amount of metal ions, preferably up to 25 wt%, more preferably up to 10 wt%, e.g. up to 5 wt%.

The Zr-MOFs of the invention particularly preferably have cornerstones having at least 12 coordination sites for the organic linkers, e.g. 12-36, especially preferably at least 14, 16 or 18, most especially 24. In this way at least 6, more preferably at least 8, especially at least 12 bidentate ligand groups of the organic linkers can bind to each cornerstone.

In another preferred embodiment the Zr-MOF of the invention particularly preferably has cornerstones having at least 6 coordination sites for the organic linkers, e.g. 6-36, especially preferably at least 6, 12, 18, most especially 24. In this way at least 6, more preferably at least 8, especially at least 12 bidentate or at least 6 tridentate or hexadentate ligand group of the organic linkers can bind to each cornerstone. The structure of the MOFs of the invention may be one- two- or three- dimensional. The MOF usually comprises pores which are present in the voids between the coordinated network of zirconium ions and organic linker compounds. The pores are typically micropores, having a diameter of 2 nm or less, or mesopores, having a diameter of 2 to 50 nm.

In all embodiments, the surface area of the MOF is preferably at least 400 m²/g, more preferably at least 500 m²/g, especially at least 700 m²/g, such as at least 1020 m²/g, for example at least 1050 m²/g, e.g. at least 1200 m²/g, as measured by nitrogen adsorption at 77 K, using BET method. The surface area may be up to 10000 m²/g, especially up to 5000 m²/g. It will be understood that, where functionalised organic linker compounds are used, the presence of additional, and often bulky, groups may affect (i.e. reduce) the surface area of the MOF.

In addition to the at least one metal ion or cluster of metal ions, the MOFs of the invention comprise at least one organic linker compound. The organic linker compound is typically at least bidentate, i.e. has at least two functional groups capable of coordinating to the metal ion. The organic linker compound may also be tridentate (i.e. containing three functional groups) or tetradentate (i.e. containing four functional groups). In one embodiment, the organic linker coordinates between 2 and 20 metal ions. In a preferred embodiment, the organic ligand coordinates between 2 and 12 metal ions. In a more preferred embodiment, the organic ligand coordinates between 2 and 8 metal ions.

The MOF may have a metal ion to organic linker molecule ratio of from 1 :0.30 to 1 :0.55, especially 1 :0.33 to 1 :0.51, particularly 1 :0.33. Other preferred metal ion to organic linker molecule ratios are 0.5: 1, 1 : 1, 3: 1 and 1 :3, especially 1 : 1.

The organic linker compounds of the MOFs of the invention may be any organic linker molecule or molecule combination capable of binding to at least two inorganic cornerstones and comprising an organic moiety. By“organic” moiety we mean a carbon based group which comprises at least one C-H bond and which may optionally comprise one or more heteroatoms such as N, O, S, B, P, Si. Typically, the organic moiety will contain 1 to 50 carbon atoms.

The organic linker compound may be any of the linkers conventionally used in MOF production. These are generally compounds with at least two cornerstone binding groups, e.g. carboxylates, optionally with extra functional groups which do not bind the cornerstones but may bind metal ions on other materials it is desired to load into the MOF. The introduction of such extra functionalities is known in the art and is described for example by Campbell in JACS 82:3126-3128 (1960).

The organic linker compound may be in the form of the compound itself or a salt thereof, e.g. a disodium 1 ,4-benzenedicarboxylate salt or a monosodium 2- sulfoterephthalate salt.

The organic linker compound is preferably soluble in the GVL solvent employed in the processes of the invention. By“soluble” we mean that it preferably has a solubility which is high enough to enable the formation of a homogenous solution. The solubility of the organic linker compound in GVL may be at least 1 g/L at room temperature and pressure (RTP), preferably at least 2 g/L, more preferably at least 5 g/L.

The organic linker compound typically comprises at least two functional groups capable of binding to the inorganic cornerstone. By“binding” we mean linking to the inorganic cornerstone by donation of electrons (e.g. an electron pair) from the linker to the cornerstone. Preferably, the linker comprises two, three or four functional groups capable of such binding.

Non-limiting functional groups that can be contained by the organic ligand to form a MOF according to the invention are -COOH, -CSSH, -N0₂, - B(OH)₂, - S0₃H, -Ge(OH)₃, -Sn(OH)₃, -Si(SH)₄, -Ge(SH)₄, -Sn (SH)₃, -P0₃H, - As0₃H, - AS0₄H, -P(SH)₃, AS(SH)₃, C₄H₂0₄, -RSH, -RNH₂, -RNR-, -ROH, - RCN, - PO(OR)₂, -RN₃, where R is hydrogen, alkyl, alkylene, preferably Cl, C2, C3, C4 or C5 alkylene, or aryl group, preferably comprising 1 or 2 aromatic nuclei. Typically, the organic linker comprises at least two functional groups selected from the group of carboxylate (COOH), amine (NH₂), nitro (N0₂), anhydride and hydroxyl (OH) or a mixture thereof. In a preferable embodiment, the linker comprises two, three or four carboxylate groups.

The organic linker compound may be based on a saturated or unsaturated aliphatic compound or an aromatic compound. Alternatively, the organic linker compound may contain both aromatic and aliphatic moieties. In one embodiment, the aliphatic organic linker compound may comprise a linear or branched Ci_₂o alkyl group or a C₃_i₂ cycloalkyl group. The term "alkyl" is intended to cover linear or branched alkyl groups such as all isomers of propyl, butyl, pentyl and hexyl. In all embodiments, the alkyl group is preferably linear. Particularly preferred cycloalkyl groups include cyclopentyl and cyclohexyl.

In one preferred embodiment, the organic linker compound comprises an aromatic moiety. The aromatic moiety can have one or more aromatic rings, for example two, three, four or five rings, with the rings being able to be present separately from one another and/or at least two rings being able to be present in condensed form. The aromatic moiety particularly preferably has one, two or three rings, with one or two rings being particularly preferred, most preferably one ring. Each ring of said moiety can independently comprise at least one heteroatom such as N, O, S, B, P, Si, preferably N, O and/or S.

The aromatic moiety preferably comprises one or two aromatic C6 rings, with the two rings being present either separately or in condensed form. Particularly preferred aromatic moieties are benzene, naphthalene, biphenyl, bipyridyl and pyridyl, especially benzene.

Examples of suitable organic linker compounds include oxalic acid, ethyloxalic acid, fumaric acid, 1,3, 5-benzene tricarboxylic acid (BTC), 1,1’- binaphthyl 4,4'-dicarboxylic acid (BINAP-H₂), 1,3, 5-benzene tribenzoic acid (BTB), benzene tribiphenylcarboxylic acid (BBC), 5, 15-bis (4-carboxyphenyl) zinc (II) porphyrin (BCPP), 1, 4-benzene dicarboxylic acid (BDC), 2-amino- 1, 4-benzene dicarboxylic acid (R3-BDC or H2N BDC), 1,2, 4, 5-benzene tetracarboxylic acid, 2- nitro-l, 4-benzene dicarboxylic acid l,l'-azo-diphenyl 4,4'-dicarboxylic acid, eye lo butyl- 1, 4-benzene dicarboxylic acid (R6-BDC), 1,2, 4-benzene tricarboxylic acid, 2,6-naphthalene dicarboxylic acid (NDC), l,l'-biphenyl 4,4'-dicarboxylic acid (BPDC), 2,2'-bipyridyl-5,5'-dicarboxylic acid, adamantane tetracaboxylic acid (ATC), adamantane dibenzoic acid (ADB), adamantane teracarboxylic acid (ATC), dihydroxyterephthalic acid (DHBDC), biphenyltetracarboxylic acid (BPTC), tetrahydropyrene 2,7-dicarboxylic acid (HPDC), pyrene 2,7-dicarboxylic acid (PDC), pyrazine dicarboxylic acid, acetylene dicarboxylic acid (ADC), camphor dicarboxylic acid, benzene tetracarboxylic acid, l,4-bis(4-carboxyphenyl)butadiyne, nicotinic acid, and terphenyl dicarboxylic acid (TPDC). Other acids besides carboxylic acids, e.g. boronic acids may also be used. Anhydrides may also be used.

In a particularly preferred embodiment, the organic linker compound is selected from the group consisting of 1 ,4-benzene dicarboxylic acid (BDC), fumaric acid, 1,3, 5-benzene tricarboxylic acid (BTC), 1 , G-binaphthyl 4,4'-dicarboxylic acid (BINAP-H₂) or mixtures thereof.

A mixture of two or more of the above-mentioned linkers may be used. It is preferable, however, if only one type of linker is used.

Where the MOF is a Zr-MOF with a bidentate organic linker it is preferably of UiO-66 type. UiO-66 type Zr-MOFs cover structures in which the zirconium inorganic groups are Zr₆(0)₄(0H)₄ and the organic linker compound is 1 ,4-benzene dicarboxylic acid or a derivative thereof. Derivatives of 1 ,4-benzene dicarboxylic acid used in UiO-66 type Zr-MOFs include 2-amino- 1, 4-benzene dicarboxylic acid, 2 -nitro-l, 4-benzene dicarboxylic acid, 1,2, 4-benzene tricarboxylic acid and 1,2, 4,5- benzene tetracarboxylic acid.

When the linker is 1 ,4-benzene dicarboxylic acid, the resulting MOF may be referred to as UiO-66(Zr). When the linker is 2-amino- 1, 4-benzene dicarboxylic acid, the resulting MOF may be referred to as UiO-66(Zr)-NH₂. When the linker is 1,2, 4-benzene tricarboxylic acid, the resulting MOF may be referred to as UiO- 66(Zr)-COOH. When the linker is 1,2, 4, 5-benzene tetracarboxylic acid, the resulting MOF may be referred to as UiO-66(Zr)-2COOH.

Where the MOF is a Zr-MOF with a tridentate organic linker it is preferably of MOF-8O8 type. Where the MOF is a Zr-MOF with, tetradentate or hexadentate organic linker it is preferably of NU- 1000, pbz-MOF-l type structure respectively.

A mixture of linkers may be used to introduce one or more functional groups within the pore space, e.g. by using aminobenzoic acid to provide free amine groups or by using a shorter linker such as oxalic acid. This introduction of functionalised linkers is facilitated by having a MOF with inorganic cornerstones with a high number of coordination sites. Where the number of these coordination sites exceed the number required to form the stable 3D MOF structure, functionalisation of the organic linkers may be effected, e.g. to carry catalytic sites, without seriously weakening the MOF structure. By“functionalised MOF” we mean a MOF wherein one or more of the backbone atoms of the organic linkers carries a pendant functional group or itself forms a functional group. Functional groups are typically groups capable of reacting with compounds entering the MOF or acting as catalytic sites for reaction of compounds entering the MOF. Suitable functional groups will be apparent to a person skilled in the art and in preferred embodiments of the invention include amino, nitro, thiol, oxyacid, halo (e.g. chloro, bromo, fluoro) and cyano groups or heterocyclic groups (e.g. pyridine), each optionally linked by a linker group, such as carbonyl. The functional group may also be a phosphorus-or sulfur-containing acid.

A particularly preferred functional group is halo, most preferably a fluoro group.

Preferably, the functionalised MOF has a surface area of at least 400 m²/g, more preferably at least 500 m²/g, especially at least 700 m²/g, such as at least 1020 m²/g.

Process

The process of the invention comprises at least the steps of:

(ii) heating the reaction mixture from step (i).

The organic linker compound may be any organic linker as hereinbefore defined. It will be understood that the organic linker described in the context of the MOF produced by the processes of the invention is the same organic linker which is used as a starting material in step (i) of the process of the invention, albeit that once bound to the inorganic cornerstone the organic linker will be deprotonated. Thus all preferable embodiments defined above relating to the organic linker in the context of the MOF apply equally to this compound as a starting material.

The metal ions of the MOF are provided in the form of at least one metal salt, which may or may not be in its hydrated form. Whilst the use of a mixture of two or more different salts is encompassed by the invention, it is preferable if one salt is used.

The metal salt is usually soluble in GVL, i.e. preferably having a solubility of at least 1 g/L at room temperature (i.e. 18 to 30 °C) and pressure (i.e. 0.5 to 3 bar) (RTP), preferably at least 2 g/L, more preferably at least 5 g/L.

Preferable metal ions are discussed above in the context of the MOF and all embodiments discussed therein apply equally here. Suitable counter-ions will be familiar to the skilled worker and may include halides (e.g. chlorides and bromides), acetates, nitrates, formats, oxalates, acetylacetonates, carbonates, tatrates, oxides, acrylates, carboxylates, sulfates, hydroxides, perchlorates, oxynitrates and oxychlorides.

Where the metal salt is a zirconium salt, examples of preferable metal salts include zirconium sulfate, zirconium hydroxide, zirconium acetylacetonate, zirconium chloride (ZrCl₄) and zirconyl chloride (ZrOCf nFLO, wherein n is an integer from 1 to 10, preferably 8).

In some embodiments, the reaction mixture preferably further comprises a growth modulator. By“growth modulator” we mean a compound that affects the rate of crystal growth, making it slower or faster. Suitable growth modulators are known in the art. Non-limiting examples of growth modulator compounds for use in the invention are monocarboxylic acids compounds (such as acetic acid, benzoic acid, formic acid, trifluroacetic acid or amino acids), inorganic acids (such as hydrochloric acids, hydrofluoric acid, sulfuric acids). Basic compounds such as alkali hydroxide (e.g. NaOH or KOH) or ammonium hydroxide could also be used as a growth modulator

The reaction mixture prepared in step (i) of the processes of the invention is typically prepared by mixing the various components together in the GVL solvent. Mixing may be carried out by any known method in the art, e.g. mechanical stirring. The mixing is preferably carried out at temperature between 18 and 50 °C. Usually, step (i) is carried out at or around atmospheric pressure, i.e. 0.5 to 2 bar, especially 1 bar.

In step (ii) of the process, the reaction mixture prepared in step (i) is heated. Heating is usually carried out to a temperature at which the reaction mixture boils. Preferably, the temperature is increased to 50 - 150 °C, more preferably 60 - 130 °C, such as 80-120 °C. Usually, step (ii) is carried out at or around atmospheric pressure, i.e. 0.5 to 2 bar, especially 1 bar.

The reaction mixture is preferably heated for a period of time of at least 20 minutes, more preferably at least 30 minutes, even more preferably at least 50 minutes, i.e. at least 60 minutes. The reaction mixture is preferably heated for not more than 10 hours, more preferably not more than 5 hours, especially not more than 2 hours.

Step (ii) is generally carried out by heating the reaction mixture from step (i) under reflux at the temperature and for the time periods as hereinbefore defined.

The skilled man will appreciate that heating under reflux is a routine procedure with which anyone working in the field of the invention would be familiar.

The method of heating may be by any known method in the art, such as heating in a conventional oven, a microwave oven or heating in an oil bath.

The high boiling point (207 °C) and high flash point (97 °C) of GVL offers numerous advantages over those of previous methods wherein DMF, DMSO and DMA solvents were used as the reaction medium. The mild reactions conditions and high stability of the solvent used in the process of the invention offer the possibility of solvent recycling. GVL is also considered as a potential fuel; therefore the solvent waste can be used as a fuel to produce energy thus making the overall processes more economical. GVL upon burning will produce C0₂ while DMF and DMSO will produce toxic nitrogen and sulfur-containing compounds. Alternatively, because of the high solubility of GVL in water, biodegradation can be pursued to manage the waste. This offers improvements in terms of costs, safety and suitability for industrial scale-up.

The molar ratio of total metal ions to total organic linker compound(s) present in the reaction mixture prepared in step (i) is typically between 1 :0.30 and 1 :1, however in some embodiments an excess of the organic linker compound may be used. Thus, in some embodiments, the molar ratio of total metal ions to total organic linker compound(s) in the reaction mixture is in the range 1 : 0.30 to 1 :5, such as 1 :1 or 1 :4. It will be appreciated that the MOF product forms during step (ii) of the process.

The processes of the invention usually comprise a further step (iii) isolating the MOF.

Advantageously, the MOF is usually formed as a crystalline product which can be isolated quickly and simply by methods such as filtration, or centrifugation. This offers an improvement over some methods of the prior art which produce an amorphous or gel-like product which must be further recrystallized before it can be isolated. The processes of the present invention thus preferably eliminate the need for these additional steps.

The isolation step (iii) is typically carried out by filtration, but isolation may also be performed by processes such as centrifugation, solid-liquid separations or extraction. After isolation, the MOF is preferably obtained as a fine crystalline powder having crystal size of 0.1 to 100 pm, such as 10 to 50 pm.

In addition to steps (i), (ii) and (iii), the processes of the invention may comprise additional steps, such as drying and/or cooling. Typically, there will be a cooling step between steps (ii) and (iii). Cooling usually involves bringing the temperature of the reaction mixture back to room temperature, i.e. 18-30 °C.

In a further embodiment, the invention relates to a metal organic framework (MOF) produced or formable by the processes as herein described.

Applications

The MOF produced or formable by the processes of the present invention may be employed in any known application for such materials. Applications therefore include, but are not restricted to, electrode materials, drug reservoirs, catalyst materials, adsorbents and cooling media.

Figures

Figure 1: Drawing of molecular structure of gamma- valero lactone (GYL). Figure 2. Structure of UiO-66-BDC.

Figure 3a-b. Powder X-ray diffraction patterns of the UiO-66-BDC product from the synthesis 1-11.

Figure 4. Powder X-ray diffraction pattern, Thermogravimetric analysis, nitrogen sorption and Scanning electron microscopy of UiO-66-BDC obtained in upscale synthesis 10. Figure 5. Powder X-ray diffraction pattern, Thermogravimetric analysis, nitrogen sorption and Scanning electron microscopy of UiO-66-BDC obtained in upscale synthesis 11.

Figure 6. Structure of Zr-Fumarate.

Figure 7a-b. Powder X-ray diffraction patterns of the UiO-66-BDC product from the syntheses 12-21

Figure 8. Powder X-ray diffraction pattern and Thermogravimetric analysis of Zr- Fumarate obtained from upscaled synthesis 12.

Figure 9. Powder X-ray diffraction pattern, Thermogravimetric analysis, nitrogen sorption isptherm and scanning electron microscopy of Zr-Fumarate obtained in upscale synthesis 13.

Figure 10. Powder X-ray diffraction pattern, Thermogravimetric analysis, nitrogen sorption isotherm and scanning electron microscopy of Zr-Fumarate obtained in upscale synthesis 21.

Figure 11. Structure of MOF-808. Figure 12. Powder X-ray diffraction pattern and Thermogravimetric analysis of MOF-808 obtained by process of invention.

Figure 13. Powder X-ray diffraction pattern of UiO-67-BINAP obtained by process of invention.

Examples

Techniques

Surface Area measurement

The specific surface area was determined by means of N₂ physisorption measured on a Belsorp-mini apparatus at 77 K. Prior to the measurement the sample was activated at 423 K under vacuum for 3 h to remove occluded water molecules. The surface area was calculated by the BET-method (DIN 66131) and the Langmuir method (DIN 66135).

X-ray crystallography

All powder X-ray diffraction patterns were collected on a Bruker D8 Discovery diffractometer equipped with a focusing Ge-monochromator, using Cu-Ka radiation(xx=l.54l8 A) and Bruker LYNXEYE detector. Patterns were collected in reflectance Bragg-Brentano geometry in the 2 Q range from 2 to 50°.

Thermogravimetric analysis

Measurements were made with a Stanton Redcroft TGA-DSC, in which ca. 30 mg of powdered sample was loaded inside a platinum crucible. Samples were heated to 900 °C at a rate of 5 °C per minute while exposed to a continuous flow of both N2 (20 mL/min) and 02 (5 mL/min).

Scanning electron microscopy (SEM) An ultrahigh resolution scanning electron microscope Hitachi SU8230 with a cold cathode field emission type electron gun was used to obtained high resolution images of the materials.

Synthesis

UiO-66-BDC (Figure 2) is a prototype MOF of UiO-66 series with hexanuclear Zr₆ cluster as a inorganic comer stone connected by Benzene- 1 ,4-dicarboxylic acid (BDC-H₂) as an organic linker. This is one of the most thermally and chemically stable MOF. It contains octahedral and tetrahedral cadges accessible via triangular window. We have found several conditions using: ZrCl₄, Zr0CL₂.8H₂0, and Zr(acac)₄ (acac: acetylacetonate) as a zirconium source, with and without Formic acid and acetic acid as a modulator.

A synthesis screening was performed with the metal: linker: solvent molar ratio set to 1 : 1 :52 respectively while changing the modulator type (acetic acid, formic acid) and modulator amount (0, 10, 20, 30). The reaction mixture was transfer in glass vial and heated at 120 °C inside heating oven. The details of the reagent amount are given in a Table 1. The final product was separated by centrifugation and washed with GVL once at room temperature before drying at 100 °C. The process provides a space time yield of 250-334 kg/ m³ day. Figure 3a and b show the PXRD patterns of the obtained products.

Synthesis 10 and 11 - Scale up to gm scale:

Synthesis 10: 1.161 gm of Zr0Cl₂.8H20; 0.599 gm of 1 ,4-benzenedicarboxylic acid and 4.078 ml of formic acid were mixed in 17.95 ml of GVL solution in round bottom flask. The reaction mixture was refluxed at 120 °C. The product was separated by filtration and washed with GVL before drying at 150 °C. Figure 4 shows the PXRD, TGA, SEM and nitrogen sorption isotherm of the product calcined at 270 °C.

Synthesis 11: 1.756 gm of Zr(acac)₄; 0.599 gm of 1 ,4-benzenedicarboxylic acid and 1.359 ml of formic acid were mixed in 17.95 ml of GVL solution in round bottom flask. The reaction mixture was refluxed at 120 °C. The product was separated by filtration and washed with GVL before drying at 150 °C. Figure 5 shows the PXRD, TGA, SEM and nitrogen sorption isotherm of the product calcined at 270 °C. Table 1. Reagents quantities used to screen for the synthesis of UiO-66-BDC.

Zr-Fumarate (Figure 6) also contains hexanuclear Zr₆ cluster as an inorganic comer stone but they are connected by Fumarate(FA). Fumaric acid is shorter linker than Benzene- 1 ,4-dicarboxylic acid therefore Zr-Fumarate contains octahedral and tetrahedral cadges smaller than UiO-66-BDC. Zr-Fumarate MOF has a very high potential in natural gas dehydration, adsorption cooling, and toxic gas capture. We have found several conditions using ZrCl₄, Zr0CL₂.8H₂0, and Zr(acac)₄ as a zirconium source, with and without Formic acid and acetic acid as a modulator. A synthesis screening was performed with the metal: linker: solvent molar ratio set to 1 :1 :37 respectively while changing the modulator type (acetic acid, formic acid) and modulator amount (0, 10, 20, 30). The reaction mixture was transfer in glass vial and heated at 120 °C inside heating oven. The details of the reagent amount are given in a Table 2. The final product was separated by centrifugation and washed with GVL ones at room temperature before drying at 100 °C. The process provide space time yield of 340-391 kg/ m³ day. Figure 7 a and b show the PXRD of the products.

Scale up synthesis 12,13 and 21 to gm scale:

Synthesis 12: 1.025 gm of ZrCl₄; 0.511 gm of Fumaric acid and 2.515 ml of acetic acid were mixed in 15.31 ml of GVL solution in round bottom flask. The reaction mixture was refluxed at 120 °C. The product was separated by filtration and washed with GVL before drying at 130 °C. Figure 8 shows the PXRD and TGA of the product.

Synthesis 13: 1.025 gm of ZrCl₄; 0.511 gm of Fumaric acid and 7.545 ml of acetic acid were mixed in 15.31 ml of GVL solution in round bottom flask. The reaction mixture was refluxed at 120 °C. The product was separated by filtration and washed with GVL before drying at 130 °C. Figure 9 shows the PXRD, TGA, SEM and nitrogen sorption isotherm of the product.

Synthesis 21: 1.967 gm of Zr(acac)₄; 0.511 gm of Fumaric acid and 7.545 ml of acetic acid were mixed in 15.31 ml of GVL solution in round bottom flask. The reaction mixture was refluxed at 120 °C. The product was separated by filtration and washed with GVL before drying at 130 °C. Figure 10 show the PXRD, TGA, SEM and nitrogen sorption isotherm of the product.

Table 2. Reagents quantities used to screen for the synthesis of Zr-Fumarate.

O -gOg(Zr^OUOHUBTCUHCOO^

MOF-808 (Figure 11) is a three dimensional framework and contains Zr₆ cluster connected by tritopic 1,3, 5-benzene tricarboxylic acid (BTC) linker. Each cluster is coordinated by six BTC linker and six formate ligands. MOF-808 contains tetrahedral cages of pore diameter 4.8 A and large adamantine cages of pore diameter 18.4 A. The published procedure for preparing this MOF is a very dilute synthesis using excess of DMF and formic acid. With the process of invention we have not only replaced DMF by GVL but also reduced the solvent in the synthesis by 83%.

83 mg ofZrCU; 25 mg of 1,3,5- benzene tricarboxyl acid (BTC-H₂) and 0.673 ml of acetic acid were mixed in 1.138 ml of GVL solution in glass vial. The reaction mixture was heated at 120 °C. The product was separated by filtration and washed with GVL before drying at 150 °C. Ligure 12 shows the PXRD, and TGA, of the product calcined at 200 °C

UiO-67 -BINAP (BINAP: L G-binaphthyl 4,4'-dicarboxylic acid)

UiO-67-BNDC is a isostructural to UiO-67 MOP with 1,1 -binaphthyl-4,4- dicarboxylic acid as a linker. We have prepared this MOP in GVL with amino acid as a modulator.

87 mg ofZrCU; 127 mg of 1 , G-binaphthyl 4,4'-dicarboxylic acid (BINAP-Fp) and 2l4mg of L-Proline, 0.0013 ml cone. HCL were mixed in 10.23 ml of GVL solution in glass vial. The reaction mixture was heated at 120 °C. The product was separated by centrifugation and washed with GVL before drying at 130 °C. Ligure 13 shows the PXRD, of the final product.

Claims

1. A process for preparing a metal organic framework (MOF), comprising the steps:

(ii) heating the reaction mixture from step (i).

2. A process as claimed in claim 1, wherein the metal salt comprises a metal ion selected from the group consisting of, zirconium, magnesium, zinc, aluminium, iron, cerium, hafnium and yttrium, preferably zirconium.

3. A process as claimed in claim 1 or 2, wherein the metal salt(s) is selected from the group consisting of zirconium sulfate, zirconium hydroxide, zirconium acetylacetonate, zirconium chloride (ZrC^’f) and zirconyl chloride (ZrOCf nFTO, wherein n is an integer from 1 to 10, preferably 8).

4. A process as claimed in any of claims 1 to 3, wherein the at least one organic linker compound comprises at least two functional groups selected from the group consisting of carboxylate (COOH), amine (NH₂), anhydride and hydroxyl (OH) or a mixture thereof.

5. A process as claimed in any of claims 1 to 4, wherein the at least one organic linker compound comprises a linear or branched Ci_₂o alkyl group, a C_3-i2 cycloalkyl group and/or an aromatic moiety, preferably an aromatic moiety such as benzene, naphthalene, biphenyl, bipyridyl or pyridyl.

6. A process as claimed in any of claims 1 to 5, wherein the organic linker compound is selected from the group consisting of 1 ,4-benzene dicarboxylic acid (BDC), fumaric acid, 1,3, 5-benzene tricarboxylic acid (BTC), 1,1’- binaphthyl 4,4'-dicarboxylic acid (BINAP-H₂) or mixtures thereof.

7. A process as claimed in any of claims 1 to 6, wherein the reaction mixture in step (i) further comprises a growth modulator.

8. A process as claimed in claim 7, wherein said growth modulator is selected from the group consisting of monocarboxylic acids and inorganic acids.

9. A process as claimed in any of claims 1 to 8, wherein step (i) is carried out at a temperature between 18 and 50 °C.

10. A process as claimed in any of claims 1 to 9, wherein step (i) is carried out at or around atmospheric pressure, preferably 0.5 to 2 bar.

11. A process as claimed in any of claims 1 to 10 wherein in step (ii) of the

process, the reaction mixture from step (i) is heated to a temperature in the range 50 - 150 °C.

12. A process as claimed in any of claims 1 to 11, wherein step (ii) is performed for a time period of at least 20 minutes.

13. A process as claimed in any of claims 1 to 12, wherein the MOF is produced as a crystalline powder.

14. A metal organic framework (MOF) produced by the process as defined in any of claims 1 to 13.