Tungsten catalysts for preparing mono ethylene glycol (MEG) from a carbohydrate

Abstract

The invention relates to a process for preparing a tungsten catalyst, and a process for preparing monoethylene glycol (MEG) from a carbohydrate such as glucose in the presence of the catalyst. It also relates to the tungsten catalyst, as well as the use of the tungsten catalyst for preparing MEG from a carbohydrate. The catalyst can be prepared from sodium tungstate and aqueous acetic acid in a pressurised reactor.

Description

[0001] Tungsten catalysts for preparing mono ethylene glycol (MEG) from a carbohydrate Technical Field of the Invention The present invention relates to a process for preparing a tungsten catalyst, and processes for preparing MEG from a carbohydrate in the presence of the catalyst. It also relates to the tungsten catalyst, as well as the use of the tungsten catalyst for preparing MEG from a carbohydrate. Background Art Conventional methods for producing MEG involve the use of non- renewable resources. The inventors have recognized the need to provide a method for producing MEG using biobased materials. Direct hydrogenolysis of carbohydrates is a promising field of technology to directly obtain biobased MEG. It is commonly understood that the reaction mechanism involves a retro aldol (RA) reaction step that cleaves the carbohydrate into C2 (glycolaldehyde) and C3 fragments (dihydroxy acetone, glyceraldehyde, pyruvaldehyde). The C2 and C3 fragments are then converted to MEG and monopropylene glycol (MPG) respectively in the presence of hydrogen and a suitable hydrogenation catalyst usually selected from the transition metals of group 8-10 of the periodic table. To catalyze the RA-step, a tungsten catalyst such as sodium tungstate or tungstic acid is typically added such as in WO 2019 / 175369. However, the MEG yields and MEG / MPG selectivity are not optimal. Further optimization of this reaction is hampered by the fact that the active form of the tungsten catalyst is not known. Technical Problem Accordingly, in view of the prior art there is a demand for a process for preparing MEG from a carbohydrate with improved MEG yields and improved MEG / MPG selectivity. The invention may be applied on an industrial scale. To reduce the resources required, the purpose of the present invention is also to develop a process which is capable of delivering improved MEG yields and improved MEG / MPG selectivity requiring the use of a minimum number of heavy metals. Summary of the Invention The present invention surprisingly solves the above problems by providing a process for preparing a tungsten catalyst, processes for preparing MEG from a carbohydrate in the presence of the tungsten catalyst, the tungsten catalyst, and the use of the tungsten catalyst for preparing MEG from a carbohydrate. The invention encompasses the following embodiments: 1. A process for preparing a tungsten catalyst comprising contacting a tungsten compound with acid, wherein the tungsten catalyst is suitable for preparing mono ethylene glycol (MEG) from a carbohydrate. 2. The process of embodiment 1, wherein the tungsten compound comprises or consists of at least one of tungsten sulfide, tungsten hydroxide, alkali metal tungstate, alkaline earth metal tungstate, metal tungstate with metal selected from group 11 of periodic table, ammonium tungstate, metatungstate acid, metatungstate, paratungstate acid, para-tungstate, peroxotungstic acid, pertungstate, and hetero-poly acid containing tungsten; preferably wherein the tungsten compound consists of an alkali metal tungstate; and / or wherein the tungsten catalyst does not comprise a lanthanide and / or actinide and / or does not comprise a transition metal selected from groups 5 and 6 of the Periodic Table other than tungsten. 3. The process of any preceding embodiment, wherein the tungsten catalyst comprises or consists of the compound of the following formula (1): MxHyWOz· n H2O, wherein: M is selected from one or more alkali metals, alkaline earth metals, metals of group 11 of the periodic table, or ammonium; 0.4 ≤ x ≤ 0.6 when M is monovalent and 0.2 ≤ x ≤ 0.3 when M is divalent; 0 ≤ y ≤ 1.0; 3.2 ≤ z ≤ 3.6; and 0 ≤ n ≤ 3. 4. The process of any preceding embodiment, wherein the acid comprises or consists of an organic acid, preferably a non- reducing organic acid, more preferably an alkanoic acid, most preferably acetic acid. 5. The process of any preceding embodiment, wherein the molar ratio of tungsten compound:acid is in the range of 1:0.1 – 1:10, preferably 1:1 – 1:5, most preferably 1:2; and / or wherein the process comprises contacting a tungsten compound with acid in the presence of hydrogen and / or an inert gas; and / or wherein the contacting is carried out at a temperature of 120 – 300 °C, or 180 – 270 °C, or 230 – 270 °C; and / or wherein the pressure in the contacting is 1 – 20 MPa, or 3 – 15 MPa; and / or wherein the time that the tungsten compound is contacted is 5 minutes – 3 hours, or 30 minutes – 1.5 hours. 6. A process for preparing MEG from a carbohydrate, comprising: a) the process for preparing the tungsten catalyst of any preceding embodiment, and b) introducing a catalytic system, the carbohydrate and hydrogen into a reactor, and c) reacting the carbohydrate with the hydrogen in the presence of the catalytic system to deliver MEG, wherein the catalytic system comprises: i) at least one active metal component selected from groups 8, 9 or 10 of the Periodic Table; and ii) the tungsten catalyst. 7. The process of embodiment 6, wherein the tungsten catalyst is isolated after a) and before b), and b) and c) are carried out using the isolated tungsten catalyst. 8. The process according to embodiment 6 or 7, wherein the at least one active metal component is selected from iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, and mixtures thereof; wherein the at least one active metal component comprises or consists of a heterogeneous Ru-catalyst, preferably Ru / C. 9. The process according to any of embodiments 6 - 8, wherein c) is carried out at a temperature of 120 – 300 °C, or 180 – 270 °C, or 230 – 270 °C; and / or wherein the pressure in c) is 1 – 20 MPa, or 10 – 14 MPa; and / or wherein the time that the carbohydrate is reacted in c) is 5 minutes – 3 hours, or 30 minutes – 1.5 hours. 10. Process according to any of embodiments 6 - 9, wherein in c): the mass ratio of i) calculated as the metal to ii) is in the range of 0.001 to 100, preferably from 0.01 to 5; and / or the mass ratio of carbohydrate to ii) is 2 to 1000, preferably 10 to 100, preferably 12 to 50; and / or the mass ratio of carbohydrate to i) is 2 – 1000; and / or the MEG / MPG molar selectivity is higher than 6; and / or the MEG molar yield is at least 55%. 11. The process according to any of embodiments 6 - 10, wherein c) is carried out in the presence of a solvent, wherein the solvent preferably comprises water. 12. The process according to any of embodiments 6 - 11, wherein the carbohydrate comprises C6 and / or C5 sugars; preferably wherein the carbohydrate comprises monosaccharides, disaccharides, oligosaccharides, and / or polysaccharides; most preferably wherein the carbohydrate comprises galactose, glucose, mannose, arabinose, xylose, glucuronic acid and / or galacturonic acid. 13. A process for preparing MEG from a carbohydrate, comprising reacting the carbohydrate with hydrogen in the presence of a catalytic system to deliver MEG, wherein the catalytic system comprises: i) at least one active metal component selected from groups 8, 9 or 10 of the Periodic Table; and ii) the tungsten catalyst obtainable according to the process of any one of embodiments 1 - 5. 14. A tungsten catalyst for preparing MEG from a carbohydrate comprising or consisting of the compound of the following formula (1): MxHyWOz· n H2O, wherein: M is selected from one or more alkali metals, alkaline earth metals, metals of group 11 of the periodic table, and ammonium; 0.4 ≤ x ≤ 0.6 when M is monovalent and 0.2 ≤ x ≤ 0.3 when M is divalent; 0 ≤ y ≤ 1.0; 3.2 ≤ z ≤ 3.6; and 0 ≤ n ≤ 3. 15. Use of the tungsten catalyst obtainable according to the process of any one of embodiments 1 - 5 for preparing MEG from a carbohydrate. Where the present description refers to “preferred” features, combinations of these “preferred” features shall also be deemed as disclosed as long as this combination of “preferred” features is technically meaningful. Hereinafter, the use of the term “comprising” should be understood as disclosing, as a more restricted embodiment, the term “consisting of” as well, as long as this is technically meaningful. Brief Description of the Figures Figure 1: X-ray diffraction (XRD) spectrum of catalyst 1A Figure 2: XRD spectrum of catalyst 1B Detailed Description of the Invention The present invention relates to a process for preparing a tungsten catalyst comprising contacting a tungsten compound with acid, wherein the tungsten catalyst is for preparing MEG from a carbohydrate. The process of the invention delivers a tungsten catalyst. The tungsten catalyst is a composition comprising tungsten, which is capable of increasing the rate of the reaction of a carbohydrate to deliver MEG without modifying the overall standard Gibbs energy change in this reaction. Without wishing to be bound by theory, the tungsten catalyst may be capable of catalyzing the RA reaction of the carbohydrate. The tungsten catalyst optionally does not comprise a lanthanide and / or actinide. The lanthanides are the elements with atomic numbers 57–70 and actinides are the elements with atomic numbers 89-102. The tungsten catalyst optionally does not comprise one or more of La, Ce, Pr, Sm and Nd. The tungsten catalyst optionally does not comprise another transition metal apart from tungsten selected from groups 5 and 6 of the Periodic Table. Such transition metals are V, Nb, Ta, Cr and Mo. In particular, the tungsten catalyst optionally does not comprise one or more of the elements V, Nb, and Mo. In the invention, tungsten may be the only d-block element (i.e. the elements in groups 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 of the periodic table) in the tungsten catalyst. By reducing the number of different heavy metals in the catalysts, the resources required by the process can be reduced, allowing the invention to have an improved environmental footprint. The tungsten catalyst is the catalyst obtainable from the process of the invention. It may be a tungsten bronze. It may comprise or consist of the compound of the following formula (1): MxHyWOz· n H2O, wherein: M is selected from one or more alkali metals, alkaline earth metals, metals of group 11 of the periodic table, or ammonium; 0.4 ≤ x ≤ 0.6 when M is monovalent and 0.2 ≤ x ≤ 0.3 when M is divalent; 0 ≤ y ≤ 1.0; 3.2 ≤ z ≤ 3.6; and 0 ≤ n ≤ 3. Alkali metals comprise Li, Na, K, Rb, and Cs. Alkaline earth metals comprise Be, Mg, Ca, Sr and Ba. The metals of group 11 of the periodic table comprise Cu, Ag and Au. Ammonium is NH4+. Li, Na and Ag are preferred and Na is most preferred. The tungsten catalysts defined above are preferred as they deliver more stable tungsten catalysts, which can be isolated and stored. They are also preferred as they improve the MEG yield and MEG / MPG selectivity in a subsequent process for preparing MEG from a carbohydrate. More preferably, 0.42 ≤ x ≤ 0.55, or x = 0.42 or 0.55 when M is monovalent. More preferably, 0.22 ≤ x ≤ 0.275 or x = 0.22 or 0.275 when M is divalent. Where M comprises a mixture of monovalent and divalent groups, the value of x is adjusted accordingly. H may be present or absent. When present, it is preferably 0.7 ≤ y ≤ 1.0, and more preferably y = 0.805. Hycan be distinguished from H in the hydrate using thermogravimetric analysis (TGA) to determine the amount of water and redox titration to determine the amount of hydride. More preferably, 3.25 ≤ z ≤ 3.55, more preferably 3.28 ≤ z ≤ 3.49 and most preferably z = 3.49 or z = 3.28. Ozcan be distinguished from O in the hydrate using TGA to determine the amount of water. In general, the tungsten catalyst may or may not be a hydrate. Preferably 0 ≤ n ≤ 1. Preferably the tungsten catalyst comprises or consists of the compound of the above formula: wherein M is selected from one or more of Na, Li, and Ag; 0.42 ≤ x ≤ 0.55; 0 ≤ y ≤ 0.805; 3.25 ≤ z ≤ 3.55; and 0 ≤ n ≤ 1. Preferably, the tungsten catalyst comprises or consists of the compound of the formula Na0.42H0.805WO3.49, Na0.55WO3.28*0.7H2O, Ag0.55WO3.28, and Na0.55WO3.28. Of these, Na0.55WO3.28*0.7H2O is preferred as it delivers particularly improved MEG yield and selectivity. The tungsten catalyst may be a tungsten bronze with a pyrochlore structure. The structure may be determined by XRD. For the XRD experiments 100 mg of the powdered catalyst is dispersed on an amorphous silicium wafer. The wafer is introduced to an X-ray diffractometer, and the diffraction is carried our using Copper K-α as the X-ray energy source. The tungsten catalyst structure Na0.42H0.805WO3.49has the following peaks in the XRD spectrum at 2θ: °2θ Rel. intensity [%]14.8 3728.7 4230.0 10034.6 4137.9 1745.5 1850.3 2759 28Alternatively, the tungsten catalyst structure is Na0.55WO3.28*0.7H2O and has the following peaks in the XRD spectrum at 2θ:

[0002] °2θ Rel. intensity [%]14.6 2715.0 2628.8 4429 2830.1 10034.7 4037.8 1345.6 15.749.6 2452.4 2758.8 2759.3 3862.4 20The tungsten catalyst may be obtained from the process in a composition comprising or consisting of the tungsten catalyst. When the composition comprises the tungsten catalyst, it may comprise one or more other components selected from solvents (optionally as defined below), acids (optionally as defined below), one or more tungsten compounds (optionally as defined below), and one or more metal hydroxides. The metal hydroxides may include alkali metal and alkaline earth metal hydroxides. The tungsten catalyst may be present at a concentration of 1 – 100 wt%, optionally 5 – 95 wt% based on the total weight of the composition. The solvent may be present at a concentration of 0 – 95 wt%, optionally 85 – 95 wt% based on the total weight of the composition. The tungsten compound may be present at a concentration of 10 wt% or less, preferably 5 wt% or less based on the total weight of the composition. The tungsten compound is a starting material in the process for preparation of the tungsten catalyst. It may itself be a tungsten catalyst, but has a different chemical composition from the tungsten catalyst obtainable from the process of the present invention. The tungsten catalyst is therefore different to the following tungsten compounds. The tungsten compound comprises or consists of at least one of tungsten sulfide (WS3), tungsten hydroxide(W(OH)6), alkali metal tungstate (e.g. Li2WO4, Na2WO4, K2WO4, Rb2WO4, Cs2WO4) alkaline earth metal tungstate (e.g. BeWO4, MgWO4, CaWO4, SrWO4, BaWO4), metal tungstate with metal selected from group 11 of periodic table (e.g. Ag2WO4, Cu2WO4), ammonium tungstate ((NH4)2WO4), metatungstate acid (H8W12O40), metatungstate (e.g. Li8W12O40, Na8W12O40, and (NH4)8W12O40), paratungstic acid (H12W12O42), paratungstate (e.g. (NH4)10(H2W12O42), Li10(H2W12O42), and Na10(H2W12O42)), peroxotungstic acid (H16W12O38(O2)6), pertungstate (e.g. Na16W12O38(O2)6, Li16W12O38(O2)6), and hetero- poly acid containing tungsten (H3PW12O40). More generally, any tungstate can be employed as the tungsten compound. Of the tungstate, metatungstates, paratungstates, and pertungstates listed above, those formed with one or more alkali metals, alkaline earth metals, metals selected from group 11 of periodic table (e.g. Ag2WO4, Cu2WO4), and ammonium are preferred. The hydrates and solvates of each of these tungsten compounds are included in the general terms used in the claims. For example, the tungsten compound may comprise or consist of Na2WO4*2H2O. Preferably the tungsten compound consists of one or more selected from an alkali metal tungstate, alkaline earth metal tungstate, metal tungstate with metal selected from group 11 of periodic table, and ammonium tungstate. These tungsten compounds are preferred as they deliver more stable tungsten catalysts, which can be isolated and stored and improve the yield and selectivity for MEG. Preferably, the tungsten compound may comprise or consist of Na2WO4*2H2O. The acid reacts with the tungsten compound to deliver the tungsten catalyst of the invention. An acid is a compound which is capable of donating a proton. The acid in the invention is different to the tungsten compound of the invention. For example, paratungstic acid is not an acid within the meaning of the present invention, as it is a tungsten compound. The acid of the invention is preferably not any compound comprising tungsten. The acid may comprise or consist of an organic acid. An organic acid is an organic compound with acidic properties. It may be a carboxylic acid or a sulfonic acid. The acid preferably comprises or consists of an alkanoic acid, which is an alkyl (−CnH2n+1) or cycloalkyl group (−CmH2m−1) substituted with a carboxylic acid group, where n may be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 and m may be 3, 4, 5, 6, 7, 8, 9, or 10. The acid most preferably comprises or consists of acetic acid. The acid of the invention may comprise of consist of non- reducing acids, i.e. (organic) acids with no reducing properties. The acid of the invention preferably does not comprise or consist of one or more of citric acid, oxalic acid, lactic acid and sorbic acid. When the acid is contacted with the tungsten compound, the pH of the resultant mixture of acid and tungsten compound may be less than 7, more preferably in the range of 3 – 6, and most preferably in the range of 4 – 5. Contacting the acid with the tungsten compound delivers a tungsten catalyst which improves the MEG yield and MEG / MPG selectivity when used to catalyse a process for preparing MEG from a carbohydrate. It also facilitates storage of the tungsten catalyst. The process for preparing a tungsten catalyst may comprise or consist of contacting the tungsten compound with the acid. Preparing the tungsten catalyst means that a chemical reaction takes place which changes the chemical composition of the tungsten compound starting material into the tungsten catalyst product. Changes to the chemical composition mean changes to the identity, arrangement, and ratio of the chemical elements making up the tungsten compound. Contacting a tungsten compound with acid means that the tungsten compound and the acid are positioned such that the chemical reaction can take place between them to transform the tungsten compound starting material into the tungsten catalyst product. The contacting may take place in a reactor. The contacting may take place in the same reactor used for the subsequent preparation of MEG from a carbohydrate. The tungsten compound and acid may be introduced into the reactor. One or more of the tungsten compound and acid may be in solution, optionally in the same solvent discussed below. The tungsten compound may be placed in the reactor first, before subsequent addition of the acid. In the step of contacting the tungsten compound with acid, solvent may be present. The solvent is a liquid in which the acid and / or tungsten compound is soluble at 25 °C and atmospheric pressure. The solvent may comprise or consist of one or more compounds, optionally selected from water, methanol, ethanol, MEG, PEG, or C1-6alcohols. The solvent preferably comprises or consists of water from the perspective of maximising the industrial applicability of the invention. Some or all of the solvent is preferably introduced into the reactor at the same time as the acid. The step of contacting the tungsten compound with acid may be carried out in the presence of hydrogen (i.e. molecular hydrogen, H2) and / or an inert gas (i.e. a gas which does not react with the tungsten compound, the acid, or the tungsten catalyst, such as molecular nitrogen N2or argon). When hydrogen is not present and the contacting is carried out in the presence of an inert gas in the step of contacting the tungsten compound with acid, the MEG / MPG selectivity in a subsequent process for preparing MEG from a carbohydrate may be improved. It is preferred that the step of contacting the tungsten compound with acid is carried out in the absence of carbohydrates. Instead, it is preferred that the tungsten catalyst is prepared in a first step before being used in the process for preparing MEG from a carbohydrate. This is in order to improve the MEG yield and MEG / MPG selectivity in a subsequent process for preparing MEG from a carbohydrate. In the contacting step, the molar ratio of tungsten compound:acid may be in the range of 1:0.1 – 1:10, preferably 1:1 – 1:5, most preferably 1:2. Using higher amounts of acid has been shown to improve the MEG yield and MEG / MPG selectivity in a subsequent process for preparing MEG from a carbohydrate. The tungsten compound and acid contacting step may be carried out at a temperature of 120 – 300 °C, or 180 – 270 °C, or 230 – 270 °C. This means that the tungsten compound and acid are both present in the reactor at this temperature. The pressure in the contacting step is preferably 1 – 20 MPa, or 3 – 15 MPa. The pressure may be due to the introduction of hydrogen or nitrogen gas. The time that the tungsten compound is contacted may be 5 minutes – 3 hours, or 30 minutes – 1.5 hours. Shorter contacting times are more energy efficient.The process for preparing the tungsten catalyst may be carriedout in a reactor, which may be a hydrogenation reactor and maybe a batch or continuous reactor. It may be the same as or different to the reactor used in any subsequent step of preparing MEG from a carbohydrate. The reactor may be one or more continuously stirred tank (CSTR) reactor. Where there is more than one CSTR, they may be configured as a cascade of CSTRs. The reaction may be operated in batch- or fed-batch mode or continuously, and the reactor may be configured to be operated in batch- or fed-batch mode or continuously. The process for preparing the tungsten catalyst may use more than 10 g, preferably more than 100 g, preferably more than 1 kg, preferably more than 10 kg, preferably more than 100 kg tungsten compound as starting material. The process may deliver more than 10 g, preferably more than 100 g, preferably more than 1 kg, preferably more than 10 kg, preferably more than 100 kg tungsten catalyst. The process for preparing the tungsten catalyst may have a mass yield based on the mass of the tungsten compound of greater than 20%, greater than 30 wt%, greater than 50%, or greater than 80%. The process may also include a step of isolating the tungsten catalyst. This means that one or more of the solvents, acid, tungsten compound starting materials or metal hydroxides is removed from the composition comprising the tungsten catalyst. The isolating process may include one or more of distillation, rotary evaporation, recrystallization, and decantation. For decantation the solvent above may be used either alone or optionally in combination with a decantation solvent. From the perspective of obtaining high yield and purity of the tungsten catalyst, as the decantation solvent C1-6alcohols are preferred, preferably iso-propanol. The composition comprising the tungsten catalyst after the reaction may be added to the decantation solvent prior to the decantation. The isolated tungsten catalyst composition may comprise or consist of the tungsten catalyst. When it comprises the tungsten catalyst, it may additionally include one or more tungsten compound starting materials defined above, or one or more metal hydroxides. Use of isolated tungsten catalyst gives a higher yield and selectivity in preparing MEG from a carbohydrate. Without wishing to be bound by theory, it is postulated that by using an isolated tungsten catalyst in the MEG preparation reaction, there may be fewer species in the reaction mixture leading to fewer side reactions. It is also more convenient as it allows the preparation of the tungsten catalyst and preparation of the MEG to be carried out at separate times and / or locations. It also delivers an improved platform for improving the process conditions, by reducing the number of variables to be studied. The process for preparing the tungsten catalyst may also comprise a step of storing the tungsten catalyst. The composition comprising the tungsten catalyst obtained directly from the reaction can be stored. Alternatively, the isolated tungsten catalyst may be stored. The latter is preferred in terms of stability of the tungsten catalyst. Storage is particularly preferred for tungsten catalysts of formula (1) as they deliver more stable tungsten catalysts, which can be stored for longer periods. Isolated tungsten catalysts of formula (1) may be stored for at least 1 month, at least 6 months, at least 1 year, or at least 2 years at 25°C. The step of storing the tungsten catalyst may comprise placing the composition comprising or consisting of the tungsten catalyst in a container, and closing the container. Preferably this occurs after the step of isolating the tungsten catalyst discussed above. The container may be an ampoule, vial, jar, or bottle. The container may have a label. It may be air-tight and / or resealable. The atmosphere in the container may comprise or consist of an inert gas, and is preferably nitrogen (N2) or argon. The present invention relates to a process for preparing MEG from a carbohydrate, comprising: a) the process for preparing the tungsten catalyst discussed above, and b) introducing a catalytic system, the carbohydrate and hydrogen into a reactor, and c) reacting the carbohydrate with the hydrogen in the presence of the catalytic system to deliver MEG, wherein the catalytic system comprises: i) at least one active metal component selected from groups 8, 9 or 10 of the Periodic Table; and ii) the tungsten catalyst. The process of the invention delivers MEG, also called 1,2- ethanediol. This may be biobased, meaning that it is derived from biological feedstocks. Such biobased, renewably sourced materials can be differentiated from their non-renewable counterparts by their carbon isotope ratios using ASTM International Radioisotope Standard Method D 6866-21. Biobased means at least about 20 percent or more of the carbon content is derived from biological feedstocks as shown by ASTM D 6866-21. The process of the invention may deliver a product composition comprising or consisting of MEG. The product composition may comprise or consist of a solvent as defined below, MPG (also called 1,2-propanediol), MEG, and 1,2-butane diol (BDO, also called butylene glycol). The total diol concentration of the product composition may be 0.1 - 40 weight-% based on the total weight of the composition. The product composition may also comprise other side products. The first step of the process for preparing MEG from a carbohydrate is the process defined above for preparing the tungsten catalyst. Thus, step a) is carried out before steps b) and c). Steps a), b) and c) can be carried out in a single reactor in a “one pot” synthesis. However, to maximise the yield of MEG it is preferred that the tungsten catalyst from step a) is isolated prior to step b), e.g. that the tungsten catalyst is isolated after a) and before b), and b) and c) are carried out using the isolated tungsten catalyst. The process in step b) of the invention comprises introducing a catalytic system, hydrogen and a carbohydrate into a reactor. This may be achieved by physically placing the catalytic system, hydrogen and carbohydrate in the reactor, or one or more of these components may be produced in the reactor. For example, in a less preferred embodiment of the invention, step a) may be carried out in the same reactor prior to steps b) and c) to introduce component ii) of the catalytic system into the reactor. The catalytic system, hydrogen and a carbohydrate may be introduced into the reactor simultaneously or sequentially. It is preferred that they are introduced sequentially in the order: 1) catalytic system, 2) hydrogen and 3) carbohydrate. The catalytic system increases the rate of the reaction of the carbohydrate with hydrogen to deliver MEG without modifying the overall standard Gibbs energy change in this reaction. The catalytic system is defined at the time of introduction into the reactor. It may change during the reaction. The catalytic system of the invention comprises or consists of components i) and ii). Prior to introduction to the reactor, components i) and ii) may be part of a single catalytic composition comprising both i) and ii). They are preferably separate components. Component i) of the catalytic system of the invention is at least one active metal component selected from groups 8, 9 or 10 of the Periodic Table. It catalyses the hydrogenation reaction. Preferably the at least one active metal component is selected from iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, and mixtures thereof. The at least one active metal component may be heterogeneous, meaning that it remains solid and does not dissolve during the reaction. The at least one active metal component may comprise or consist of a heterogeneous Ru catalyst, preferably Ru / C. Most preferably, the catalytic system component i) has at least one active metal component selected from group 8 of the periodic table, preferably Ru. The combination of this with the tungsten catalyst of the invention delivers synergistically improved MEG yield and MEG / MPG selectivity. The active metal component of i) of the catalytic system may be supported by a carrier comprising activated carbon, alumina, silica, silicon carbide, zirconia, zinc oxide, titanium dioxide, or a mixture thereof. The active metal component of i) may account for 0.05 - 70 weight-% of the total weight of component i) of the catalytic system. For the preferred at least one active metal component selected from group 8 of the periodic table, the active metal component of i) preferably accounts for 1 - 10 weight-% of the total weight of component i) of the catalytic system, more preferably 5 weight-% of the total weight of component i) of the catalytic system. Component i) of the catalytic system may be introduced into the reactor in the form of a slurry. The slurry may comprise 1 – 20% w / w, optionally 5 – 15% w / w of component i) of the catalytic system based on the total weight of the slurry. The liquid for the slurry may comprise or consist of the solvent defined below. The liquid for the slurry preferably comprises or consists of water. Component ii) of the catalytic system of the invention comprises or consists of the tungsten catalyst obtained or obtainable from step a) of the process for preparing MEG from a carbohydrate. Component ii) may catalyze the RA reaction. The component ii) of the catalytic system of the invention may be homogeneous, meaning that it is in the dissolved state during the reaction of carbohydrate to deliver MEG. Including the tungsten catalyst in component ii) of the catalytic system of the invention allows the preparation of MEG having improved yield and selectivity for MEG relative to the known catalysts. The process of the invention may include a step of pretreating the catalytic system before addition of the carbohydrate. The pretreatment may be carried out at a temperature of 120 – 300 °C, preferably 180 – 270 °C, preferably 230 – 270 °C, and preferably 250 °C. The pretreatment may be carried out at a pressure of 1 – 20 MPa, preferably 3 – 15 MPa. The pretreatment may be carried out until the temperature and pressure are constant. It may be carried out for a time in the range of 10 seconds – 30 minutes, and preferably 1 minute – 5 minutes. The pretreatment may be carried out in the presence of hydrogen. Prior to the introduction of hydrogen in the pretreatment step, an inert gas may be used as the atmosphere in the reactor. The inert gas is preferably molecular nitrogen (N2). The carbohydrate comprises one or more compounds which react to deliver MEG. The carbohydrate may comprise or consist of one or more components selected from monosaccharides, disaccharides, oligosaccharides made of three to ten monosaccharide units and / or polysaccharides made of greater than ten monosaccharide units. In the invention, the carbohydrate may comprise C6 and / or C5 sugars. The carbohydrate may comprise galactose, glucose, mannose, arabinose, xylose, glucuronic acid and / or galacturonic acid. For reasons of using an abundant biobased feedstock maximising the industrial applicability of the invention, the carbohydrates preferably comprise or consist of cellulose, glucose, fructose and / or xylose. They most preferably comprise or consist of glucose, fructose and / or xylose. In the process of the invention, a solvent may be introduced into the reactor. The solvent may be a liquid in which the at least some of the carbohydrate and / or the tungsten catalyst is soluble at 25 °C and atmospheric pressure. The solvent may comprise or consist of one or more compounds, optionally selected from water, methanol, ethanol, MEG, MPG, BDO, PEG, or C alcohols. As such, the solvent may be the product composition defined above comprising or consisting of water, MPG, MEG, and optionally BDO. The solvent preferably comprisesor consists of water from the perspective of maximising theindustrial applicability of the invention. Some or all of the solvent is preferably introduced into the reactor at the same time as the carbohydrate, and preferably the carbohydrate is introduced into the reactor dissolved in some or all of the solvent. Alternatively, the solvent and carbohydrate may be introduced into the reactor separately. In the reaction, carbohydrates may be present in a total amount of 5 – 100% w / w, optionally 30 – 50% w / w based on the total combined weight of the carbohydrate and solvent introduced into the reactor. The reactor is a hydrogenation reactor and may be a batch or continuous reactor. The reactor may be one or more continuously stirred tank (CSTR) reactor. Where there is more than one CSTR, they may be configured as a cascade of CSTRs. The reaction may be operated in batch- or fed-batch mode or continuously, and the reactor may be configured to be operated in batch- or fed- batch mode or continuously. In the reaction in step c), the carbohydrate is reacted with hydrogen in the presence of the catalytic system to deliver MEG. This means that the carbohydrate is contacted with the catalytic system and the hydrogen to allow the reaction of the carbohydrate to MEG to take place. Without wishing to be bound by theory, the carbohydrates may undergo a RA reaction catalysed by component (ii) of the catalytic system. The product of the RA reaction may subsequently be reduced to MEG by hydrogen in a reaction catalysed by component (i) of the catalytic system. Steps b) and c) of the process of the invention are a one-step conversion of the carbohydrate to MEG. Prior to the introduction of hydrogen, an inert gas may be used as the atmosphere in the reactor. The inert gas is preferably nitrogen. The hydrogen may be introduced to create a pressure of 1 – 20 MPa, preferably 3 – 15 MPa; preferably 10 – 14 MPa. The reaction may then be carried out at a pressure of 1 – 20 MPa, preferably 3 – 15 MPa; preferably 10 – 14 MPa. The reaction may be initiated by introducing carbohydrate into a reactor containing hydrogen and the catalytic system. The carbohydrate may optionally be introduced dissolved in the solvent. The reaction may be carried out at a temperature of 120 – 300 °C, preferably 180 – 270 °C, preferably 230 – 270 °C, preferably 250 °C. The reaction may be carried out for a time in the range of 5 minutes – 3 hours, preferably 30 minutes – 1.5 hours, most preferably 45 minutes – 75 minutes. The reaction may be carried out batch-wise, semi-batch-wise, or in a continuous process. In a continuous process, the carbohydrate is a feedstock. The liquid hourly space velocity (LHSV) is a volume of the reactant (comprising the carbohydrate and the hydrogen) per unit volume of catalyst per hour. In the process of the invention in a continuous process the LHSV may be 0.2 hr-1to 2 hr-1. The mass ratio of i) to ii) in the catalytic system may be in the range of 0.001 to 100, preferably from 0.01 to 5 (where the mass of i) is calculated based only on the mass of the active metal component selected from groups 8, 9 or 10 of the Periodic Table). Where i) comprises Ru, the mass ratio of i) (calculated as the metal) to ii) may be 0.01 – 0.1. The mass ratio of carbohydrate to ii) may be in the range of 2 – 1000, preferably 10 to 100, preferably 12 to 150, more preferably 15 – 50. The mass ratio of carbohydrate to i) (where the mass of i) is calculated based only on the mass of the active metal component selected from groups 8, 9 or 10 of the Periodic Table) may be 2 – 1000, preferably 2 - 500. Where i) comprises Ru, the mass ratio of carbohydrate to i) (calculated as the metal) may be 100 – 500. The mass ratio of i) (calculated based only on the mass of the active metal component selected from groups 8, 9 or 10 of the Periodic Table) in the reactor based on the total mass of the catalytic system, the carbohydrate and the solvent may be in the range of 0.01 – 15% by mass, preferably 0.05 – 12% by mass. The mass ratio of ii) in the reactor based on the total mass of the catalytic system, the carbohydrate and the solvent may be in the range of 0.1 – 4% by mass, preferably 1 – 3% by mass. The mass ratio of the carbohydrate in the reactor based on the total mass of the catalytic system, the carbohydrate and the solvent may be in the range of 5 – 60% by mass, preferably 20 – 40% by mass. The mass ratio of the solvent in the reactor based on the total mass of the catalytic system, the carbohydrate and the solvent may be in the range of 10 – 90% by mass, preferably 60 – 80% by mass. The catalytic system comprises several components as discussed above. These components of the catalytic system may be introduced into the reactor together, or they may be introduced separately. The carbohydrate may comprise several components as discussed above. These components may be introduced together, or they may be introduced separately. The carbohydrate components may be introduced after the pretreatment of the catalytic system described above. The process may have a higher selectivity for MEG than MPG. This MEG / MPG selectivity is the ratio of the molar yield of MEG and molar yield of MPG based on the carbohydrate. The MEG / MPG selectivity is preferably higher than 6, more preferably higher than 9. The calculation of the molar yields is carried out in the following way: ^^ ^^^^^^^^^^= ^^^× 100^^^^^^^^^Index i refers to the product (MEG or MPG), index g refers tostarting carbohydrate, w is the mass fraction of the component[g / g] in the reaction mixture, M the molar mass of thecomponent [g / mol], ν is the stochiometric factor in theconversion of the carbohydrate to the product (e.g. in thecase of glucose: νMEG=3 and νMPG=2, since glucose is C6 so 1mole of glucose theoretically can give 3 moles of MEG or 2 moles of MPG). The process may have an MEG molar yield of at least 55%, preferably at least 60%, more preferably at least 64% based on the carbohydrate. The process may have a carbohydrate conversion of at least 90%, preferably at least 95%. The process of the invention may comprise or consist of the steps specified in the claims. When the process comprises the steps in the claims, the process may also comprise providing a biological feedstock and subjecting the feedstock to at least one pretreatment to form a liquid fraction and a fraction comprising solid cellulose particles and subsequently subjecting the fraction comprising solid cellulose particles to enzymatic hydrolysis to form a lignin fraction and a carbohydrate fraction, wherein the carbohydrate introduced in step b) of the invention comprises at least part of the carbohydrate fraction. The process may also comprise recovering one or both components of the catalytic system. The process may also comprise recovering MEG from the composition obtained from the process of the invention. The MEG of the invention may be further reacted in downstream processes. Component i) of the catalytic system of the invention may be a heterogenous catalyst and may be recovered by solid / liquid separation and recycled to be reused in the process of the invention. Component ii) of the catalytic system of the invention may be a homogenous catalyst and may be recovered from the composition comprising of MEG obtained from the process of the invention during the MEG recovery step discussed below. It may subsequently be recycled to be reused in the process of the invention.The process of the invention may deliver MEG as a compositioncomprising of MEG. Recovering MEG from the compositioncomprising of MEG obtained from the process of the invention may be conducted by a separation technique selected form adsorption, evaporation, distillation, extractive distillation, azeotrope distillation, vacuum distillation, atmospheric distillation, membrane separation, filtration, reactive purification or a combination of them. The MEG may be recovered by distillation. The distillation may be carried out in at least one distillation column. The distillation may be carried out at a temperature of 50 - 250°C, or of 100 - 200°C. The distillation may be carried out at a pressure of at least 0.1 kPa, or at least 10 kPa, or at least 50 kPa. The pressure may be at most 400 kPa, or at most 200 kPa, or at most 120 kPa. It will be clear to the skilled person to vary the temperature and pressure in relation to each other in order to achieve suitable conditions. The MEG obtained from the process of the invention may be used to synthesise polyesters. The MEG may be reacted with a dicarboxylic acid such as terephthalic acid or a diester such as dimethyl terephthalate to deliver a polyester such as polyterephthalate. The invention may also relate to a process for preparing a polyester, comprising a first step of preparing MEG according to the present invention and a second step of reacting the MEG with a dicarboxylic acid and / or diester to deliver the polyester. The present invention also relates to a process for preparing MEG from a carbohydrate, comprising reacting the carbohydrate with hydrogen in the presence of a catalytic system to deliver MEG, wherein the catalytic system comprises: i) at least one active metal component selected from groups 8, 9 or 10 of the Periodic Table; and ii) the tungsten catalyst which has been obtained or is obtainable according to the process for preparing a tungsten catalyst of the invention. Alternatively, the tungsten catalyst may be that defined in the following section. All other aspects of this process are the same as described for the process for preparing MEG from a carbohydrate above. Using the tungsten catalyst of the invention in this process delivers improved MEG selectivity, and the MEG yield is also improved. The present invention also relates to a tungsten catalyst for preparing MEG from a carbohydrate comprising or consisting of the compound of the following formula (1): MxHyWOz· n H2O, wherein: M is selected from one or more alkali metals, alkaline earth metals, metals of group 11 of the periodic table, and ammonium; 0.4 ≤ x ≤ 0.6 when M is monovalent and 0.2 ≤ x ≤ 0.3 when M is divalent; 0 ≤ y ≤ 1.0; 3.2 ≤ z ≤ 3.6; and 0 ≤ n ≤ 3. The description above relating to the catalyst and formula (1) applies accordingly. The tungsten catalyst of the invention delivers improved MEG selectivity, and the MEG yield is also improved. The present invention also relates to the use of the tungsten catalyst obtainable according to the process defined above for preparing MEG from a carbohydrate. It also relates to the use of the tungsten catalyst defined above for preparing MEG from a carbohydrate. The tungsten catalyst, MEG and carbohydrate are as defined in detail above. The use also includes all aspects of the invention discussed above. The use of the tungsten catalyst of the invention delivers improved MEG selectivity, and the MEG yield is also improved. Experimental Part Example 1: process for preparing and isolating tungsten catalysts 1A – 1C The tungsten catalyst of the invention was prepared and isolated using the following steps: 1. Na2WO4*2H2O was weighed in the amount shown in table 1 andadded to a 50 mol stirred pressure reactor. 2. Acetic acid in a beaker was diluted with the specifiedamount of deionized water. 3. The acetic acid solution was added to the Na2WO4*2H2O.4. The reactor was closed.5. The reactor was flushed 3 times with hydrogen or nitrogengas (the hydrogen or nitrogen was added until a pressure of 6 MPa was reached and then the pressure was released to 0.3-0.5 MPa overpressure). 6. The pressure was increased to 6 Mpa.7. The reactor and reaction mixture was heated to 255°C.8. When the reaction temperature was reached, the hydrogenpressure was increased up to 12 MPa. 9. The reaction mixture was stirred under these reactionconditions for 60 minutes. 10. The hydrogen or nitrogen supply was stopped and thereaction mixture was allowed to cool to room temperature 11. The hydrogen or nitrogen pressure was released andthe reactor was opened. 12. The catalyst was visually inspected.The reaction mixture was added to 200 ml ofisopropanol and purified by decantation. The isopropanol and residual water was removed byrotary evaporation at 55°C. The catalyst was the dried under vacuum. After 3 hours drying the yield was determined. Thestructure was determined using XRD, and the spectra for catalysts 1A and 1B are shown in Figures 1 and 2. For the XRD experiments 100 mg of the powdered catalyst was dispersed on an amorphous silicium wafer. The wafer was introduced to the X-ray diffractometer, and the diffraction was carried our using Copper K-α as the X-ray energy source. The catalyst was then transferred to a Schlenk-Tube and pressurised with inert gas. The catalyst was stored under inert gas.

[0003] Table 1 Experiment 1A 1B 1Cm (Na2WO4 *2H2O) [g] 2.0 2.0 2.0n[mmol] 6.2 6.1 6.1w / w [%] 9.1 8.8 8.8m H2O [g] 17.6 17.6 17.6n[mmol] 989.9 989.8 990.9w / w [%] 89.1 87.6 87.6m Acetic acid [g] 0.4 0.7 0.7n[mmol] 6.0 12.2 12.1w / w [%] 1.8 3.6 3.6Atmosphere Hydrogen Hydrogen Nitrogenm total [g] 20 20 20Yield [g] 0.49 1.09 0.75Visual inspection Blue Blue BlueNa0.84H1.61W2O6.98Na1.1W2O6.55Na1.1W2O6.55Composition 1.4H2O 1.4H2O Structure Pyrochlore Pyrochlore PyrochloreComparative Example 1: using tungstic acid starting material This comparative example was carried out in the same manner as examples 1A and 1B respectively, except that tungstic acid was used as the starting material instead of Na2WO4*2H2O. However, attempts to isolate the product yielded only WO3. Examples 3A-3C: process for preparing ethylene glycol from a carbohydrate using tungsten catalysts 1A – 1C A 50 ml hydrogenation reactor equipped with an overhead stirrer was charged with 10g of water and 250 mg of catalytic system component i) in which the at least one active metal component is Ru / C, containing 5% w / w Ru. This was followed by addition of the tungsten catalyst 1A, 1B, or 1C to the reactor in the amount specified in table 2 below. After purging with nitrogen, the reactor was pressurized with hydrogen to 6 MPa and the stirring started. The reactor was heated to 250°C, and at this temperature the pressure was increased to 12 MPa H2. When the conditions were stable, 9.4 g of an aqueous glucose solution (45% w / w) were added over the course of 30 minutes. This corresponds to an amount of glucose:tungsten catalyst of 17 g / g. During this time the pressure in the reactor was maintained at 12 MPa by co-feeding hydrogen gas. After the addition of the glucose solution the reaction mixture is stirred for another 40 minutes and subsequently allowed to cool to room temperature. Afterwards samples were taken, filtered and analyzed by HPLC. The results are shown in table 2. These demonstrate that the tungsten catalyst of the invention delivers improved MEG yield and improved MEG / MPG selectivity relative to Na2WO4·2H2O. Using higher concentrations of acid in the synthesis of the tungsten catalyst in examples 1B and 1C delivers further improved MEG / MPG selectivity. Synthesis of the tungsten catalyst in the presence of nitrogen in example 1C delivers further improved MEG / MPG selectivity. Comparative Example 2: process for preparing ethylene glycol from a carbohydrate using Na2WO4·2H2O The reaction was carried out in the same way as example 3, except that Na2WO4·2H2O was used as the catalyst. The results are shown in table 2. Table 2Example Co-m(Co- X Y(MEG) Y(MPG) Y(MEG) Catalyst Catalyst) (Glucose) [%] [%] / [mg] Y(MPG) 3A 1A 250 >99% 65 9 7.23B 1B 250 >99% 67 6 11.23C 1C 250 >99% 64 5 12.8Comp. NaWO250 >99% 53 12 4.4example ·2HO 2aConversion of glucose; bYields of MEG resp. MPG in mol[%] ofconverted glucose Calculation of molar yields: ^^ ^^^^^^^^^^= ^^× 100^^^^^^^^^^Index i refers to the product(MEG or MPG), index g refers tostarting carbohydrate (i.e. glucose here), w is the massfraction of the component [g / g] in the reaction mixture, M themolar mass of the component [g / mol], ν is the stochiometricfactor in the conversion of the carbohydrate to the product.In the case of glucose: νMEG=3; νMPG=2.

Claims

Claims 1. A process for preparing a tungsten catalyst comprising contacting a tungsten compound with acid, wherein the tungsten catalyst is suitable for preparing mono ethylene glycol (MEG) from a carbohydrate.

2. The process of claim 1, wherein the tungsten compound comprises or consists of at least one of tungsten sulfide, tungsten hydroxide, alkali metal tungstate, alkaline earth metal tungstate, metal tungstate with metal selected from group 11 of periodic table, ammonium tungstate, metatungstate acid, metatungstate, paratungstate acid, para-tungstate, peroxotungstic acid, pertungstate, and hetero-poly acid containing tungsten; preferably wherein the tungsten compound consists of an alkali metal tungstate; and / or wherein the tungsten catalyst does not comprise a lanthanide and / or actinide and / or does not comprise a transition metal selected from groups 5 and 6 of the Periodic Table other than tungsten.

3. The process of any preceding claim, wherein the tungsten catalyst comprises or consists of the compound of the following formula (1): MxHyWOz· n H2O, wherein: M is selected from one or more alkali metals, alkaline earth metals, metals of group 11 of the periodic table, or ammonium; 0.4 ≤ x ≤ 0.6 when M is monovalent and 0.2 ≤ x ≤ 0.3 when M is divalent; 0 ≤ y ≤ 1.0; 3.2 ≤ z ≤ 3.6; and 0 ≤ n ≤ 3.

4. The process of any preceding claim, wherein the acid comprises or consists of an organic acid, preferably a non-reducing organic acid, more preferably an alkanoic acid, most preferably acetic acid.

5. The process of any preceding claim, wherein the molar ratio of tungsten compound:acid is in the range of 1:0.1 – 1:10, preferably 1:1 – 1:5, most preferably 1:2; and / or wherein the process comprises contacting a tungsten compound with acid in the presence of hydrogen and / or an inert gas; and / or wherein the contacting is carried out at a temperature of 120 – 300 °C, or 180 – 270 °C, or 230 – 270 °C; and / or wherein the pressure in the contacting is 1 – 20 MPa, or 3 – 15 MPa; and / or wherein the time that the tungsten compound is contacted is 5 minutes – 3 hours, or 30 minutes – 1.5 hours.

6. A process for preparing MEG from a carbohydrate, comprising: a) the process for preparing the tungsten catalyst of any preceding claim, and b) introducing a catalytic system, the carbohydrate and hydrogen into a reactor, and c) reacting the carbohydrate with the hydrogen in the presence of the catalytic system to deliver MEG, wherein the catalytic system comprises: i) at least one active metal component selected from groups 8, 9 or 10 of the Periodic Table; and ii) the tungsten catalyst.

7. The process of claim 6, wherein the tungsten catalyst is isolated after a) and before b), and b) and c) are carried out using the isolated tungsten catalyst.

8. The process according to claim 6 or 7, wherein the at least one active metal component is selected from iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, and mixtures thereof;wherein the at least one active metal component comprises or consists of a heterogeneous Ru-catalyst, preferably Ru / C.

9. The process according to any of claims 6 - 8, wherein c) is carried out at a temperature of 120 – 300 °C, or 180 – 270 °C, or 230 – 270 °C; and / or wherein the pressure in c) is 1 – 20 MPa, or 10 – 14 MPa; and / or wherein the time that the carbohydrate is reacted in c) is 5 minutes – 3 hours, or 30 minutes – 1.5 hours.

10. Process according to any of claims 6 - 9, wherein in c): the mass ratio of i) calculated as the metal to ii) is in the range of 0.001 to 100, preferably from 0.01 to 5; and / or the mass ratio of carbohydrate to ii) is 2 to 1000, preferably 10 to 100, preferably 12 to 50; and / or the mass ratio of carbohydrate to i) is 2 – 1000; and / or the MEG / MPG molar selectivity is higher than 6; and / or the MEG molar yield is at least 55%.

11. The process according to any of claims 6 - 10, wherein c) is carried out in the presence of a solvent, wherein the solvent preferably comprises water.

12. The process according to any of claims 6 - 11, wherein the carbohydrate comprises C6 and / or C5 sugars; preferably wherein the carbohydrate comprises monosaccharides, disaccharides, oligosaccharides, and / or polysaccharides; most preferably wherein the carbohydrate comprises galactose, glucose, mannose, arabinose, xylose, glucuronic acid and / or galacturonic acid.

13. A process for preparing MEG from a carbohydrate, comprising reacting the carbohydrate with hydrogen in the presence of a catalytic system to deliver MEG, wherein the catalytic system comprises:i) at least one active metal component selected from groups 8, 9 or 10 of the Periodic Table; and ii) the tungsten catalyst obtainable according to the process of any one of claims 1 - 5.

14. A tungsten catalyst for preparing MEG from a carbohydrate comprising or consisting of the compound of the following formula (1): MxHyWOz· n H2O, wherein: M is selected from one or more alkali metals, alkaline earth metals, metals of group 11 of the periodic table, and ammonium; 0.4 ≤ x ≤ 0.6 when M is monovalent and 0.2 ≤ x ≤ 0.3 when M is divalent; 0 ≤ y ≤ 1.0; 3.2 ≤ z ≤ 3.6; and 0 ≤ n ≤ 3.

15. Use of the tungsten catalyst obtainable according to the process of any one of claims 1 - 5 for preparing MEG from a carbohydrate.

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