PAIRED ELECTROCHEMICAL SYNTHESIS OF OXYMETHYLENE DIMETHYL ETHERS

Abstract

 The invention relates to the electrochemical synthesis of oxymethylene dimethyl ethers via paired electrolysis.

Description

[0001] The invention relates to the field of electrochemistry. In general, the invention relates to electrochemical synthesis. More in particular, the invention relates to an electrochemical route to oxymethylene dimethyl ethers.

[0002] Oxymethylene dimethyl ethers (OME) are represented by the general formula CH₃(OCH₂)_nOCH₃, wherein "n" is an integer. The integer "n" can be 1 or more, such as 2 or more. In particular, the "n" in the general formula can be an integer of 2-10. OME, in particular wherein n = 1-7, are promising as synthetic fuels, fuel additives and solvents. Their combustion properties enable a reduction in pollutant formation, such as particulate soot matter and NO_x.

[0003] Methanol can be produced by reacting hydrogen with carbon dioxide. Formaldehyde is typically produced via oxidative dehydrogenation of methanol. As an example, US-A-2014/0 367 274 describes an electrochemical method for formaldehyde synthesis via methanol oxidation at a cathode. Two separate product streams are produced since the products at the anode and cathode are incompatible. The method is not designed to form OME.

[0004] Methods for preparing OME non-electrochemically are known, such as the aqueous acid-catalysed condensation reaction of methanol with formaldehyde (or trioxane).

[0005] For example, Kröcher et al. (Appl. Catal. B-Environ. 2017, 217, 407-420) describes the acid-catalysed synthesis of OME, reaction mechanism and catalyst types. Such acid-catalysed synthesis is considered costly and less efficient due to process step numbers, water management and complex reactants.

[0006] Mitsos et al. (Ind. Eng. Chem. Res. 2019, 58(12), 4881-4889) describes the production of CH₃O(CH₂O)₁CH₃ from hydrogen and carbon dioxide via excess methanol and aqueous formaldehyde, in a fixed-bed reactor. Mitsos et al. (Ind. Eng. Chem. Res. 2019, 58(14), 5567-5578) describes the production of OME (n = 3-5), from OME (n = 1) and trioxane. The use of trioxane renders the production less energy efficient due to its heat demand.

[0007] There remains a need in the art for a more energy efficient method to produce OME.

[0008] It is an objective of the invention to address this need in the art. Another objective of the invention is to provide a convenient electrochemical route to OME that requires few steps. It is another objective of the invention to provide a cost-efficient route to OME.

[0009] The inventors surprisingly found that these objectives can, at least in part, be met by the paired electrosynthesis of reactants for forming OME (OME reactants).

[0010] Accordingly, in a first aspect, the invention is directed to a method of producing oxymethylene dimethyl ether (OME), comprising preparing OME via paired electrosynthesis.

[0011] Compared to known non-electrochemical syntheses of OME, the invention takes a new and innovative approach to improve the energy and ecological efficiency. The approach includes paired electrochemical reduction and oxidation reactions.

[0012] An advantage of pairing electrochemical reduction with electrochemical oxidation (i.e., paired electrosynthesis) is that compounds are generated via both anodic oxidation and cathodic reduction during electrolysis. That is, the anodic reactions and cathodic reactions are both of synthetic interest. The term "paired electrosynthesis" is meant to indicate that both anodic and cathodic reactions form at least one intermediate compound (reactant) to the formation of OME, such as formaldehyde, and/or form (a) desired product(s), such as OME and/or formaldehyde. The intermediate compound(s) (reactant(s)) and/or product(s) formed by both the anodic and cathodic reactions can be the same or different. In particular, the anodic and cathodic reactions may form the same intermediate compound (reactant) and/or product. Preferably, the paired electrosynthesis comprises the formation of formaldehyde by anodic and cathodic reactions. The paired electrosynthesis can comprise the formation of one product from two or more starting materials, or the formation of two or more products, including OME, from one or more starting materials. With paired electrosynthesis, anodic and cathodic reactions are combined into one overall reaction and are preferably allowed to occur simultaneously. The paired electrosynthesis can be performed in a single compartment or in multiple separate compartments, such as in two separate compartments. Preferably, the paired electrosynthesis is performed in multiple separate compartments, such as in two separate compartments.

[0013] Hence, in a further aspect, the invention is directed to a method of producing oxymethylene dimethyl ether reactants (OME reactants), comprising electrochemically preparing said reactants, comprising formaldehyde and optionally methanol, by paired electrosynthesis. The reactants are suitable for forming OME.

[0014] The method, according to the first aspect, may be a one-step or two-step method of producing OME. For example, the method may comprise a step of forming formaldehyde in an anodic reaction mixture and/or in a cathodic reaction mixture, preferably at least in the cathodic reaction mixture; and a step of forming OME in the anodic reaction mixture and/or in the cathodic reaction mixture. Alternatively, the method may comprise a step of forming formaldehyde, preferably with OME, in a cathodic reaction mixture, and preferably formaldehyde, optionally with OME, in an anodic reaction mixture. Alternatively, the method may comprise a step of forming formaldehyde, in an electrochemical cell, both at an anode and at a cathode; and a step of collecting the formaldehyde and reacting it with an alcohol, preferably comprising methanol, to form OME. The method is schematically illustrated in the flowcharts of Figures 1 and 2.

[0015] It is based on judicious insight that OME are formed in the anodic reaction mixture and/or cathodic reaction mixture. The method allows OME to be produced in as few as one or two steps.

[0016] The method can be carried out in one or more electrochemical reactors. In principle, any type of reactor may be usable. The reactor may be operated in batch condition, in semi-continuous condition or in continuous condition. Batch processing has a lower risk of failure and is characterised by long reaction times, yet lower production rates are typically a result. Continuous processing may be more efficient and lucrative, as product(s) can be obtained in significantly larger amounts and require lower operating costs. Preferably, the method is carried out under continuous operating conditions. The electrochemical reactor can comprise a single compartment wherein the reduction and oxidation reactions may happen. The reactor can comprise two or more compartments, including a cathodic compartment with a cathode at which, for example, the carbon monoxide and/or carbon dioxide can be reduced. Whereas the paired electrosynthesis may be performed in an electrochemical reactor, the preparing of the reaction product comprising OME may be performed within the same electrochemical reactor or outside the electrochemical reactor.

[0017] Carbon monoxide and/or carbon dioxide may be electrochemically reduced. The carbon monoxide and/or carbon dioxide do not have to be of a specific origin or purity, although it can be beneficial from a process perspective. Either reactant may be part of a stream that comprises, for example, nitrogen and/or hydrogen. For example, the carbon monoxide and/or carbon dioxide can originate from a (pre)combustion process in, for example, the steel industry; a natural gas stream; a biogas stream; synthesis gas; water, and/or air.

[0018] The reduction can be carried out at atmospheric pressure, for example, approximately 1 bar. It is preferred to carry out the reduction at an elevated pressure. In particular, the reduction may be carried out at an absolute pressure of 10 bar or more, such as 30 bar or more; 50 bar or more; 70 bar or more, and, for example, 200 bar or less, such as 170 bar or less; 150 bar or less, or 130 bar or less. Preferably, the reduction is carried out at an absolute pressure of 30 bar or more and/or 150 bar or less, such as 30-150 bar or 50-130 bar.

[0019] The reduction can be carried out at ambient temperature (e.g., room temperature). In particular, the reduction can be carried out at 0 °C or higher, such as 10 °C or higher, 20 °C or higher, or 30 °C or higher. Preferably, the reduction is carried out at 0-70 °C, such as 10-60 °C. More preferably, the reduction is carried out at 20-50 °C.

[0020] The reduction can be carried out in a single compartment or a cathodic compartment of, for example, an electrochemical reactor, such as described in this disclosure. The reduction can result in, for example, carbon monoxide, methanol and/or formaldehyde.

[0021] The single compartment or cathodic compartment comprises a cathode. The cathode may comprise one or more selected from the group consisting of metals, doped carbon materials and carbon-based materials. Suitable metals include platinum, palladium, rhodium, osmium, gold, silver, titanium, copper, iridium, ruthenium, lead, nickel, cobalt, zinc, cadmium, tin, iron, gallium, thallium, tungsten, indium, antimony, and bismuth, oxides and/or alloys thereof, mixed metal oxides, dimensionally stable electrode (DSA^®), stainless steel, brass, and the like. Suitable carbon-based materials include graphite, carbon felt, glassy carbon, and the like. Preferably, the cathode comprises boron-doped diamond (BDD).

[0022] The cathode can comprise a plate electrode; a foam electrode; a mesh electrode (3-D electrode); a gas diffusion electrode, or a combination thereof.

[0023] The electrochemical reduction can be carried out in a catholyte. The catholyte may refer to a single solvent or to a mixture of solvents. The catholyte can comprise a (first) non-aqueous solvent. The solvent may be polar or apolar (dielectric constant of 10 or less). The solvent can be an organic solvent. The organic solvent is preferably a polar organic solvent or a protic organic solvent, such as a polar protic organic solvent.

[0024] The catholyte can comprise one or more alcohols. The one or more alcohols can be selected from C₁-C₈ alcohols. Preferably, the alcohol is selected from the group consisting of methanol; ethanol; n-propanol; iso-propanol; n-butanol; iso-butanol; tert-butanol; n-pentanol, and tert-pentyl alcohol. More preferably, the non-aqueous solvent comprises methanol.

[0025] The catholyte can comprise 20 % water or less, based on the total weight of the catholyte. In particular, the catholyte can comprise 15 wt.% or less of water, such as 12 wt.% or less; 10 wt.% or less, or 8 wt.% or less. Preferably, the catholyte comprises 6 wt.% or less of water, such as 5 wt.% or less, 4 wt.% or less, or 3 wt.% or less. More preferably, the catholyte comprises 2 wt.% or less of water. Even more preferably, the catholyte is essentially free of water (i.e., 1 wt.% or less of water, such as 0.5 wt.% or less).

[0026] The electrochemical reactor comprising a cathodic compartment can further comprise an anodic compartment with an anode at which an alcohol can be oxidised. The alcohol can be selected from C₁-C₈ alcohols. In particular, the alcohol is selected from the group consisting of methanol; ethanol; n-propanol; iso-propanol; n-butanol; iso-butanol; tert-butanol; n-pentanol, and tert-pentyl alcohol. Preferably, the alcohol is methanol. The methanol can be formed by a reaction of hydrogen and carbon dioxide. However, the methanol does not have to be of a specific origin or purity.

[0027] The oxidation can be carried out at atmospheric pressure, for example, approximately 1 bar, or at an elevated pressure. In particular, the oxidation may be carried out at an absolute pressure of 10 bar or more, such as 30 bar or more; 50 bar or more; 70 bar or more, and, for example, 200 bar or less, such as 170 bar or less; 150 bar or less, or 130 bar or less. Preferably, the oxidation is carried out at an absolute pressure of 30 bar or more and/or 150 bar or less, such as 30-150 bar or 50-130 bar.

[0028] The oxidation can be carried out at ambient temperature (room temperature). In particular, the oxidation can be carried out at a temperature of 0 °C or higher, such as 10 °C or higher, 20 °C or higher, or 30 °C or higher. Preferably, the oxidation is carried out at a temperature of 0-70 °C, such as 10-60 °C. More preferably, the oxidation is carried out at 20-50 °C.

[0029] The oxidation can be carried out in an anodic compartment of, for example, an electrochemical reactor. The oxidation can result in, for example, formaldehyde, carbon dioxide, and/or formic acid.

[0030] The anodic compartment comprises an anode. The anode may comprise one or more metals. Preferably, the anode comprises platinum.

[0031] The oxidation can be carried out in an anolyte. The anolyte may refer to a single solvent or to a mixture of solvents. The anolyte can comprise a (second) non-aqueous solvent. The solvent may be polar or apolar. The non-aqueous solvent can comprise an organic solvent. The organic solvent is preferably a polar organic solvent or a protic organic solvent, such as a polar protic organic solvent.

[0032] The non-aqueous solvent can comprise one or more alcohols. The one or more alcohols can be selected from C₁-C₈ alcohols. Preferably, the alcohol is selected from the group consisting of methanol; ethanol; n-propanol; iso-propanol; n-butanol; iso-butanol; tert-butanol; n-pentanol, and tert-pentyl alcohol. More preferably, the non-aqueous solvent comprises methanol. An advantage of using methanol is that it can act as both a solvent as well as a reactant.

[0033] The anolyte can comprise 20 % water or less, based on the total weight of the anolyte. In particular, the anolyte can comprise 15 wt.% or less of water, such as 12 wt.% or less; 10 wt.% or less, or 8 wt.% or less. Preferably, the catholyte comprises 6 wt.% or less of water, such as 5 wt.% or less; 4 wt.% or less, or 3 wt.% or less. More preferably, the anolyte comprises 2 wt.% or less of water. Even more preferably, the anolyte is essentially free of water (i.e., 1 wt.% or less of water, such as 0.5 wt.% or less). The lower the amount of water in the anolyte, the better the oxidation reaction can be carried out.

[0034] Alternatively, if the method of the invention is performed in a single compartment, both the reduction and oxidation can be carried out in an electrolyte. The electrolyte may refer to a single solvent or to a mixture of solvents. The electrolyte can comprise a non-aqueous solvent. The solvent may be polar or apolar (dielectric constant of 10 or less). The solvent can be an organic solvent. The organic solvent is preferably a polar organic solvent or a protic organic solvent, such as a polar protic organic solvent.

[0035] The electrolyte can comprise one or more alcohols. The one or more alcohols can be selected from C₁-C₈ alcohols. Preferably, the alcohol is selected from the group consisting of methanol; ethanol; n-propanol; iso-propanol; n-butanol; iso-butanol; tert-butanol; n-pentanol, and tert-pentyl alcohol. More preferably, the non-aqueous solvent comprises methanol.

[0036] The electrolyte can comprise 20 % water or less, based on the total weight of the electrolyte. In particular, the electrolyte can comprise 15 wt.% or less of water, such as 12 wt.% or less; 10 wt.% or less, or 8 wt.% or less. Preferably, the electrolyte comprises 6 wt.% or less of water, such as 5 wt.% or less, 4 wt.% or less, or 3 wt.% or less. More preferably, the electrolyte comprises 2 wt.% or less of water. Even more preferably, the electrolyte is essentially free of water (i.e., 1 wt.% or less of water, such as 0.5 wt.% or less).

[0037] The reduction and oxidation in the single compartment can be carried out at atmospheric pressure, for example, approximately 1 bar, or at an elevated pressure. In particular, both reactions may be carried out at an absolute pressure of 10 bar or more, such as 30 bar or more; 50 bar or more; 70 bar or more, and, for example, 200 bar or less, such as 170 bar or less; 150 bar or less, or 130 bar or less. Preferably, the reactions are carried out at an absolute pressure of 30 bar or more and/or 150 bar or less, such as 30-150 bar or 50-130 bar.

[0038] Both reactions can be carried out at ambient temperature (room temperature). In particular, both reactions can be carried out at a temperature of 0 °C or higher, such as 10 °C or higher, 20 °C or higher, or 30 °C or higher. Preferably, both reactions are carried out at a temperature of 0-70 °C, such as 10-60 °C. More preferably, both reactions are carried out at 20-50 °C.

[0039] By electrochemically reducing carbon monoxide and/or carbon dioxide, formaldehyde can be formed. The inventors describe this surprising finding, in particular for carbon monoxide, in WO-A-2021/150117. In particular, with the method of the invention the paired electrosynthesis may comprise electrochemically reducing carbon monoxide and/or carbon dioxide and electrochemically oxidising an alcohol as described in this disclosure, wherein the electrochemical reduction forms formaldehyde. The electrochemical oxidation of methanol can form formaldehyde. Preferably, the paired electrosynthesis comprises electrochemically reducing carbon monoxide and/or carbon dioxide and electrochemically oxidising methanol, wherein both the electrochemical reduction of carbon monoxide and/or carbon dioxide, and the electrochemical oxidation of methanol form formaldehyde.

[0040] In an embodiment, carbon monoxide and/or carbon dioxide is electrochemically reduced in a compartment comprising a cathode, wherein said cathode comprises one or more of the groups consisting of metals, carbon-doped materials, and carbon-based materials; and/or alcohol is electrochemically oxidised in a compartment comprising an anode, said anode comprising one or more metals. The method is preferably performed in an electrochemical reactor. Preferably, the cathode comprises boron-doped diamond (BDD). The anode preferably comprises platinum.

[0041] In a preferred embodiment, the method of the invention is performed in an electrochemical reactor as described in this disclosure, and the method comprises feeding a non-aqueous mixture comprising carbon monoxide and/or carbon dioxide, and methanol to a compartment comprising a cathode (a cathodic compartment), wherein the cathode comprises boron-doped diamond (BDD). According to this preferred embodiment, a non-aqueous mixture comprising an alcohol, such as methanol, is fed to a compartment comprising an anode (an anodic compartment), wherein the anode comprises platinum. This preferred method also comprises combining the mixtures of said compartments into one reaction mixture, which is suitable for forming OME.

[0042] The reaction mixture comprises formaldehyde, such as from the electrochemical reduction of carbon monoxide and/or carbon dioxide, and preferably formaldehyde from the electrochemical oxidation of methanol. The reaction mixture may comprise OME, as explained herein. The component(s) of the reaction mixture, which may include methanol, may be reacted to form OME. Methanol and/or formaldehyde may be added to the reaction mixture to react with the component(s) of the reaction mixture. The formation of OME may be performed in the electrochemical reactor where the paired electrosynthesis is performed, or outside the electrochemical reactor. The heat produced with the paired electrosynthesis is preferably used in the OME formation reaction.

[0043] Also provided is OME obtainable by the method of the invention. In particular, the method further comprises isolating OME, for example, from the reaction mixture.

[0044] OME comprises one or more compounds represented by general formula CH₃O(CH₂O)_nCH₃, wherein "n" is 1 or more. In particular, OME comprises 75 % or more of CH₃O(CH₂O)₁CH₃, based on the total weight of OME. Preferably, this comprises 80 wt.% or more of CH₃O(CH₂O)₁CH₃, such as 85 wt.% or more, or 90 wt.% or more and, for example, less than 100 wt.%, such as 99 wt.% or less, or 95 wt.% or less. More preferably, OME comprises 80-99 wt.% of CH₃O(CH₂O)₁CH₃, such as 85-95 wt.%.

[0045] OME obtainable by the method of the invention may comprise a small and/or number of impurities, such as methanol, water, formic acid, formaldehyde, and the like. OME can comprise 10 % or less of impurities by total weight of the oxymethylene dimethyl ether. In particular, OME can comprise 7 wt.% or less of impurities, such as 5 wt.% or less, or 3 wt.% or less. Preferably, OME comprises 2 wt.% or less of impurities, such as 1 wt.% or less, or 0.5 wt.% or less.

[0046] OME can be used for the synthesis of longer chain or polymeric oxymethylene dimethyl ether.

[0047] The inventors surprisingly found that the anodic and cathodic products, or product mixtures, can be combined for direct use in the synthesis of OME.

[0048] The method of the invention may further comprise the formed OME with formaldehyde, thereby forming longer chain or polymeric OME. The formaldehyde can be as obtained by the method of the invention. The longer chain or polymeric oxymethylene dimethyl ether may comprise one or more compounds represented by general formula CH₃O(CH₂O)_nCH₃, wherein "n" is an integer of 3 or more. Preferably, "n" is an integer of 3-10. More preferably, "n" is 3, 4 or 5.

[0049] OME, wherein "n" in the general formula is an integer of 3, 4 or 5, can be used as a synthetic fuel or fuel additive.

[0050] Further provided is longer chain or polymeric oxymethylene dimethyl ether obtainable by the method of producing oxymethylene dimethyl ether of the invention that further comprises reacting OME with formaldehyde to form a longer chain or polymeric oxymethylene dimethyl ether.

[0051] The longer chain oxymethylene dimethyl ether may comprise 75 % or more of compounds of CH₃O(CH₂O)_nCH₃, wherein "n" is 2 or more, based on the total weight of the oxymethylene dimethyl ether. Preferably, the oxymethylene dimethyl ether comprises 80 wt.% or more of compounds of CH₃O(CH₂O)_nCH₃, wherein "n" is 2 or more, such as 85 wt.% or more, or 90 wt.% or more and, for example, less than 100 wt.%, such as 99 wt.% or less, or 95 wt.% or less. More preferably, the oxymethylene dimethyl ether comprises 80-99 wt.% of compounds of CH₃O(CH₂O)_nCH₃, wherein "n" is 2 or more, such as 85-95 wt.%.

[0052] The longer chain oxymethylene dimethyl ether may comprise a small and/or number of impurities, such as oxymethylene dimethyl ether (e.g., wherein "n" in the general formula is 1), methanol, water, formic acid, formaldehyde, and the like. The longer chain oxymethylene dimethyl ether can comprise 10 % or less of impurities by total weight of the longer chain oxymethylene dimethyl ether. In particular, the longer chain oxymethylene dimethyl ether can comprise 7 wt.% or less of impurities, such as 5 wt.% or less, or 3 wt.% or less. Preferably, the longer chain oxymethylene dimethyl ether comprises 2 wt.% or less of impurities, such as 1 wt.% or less, or 0.5 wt.% or less.

[0053] OME produced with the method of the invention can be represented by general formula CH₃O(CH₂O)_nCH₃, wherein "n" is an integer of 2 or more. In particular, "n" can be 5 or more or 10 or more and, for example, 20 or less or 15 or less, such as 2-20. Preferably, "n" is an integer selected from 2-10. More preferably, "n" is 3, 4 or 5. OME of CH₃O(CH₂O)_nCH₃, where "n" is 3, 4 or 5 are considered particularly suitable as synthetic fuels and fuel additives. Hence, there is also provided the use of such OME as synthetic fuel or fuel additive.

[0054] In another aspect, the invention is directed to a method of producing a polyoxymethylene dimethyl ether. The method comprises preparing oxymethylene dimethyl ether according to the method of the invention. The method further comprises reacting the oxymethylene dimethyl ether with formaldehyde to form the polyoxymethylene dimethyl ether. The formaldehyde may originate from any source, but particularly from the methods of the invention, such as the reduction and/or oxidation reactions. The polyoxymethylene dimethyl ether is a longer chain or polymeric oxymethylene dimethyl ether, such as described in this disclosure. In particular, the polyoxymethylene dimethyl ether comprises one or more compounds represented by general formula CH₃O(CH₂O)_nCH₃, wherein "n" is an integer of 3 or more.

[0055] Further provided is a method of producing a functionalised oxymethylene dimethyl ether. The method comprises preparing oxymethylene dimethyl ether according to the method of the invention. The method further comprises reacting the oxymethylene dimethyl ether with one or more aldehydes to form a functionalised oxymethylene dimethyl ether. The one or more aldehydes may be selected from the group consisting of acyclic aldehydes and arylaldehydes. Preferably, the one or more aldehydes are selected from C₁-C₈ acyclic aldehydes, such as acetaldehyde, propanal and butanal; benzaldehyde; and derivatives thereof.

[0056] Further provided is the use of paired electrolysis to electrosynthesis of OME. In view of the methods known to synthesise OME, the use of paired electrolysis is new and innovative, and results in an energy efficient and convenient preparing of OME, which can be used for further formation of longer chain or polymeric OME, or functionalised OME. In particular, the paired electrolysis comprises the electrochemical oxidation of methanol paired with the electrochemical reduction of carbon monoxide and/or carbon dioxide.

[0057] The invention has been described by reference to various embodiments, and methods. The skilled person understands that features of various embodiments and methods can be combined with each other.

[0058] All references cited herein are hereby completely incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0059] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms "comprising", "having", "including" and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to") unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. For the purpose of the description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include any combination of the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

[0060] Preferred embodiments of this invention are described herein. Variation of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject-matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art.

[0061] For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described.

Claims

1. Method of producing oxymethylene dimethyl ether, comprising preparing oxymethylene dimethyl ether via paired electrosynthesis.

2. Method of producing oxymethylene dimethyl ether reactants, comprising electrochemically preparing said reactants, comprising formaldehyde, by paired electrosynthesis.

3. Method according to claim 1 or 2, wherein the paired electrosynthesis comprises:

- electrochemically reducing carbon monoxide and/or carbon dioxide; and/or

- electrochemically oxidising an alcohol, preferably a C₁-C₈ alcohol, such as methanol.

4. Method according to any one of claims 1-3, wherein

- the paired electrosynthesis is carried out in an electrolyte; or

- the electrochemically reducing carbon monoxide and/or carbon dioxide is carried out in a catholyte; and/or

- the electrochemically oxidising an alcohol is carried out in an anolyte.

5. Method according to claim 4, wherein

- the electrolyte comprises a non-aqueous solvent, preferably comprising an organic solvent, more preferably a polar organic solvent or a protic organic solvent; or

- the catholyte comprises a first non-aqueous solvent, preferably comprising an organic solvent, more preferably a polar organic solvent or a protic organic solvent; and/or

- the anolyte comprises a second non-aqueous solvent, preferably comprising an organic solvent, more preferably a polar organic solvent or a protic organic solvent.

6. Method according to claim 5, wherein the non-aqueous solvent, or first non-aqueous solvent and/or the second non-aqueous solvent comprise one or more alcohols, preferably one or more C₁-C₈ alcohols, more preferably one or more alcohols selected from the group consisting of methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, tert-butanol, n-pentanol, and tert-pentyl alcohol, even more preferably methanol.

7. Method according to any one of claims 4-6, wherein

- the electrolyte comprises 10 % or less of water, preferably 5 % or less of water, more preferably 2 % or less of water, based on the total weight of the electrolyte; or

- the anolyte comprises 10 % or less of water, preferably 5 % or less of water, more preferably 2 % or less of water, based on the total weight of the anolyte; and/or

- the catholyte comprises 10 % or less of water, preferably 5 % or less of water, more preferably 2 % or less of water, based on the total weight of the catholyte.

8. Method according to any one of claims 3-7, wherein at least part of the carbon monoxide and/or at least part of the carbon dioxide originates from a (pre-)combustion process, a natural gas stream, a biogas stream, synthesis gas, water, and/or air.

9. Method according to any one of claims 3-8, preferably performed in an electrochemical reactor, wherein

- the carbon monoxide and/or carbon dioxide is electrochemically reduced in a compartment, preferably a cathodic compartment, comprising a cathode, said cathode comprising one or more of the groups consisting of metals, carbon-doped materials, and carbon-based materials, preferably comprising boron-doped diamond (BDD); and/or

- the alcohol is electrochemically oxidised in a compartment, preferably an anodic compartment, comprising an anode, said anode comprising one or more metals, preferably platinum.

10. Method according to claim 9, comprising:

- feeding a non-aqueous mixture comprising carbon monoxide and/or carbon dioxide, and methanol to the compartment, wherein the cathode comprises BDD;

- feeding a non-aqueous mixture comprising alcohol to the compartment, wherein the anode comprises platinum; and

- combining the mixtures of said compartments into one reaction mixture,wherein the reaction mixture comprises formaldehyde and methanol.

11. Method according to claim 9 or 10, wherein oxymethylene dimethyl ether is formed in the compartment comprising the anode and/or the compartment comprising the cathode.

12. Method according to any one of claims 9-11, wherein said compartments are the same compartment.

13. Method according to any one of claims 1-12, wherein the paired electrosynthesis is carried out at:

- atmospheric pressure or higher, preferably at an absolute pressure of 10-200 bar, more preferably 30-150 bar; and/or

- a temperature of 0 °C or higher, preferably 10-60 °C, more preferably 20-50 °C.

14. Method according to any one of claims 10-13, comprising reacting the reaction mixture to form oxymethylene dimethyl ether.

15. Method according to claim 14, wherein the reaction is carried out at:

- atmospheric pressure or higher, preferably at an absolute pressure of 10-200 bar, more preferably 30-150 bar; and/or

- a temperature of 0 °C or higher, preferably 10-60 °C, more preferably 20-50 °C.

16. Method according to claim any one of claims 1 and 3-15, wherein the oxymethylene dimethyl ether comprises one or more compounds represented by general formula CH₃O(CH₂O)_nCH₃, wherein "n" is an integer of 1 or more, preferably 2-10, more preferably 3, 4 or 5.

17. Method of producing a polyoxymethylene dimethyl ether, comprising:

- preparing oxymethylene dimethyl ether according to the method of any one of claims 1 and 3-15; and

- reacting the oxymethylene dimethyl ether with formaldehyde, preferably as obtained by the method of any one of claims 2-15, thereby forming the polyoxymethylene dimethyl ether.

Drawing