WO2024050745A1

WO2024050745A1 - Electrochemical method for hydrogenating 2-alkylanthraquinone to 2- alkylanthracene-9, 10-diol

Info

Publication number: WO2024050745A1
Application number: PCT/CN2022/117724
Authority: WO
Inventors: Renate Schwiedernoch; Pascal Metivier; Daniele Facchi; Nuno FORMIGA; Tingting Liu; Li Fan
Original assignee: Solvay Sa
Priority date: 2022-09-08
Filing date: 2022-09-08
Publication date: 2024-03-14

Abstract

An electrochemical method for hydrogenating 2-alkylanthraquinone to 2-alkylanthracene-9, 10-diol is provided, which features a simple and environmentally-friendly process. Advantageously, the solution in the cathode chamber can be completely free or substantially free from an electrolyte and the hydrogenation reaction can be carried out in a working solution. The method is more suitable for industrialization.

Description

ELECTROCHEMICAL METHOD FOR HYDROGENATING 2-ALKYLANTHRAQUINONE TO 2- ALKYLANTHRACENE-9, 10-DIOL

TECHNICAL FIELD

The present disclosure relates to a method for hydrogenating 2-alkylanthraquinone to 2-alkylanthracene-9, 10-diol.

BACKGROUND

The following discussion of the prior art is provided to place the disclosure in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of common general knowledge in the field.

Hydrogen peroxide (H ₂O ₂) is an important green basic chemical for industry. The use of alkyl-substituted anthraquinones for the production of hydrogen peroxide is well known. In this process, substituted anthraquinones and/or tetrahydro anthraquinones dissolved in a suitable organic solvent mixture, a so-called working solution, are hydrogenated to form the corresponding hydroquinones. The hydroquinones are then oxidized back to quinones with oxygen (usually air) with simultaneous formation of hydrogen peroxide, which then can be extracted with water while the quinones are returned with the working solution to the hydrogenation step.

Electrochemical methods for synthesis of hydrogen peroxide using organic quinone mediators has been widely reported. For example, Joule 3, 2942-2954, December 18, 2019 reports an improved method by coupling electrochemistry with phase-transfer catalysis using organic quinone mediators to furnish continuous H ₂O ₂ synthesis and separation. Specifically, the following three-step sequence could allow for rapid, continuous H ₂O ₂ production and separation without the use of precious metal catalysts (Figure 1) : the electrochemical reduction of a quinone to a hydroquinone in aqueous electrolyte; phase transfer of the hydroquinone into an immiscible solvent phase; and reaction of the hydroquinone with an oxygenated pure water stream to generate H ₂O ₂ and regenerate the original quinone for recycling to the electrochemical cell. Disadvantageously, salts of anthraquinone were required to ensure that the hydrogenation of quinone can be carried out in a conductive solution. Furthermore, it is necessary to transfer hydroquinone into an organic phase before H ₂O ₂ synthesis. The quinone has to be transferred back to the water phase for hydrogenation.

Journal of the Electrochemical Society (1992) , 139 (4) , 948-954 teaches a process for the electrochemical reduction of 2-ethyl anthraquinone (EAQ) . The apparatus is a cell in which the cylindrical cathode was separated from the cylindrical anode by a Nifon membrane. At cathode side, an organic solution was dispersed with the aqueous phase (2M NaOH) to perform the reaction with better conductivity. Therefore, this process also needs a conductive aqueous solution when reducing EAQ.

Journal of Electroanalytical Chemistry (1997) , 420 (1-2) , 31-34 discloses a study on the electrochemical behaviour of 2-ethyl anthraquinone (EAQ) at the powder graphite|Nafion membrane interface of a solid polymer electrolyte composite electrode. Specifically, EAQ was firstly dissolved in ethanol to form a solution. A dried Nafion membrane was immersed in the solution for a certain time so that EAQ can dissolve in the membrane. No electrolysis was carried out. Only CV analysis was mentioned in this publication.

SUMMARY

The Applicant perceived that there is still the need for an electrochemical method for hydrogenating 2-alkylanthraquinone to 2-alkylanthracene-9, 10-diol, which features a simple and environmentally-friendly process.

It has now been discovered that the electrochemical method according to the present invention can hydrogenate 2-alkylanthraquinone to 2-alkylanthracene-9, 10-diol, preferably without using an aqueous solution dissolved with an electrolyte. Advantageously, the hydrogenation reaction can be carried out in a working solution directly. In some cases, hydrogen peroxide is in-situ formed subsequently in the working solution. Thus, the method is more suitable for industrialization. Furthermore, a very small amount of hydrogen gas was formed and said method is therefore safer compared to the prior art.

Other subjects and characteristics, aspects and advantages of the present invention will emerge even more clearly on reading the detailed description and the examples that follow.

BRRIEF OF DESCRIPTION OF DRAWINGS

Fig. 1. The PEM electrolyzer;

Fig. 2. 1-Heating block;

Fig. 3. 2-Al block with water inlet and water/O ₂ outlet;

Fig. 4. 3-PTFE sealing with water inlet and water/O ₂ outlet;

Fig. 5 4-Electron collector with water inlet and water/O ₂ outlet;

Fig. 6 5-PTFE frame with an electron conductive layer (ECL) ;

Fig. 7 6-MEA;

Fig. 8 7-PTFE frame with an electron conductive layer (ECL) or an electron conductive layer (ECL) treated by a proton conductive material;

Fig. 9 8-Electron collector with working solution inlet and outlet;

Fig. 10 9-PTFE sealing with working solution inlet and outlet;

Fig. 11. 10-Al block with working solution inlet and outlet;

Fig. 12. 11-Heating block;

Fig. 13 Setup for the electrochemical hydrogenation of 2-alkylanthraquinone.

DEFINITIONS

Throughout the description, including the claims, the term "comprising one" should be understood as being synonymous with the term "comprising at least one" , unless otherwise specified, and "between" should be understood as being inclusive of the limits.

As used herein, the terminology " (C _n-C _m) " in reference to an organic group, wherein n and m are both integers, indicates that the group may contain from n carbon atoms to m carbon atoms per group.

The articles "a" , "an" and "the" are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

The term "and/or" includes the meanings "and" , "or" and also all the other possible combinations of the elements connected to this term.

It is specified that, in the continuation of the description, unless otherwise indicated, the values at the limits are included in the ranges of values which are given.

As used herein, the term "MEA (membrane electrode assembly) " means an assembled stack comprising at least one proton-exchange membrane (PEM) , an anode catalyst coating layer and optionally a cathode catalyst coating layer.

Ratios, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also all the individual numerical values or sub-ranges encompassed within that range as if each numerical value or sub-range is explicitly recited.

DETAILS OF THE INVENTION

The present invention provides a method for hydrogenating 2-alkylanthraquinone to 2-alkylanthracene-9, 10-diol, comprising the following steps:

a) providing an electrochemical cell having an anode chamber containing an anode, a cathode chamber containing a cathode, and a proton exchange membrane (PEM) between the anode and the cathode;

b) feeding deionized water to the anode chamber and a solution comprising 2-alkylanthraquinone to the cathode chamber;

c) passing an electric current between the anode and the cathode to hydrogenate 2-alkylanthraquinone to 2-alkylanthracene-9, 10-diol;

wherein:

- the surface of the proton exchange membrane (PEM) exposed to the anode is coated with a layer comprising an anode catalyst, a proton conductive material and optionally an electron conductive material;

- the surface of the proton exchange membrane (PEM) exposed to the cathode contacts a proton and electron conductive layer (PECL) .

As used herein, the term "alkyl" in the 2-alkylanthraquinone or the 2-alkylanthracene-9, 10-diol means a saturated hydrocarbon radical, which may be straight, or branched, such as, methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, t-butyl, pentyl, n-hexyl. Alkyl preferably contains 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms, particularly 1 to 10 carbon atoms, for instance 1 to 8 carbon atoms, or even 1 to 6 carbon atoms. Most preferably, alkyl is ethyl or amyl.

The thickness of the PEM can be from 50 μm to 500 μm and preferably from 50 μm to 185 μm. The person skilled in the art will adjust the thickness based on the production scale.

Preferably, there is no gap between the proton exchange membrane and the cathode.

Preferably, there is no gap between the proton exchange membrane and the anode.

The expression "no gap" is generally understood to mean that the distance between the PEM and the two electrodes is less than 1 mm, preferably less than 0.5 mm, particularly less than 0.1 mm, more particularly less than 0.05 mm, for instance less than 0.01 mm, or even less than 0.005 mm, or can be less than 0.001 mm.

For the purpose of the present invention, the PEM can be a membrane made from a polymer (F) comprising:

- recurring units derived from at least one ethylenically unsaturated monomer comprising at least one fluorine atom (fluorinated monomer, hereinafter) ; and

- a substantial amount of recurring units derived from at least one ethylenically unsaturated monomer comprising at least one ion exchange group (functional monomer, hereinafter) .

The expression “at least one ethylenically unsaturated monomer comprising at least one fluorine atom [fluorinated monomer] ” is understood to mean that the polymer (F) can comprise recurring units derived from one or more than one fluorinated monomer.

In the remainder of the text, the expression "fluorinated monomer” is to be understood, for the purposes of the present invention, both in the plural and in the singular.

The fluorinated monomer can further comprise one or more other halogen atoms (in particular Cl, Br, I) . When the fluorinated monomer is free of hydrogen atom, it is designated as “per (halo) fluoromonomer” . When the fluorinated monomer comprises at least one hydrogen atom, it is designated as “hydrogen-containing fluorinated monomer” .

Non limitative examples of fluorinated monomers are notably tetrafluoroethylene (TFE) , vinylidene fluoride (VdF) , chlorotrifluoroethylene (CTFE) , and mixtures thereof.

Optionally, the polymer (F) may comprise recurring units derived from one first monomer, said monomer being a fluorinated monomer as above described, and at least one other monomer [comonomer (CM) , hereinafter] .

Hereinafter, the term comonomer (CM) should be intended to encompass both one comonomer and two or more comonomers.

The comonomer (CM) can notably be either hydrogenated (i.e. free of fluorine atoms) [comonomer (HCM) , hereinafter] or fluorinated (i.e. containing at least one fluorine atom) [comonomer (FCM) , hereinafter] .

Non limitative examples of suitable hydrogenated comonomers (HCM) are notably ethylene, propylene, vinyl monomers such as vinyl acetate, acrylic monomers, like methyl methacrylate, acrylic acid, methacrylic acid and hydroxyethyl acrylate, as well as styrene monomers, like styrene and p-methylstyrene.

Non limitative examples of suitable fluorinated comonomers (FCM) are notably:

- C ₃-C ₈ fluoro-and/or perfluoroolefins, such as hexafluoropropene, pentafluoropropylene, and hexafluoroisobutylene;

- C ₂-C ₈hydrogenated monofluoroolefins, such as vinyl fluoride;

- 1, 2-difluoroethylene, vinylidene fluoride and trifluoroethylene;

- perfluoroalkylethylenes complying with formula CH ₂=CH-R _f0, in which R _f0 is a C ₁-C ₆ perfluoroalkyl;

- chloro-and/or bromo-and/or iodo-C ₂-C ₆ fluoroolefins, like chlorotrifluoroethylene;

- fluoroalkylvinylethers complying with formula CF ₂=CFOR _f1 in which R _f1 is a C ₁-C ₆ fluoro-or perfluoroalkyl, e.g. -CF ₃, -C ₂F ₅, -C ₃F ₇;

- fluoro-oxyalkylvinylethers complying with formula CF ₂=CFOX ₀, in which X ₀ is a C ₁-C ₁₂ oxyalkyl, or a C ₁-C ₁₂ (per) fluorooxyalkyl having one or more ether groups, like perfluoro-2-propoxy-propyl;

- fluoroalkyl-methoxy-vinylethers complying with formula CF ₂=CFOCF ₂OR _f2in which R _f2is a C ₁-C ₆ fluoro-or perfluoroalkyl, e.g. -CF ₃, -C ₂F ₅, -C ₃F ₇ or a C ₁-C ₆ (per) fluorooxyalkyl having one or more ether groups, like-C ₂F ₅-O-CF ₃;

- fluorodioxoles, of formula:

wherein each of R _f3, R _f4, R _f5, R _f6, equal or different each other, is independently a fluorine atom, a C ₁-C ₆ fluoro-or per (halo) fluoroalkyl, optionally comprising one or more oxygen atom, e.g. -CF ₃, -C ₂F ₅, -C ₃F ₇, -OCF ₃, -OCF ₂CF ₂OCF ₃.

As defined above, the polymer (F) useful for the method of the present invention comprises a substantial amount of recurring units derived from at least one functional monomer.

The expression “substantial amount” in the definition here above is intended to denote an amount of recurring units derived from the functional monomer which is effective to modify the polymer in its properties. Generally, a substantial amount is of at least 1%by moles, preferably at least 2%by moles, for example at least 3 or 5%by moles, or even at least 10%by moles, based on the total moles of recurring units.

The expression "ion exchange group" is used here in its general meaning as intended in organic chemistry and it preferably encompasses atoms or combination of atoms bonded to the carbon skeleton of the ethylenically unsaturated monomer, which confers to said ethylenically unsaturated monomer ability to trap and release (i.e. exchange) ions in a process called ion exchange. Generally cation exchange groups are negatively charged moieties while anion exchange groups are positively charged moieties.

Non limitative examples of ion exchange groups are notably those complying with formula:

--SO ₂X, wherein X is chosen among halogens (as Cl, F, Br, I) , -O ^-M ⁺, wherein M ⁺is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺, or mixtures thereof; preferably X=-O ^-H ⁺.

--COY, wherein Y is chosen among halogens (as Cl, F, Br, I) ; -O ^-M ⁺, wherein M ⁺is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺; -OR _Hywherein R _Hy is a C ₁-C ₆ hydrocarbon group; -OR _Hfwherein R _Hf is a C ₁-C ₆ fluorocarbon or per (halo) fluorocarbon group; -N (R _Hy*) ₂, wherein R _Hy*, equal or different at each occurrence, is hydrogen or a C ₁-C ₆ hydrocarbon group, or mixtures thereof; preferably Y=-O ^-H ⁺.

--PO ₂Z, wherein Z is chosen among halogens (as Cl, F, Br, I) ; -O ^-M ⁺, wherein M ⁺is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺; -OR _Hy wherein R _Hy is a C ₁-C ₆ hydrocarbon group, and-OR _Hf’ wherein R _Hf is a C ₁-C ₆ fluorocarbon or per (halo) fluorocarbon group, or mixture thereof; preferably Z=-O ^-H ⁺.

For the purpose of the invention, a preferred cation exchange group in the polymer (F) complies with formula-SO ₂X as described above.

The polymer (F) comprises advantageously at least 1%, preferably at least 2%,more preferably at least 3%, for example at least 5%, by mole of recurring units derived from at least one monomer bearing a cation exchange group [ “functional monomer” , hereinafter] , based on the total moles of recurring units.

The polymer (F) comprises advantageously at most 75%, preferably at most 50%, more preferably at most 30%, even most preferably at most 25%by moles of recurring units derived from at least one functional monomer, based on the total moles of recurring units.

Should the functional monomer comprise, in addition to fluorine atoms optionally comprised in the functional group, at least one fluorine atom which is not comprised in the functional group, it is designated as fluorinated functional monomer. Should the functional monomer be free of fluorine atoms other than those optionally comprised in the functional group, it is designated as hydrogenated functional monomer.

The fluorinated monomer and the fluorinated functional monomer may be the same monomer or may be different monomers, that is to say that the polymer (F) can be a homopolymer of a fluorinated functional monomer, or can be a copolymer of one or more than one fluorinated monomer and one or more than one functional monomer, fluorinated or hydrogenated.

Preferably, the polymer (F) comprises recurring units derived from at least one fluorinated functional monomer chosen among:

(M1) sulfonated perfluoroolefin of formula (M1)

wherein n is an integer between 0 and 6 and X’ is chosen among halogens (as Cl, F, Br, I) , -O ^-M ⁺, wherein M ⁺is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺, or mixtures thereof; preferably X’ =-O ^-H ⁺; preferred sulfonated perfluoroolefin are those complying with formulae (M1-A) and (M1-B) :

wherein X’ has the same meaning as above defined;

(M2) sulfonated perfluorovinylethers of formula (M2) :

wherein m is an integer between 1 and 10 and X’ is chosen among halogens (as Cl, F, Br, I) , -O ^-M ⁺, wherein M ⁺is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺, or mixtures thereof; preferably X’ =-O ^-H ⁺; preferred sulfonated perfluorovinylethers are those complying with formulae (M2-A) , (M2-B) and (M2-C) :

wherein X’ has the same meaning as above defined; most preferably, the sulfonated perfluorovinylether is perfuoro-5-sulphonylfluoride-3-oxa-1-pentene (also known as “SFVE” ) of formula (M2-D) :

which can be in its–SO ₂F form or, preferably, in any of the–SO ₂X’ forms, as above detailed, more preferably in its–SO ₃H form.

(M3) sulfonated perfluoroalkoxyvinylethers of formula (M3) :

wherein w is an integer between 0 and 2, RF ₁ and RF ₂, equal or different from each other and at each occurrence, are independently–F, -Cl or a C _1-10 perfluoroalkyl group, optionally substituted with one or more ether oxygens, y is an integer between 0 and 6 and X’ is chosen among H, halogens (as Cl, F, Br, I) , -O ^-M ⁺, wherein M ⁺is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺, or mixtures thereof; preferably X’ is-O ^-H ⁺; preferred sulfonated perfluoroalkoxyvinylether complies with formula (M3) here above, wherein w is 1, RF ₁ is–CF ₃, y is 1 and RF ₂ is–F and X’ is F [formula (M3-A) , also called “PSEPVE” (perfluoro-2- (2-fluorosulfonylethoxy) propylvinyl ether) ] :

(M4) perfluoroalkoxyvinylether carboxylates of formula (M4) :

wherein w, y, RF ₁ and RF ₂ have the same meaning as above defined, and R _H§ is a C _1-10 alkyl or fluoroalkyl group; preferred perfluoroalkoxyvinylether carboxylate complies with formula (M4) here above, wherein w is 0, y is 2, R _H§ is methyl and RF ₂ is–F [formula (M4-A) ] :

(M5) sulfonated aromatic (per) fluoroolefins of formula (M5) :

wherein Ar is a C _3-15aromatic or heteroaromatic moiety and X’ is chosen among halogens (as Cl, F, Br, I) , -O ^-M ⁺, wherein M ⁺is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺, or mixtures thereof; preferably X’ =-O ^-H ⁺; and

(M6) mixtures thereof.

Optionally, in addition to recurring units derived from fluorinated monomer (s) and functional monomer (s) , the polymer (F) can further comprise recurring units derived from at least one bis-olefin chosen among those of formulae:

(OF-1)

wherein j is an integer between 2 and 10, preferably between 4 and 8, and R1, R2, R3, R4, equal or different from each other, are H, F or C _1-5 alkyl or (per) fluoroalkyl group;

(OF-2)

wherein each of A, equal or different from each other and at each occurrence, is independently selected from F, Cl, and H; each of B, equal or different from each other and at each occurrence, is independently selected from F, Cl, H and OR _B, wherein R _B is a branched or straight chain alkyl radical which can be partially, substantially or completely fluorinated or chlorinated; E is a divalent group having 2 to 10 carbon atoms, optionally fluorinated, which may be inserted with ether linkages; preferably E is a– (CF ₂) _m-group, with m being an integer from 3 to 5; a preferred bis-olefin of (OF-2) formula is F ₂C=CF-O- (CF ₂) ₅-O-CF=CF ₂.

(OF-3)

wherein E, A and B have the same meaning as above defined; R5, R6, R7, equal or different from each other, are H, F or C _1-5 alkyl or (per) fluoroalkyl group.

Should the polymer (F) comprise recurring units derived from a bis-olefin as above defined, it advantageously comprises said recurring units in an amount in the range from 0.01 to 5%by moles, with respect to all recurring units of polymer (F) .

Preferably, the polymer (F) is free from recurring units derived from bis-olefins as above specified.

The polymer (F) is preferably a per (halo) fluoroionomer.

For the purpose of the invention, the term “per (halo) fluoroionomer” is usually intended to denote a polymer (F) substantially free of hydrogen atoms.

The term “substantially free of hydrogen atom” is generally understood to mean that the per (halo) fluoroionomer consists essentially of:

- recurring units derived from one or more than one ethylenically unsaturated monomer comprising at least one fluorine atom and free from hydrogen atoms (per (halo) fluoromonomer, hereinafter) ; and

- recurring units derived from one or more than one ethylenically unsaturated monomer comprising at least one fluorine atom and at least one ion exchange group, and free from hydrogen atoms (except those optionally comprised in the ion exchange group) (functional per (halo) fluoromonomer, hereinafter) .

The per (halo) fluoromonomer and the functional per (halo) fluoromonomer may be the same monomer or may be different monomers, that is to say that the per (halo) fluoroionomer can be a homopolymer of a functional per (halo) fluoromonomer, or can be a copolymer of one or more than one per (halo) fluoromonomer and one or more than one functional per (halo) fluoromonomer.

The expression “consisting essentially of” when used in connection with the composition of the polymer (F) should be interpreted to mean that the polymer (F) consists of the indicated monomeric units with the sole addition of the chain-end groups which may derive from the initiator and possibly chain transfer agent used in the polymerization reaction, as known in the art.

Preferably polymer (F) is chosen among per (halo) fluoroionomer comprising (preferably consisting essentially of) recurring units derived from at least one functional per (halo) fluoromonomer and at least one per(halo) fluoromonomer chosen among:

- C ₃-C ₈ perfluoroolefins, preferably tetrafluoroethylene (TFE) and/or hexafluoropropylene (HFP) ;

- chloro-and/or bromo-and/or iodo-C ₂-C ₆ per (halo) fluoroolefins, like chlorotrifluoroethylene (CTFE) and/or bromotrifluoroethylene;

- perfluoroalkylvinylethers (PAVE) complying with formula CF ₂=CFOR _f1 in which R _f1 is a C ₁-C ₆ perfluoroalkyl, e.g. -CF ₃, -C ₂F ₅, -C ₃F ₇;

- perfluoro-oxyalkylvinylethers complying with formula CF ₂=CFOX ₀, in which X ₀ is a C ₁-C ₁₂ perfluorooxyalkyl having one or more ether groups, like perfluoro-2-propoxy-propyl.

Still preferably polymer (F) is chosen among tetrafluoroethylene (TFE) copolymers comprising (preferably consisting essentially of) recurring units derived from at least one functional per (halo) fluoromonomer as defined above.

More preferably polymer (F) is chosen among tetrafluoroethylene (TFE) copolymers comprising (preferably consisting essentially of) recurring units derived from at least one functional per (halo) fluoromonomer M1 to M6 as above defined.

Preferred functional per (halo) fluoromonomers are notably sulfonated perfluorovinylethers of formula (M2) as above detailed and sulfonated perfluoroalkoxyvinylethers of formula (M3) as above detailed, and mixtures thereof.

Even more preferably polymer (F) is selected among TFE copolymers comprising (preferably consisting essentially of) recurring units derived from PSEPVE (formula M3-A here above) and/or SFVE (formula M2-D here above) , in their–SO ₂F or–SO ₂X” form, wherein X” is chosen among halogens (as Cl, Br, I) , -O ^-M ⁺, wherein M ⁺is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺, or mixtures thereof.

Still more preferably polymer (F) is selected among TFE copolymers comprising (preferably consisting essentially of) :

- from 5 to 30%by moles of recurring units derived from PSEPVE and/or SFVE, in their–SO ₂F or–SO ₂X” form, wherein X” is chosen among halogens (as Cl, Br, I) , -O ^-M ⁺, wherein M ⁺is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺, or mixtures thereof; and

- from 95 to 70%by moles of recurring units derived from TFE.

According to a preferred embodiment of the invention, the polymer (F) is chosen among TFE copolymers as above described wherein the functional monomer is SFVE, in its–SO ₂F or–SO ₂X” form, wherein X” is chosen among halogens (as Cl, Br, I) , -O ^-M ⁺, wherein M is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺, or mixtures thereof.

Examples of commercial PEM made from the polymer (F) include: Solvay

PFSA polymers, such as those having the trade designations “

E98-09S” , “

E98-15S” and “

E87-12S” .

For the purpose of the present invention, the PEM can be a

membrane. Examples of suitable commercial

membranes include:

212,

115,

117 and

1110.

The anode catalyst can comprise at least one metal element in elemental form and/or at least one metal oxide.

In some embodiments, the anode catalyst comprises at least one metal in elemental form, at least two metals in elemental form or three metals in elemental form.

In a particular embodiment, the anode catalyst comprises a metal alloy.

A metal alloy can be viewed as a solid metal-solid metal mixture wherein a primary metal acts as solvent while other metal (s) act (s) as solute; in a metal alloy the concentration of the metal solute does not exceed the limit of solubility of the metal solvent.

In some embodiments, the anode catalyst comprises at least one metal in elemental form and its corresponding metal oxide, at least two metals in elemental form and their corresponding metal oxides, or at least three metals in elemental form and their corresponding metal oxides.

Advantageously, the anode catalyst comprises at least one metal oxide, at least two metal oxides, or at least three metal oxides.

Preferably, said metal is a transition metal or an alkali metal.

As used herein, metals of group IB, IIB, IIIB, IVB, VB, VIB, VIIB and VIIIB are often referred to as transition metals. This group comprises the elements with atomic number 21 to 30 (Sc to Zn) , 39 to 48 (Y to Cd) , 72 to 80 (Hf to Hg) and 104 to 112 (Rfto Cn) .

As used herein, the term "alkali metal" refers to any of the six chemical elements that make up Group 1 (Ia) of the periodic table, namely, lithium (Li) , sodium (Na) , potassium (K) , rubidium (Rb) , cesium (Cs) , and francium (Fr) .

More preferably, said metal is selected from the group consisting of iron (Fe) , nickel (Ni) , cobalt (Co) , copper (Cu) , chromium (Cr) , platinum (Pt) , palladium (Pd) , rhodium (Rh) , ruthenium (Ru) , iridium (Ir) , silver (Ag) , gold (Au) , rhenium (Re) , cesium (Cs) , tungsten (W) and vanadium (V) , particularly selected from the group consisting of Fe, Ni, Co, Ir, Ru, Cs, W and V and preferably Ir or Ru.

In some embodiments, the anode catalyst comprises one doped metal oxide. The dopant can be a metal or non-metal element, preferably a metal element.

In a preferred embodiment, the anode catalyst comprises iridium oxide (IrO _x) . The iridium oxide (IrO _x) can comprise here predominantly iridium (IV) -oxide (IrO ₂) , however, depending on the manufacturing process, various amounts of iridium (III) -oxide (Ir ₂O ₃) may be present.

In another preferred embodiment, the anode catalyst comprises ruthenium oxide (RuO _X) . The ruthenium oxide may be present as ruthenium (IV) -oxide (RuO ₂) , but ruthenium (III) -oxide (Ru ₂O ₃) may also be present in minor amounts.

In a third preferred embodiment, the anode catalyst comprises iridium oxide (IrO _x) and ruthenium oxide (RuO _X) as identified above. The atomic ratio of Ir/Ru can be in the range of 4: 1 to 1: 4.

In a fourth preferred embodiment, the anode catalyst comprises cesium doped tungsten oxide (Cs _0.33WO ₃) .

In a fifth preferred embodiment, the anode catalyst comprises tungsten doped vanadium (IV) oxide (W-VO ₂) .

The person skilled in the art will select the proper BET surface area of the metal or metal oxide by considering the desired catalytic capacity. For example, the BET surface area of IrO _x can be from 10 to 100 m ²/g and preferably from 20 to 40 m ²/g.

In the continuation of the description, the term “BET surface area” is understood to mean the BET specific surface area determined by nitrogen adsorption in accordance with standard ASTM D 3663-78 laid down from the Brunauer-Emmett-Teller method described in the periodical “The Journal of the American Chemical Society, 60, 309 (1938) ” .

The person skilled in the art will select the proper particle size of the metal or metal oxide by considering the desired catalytic capacity. For example, the average diameter of IrO _x can be from 1 nm to 100 nm, which is measured using transmission electron microscopy (TEM) . In a particular embodiment, the average diameter of IrO _x can be from 20 nm to 30 nm.

Some known measure methods can be used for determining the particle size. For example, the person skilled in the art can prepare such a TEM image and determine the particle size based on the magnification. Specifically, a JEOL 2100 with Filament LaB6 having an acceleration voltage of 200 kV equipped with a camera Gatan 832 CCD was used. As support, square 230 mesh TEM support grids (copper) were used. The magnification factor had a range of '10,000～' 600,000. For 50 nm: magnification factor was 40,000～50,000; for 20 nm: 60,000～120,000; for 10 nm: 250,000; for 5 nm: 400,000; for 2 nm: 500,000～600,000. Samples of nanoparticles in a suspension were measured. The obtained results were analyzed using the DigitalMicrograph software. For each sample, two pictures were taken and a total of 100 nanoparticles were analyzed for obtaining the described size distribution. From this size distribution, the average particle size of the nanoparticles was obtained. The software used to measure the size of the nanoparticles was ImageJ thereby approximating the particles to be spherical. After setting the scale, the maximum diameter of the particles was manually measured one by one to a total number of particles measured of 100. Every particle has been measured 3 times to obtain an average size.

The metal loading on the PEM surface exposed to the anode can be from 0.1 mg/cm ²to 15 mg/cm ², preferably from 0.5 mg/cm ² to 10 mg/cm ² and more preferably from 1.0 mg/cm ²to 5.0 mg/cm ². The metal loading can be equal for example to 1.5 mg/cm ², 1.6 mg/cm ², 1.7 mg/cm ², 1.8 mg/cm ², 1.9 mg/cm ², 2.0 mg/cm ², 2.1 mg/cm ², 2.2 mg/cm ², 2.3 mg/cm ², 2.4 mg/cm ², 2.5 mg/cm ², or any range between these values.

The proton conductive material is not particularly limited and can preferably be a proton conductive polymer in any form.

In some embodiments, the proton conductive polymer can be a

polymer.

In some embodiments, the proton conductive polymer can be the polymer (F) above defined.

Examples of commercial proton conductive materials include “

D98-25BS” and “

D79-20BS” .

The electron conductive material can be any form of carbon, such as for example carbon nanotube, graphite, or carbon powder. Such electron conductive material may further comprise an inorganic oxide, such as for example a metal oxide, a metalloid oxide and their mixtures thereof. Said metal oxide can be a lanthanide metal oxide, such as cerium oxide (ceria) . Said metal oxide can also be aluminium or titanium dioxide. Said metalloid oxide can specifically be silica. The anode catalyst which is electron conductive can be considered as an electron conductive material.

Advantageously, the layer coated to the surface of the PEM exposed to the anode is proton and electron conductive. The skilled person can decide whether to use the electron conductive material by considering the electron conductive capacity of ingredients in the coating layer. For example, when the anode catalyst having enough electron conductive capacity, such as iridium oxide (IrO _x) , is present, the additional electron conductive material may not be necessary.

The PEM can be coated by some known methods. For example, a solution comprising an anode catalyst, proton conductive polymer dispersions, and optionally an electron conductive material is prepared and then coated to the PEM.

The thickness of the layer coated to the surface of the PEM exposed to the anode can be from 10 μm to 100 μm, preferably from 20 μm to 60 μm and more preferably from 15 μm to 45 μm.

As previously mentioned, the proton exchange membrane (PEM) exposed to the cathode contacts a proton and electron conductive layer (PECL) .

In a first main embodiment, the PECL can be an electron conductive layer (ECL) made of an electron conductive material, which is treated by a proton conductive material and optionally a cathode catalyst.

When the cathode catalyst is present, the weight ratio of the cathode catalyst to the proton conductive material can be from 1: 20 to 1: 1 and preferably from 1: 10 to 1: 15.

The proton conductive polymer can be a

polymer.

The proton conductive polymer can be the polymer (F) above defined.

Examples of commercial proton conductive materials include “

D98-25BS” and “

D79-20BS” .

The electron conductive layer (ECL) can be a carbon or graphite felt, sintered metal or metal foam comprising Al, stainless steel, Ti, Cu, or Ni and preferably a carbon or graphite felt.

The method for treating the ECL by a proton conductive material is not particularly limited and generally depends on the morphology of the ECL. For example, the carbon felt can be coated based on the publication of Ross in 2012 (A.E. Ross, B.J. Venton, "Nafion-CNT coated carbon-fiber microelectrodes for enhanced detection of adenosine" , Analyst (2012) , 137, pp. 3045-3051; (doi: https: //dx. doi. org/10.1039/c2an35297d) ) .

Advantageously, the ECL, particularly those having porous morphology, can be coated with a proton conductive polymer before contacting PEM. By this treatment, at least the surfaces of the ECL are preferably coated with the proton conductive polymer.

For example, the electron conductive layer (ECL) can be coated with the polymer (F) by a process having the following steps:

i. cleaning and drying an electron conductive layer (ECL) to obtain an electron conductive layer (ECL*) ;

ii. immersing the electron conductive layer (ECL*) to a solution comprising a polymer (F) to prepare a proton and electron conductive layer (PECL*) , at least the surfaces of which are coated with the polymer (F) ;

iii. drying the proton and electron conductive layer (PECL*) to obtain a proton and electron conductive layer (PECL**) ;

iv. optionally repeating at least once the steps ii and iii by treating the proton and electron conductive layer (PECL**) to obtain a proton and electron conductive layer (PECL**) -x; and

v. annealing the proton and electron conductive layer (PECL**) or the proton and electron conductive layer (PECL**) -x to obtain a proton and electron conductive layer (PECL) .

In step i, the electron conductive layer (ECL) can be rinsed with water first and then cleaned by deionized (DI) water. Preferably, an ultrasonic cleaning system can be used when the conductive layer is cleaned by DI water.

In step i, the electron conductive layer (ECL) can be dried, generally in air, at a temperature from 50 to 100℃ and preferably from 60 to 80℃, usually for 3 to 24 hours and preferably from 6 to 12 hours.

In step ii, the polymer (F) is preferably dispersed in the solution. Commercial products such as “

D98-25BS” and “

D79-20BS” can be used for preparing said solution.

The solvent in the solution is not particularly limited, as long as the polymer (F) has good dispersion in the solution. The solvent can preferably be a mixture of water and alcohol. Said alcohol can be methanol, ethanol, 1-propanol, 2-propanol, 2-butanol and tert-butyl alcohol, and so on. Among them, methanol and ethanol are preferable. The skilled person will determine the volume ratio of water to the alcohol based on the wettability of the conductive layer. The volume ratio of water to the alcohol can be from 0.1: 1 to 1: 0.1, preferably from 0.2: 1 to 1: 1, more preferably from 0.3: 1 to 0.5: 1.

Advantageously, the concentration of the polymer (F) in the solution is from 1 to 10%, preferably from 2 to 8%, and more preferably from 3 to 6%. The%are referred to polymer concentration in grams per 100 ml of solvent.

In step ii, the electron conductive layer (ECL*) is completely immersed into the solution to ensure the surfaces are coated with the polymer (F) . The staying time depends on the surface area of the conductive layer. In some embodiments, the staying time can be from 2 to 60 minutes, preferably from 5 to 40 minutes, more preferably from 10 to 30 minutes.

When the electron conductive layer (ECL) has a porous morphology, such as a carbon felt, at least part of the polymer (F) may be infused into the pores of the carbon felt.

In step iii, the proton and electron conductive layer obtained at step ii can be dried in air at room temperature (e.g. 20-25℃) for 3 to 24 hours and preferably from 6 to 12 hours.

For sake of clarity, the “x” in (PECL**) -x is used to indicate that different proton and electron conductive layers are obtained each time steps ii and iii are repeated.

The repeat times of step iv depend on the desired mass of the polymer (F) on the electron conductive layer (ECL) . Preferably, the weight ratio of the polymer (F) to the electron conductive layer (ECL) is from 0.01: 1 to 2: 1 and specifically from 0.4: 1 to 1: 1.

In step v, the annealing may preferably be carried out in the presence of air. The annealing temperature may be from 150 to 250℃, preferably from 160 to 220℃ and more preferably from 180 to 200℃.

A cathode catalyst can be dispersed in the solution comprising a polymer (F) in step ii so that it can be coated to the ECL.

Optionally, additional conductive materials are dispersed in the solution comprising a polymer (F) in step ii so that it can be coated to the ECL.

The thickness of the electron conductive layer (ECL) can be from 0.1 mm to 6 mm and preferably from 1 mm to 3 mm.

In a second main embodiment, the PECL can be a proton and electron conductive coating layer to the surface of the proton exchange membrane (PEM) exposed to the cathode. Said coating layer comprises a proton conductive material, optionally a cathode catalyst, and optionally an electron conductive material. In this embodiment, the thickness of the coating layer can be from 10 μm to 100 μm, preferably from 20 μm to 60 μm and more preferably from 15 μm to 45 μm.

The proton conductive material and the electron conductive material have the same meanings as defined for the materials at anode side. Specifically, the cathode catalyst which is electron conductive can be considered as an electron conductive material.

The skilled person will decide whether to use the electron conductive material by considering the electron conductive capacity of other ingredients in the coating layer. For example, when a cathode catalyst having enough electron conductive capacity, such as Pd or Pt is present, the additional electron conductive material may not be necessary. For another example, when other ingredients in the coating layer are all not electron conductive, then the electron conductive material must preferably be used.

When the cathode catalyst or the electron conductive material is present, the weight ratio of the cathode catalyst or the electron conductive material to the proton conductive material can be from 1: 20 to 1: 1 and preferably from 1: 10 to 1: 15.

In a third main embodiment, the PECL comprises both treated electron conductive layer (ECL) of the first main embodiment and coating layer of the second main embodiment. The catalyst can be in both layers or in any one of the layers.

In some variants, the cathode does not comprise a cathode catalyst.

Alternatively, in some other variants, the cathode comprises a cathode catalyst.

The cathode catalyst can comprise at least one metal element in elemental form and/or at least one metal oxide.

Advantageously, the cathode catalyst may comprise at least one metal in elemental form, or at least two metals in elemental form or three metals in elemental form.

The cathode catalyst can comprise a metal alloy.

The cathode catalyst may comprise at least one metal in elemental form and its corresponding metal oxide, or at least two metals in elemental form and their corresponding metal oxides, or at least three metals in elemental form and their corresponding metal oxides.

Advantageously, the metal is a noble metal.

As used herein, the expression "noble metal" refers to metals that are normally valuable and resistant to corrosion and oxidation in moist air.

The metal can preferably be selected from a group consisting of iron (Fe) , cobalt (Co) , nickel (Ni) ruthenium (Ru) , rhodium (Rh) , palladium (Pd) , silver (Ag) , osmium (Os) , iridium (Ir) , platinum (Pt) , copper (Cu) and gold (Au) . Pt and Pd are preferred among these metals.

Preferably, the metal is supported on a support. The support to the metal catalyst is not particularly limited. It can notably be a metal oxide, a zeolite or Kieselguhr, clay or, preferably, carbon.

According to the first main embodiment above mentioned, a cathode catalyst may be coated to the ECL. The weight ratio of the metal can be from 1.0 wt. %to 15.0 wt. %, preferably from 2.0 wt. %to 8.0 wt. %, and more preferably from 2.0 wt. %to 6.0 wt. %, based on the total weight of the treated ECL.

According to the second main embodiment above mentioned, a cathode catalyst may be coated to the PEM surface. The metal loading can be from 0.1 mg/cm ²to 15 mg/cm ², preferably from 0.5 mg/cm ² to 10 mg/cm ² and more preferably from 1.0 mg/cm ²to 5.0 mg/cm ². The metal loading can be equal for example to 1.5 mg/cm ², 1.6 mg/cm ², 1.7 mg/cm ², 1.8 mg/cm ², 1.9 mg/cm ², 2.0 mg/cm ², 2.1 mg/cm ², 2.2 mg/cm ², 2.3 mg/cm ², 2.4 mg/cm ², 2.5 mg/cm ², or any range between these values.

In any one of steps a) to c) , the temperature of the anode chamber can be from room temperature (e.g. 20-25℃) to 40℃.

In any one of steps a) to c) , the temperature of the cathode chamber generally depends on the solvent of working solution (WS) .

The temperature of the cathode chamber can be of at least 10℃, in particular of at least 20℃, for example of at least 30℃, or even of at least 40℃.

Additionally or alternatively, temperature of the cathode chamber can be of no more than 200℃, in particular of no more than 180℃, for example of no more than 120℃, or even of no more than 100℃.

In a particular embodiment, temperature of the cathode chamber is from room temperature (e.g. 20-25℃) to 80℃. In step b) , the solution comprising 2-alkylanthraquinone is particularly a working solution (WS) dissolved with 2-alkylanthraquinone. Advantageously, 2-alkylanthraquinone can be converted to 2-alkylanthracene-9, 10-diol in the WS directly, which provides a simple process for preparing 2-alkylanthracene-9, 10-diol and H ₂O ₂.

On an industrial scale, hydrogen peroxide is mainly produced by an anthraquinone process. In this process, anthraquinones dissolved in an appropriate organic solvent are used as a reaction media. The organic solvent is usually a mixture of several organic solvents. Typical organic solvents are methyl cyclohexyl acetate (Sextate) , trioctylphosphate (TOP) , tetrabutylurea (TBU) , carbonyldiamide (Urea) , diisobutyl carbinol (DIBC) , Caromax 20, and so on. The solution obtained by dissolving the anthraquinones in the organic solvent is called “a working solution” .

The concentration of the 2-alkylanthraquinone in the solution mainly depends on its solubility in the specific organic solvent. For example, the organic solvent can be diisobutyl carbinol (DIBC) and/or Caromax 20. In this case, the concentration of the 2-alkylanthraquinone in the solution can be from 0.1 wt. %to 50.0 wt. %, preferably 1.0 wt. %to 30.0 wt. %, more preferably from 2.0 wt. %to 25.0 wt. %.

Very advantageously, the solution in the cathode chamber of step b) can be completely free or substantially free from an electrolyte.

The term “electrolyte” is understood here in its normal accepted meaning, i.e. it means any ionic or molecular substance which, when in solution, decomposes or dissociates to form ions or charged particles, or any ionic liquid.

As used herein, the expression “ionic liquid” means a compound completely composed of ions. Ionic liquids are salts that have low melting points, such as below 100℃, normally at room temperature. Said ionic liquid can be those discribed in ionic liquids as electrolytes, Electrochimica Acta, Volume 51, Issue 26, 2006, Pages 5567-5580.

The electrolyte can be an inorganic or organic electrolyte.

As electrolyte, mention may be made of a compound comprising an organic or inorganic anion which is selected from the group consisting of SO ₄ ^2-, PO ₄ ^2-, HPO ₄ ^-, OH ^-, Br ^-, I ^-, Cl ^-, TFSI, CO ₃ ^2-, ClO ₄ ^-, NO ₃ ^-, BF ₄ ^-, PF ₆ ^-, [CF ₃SO ₃] ^-, [CF ₃CO ₂] ^-, [N (CF ₃SO ₂) ₂] ^-, [CF ₃CONCF ₃SO ₂] ^-, [C (CF ₃SO ₂) ₃] ^-, anions based on cyano groups, such as ( [Ag (CN) ₂] ^-, [C (CN) ₃] ^-and [N (CN) ₂] ^-) , perfluoroalkyl sulfonates, such as [C ₄F ₉SO ₃] ^-, and haloaluminates.

As electrolyte, mention may be made of a compound comprising an organic or inorganic cation which is selected from the group consisting of H ⁺, alkali metal cations, such as K ⁺, Na ⁺and Li ⁺, alkaline-earth metal cations, such as Mg ²⁺, Ca ²⁺, transition metal cations, such as Cu ²⁺, Cu ⁺, Ag ⁺, Fe ²⁺, and Fe ³⁺, mono-, di-, tri-and tetraalkylammoniums, mono-, di-, and trialkylsulfoniums, mono-, di-, tri-and tetraalkylphosphoniums, dialkylimidazolium, dialkylpyrrolidinium, dialkylpiperidinium and alkylpyridinium.

As used herein, the expression "completely free of an electrolyte" when used with reference to the solution means that the solution comprises no electrolyte at all.

As used herein, the expression "substantially free of an electrolyte" when used with reference to the solution means that the solution comprises no more than 0.5 wt. %, preferably no more than 0.2 wt. %of electrolyte, for example no more than 0.2 wt. %of electrolyte, based on the total weight of the solution.

In step c) , the current density can be of at least 1 mA/cm ², in particular of at least 20 mA/cm ², for example of at least 50 mA/cm ², or even of at least 100 mA/cm ².

Additionally or alternatively, the current density can be of no more than 300 mA/cm ², in particular of no more than 250 mA/cm ², for example of no more than 200 mA/cm ², or even of no more than 100 mA/cm ².

In a particular embodiment, the current density can be from 1 to 80 mA/cm ², preferably from 2 to10 mA/cm ², and more preferably from 3 to 8 mA/cm ².

The electrochemical reactions of the method according to the present invention may be carried out either in batch, semi-batch or, preferably, in continuous mode.

When the reactions are carried out in continuous mode, the contact time of the reaction feed with the anode or the cathode catalyst can be varied over a wide range. Thus the method according to the present invention can be carried out, generally under ambient pressure, by keeping the reaction feed in contact with the catalyst for 5 to 500 seconds, mainly depending on the production scale.

In a particular embodiment, the contact time of the reaction feed with the anode or the cathode catalyst can be from 10 to 450 seconds, preferably from 15 to 400 seconds.

In a preferred embodiment, the electrochemical cell comprises:

A. an anode chamber containing an anode comprising at least an electron collector plate and an electron conductive layer (ECL’) , one side of the electron collector plate is in contact with one side of the ECL’;

B. a cathode chamber containing a cathode comprising at least an electron collector plate and an electron conductive layer (ECL”) , one side of the electron collector plate is in contact with one side of the ECL”; and

C. a proton exchange membrane (PEM) , contacting another side of the ECL’ and another side of the ECL”;

wherein:

- the surface of the proton exchange membrane (PEM) contacting the ECL’ is coated with a layer comprising an anode catalyst, a proton conductive material, and, optionally, an electron conductive material,

- the surface of the proton exchange membrane (PEM) contacting the ECL” is coated with a layer comprising a proton conductive material, optionally a cathode catalyst, and, optionally, an electron conductive material and/or the ECL” is coated with a proton conductive material, and, optionally, a cathode catalyst.

The ECL’ or ECL” can be a carbon or graphite felt, sintered metal or metal foam comprising Al, stainless steel, Ti, Cu, or Ni. Preferably the ECL’ or ECL” is a carbon or graphite felt.

Preferably, there is no gap between the PEM and the ECL’ and no gap between the ECL’ and the electron collector plate.

Preferably, there is no gap between the PEM and the ECL” and no gap between the ECL” and the electron collector plate.

In a preferred embodiment, another side of the electron collector plate of the anode contacts a metal block. In this embodiment, both electron collector plate and metal block have DI water inlet holes and water/O ₂ outlet holes and are closed tightly. The inlet holes are well aligned and outlet holes are well aligned so that DI water can continuously flow in the electron collector plate through the inlet hole in the metal block and water/O ₂ can continuously flow out the electron collector plate through the outlet hole in the metal block. Preferably, the electron collector plate is designed with flow patterns. The flow patterns face the ECL’.

Similarly, another side of the electron collector plate of the cathode contacts a metal block. In this embodiment, both electron collector plate and metal block have working solution (WS) inlet holes and working solution (WS) outlet holes and are closed tightly. The inlet holes are well aligned and outlet holes are well aligned so that working solution (WS) before hydrogenation can continuously flow in the electron collector plate through the inlet hole in the metal block and working solution (WS) after hydrogenation can continuously flow out the electron collector plate through the outlet hole in the metal block. Preferably, the electron collector plate is designed with flow patterns. The flow patterns face the ECL”.

Optionally, a sealing plate is placed between the electron collector plate at anode or cathode side and the metal block.

Optionally, a heating block contacts the metal block at anode or cathode side, preferably to obtain a desired temperature required for the anode chamber and/or the cathode chamber.

The following examples are included to illustrate embodiments of the invention. The disclosure is not limited to such examples.

EXAMPLES

Materials

- 2-Amylanthraquinone, CAS No. 32588-54-8, from Solvay SA

- Caromax, EC No. 919-284-0, from Solvay SA

- 2, 6-Dimethyl-4-heptanol, DIBC, CAS No. 08-82-7, from Biosolve

- Carbon felt, from Q-Carbon Material Co., Ltd

- Iridium oxide nanopowder, CAS No. 12030-49-8, from SAT nano technology material Co,. Ltd

- Carbon black, CAS No. 1333-86-4, from SAT nano technology material Co,. Ltd

- 20%Pd on Vulcan (No. P30A200) , from Premetec Co

- Carbon nanotubes, CAS No. 1333-86-4, from SAT nano technology material Co,. Ltd

- Methanol, CAS No. 67-56-1, from Sinopharm

-

D79-20BS, from Solvay SA

-

E98-09S, from Solvay SA

Example 1

Treatment of a carbon felt

In order to remove leftover dust and particles, a carbon felt was first rinsed with water and then cleaned in an ultrasonic bath in DI water for three times. Before coating the felt was dried in an oven at 70℃ overnight.

For the coating, 20 ml of 5%Aquivion D79-20BS in a mixed solvent of water and methanol (volume ratio 1: 3) was prepared (5 ml of the 20%dispersion is mixed with 15 ml methanol) .

The solution was placed in a petri-dish and the carbon felt inserted for 10 minutes.

The felt was hung for air drying before it was annealed at 190℃ for 30 minutes in air.

Assembly of electrolyzer

The PEM electrolyzer was obtained by modification of a commercial electrolyzer (Model PEM-150, from Junjikeji) and composed of:

● 1-Heating block;

● 2-Al block with water inlet and water/O ₂ outlet;

● 3-PTFE sealing with water inlet and water/O ₂ outlet;

● 4-Electron collector with water inlet and water/O ₂ outlet;

● 5-PTFE frame with an ECL;

● 6-MEA;

● 7-PTFE frame with an ECL or an ECL treated by a proton conductive material;

● 8-Electron collector with working solution inlet and outlet;

● 9-PTFE sealing with working solution inlet and outlet;

● 10-Al block with working solution inlet and outlet;

● 11-Heating block.

The electrolyer was assembled as shown in Fig. 1. The anode chamber was assembled by placing 1-heating block (80 mm thick) , 2-Al block (120 mm thick) , 3-PTFE sealing (1.5 mm thick) , 4-electron collector (Ti plate with flow pattern: 5 cm x 5 cm=25 cm ², 1.5 mm thick) , and 5-PTFE frame with an ECL (sintered Ti plate: 6 cm x 6 cm=36 cm ², 1 mm thick) in sequence. The cathode chamber was assembled by placing 11-heating block (80 mm thick) , 10-Al block (120 mm thick) , 9-PTFE sealing (1.5 mm thick) , 8-electron collector (Ti plate with flow pattern: 5 cm x 5 cm=25 cm ², 1.5 mm thick) , and 7-PTFE frame with an ECL or an ECL treated by a proton conductive material (sintered Ti plate or Aquivion coated carbon felt: 6 cm x 6 cm=36 cm ², 1-6 mm thick) in sequence. 6-MEA was placed between 5 and 7.

The combination of conductive parts at anode side, such as 4-electron collector and 5-PTFE frame with an ECL and the coating layer on the PEM are considered as the anode.

The combination of conductive parts at cathode side, such as 7-PTFE frame with an ECL or an ECL treated by a proton conductive material, 8-electron collector and the coating layer on the PEM (if any) are considered as the cathode.

The electrolyzer was closed tightly by four screws through the screw holes 1a-11a, 1b-11b, 1c-11c and 1d-11d to ensure no gap between the two electrodes and 6-MEA.

6-MEA was an Aquivion membrane (E98-09S) coated with an anode catalyst layer 6e.

Heating tapes

1e and 11e were attached to Al blocks to form heating blocks 1 and 11. The two heating tapes were heated by the electricity connected and transferred the heat to the Al blocks.

DI water inlet 2f and inlet holes 3f-4fwere strictly aligned to form a channel so that the water can flow in the anode chamber through the only channel.

Water/O ₂ outlet 2e and outlet holes 3e-4e were strictly aligned to form a channel so that the water/O ₂ can flow out the anode chamber through the only channel.

Similarly, working solution (WS) inlet 10f and inlet holes 8f-9fwere strictly aligned to form a channel so that working solution can flow in the cathode chamber through the only channel.

Working solution (WS) outlet 10e and outlet holes 8e-9e were strictly aligned to form a channel so that WS can flow out the cathode chamber through the only channel.

Flow pattern4h faced the sintered Ti plate 5e. Similarly, flow pattern 8h faced the conductive layer 7e.

An electric current was passed between the anode and the cathode through

connectors

4g and 8g.

The electrolyzer was assembled using a 90μm thick Aquivion membrane with 0.55 mg/cm ² of iridium oxide coating on the water splitting (anode) side. The cathode side was equipped with a 1 mm thick Aquivion coated carbon felt.

After installing the electrolyzer, both sides were checked for leakage using water flow.

As shown by Fig. 13, the anode chamber was connected to an anode reservoir having a DI water outlet, an O ₂ outlet and a water/O ₂ inlet. The cathode chamber was connected to a cathode reservoir.

The cathode reservoir consisted of a three neck round flask. The vacuum bubbler was applied to the middle opening of the flask and connected to the Schlenk line which could provide Ar supply or vacuum. The inlet and outlet tubings entered the reservoir through one of the openings of the flask and were sealed with parafilm to inhibit air exposure. The outlet tubing was connected to the pump and from the pump to the electrolyzer inlet. The outlet of the electrolyzer was connected with the inlet tubing of the reservoir. In the third opening the in-situ IR probe was inserted to follow the reaction composition by an in-situ IR. The whole cathode reservoir was sealed to prevent air intake. The vacuum bubbler allowed possible formed H ₂ to escape the reservoir.

Before the reservoir was filled with the chemicals, the atmosphere was replaced with Ar using the Schlenk technique (the so-called Schlenk technique was replacing the atmosphere of a closed system by applying shortly vacuum followed by inert gas flow until the normal pressure was reached (vacuum bubbler showed bubbles) ; this process was repeated at least two times) . While filling in the organic compounds, continuous Ar flow was applied to prevent air intake. When everything was in the reservoir, it was closed and the atmosphere exchanged using the Schlenck technique.

Then the cathode chamber was heated to 55℃ and the anode chamber to 30℃. Both reservoirs were not heated.

The anode reservoir was filled with 100 ml DI water.

The cathode chamber was filled with about 80 ml of a solution of 5.4 wt. %2-amylanthraquinone (AQ) in 19.8 wt. %Diisobutyl carbinol (DIBC) and 74.9 wt. %Caromax 20.

The in-situ IR sensor was placed into the reservoir of the cathode (WS) .

The cathode chamber was filled with Ar using the Schlenck technique in order to remove all air that was in the system.

The flow rates of the chambers were set to 10 ml/min for the cathode and 20 ml for the anode respectively.

Once the temperature in the electrolyzer remained stable a current of 100 mA (=4 mA/cm ²) was applied to the electrolyzer for 24 hours.

In order to monitor the reaction by IR, the decrease of the peak representing the C=O vibration of the reactant and the increase of the vibration of the C-OH bond of the product was observed.

After 24 hours no further reaction was observed. Iodometric redox titration of 2-amylanthracene-9, 10-diol (H ₂AQ) revealed a conversion of 68%±6%and a selectivity of 100%.

Example 2

Treatment of a carbon felt

In order to remove leftover dust and particles, a carbon felt was first rinsed with water and then cleaned in an ultrasonic bath in DI water for 3 times. Before coating the felt was dried in an oven at 70℃ overnight.

A narrow Schlenk flask was prepared and filled with Ar using the Schlenk technique. While under Ar flow, a mixture of 5.0744 g Aquivion Dispersion D79-20BS with 16.0350 g methanol is filled inside and stirred for 5 minutes under Ar. Ar flow was turned off and 0.2687g Pd/C was added to the solution.

The Schlenk flask was closed and stirred under Ar for an additional 20 minutes.

The carbon felt was placed in a Petri dish and covered with the solution using a pipette.

The weight of the carbon felt before coating was 1.0592g. After coating, the weight of the carbon felt is 2.0822g, including 0.7642 g Aquivion (39%) ; mass catalyst 0.2134 g Pd/C (10.2%) [mass active metal (Pd) 0.0243g (2.0%) ] , and carbon (8.2%) .

Hydrogenation of 10 wt. %AQ by electrochemistry with a Pd/C-Aquivion coated 3 mm thick carbon felt by using the same equipment as Example 1.

The electrolyzer was assembled using a 90 μm thick Aquivion membrane with 0.55 mg/cm ²of iridium oxide coating on the water splitting (anode) side. The cathode side was equipped with a 3 mm thick Pd/C-Aquivion coated carbon felt.

Then the cathode chamber was heated to 65℃ and the anode chamber to 30℃. In addition the cathode reservoir was heated to 65℃.

The anode reservoir was filled with 100 ml DI water.

The cathode chamber was filled with about 80 ml of a solution of 10 wt. %2-amylanthraquinone (AQ) in 24 wt. %Diisobutyl carbinol (DIBC) and 66 wt. %Caromax 20 (ratio of Caromax to DIBC=2.75) .

The flow rates of the chambers were set to 20 ml/min for the cathode and 20 ml for the anode respectively.

After 24 hours no further reaction was observed. Iodometric redox titration of 2-amylanthracene-9, 10-diol (H ₂AQ) revealed a conversion of 48%±5%.

In order to check the selectivity of the formed hydroanthraquinones, a sample was taken and oxygen bubbled through for 30 minutes. The so formed H ₂O ₂ was extracted with water and the amount of H ₂O ₂ determined by oxidative titration. The calculated conversion based on H ₂O ₂ gave the amount of useful anthraquinone. The titration result showed again a conversion of 48%±1%. It could be concluded that the selectivity was 100%.

Example 3

The electrolyzer was assembled using a 90 μm thick Aquivion membrane with 2 mg/cm ² of iridium oxide coating on the water splitting (anode) side and 0.2 mg/cm ²carbon nanotubes (CNT) coating on the cathode side. The cathode side was equipped with a 1 mm thick Aquivion coated carbon felt.

The cathode reservoir consisted of a three neck round flask, a vacuum bubbler with Ar inlet, and an inlet and outlet for the flow of the reaction solution. The vacuum bubbler was applied to the middle opening of the flask and connected to the Schlenk line which could provide Ar supply or vacuum. The inlet and outlet tubings entered the reservoir through one of the openings of the flask and were sealed with parafilm to inhibit air exposure. The outlet tubing was connected to the pump and from the pump to the electrolyzer inlet. The outlet of the electrolyzer was connected with the inlet tubing of the reservoir. In the third opening the in-situ IR probe was inserted to follow the reaction composition by an in-situ IR. The whole cathode reservoir was sealed to prevent air intake. The vacuum bubbler allowed possible formed H ₂ to escape the reservoir.

Before the reservoir was filled with the chemicals, the atmosphere was replaced with Ar using the Schlenk technique (as mentioned previously, the so-called Schlenk technique was replacing the atmosphere of a closed system by applying shortly vacuum followed by inert gas flow until the normal pressure was reached (vacuum bubbler showed bubbles) ; this process was repeated at least two times) . While filling in the organic compounds, continuous Ar flow was applied to prevent air intake. When everything was in the reservoir, it was closed and the atmosphere exchanged using the Schlenck technique.

Then the cathode chamber was heated to 65℃ and the anode chamber to 30℃. Both reservoirs were not heated. In addition the inlet and outlet tubing of the cathode side were heated to 70℃

The anode reservoir was filled with 100 ml DI water.

The cathode chamber was filled with about 80 ml of a solution of 25 wt. %2-amylanthraquinone (AQ) in 19.7 wt. %Diisobutyl carbinol (DIBC) and 54.1 wt. %Caromax 20.

The in-situ IR sensor was placed into the reservoir of the cathode (WS) .

Once the temperature in the electrolyzer remained stable a current of 400 mA (=16 mA/cm ²) was applied to the electrolyzer for 20 hours.

After 20 hours no further reaction was observed. Iodometric redox titration of 2-amylanthracene-9, 10-diol (H ₂AQ) revealed a conversion of 45%±5%and a selectivity of 100%.

Example 4

Electrochemical H ₂O ₂ formation by in-situ reaction with 2-amylanthracene-9, 10-diol (H ₂AQ)

The electrolyzer was assembled using a commercial membrane (A50μm thick Nafion membrane with of iridium oxide coating (in original commercial electrolyzer) on the water splitting (anode) side) and Pt coating on the cathode side. The cathode side was equipped with a 1 mm thick sintered Ti.

The anode reservoir was filled with 100 ml DI water.

The cathode chamber was filled with about 80 ml of a solution of 3.4 wt%AQ in 48.3%DIBC and 48.3%Caromax 20.

Once the temperature in the electrolyzer remained stable a current of 1000 mA (=40 mA/cm ²) was applied to the electrolyzer for 36 hours.

During the experiment about 1 ml water crossed over per h. There was no organic crossover observed. After experiment the concentration of 2-amylanthracene-9, 10-diol (H ₂AQ) in the organic phase was determined by iodometric redox titration and the H ₂O ₂ content in the separated water solution by semi-quantitative measurement using indicator stripes.

The water phase showed about400 mg/L H ₂O ₂ content. The organic phase contained0.2 g/L H ₂AQ.

Claims

A method for hydrogenating 2-alkylanthraquinone to 2-alkylanthracene-9, 10-diol, comprising the following steps:

a) providing an electrochemical cell having an anode chamber containing an anode, a cathode chamber containing a cathode, and a proton exchange membrane (PEM) between the anode and the cathode;

b) feeding deionized water to the anode chamber and a solution comprising 2-alkylanthraquinone to the cathode chamber;

c) passing an electric current between the anode and the cathode to hydrogenate 2-alkylanthraquinone to 2-alkylanthracene-9, 10-diol; wherein:

- the surface of the proton exchange membrane (PEM) exposed to the anode is coated with a layer comprising an anode catalyst, a proton conductive material and optionally an electron conductive material;

- the surface of the proton exchange membrane (PEM) exposed to the cathode contacts a proton and electron conductive layer (PECL) .
The method according to Claim 1, wherein there is no gap between the proton exchange membrane (PEM) and the cathode.
The method according to Claim 1 or 2, wherein the distance between the proton exchange membrane (PEM) and the cathode is less than 1 mm, preferably less than 0.5 mm, particularly less than 0.1 mm, more particularly less than 0.05mm, for instance less than 0.01 mm, even less than 0.005 mm or less than 0.001 mm.
The method according to any one of preceding claims, wherein the alkyl contains 1 to 20 carbon atoms, preferably 1 to 12 carbon atoms, particularly 1 to 10 carbon atoms, for instance 1 to 8 carbon atoms, or even 1 to 6 carbon atoms.
The method according to any one of preceding claims, the proton exchange membrane (PEM) is made from a polymer (F) comprising:

- recurring units derived from at least one ethylenically unsaturated monomer comprising at least one fluorine atom; and

- a substantial amount of recurring units derived from at least one ethylenically unsaturated monomer comprising at least one ion exchange group, wherein said ion exchange group is selected from the group consisting of:

- -SO ₂X, wherein X is chosen among halogens, -O ^-M ⁺, wherein M ⁺is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺, or mixtures thereof; preferably X=-O ^-H ⁺,

- -COY, wherein Y is chosen among halogens; -O ^-M ⁺, wherein M ⁺is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺; -OR _Hy wherein R _Hy is aC ₁-C ₆ hydrocarbon group; -OR _Hfwherein R _Hfis a C ₁-C ₆ fluorocarbon or per (halo) fluorocarbon group; -N (R _Hy*) ₂, wherein R _Hy*, equal or different at each occurrence, is hydrogen or a C ₁-C ₆ hydrocarbon group, or mixtures thereof; preferably Y=-O ^-H ⁺, and

- -PO ₂Z, wherein Z is chosen among halogens; -O ^-M ⁺, wherein M ⁺is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺; -OR _Hy wherein R _Hy is aC ₁-C ₆ hydrocarbon group, and-OR _Hf’ wherein R _Hf is a C ₁-C ₆ fluorocarbon or per (halo) fluorocarbon group, or mixture thereof; preferably Z=-O ^-H ⁺.
The method according to any one of preceding claims, wherein the polymer (F) comprises recurring units derived from at least one fluorinated functional monomer chosen among:

(M1) sulfonated perfluoroolefin of formula (M1)

wherein n is an integer between 0 and 6 and X’ is chosen among halogens, -O ^-M ⁺, wherein M ⁺ is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺, or mixtures thereof;

(M2) sulfonated perfluorovinylethers of formula (M2) :

wherein m is an integer between 1 and 10 and X’ is chosen among halogens, -O ^-M ⁺, wherein M ⁺is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺, or mixtures thereof, preferably X’ =-O ^-H ⁺;

(M3) sulfonated perfluoroalkoxyvinylethers of formula (M3) :

wherein w is an integer between 0 and 2, RF ₁ and RF ₂, equal or different from each other and at each occurrence, are independently –F, -Cl or a C _1-10 perfluoroalkyl group, optionally substituted with one or more ether oxygens, y is an integer between 0 and 6 and X’ is chosen among H, halogens, -O ^-M ⁺, wherein M ⁺ is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺, or mixtures thereof; preferably X’ is-O ^-H ⁺;

(M4) perfluoroalkoxyvinylether carboxylates of formula (M4) :

wherein w, y, RF ₁ and RF ₂ have the same meaning as above defined, and R _H§ is a C _1-10 alkyl or fluoroalkyl group;

(M5) sulfonated aromatic (per) fluoroolefins of formula (M5) :

wherein Ar is a C _3-15aromatic or heteroaromatic moiety and X’ is chosen among halogens, -O ^-M ⁺, wherein M ⁺ is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺, or mixtures thereof, preferably X’ =-O ^-H ⁺; and

(M6) mixtures thereof.
The method according to any one of Claims 1 to 5, wherein the polymer (F) is selected among tetrafluoroethylene (TFE) copolymers comprising recurring units derived from at least one functional per (halo) fluoromonomer.
The method according to any one of preceding claims, wherein the polymer (F) is selected among TFE copolymers comprising recurring units derived from perfluoro-2- (2-fluorosulfonylethoxy) propylvinyl ether [formula (M3-A) ] ] :

and/or from sulfonated perfluorovinylethers of formulae (M2-A) , (M2-B) and (M2-C) :

in their–SO ₂F or–SO ₂X” form, wherein X” is chosen among halogens (Cl, Br, I) , -O ^-M ⁺, wherein M ⁺is a cation selected among H ⁺, NH ₄ ⁺, K ⁺, Li ⁺, Na ⁺, or mixtures thereof.
The method according to any one of preceding claims, wherein the concentration of the 2-alkylanthraquinone in the solution is from 0.1 wt. %to 50.0 wt. %, preferably from 1.0 wt. %to 30.0 wt. %, more preferably from 2.0 wt. %to 25.0 wt. %.
The method according to any one of preceding claims, wherein the solution in the cathode chamber of step b) is completely free or substantially free from an electrolyte.
The method according to any one of preceding claims, wherein the anode catalyst is a catalyst comprising at least one metal element in elemental form and/or at least one metal oxide, said metal is a transition metal or an alkali metal.
The method according to Claim 11, wherein said metal is selected from the group consisting of iron (Fe) , nickel (Ni) , cobalt (Co) , copper (Cu) , chromium (Cr) , platinum (Pt) , palladium (Pd) , rhodium (Rh) , ruthenium (Ru) , iridium (Ir) , silver (Ag) , gold (Au) , rhenium (Re) , cesium (Cs) , tungsten (W) and vanadium (V) , preferably selected from the group consisting of Fe, Ni, Co, Ir, Ru, Cs, W and V, and more preferably Ir or Ru.
The method according to any one of preceding claims, wherein the proton and electron conductive layer (PECL) is a layer coated to the surface of the proton exchange membrane (PEM) exposed to the cathode, said layer comprises a proton conductive material, optionally a cathode catalyst, and optionally an electron conductive material.
The method according to any one of preceding claims, wherein the proton and electron conductive layer (PECL) is an electron conductive layer (ECL) treated by a proton conductive material and optionally a cathode catalyst.
The method according to claim 14, wherein the proton conductive material is the polymer (F) of any one of claims 5 to 8 and the weight ratio of the polymer (F) to the conductive the weight ratio of the polymer (F) to the electron conductive layer (ECL) is from 0.01: 1 to 2: 1 and preferably from 0.4: 1 to 1: 1.
The method according to Claim 14 or 15, wherein the electron conductive layer (ECL) is a carbon or graphite felt, sintered metal or metal foam comprising Al, stainless steel, Ti, Cu, or Ni, and preferably a carbon or graphite felt.
The method according to any one of preceding claims, wherein the cathode catalyst comprises at least one metal element in elemental form and/or at least one metal oxide, said metal is selected from a group consisting of iron (Fe) , cobalt (Co) , nickel (Ni) ruthenium (Ru) , rhodium (Rh) , palladium (Pd) , silver (Ag) , osmium (Os) , iridium (Ir) , platinum (Pt) , copper (Cu) and gold (Au) , and preferably Pt or Pd.
The method according to any one of preceding claims, for hydrogenating 2-amylanthraquinone (respectively 2-ethylanthraquinone) to 2-amylanthracene-9, 10-diol (respectively 2-ethylanthracene-9, 10-diol) .
The method according to any one of preceding claims, for hydrogenating 2-amylanthraquinone to 2-amylanthracene-9, 10-diol, wherein the solution in the cathode chamber of step b) is completely free from electrolyte.