Redox flow battery electrolytes

Abstract

The present invention relates to novel combinations of redox active compounds for use as redox flow battery electrolytes. The invention further provides kits comprising these combinations, redox flow batteries, and method using the combinations, kits and redox flow batteries of the invention.

Claims

1. A combination comprising: (a) a first redox active composition comprising a first redox active compound, the first redox active compound corresponding in structure to any one of general formulas (1′)-(3′), or mixtures thereof; and (b) a second redox active composition comprising: (i) a second redox active compound, the second redox active compound corresponding in structure to any one of general formulas (1′)-(3′), or mixtures thereof; and/or (ii) an another second redox active compound; wherein General Formula (1′) is: ##STR00071## General Formula (2′) is: ##STR00072## General Formula (3′) is: ##STR00073## wherein each of R.sup.1-R.sup.18 is independently selected from hydrogen; hydroxyl; carboxy; linear or branched, optionally substituted C.sub.1-6 alkyl optionally comprising at least one heteroatom selected from N, O and S; a carboxylic acid; an ester; a halogen; optionally substituted C.sub.1-6 alkoxy; optionally substituted amino; amide; nitro; carbonyl; phosphoryl; phosphonyl; cyanide; and sulfonyl; wherein at least one of R.sup.1-R.sup.4 in General Formula (1′), at least one of R.sup.5-R.sup.10 in General Formula (2′) and/or at least one of R.sup.11-R.sup.18 in General Formula (3′) of the first redox active compound is a substituted amine selected from —NHR/N.sub.2R.sup.+, —NR.sub.2/NHR.sub.2.sup.+ and —NR.sub.3.sup.+, where R is selected from the group consisting of —C.sub.nH.sub.2nOH, —C.sub.nH.sub.2nNH.sub.2, —C.sub.nH.sub.2nNR.sub.2, —C.sub.nH.sub.2nCO.sub.2H and —C.sub.nH.sub.2nSO.sub.3H, wherein n is an integer selected from 1, 2, 3, 4, 5, or 6, where R is H, C.sub.1-6 alkyl, or substituted C.sub.1-6 alkyl comprising at least one heteroatom selected from N, O and S.

2. The combination according to claim 1, wherein the first and the second composition are different and liquid or semi-liquid.

3. The combination according to claim 1, wherein the first and second redox active compound correspond in structure to different General Formulas (1′)-(3′).

4. The combination according to claim 1, wherein said first and second redox active compound are water-soluble.

5. The combination according to claim 1, wherein said first and second redox active composition are liquid.

6. The combination according to claim 1, wherein the first and second redox active composition are provided in separate compartments.

7. The combination according to claim 6, wherein the first and second redox active composition are each provided in a half-cell of a redox flow battery.

8. The combination according to claim 1, wherein the first redox active composition comprises at least one first redox active compound corresponding in structure to any one of General Formulas (1′), (2′) or (3′), or mixtures thereof; optionally including at least one reduction and/or oxidation product thereof corresponding in structure to General Formula (1′)(a) or (b), (2′)(a) or (b), or (3′)(a) or (b); or mixtures thereof.

9. The combination according to claim 1, wherein the second redox active composition comprises at least one second redox active compound corresponding in structure to any one of General Formulas (1′), (2′) or (3′), or mixtures thereof; optionally including at least one reduction and/or oxidation product thereof corresponding in structure to General Formula (1′)(a) or (b), (2′)(a) or (b), or (3′)(a) or (b); or mixtures thereof.

10. The combination according to claim 1, wherein the first redox active composition comprises as the first redox active compound at least one benzohydroquinone corresponding in structure to General Formula (1′), optionally including at least one reduction and/or oxidation product thereof corresponding in structure to General Formula (1′)(a) or (b); or mixtures thereof.

11. The combination according to claim 1, wherein the second redox active composition comprises as a second redox active compound at least one anthraquinone corresponding in structure to General formula (3′), optionally including at least one reduction and/or oxidation product thereof as characterized by General formula (3′) (a) or (b); or as the second redox active compound at least one benzohydroquinone corresponding in structure to General Formula (1′), optionally including at least one reduction and/or oxidation product thereof as characterized by General Formula (1′)(a) or (b); or mixtures thereof; or as the second redox active compound at least one naphthoquinone corresponding in structure to General formula (2′), optionally including at least one reduction and/or oxidation product thereof as characterized by General formula (2′)(a) or (b); or mixtures thereof.

12. The combination according to claim 1, wherein in General Formula (1): R.sup.1 is selected from —H, —SO.sub.3H, optionally substituted C.sub.1-6 alkyl and optionally substituted amine; R.sup.2 is selected from —H, —OH, —SO.sub.3H, C.sub.1-6 alkoxy, and optionally substituted amine; R.sup.3 is selected from —H, —OH and C.sub.1-6 alkoxy; and R.sup.4 is selected from —H, —SO.sub.3H, optionally substituted C.sub.1-6 alkyl, optionally substituted amine and halogen.

13. The combination according to claim 12, wherein R.sup.1 and/or R.sup.4 are independently selected from substituted C.sub.1-6 alkyl selected from R.sup.5—SO.sub.3H and R.sup.5—CO.sub.2H, wherein R.sup.5 is a C.sub.1-6 alkyl optionally comprising at least one heteroatom selected from N, O or S.

14. The combination according to claim 13, comprising (a) the first redox active compound selected from at least one of the following benzohydroquinones: ##STR00074## or mixtures thereof, and optionally oxidation products thereof; and (b) the second redox active compound selected from the following at least one anthraquinone: ##STR00075## and optionally a reduction product thereof; or at least one of the following benzohydroquinones: ##STR00076## or a mixture thereof, and optionally an oxidation product thereof.

15. The combination according to claim 12, wherein R.sup.1, R.sup.2 and/or R.sup.4 are independently selected from —NH.sub.2/NH.sub.3.sup.+, —NHR/NH.sub.2R.sup.+, —NR.sub.2/NHR.sub.2.sup.+ and —NR.sub.3.sup.+, where R is H or optionally substituted C.sub.1-6 alkyl, or optionally substituted C.sub.1-6 alkoxyl optionally comprising at least one heteroatom selected from N, O and S.

16. The combination according to claim 15, wherein the compounds of General Formula (1′) is one of the following compounds: ##STR00077## ##STR00078## or a quinone form thereof.

17. The combination according to claim 1, wherein in General Formula (2′): R.sup.5 and R.sup.6 are independently selected from —H, —OH and C.sub.1-6 alkoxy; and R.sup.7-R.sup.10 are independently selected from —H and —SO.sub.3H.

18. The combination according to claim 1, wherein in General Formula (3′): R.sup.11, R.sup.12 and R.sup.14 are independently selected from —H, —OH and optionally substituted C.sub.1-6 alkoxy; and R.sup.13 and R.sup.15-R.sup.18 are independently selected from —H and —SO.sub.3H.

19. The combination according to claim 1, wherein in General Formula (3′): R.sup.11 is —SO.sub.3H; R.sup.12 is —SO.sub.3H, R.sup.11, R.sup.13 and R.sup.14 are —OH; R.sup.16 is —SO.sub.3H, R.sup.11 and R.sup.14 or R.sup.11, R.sup.12 and R.sup.14 are —OH; R.sup.12 and R.sup.16 are —SO.sub.3H, R.sup.11 and R.sup.14 or R.sup.11, R.sup.13 and R.sup.14 are —OH; R.sup.13 and R.sup.16 are —SO.sub.3H, R.sup.11, R.sup.12 and R.sup.14 are —OH; R.sup.12 and R.sup.17 are —SO.sub.3H; or R.sup.11 and R.sup.14 are —SO.sub.3H; wherein each of the others of R.sup.11-R.sup.18 is/are C.sub.1-6 alkoxy or —H.

20. The combination according to claim 19, wherein the compound of General Formula (3′) is the compound below, or a hydroquinone form thereof: ##STR00079##

21. The combination according to claim 1, wherein the first redox active composition and/or the second redox active composition is a liquid.

22. The combination according to claim 1, wherein the first and/or the second redox active composition further comprises a solvent, optionally selected from water, an ionic liquid, methanol, ethanol, propanol, isopropanol, acetonitrile, acetone, dimethylsulfoxide, glycol, a carbonate, a polyether, tetrahydrofuran, dioxolane, sulfolane, dimethylformamide, diethylformamide, CO.sub.2, supercritical CO.sub.2, and a mixture thereof.

23. The combination according to claim 22, wherein the solvent comprises at least at least about 40 wt %, at least about 50 wt %, at least about 60 wt %, at least about 70 wt %, at least about 75 wt %, at least about 80 wt %, at least about 85 wt %, at least about 90 wt %, at least about 95 wt %, or at least about 98 wt % water, relative to the total solvent.

24. The combination according to claim 1 wherein the first and/or the second redox active composition further comprises an additive selected from co-solvents; salts; buffering agents; emulsifying agents; further redox active compounds; supporting electrolytes; ionic liquids; acids; bases; viscosity modifiers; wetting agents; stabilizers; and combinations thereof.

25. The combination according to claim 22, wherein the carbonate is selected from the group consisting of propylenecarbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate and the polyether is selected from the group consisting of dimethoxyethane and γ-butyrolactone.

26. The combination according to claim 1, wherein the first and/or the second redox active composition has a pH between about 7 and about 14, between about 9 to about 14, between about 10 and about 12, or between about 12 and about 14.

27. The combination according to claim 1, wherein the first and/or the second redox active compound are present in a concentration of between about 0.3 M and about 12 M, between about 0.5 M and about 2 M, between about 2 M and about 4 M, between about 4 M and about 6 M, or between about 6 M and about 10 M.

28. The combination according to claim 1, wherein the first redox active compound has a standard reduction potential that is at least 0.3 volts higher than the standard reduction potential of the second redox active compound.

29. The combination according to claim 1, wherein the first redox active compound has a standard reduction potential of at least about 0.0 volts, at least about +0.5 V, at least about +0.6 V, at least about +0.7 V or more against a standard hydrogen electrode; and/or wherein the second redox active compound has a standard electrode potential of about +0.3 V or less, about +0.1 V or less, about 0.0 V or less, about −0.5 V or less, about −0.6V or less, about −1.0V or less or about −1.2 V or less against a standard hydrogen electrode.

30. A kit comprising the combination according to claim 1, wherein the first and second redox active composition are provided in separate containers.

31. A method of preparing a redox flow battery electrolyte, the method comprising providing the combination of claim 1 in liquid form, wherein the first redox active composition is used as a positive electrode electrolyte, and the second redox active composition is used as a negative electrode electrolyte.

32. A redox flow battery comprising: a positive electrode; a first redox active composition according to claim 1 as a positive electrode electrolyte, the positive electrode electrolyte contacting the positive electrode; a negative electrode; a second redox active composition according to claim 1 as a negative electrode electrolyte, the negative electrode electrolyte contacting the negative electrode; and a separator interposed between the positive electrode and the negative electrode.

33. The redox flow battery according to claim 32, further comprising: a positive electrode reservoir comprising the positive electrode immersed within the positive electrode electrolyte, said positive electrode reservoir forming the first redox flow battery half-cell; and a negative electrode reservoir comprising the negative electrode immersed within the negative electrode electrolyte, said negative electrode reservoir forming the second redox flow battery half-cell.

34. The redox flow battery according to claim 33, wherein said redox flow battery is charged by applying a potential difference across the first and second electrode, such that the first redox active compound is oxidized and the second redox active compound is reduced.

35. The redox flow battery according to claim 34, wherein the redox flow battery is discharged by applying a potential difference across the first and second electrode such that the first redox active compound is reduced, and the second redox active compound comprised by said composition is oxidized.

36. The redox flow battery according to claim 32, wherein the separator comprises or essentially consists of a cation exchange membrane, optionally selected from a polymer membrane, more preferably from a sulfonate containing fluoropolymer or from a carbon backbone membrane.

37. The redox flow battery according to claim 32, wherein the positive and negative electrode comprise or essentially consist of a metal, a carbon material or an electro-conductive polymer.

38. The redox flow battery according to claim 32, further comprising: a first circulation loop comprising a storage tank containing the positive electrode electrolyte, piping for transporting the positive electrode electrolyte, a chamber in which the first electrode is in contact with the positive electrode electrolyte, and a pump to circulate the positive electrode electrolyte through the circulation loop; optionally a second circulation loop comprising a storage tank containing the negative electrode electrolyte, piping for transporting the negative electrode electrolyte, a chamber in which the second electrode is in contact with the negative electrode electrolyte, and a pump to circulate the negative electrode electrolyte through the circulation loop; and optionally control hardware and software.

39. A redox flow battery cell stack comprising at least two redox flow batteries according to claim 32.

40. An energy storage system comprising a redox flow battery according to claim 32; connected to an electrical grid.

41. A method of storing electrical energy, comprising applying a potential difference across the first and second electrode of a redox flow battery according to claim 32, wherein the first redox active compound is oxidized.

42. The method according to claim 41, wherein the second redox active compound comprised by the second redox active composition is reduced.

43. A method of providing electrical energy, comprising applying a potential difference across the first and second electrode of a redox flow battery according to claim 32, wherein the first redox active compound is reduced.

44. The method according to claim 43, wherein the second redox active compound is oxidized.

45. The combination according to claim 1, wherein the first redox active compound corresponds in structure to general formula (1′) or (2′) or general formal (2′) or (3′) and the second redox active compound corresponds in structure to general formula (2′) or (3′).

46. The combination according to claim 1, wherein the first redox active compound corresponds in structure to general formula (1′) or (3′) and the second redox active compound corresponds in structure to general formula (3′).

47. The combination according to claim 1, wherein the optionally substituted C.sub.1-6 alkyl is selected from —C.sub.nH.sub.2nOH, —C.sub.nH.sub.2nNH.sub.2 and —C.sub.nH.sub.2nSO.sub.3H, wherein n is an integer selected from 1, 2, 3, 4, 5, or 6, and the optionally substituted amino is selected from —NH.sub.2/NH.sub.3.sup.+, —NHR/NH.sub.2R.sup.+, —NR.sub.2/NHR.sub.2.sup.+ and —NR.sub.3.sup.+, where R is H or optionally substituted C.sub.1-6 alkyl optionally comprising at least one heteroatom selected from N, O and S.

48. The combination according to claim 1, wherein the optionally substituted C.sub.1-6 alkoxy is methoxy or ethoxy.

49. The combination according to claim 1, wherein at least one of R.sup.1-R.sup.4 in general formula (1′), at least one of R.sup.5-R.sup.10 in general formula (2′) and/or at least one of R.sup.11-R.sup.18 in general formula (3′) is selected from —SO.sub.3H; optionally substituted C.sub.1-6 alkyl or optionally substituted C.sub.1-6 alkoxy, optionally comprising at least one heteroatom selected from N, O and S; and optionally substituted amino.

50. The combination according to claim 1, wherein the first and/or the second redox active compound are present in a concentration of at least about 0.3 M, at least about 0.5 M, at least about 1 M, at least about 2 M, at least about 4 M, or at least about 6 M.

51. The combination according to claim 1, wherein the first redox active composition further comprises an additional first redox active compound.

52. The combination according to claim 1, where the another second redox active compound is selected from the group consisting of a metal, a metal oxide, a metal-ligand coordination compound, bromine, chlorine, iodine, oxygen, an organic dye, an organic compound, a salt thereof, and a mixture thereof.

53. The combination according to claim 1, where the another second redox active compound is selected from the group consisting of vanadium, iron, chromium, cobalt, nickel, copper, lead, manganese, titanium, zinc or oxides thereof, ferrocyanide, indigo carmine, viologen, methyl viologen or benzylviologen, tetrazole, diaryl ketone, dipyridyl ketone, dialkoxy benzene, phenothiazine, catechol, catechol ether, catechol phenylborate ester, tetrafluorocatechol, 5-mercapto-1-methyltetrazoledi-(2-pyridyl)-ketone, 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene, 2,5-di-tert-butyl-1,4-dimethoxybenzene, 2,5-di-tert-butyl-1,4-bis(2,2,2-trifluoroethoxy)benzene, 5,6,7,8-tetrafluoro-2,3-dihydrobenzodioxine, a salt thereof, and a mixture thereof.

Description

9. Description of the Figures

(1) FIG. 1 schematically illustrates a redox flow battery comprising the inventive combination of redox active compositions and its function.

(2) FIG. 2 A-K shows charge/discharge curves of selected redox active quinone compounds on graphite electrodes.

(3) FIG. 3 shows further preferred compounds according to General Formulas (1), (2) and (3) or General Formulas (1′), (2′) and (3′).

(4) FIG. 4 shows charge/discharges curves for redox active compounds in Example 12.

10. Examples

(5) In the following, particular examples illustrating various embodiments and aspects of the invention are presented. However, the present invention shall not to be limited in scope by the specific embodiments described herein. The following preparations and examples are given to enable those skilled in the art to more clearly understand and to practice the present invention. The present invention, however, is not limited in scope by the exemplified embodiments, which are intended as illustrations of single aspects of the invention only, and methods which are functionally equivalent are within the scope of the invention. Indeed, various modifications of the invention in addition to those described herein will become readily apparent to those skilled in the art from the foregoing description, accompanying figures and the examples below. All such modifications fall within the scope of the appended claims.

Example 1: Preparation of Low Molecular Weight Aromatic Lignin-Derived Compounds by Cracking and Reduction by a Nickel Catalyst

(6) Reductive cracking of a modified lignin-derived component was carried out by means of a catalyst comprising nickel, e.g. supported on activated carbon (Ni/C). The catalysts are typically prepared by an incipient-wetness impregnation method and further treated by a carbothermal reduction method known in the art.

(7) Herein, nickel nitrate(II) hexahydrate [Ni(NO.sub.3).sub.2 6H.sub.2O] is used and optionally added into water in a beaker known in the art. The solution is then stirred, e.g. for at least 30 min, to prepare an impregnation stock solution. Activated carbon having a water absorption capacity of typically above 1.8 mL g.sup.−1 is added into the solution and the beaker may then covered by a culture dish to keep the sample wet for a prescribed time, preferably more than 12 h, more preferably 24 h. The sample is then dried at a temperature above 80° C., e.g. 120° C. overnight. The actual reduction is carried out in a container such as a preferably horizontal furnace in a flow of inert gas such as N.sub.2. The flow is, e.g., 10 mL min.sup.−1 or more, preferably 30 mL min.sup.−1 or more. The reduction temperature preferably reaches at least 400° C., preferably 450° C., e.g. over set time period such as at least 30 min, preferably at least 60 min. The temperature for conducting the reduction is maintained at 450° C. for at least 1 h, more preferably for at least 2 h. The Ni/SBA-15 catalysts are reduced at 550° C. for 2 h. The Ni/Al.sub.2O.sub.3 catalyst is reduced at 700° C. for 2 h. The metal loading for each nickel- and copper-based catalyst is 10% (w/w) relative to the support. Herein, birch sawdust serves as lignocellulosic material and is treated with the ethanol-benzene mixture (v/v ratio 1:2) for 12 h. The treated birch sawdust, solvent (m/v 1:20), and catalyst (w/w 20:1) are placed in an autoclave reactor. The reactor is sealed and purged with Ar 4 to 6 times to expel air. Then, the reducing reaction is conducted at 200° C. at a stirring speed of at least 300 rpm, preferably 500 rpm. When the desired reaction time (usually 2 to 10 h) is reached, the reactor is cooled to ambient temperature before sampling.

(8) Typically, the reaction generates 4-propylguaiacol and 4-propylsyringol as major products, together with minor alkene-substituted 4-propylguaiacol and 4-propylsyringol, as determined by standard gas chromatography. The compounds are isolated according to step (F), preferably by extraction.

Example 2

(9) Lignin-Fragmentation Reaction

(10) Lignosulfonate solution (220 g/L Lignin, 125 mL), which was obtained by the sulphite process (as e.g. applied by step 2) of the inventive method), was mixed with methanol (125 mL) and the pH-value was set to 2 by addition of sulfuric acid (2M). The conditions applied emulate oxidative cracking as an exemplary decomposition step ((step 5) of the inventive method). In this regard, the Iron(111) phosphate dihydrate (0.25 g, 1.34 mmol) was added as catalyst and the suspension was filled into a stirred pressure reactor. The mixture was flushed with Oxygen for 1 minute, then the reactor was sealed and an oxygen pressure of 10 bar was adjusted. The reactor was heated to 170° C. within 65 minutes and kept at this temperature for 20 minutes. The pressure raised to 26 bar. Afterwards the reaction mixture was cooled down to 40-50° C. within 90 minutes and the remaining pressure (2-3 bar) was released. The insoluble components in the obtained mixture were filtered off. The reaction mixture was analyzed via HPLC.

(11) The resulting components of the reaction mixture were characterized and have a molecular weight of between 75 and 500 Da, whereby the average molecular weight is in the range of 120 to 180 Da.

(12) In general, lignin fragmentation reactions, in particular based on oxidative cracking are preferably carried out by the use metal catalysts, in particular catalysts selected from Co(II), Cu(II), Mo(II)/(II)/(IV)/(VI), specifically Mo(II), Fe(II) and Fe(III), more preferably Fe(III), or metalloid elements, or combinations thereof. They are typically provided as salts (e.g. phosphates, cyanates, carbonates, or halogenides), e.g. as Fe phosphate such as Fe(III) phosphate.

Example 3: Preparation of Monomeric Aromatic Lignin-Derived Molecules from Lignosulfonate of a Sulfite Process by Electrooxidation

(13) A 1 M aqueous NaOH solution of lignosulfonate is prepared, comprising 1% (W/W) lignosulfonate. Said solution is subjected to an electrooxidation. Therein, the solution is employed as anolyte. A 1 M aqueous solution is employed as catalyte. A flow cell with a flow rate of 250 ml/min is used. Electrolysis is allowed to take place galvanostatically for 8 h applying current of 1 mA/cm.sup.2. A typical resulting voltage is 1.4 V. The voltage curve typically is asymptotic and the solution changes preferably color from brown to dark brown.

(14) Samples of the solution are taken every hour over a time span of 8 h and subsequently examined photometrically. Thereof, an absorption profile typical for ortho-benzoquinone is determined. Hence, a lower molecular weight aromatic lignin-derived compound, quinone compound, is prepared by said method.

(15) Said compound is then isolated. Therefore, said compound is extracted by dichloromethane and subsequently subjected to cycles of charging and discharging processes in a flow cell. The voltage curve shows that the compound is redox active, which may be reversibly electrolyzed.

Example 4: Preparation of an Annulated Quinone Compound by a Friedel-Crafts Acylation

(16) Vanillin as a low molecular weight aromatic lignin-derived compound is provided and further annulated and oxidized in five steps as follows:

(i) Synthesis of 4-(benzyloxy)-3-methoxybenzaldehyde (2)

(17) ##STR00018##

(18) Vanillin (1) (1.0 eq.) and benzyl chloride (1.2 eq.) are dissolved in N,N-dimethylformamide and potassium iodine (0.5 mol %) is added. Afterwards potassium carbonate is added and the reaction is stirred above 60° C., preferably between 60 to 120° C. for at least 1 h, preferably 1 to 8 h. After completion of the reaction, the solution is diluted with distilled water and extracted with an appropriate solvent. The organic phase is washed with brine and the product is then isolated from the organic phase.

(ii) Synthesis of 4-(benzyloxy)-3-methoxybenzoic acid (3)

(19) ##STR00019##

(20) A mixture of 1,2-dimethoxyethane and potassium hydroxide (5 to 20 eq.) is purged with oxygen and the calculated amount of isolated product 2 (1.0 eq.) is added. After the absorption of oxygen ceases, the mixture is diluted with distilled water and neutral organic products are extracted with an appropriate solvent. The aqueous layer is acidified and the acidic organic products are extracted with an appropriate solvent. Product 3 is isolated from the organic layer.

(iii) Synthesis of 4-(benzyloxy)-3-methoxybenzoyl chloride (4)

(21) ##STR00020##

(22) Isolated product 3 (1.0 eq.) is dissolved in thionyl chloride (5-20 eq.) and the mixture is stirred at 60 to 120° C. for 1 to 8 h. After completion of the reaction excess thionyl chloride is evaporated to yield desired acyl chloride 4.

(iv) Synthesis of Anthraquinones (5-7)

(23) ##STR00021##

(24) Aluminiumtrichloride (0.1 eq.) is added to the crude acyl chloride 4 and the mixture is stirred for 30 to 300 min at −20 to 60° C. After completion of the reaction the mixture is carefully quenched with bicarb solution. The product is extracted with an appropriate solvent and the organic layer is washed with brine. The product is then isolated from the organic phase.

(v) Synthesis of 2,6-dihydroxy-3,7-dimethoxyanthracene-9,10-dione 8 and 2,6-dihydroxy-1,7-dimethoxyanthracene-9,10-dione 9

(25) ##STR00022##

(26) Anthraquinone 5 or 6 are dissolved in ethyl acetate, methanol or ethanol and palladium on charcoal (1 to 30 weight %) is added. The mixture is stirred at room temperature under hydrogen atmosphere (1-10 bar). The catalyst is filtered off and the product (9) is isolated from the mixture.

(27) The product is then characterized by spectrographic means, and provided as redox active compound according to the present invention.

Example 5: Derivatization of (Hydro-)quinones

(28) Substituents were introduced into the low molecular weight lignin-derived components.

Example 5.1 Reduction of Dimethoxy Benzoquinone

(29) ##STR00023##

(30) 23.2 g of sodium dithionite (0.134 mol, 1.32 eq.) was added to the suspension of 17.0 g (0.101 mol, 1.0 eq.) 2,6-dimethoxycyclohexa-2,5-diene-1,4-dione in 100 mL H.sub.2O. After 2 h stirring at room temperature the precipitate was filtered off and dried in the air to give 15.85 g (0.093 mol, 92% yield) of 2,6-dimethoxybenzene-1,4-diol as a white solid.

Example 5.2: Oxidation of Methoxy benzohydroquinone

(31) ##STR00024##

(32) 1.4 g of catalyst Cu/AlO(OH) was added to a solution of 8.2 g (0.059 mol) 2-methoxy-1,4-dihydroxybenzene in 250 mL ethyl acetate, and the reaction mixture was stirred at room temperature for 147 h under an O.sub.2 atmosphere. After the conversion determined by HPLC reached 99%, the reaction mixture was filtered, and the recovered catalyst was washed with ethyl acetate (100 mL×3). The filtrate was collected and solvent was removed in vacuo to give 7.66 g (0.055 mol, 95% yield) of 2-methoxycyclohexa-2,5-diene-1,4-dione as a yellow-brownish solid.

Example 5.3: Acetylation of Methoxy Benzohydroquinone

(33) 8.24 g (0.059 mol, 1.0 eq.) of 2-methoxybenzene-1,4-diol was weighed into a 250 mL reaction flask equipped with a reflux condenser. 60 mL of dichloroethane and 15 mL (0.159 mol, 2.7 eq.) of acetic anhydride were added. 12 mL (0.096 mol, 1.63 eq.) of boron trifluoride ether solution was then slowly added at room temperature with stirring. The reaction mixture was heated to 90° C. for 20 hours. The mixture was cooled to 60° C., 30 mL H.sub.2O was added followed by 10 mL HCl (6 M). The resulting mixture was heated to 100° C. for 30 min, cooled down and extracted with ethyl acetate (150 mL×3). The combined extracts were washed sequentially with H.sub.2O (100 mL), saturated sodium bicarbonate (100 mL) and H2O (100 mL) and then dried with anhydrous sodium sulfate. The solvent was removed in vacuo to give a brown solid residue, which was washed with methanol to give 7.49 g (0.041 mol, 70% yield) of 1-(2,5-dihydroxy-4-methoxyphenyl)ethan-1-one as a beige solid.

Example 5.4 Addition of Isonicotinic Acid to Benzoquinone

(34) 2.16 g (0.02 mol, 1.0 eq.) of p-benzoquinone was suspended in 6.4 mL of acetic acid. 2.46 g (0.02 mol, 1.0 eq.) of nicotinic acid was added and the mixture was stirred for 2 h at rt. The resulting dark mixture was diluted with 3 mL of water and treated with 6.6 mL of HCl (6 M). On cooling, solid precipitated which was filtered off and dried overnight at 60° C. to give 3.13 g (0.012 mol, 59% yield) of 3-carboxy-1-(2,5-dihydroxyphenyl)pyridin-1-ium chloride as an yellow solid.

Example 5.5 Sulfonation of Anthraquinone

(35) ##STR00025##

(36) A solution of anthraquinone was heated (180° C.) in a solution of 20%-40% SO.sub.3 in concentrated sulfuric acid (oleum), resulting in a mixture of sulfonated anthraquinones. The crude mixture was poured onto ice and partially neutralized with calcium hydroxide. Subsequently, the mixture was filtrated and concentrated to yield the final product.

Example 5.6: Sulfonation of Hydroquinone (1,4-Dihydroxybenzene)

(37) ##STR00026##

(38) A solution of hydroquinone was heated (80° C.) in a solution of 20%-40% SO.sub.3 in concentrated sulfuric acid (oleum), resulting in a mixture of sulfonated hydroquinones. The crude mixture was poured onto ice and partially neutralized with calcium hydroxide. Subsequently, the mixture was filtrated and concentrated to yield the final product.

Example 5.7: Sulfonation of 1,4-Dihydroxy-2,6-dimethoxybenzene

(39) A solution of hydroquinone was heated (80° C.) in a solution of 20%-35% SO.sub.3 in concentrated sulfuric

(40) ##STR00027##

(41) acid (oleum), resulting in a mixture of sulfonated 1,4-dihydroxy-2,6-dimethoxybenzenes. The crude mixture was poured onto ice and partially neutralized with calcium hydroxide. Subsequently, the mixture was filtrated and concentrated to yield the final product.

Example 5.8: Sulfonation of 2-Methoxyhydroquinone

(42) ##STR00028##

(43) A solution of 2-methoxyhydroquinone was heated (80° C.) in a solution of 20%-40% SO.sub.3 in concentrated sulfuric acid (oleum), resulting in a mixture of sulfonated 2-methoxyhydroquinones. The crude mixture was poured onto ice and partially neutralized with calcium hydroxide. Subsequently, the mixture was filtrated and concentrated to yield the final product.

Example 5.9: Synthesis of 2,5-bis{[(2-hydroxyethyl)(methyl)amino]methyl}benzene-1,4-diol

(44) ##STR00029##

(45) In a round-bottom flask 40.0 g hydroquinone (0.36 mol, 1 eq) and 24.0 g paraformaldehyde (0.80 mol, 2.2 eq) were dissolved in toluene (200 mL). 64 mL 2-(methylamino)ethanol (0.80 mol, 2.2 eq) was added and the reaction mixture was heated under reflux for 20 h. After cooling to room temperature the solvent was removed in vacuum and the residue was recrystallized from acetone to yield 65.2 g of product (63% yield) as an off-white solid.

Example 5.10: Synthesis of 2,6-bis[(dimethylamino)methyl]-3,5-dimethoxybenzene-1,4-diol

(46) ##STR00030##

(47) 8.51 g 2,6-dimethoxyhydroquinone (50 mmol, 1 eq) and 3.30 g paraformaldehyde (110 mmol, 2.2 eq) were dissolved in ethanol (130 mL). 19 mL of dimethylamine solution in ethanol (5.6 M, 110 mmol, 2.2 eq) was added and the reaction mixture was stirred at room temperature for 20 h. After completion of the reaction, the solvent was removed in vacuum to obtain 12.2 g of product (86% yield). Analytically pure sample was obtained by recrystallization from acetone.

Example 6

Oxidation of Vanillin to 2-Methoxy-1,4-benzoquinone

(48) Vanillin of e.g. any of process streams A, B or C may be further chemically derivatized, e.g. oxidized, to yield a benzoquinone compound. The oxidation reaction may e.g. be implemented as step 7) following step 6) of the inventive method. By the below oxidation reaction of vanillin 2-Methoxy-1,4-benzoquinone was obtained:

(49) ##STR00031##

(50) By a first step the Dakin-Reaction was carried out. 20.0 g vanillin (131 mmol) were suspended in an Erlenmeyer flask in 100 mL deionized water (pH 5.6). The mixture was stirred in an ice bath and 16 mL hydrogen peroxide solution (30% in water, 155 mmol, 1.2 eq.) were added (pH 5.2). 65 mL NaOH (2 M, 130 mmol, 1.0 eq.) were slowly added until a pH-value of 7.2 was adjusted. After the addition the reaction mixture was stirred for additional 1 h. The progress of the reaction was monitored by HPLC (97.4% conversion after 1 h).

(51) By a subsequent second step oxidation to yield a quinone compound was carried out under the following reaction conditions. The pH value of the reaction mixture was adjusted to 3.5 by addition of 17.5 ml sulfuric acid (2M). While cooling in an ice bath, 0.4 g potassium iodide (2.4 mmol, 1.8 mol %) and then 24 mL hydrogen peroxide solution (30% in Wasser, 235 mmol, 1.8 eq.) were added dropwise. The progress of the reaction was monitored by HPLC. After stirring for 3 h, the solids were filtered off, washed with small amount of water and dried at 60° C.

(52) The product 2-methoxy-1,4-benzoquinone was obtained as a green to yellow solid (16.0 g, 88% yield).

Example 7

Oxidation of Syringaldehyde to 2,6-dimethoxybenzoquinone

(53) For the present Example, syringaldehyd, which may represent a lignin-derived compound A, was oxidized, e.g. exemplifying step 7) of the inventive method to yield 2,6-dimethoxybenzoquinone.

(54) ##STR00032##

(55) By an initial step, the Dakin-Reaction was carried out. 150 g syringaldehyde (0.82 mol) were suspended in a 4 L round-bottom flask in 750 mL deionized water. The mixture was stirred in an ice bath and 411 mL NaOH (2 M, 0.82 mol, 1.0 eq.) followed by 203 mL hydrogen peroxide solution (30% in water, 1.97 mol, 2.4 eq.) were slowly added over 2 h. After the addition the reaction mixture was stirred for additional 5 h. The progress of the reaction was monitored by HPLC.

(56) By a subsequent step, an oxidation reaction to yield a quinone compound was carried out under the following reaction conditions. While cooling in an ice bath, a solution of 6.0 g potassium iodide (36 mmol, 4 mol %) in 225 mL water was added followed by dropwise addition of 101 mL hydrogen peroxide solution (30% in water, 0.98 mol, 1.2 eq.). After stirring for 16 h at room temperature, the precipitate was filtered off, washed with water and dried at 60° C.

(57) The product 2,6-dimethoxybenzoquinone was obtained as an orange solid (118.6 g, 86% yield).

Example 8

Sulfonation of Anthraquinone

(58) E.g. upon annulation of monocyclic compounds (obtained as e.g. lignin-derived compound A) and subsequent oxidation to yield an anthrachinone compound, the anthraquinone compound may be further derivatized, e.g. by a substitution reaction or sulfonation. An example for a sulfonation reaction was carried as follows:

(59) ##STR00033##

(60) 35 ml H.sub.2SO.sub.4 (96%) were added to 50 g anthraquinone (0.24 mol, 1.0 eq) in a 250 mL round-bottom flask. The mixture was preheated to 60° C. and 53 ml oleum (65% SO.sub.3, 0.74 mol SO.sub.3, 3.08 eq) were added dropwise. The reaction mixture was stirred at 170° C. for 3 h. After cooling to 120° C., the mixture was quenched by pouring it into 500 g ice. 54 g Ca(OH).sub.2 were added portion wise while stirring vigorously. After 1 h the precipitate was filtered off, the filtrate was concentrated under vacuum to 250 mL. Precipitated solids were removed by filtration and the obtained filtrate was used as an electrolyte solution.

Example 9

Sulfonation of Hydroquinone

(61) Another example of a sulfonation reaction, e.g. of monocyclic compounds (e.g. compound A), e.g. obtained upon oxidation yielding a hydroquinone, was carried out as follows:

(62) ##STR00034##

(63) Hereby, 55 ml H.sub.2SO.sub.4 (96%) were added to 30 g hydroquinone (0.27 mol, 1.0 eq) in a 250 mL round-bottom flask. 67 ml oleum (65% SO.sub.3, 0.79 mol SO.sub.3, 2.93 eq) were added dropwise and the reaction mixture was stirred at 90° C. for 2.5 h. After cooling to rt, the mixture was quenched by pouring it into 600 g ice. 130 g Ca(OH).sub.2 were added portion wise while stirring vigorously. After 1 h the precipitate was filtered off, the filtrate was concentrated under vacuum to 300 mL. Precipitated solids were removed by filtration and the obtained filtrate was used as an electrolyte solution.

Example 10

Synthesis of 2,5-bis{[(2-hydroxyethyl)(methyl)amino]methyl}benzene-1,4-diol

(64) As an example of a substitution reaction, e.g. starting from a hydroquinone, was carried out as follows:

(65) ##STR00035##

(66) In a round-bottom flask 40.0 g hydroquinone (0.36 mol, 1 eq), 24.0 g paraformaldehyde (0.80 mol, 2.2 eq) and 64 mL 2-(methylamino)ethanol (0.80 mol, 2.2 eq) were added and the reaction mixture was heated at 120° C. for 20 h. After cooling to room temperature, the residue was dissolved in 360 mL H.sub.2SO.sub.4 (3M) to yield the 1.0 M solution of electrolyte.

Example 11

Synthesis of 2-[(dimethylamino)methyl]-3,5-dimethoxybenzene-1,4-diol

(67) Another example for a substitution reaction was carried starting from a 2,6-dimethoxybenzene-1,4-diol.

(68) ##STR00036##

(69) A round-bottom flask was charged with 10 g 2,6-dimethoxyhydroquinone (59 mmol, 1 eq), and the mixture of 4.9 ml 37% formaldehyde solution (65 mmol, 1.1 eq) and 23.2 mL dimethylamine solution in ethanol (5.6 M, 130 mmol, 2.2 eq) was added. The reaction mixture was stirred at room temperature for 4 h. The solvent and excess amine were distilled off under the vacuum to give 13.9 g of product (99% yield). The crude product was dissolved in 90 mL H.sub.2SO.sub.4 (2M) to obtain the 0.67 M solution of electrolyte.

Example 12: Cycling Tests of Different Combinations of Redox Active Quinone Compounds

(70) Cycling Tests

(71) Selected redox active compositions were subjected to electrochemical measurements. Therefore, a small laboratory cell employing selected quinones/hydroquinones in different combinations as positive and negative redox active compounds were evaluated with constant-current charge-discharge experiments and open-circuit voltage measurement with a BaSyTec battery test system (BaSyTec GmbH, 89176 Asselfingen, Germany) or a Bio-Logic battery test System (Bio-Logic Science Instruments, 38170 Seyssinet-Pariset, France). This cell consists of four main parts: a graphite felt (with an area of 6 cm.sup.2, 6 mm in thickness) was employed as the positive and negative electrode, and a cation exchange membrane was used to separate the positive and negative electrolytes. Positive and negative electrolytes evaluated in each cycling test are specified in table 5 below. The electrolytes were provided in either an aqueous solution of 20% sulfuric acid in water or a solution of 8% sodium hydroxide. The pH of the electrolyte solutions was <0 or >14 respectively. No additives were used. The electrolytes were pumped by peristaltic pumps to the corresponding electrodes, respectively. In the charge-discharge cycles, the cell was charged at a current density of 10 mA cm.sup.2 up to 1.2 V or typically 25 mA cm.sup.2 up to 1.0 V and discharged at the same current density down to −0.4 V or typically 0.0 V cut-off for acidic cells and at a current density of 25 mA cm.sup.2 up to 1.5 V and discharged at the same current density down to 0.7 V cut-off for alkaline cells.

(72) TABLE-US-00005 TABLE 5 Evaluated electrolyte combinations Open Circuit Coulombic # Posolyte Negolyte Voltage (OCV) efficiency (CE) Figure  1 0.69 V   97% 2A  2 0 0.79 V   93% 2B  3 0.70 V   97% 2C  4 0.64 V   98% 2D  5 0.72 V   97% 2E  6 0.66 V   99% 2F  7 0 0.71 V   91% 2G  8 0.68 V   90% 2H  9 0.75 V 99.5% 2I 10 0.73 V   96% 2J 0 11 0.68 V   96% 2K

(73) FIG. 2A-K show the charge/discharge curves of selected redox active quinone compounds on graphite electrodes.

(74) Further, charge/discharge curves are shown for redox active compounds in in FIG. 4.

Example 13: Synthesis of 3,3′-Disulfonsäure-4,4′biphenyldiol

(75) ##STR00065##

(76) 15 mL H.sub.2SO.sub.4 (96%) were added to 3.72 g (20 mmol, 1 eq) of 4,4′-Biphenol in a 100 mL round-bottom flask equipped with a reflux condenser. After stirring at 150° C. for 4 h, the hot reaction mixture was poured into 80 g ice. The flask was rinsed with additional 30 mL water. 12 g Ca(OH).sub.2 were added to the solution while stirring continuously. After 5 min the precipitate was filtered off, the filtrate was concentrated to 40 ml and the calcium salts were filtered off. The filtrate was used as an electrolyte solution.

Example 14: Synthesis of 4,4′-((9,10-Anthraquinone-1,4-diyl)dioxy)dibutyric Acid (1,4-DBEAQ)

(77) Step 1:

(78) ##STR00066##

(79) 1,4-dihydroxyanthraquinone (2.52 g, 10.5 mmol, 1 eq) was weighed into a 500 mL round bottom flask and dissolved in dimethylformamide (100 mL). While stirring vigorously, potassium tert-butoxide (4.35 g, 36.8 mmol, 3.5 eq) was added and the reaction mixture was stirred for 15 min at ambient temperature. The formed potassium salt of 1,4-dihydroxyanthraquinone was then reacted with methyl 4-bromobutyrate (9.5 g, 52.5 mmol, 5 eq) in the presence of anhydrous K.sub.2CO.sub.3 (7.26 g, 52.5 mmol, 5 eq). After stirring at 95° C. overnight the reaction mixture was cooled to 0° C. and deionized (DI) water (200 mL) was added to precipitate the ester (1,4-DBEAQ-Me). The precipitate was filtered off and washed with DI water (100 mL) to remove the inorganic salt. The formed product was used for the next step without further purification.

(80) Step 2:

(81) ##STR00067##

(82) The 1,4-DBEAQ precursor (2.7 g, 7.03 mmol, 1 eq) and KOH (1.58 g, 28.1 mmol, 4 eq) were weighed into a 500 mL round bottom flask and filled with a water-isopropanol mixture (2:1 v/v, 90 mL). The suspension was heated at 60° C. until all solids were dissolved (13 hours) and a dark red solution was formed. The reaction mixture was diluted with DI water (250 mL) and the pH was set to 4 using glacial acetic acid. After stirring for 1 h at room temperature the precipitate was isolated by vacuum filtration and washing with DI water (100 mL). Drying at 60° C. overnight gave a yellow product of 1,4-DBEAQ (25%, 0.91 g, 2.6 mmol).

Example 15: Synthesis of 4,4′-((9,10-Anthraquinone-2,6-diyl)dioxy)dibutyric Acid (2,6-DBEAQ)

(83) Step 1:

(84) ##STR00068##

(85) 2,6-dihydroxyanthraquinone (6 g, 25 mmol, 1 eq) was weighed into a 1 L round bottom flask and dissolved in dimethylformamide (400 mL). While stirring vigorously, potassium ethoxide (7.36 g, 87.5 mmol, 3.5 eq) was added and the reaction mixture was stirred for 15 min at ambient temperature. The formed potassium salt of 2,6-dihydroxyanthraquinone was then reacted with methyl 4-bromobutyrate (22.6 g, 125 mmol, 5 eq) in the presence of anhydrous K.sub.2CO.sub.3 (17 g, 125 mmol, 5 eq). After stirring at 95° C. overnight the reaction mixture was cooled to 0° C. and deionized (DI) water (200 mL) was added to precipitate the ester (2,6-DBEAQ-Me). The precipitate was filtered off and washed with DI water (100 mL) to remove the inorganic salt. The formed product (15 g, 34 mmol) was used for the next step without further purification.

(86) Step 2:

(87) ##STR00069##

(88) The 2,6-DBEAQ precursor (15 g, 34 mmol, 1 eq) and KOH (8.1 g, 144 mmol, 4 eq) were weighed into a 500 mL round bottom flask and filled with a water-isopropanol mixture (2:1 v/v, 300 mL). The suspension was heated at 60° C. until all solids were dissolved (16 hours) and a dark red solution was formed. The reaction mixture was transferred to a 1 L Erlenmeyer flask and diluted with DI water (300 mL). The pH of the solution was set to 4 using glacial acetic acid. After stirring for 1 h at room temperature the precipitate was isolated by vacuum filtration and washing with DI water (100 mL). Drying at 60° C. overnight gave a yellow product of 2,6-DBEAQ (97%, 10 g, 24.2 mmol).

Example 16: Synthesis of 4,4′-((9,10-Anthraquinone-1,4-diyl)dioxy)dipropionic Sulfonic Acid (1,4-DPSAQ)

(89) ##STR00070##

(90) 1,4-dihydroxyanthraquinone (2 g, 8.3 mmol, 1 eq) was weighed into a 100 mL round bottom flask and suspended in deionized (DI) water (20 mL). While stirring vigorously, potassium tert-butoxide (2.8 g, 24.9 mmol, 3 eq) and 1,3-propanesultone (2.9 mL, 33.2 mmol, 4 eq) were added. The dark red reaction mixture was stirred for 16 h at 70° C. The formed precipitate was filtered off and the filtrate was evaporated to give the product as a red solid (5.5 g, 11.4 mmol).