Improving the productivity of reaction products from electrosynthesis reactions

Abstract

Conventional redox flow batteries may be limited by the solubility of the raw materials used to produce Negolite. This specification describes a method for improving the solubility of Negolite raw materials by converting them into more soluble compounds that also exhibit the desired reactivity with Negolite reagents under operating conditions.

Description

Technical Field

[0001] Cross - reference to related applications This application is filed as a PCT international application on May 14, 2024, claiming the benefit and priority of U.S. Provisional Patent Application No. 63 / 502,397, filed on May 15, 2023, the description of which is incorporated herein by reference in its entirety.

[0002] The present invention generally relates to the electrochemical synthesis of compounds. More specifically, the present invention relates to the production of compounds produced by chemical or electrochemical reduction of starting materials, generating reactive intermediates that then react with reagents to produce the compounds. By using a redox - active compound called a solubility shuttle, compounds with high water - solubility can be readily produced first from starting materials with low water - solubility or no water - solubility. Some of the compounds are useful as negative electrode active materials in redox flow batteries and further consist of only earth - abundant elements and have high chemical or electrochemical stability.

[0003] Statement regarding government interests Certain aspects of the present invention were made with government support from the U.S. Department of Energy (award number DE - EE0009795). The government has certain rights in the invention.

Background Art

[0004] In the manufacture of specialty chemicals, including the production of chemical reactants for organic redox flow batteries (RFBs), the cost of production is very important for the commercial viability of systems or materials that use such specialty chemicals. The overall cost of production depends greatly on specific factors such as yield, cost of raw materials, ease of purification and purification steps, waste disposal, production rate, etc.

[0005] An inventive method for the production of RFB negative electrodes is described in co - owned patent application U.S. 63 / 215,079 (the “‘079 application”), the content of which is incorporated herein by reference in its entirety.

[0006] The '079 application describes an electrochemical process that begins with the conversion of a substituted anthraquinone starting material to a dihydroxyanthracene species (reduced anthraquinone) by electrochemical reduction using an electrochemical system. The dihydroxyanthracene species acts as a reactive intermediate, reacting with a negolite reagent (often an interconvertible aldehyde such as reducing sugar-like glucose, as well as an aldehyde) to produce a carbon-carbon bond at the 2-position of the anthraquinone / anthracene skeleton, which has a substantial effect of adding a side chain to the skeleton. Subsequent heating regenerates the anthraquinone skeleton by a disproportionation reaction, or the anthraquinone skeleton can be regenerated in the electrochemical system by exposure to oxygen in the atmosphere, or by electrochemical re-oxidation. Depending on the selection of the negolite reagent, the side chain imparts desirable properties to the resulting RFB negolite. Such desirable properties include increased water solubility, increased energy density of RFB, increased cell voltage, increased reduction potential for more negatively charged cells, and thus also increased energy density. Other desirable properties include improved chemical and electrochemical stability when the generated RFB negolite is circulated within the RFB.

[0007] One limitation not addressed by the method in the '079 application is the solubility of the anthraquinone raw material. The raw material is supplied to an electrochemical system in a liquid medium and flows as a soluble species or solid slurry through or beyond the electron-supplying electrode to produce a reactive intermediate, the reduced anthraquinone raw material. Often, the raw material has very low solubility in a solvent (e.g., water) compared to the reactive intermediate or the resulting RFB negolite. However, electrochemical systems can often use many components that are prone to clogging even with small amounts of suspended solids, such as porous electrodes designed for fluid passage or flow plates with narrow channels.

[0008] To convert all or part of the starting materials into a more soluble reactive intermediate, the less soluble starting materials may need to be added to the reaction vessel very slowly so that they remain below their solubility limit, a co-solvent may need to be used, or a non-electrochemical method such as hydrogenation or chemical reduction with a reducing agent may need to be used. All of the aforementioned methods have some drawbacks, such as increased complexity of the method or the introduction of additional chemical species or solvents that may need to be removed after the reaction is complete. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] USA 63 / 215,079 [Overview of the project] [Problems that the invention aims to solve]

[0010] This invention solves the problem of low starting material solubility by introducing the use of a "solubility shuttle," a chemical species present in the reaction mixture. The chemical species has high solubility in its reduced and oxidized states and has a more negative reduction potential than the anthraquinone starting material. In other words, the reduced form of the solubility shuttle can react with the anthraquinone starting material to reduce it and produce a reactive intermediate with increased solubility. The solubility shuttle can be continuously circulated in an electrochemical system for regeneration by electrochemical reduction, and the reduced solubility shuttle can be returned to the mixing vessel to which the anthraquinone starting material is added and dissolved as a result of its conversion to the reactive intermediate. The solubility shuttle can be any chemical species, and may even be the produced RFB negolite itself. [Means for solving the problem]

[0011] This abstract is provided as an introduction to the conceptual selection, in a simplified form that is further described in the detailed description of the invention below. This abstract is not intended to identify any essential or intrinsic features of the claimed invention, nor is it intended to be used to limit the scope of the claimed invention.

[0012] This specification is directed to methods for improving the handling ease of reactants in electrochemical reactions, and to liquid compositions comprising electrochemically active reagents and solubilizers. These agents improve the solubility of the starting materials in the reaction mixture through the use of solubilizing compounds.

[0013] Various additional inventive aspects are described below. These inventive aspects may relate to individual embodiments and combinations of embodiments. It should be understood that both the general description above and the detailed description below are examples and for illustrative purposes only, and do not limit the broader concept of the invention on which the embodiments described herein are based. [Brief explanation of the drawing]

[0014] The accompanying drawings, incorporated herein and constituting part of the specification, illustrate several aspects of this disclosure. A brief description of the drawings is as follows:

[0015] [Figure 1] This is a schematic diagram of an electrochemical system, including a separated electrochemical flow cell, corresponding to the soluble shuttle method described herein. [Modes for carrying out the invention]

[0016] definition To more clearly define the terms used herein, the following definitions are provided. Unless otherwise indicated, the following definitions are applicable herein. Where a term is used herein but not specifically defined herein, the definition from IUPAC Compendium of Chemical Terminology, 2nd Ed (1997) may be applied, provided that it does not conflict with any other statement or definition applicable herein, or invalidate or void any claim relating to the application of that definition. To the extent that any definition or use provided in reference or cited literature conflicts with the definition or use provided herein, the definition or use provided herein shall prevail.

[0017] In this specification, compositions and methods are described using the term “including” various components or steps, but unless otherwise indicated, compositions and methods may also “essentially consist of” or “consist of” various components or steps. For example, a solubility shuttle consistent with aspects of the present invention may include; anthraquinone compounds, flavin compounds, phenazine compounds, viologen compounds, vanadium(II / III) ions, chromium(II / III) ions, metal coordination complexes, and other species commonly treated as RFB negolites; alternatively, essentially consist of; or alternatively, consist of.

[0018] Generally, groups of elements are indicated using the numbering system suggested in the edition of the periodic table published in Chemical and Engineering News, 63(5), 27, 1985. In some cases, groups of elements may be indicated using the common name assigned to that group; for example, Group 1 is called alkali metals, Group 2 is called alkaline earth metals, Groups 3-12 are called transition metals, and Group 17 is called halogens or halides.

[0019] For any specific formula or name expressed, the general formula or name shown also encompasses all conformational isomers, positional isomers, and stereoisomers that can arise from a particular set of substituents.

[0020] As used herein, the term "contacting" is used to describe compositions, processes, and methods in which materials or components are combined in any order, manner, and duration, unless otherwise specified. For example, materials or components can be blended, mixed, slurried, dissolved, reacted, processed, compounded, or otherwise contacted or combined by other methods, or suitable methods or techniques.

[0021] For the components of the compositions described herein and the amounts of other physical properties, the terms "substantial" or "about" may be used to indicate a degree. For example, a substantially soluble substance need not be purely soluble and may be expected to have some insolubility. Dimensions, ratios, and other measurable quantities should be understood to be approximately determined by processing variations, manufacturing variations, measurement limitations, etc. "High purity" materials described herein are understood to represent a higher purity than the typical conventional purity of the material and can be higher than 80%, 90%, 95%, or 99%, and even strongly depend on the resulting material.

[0022] Methods, devices, and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, but typical methods, devices, and materials are described herein.

[0023] All documents and patents mentioned herein are incorporated herein by reference in their entirety for the purpose of describing and disclosing, for example, the construction concepts and methodologies described in the documents and patents, and may be used in connection with the presently described invention.

[0024] Several types of ranges are described in this invention. Where any type of range is described or claimed, the intent is to individually disclose or assert each possible numerical value that the range reasonably may encompass, including the endpoints of the range, as well as the subranges and combinations of subranges that are included within that range. For example, where solubility within a particular range is described or asserted, the intent is to describe or assert all possible numerical values ​​that such a range may encompass, consistent with the description herein. For example, a description of solubility in the range of 0.01 mol / L to 10 mol / L, as used herein, represents solubility in the ranges of 0.1 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, or 10 mol / L, and any range between those two numbers (e.g., 1 mol / L to 2 mol / L). The unit "M" also represents "moles per liter" and is used interchangeably with "mol / L".

[0025] Generally, quantities, sizes, formulations, parameters, ranges, or other quantities or characteristics are "about" or "approximate," whether explicitly stated or not. Whether modified by the terms "about" or "approximate," the claims include equivalents to the quantities or characteristics.

[0026] Detailed description of the invention The following information describes embodiments with reference to the attached figures, but these can be embodied in many different forms and should not be construed as being limited to the illustrated embodiments described herein.

[0027] This specification relates to an electrochemical method comprising the steps of: preparing an aqueous solution containing a first redox active species having the properties and functions of a soluble shuttle in a first tank of an electrochemical system, which is fluid-coupled to the cathode; preparing an oxidizable species in a second tank of an electrochemical system, which is fluid-coupled to the anode; circulating the aqueous solution from the first tank to the cathode and the oxidizable species from the second tank to the anode; applying a reduction voltage to electrochemically reduce the soluble shuttle and electrochemically oxidize the oxidizable species; and adding a Negorite raw material and a Negorite reagent to the first tank. In certain embodiments, the soluble shuttle may have a lower reduction potential than the Negorite raw material, and the Negorite raw material is reduced by reaction with the reduced soluble shuttle, thereby producing a reduced Negorite raw material and an oxidized soluble shuttle as reactive intermediates, the latter remaining in the solution.

[0028] This specification also relates to anthraquinones having an amine group which may be an unsubstituted amine, a monoalkylated amine, or a dialkylated amine, which are substituted at position 1 with a hydroxyl group or an amine group and have no substituent at position 2; substituted dihydroxyanthracenes which are equivalent to reduced substituted anthraquinones; secondary quinones which have a lower reduction potential than substituted anthraquinones and are more than 0.1 mol / L soluble in water at pH 14; negolite reagents; generated RFB negolite; bases such as sodium hydroxide or potassium hydroxide; and aqueous negolite solutions containing water.

[0029] This specification relates to an electrochemical system for performing electrochemical reactions that generate electric current as an energy storage device. In certain embodiments, the system described herein may include a separate electrochemical cell, a first tank fluidly connected to the cathode of the separate electrochemical cell, a second tank fluidly connected to the anode of the separate electrochemical cell, and a number of pumps for circulating and returning the contents of each tank to and from the respective electrodes. In certain embodiments, the first tank may contain an aqueous solution of negolite as described herein. In other embodiments, the second tank may contain an oxidizable species capable of supplying electrons to the cathode upon contact with the anode.

[0030] In the prior art, among the various types of quinones reported for flow batteries, anthraquinones produced by the Marschalk reaction (chemically or electrochemically, as described in the '079 application) have known utility as negolites in the electrochemical process in redox flow batteries. Generally, the method proceeds according to Scheme 1 below, using 1,8-DHAQ as an example of a negolite starting material in the presence of a base to produce 1,8,9,10-tetrahydroxyanthracene, a reduced, reactive intermediate of the negolite starting material. 1,8,9,10-tetrahydroxyanthracene reacts with glyoxylic acid (as an example of a negolite reagent) to produce a second intermediate, which is then disproportionated. The resulting quinone is reduced again and disproportionated a second time to produce a third intermediate, producing the RFB negolite, 2,7-bis(carboxymethyl)-1,8-dihydroxyanthraquinone (1,8-DCDHAQ). A similar process exists for 1-hydroxyanthraquinone, where the first disproportionation process does not require a second reduction and disproportionation, directly producing the desired product, 2-(carboxymethyl)-1-hydroxyanthraquinone. [ka]

[0031] The above process requires the oxidative and reducing dissolution of the negorite raw materials and subsequent intermediates in a basic aqueous solution, thereby enabling efficient transport to the electrochemical system for the reduction reaction. However, some negorite raw materials, such as 1,8-DHAQ, have low solubility in basic aqueous solutions, limiting the final concentration of the resulting RFB negorite. The method described herein can obtain a more concentrated resulting RFB negorite without requiring additional cumbersome process steps, and by further advancing and completing the electrochemical process, it may be possible to eliminate the need for a downstream evaporation step to concentrate the negorite product. In certain embodiments, as described in Scheme 2, the compound used as a solubility shuttle may be present in the negorite mixture or solution and acts to improve the apparent solubility of the negorite raw materials. Generally, the solubility shuttle may have a reduction potential comparable to or more negative than that of the raw materials, thereby allowing the solubility shuttle to be reduced in the electrochemical system, subsequently reducing the negorite raw materials from a more soluble oxidized form to a reduced form (i.e., reduced negorite raw materials). As shown below, a small amount of THAQ as a soluble shuttle is supplied to the electrochemical system and may be reduced to hexahydroxyanthracene, which then reacts with 1,8-DHAQ located outside the cell to produce 1,8,9,10-tetrahydroxyanthracene. Compared to the oxidized form 1,8-DHAQ, 1,8,9,10-tetrahydroxyanthracene has higher solubility in aqueous solution and reacts with glyoxylic acid to further reduce and disproportionate reactions, as shown in Scheme 1 above, to produce 1,8-DCDHAQ in high concentrations. During or after the reaction pathway, the soluble shuttle can be regenerated by electrochemical reduction at the cathode of the same electrochemical system or a second electrochemical system (in other words, reduced back from the oxidized form). Alternatively, the soluble shuttle can be chemically regenerated by adding a reducing agent or by catalytic hydrogenation. [ka]

[0032] In another embodiment, as described in Scheme 3, the resulting RFB negolite is itself a soluble shuttle compound. Here, 1,8-DCDHAQ is replaced by THAQ, and the remainder of the reaction proceeds as in Scheme 2. If the soluble shuttle is also the resulting RFB negolite, the reaction mixture must first be "seeded" along with the amount of resulting RFB negolite present. [ka]

[0033] The processes described in Schemes 1-3 are not limited to 1,8-DHAQ as the Negolite starting material, but can be extended to any anthraquinone that can undergo the Marschalk reaction chemically or electrochemically. This applies to anthraquinones that are substituted with a hydroxyl or amine group at position 1 and unsubstituted at position 2, where the amine group may be an unsubstituted amine, a monoalkylated amine, or a dialkylated amine. Examples of Negolite raw materials include 1,3-DHAQ, 1,4-DHAQ, 1,5-DHAQ, 1,6-DHAQ, 1,7-DHAQ, 1,8-DHAQ, 1-hydroxyanthraquinone (1-HAQ), 1,3-diaminoanthraquinone (1,3-DAAQ), 1,4-DAAQ, 1,5-DAAQ, 1,6-DAAQ, 1,7-DAAQ, 1,8-DAAQ, 1-aminoanthraquinone (1-AAQ), 1-hydroxy-4-aminoanthraquinone, 1-hydroxy-5-aminoanthraquinone, 1-hydroxy-8-aminoanthraquinone, and many combinations thereof in which the amino group is optionally monosubstituted or disubstituted.

[0034] In other embodiments of the present invention, as described in Scheme 4 and separately in a jointly owned application relating to reductive amination, titled "System and Process for Electrochemical Functionalization of Substituted Anthraquinones," filed on the same date as this specification, some amines may follow an alternative pathway under certain reaction conditions. Instead of the Marschalk reaction, diaminoanthraquinones form imines with negolite reagents, which are then reduced to amines in a disproportionation reaction. This process is not a Marschalk reaction, but rather a reductive amination reaction. [ka]

[0035] However, even if the resulting RFB negolite is produced by one or more reductive amination reactions, or a combination of an amination reaction and a Marschalk reaction, the invention of using a soluble shuttle remains available, as shown in Scheme 5. This applies to anthraquinones substituted with one or more amine groups, where the amine group may be an unsubstituted amine or a monoalkylated amine. Examples of negolite starting materials include 1-AAQ, 1,2-DAAQ, 1,3-DAAQ, 1,4-DAAQ, 1,5-DAAQ, 1,6-DAAQ, 1,7-DAAQ, 1,8-DAAQ, 1-AAQ, 1-hydroxy-4-aminoanthraquinone, 1-hydroxy-5-aminoanthraquinone, 1-hydroxy-8-aminoanthraquinone, and many combinations thereof, where the amino group is optionally monosubstituted, such as 1-(methylamino)anthraquinone, 1-(carboxymethylamino)anthraquinone, etc. [ka]

[0036] The methods described herein may be carried out using the electrochemical systems described herein. Generally, the electrochemical system may include a set of isolated electrochemical cells or a stack containing a number of isolated electrochemical cells, a first tank fluidly connected to the cathode of the cells or stack, and a second tank fluidly connected to the anode of the cells or stack. The system may further include a power supply unit for supplying power and potential to various elements, and pumps for circulating and returning the contents of each tank to each electrode. In certain embodiments, the cells, including the cells or stack, are separated by junctions, which may be cation exchange membranes, anion exchange membranes, bipolar membranes, or porous separators. The first tank is designed to contain the cathode electrolyte, and the second tank is designed to contain the anode liquid.

[0037] In another embodiment, the second tank contains a chemical species (which is oxidized in the process) capable of supplying electrons to the anode and supplying them from the anode to the cathode (e.g., water, potassium ferrocyanate, sodium ferrocyanate, hydrazine, etc.).

[0038] The system may further include bypasses that allow fluids to be circulated through each tank using existing pumps without entering a cell or stack. The system may also include any number of heating components associated with the first or second tank or electrochemical cell to provide temperature control for reagents in electrochemical reactions or storage.

[0039] The system may further include components or subsystems located between the first tank and the cell or stack for further separating insoluble suspended material from the first tank, so that all or substantially all insoluble suspended material is separated from the cell or stack and returned to the first tank, with only liquid entering the cell or stack. Such components or subsystems include filtration, centrifugation, and hydrocyclone separators. Examples of filters include screw presses, filter presses, inline filters, filter bags, and filter cartridges. Examples of centrifugation include decanter centrifugation, bowl centrifugation, or tubular centrifugation.

[0040] The methods described herein may therefore include a step of incorporating a solubility shuttle into a conventional electrochemical process, achieving remarkable improvements in solubility and leading to increased reagent and product concentrations, as well as overall reaction efficiency.

[0041] In some aspects of the present invention, the Negolite raw material has solubility in a cathode electrolytic aqueous solution of 1.0 mol / L, 0.75 mol / L, 0.5 mol / L, 0.25 mol / L, 0.1 mol / L, 0.05 mol / L, 0.02 mol / L, 0.01 mol / L, 0.005 mol / L, 0.002 mol / L, or less than 0.001 mol / L.

[0042] In a particular aspect of the present invention, the reduced Negorite raw material (i.e., the reduced Negorite raw material) has solubility in a cathode electrolytic aqueous solution of 0.01 mol / L, 0.02 mol / L, 0.05 mol / L, 0.1 mol / L, 0.25 mol / L, 0.5 mol / L, 0.75 mol / L, or greater than 1.0 mol / L.

[0043] In some aspects of the present invention, both the oxidizing soluble shuttle and the reducing soluble shuttle have solubility in a cathode electrolytic aqueous solution of 0.01 mol / L, 0.02 mol / L, 0.05 mol / L, 0.1 mol / L, 0.25 mol / L, 0.5 mol / L, 0.75 mol / L, or greater than 1.0 mol / L.

[0044] In a particular aspect of the present invention, all reaction intermediates, in their oxidized or reduced forms, have solubility in a cathode electrolytic aqueous solution of 0.01 mol / L, 0.02 mol / L, 0.05 mol / L, 0.1 mol / L, 0.25 mol / L, 0.5 mol / L, 0.75 mol / L, or greater than 1.0 mol / L.

[0045] In some embodiments of the present invention, the Negolite material may be added to the cathode electrolytic solution as a solid (powder, lump, flake, etc.), as a slurry with a fluid, or in a molten state, or the cathode electrolytic solution may be added in place of the Negolite material. An external mixing vessel, separate from the first tank of the electrochemical system, may be used. Mixing may be achieved in various ways, such as by using a screw mixer, paddle mixer, wax or high-shear mixer, planetary mixer, etc. Dissolution or mixing may be assisted by other methods, such as the use of ultrasound, heating, high, low or neutral pH, bases or alkalis with mixed cations (such as sodium hydroxide and potassium hydroxide), acids with mixed anions (such as hydrochloric acid and sulfuric acid), salts or mixtures thereof.

[0046] In certain embodiments of the present invention, the anolyte in the second tank may additionally contain auxiliary salts or mixtures thereof. If the reaction replacing the anode is a proton-conjugated reaction (e.g., generating protons, consuming protons, generating hydroxides, or consuming hydroxides), the second tank may additionally contain a base or alkali with a single or mixed cation (such as sodium hydroxide and potassium hydroxide) or an acid with a single or mixed anion (such as hydrochloric acid and sulfuric acid). Furthermore, if the reaction replacing the anode is a proton-conjugated reaction, the pH of the anolyte may change as acid is generated or hydroxides are consumed. In further embodiments of the reaction, the concentration of the acid or base in the anolyte is maintained, if necessary, by periodic or continuous addition of the acid or base. The acid or base may be added as a solid, net liquid, concentrated solution, or diluted solution. The base may also be a reagent such as sodium hydroxide or metallic sodium that reacts with water to form hydroxide ions. The concentration of acid or base in the anodelite may differ from the concentration of acid or base in the cathode electrolyte. The counterions of acid or base in the anodelite may differ from the counterions of acid or base in the cathode electrolyte. In some embodiments of the present invention, the anodelite may contain an acid, although the cathode electrolyte contains a base; in other embodiments, the anodelite may contain a base, although the cathode electrolyte contains an acid.

[0047] In some embodiments of the present invention, ions are conducted across the junctions of separated electrochemical cells. The movement of ions is a phenomenon that involves the movement of water, which is known as electroosmosis. This has the tendency to move water in the direction of ion movement. In addition, water can be produced or consumed by electrochemical reactions at the anode. Acids or bases can be added throughout the process operation in a concentration or physical state (e.g., solid rather than solution) selected so that the volume of the anolyte, or the proton or hydroxide ion concentration, or both the volume and the proton or hydroxide ion concentration remain substantially constant.

[0048] In a particular embodiment, the method may involve filling a first tank with an aqueous solution of a soluble shuttle at a low concentration, for example, 0.001 to 0.1 mol / L, circulating the solution in the first tank to the cathode and the liquid or solution in the second tank to the anode, and applying a voltage so that the soluble shuttle is electrochemically reduced and the contents of the second tank are electrochemically oxidized (for example, water is converted to oxygen and protons, sodium ferrocyanate is converted to sodium ferricyanide, hydrazine is converted to nitrogen, etc.).

[0049] In other embodiments of the present invention, particularly when the soluble shuttle is the same as the generated RFB negolite, the soluble shuttle may be employed in a process designed to increase the overall volume of the cathode electrolyte, but not substantially alter the concentration of the generated RFB negolite (or soluble shuttle) in the cathode electrolyte, with a high initial concentration of 0.5–1.5 mol / L, 0.7–1.2 mol / L, or 0.9–1.1 mol / L.

[0050] In other embodiments of the present invention, the process may be operated as a batch, semi-batch, or continuous flow process. For example, instead of all being present at the start of the process, additional Negorite raw materials and Negorite reagents may be added to the cathode electrolyte continuously as the current passes through the electrochemical system, and some portion of the cathode electrolyte flow present in the electrochemical system is removed for downstream processing (e.g., further concentration by an evaporator, filter, etc.) and use as RFB active material, and additional KOH / NaOH may be added to the anodelite.

[0051] After a certain amount of time has elapsed, or after a certain amount of charge has flowed, the Negorite raw material and Negorite reagent (e.g., glyoxylic acid) are added to the first tank at a rate approximately equivalent to the rate at which charge (i.e., current) passes through the cell or stack, taking into account the appropriate stoichiometry between the number of electrons required for the reduction of the Negorite reagent and the Negorite raw material. The rate of addition, the current to the cell or stack, and the flow rate of the solution in the first tank should be controlled to minimize the amount of insoluble solid entering the cell or stack.

[0052] After a reference time has elapsed, or a reference charge has flowed, or a reference amount of Negorite material has been added, the flow of current is stopped. At this point, the method described herein may continue to circulate the solution in the first tank for a predetermined time without the flow of current. The temperature at this stage may be adjusted. After the Negorite material has been completely converted to generated RFB Negorite, the generated RFB Negorite may be concentrated, isolated, or purified, if desired, using methods typical to those skilled in the art, such as evaporation, distillation, drying, neutralization, precipitation, centrifugation, filtration, washing, and recrystallization.

[0053] Alternatively, a bypass may be used, in which the fluid flows from the first tank and passes through the bypass instead of through the cell or stack. In such an embodiment, stoichiometric or substoichiometric amounts of Negorite raw materials and Negorite reagents may be added. The contents of the first tank may be circulated through the bypass until the insoluble solid contents fall to a threshold concentration. The bypass can then be shut off, allowing the fluid from the first tank to return to the cell or stack and the current to be restored. In some embodiments, the bypass takes the form of a hydrocyclone separator, where the underflow with concentrated suspended solids is returned to the first tank, and the overflow from which the suspended solids have been removed is directed towards the cell or stack, or shut off from the cell or stack as needed.

[0054] The above process may be repeated until a standard amount of charge has passed through, or a standard amount of Negorite raw material has been added, or a standard concentration of generated RFB Negorite has been obtained. This alternative method is particularly useful when the Negorite raw material dissolves slowly.

[0055] While not bound by theory, the methods and systems described herein are considered to have the following advantages: Compared to conventional methods, the methods described herein can achieve high concentrations of generated RFB negolite without using special electrochemical cells resistant to suspended solids.

[0056] In certain embodiments, the soluble shuttles described herein, in both reduced and oxidized forms, have high solubility in water at the operating pH, for example, greater than 0.1 mol / L at pH 14. In other embodiments, soluble shuttles having a lower negative standard reduction potential than the Negorite starting material may nevertheless have a lower negative reduction potential than the Negorite starting material under non-standard operating conditions (temperature, pH, concentration, solvent, etc.). Examples of potential soluble shuttles include quinones (e.g., substituted benzoquinones, substituted naphthoquinones, and substituted anthraquinones), substituted flavins, substituted phenazines, viologens, non-organic species such as chromium(II) / chromium(III), metal coordination complexes such as ethylenediaminetetraacetate chromium(II) / chromium(III), and others readily apparent to those skilled in the art.

[0057] In addition, since the reaction between the reduced soluble shuttle and the Negorite raw material, which produces an oxidized soluble shuttle and a reduced Negorite raw material, is in equilibrium, the reduction potential of the soluble shuttle does not need to be less negative than the reduction potential of the Negorite raw material. If the reduction potential of the soluble shuttle is equal to or comparable to the reduction potential of the Negorite raw material (e.g., 1mV, 2mV, 5mV, 10mV, 20mV, 40mV, 60mV, 80mV, 100mV, or 120mV at most, or less negative than the Negorite raw material), then, according to the Nernst formula, a portion of the Negorite raw material is still reduced, producing a reactive intermediate that is the reduced Negorite raw material. For example, if the soluble shuttle has a reduction potential 14mV less negative than the Negorite raw material, the reduced Negorite raw material will still exist in equilibrium in a ratio of approximately 1:3 to the Negorite raw material. The reduced Negorite raw material then reacts with the Negorite reagent to produce different chemical species. The continued consumption of the reduced Negolite raw material eventually pushes the aforementioned parallel to the right, continuing until all the Negolite raw material is completely reduced and then converted into another soluble chemical species.

[0058] The above-described solubility shuttle may be usable in electrochemical processes involving a variety of reagents and reactants. In certain embodiments, the Negolite reagent may be an aldehyde or ketone when the quinone is substituted with an amino group, or an amine (as defined in the co-owned application for reductive amination filed concurrently with this specification, titled "System and Process for Electrochemical Functionalization of Substituted Anthraquinones") when the quinone is substituted with a carbonyl group, or an interconvertible aldehyde or ketone such as glucose or fructose. Examples of Negolite starting materials include quinones (e.g., substituted benzoquinones, substituted naphthoquinones, and substituted anthraquinones). [Examples]

[0059] This disclosure is further illustrated by the following embodiments, which should not be construed as limiting the scope of the invention in any way. There are various other aspects, embodiments, modifications, and equivalents that a person skilled in the art may come up with after reading this specification without departing from the spirit of the invention or the scope of the appended claims.

[0060] Raw materials and general procedures 200cm 2The "MP Cell" (ElectroCell) was generally assembled as shown in the schematic diagram in Figure 1. The MP Cell had a carbon cathode between two nickel anodes, a Nafion 115 membrane separating the MP Cell chamber, a polypropylene flow frame, and an EPDM gasket. During operation, the contents of the cathode container ("cathode electrolyte," or reaction mixture) were reduced, and oxygen gas was released at the anode. The cell was operated in recirculation mode, and the cathode electrolyte and anolyte were continuously pumped into the electrochemical cell and returned to their original containers. The cathode electrolyte container had a volume of approximately 2 L and was kept in an inert atmosphere (N2 gas) to suppress re-oxidation of the reaction mixture by oxygen in the atmosphere. The anolyte container had a volume of approximately 2 L and was open to the atmosphere. Both containers were insulated and equipped with heater tape and reflux condenser. An external mixing vessel (2L, three-necked round-bottom flask, heating mantle, and overhead stirrer) was connected to a bidirectional peristaltic pump that transported the mixture back and forth between the mixing vessel and the cathode electrolyte vessel. The speed and direction of mixing were controlled. A syringe pump and tubing were introduced to supply glyoxylic acid to the cathode electrolyte vessel. The syringe could be increased in up to 60 mL increments, and the rate of addition could be controlled. The glass external mixing vessel was equipped with a syringe line for sample collection.

[0061] The following materials were obtained from designated suppliers and used without purification: 1,3,5,7-tetrahydroxyanthraquinone (THAQ) was obtained from Sinoconvoy New Material, Co., Ltd. (China), and 1,8-dihydroxyanthraquinone (1,8-DHAQ), 96%, was obtained from Atul Ltd. (India). NaOH, 45% in water, KOH, 50% in water, and HPLC solvent were obtained from Sigma-Aldrich. Glyoxylic acid, 50% in water, "cosmetic grade," was obtained from Jinan Huashihang Chemical Co., Ltd. (China). Sodium ferrocyanide decahydrate and potassium ferrocyanide trihydrate were obtained from Kodia Chem Ltd. (China).

[0062] High-performance liquid chromatography (HPLC) measurements were performed using an Agilent-1100 Series HPLC equipped with a UV detector and an Agilent ZORBAX SB-C18 column. Product purity was determined using the peak integrated area % at 254 nm. HPLC method information: flow rate 1.0 mL / min, total run time 30 minutes, mobile phase A: water with 0.1% v / v trifluoroacetic acid, mobile phase B: acetonitrile with 0.1% v / v trifluoroacetic acid, solvent gradient 90:10 A:B to 10:90 A:B and back to 90:10 A:B, column oven temperature 40°C, 3.0 μL injection volume. Samples for HPLC analysis were prepared from 20–50 mM solutions of potassium hydroxide or sodium hydroxide in a 1 mM solution in a 50:50 A:B mixture.

[0063] (Example 1) Using cell hardware purchased from Fuel Cell Technologies, along with AvCarb EP40 pre-activated carbon paper electrodes, EPDM gaskets, and FuMATech E-620(K) cation exchange membranes, a geometric electrode area of ​​50 cm² was constructed. 2 An RFB cell was constructed. The anode liquid container was filled with 500 mL of aqueous solution containing 0.3 mol / L sodium ferrocyanate, 0.3 mol / L potassium ferrocyanate, 0.5 mol / L NaOH, and 0.5 mol / L KOH. The cathode electrolyte container (without a mixing vessel) was filled with 100 mL of aqueous solution containing 0.1 mol / L THAQ, 1.9 mol / L NaOH, and 1.9 mol / L KOH, and was equipped with a magnetic stirrer. Both the anode liquid and cathode electrolyte containers were maintained under nitrogen.

[0064] Transport to the electrochemical cell was initiated (peristaltic pump, flow rate ~50 mL / min), and the cathode electrolyte and anode solution were heated to 50°C. The current was increased rapidly when the cell voltage exceeded approximately ~1.6V, and the current density was kept at 50 mA / cm² until 2 molar equivalents of electrons per mole of THAQ present had passed through. 2 It was then subjected to a constant current flow.

[0065] While maintaining a temperature of 50°C, the current and pump were shut off, and 1.92 g of 1,8-DHAQ (8 mmol) was added to the cathode electrolyte container under a flow of nitrogen gas. After stirring for 15 minutes, 2.21 mL of 50% glyoxylic acid (20 mmol) was added dropwise over 1 minute, and stirring was continued for another 15 minutes.

[0066] Next, restart the pump and set the current to 50mA / cm². 2 The process was restarted. After 6 molar equivalents of charge had passed over the added 1,8-DHAQ, the current and pump were stopped again when the cell voltage rose sharply above approximately 1.6V. Five consecutive additions of 1,8-DHAQ (1.92g each), followed by 50% glyoxylic acid (1.10mL each), and the application of current were repeated in the same manner.

[0067] At this point, the cathode electrolyte contained ~125 mL of THAQ at a concentration of 0.08 mol / L, 1,8-DCDHAQ at a concentration of 0.32 mol / L, and total excess hydroxide at a concentration of ~1 mol / L. The cathode electrolyte was then discharged from the cathode electrolyte chamber and mixing vessel. The discharged cathode electrolyte was exposed to air. A 0.4 mol / L quinone solution (containing THAQ and 1,8-DCDHAQ) can be used as is as flow cell negolite without further purification or processing.

[0068] (Example 2) The above MP Cell was used to electrochemically synthesize DCDHAQ from 1,8-DHAQ using 1,8-DCDHAQ as a soluble shuttle, as summarized in Scheme 1 and Scheme 3 above. Generally, the Negolite starting material 1,8-DHAQ reacts with the Negolite reagent glyoxylic acid to produce 1,8-DCDHAQ.

[0069] The anode liquid container was filled with 400 mL of DI water, 306 mL of 50% NaOH (5.82 mol), and 499 mL of 45% KOH (5.82 mol). The cathode electrolyte container and mixing container were filled with a mixture carried over from previous experiments: ~400 mL of 0.7 mol / L 1,8-DCDHAQ, excess hydroxide concentrations of 0.35 mol / L NaOH and 0.35 mol / L KOH (280 mmol), 313.8 mL of 50% NaOH (5964 mmol, 3.55 equivalents relative to 1,8-DHAQ), 511.7 mL of 45% KOH (5964 mmol, 3.55 equivalents), and enough water (~400 mL) to bring the solution volume to ~1600 mL. Approximately half of the cathode electrolyte was in the cathode electrolyte container and the other half was in the mixing container. A syringe pump was prepared with 390 mL (522.4 g, 3528 mmol, 2.1 equivalents) of 50% glyoxylic acid, and the solution was added in multiple 60 mL increments.

[0070] The upper spaces of the cathode and mixing vessels were purged with nitrogen for approximately 5 minutes and maintained under an inert atmosphere. The anode vessel was opened to air. The pump to the electrochemical cell was started (peristaltic pump, flow rate approximately 100 mL / min), and the cathode electrolyte and anode solution were heated to 50°C. The current was increased to a current density of 50 mA / cm² across the carbon cathode until 2 molar equivalents of electrons per mole of 1,8-DCDHAQ had passed through, indicated by a rapid increase in cell voltage above approximately 2.0 V. 2 It was then subjected to a constant current flow.

[0071] While maintaining a temperature of 50°C, the current and transfer pump were shut off, and 30.0 grams of 1,8-DHAQ (125 mmol) were added to the mixing chamber under a flow of nitrogen gas. After stirring for 10 minutes, the transfer pump was turned on at a rate of 5 mL / min, and the syringe pump began adding 50% glyoxylic acid solution at a rate of ~14.5 mL / hour (slightly chemically in excess relative to the current), and the current was set to 50 mA / cm² relative to the carbon cathode. 2The process was restarted. Using a rapid increase in cell voltage above approximately 2.0V as an indicator, the current, transfer pump, and syringe pump were stopped after 6 molar equivalents of charge had passed over the added 1,8-DHAQ. In the same manner, 1,8-DHAQ (60.0 g, 120.0 g, and 193.6 g) was added three times in a row. Since each addition of 1,8-DHAQ was larger than the last, the amount of glyoxylic acid added in each cycle was also proportionally larger.

[0072] At this point, the Negolite contained approximately 2800 mL of DCDHAQ at a concentration of 0.7 mol / L. The cathode electrolyte solution was then discharged from the cathode electrolyte chamber and mixing vessel. The discharged cathode electrolyte solution was exposed to air and concentrated to a concentration of 1 mol / L DCDHAQ (and therefore free hydroxide) under vacuum or in a thermal evaporator. The 1 mol / L solution can be used as is as flow cell Negolite without further purification or processing.

[0073] (Example 3) The above MP Cell was used to perform the electrochemical synthesis of DCDHAQ from 1,8-DHAQ using 1,8-DCDHAQ as a soluble shuttle, as summarized in Scheme 1 and Scheme 3 above.

[0074] The anode liquid container was filled with a mixture of 400 mL of DI water, 306 mL of 50% NaOH (5.82 mol), and 499 mL of 45% KOH (5.82 mol). The cathode electrolyte container was filled with 2.2 L of a solution containing 0.64 M 1,8-DCDHAQ (1.408 mol) and 3.5 M hydroxide (equivalent to 0.95 M free hydroxide) with a Na:K ratio of ~1:1, at 50°C for ~3 hours at 10 A (50 mA / cm²) until a charge of 22.4 Ah (0.836 mol electrons) passed through. 2The solution was reduced at the cathode of an MP cell. The solution was then transferred to a mixing vessel containing 50.2 g of solid 1,8-DHAQ (96% purity by HPLC, 0.201 mol relative to the analyte purity). Both the cathode electrolyte vessel and the mixing vessel were purged with nitrogen. The solution / solid was stirred for approximately 30 minutes, enough time for all 1,8-DHAQ to dissolve. Then 60 mL of 50 wt% glyoxylic acid was added at a flow rate of 1 mL / min. The solution was stirred for one hour before being returned to the cathode electrolyte vessel. An additional 2 equivalents of charge (11.2 Ah, 0.418 mol of electrons) were passed over the solid 1,8-DHAQ, and the solution was reacted overnight at 50°C. The solution was then completely discharged using an electrochemical cell. Approximately 2.25 L of a solution containing 0.71 M of 1,8-DCDHAQ (1.598 mol) was prepared. The solution contained 1.87 M of sodium, 1.92 M of potassium, and ~0.95 M of free hydroxide.

[0075] It should be noted that during the passage of the current, additional sodium and potassium were transported from the anolyte through the cation exchange membrane. Additional hydroxides were generated through disproportionation reactions, and the addition of 1,8-DHAQ and glyoxylic acid precisely offset the amount of hydroxide consumed.

[0076] The method can be repeated to produce more DCDHAQ. Additional solution was discharged from the cathode electrolyte chamber and mixing vessel. The discharged cathode electrolyte solution was exposed to air and concentrated to a concentration of 1 M 1,8-DCDHAQ by vacuum or thermal evaporator. The 1 M solution can be used as is as flow cell negolite without further purification and processing. Alternatively, a 0.69 M 1,8-DCDHAQ solution can be used to increase the concentration without evaporation of downstream water.

[0077] The tested solubility shuttles, despite having only slightly negative reduction potentials, were able to act on and “dissolve” the Negorite raw materials more quickly than expected in each case. “Dissolution” as used herein means that the Negorite raw material is converted from a solid to several forms in solution, including dissolving the raw material in both oxidized and reduced forms (i.e., reactive intermediates, or reduced Negorite raw materials). Generally, the more negative the reduction potential of the solubility shuttle compared to the Negorite raw material, the greater the thermodynamic driving force for the dissolution of the Negorite raw material. In the case of 1,8-DCDHAQ and 1,8-DHAQ, despite the nearly identical reduction potentials of the two species, the reaction product unexpectedly acted as an effective solubility shuttle. This likely results in high concentrations of the solubility shuttle and low concentrations of dissolved Negorite raw material leading to an additional thermodynamic driving force for the redox-mediated dissolution process, or what is commonly known as the reaction quotient Q in the Nernst equation. Conversely, in the absence of an arbitrary initial solubility shuttle, negolite raw materials such as 1,8-DHAQ are extremely difficult to completely dissolve in a basic aqueous solution, often causing malfunctions in the electrochemical cell due to clogging.

[0078] While preferred embodiments and models of the Disclosure have been described herein, those skilled in the art will readily conceive of variations and equivalents of the disclosed concepts. However, such variations and equivalents are intended to be within the scope of the claims appended herein.

Claims

1. A method for manufacturing a redox flow cell (RFB) Negolite: A step of reacting a reduced soluble shuttle with a Negorite raw material to produce a reduced Negorite raw material and an oxidized soluble shuttle; and The process includes reacting a reduced Negorite raw material with a Negorite reagent to produce RFB Negorite, or a Negorite intermediate that is subsequently converted to the resulting RFB Negorite; The reduced Negolite raw material has higher water solubility than the original Negolite raw material. A manufacturing method comprising a soluble shuttle having a reduction potential comparable to or more negative than that of the Negolite raw material, thereby reducing the Negolite raw material through reaction with the soluble shuttle to produce reduced Negolite raw material.

2. The method according to claim 1, wherein the reaction of the soluble shuttle and the Negorite raw material includes the step of mixing the Negorite raw material with an aqueous solution containing a reduced soluble shuttle.

3. The process involves the reaction of reduced Negorite raw materials and Negorite reagents to produce a Negorite intermediate: The method according to claim 1, comprising the step of forming a second aqueous solution containing reduced Negorite raw material and Negorite reagent in an aqueous solution.

4. The method according to claim 3, wherein the Negorite intermediate has higher solubility than the Negorite raw material reduced in an aqueous solution.

5. The method according to claim 1, further comprising the step of regenerating a soluble shuttle by reducing an oxidized soluble shuttle to a reduced soluble shuttle.

6. The regeneration process for the soluble shuttle is: A step of circulating an aqueous solution containing an oxidizing soluble shuttle to the cathode of a separated electrochemical cell; A step of circulating an aqueous solution containing oxidizable species to the anode of a separated electrochemical cell; and The process includes the step of applying a voltage between the cathode and the anode, The method according to claim 1, wherein the soluble shuttle is converted from an oxidized form to a reduced form at the cathode, and the oxidizable species is oxidized at the anode.

7. The method according to claim 1, wherein the reaction of the soluble shuttle and the Negorite raw material includes the step of mixing an aqueous solution containing a reduced soluble shuttle with the Negorite raw material in a stirrer.

8. The oxidized form of the Negolite raw material has solubility in aqueous solution at concentrations of 0.1 M, 0.2 M, 0.5 M, or less than 1.0 M; The reduced Negolite raw material has solubility in aqueous solution of 0.01 M, 0.1 M, 0.2 M, 0.5 M, or greater than 1.0 M; or The method according to claim 1, which is a combination of those.

9. The method according to claim 1, wherein a soluble shuttle is generated in situ.

10. The formation of the soluble shuttle is: A step of preparing an aqueous solution containing a precursor of the soluble shuttle in the first tank of an electrochemical system, which is fluidly connected to the cathode; A process of preparing oxidizable species in a second tank of an electrochemical system, which is fluidly connected to the anode; A process of circulating an aqueous solution from the first tank to the cathode and oxidizable species from the second tank to the anode; and The method according to claim 9, wherein a voltage is applied between the cathode and the anode, thereby electrochemically reducing a soluble shuttle precursor to produce a soluble shuttle in oxidized or reduced form, and oxidizable species are electrochemically oxidized.

11. The method according to claim 6 or 10, wherein the oxidizable species includes water, and the application of voltage converts the water to oxygen and generates protons, or equivalently consumes hydroxide.

12. The method according to claim 11, wherein the oxidizable species includes a ferrocyanine compound.

13. The method according to claim 11, wherein the oxidizable species includes hydrazine.

14. The method according to claim 11, wherein the oxidizable species includes hydroquinone, a reduced form quinone derivative, dihydroxynaphthalene, or dihydroxyanthracene.

15. The method according to claim 1, wherein the raw material for Negolite is quinone.

16. The method according to claim 1, wherein the Negolite reagent is glyoxylic acid.

17. The method according to claim 1, wherein the soluble shuttle is 1,3,5,7-tetrahydroxyanthraquinone.

18. The method according to claim 1, wherein the soluble shuttle is the same as the generated RFB negolite.

19. The method according to claim 1, wherein the subsequent conversion of the negolite intermediate to RFB negolite includes disproportionation.

20. Separated electrochemical cells; A first tank fluid-connected to the cathode of a separated electrochemical cell; A second tank fluidly connected to the anode of a separated electrochemical cell; Multiple pumps that circulate and return the contents of each tank to their respective electrodes; and An electrochemical system including a separator located between the first tank and the separated electrochemical cells, An electrochemical system in which a separator receives a fluid containing suspended solids, generates a first separation fluid stream from which the suspended solids are removed and transferred to a separated electrochemical cell, and generates a second separation fluid stream from which the suspended solids are concentrated.

21. The electrochemical system according to claim 20, wherein the second separated fluid flow is returned to the first tank.

22. The electrochemical system according to claim 20, wherein the separated electrochemical cells are separated by a junction selected from a cation exchange membrane, an anion exchange membrane, a bipolar membrane, or a porous junction.

23. The electrochemical system according to claim 20, further comprising a first tank, a second tank, or a heater connected to both.

24. The electrochemical system according to claim 20, wherein the second tank comprises a chemical species, which is water, a ferrocyanide compound, or hydrazine, capable of supplying electrons to the anode.

25. The electrochemical system according to claim 20, further comprising a power supply device.

26. The electrochemical system according to claim 20, further comprising a bypass that allows the fluid to be circulated to each tank without entering a separate electrochemical cell.

27. The electrochemical system according to claim 20 or 21, wherein the separator includes a filter, a centrifuge, a hydrocyclone separator, or a combination thereof.

28. The electrochemical system according to claim 26, wherein the separator is located within the bypass.

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