Use of poly(hydroxy acrylic acid) in the electrolytic production of hydrogen peroxide, process for manufacturing hydrogen peroxide and electrochemical cell

Abstract

The present invention relates to the use of poly(hydroxy acrylic acid) or a salt thereof, in the production of a solution containing hydrogen peroxide by electrolysis, wherein the produced solution has an apparent pH of at least 8.0. Further, the invention relates to a process for manufacturing a solution containing hydrogen peroxide and poly(hydroxy acrylic acid) or a salt thereof, and to an electrochemical cell suitable for the inventive use and process.

Description

[0001] USE OF POLYfHYDROXY ACRYLIC ACID) IN THE ELECTROLYTIC PRODUCTION OF HYDROGEN PEROXIDE, PROCESS FOR MANUFACTURING HYDROGEN PEROXIDE AND ELECTROCHEMICAL CELL

[0002] TECHNICAL FIELD

[0003] The present invention relates to the use of poly(hydroxy acrylic acid) or a salt thereof in the electrolytic production of a solution containing hydrogen peroxide, to a process for manufacturing hydrogen peroxide and to an electrochemical cell suitable for the use and process.

[0004] TECHNICAL BACKGROUND

[0005] Hydrogen peroxide is one of the most important inorganic chemicals to be produced worldwide. Its industrial applications include textile, pulp and paper bleaching, organic synthesis (propylene oxide, caprolactam), the manufacture of inorganic chemicals and detergents, environmental and other applications. Synthesis of hydrogen peroxide is predominantly achieved by using the Riedl - Pfleiderer process (originally disclosed in U.S. Pat. Nos. 2,158,525 and 2,215,883), also called anthraquinone loop process or AO (auto-oxidation) process.

[0006] Hydrogen peroxide is used in various technical fields, also alkaline peroxide solutions are needed for specific purposes, like in the paper industry or for the domestic as a general bleaching agent and for disinfection. Recovered waste paper constitutes an important source of raw material for the papermaking industry. In general, is important to have starting pulp which has a sufficient degree of whiteness. This degree of whiteness can be achieved by resorting to so-called deinking or bleaching techniques which especially comprise a stage of disintegrating the waste paper in a pulper. Thus, it has been proposed to disintegrate the waste paper in disintegrators which function with high pulp consistencies. This operation only permits grinding and the pulps obtained must be subjected to subsequent chemical treatments in order to improve the release of the inks and / or to ensure that bleaching takes place. In order to improve the release of the inks in the disintegrator, it has been proposed to introduce basic deinking reactants into the disintegrator at the same time as the waste paper. In order to ensure that grinding, release of the inks and bleaching take place simultaneously, it has been proposed to use pulpers operating with lower pulp consistencies, not exceeding 8%, and to introduce into these at least one alkali and at least one peroxidic compound. These processes, which are generally effective, suffer from the disadvantage of requiring large amounts of reactants.

[0007] US 4,390,395 A relates to a process for the regeneration of waste paper which comprises the disintegration of the waste paper in a disintegrator directly fed from dry waste paper and functioning with a pulp consistency, at the disintegrator outlet, of between 22 and 45%, in the presence of an aqueous phase, and the improvement that at least one peroxidic bleaching agent in an amount between 0.1 and 5% by weight of the weight of the dry waste paper is introduced into the disintegrator at the same time.

[0008] It is known that peroxide solutions spontaneously decompose. The causes for such decomposition are thought to be (1) autodecomposition of the peroxide itself; and (2) catalytic decomposition caused by impurities in the peroxide solution.

[0009] Autodecomposition is commonly controlled by adjusting the pH of a peroxide solution to about 4.5 to 5.0, whereas catalytic decomposition is minimized by adding stabilizing agents to the peroxide solution. Suitable stabilizing agents are known to include such things as stannates, phosphates and 8-hydroxyquinoline.

[0010] US 4,431,494 and US 5,316,629 describe the use of EDTA as particularly suitable stabilizing agent in a process for the electrolytic production of alkaline peroxide solutions.

[0011] Electrochemical processes often use an alkaline electrolyte to produce an alkaline peroxide solution. The high pH of the electrolyte causes a substantial amount of the peroxide to decompose during electrolysis in the cell. Thus, electrical energy is wasted by producing peroxides which decompose before they can be recovered. This autodecomposition problem is compounded by the usual catalytic decomposition problem. Alternatively, electrochemical production of hydrogen peroxide can be performed under acidic conditions. Such conditions are described for instance in Berlinguette et al., “Direct H2O2 Synthesis, without H2 Gas”, J. Am. Chem. Soc. 2022, 144, 14548-14554; Perry et al., “Electrochemical synthesis of hydrogen peroxide from water and oxygen”, Nature Reviews Chemistry, June 2019.

[0012] CN 116 219 494 A discloses a method for preventing the deposition of cathode calcium and magnesium hydroxide during seawater electrolysis, including adding a metal ion chelating agent in seawater to complex the calcium and magnesium ions, wherein the metal ion chelating agent is at least one of a small molecule organic chelating agent and a polymer chelating agent.

[0013] Chaufer B et al: "Removal of metal ions by complexation-ultrafiltration using water-soluble macromolecules: perspective of application to wastewater treatment", Nuclear and Chemical Waste Management, vol. 8, no. 3, pages 175- 187 discloses that complexation of metal ions with water-soluble polymeric ligands and retention of the macromolecular complex by ultrafiltration afford a method of preconcentration of metal ions in homogeneous phase.

[0014] Convert et al: "Treatment of odorous sulphur compounds by chemical scrubbing with hydrogen peroxide-Application to a laboratory plant", Chemical Engineering Science, vol. 61, no. 22, pages 7240-7248 discloses that H2O2 decomposition in basic solutions has been investigated and slowed down by addition of the stabiliser poly-a-hydroxyacrylic acid.

[0015] SUMMARY OF THE INVENTION

[0016] The present invention relates to use of poly(hydroxy acrylic acid) or a salt thereof, in the production of a solution containing hydrogen peroxide by electrolysis, wherein the produced solution has an apparent pH of at least 8.0.

[0017] Furthermore, the present invention relates to a process for manufacturing hydrogen peroxide and to an electrochemical cell suitable for the use and process. DETAILED DESCRIPTION OF THE INVENTION

[0018] Before the use of poly(hydroxy acrylic acid) or a salt thereof, in the production of a solution containing hydrogen peroxide by electrolysis of the invention, the process for manufacturing hydrogen peroxide and the electrochemical cell of the invention will be described in detail, it is to be understood that this invention is not limited to specific process conditions described herein, since such conditions may, of course, vary.

[0019] It is also to be understood that the terminology used herein is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

[0020] As used herein, the term “in the production” means any point of time between providing an electrochemical cell for electrolysis and recovering and filing the obtained solution from the electrochemical cell. It also encompasses the preparation of solutions to be fed into the electrochemical cell and the subsequent addition of poly(hydroxy acrylic acid) or a salt thereof to the solution obtained by electrolysis. Preferably, “in the production” means “during production”, i.e., any point of time between providing an electrochemical cell for electrolysis and recovering the obtained solution from the electrochemical cell. The term “during production” encompasses the preparation of solutions to be fed into the electrochemical cell but not the subsequent addition of poly(hydroxy acrylic acid) or a salt thereof to the solution obtained by electrolysis.

[0021] As used herein, the singular forms "a", "an", and "the" include both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a compound" means one compound or more than one compound.

[0022] The terms "containing", "contains" and "contained of' as used herein are synonymous with "including", "includes" or " comprising", "comprises", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or process steps. It will be appreciated that the terms “containing”, “contains”, "comprising", "comprises" and "comprised of as used herein comprise the terms "consisting of, "consisting essentially of", "consists" and "consists of. Throughout this application, the term "about" is used to indicate that a value includes the standard deviation of error for the device or method being employed to determine the value.

[0023] As used herein, the term “average” refers to number average unless indicated otherwise.

[0024] As used herein, the terms “% by weight”, “wt.-%”, “wt%”, “weight percentage”, or “percentage by weight” are used interchangeably. The same applies to the terms “% by volume”, “vol.- %”, “vol. percentage”, or “percentage by volume”, or “% by mol”, “mol- %”, “mol percentage”, or “percentage by mol”.

[0025] The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1, 2, 3, 4 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of end points also includes the end point values themselves (e.g. from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.

[0026] All references cited in the present specification are hereby incorporated by reference in their entirety. In particular, the teachings of all references herein specifically referred to are incorporated by reference.

[0027] Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

[0028] In the following passages, different alternatives, embodiments and variants of the invention are defined in more detail. Each alternative and embodiment so defined may be combined with any other alternative and embodiment, and this for each variant unless clearly indicated to the contrary or clearly incompatible when the value range of a same parameter is disjoined. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

[0029] Furthermore, the particular features, structures or characteristics described in present description may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and from different embodiments, as would be understood by those in the art.

[0030] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0031] The term “aqueous composition”, as used herein, refers preferably to a solution or mixture in which water is the primary solvent. The term "aqueous" denotes the presence of water, and a composition labeled as such typically contains water as the solvent, with one or more solutes dissolved or suspended within it. Aqueous compositions are common in various fields, including chemistry, biology, and industry, where water serves as a versatile medium for carrying out reactions, transporting substances, or formulating products. Water might still in a more complex formulation such as bleaching composition, the primary solvent but could constitute, 51-95% , preferably 70-90 %, of the total composition, with the remainder consisting of various active ingredients, additives, and / or solubilizers.

[0032] The term “aqueous solution”, as used herein, is understood to mean a special form of the “aqueous composition” as defined above, wherein one or more solutes are dissolved in water as the primary solvent. In this application, when describing the product obtained by the inventive use or the inventive method, the terms “solution”, “aqueous solution” and “aqueous composition” are used interchangeably. The term “solution”, as used herein, refers preferably to a homogeneous mixture composed of two or more substances, where one substance (the solute) is dissolved in another substance (the solvent). Solutions are characterized by their uniformity at a molecular level and can vary in concentration depending on the amount of solute dissolved in the solvent. Preferably, the “solution” can be an “aqueous solution” as defined above.

[0033] The term “stabilizer” or “stabilizing agent”, as used herein, is understood to mean a chemical compound or additive that is used to prevent or minimize catalytic decomposition of hydrogen peroxide during electrolysis. A stabilizer is a compound that is able to inactivate at least a portion, and preferably substantially all of the catalytically active impurities. The stabilizer should be chemically, thermally, and electrically stable to the conditions of the cell.

[0034] The term “electrolysis”, as used herein, is understood to mean a chemical process in which electrical energy is used to drive a non-spontaneous reaction. This involves passing an electric current through an electrolyte, causing chemical reactions to occur at the electrodes.

[0035] The present invention relates to use of poly(hydroxy acrylic acid) or a salt thereof in the production of a solution containing hydrogen peroxide by electrolysis, wherein the produced solution has an apparent pH of at least 8.0. Preferably, the poly(hydroxy acrylic acid) or a salt thereof is used as a stabilizer of hydrogen peroxide. Preferably, the produced solution is an aqueous solution.

[0036] Further, the present invention relates to a process for manufacturing hydrogen peroxide which comprises the following steps: a) providing an electrochemical cell comprising a cathode and an anode for the production of hydrogen peroxide, b) feeding the electrochemical cell with a gas containing oxygen, preferably with oxygen saturated with water, c) feeding the electrochemical cell with a solution, preferably with an aqueous solution, comprising poly(hydroxy acrylic acid) or a salt thereof, d) carrying out the electrolysis in the electrochemical cell to produce a solution, preferably an aqueous solution, containing hydrogen peroxide and poly(hydroxy acrylic acid) or a salt thereof, wherein the produced solution has an apparent pH of at least 8.0.

[0037] It will be understood that in this application, where applicable, features described in relation to the inventive use relate also to the inventive process; and features describe in relation to the inventive process relate also to the inventive use. For instance, the disclosure of specific amounts of components, types of components or pH values apply both to the use and the process of the invention.

[0038] Preferably, in the use and the process of the present invention, the poly(hydroxy acrylic acid) or a salt thereof has general formula (I) wherein each of Ri and R2 represents hydrogen or an alkyl substituent and n is an integer of at least 3, wherein M is hydrogen, an alkali metal atom or an ammonium group.

[0039] Preferably, the poly(hydroxy acrylic acid) or a salt thereof is the sodium salt of poly(alpha-hydroxy acrylic acid), also called sodium poly(alpha-hydroxy acrylic acid) or Na-PHA in this application.

[0040] This poly (alpha-hydroxy acrylic acid), also referred to as carboxylic polymer(s), is / are a compound(s) containing a main carbon chain substituted by carboxyl groups -COOM, where M represents hydrogen, an atom of an alkali metal or an ammonium group. The poly (alpha-hydroxy acrylic acid) or a salt thereof can be a mixture of different poly (alpha-hydroxy acrylic acids) or salts thereof, as well as chosen from homopolymers and copolymers.

[0041] Preferably, M represents a hydrogen atom, a sodium or potassium atom or an ammonium group. Most preferably, M represents a sodium atom. The alkyl group, i.e the alkyl substituent of the poly (alpha-hydroxy acrylic acid) or a salt thereof of formula (I) can be a linear, a branched or a cyclo-alkyl group. It is particularly preferred that alkyl group of the compound of formula (I) is selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl and isomers thereof.

[0042] The alkyl substituent of the poly (alpha-hydroxy acrylic acid) according to the invention can also advantageously be substituted by one or more other substituents such as, for example, halogen atoms, hydroxyl groups, and / or further alkyl chains.

[0043] The poly (alpha-hydroxy acrylic acid) can also refer to hydroxy carboxylic polymer(s), i.e. (a) compound(s) containing a main carbon chain substituted by carboxyl groups -COOM, where M represents hydrogen, an atom of an alkali metal or an ammonium group. The poly (alpha-hydroxy acrylic acid) or a salt thereof can be a mixture of different poly (alpha-hydroxy acrylic acids) or a salt thereof, as well as chosen from homopolymers and copolymers.

[0044] The poly (alpha-hydroxy acrylic acid) or a salt thereof according to the invention can also be referred to as hydroxycarboxylic polymer(s), i.e. those which contain monomeric units of the formula (I) wherein each of Ri and R2 represents hydrogen or an alkyl substituent and n is an integer of at least 3, wherein M is hydrogen, an alkali metal atom or an ammonium group.

[0045] Preferably, Ri and R2 represent hydrogen or a methyl group, and can be identical or different. More preferably, Ri and R2 represent hydrogen. The poly(alpha-hydroxy acrylic acid) according to the invention can be employed in the form of salts of poly (alpha-hydroxy acrylic acids) or in the form of poly (alpha-hydroxy acrylic acids). In this latter case, they can be employed in the form of the corresponding polylactones.

[0046] Particularly preferred is sodium poly(alpha-hydroxy acrylic acid) (Na-PHA).

[0047] The inventive use and the inventive method can give an aqueous composition which preferably comprises 0.1 to 5 wt% hydrogen peroxide, based on the total weight of the aqueous composition. This range for the amount is preferred for the bleaching process in the paper industry. Preferably, the aqueous composition comprises 0.2 to 4.5 wt% hydrogen peroxide. More preferably, the aqueous composition comprises 0.2 to 4 wt% hydrogen peroxide, more preferably 0.5 to 4 wt% hydrogen peroxide.

[0048] The use of a specific amount of hydrogen peroxide in an aqueous composition obtained according to the invention is useful for its properties as a bleaching agent: Hydrogen peroxide is used as a bleaching agent to whiten paper pulp. It helps remove lignin and other colored impurities from the pulp, resulting in brighter and whiter paper products. Also, it is environmentally friendly: Compared to traditional chlorine-based bleaching agents, hydrogen peroxide is considered more environmentally friendly. It does not produce harmful chlorinated compounds as byproducts and is less damaging to the environment. It helps for odor reduction: Hydrogen peroxide helps reduce unpleasant odors associated with the pulp and papermaking process by oxidizing organic compounds responsible for the odor. The use of this specific amount of hydrogen peroxide improves the brightness: Hydrogen peroxide can improve the brightness of recycled paper pulp, making it suitable for producing high-quality paper products. The use of this specific amount of hydrogen peroxide improves the selective delignification: Hydrogen peroxide can selectively remove lignin from pulp fibers while minimizing damage to cellulose fibers, thereby improving the strength and quality of the resulting paper.

[0049] For the avoidance of doubt alkaline conditions specified conditions wherein the apparent pH of the produced solution is above 7.0, while the neutral and acidic conditions respectively refer to pH of the produced solutions of 7.0 and below 7.0. In general, suitable equipment and conditions for hydrogen peroxide production by electrolysis under alkaline or acidic conditions is described in the prior art as cited above. Unless defined otherwise in the present application, for the inventive use and process, the equipment and conditions disclosed in these publications can be employed, with the exception that according to the present invention, poly(hydroxy acrylic acid) or a salt thereof is used.

[0050] As herein used, the terms “apparent pH” merely denote the pH as it can be read on a pH-meter when measuring the pH of the hydrogen peroxide solution (which might not be a perfectly true reflection of the hydrogen ion activity, especially for a concentrated hydrogen solution). The “apparent pH’ can be measured by any method well known to the skilled person, including any potentiometric method such as the CEFIC PEROXYGENS H2O2 AM-7160 standard (March 2003).

[0051] For alkaline conditions, preferably, the produced solution containing hydrogen peroxide comprises at least one alkali metal hydroxide, preferably NaOH, in an amount of more than 0 and less than 15 wt%, preferably 1-10 wt%, more preferably 2-8 wt%, more preferably 3-7 wt%, based on the total weight of the produced solution. The alkali metal is selected from the group consisting of lithium (Li), sodium (Na), potassium (K), or mixtures thereof. Preferably the alkali metal is sodium, therefore the alkali metal hydroxide is NaOH.

[0052] The solution obtained according to the invention preferably comprises more than 0 and less than 15 wt% of NaOH, more preferably from 1 to 10 wt%, more preferably from 2 to 8 wt%, and most preferably from 3 to 7 wt%.

[0053] The produced solution has an apparent pH of at least 8.0, preferably of at least 10.0, more preferably of at least 11.0, more preferably higher than 11.5, most preferably higher than 12.

[0054] The pH of the solution is preferably adjusted within the range of 11.5 to 14. This is because over this pH-value, the bleaching action of hydrogen peroxide is more effective. The produced solution preferably has an apparent pH higher than 11.5, preferably more than 12, more preferably between 12 and 14, most preferably between 12.2 and 13.2. In order to determine the pH-value, preferably a pH meter is used as follows: Calibrate the pH meter according to the manufacturer's instructions using buffer solutions of known pH values.

[0055] Take a sample of the composition in a clean container.

[0056] Immerse the pH meter electrode into the sample.

[0057] Allow the reading to stabilize, and record the pH value displayed on the meter.

[0058] Preferably, for the inventive use of the poly (alpha-hydroxy acrylic acid), n is an integer from 18 to 9100, preferably from 45 to 7200, more preferably from 100 to 5000. Due to this size the poly (alpha-hydroxy acrylic acid) according to the invention preferably will not affect an electrolysis, for example by clotting a membrane.

[0059] Preferably, for the inventive use, the poly (alpha-hydroxy acrylic acid) or a salt thereof having general formula (I) has a mass average molar mass (Mw), measured by Gel Permeation Chromatography, of greater than 264 g / mol, in particular of from 2,000 to 1,000,000 g / mol, preferably from 5,000 to 800,000 g / mol.

[0060] Preferably, by the inventive use or the inventive method, a solution is obtained comprising 0.1 to 5 wt% hydrogen peroxide, based on the total weight of the produced solution. This range for the amount is preferred for the bleaching process in the paper industry. Preferably, the solution obtained by the inventive use or the inventive method comprises 0.2 to 4.5 wt% hydrogen peroxide, based on the total weight of the produced solution. More preferably, the solution comprises 0.2 to 4 wt% hydrogen peroxide, more preferably 0.5 to 4 wt% hydrogen peroxide.

[0061] Preferably, for the inventive use, in the produced solution, the amount of poly(hydroxy acrylic acid) or a salt thereof is in the range of more than 0 and less than 0.1 wt%, based on the total weight of the produced solution.

[0062] Preferably, for the inventive use, in the produced solution, the amount of poly(hydroxy acrylic acid) or a salt thereof is in the range from 0.001 to 0.099 wt%, based on the total weight of the produced solution. More preferably, for the inventive use, the produced solution comprises from 0.002 to 0.075 wt%, most preferably from 0.002 to 0.049 wt%, poly (alphahydroxy acrylic acid) or a salt thereof having general formula (I).

[0063] Preferably, for the inventive use, the produced solution comprises less than 0.05 wt%, preferably less than 0.04 wt%, more preferably less than 0.03 wt%, more preferably less than 0.02 wt%, more preferably less than 0.01 wt% of other stabilizers, based on the total weight of the produced solution. Preferably, the produced solution is essentially free or even completely free of other stabilizers.

[0064] Preferably, for the inventive use, the other stabilizers are selected from the group consisting of an alkali metal silicate compound, EDTA (ethylene diamine tetraacetic acid sodium salt) and mixtures thereof.

[0065] Preferably, for the inventive use, the produced solution comprises less than 0.05 wt% of an alkali metal silicate compound and / or EDTA, based on the total weight of the produced solution. More preferably, it comprises less than 0.01 wt%, most preferably less than 0.001 wt%, of an alkali metal silicate compound and / or EDTA, based on the total weight of the produced solution.

[0066] A further embodiment of the invention relates to a process for manufacturing hydrogen peroxide, comprising the following steps: a) providing an electrochemical cell for the production of hydrogen peroxide, b) feeding the electrochemical cell with a gas containing oxygen, c) feeding the electrochemical cell with a solution comprising poly(hydroxy acrylic acid) or a salt thereof, d) carrying out the electrolysis in the electrochemical cell to produce a solution containing hydrogen peroxide and poly(hydroxy acrylic acid) or a salt thereof, wherein the produced solution has an apparent pH of at least 8.0.

[0067] Preferably, the inventive process comprises the following steps: a) providing the electrochemical cell, b) feeding the anodic compartment

[0068] - with a gas containing oxygen, preferably saturated with water, and a solution, preferably an aqueous solution, comprising at least one alkali metal hydroxide, and / or

[0069] - with a solution, preferably an aqueous solution, comprising at least one alkali metal hydroxide and oxygen dissolved therein, c) feeding the cathodic compartment with a solution, preferably with an aqueous solution, comprising at least one alkali metal hydroxide and poly(hydroxy acrylic acid) or a salt thereof, and d) carrying out the electrolysis in the electrochemical cell to produce in the cathodic compartment a solution, preferably an aqueous solution, containing hydrogen peroxide, at least one alkali metal hydroxide and poly(hydroxy acrylic acid) or a salt thereof.

[0070] Preferably, in the inventive process, (i) the electrochemical cell contains a cathodic compartment comprising a cathode, an anodic compartment comprising an anode and either a diaphragm or an ion exchange membrane separating the cathodic compartment and the anodic compartment, (ii) a solution, preferably an aqueous solution, comprising poly(hydroxy acrylic acid) or a salt thereof is fed at least in the cathodic compartment, and (iii) the produced solution comprising hydrogen peroxide and poly(hydroxy acrylic acid) or salt thereof is produced at least in the cathodic compartment.

[0071] Preferably, in the inventive process, the hydrogen peroxide is produced at least in the cathodic compartment and the poly(hydroxy acrylic acid) or salt thereof is added at least in the cathodic compartment.

[0072] Preferably, the hydrogen peroxide is produced only in the cathodic compartment and the stabilizer is added either only in the cathodic compartment or in both the cathodic compartment and the anodic compartment.

[0073] Preferably, the aqueous solution that is fed at step c) further comprises an alkali metal hydroxide, preferably sodium hydroxide. Preferably, if the aqueous solution that is fed at step c) further comprises an alkali metal hydroxide, the hydrogen peroxide is produced only in the cathodic compartment and the poly(hydroxy acrylic acid) or a salt thereof (as stabilizer) is added either only in the cathodic compartment or in both the cathodic compartment and the anodic compartment. In this case, the aqueous solution that is comprised in both the cathodic compartment and anodic compartment preferably has an apparent pH of at least 10.0, more preferably at least 11.0, more preferably at least 11.5.

[0074] For example, one compartment of the electrochemical cell comprises an anode on one side and a membrane (e.g., an ion exchange membrane) on the opposite side, and the other compartment comprises the membrane on one side and a cathode on the opposite side. For instance, one compartment comprises an anode on the left side and a membrane on the right side, and the other compartment comprises the membrane on the left side and a cathode on the right side. A suitable electrochemical cell, i.e., a device for electrolysis, is described in connection with Examples la and lb below.

[0075] Preferably, in the inventive use and the inventive process, the poly(hydroxy acrylic acid) or a salt thereof has general formula (I): wherein each of Ri and R2 represents hydrogen or an alkyl substituent and n is an integer of at least 3, wherein M is hydrogen, an alkali metal atom or an ammonium group.

[0076] In a particular embodiment of the invention, suitable equipment and conditions for hydrogen peroxide production under alkaline conditions in an electrochemical cell comprising at least 3 compartments, especially the electrochemical cell itself and its operating conditions, are as defined as in any one of U.S. patent No. 6,254,762 to Permelec Electrode Ltd., U.S. patent No. 7,754,064 to Eltron Research & Development, U.S. patent No. 11,091,846 to Stichting Wageningen Research and international application WO 2021 / 160759 to HPNow APD, except that poly(alpha-hydroxy acrylic acid) or salt thereof is present in at least one of the one or more compartments of the electrochemical cell where hydrogen peroxide is also present. In accordance of this particular embodiment of the present invention, poly(alpha-hydroxy acrylic acid) or salt thereof is preferably present in a cathodic compartment wherein hydrogen peroxide is produced at a cathode; poly(alpha-hydroxy acrylic acid) or salt thereof is also preferably present in a compartment, e.g. in a central compartment of a three-compartment cell, into which hydrogen peroxide has migrated in the form of HCU ions from a cathodic compartment where HCU ions have been produced. More preferably, poly(alpha-hydroxy acrylic acid) or salt thereof is present in all the compartments of the electrochemical cell wherein hydrogen peroxide is present, i.e. it is present in the one or more cathodic compartments wherein hydrogen peroxide is produced at a cathode; poly(alpha-hydroxy acrylic acid) or salt thereof is also preferably present in a compartment, e.g. in a central compartment of a three-compartment cell, into which hydrogen peroxide has migrated in the form of HCU ions from a cathodic compartment where HCU ions have been produced

[0077] The whole content of U.S. 6,254,762 U.S. 7,754,064, U.S. 11,091,846 and WO 2021 / 160759 is herein incorporated by reference for all purposes, including for supplementing the description of this particular embodiment of the present invention.

[0078] Electrochemical synthesis of hydrogen peroxide typically takes place in an electrochemical cell with oxygen reduction to hydrogen peroxide at the cathode, and water oxidation at the anode, according to the below chemical reactions:

[0079] Alkaline conditions:

[0080] Anode: 2OH~ — > U O2 + H2O + 2e~

[0081] Cathode: H2O + O2+ 2e HO2 + OH'

[0082] Acidic conditions:

[0083] Anode: 2H2O — > H2O2 + 2H++ 2e~

[0084] Cathode: O2+ 2H++ 2e H2O2 Such a cell enables the generation of hydrogen peroxide at the point of use, preferably using only readily available substances such as oxygen (from the air), and water. Therefore, in step b) feeding the electrochemical cell with a gas containing oxygen takes place. The oxygen content in the gas is advantageously of at least 20.0 mole %, preferably of at least 50.0 mole % and more preferably of at least 90.0 mole %, based on the total number of moles of gas. The gas containing oxygen can be chosen from dry air, air that is partially saturated with water, air saturated with water, dry oxy gen-enriched air, oxy gen-enriched air that is partially saturated with water, oxy gen-enriched air that is saturated with water, dry oxygen, oxygen that is partially saturated with water and oxygen saturated with water. Oxygen may be obtained from air. Other oxygen sources preferably include oxygen generated on site (for example through a pressure swing adsorption system), and oxygen gas cylinders. This has numerous advantages over purchasing bulk hydrogen peroxide, including supply security, CO2 neutrality and safety. Good results are obtained when the gas is dry oxygen, dry oxygen that is partially saturated with water or oxygen saturated with water. Excellent results were obtained when the gas was oxygen saturated with water.

[0085] The invention further relates to an electrochemical cell comprising a cathode, an anode and an aqueous solution comprising a poly(hydroxy acrylic) acid or a salt thereof.

[0086] The electrochemical cell further comprises oxygen saturated with water and hydrogen peroxide.

[0087] Further, the electrochemical cell comprises:

[0088] - a cathodic compartment comprising the cathode, water and part or all of the poly(hydroxy acrylic) acid or a salt thereof,

[0089] - an anodic compartment comprising the anode and water and

[0090] - either a membrane or a diaphragm separating the cathodic and the anodic compartment.

[0091] Preferably, the anodic compartment further comprises oxygen saturated with water, and the cathodic compartment further comprises hydrogen peroxide. Preferably, the anodic compartment and the cathodic compartment further comprise an alkali metal hydroxide.

[0092] Preferably, in the process and electrochemical cell of the invention, the cathode comprises a cathode catalyst layer and a cathode gas diffusion layer that are in intimate contact with each other. Preferably, the anode is made of a metal or metal alloy, such as Pt / Ti, Ir or Nb.

[0093] Preferably, in the process and electrochemical cell of the invention, the ion exchange membrane is a polymeric proton exchange membrane, preferably a sulfonated tetrafluoroethylene-based copolymer, more preferably a fluorinated copolymer incorporating perfluorovinyl ether groups terminated with sulfonate groups onto a tetrafluoroethylene backbone. Suitable membranes are known under the brand name Nafion.

[0094] The anode acts as a proton source for the cathode, and while water is the most common reactant under acidic conditions, other proton sources such as protic solvents, alcohols (methanol, ethanol, etc.) or molecular hydrogen could be used without affecting the nature of the invention. If other proton sources are used anodes for water oxidation to oxygen are well-known to those skilled in the art.

[0095] Preferably, the cathode reduces oxygen into hydrogen peroxide. In a preferred embodiment, oxygen could come from air, an oxygen concentrator or from a bottle of compressed gas. Cathodes can consist of a cathode catalyst layer and a cathode gas diffusion layer that are in intimate contact with each other. The gas diffusion layer is porous and made of an electrically conducting material to enable transport of oxygen, water and hydrogen peroxide to / from the cathode catalyst layer.

[0096] Alternatively, catalyst ink could be sprayed directly on a polymer exchange membrane, forming a catalyst coated membrane, with the gas diffusion layer added afterwards. It is also possible to combine both a catalyst coated membrane and a gas diffusion electrode.

[0097] The cathode can be placed with its catalyst layer facing the polymer exchange membrane, and typically the application of heat and pressure ensures cathode and membrane are physically attached. This is often done together with the application of heat and pressure for the anode side. The anode current collector can also be pressed on the opposite side of the membrane for a single-step pressing. This results in a single mechanical entity containing cathode and anode electrode, as well as polymer exchange membrane, which is known as a membrane-electrode assembly (MEA).

[0098] Preferably in the inventive process, the produced solution comprises the at least one alkali metal hydroxide in an amount of more than 0 and less than 15 wt%, preferably 1-10 wt%, more preferably 2-8 wt%, more preferably 3-7 wt%, based on the total weight of the produced solution; and the poly(hydroxy acrylic acid) or a salt thereof is used in an amount of more than 0 and less than 0.1 wt%, preferably from 0.001 to 0.099 wt%, based on the total weight of the produced solution.

[0099] In the inventive process the electrolysis is carried out with a current density which is generally of at least 1 A / m2and of at most 10000 A / m2The current density is preferably of at least 10 A / m2, more preferably of at least 100 A / m2and still more preferably of at least 500 A / m2, at least 1000 A / m2or even at least 1500 A / m2. Besides, the current density is preferably of at most 4000 A / m2, and more preferably of at most 3000 A / m2, at most 2500 A / m2or even at most 2000 A / m2. Suitable current density ranges to carry out the electrolysis in the inventive process may be notably between 1 A / m2and 4000 A / m2, between 1 A / m2and 3000 A / m2, between 1 A / m2and 2000 A / m2, between 10 A / m2and 4000 A / m2, between 10 A / m2and 3000 A / m2, between 10 A / m2and 2000 A / m2, between 100 A / m2and 4000 A / m2, between 100 A / m2and 3000 A / m2or between 100 A / m2and 2000 A / m2. Good results were achieved when carrying out the electrolysis with a current density of between 100 A / m2and 500 A / m2, e.g. at about 200 A / m2. Excellent results are achieved when carrying out the electrolysis with a current density from 500 to 2500 A / m2, e.g. at about 2000 A / m2.

[0100] Preferably, the inventive process is a continuous process, i.e., electrolysis is carried out as a continuous process.

[0101] In the inventive process, the electrolysis is carried out at a temperature which is generally above 0°C and below 80°C. The temperature is typically at least 5°C, preferably at least 10°C, more preferably at least 20°C, still more preferably at least 30°C, the most preferably at least 35°C. Besides, the temperature is preferably at most 60°C, more preferably at most 50°C, still more preferably at most 45°C, the most preferably at most 40°C. Suitable temperature ranges to carry out the electrolysis in the inventive process may be notably between 0°C and 80°C, between 0°C and 60°C, between 0°C and 50°C, between 0°C and 45°C, between 0°C and 40°C, between 5°C and 80°C, between 5°C and 60°C, between 5°C and 50°C, between 5°C and 45°C, between 5°C and 40°C, between 10°C and 80°C, between 10°C and 60°C, between 10°C and 50°C, between 10°C and 45°C, between 10°C and 40°C, between 20°C and 80°C, between 20°C and 60°C, between 20°C and 50°C, between 20°C and 45°C, between 20°C and 40°C, between 30°C and 80°C, between 30°C and 60°C, between 30°C and 50°C, between 30°C and 45°C, between 30°C and 40°C, between 35°C and 80°C, between 35°C and 60°C, between 35°C and 50°C, between 35°C and 45°C, between 35°C and 40°C. Preferably the temperature is between 5°C and 60°C, more preferably between 10°C and 50°C, more preferably between 20°C and 45°C, more preferably between 30°C and 45°C, more preferably between 35°C and 40°C. Good results are obtained when carrying out the electrolysis at a temperature between 5 and 50°C, preferably between 10 and 30°C, e.g. at about 20°C. Excellent results are obtained when carrying out the electrolysis at a temperature between 30 and 50°C, e.g. at about 35 to 40°C.

[0102] Preferably, in the inventive continuous process, a permanent flow of the gas containing oxygen, expressed as pure (100%) oxygen flow, preferably saturated with water, preferably at the cathode side, from 0.1 L O2 / (min*dm2) to 10 L O2 / (min*dm2) is fed to the electrochemical cell, more preferably from 0.2 L O2 / (min*dm2) to 8 L O2 / (min*dm2), and most preferably from 0.5L O2 / (min*dm2) to 7 L O2 / (min*dm2). The unit “dm2” corresponds to the surface of the electrode.

[0103] In the inventive process, the electrolysis is carried out at a pressure which is generally above 0 mbar and at most 1000 mbar. The pressure is preferably at least 10 mbar, more preferably at least 20 mbar, still more preferably at least 40 mbar. Besides, the pressure is preferably at most 500 mbar, more preferably at most 200 mbar, still more preferably at most 100 mbar. Suitable pressure ranges to carry out the electrolysis in the inventive process may be notably between more than 0 mbar and 1000 mbar, between 10 mbar and 1000 mbar, between 20 mbar and 1000 mbar, between 40 mbar and 1000 mbar, between more than 0 mbar and 500 mbar, between 10 mbar and 500 mbar, between 20 mbar and 500 mbar, between 40 mbar and 500 mbar, between more than 0 mbar and 200 mbar, between 10 mbar and 200 mbar, between 20 mbar and 200 mbar, between 40 mbar and 200 mbar, between more than 0 mbar and 100 mbar, between 10 mbar and 100 mbar, between 20 mbar and 100 mbar, between 40 mbar and 100 mbar. Preferably, the pressure is between 10 mbar and 1000 mbar, more preferably between 20 mbar and 500 mbar, more preferably between 40 mbar and 200 mbar, more preferably between 40 mbar and 100 mbar. Good results are obtained when carrying out the electrolysis at a pressure greater than 200 mbar up to 1 bar, e.g. at about 500 mbar. Excellent results are obtained when carrying out the electrolysis at a pressure greater than 0 mbar up to 200 mbar, e.g. at about 50 mbar.

[0104] Preferably, in the inventive continuous process the productivity of the hydrogen peroxide is from 1.30 g of H2O2 / (kg*h) to 2.10 g of H2O2 / (kg*h), based on 1 L / min of oxygen contained in the oxygen-containing gas,, more preferably from 1.40 g of H2O2 / (kg*h) to 2.10 g of H2O2 / (kg*h) , based on 1 L / min of oxygen contained in the oxygen-containing gas. The productivity is determined experimentally as shown in the Examples below. The measured hydrogen peroxide concentration is plotted against the time and the measuring points are fitted to a straight. The slope of this straight corresponds to the productivity.

[0105] Recovered waste paper constitutes an important source of raw material for the papermaking industry, especially for the manufacture of papers.

[0106] Therefore, another embodiment of the invention refers to the use of the solution containing hydrogen peroxide obtained by the inventive use or the inventive method, in the pulp and paper industry, such as for bleaching chemical or mechanical paper pulp or for regenerating waste paper.

[0107] Mechanical pulping is the original form of pulping for paper. It has been largely replaced by chemical pulping, is still used for lower grade papers such as newsprint, and is the only process used for recycled paper. Mechanical pulping relies more so on mechanical actions to separate and develop wood fibers, rather than using chemical means. Electricity is the main source of energy for generating the mechanical forces necessary to produce mechanical pulp. The main subdivisions of this method are stone groundwood pulping (SGW), refiner pulping, thermomechanical pulping (TMP), chemithermomechanical pulping (CTMP), and recycled paper pulping.

[0108] The consistency of the paper pulp can be highly variable within the range from 1 to 50 % by weight of dry paper pulp and will be adapted to the type of equipment available for mixing the chelating agents into the process. In the majority of the cases, a consistency of less than or equal to 10 % by weight of dry paper pulp, for instance from 3 to 4 % by weight of dry paper pulp, will be suitable. In special cases, higher values, up to 45 % by weight of dry paper pulp can be used.

[0109] It is known, as outlined above, that electrochemical processes use an alkaline electrolyte to produce an alkaline peroxide solution. The high pH of the electrolyte causes a substantial amount of the peroxide to decompose during electrolysis in the cell. Thus, electrical energy is wasted by producing peroxides which decompose before they can be recovered. This autodecomposition problem is compounded by the usual catalytic decomposition problem.

[0110] Preferred is therefore a use, wherein the aqueous composition has been produced by electrolysis on the site of the paper plant by the inventive use or the inventive method.

[0111] In a further embodiment, the present invention relates therefore to an integrated process comprising the steps of :

[0112] (a) producing a solution containing hydrogen peroxide according to the inventive use

[0113] (b) the so produced solution containing hydrogen peroxide is directly used in a paper mill.

[0114] Directly used in a paper mill means preferably that the produced aqueous hydrogen peroxide composition is transferred within 10 seconds to 5 hours to the paper mill. This arrangement of the integrated system and the direct use of the aqueous hydrogen peroxide composition allows it to save transporting costs. The present invention is further illustrated by the following examples. It should be understood that the following examples are for illustration purposes only and are not used to limit the present invention thereto.

[0115] EXAMPLES

[0116] EXAMPLE la

[0117] In Fig .1 a continuous process for the production of the solution / composition containing hydrogen peroxide according to the invention is illustrated.

[0118] As part of the production of a hydrogen peroxide solution in an alkaline medium by electrochemistry, IL of an aqueous solution containing 6% of sodium hydroxide and 0.435g / kg of a 23% aqueous solution of sodium salt of poly (hydroxy acrylic acid) is introduced into the catholyte tank (2) of a device for electrolysis comprising an electrolytic cell (1) comprising a cathode (la), an anode (lb) and an ion exchange membrane (1c). 4L of the same solution are introduced into the anolyte tank (3).

[0119] The 2 solutions, at ambient temperature (about 20°C), are then pumped as catholyte solution (5) and anolyte solution (6) through the electrolytic cell (1) at a flow of 0.55L / min and a permanent flow of 1 L / min of oxygen saturated with water (4) is introduced into the catholyte side. At the outlet, the 2 solutions are returned to their respective initial tanks by recirculation. The current density applied is 400 A / m2. The hydrogen peroxide concentration increases progressively into the catholyte solution (5) and the installation is stopped when the hydrogen peroxide concentration reaches 5%.

[0120] The same trial under the same working conditions is then conducted with an electrolyte solution containing 6% of sodium hydroxide and O.lg / kg of EDTA which is considered as the reference stabilizer.

[0121] The typical configuration and parameters of the electrolytic cell equipment are: Equipment used (typical equipment used for electrochemical process)

[0122] • Electro MP Cell from Electrocell Europe A / S Company, dimensions: 306 X 182mm, active surface = ldm2

[0123] • Cathode collector: Nickel black plate

[0124] • Anode: Platinum / titanium

[0125] • Gas diffusion electrode: carbon black uncatalyzed on cloth with MPL ref : W1S1011 from Fuel Cell Store Company (all types of uncatalyzed carbon black GDE can be convenient)

[0126] • Ion exchange membrane: Nafion™ N117 or Aquivion® E98-15S (all cations exchange membranes can be convenient)

[0127] Parameters used

[0128] • Temperature: typically 20°C, T from 5 to 50°C could be convenient, possibly between 10 to 30°C

[0129] • Pressure: typically 50mbar, preferably above 0 up to 200mbar but pressure greater than 200 mbar up to 1 bar could also be convenient (pressure is given by the system and not controlled)

[0130] • Flow of electrolytic solutions: 0.55 l / min, not relevant as solutions are recirculated permanently (batch system)

[0131] • Sodium hydroxide is analytical grade from Supelco, Merck Germany

[0132] • Solutions are prepared with demineralized water.

[0133] Analytical measurements

[0134] • Hydrogen peroxide concentrations in solution are measured by spectrophotometry after reaction with titanium acidic sulfate solution.

[0135] Results

[0136] The results obtained in Example la are shown in Table 1 and Figures 2 and 3. Figure 2 is a graph showing the results of productivity measurements for hydrogen peroxide production using the sodium salt of poly(alpha-hydroxy acrylic acid) or EDTA as stabilizer. Na-PHA was obtained from ZHEJIANG JIAHONG PRINTING AND DYEING TECHNOLOGY CO LTD. Figure 3 is a diagram comparing the productivity for hydrogen peroxide production using the sodium salt of poly(alpha-hydroxy acrylic acid) or EDTA as stabilizer. The productivity can be extrapolated from the graphs in Figure 2.

[0137] Based on these results, the productivity obtained in both trials are respectively:

[0138] - with sodium salt of poly (alpha-hydroxy acrylic acid): Productivity = 1.79g of H2O2 / (kg*h)

[0139] - with EDTA : productivity = 1.29g of H2O2 / (kg*h)

[0140] These results show an increase of productivity of about 39% in favor of Na-PHA compared to EDTA.

[0141] Table 1 : Comparative results between sodium salt of poly(alpha-hydroxy acrylic acid (Na-PHA) and EDTA (Example la). The values are given as produced H2O2[g] per kg of the aqueous solution.

[0142] Example lb

[0143] Example lb is similar to Example la, but several process conditions were further improved.

[0144] As part of the production of a hydrogen peroxide solution in an alkaline medium by electrochemistry, IL of an aqueous solution containing 6% of sodium hydroxide and 0.435g / kg of a 23% aqueous solution of sodium salt of poly (hydroxy acrylic acid) is introduced into the catholyte tank (2) of a device for electrolysis comprising an electrolytic cell (1) comprising a cathode (la), an anode (lb) and an ion exchange membrane (1c). The anolyte tank (3) uses a 15% NaOH solution, it is filled with 1.5 L of 15% NaOH.

[0145] Further, in the device, plastic connectors are used to avoid metal leaching which can occur in common H2O2 production plants which often use metal connections made of stainless steel. Under alkaline conditions, metals can leach out into the solution and help the decomposition of peroxide. Thus, plastic connectors can improve the stability of hydrogen peroxide produced under alkaline conditions. Further, in the device, the distance between anode and cathode was set at around 1 mm. When the distance is kept short, the amount of electrolyte / liquid and between the electrodes is low, i.e. the resistance caused by the liquid is reduced, which leads to less ohmic losses and improved efficacy.

[0146] The 2 solutions, at 35 to 40°C, are then pumped as catholyte solution (5) and anolyte solution (6) through the electrolytic cell (1) at a flow of 2 L / min and a permanent flow of 0.5 L / min of oxygen saturated with water (4) is introduced into the catholyte side. At the outlet, the 2 solutions are returned to their respective initial tanks by recirculation. The current density applied is 2000 A / m2. The hydrogen peroxide concentration increases progressively into the catholyte solution (5) and the installation is stopped when the hydrogen peroxide concentration reaches 5%.

[0147] The same trial under the same working conditions is then conducted with an electrolyte solution containing 6% of sodium hydroxide and O.lg / kg of EDTA which is considered as the reference stabilizer.

[0148] The typical configuration and parameters of the electrolytic cell equipment are:

[0149] Equipment used (typical equipment used for electrochemical process)

[0150] • Electro MP Cell from Electrocell Europe A / S Company, dimensions: 306 X 182mm, active surface = ldm2

[0151] • Cathode collector: Titanium coated with Iridium and Tantalum Grid

[0152] • Anode: Titanium coated with Iridium and Tantalum Grid • Gas diffusion electrode: carbon black uncatalyzed on cloth with MPL ref: W1S1011 from Fuel Cell Store Company (all types of uncatalyzed carbon black GDE can be convenient)

[0153] • Ion exchange membrane: FKS-30 (Fumasep FKS-30 is a particularly thin PET membrane having a thickness of about 30 pm which can help to reach a higher productivity rate. The main difference between Fumasep FKS-30 and other commonly used membranes is the thickness, otherwise it has the same mechanism as other ion exchange membranes).

[0154] Parameters used

[0155] • Temperature: from 35 to 40 °C, this temperature range helps in increasing the conductivity of the solution

[0156] • Pressure: typically 50mbar, preferably above 0 up to 200 mbar but pressure greater than 200 mbar up to 1 bar could also be convenient (pressure is given by the system and not controlled)

[0157] • Flow of electrolytic solutions: 2 l / min, not relevant as solutions are recirculated permanently (batch system)

[0158] • Sodium hydroxide is analytical grade from Supelco, Merck Germany

[0159] • Solutions are prepared with demineralized water.

[0160] Analytical measurements

[0161] • Hydrogen peroxide concentrations in solution are measured by spectrophotometry after reaction with titanium acidic sulfate solution.

[0162] Results

[0163] The results obtained in Example lb are shown in Table 2 and Figure 12. Figure 12 is a graph showing the results of productivity measurements for hydrogen peroxide production using the sodium salt of poly(alpha-hydroxy acrylic acid) or EDTA as stabilizer. Na-PHA was obtained from ZHEJIANG JIAHONG PRINTING AND DYEING TECHNOLOGY CO LTD.

[0164] In Fig. 12, triangles show the Faradaic efficiency obtained with Na-PHA, diamonds show the Faradaic efficiency obtained with EDTA, and circles show the yield obtained with Na-PHA and EDTA, respectively. Fig. 12 and Table 2 demonstrate the superiority of Na-PHA compared to EDTA both in the case of a shorter and a longer reaction. After 120 minutes, the yield of H2O2 is close to zero for EDTA due to decomposition of hydrogen peroxide, whereas the yield continues to increase with Na-PHA. Further, the data shows that during the first hour of the test, the faradaic efficiency for Na-PHA is improved in comparison to EDTA. Faradaic efficiency refers to the percentage of the total electrical charge passed during an electrochemical reaction that is effectively used to produce H2O2.

[0165] Table 2: Comparative results between sodium salt of poly(alpha-hydroxy acrylic acid (Na-PHA) and EDTA (Example lb). The values are given as produced H2O2 [g] per kg of the aqueous solution.

[0166] EXAMPLE 2

[0167] To compare the capability of different compounds to stabilize hydrogen peroxide, aqueous solutions comprising H2O2, NaOH and different stabilizers were prepared and the amount of H2O2 remaining in the solution after 1, 2, 3, 6, and 8 days was investigated. The initial concentrations, based on the total weight of the aqueous solution, were as follows:

[0168] - initial concentration of H2O2: 5 wt%

[0169] - initial concentration of NaOH: 6 wt%

[0170] - concentration of stabilizer: 100 ppm

[0171] The results are shown in Table 2 and Figure 4. Figure 4 is a diagram showing the decrease of hydrogen peroxide concentration over time in the presence of different stabilizers. In the sample containing the sodium salt of poly(alpha- hydroxy acrylic acid) (Na-PHA) as stabilizer, the highest amounts of H2O2 were observed throughout the experiment.

[0172] Table 2: Amounts of H2O2 in the sample containing the sodium salt of poly(alpha-hydroxy acrylic acid) (Na-PHA) as stabilizer. The amounts are given as value in g per kg of the aqueous solution and as percentage of the initial concentration.

[0173] EXAMPLE 3

[0174] To compare the capability of different concentrations of Na-PHA to stabilize hydrogen peroxide, aqueous solutions comprising H2O2, NaOH and different concentrations of Na-PHA were prepared and the amount of H2O2 remaining in the solution after 1, 2, 3, 4, and 7 days was investigated. The initial concentrations, based on based on the total weight of the aqueous solution, were as follows:

[0175] - initial concentration of H2O2: 5 wt%

[0176] - initial concentration of NaOH: 5 wt%

[0177] - concentration of Na-PHA: 0 - 0.099 wt% (see Table 3)

[0178] The results are shown in Table 3 and Figure 5. Figure 5 is a diagram showing the decrease of hydrogen peroxide concentration over time in the presence of different concentrations of Na-PHA as stabilizer. In the sample without Na-PHA, at Day 7, only 22% of the initial hydrogen peroxide concentration is still present in the sample. On the contrary, in the samples containing different amounts of Na-PHA, degradation of H2O2 was prevented, such that at Day 7, 59% (10 mg / kg Na-PHA), 69% (100 mg / kg Na-PHA), and 82% (990 mg / kg Na-PHA), respectively, of the initial hydrogen peroxide concentration is still present in the sample.

[0179] Table 3: Concentration of H2O2 (expressed in wt.%, based on the total weight of the aqueous solution) in solutions containing different amounts of Na-PHA.

[0180] EXAMPLE 4

[0181] To investigate the productivity for H2O2 synthesis by electrolysis with different concentration of Na-PHA, hydrogen peroxide was produced with the same set-up as in Example 1. The working conditions were as follows:

[0182] Catholyte 5 wt% NaOH

[0183] Anolyte Solution 15 wt% NaOH Stabilizer concentration Depending on trial (see Table 4) Temperature (°C) 30 O2 flow (ml / min) 525

[0184] Solution flow rate (L / min) 2.5 Current density (A / m2) 2000

[0185] The results are shown in Table 4 and Figures 6-11. Figure 6 is a diagram comparing the productivity for hydrogen peroxide production using different amounts of Na-PHA or EDTA as stabilizer. The productivity can be extrapolated from the graphs in Figures 7-11. Figures 7-11 are graphs showing the results of productivity measurements for hydrogen peroxide production using different amounts of Na-PHA or EDTA as stabilizer. In all samples containing Na-PHA, the productivity is higher both in comparison to a sample containing no stabilizer, and in comparison to a sample containing 100 mg / kg EDTA as stabilizer. The productivity when using Na-PHA was improved in comparison to EDTA even when the amount of stabilizer was decreased by a factor of 10: productivity of 1.28 g / H2O2 / (kg*h) for 100 mg / kg EDTA; productivity of 1.37 g / H2O2 / (kg*h) for 10 mg / kg EDTA. Therefore, it was shown that already small amounts of Na-PHA remarkably improve hydrogen peroxide productivity.

[0186] Table 4: Concentration of H2O2 (expressed in wt.%, based on the total weight of the aqueous solution) produced by electrolysis using different amounts of Na- PHA or EDTA as stabilizer, and productivity of the individual experiments.

Claims

CLAIMS1. Use of poly(hydroxy acrylic acid) or a salt thereof, in the production of a solution containing hydrogen peroxide by electrolysis, wherein the produced solution has an apparent pH of at least 8.0.

2. The use according to claim 1, wherein in the produced solution, the amount of poly(hydroxy acrylic acid) or a salt thereof is in the range of more than 0 and less than 0.1 wt%, based on the total weight of the produced solution.

3. The use according to claim 1 or 2, wherein the produced solution comprises less than 0.05 wt% of other stabilizers, selected from the group consisting of an alkali metal silicate compound, EDTA and mixtures thereof, based on the total weight of the produced solution.

4. A process for manufacturing hydrogen peroxide which comprises the following steps: a) providing an electrochemical cell comprising a cathode and an anode for the production of hydrogen peroxide, b) feeding the electrochemical cell with a gas containing oxygen, c) feeding the electrochemical cell with a solution comprising poly(hydroxy acrylic acid) or a salt thereof, d) carrying out the electrolysis in the electrochemical cell to produce a solution containing hydrogen peroxide and poly(hydroxy acrylic acid) or a salt thereof, wherein the produced solution has an apparent pH of at least 8.0.

5. The process according to claim 4, wherein(i) the electrochemical cell contains a cathodic compartment comprising a cathode, an anodic compartment comprising an anode and either a diaphragm or an ion exchange membrane separating the cathodic compartment and the anodic compartment,(ii) the solution, comprising poly(hydroxy acrylic acid) or a salt thereof is fed at least in the cathodic compartment, and(iii) the produced solution comprising hydrogen peroxide andpoly(hydroxy acrylic acid) or salt thereof is produced at least in the cathodic compartment.

6. The process according to claim 4 or 5, wherein the aqueous solution that is fed at step c) further comprises an alkali metal hydroxide.

7. The process according to claim 6, wherein the aqueous solution that is fed at step c) further comprises an alkali metal hydroxide, and the hydrogen peroxide is produced only in the cathodic compartment and the poly(hydroxy acrylic acid) or a salt thereof is added either only in the cathodic compartment or in both the cathodic compartment and the anodic compartment.

8. The process according to claim 6 or 7, wherein the aqueous solution that is fed at step c) further comprises an alkali metal hydroxide, and the aqueous solution comprised in both the cathodic compartment and anodic compartment has an apparent pH of at least 10.0.

9. The use according to any of claims 1 to 3 or the process according to any of claims 4 to 8, wherein the poly(hydroxy acrylic acid) or a salt thereof has general formula (I)wherein each of Ri and R2 represents hydrogen or an alkyl substituent, selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl and isomers thereof, and n is an integer of at least 3, wherein M is hydrogen, an alkali metal atom or an ammonium group.

10. An electrochemical cell comprising a cathode, an anode and an aqueous solution comprising a poly(hydroxy acrylic) acid or a salt thereof, wherein the electrochemical cell comprises:- a cathodic compartment comprising the cathode, water and part or all of the poly(hydroxy acrylic) acid or a salt thereof,- an anodic compartment comprising the anode and water, and- either a membrane or a diaphragm separating the cathodic and the anodic compartment, wherein the anodic compartment further comprises oxygen saturated with water, and the cathodic compartment further comprises hydrogen peroxide.

11. The electrochemical cell according to claim 10, wherein the anodic compartment and the cathodic compartment further comprise an alkali metal hydroxide.

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