Method for producing metal borohydride or boric acid from metal metaborates

Abstract

In a process for producing a metal borohydride M (BH4) n from a metal metaborate M (BO2) n, where M is a metal, such as a metallic metal, an alkali metal, an alkaline earth metal, a transition metal or a chemical compound exhibiting metallic properties, and n is the valence of the metal, the metal borohydride is formed by reacting a metal hydride MHn with trimethyl borate B (OMe) 3, and the metal trimethyl borate is formed by the reaction of boric acid H3BO3 and methanol MeOH under the removal of water H2O. In an electrochemical cell, the electrochemical cell is used to convert metal metaborate and water H2O into boric acid. An electrochemical cell has an anode half-cell and a cathode half-cell separated by a cation exchange membrane, and both the anode half-cell and the cathode half-cell are provided with a solvent and water. The metal metaborate is provided to the anode half-cell wherein acid ions H + and electrons e-are generated at the anode by electrolysis of water, and H + reacts with the metal metaborate and water. The cation exchange membrane may transfer the metal ion Mn + from the anode half-cell to the cathode half-cell and form a metal hydroxide M (OH) n in the cathode half-cell.

Description

Technical Field

[0001] The present invention relates to a metal metaborate or one of its hydrates M(BO2) n As starting material to generate metal borohydride M(BH4) n The method wherein M is a metal, such as a metallic metal, an alkali metal, an alkaline earth metal, a transition metal or a chemical compound exhibiting metallic properties, and n is the valence of the metal. The metal borohydride is obtained by reacting a metal hydride MH n It is produced by reacting with trimethyl borate B(OMe)3, and trimethyl borate is produced by reacting boric acid H3BO3 with methanol MEOH (without water H2O). Background Art

[0002] Sodium borohydride NaBH4 is widely used in industry. It is used as a reducing agent for the reduction of aldehydes and ketones, etc., and is produced in tonnage quantities. A particularly important industrial reaction of NaBH4 is the reduction of sulfur dioxide or sodium bisulfite to sodium dithionite, as shown in the following reaction formula:

[0003] NaBH4+8NaOH+8SO2→Na2S2O4+NaBO2+6H2O.

[0004] Sodium dithionite is a bleaching agent used in paper production. This process currently constitutes the largest application of NaBH4.

[0005] Another application being explored is the use of metal borohydrides, such as sodium borohydride NaBH4, as hydrogen storage medium. Hydrogen H2 is often proposed as a key energy carrier in the renewable energy transition because of its high energy capacity of 122MJ / kg. However, hydrogen has a low density and, therefore, a low volumetric energy capacity. At room temperature, 1kg of H2 occupies a volume of 11m 3 Therefore, the storage of H2 is a major obstacle in its application as an energy carrier. Sodium borohydride NaBH4 can act as a solid storage medium and release four equivalents of H2 when hydrolyzed with water or alcohol, as shown in the following reaction formula.

[0006] NaBH4+2H2O→NaBO2+4H2.

[0007] Other metal borohydrides M(BH4) n, where M represents a metal and n is the valence of the metal, can also be used for the same purpose, such as LiBH4, KBH4, Mg(BH4)2, Al(BH4)3, etc. Generally, the metal M can be a metallic metal, such as magnesium Mg or aluminum Al; an alkali metal or alkaline earth metal, such as sodium Na, potassium K or calcium Ca; a transition metal or a compound showing metallic properties. The general reaction formula for the generation of hydrogen from metal borohydrides is as follows:

[0008] M(BH4) n +2n H2O→M(BO2) n +4n H2.

[0009] In every application, borohydride BH4 is used - A disadvantage of such processes (e.g. sodium borohydride NaBH4) is the waste product metaborate (e.g. sodium metaborate NaBO2) or usually the formed metal metaborate, since there are currently no major applications for metaborate (e.g. sodium metaborate NaBO2).

[0010] Currently, NaBH4 is produced industrially through two main processes, one of which is the Bayer process (SS Muir, Sodium Borohydride Production and Utilisation for Improved Hydrogen Storage, The University of Queensland, Australia, 2013). In this process, borax NaB4O7 (a naturally occurring mineral) is added as a boron source along with silicon dioxide SiO2 and metallic sodium. The overall reaction is:

[0011] Na2B4O7+7SiO2+16Na+8H2→4NaBH4+7NaSiO3.

[0012] Another process used in industry to produce sodium borohydride is the Brown-Schlesinger process, such as Figure 1As shown, borax is also used as a boron source (SS Muir, Sodium Borohydride Production and Utilisation for Improved Hydrogen Storage, The University of Queensland, Australia, 2013). The first step is to produce hydrogen from methane. In step 3, hydrogen is combined with the metallic sodium obtained by electrolysis of sodium chloride in step 2 to produce sodium hydride NaH. At the same time, in step 4, borax and sulfuric acid H2SO4 are converted into boric acid H3BO3. In step 5, trimethyl borate B(OMe)3 is subsequently formed by adding methanol MeOH and removing water H2O. In the last step (step 6), sodium hydride and trimethyl borate react to obtain sodium borohydride NaBH4. Sodium methylate NaOMe (formed as a byproduct in step 6) is circulated as methanol with the help of water.

[0013] Both processes currently used for the production of sodium borohydride NaBH4 utilize fossil borax obtained by mining. A disadvantage of using NaBH4 in widely used applications is the waste product sodium metaborate NaBO2, or generally the metal metaborates formed, since there are currently no major applications for NaBO2. Another disadvantage relates to the waste generated during the synthesis of the borohydride, such as sodium sulfate generated in the case of the Brown-Schlesinger process due to the use of sulfuric acid H2SO4 and chlorine Cl2. Summary of the invention

[0014] It is an object of the present invention to provide a process for producing metal borohydrides such as, for example, sodium borohydride using metal metaborate or a hydrate thereof such as, for example, sodium metaborate as a boron source.

[0015] It is another or alternative object of the present invention to provide a cyclic process for producing metal borohydrides, such as, for example, sodium borohydride.

[0016] It is a further or alternative object of the present invention to provide a process for producing boric acid from metal metaborate (such as, for example, sodium metaborate), which boric acid can be further used, for example, to produce metal borohydrides.

[0017] It is a further or alternative object of the present invention to provide a clean, waste-free process for producing boric acid, for example, for further use in producing metal borohydrides.

[0018] It is a further or alternative object of the present invention to provide a clean, waste-free recycling process for chemically storing renewable energy, particularly renewable electrical energy, for use at a future time and / or elsewhere.

[0019] In one aspect, the present invention provides a method of preparing a metal metaborate M(BO2)n or one of its hydrates M(BO2) n xH2O as starting material to produce metal borohydride M(BH4) n A method wherein M is a metal, such as a metallic metal, an alkali metal, an alkaline earth metal, a transition metal or a chemical compound exhibiting metallic properties, n is the valence of the metal, and x is the number of water molecules attached to the metal metaborate in each hydrate, the metal borohydride being reacted by a metal hydride MH n It is formed by reacting with trimethyl borate B(OMe)3, and trimethyl borate is formed by reacting boric acid H3BO3 with methanol MeOH (without water H2O),

[0020] Wherein, the electrochemical cell (100) is used to convert metal metaborate and water H2O into boric acid in the electrochemical cell according to an overall reaction at least substantially in accordance with the following reaction formula:

[0021] 4M(BO2) n +10n H2O→4n H3BO3+4M(OH) n +n O2+2n H2,

[0022] wherein the electrochemical cell comprises an anode half-cell with an anode and in which at least substantially water is present as the liquid, a cathode half-cell with a cathode and in which at least substantially only water is present as the liquid, and a cation exchange membrane separating the anode half-cell from the cathode half-cell,

[0023] The positive pole and negative pole of the potential source are connected to the anode and cathode respectively.

[0024] wherein, in the anode half-cell, the metal metaborate is at least substantially provided to water to provide an aqueous solution of the metal metaborate in the anode half-cell, and, in the anode half-cell, acid ions H are generated by electrolysis of water at the anode + and electronic - , so that H + Reacts with metal metaborate and water according to the following reaction:

[0025] 2n H2O→4n H + +n O2+4n e - ,and

[0026] 4M(BO2) n +4nH + +4n H2O→4n H3BO3+4M n+ ,

[0027] The overall reaction in the anode half-cell is at least substantially in accordance with the following reaction formula:

[0028] 4M(BO2) n +6n H2O→4n H3BO3+n O2+4M n+ +4n e - ,

[0029] The cation exchange membrane can transfer metal ions M n+ from the anode half-cell to the cathode half-cell, and

[0030] In the cathode half-cell, water and electrons e from the cathode - Hydroxyl ions OH are generated at the cathode - , to form metal hydroxide M(OH) from metal ions and water n , according to the following reaction formula:

[0031] 4n H2O+4n e - →2n H2+4n OH - ,and

[0032] 4M n+ +4n OH - →4M(OH) n ,

[0033] In the cathode half-cell, the overall reaction is at least substantially according to the following reaction formula:

[0034] 4M n+ +4n H2O+4n e - →4M(OH) n +2n H2.

[0035] The reactions defined by the reaction formula are intended to be understood as the main reactions that occur. The phrase "at least substantially" can be understood as "mainly". These reactions should be understood to occur at least substantially, because they may also occur as a minority reaction in some other reactions. The main reactions that occur are those specified above. Additional solvents and / or materials may also be used, but only to the extent that they do not prevent the main reactions from occurring according to the present invention.

[0036] In an embodiment, the metal hydride is produced by converting the metal hydroxide to a metallic metal in an electrochemical cell and subsequently reacting with hydrogen gas H2.

[0037] In an embodiment, the electrochemical cell is a Castner cell.

[0038] In an embodiment, the hydrogen gas that reacts with the metallic metal is produced by the electrolysis of water.

[0039] In an embodiment, hydrogen gas generated in the cathode half-cell of an electrochemical cell for converting metal metaborate and water, H2O, into boric acid is used to react with a metallic metal.

[0040] In one aspect, the present invention provides a method of preparing a metal metaborate M(BO2) n or one of its hydrates M(BO2) n A method for producing boric acid H3BO3 using xH2O as a starting material, wherein M is a metal, such as a metallic metal, an alkali metal, an alkaline earth metal, or a transition metal, or a compound exhibiting metallic properties, n is the valence of the metal, and x is the number of water molecules attached to the metal metaborate in the respective hydrate,

[0041] Wherein, the electrochemical cell (100) is used to convert metal metaborate and water H2O into boric acid in an electrochemical cell according to an overall reaction at least substantially in accordance with the following reaction formula:

[0042] 4M(BO2) n +10n H2O→4n H3BO3+4M(OH) n +n O2+2n H2,

[0043] wherein the electrochemical cell comprises an anode half-cell with an anode and in which at least substantially water is present as the liquid, a cathode half-cell with a cathode and in which at least substantially only water is present as the liquid, and a cation exchange membrane separating the anode half-cell from the cathode half-cell,

[0044] The positive and negative electrodes of the potential source are connected to the anode and cathode respectively.

[0045] wherein the metal metaborate is at least substantially provided to water in the anode half-cell to provide an aqueous solution of the metal metaborate in the anode half-cell, and, in the anode half-cell, acid ions H are generated by electrolysis of water at the anode + and electronic - , so that H + Reacts with metal metaborate and water according to the following reaction:

[0046] 2n H2O→4n H + +n O2+4n e - ,and

[0047] 4M(BO2) n +4nH + +4n H2O→4n H3BO3+4M n+ ,

[0048] The overall reaction in the anode half-cell is at least substantially in accordance with the following reaction formula:

[0049] 4M(BO2) n +6n H2O→4n H3BO3+n O2+4M n+ +4n e - ,

[0050] The cation exchange membrane can transfer metal ions M n+ from the anode half-cell to the cathode half-cell, and

[0051] In the cathode half-cell, water and electrons e from the cathode - Hydroxyl ions OH are generated at the cathode - , to form metal hydroxide M(OH) from metal ions and water n , according to the following reaction formula:

[0052] 4n H2O+4n e - →2n H2+4n OH - ,and

[0053] 4M n+ +4n OH - →4M(OH) n ,

[0054] The cathode half-cell may have an overall reaction at least substantially according to the following reaction formula:

[0055] 4M n+ +4n H2O+4n e - →4M(OH) n +2n H2.

[0056] The reactions defined by the reaction formula are intended to be understood as the main reactions that occur. The phrase "at least substantially" can be understood as "mainly". These reactions should be understood to occur at least substantially, because they may also occur as a minority reaction in some other reactions. The main reactions that occur are those specified above. Additional solvents and / or materials may also be used, but only to the extent that they do not prevent the main reactions from occurring according to the present invention.

[0057] In an embodiment, the metal M is selected from at least one of lithium Li, sodium Na, potassium K, magnesium Mg, calcium Ca, and aluminum Al.

[0058] In an embodiment, the concentration of metal metaborate in water ranges from 0.2M to 8M.

[0059] In an embodiment, a metal hydroxide is added to at least one of the positive half-cell and the negative half-cell to increase conductivity.

[0060] In an embodiment, the concentration of the metal hydroxide in water ranges from 0M to 3M.

[0061] In an embodiment, the source of electrical potential is provided by, for example, a potentiostat, a galvanostat, or a battery.

[0062] In an embodiment, the potential source provides a potential in the range of 2V to 12V between the anode and the cathode.

[0063] In an embodiment, the material of the anode is selected from at least one of stainless steel, mild steel, nickel, Raney nickel, or Raney nickel contaminated with a small amount of other metals.

[0064] In an embodiment, the cathode material is selected from at least one of DSA platinum-coated titanium and any other type of platinum-based material.

[0065] In an embodiment, the electrochemical cell for converting metal metaborate and water H2O into boric acid is an electrochemical flow cell or a batch electrochemical cell.

[0066] In an embodiment, the boric acid provided by the electrochemical cell is in the form of a boric acid solution dissolved in water, and the boric acid is precipitated from the boric acid solution dissolved in water by at least one of cooling and concentrating. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Further features and advantages of the present invention will become apparent from the description of the present invention by way of non-limiting and non-exclusive embodiments. These embodiments should not be construed as limiting the scope of protection. Those skilled in the art will recognize that other alternatives and equivalent embodiments of the present invention may be conceived and reduced to practice without departing from the scope of the present invention. Embodiments of the present invention will be described with reference to the accompanying drawings, in which similar or identical reference symbols represent similar, identical or corresponding parts, and in which

[0068] Figure 1 A schematic diagram of a prior art Brown-Schlesinger process for producing sodium borohydride is shown;

[0069] Figure 2 shows a schematic diagram of an electrochemical cell for producing boric acid from a metal metaborate according to an embodiment of the present invention; and

[0070] Figure 3 A schematic diagram of a cyclic process for producing sodium borohydride according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0071] Figure 2 A schematic diagram of an electrochemical cell 100 used in a step of converting sodium metaborate NaBO2 into boric acid HBO3 according to an embodiment of the present invention is shown. The electrochemical cell 100 is embodied as an electrochemical flow battery in the embodiment shown. In another embodiment, for example, the electrochemical cell can be an intermittent electrochemical cell. The electrochemical flow battery 100 has a positive half-cell 110 with an anode 115 and a negative half-cell 120 with a cathode 125. The anode 115 and the cathode 125 are connected by an electric potential source 130, which has a positive electrode 131 connected to the anode 115, and a negative electrode 132 connected to the cathode 125 to allow electrons e - From the anode 115 to the cathode 125. The anode half cell 110 and the cathode half cell 120 are separated by a cation exchange membrane 140 to allow cations to be transferred from one half cell to the other. Water H2O is provided to the anode half cell 110 and the cathode half cell 120 in a flowing form. In the various reactions that occur, water is both a solvent and a reactant. Water is primarily used in both half cells, but one or more other solvents may also be used in addition.

[0072] Along with water H2O, sodium metaborate NaBO2 is also provided to the anode half-cell. In practice, sodium metaborate is provided in the form of an aqueous solution, which serves as an electrolyte in the anode half-cell 110. The potential source 130 provides sufficient potential on the anode 115 and the cathode 125 so that the water electrolysis reaction of the anode half-cell occurs according to the following reaction formula:

[0073] 2H2O→4H + +O2+4e - ,

[0074] It provides the acid in situ from the water of the anolyte solution. The acid together with the water then converts the sodium metaborate NaBO2 into boric acid H3BO3 according to the following reaction:

[0075] 4NaBO2+4H + +4H2O→4H3BO3+4Na + .

[0076] The above two reactions are a fairly formal approach to the reaction mechanism. The latter reaction is an equilibrium between metaborate, tetraborate and boric acid, and other intermediates are also possible. In practice, these reactions occur simultaneously in the anode half-cell 110, so that the overall reaction in the anode half-cell is as follows:

[0077] 4NaBO2+6H2O→4H3BO3+O2+4Na + +4e - .

[0078] Sodium metaborate is provided as an anode electrolyte in an aqueous solution at a selected concentration to the anode half-cell 110, and boric acid in the aqueous solution leaves the anode half-cell together with oxygen O2. In the illustrated electrochemical flow battery 100, a water flow is provided to fill the anode half-cell 110 with sodium metaborate, and boric acid and oxygen are released from the anode half-cell 110. In an embodiment, the concentration of sodium metaborate in water at the anode half-cell may be in the range of 0.2M (mol / dm 3 ) to 8 M. The concentration used should be selected based on, for example, the solubility of the starting materials, intermediates, and products at the working temperature.

[0079] Water is also provided in a flowing form to the cathode half-cell 120 of the electrochemical flow cell 100 (preferably, an aqueous solution of sodium hydroxide is provided). In the cathode half-cell 120, water is reduced at the cathode 125 in a hydrogen evolution reaction to form hydrogen gas H2 and hydroxide ions OH according to the following reaction formula: - :

[0080] 4H2O+4e - →2H2+4OH - .

[0081] The anode half cell 110 and the cathode half cell 120 are separated by a cation exchange membrane 140, which allows the sodium ions Na formed in the anode half cell 110 to + From the anode half-cell to the cathode half-cell. In the cathode half-cell, sodium ions and hydroxide ions provide sodium hydroxide solution in water, which can be represented by the following reaction formula:

[0082] 4Na + +4OH - →4NaOH.

[0083] The above two reaction formulas are a fairly formal approach to the reaction mechanism. In fact, the two reactions occur simultaneously in the cathode half-cell 120, so that the overall reaction in the cathode half-cell is as follows:

[0084] 4Na + +4H2O+4e - →4NaOH+2H2.

[0085] The water flow provided to and released from the cathode half-cell 120 of the electrochemical flow cell 100 will release the sodium hydroxide solution and hydrogen gas formed in the cathode half-cell 120 .

[0086] The cation exchange membrane 140 should be permeable for the transfer of sodium ions Na+ from the anolyte solution to the cathode electrolyte solution. Suitable cation exchange membranes for this purpose are, for example, Nafion TM324, 424 or 551 membranes, which are fluorinated polymer membranes, or NaSICON (sodium Na super ion conductor) membranes.

[0087] The reactions in the anode half-cell 110 and the cathode half-cell 120 occur simultaneously and maintain equilibrium, and the overall reaction in the electrochemical cell 100 is as follows:

[0088] 4NaBO2+10H2O→4H3BO3+4NaOH+O2+2H2.

[0089] It is often advantageous to heat the electrochemical cell to, for example, 80° C. The actual operating temperature selected will be based on the concentration and solubility of the materials (reactants, intermediates, and products) in the solution, the characteristics of the cation exchange membrane used, the flow rate of the electrolyte solution, etc.

[0090] Preferably, a concentration of sodium hydroxide is provided in the water flowing into the cathode half-cell 120 to provide sufficient conductivity to the negative electrolyte solution of the electrochemical cell 100. In an embodiment, the concentration of sodium hydroxide in water may range from 0M to 3M for the cathode half-cell. The lower concentration end provides a more favorable concentration difference across the membrane, whereas the higher concentration provides higher conductivity and lower required potential. The inflowing anolyte solution of the anode half-cell 110 may be heated to provide sufficient solubility of the sodium metaborate, intermediates, and products in the anolyte solution.

[0091] The outgoing anode stream can be cooled to crystallize (precipitate) boric acid from the solution released from the anode half-cell 110. Various conditions (e.g., flow rate and temperature) can be selected so that most of the boric acid crystallizes from the stream released from the positive half-cell, after which the stream is circulated back to the inflow end of the anode half-cell, where additional sodium metaborate is added to any sodium metaborate still remaining in the stream released from the positive half-cell. The solubility of any intermediates (such as, for example, tetraborates) should also be considered. The solubility of sodium metaborate and boric acid at different temperatures is as follows, which should be considered when selecting the temperature.

[0092] Table 1: Solubility of sodium metaborate and boric acid in water at different temperatures

[0093]

[0094] Data from Blasdale, WC; Slansky, CMJ Am. Chem. Soc. 1939, 61(4), 917-920.

[0095] The same type of considerations apply to the streams coming out of and into the negative half-cell 120. The sodium hydroxide formed in the negative half-cell is removed from the stream, but when the stream is circulated back into the negative half-cell 120, some sodium hydroxide may remain in the electrochemical cell 100 to have a sufficient potential.

[0096] Additional solvents to the water may also be used in the half-cells, and more than one solvent may be used. Additional electrolytes and soluble materials (e.g., salts) may be added to one or both half-cells to enhance conductivity or other considerations. However, such additional solvents and materials should not hinder the primary reaction. They should be additionally enhancing the primary reaction.

[0097] The potential source 130 is implemented as a so-called potentiostat for generating a battery voltage ranging from 2V to 12V between the anode 115 and the cathode 125. In another embodiment, the potential source is a constant current device. In theory, the minimum voltage required is 1.23V, which is higher in reality due to the overpotential on the electrode and the resistance of the electrolyte. The distance between the anode and the cathode can be selected according to, for example, the flow rate and concentration used. The anode and the cathode can be made of various suitable materials, such as, for example, stainless steel, low carbon steel, nickel or Raney nickel (a porous nickel metal that may be contaminated by a small amount of other metals) to make the anode, and such as, for example, DSA platinized titanium or any other type of platinum-based material to make the cathode.

[0098] The production of boric acid and the corresponding reactions for producing boric acid in an electrochemical cell have been described above using sodium. However, other metals M (in addition to or in place of sodium Na) may also be used in the various chemical compounds used. Metallic metals such as, for example, magnesium Mg or aluminum Al; alkali metals or alkaline earth metals such as, for example, lithium Li, calcium Ca and potassium K; transition metals; or chemical compounds exhibiting metallic properties may be used in the various reactions and chemical compounds disclosed above. n 、Metal borate M(BO2) n and metal hydroxide M(OH) n is used as metal M, where n is the valence number of metal M. The exchange membrane should be selected based on the cation of the selected material. The overall reaction in the electrochemical cell can then be written as:

[0099] 4M(BO2) n +10n H2O→4n H3BO3+4M(OH) n +n O2+2n H2, where the reaction equation in the anode half-cell can be written as:

[0100] 2n H2O→4n H + +n O2+4n e - ,and

[0101] 4M(BO2) n +4nH + +4n H2O→4n H3BO3+4M n+ ,

[0102] The overall reaction is carried out in the anode half-cell according to the following reaction formula:

[0103] 4M(BO 2)n +6n H2O→4n H3BO3+n O2+4M n+ +4n e - , and the reaction equation in the cathode half-cell should be written as:

[0104] 4n H2O+4n e - →2n H2+4n OH - ,and

[0105] 4M n+ +4n OH-→4M(OH) n ,

[0106] The overall reaction in the cathode half-cell is as follows:

[0107] 4M n+ +4n H2O+4n e - →4M(OH) n +2n H2.

[0108] Figure 3 A schematic diagram of a cyclic process for producing sodium borohydride NaBH4 according to an embodiment of the present invention (as an example), but the basic principle is applicable to any metal borohydride M(BH4) n The production of. Figure 3 The outlined step 90 does not actually involve a sodium borohydride generation step, but involves the generation of hydrogen H2 using sodium borohydride according to the reaction formula given in the background of the invention and reproduced below:

[0109] NaBH4+2H2O→NaBO2+4H2,

[0110] Or for the conversion of general metal borohydrides:

[0111] M(BH4) n +2n H2O→M(BO2) n +4n H2.

[0112] In addition to using metal borohydrides to generate hydrogen, metal borohydrides can also be used as reducing agents. For example, after quenching with water or any acid, the corresponding metal metaborate can be obtained.

[0113] The byproduct of the conversion of sodium borohydride to hydrogen is sodium metaborate (or usually metal metaborate, M(BO2) n In the case of sodium, the hydrate of sodium metaborate NaBO2·xH2O is usually the result of the conversion reaction, which can also be called sodium tetrahydroxyborate NaB(OH)4. The sodium metaborate byproduct of hydrogen formation in step 90 is used as Figure 3 The input material of process step 10 in process step 10 is as follows Figure 2 An electrochemical cell 100 for converting sodium metaborate to boric acid H3BO3 is described and relates to the electrochemical cell 100. Since sodium metaborate is dissolved in water, and water is a reactant during process step 10, the fact that any sodium metaborate hydrate that may be produced from the hydrogen generation step 90 will not have a negative impact on the process of step 10.

[0114] Process step 20 from about Figure 1 The Brown-Schlesinger process described above is known in the art and involves the formation of trimethyl borate B(OMe)3 (Me represents a methyl group) from the boric acid formed in step 10 by adding methanol MeOH and removing water. To produce sodium metaborate, the trimethyl borate from step 20 is finally reacted with sodium hydride in process step 60. In the embodiment shown, the by-product sodium methoxide NaOMe from step 60 is reacted with water in process step 70 to recover methanol (which is added again in process step 20) and sodium hydroxide NaOH.

[0115] Figure 3 The overall metal borohydride M(BH4) in the embodiment of n Production process relative to Figure 1The Brown-Schlesinger process of the invention is modified with respect to the boric acid formation step 10, but there are also some other changes. In the sodium metal conversion process step 30, the sodium hydroxide formed in the process steps 10 and 70 (instead of sodium chloride) is used as the sodium source, which can be carried out by the Castner process using electrochemical cells (Castner cells, such as disclosed in US Pat. No. 2,461,661 to S. F. Skala, entitled "electrolytic anolyte dehydration of castner cells"). The sodium metal formed in the process step 30 is used in the process step 50 together with the hydrogen formed in the process step 10 and / or possibly step 40 (instead of using hydrogen from methane) to obtain sodium hydride NaH for the final sodium borohydride production process step 60.

[0116] By these changes, various types of waste formation are avoided. The release of the greenhouse gas carbon dioxide CO2 when producing hydrogen H2; the formation of toxic chloride gas Cl2 when producing metallic sodium; and the production of sodium sulfate Na2SO4 when converting borax Na2B4O7 to boric acid H3BO3, which cannot be used in any other step of the process. In addition, the use of the irritating reactant sulfuric acid H2SO4 (which is required for step 4 of the original Brown-Schlesinger process) is bypassed. Finally, the need to extract the raw material borax is eliminated. The proposed metal borohydride production process, combined with the metal borohydride hydrogen production process, is therefore highly atom-economical, waste-free, inherently milder, recyclable, and the electrochemical processes (i.e., H2O electrolysis, boric acid production, and Castner process) can be carried out using renewable energy. This makes this new process very sustainable and future-proof.

Claims

1. A metal metaborate M(BO2) n or its hydrate M(BO2) n One of the xH2O as starting materials produces metal borohydride M(BH4) n A method wherein M is a metal, such as a metallic metal, an alkali metal, an alkaline earth metal, a transition metal or a chemical compound that behaves like a metal, n is the valence of the metal, and x is the number of water molecules attached to the metal metaborate in the respective hydrate, the metal borohydride being reacted by the metal hydride MH n With trimethyl borate B(OMe)3, and trimethyl borate is formed by the reaction of boric acid H3BO3 with methanol MeOH under the removal of water H2O, in, The electrochemical cell (100) is used to convert metal metaborate and water, H2O, into boric acid in the electrochemical cell according to an overall reaction at least substantially in accordance with the following reaction formula: <h2 style=";text-align:left;direction:ltr">4M(BO2)<h2 style=";text-align:left;direction:ltr"> n <h2 style=";text-align:left;direction:ltr"> +10n H2O→4n H3BO3+4M(OH)<h2 style=";text-align:left;direction:ltr"> n <h2 style=";text-align:left;direction:ltr"> +n O2+2n H2, The electrochemical cell comprises an anode half-cell (110) with an anode (115) and in which at least substantially water is present as the liquid, a cathode half-cell (120) with a cathode (125) and in which at least substantially water is present as the liquid, and a cation exchange membrane separating the anode half-cell from the cathode half-cell, wherein the positive electrode and the negative electrode of the potential source are connected to the anode and the cathode respectively, wherein the metal metaborate is at least substantially provided to water in the anode half-cell to provide an aqueous solution of the metal metaborate in the anode half-cell, and in the anode half-cell, acid ions H are generated by electrolysis of water at the anode according to the following reaction formula: + and electrons e-, used to make H + Reacts with metal metaborates and water: 2n H2O→4n H + +n O2+4n e - ,and <h2 style=";text-align:left;direction:ltr">4M(BO2)<h2 style=";text-align:left;direction:ltr"> n <h2 style=";text-align:left;direction:ltr"> +4n H<h2 style=";text-align:left;direction:ltr"> + <h2 style=";text-align:left;direction:ltr"> +4n H2O→4n H3BO3+4M<h2 style=";text-align:left;direction:ltr"> n+ <h2 style=";text-align:left;direction:ltr"> , The anode half-cell may have an overall reaction at least substantially according to the following reaction formula: <h2 style=";text-align:left;direction:ltr">4M(BO2)<h2 style=";text-align:left;direction:ltr"> n <h2 style=";text-align:left;direction:ltr"> +6n H2O→4n H3BO3+n O2+4M<h2 style=";text-align:left;direction:ltr"> n+ <h2 style=";text-align:left;direction:ltr"> +4n e<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , The cation exchange membrane converts the metal ions M n+ from the anode half-cell to the cathode half-cell, and In the cathode half-cell, water and electrons e from the cathode are reacted according to the following reaction formula: - Hydroxyl ions OH are generated at the cathode - , to form metal hydroxide M(OH) from metal ions and water n : 4n H2O+4n e - →2n H2+4n OH-, and 4M n+ +4n OH - →4M(OH) n , The cathode half-cell has at least substantially an overall reaction according to the following reaction formula: <h2 style=";text-align:left;direction:ltr">4M<h2 style=";text-align:left;direction:ltr"> n+ <h2 style=";text-align:left;direction:ltr"> +4n H2O+4n e<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> →4M(OH)<h2 style=";text-align:left;direction:ltr"> n <h2 style=";text-align:left;direction:ltr"> +2n H2.

2. The method according to claim 1, wherein the metal hydride is produced by conversion of the metal hydroxide into a metallic metal in an electrochemical cell and subsequent reaction with hydrogen H2.

3. The method according to the preceding claim, wherein the electrochemical cell is a Kasner cell.

4. The method according to any one of the two preceding claims, wherein the hydrogen used for the reaction with the metallic metal is produced by electrolysis of water.

5. The method according to any of the three preceding claims, wherein the hydrogen produced in the cathode half-cell of the electrochemical cell for converting metal metaborate and water H2O into boric acid is used for reacting with a metallic metal.

6. A metal metaborate M(BO2) n or its hydrate M(BO2) n xH2O as a starting material, wherein M is a metal, such as a metallic metal, an alkali metal, an alkaline earth metal, or a transition metal, or a chemical compound that behaves like a metal, n is the valence of the metal, and x is the number of water molecules attached to the metal metaborate in the respective hydrate, in, The electrochemical cell (100) is used to convert metal metaborate and water, H2O, into boric acid in the electrochemical cell according to an overall reaction at least substantially in accordance with the following reaction formula: <h2 style=";text-align:left;direction:ltr">4M(BO2)<h2 style=";text-align:left;direction:ltr"> n <h2 style=";text-align:left;direction:ltr"> +10n H2O→4n H3BO3+4M(OH)<h2 style=";text-align:left;direction:ltr"> n <h2 style=";text-align:left;direction:ltr"> +n O2+2n H2, wherein the electrochemical cell comprises an anode half-cell (110) with an anode (115) and in which at least substantially water is present as the liquid, a cathode half-cell (120) with a cathode (125) and in which at least substantially only water is present as the liquid, and a cation exchange membrane separating the anode half-cell from the cathode half-cell, wherein the positive electrode and the negative electrode of the potential source are connected to the anode and the cathode respectively, wherein the metal metaborate is at least substantially provided to water in the anode half-cell to provide an aqueous solution of the metal metaborate in the anode half-cell, and in the anode half-cell, acid ions H are generated by electrolysis of water at the anode according to the following reaction formula: + and electrons e-, used to make H + Reacts with metal metaborates and water: 2n H2O→4n H + +n O2+4n e - ,and <h2 style=";text-align:left;direction:ltr">4M(BO2)<h2 style=";text-align:left;direction:ltr"> n <h2 style=";text-align:left;direction:ltr"> +4n H<h2 style=";text-align:left;direction:ltr"> + <h2 style=";text-align:left;direction:ltr"> +4n H2O→4n H3BO3+4M<h2 style=";text-align:left;direction:ltr"> n+ <h2 style=";text-align:left;direction:ltr"> , The anode half-cell may have an overall reaction at least substantially according to the following reaction formula: <h2 style=";text-align:left;direction:ltr">4M(BO2)<h2 style=";text-align:left;direction:ltr"> n <h2 style=";text-align:left;direction:ltr"> +6n H2O→4n H3BO3+n O2+4M<h2 style=";text-align:left;direction:ltr"> n+ <h2 style=";text-align:left;direction:ltr"> +4n e<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , The cation exchange membrane converts the metal ions M n+ from the anode half-cell to the cathode half-cell, and In the cathode half-cell, water and electrons e from the cathode are reacted according to the following reaction formula: - Hydroxyl ions OH are generated at the cathode - , to form metal hydroxide M(OH) from metal ions and water n : 4n H2O+4n e - →2n H2+4n OH - ,and 4M n+ +4n OH - →4M(OH) n , The cathode half-cell has at least substantially an overall reaction according to the following reaction formula: <h2 style=";text-align:left;direction:ltr">4M<h2 style=";text-align:left;direction:ltr"> n+ <h2 style=";text-align:left;direction:ltr"> +4n H2O+4n e<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> →4M(OH)<h2 style=";text-align:left;direction:ltr"> n <h2 style=";text-align:left;direction:ltr"> +2n H2.

7. The method according to any one of the preceding claims, wherein the metal M is selected from at least one of lithium Li, sodium Na, potassium K, magnesium Mg, calcium Ca and aluminum Al.

8. A method according to any one of the preceding claims, wherein the concentration of metal metaborate in water is in the range of 0.2M to 8M.

9. A method according to any one of the preceding claims, wherein a metal hydroxide is added to the cathode half-cell to increase conductivity.

10. A process according to the preceding claim, wherein the concentration of the metal hydroxide in water is in the range of 0 M to 3 M.

11. A method according to any one of the preceding claims, wherein the source of electrical potential is provided by a potentiostat, a galvanostat or a battery.

12. A method according to any one of the preceding claims, wherein the potential provided by the source of potential between the anode and the cathode is in the range of 2V to 12V.

13. The method according to any one of the preceding claims, wherein the material of the anode is selected from at least one of stainless steel, low carbon steel, nickel, Raney nickel, or Raney nickel contaminated with small amounts of other metals.

14. The method according to any one of the preceding claims, wherein the material of the cathode is selected from at least one of DSA platinum-coated titanium and any other type of platinum-based material.

15. The method according to any one of the preceding claims, wherein the electrochemical cell for converting metal metaborate and water H2O into boric acid is an electrochemical flow cell or a batch electrochemical cell.

16. The method according to any one of the preceding claims, wherein the boric acid provided by the electrochemical cell is available in the form of a boric acid solution dissolved in water, and the boric acid solution dissolved in water obtains the boric acid by precipitation by at least one of cooling and concentrating.

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