Method for producing metal borohydrides or boric acid from metal metaborate salts

Abstract

Metal Metaborate M(BO2) n Metal borohydride M(BH4) n wherein M is a metal, e.g., a metallic metal, an alkali metal, an alkaline earth metal, a transition metal, or a compound behaving as a metal, n is the valence value of the metal, and the metal borohydride is a metal hydride MH n and trimethyl borate B(OMe)3, and metal trimethyl borates are formed by the reaction of boric acid H3BO3 and methanol MeOH under dehydration H2O. An electrochemical cell is used to convert metal metaborate and water H2O to boric acid in the electrochemical cell. The electrochemical cell has an anode half-cell and a cathode half-cell separated by a cation exchange membrane, and a solvent and water are fed to both the anode half-cell and the cathode half-cell. Metal metaborate is fed to the anode half-cell and acid ions H + , and electron e - is produced at the anode by electrolysis of water, and H + reacts with metal metaborate and water. The cation exchange membrane transports metal ions M from the anode half-cell to the cathode half-cell. n+ Metal hydroxide M(OH) n is formed in the cathode half-cell.

Description

[Technical field]

[0001] The present invention uses as a starting material a metal metaborate M(BO2) n or one of its hydrates to obtain metal borohydride M(BH4) n wherein M is a metal, e.g., a metallic metal, an alkali metal, an alkaline earth metal, a transition metal, or a compound behaving as a metal, and n is the value of the valence of the metal. Metal borohydrides are prepared by the process of producing metal hydrides MH n It is formed by the reaction of trimethyl borate, B(OMe)3, with boric acid, H3BO3, and methanol, MeOH, under dehydration, H2O. [Background technology]

[0002] Sodium borohydride NaBH4 is widely used in industry. It is used as a reducing agent, inter alia, for the reduction of aldehydes and ketones, and is produced in ton quantities. A particularly important industrial reaction with NaBH4 is the reduction of sulfur dioxide or sodium bisulfite to sodium dithionite, as shown in the following reaction scheme: NaBH4+8NaOH+8SO2→Na2S2O4+NaBO2+6H2O Sodium dithionite is a bleaching agent used in papermaking, which currently accounts for the largest proportion of NaBH4 uses.

[0003] Another application currently being explored is metal borohydrides, e.g. sodium borohydride NaBH4, as hydrogen storage media. Hydrogen gas, H2, is often proposed as an important energy carrier in the transition to renewable energies, since it has a high energy capacity of 122 MJ / kg. Nevertheless, hydrogen gas has a low volumetric energy capacity due to its low density. At room temperature, 1 kg of H2 has a volume of 11 m 3of volume. Therefore, H2 storage is a major barrier to its application as an energy carrier. Sodium borohydride NaBH4 can function as a solid storage medium, and upon hydrolysis with water or alcohol, releases four equivalents of H2, as shown in the following reaction: NaBH4+2H2O→NaBO2+4H2 Other metal borohydrides M(BH4) n (wherein M represents a metal and n is the valence value of the metal) can also be employed for the same purpose, for example LiBH4, KBH4, Mg(BH4)2, Al(BH4)3, etc. In general, the metal M may 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 behaving as a metal. The reaction equation for a typical metal borohydride to produce hydrogen gas is as follows: M(BH4) n +2nH2O→M(BO2) n +4nH2

[0004] Boron hydride BH4 for all applications - A disadvantage of the use of, for example, sodium borohydride NaBH4 is the formation of metaborates, for example, sodium metaborate NaBO2, or metal metaborates, which are generally waste products since there are currently no major uses for metaborates such as sodium metaborate NaBO2.

[0005] Currently, NaBH4 is produced industrially via two main methods, one of these being the Bayer process (SS Muir, Sodium Borohydride Production and Utilisation for Improved Hydrogen Storage, The University of Queensland, Australia, 2013). In this process, the naturally occurring mineral borax Na2B4O7 is used as the boron source, and silica SiO2 and metallic sodium are added. The overall reaction is: Na2B4O7+7SiO2+16Na+8H2→4NaBH4+7NaSiO3

[0006] Another process used industrially for the production of sodium borohydride is the Brown-Schlesinger process shown in Figure 1, which also uses borax as the boron source (SS Muir, Sodium Borohydride Production and Utilisation for Improved Hydrogen Storage, The University of Queensland, Australia, 2013). The first step is the production of hydrogen gas from methane. In step 3, sodium metal and hydrogen obtained from the electrolysis of sodium chloride in step 2 are combined to produce sodium hydride NaH. At the same time, in step 4, borax is converted to boric acid H3BO3 with sulfuric acid H2SO4. In step 5, trimethyl borate B(OMe)3 is subsequently formed by the addition of methanol MeOH and dehydration H2O. In the last step, step 6, sodium hydride and trimethyl borate are reacted to obtain sodium borohydride NaBH4. Sodium methoxide NaOMe formed as a by-product in step 6 is recycled to methanol with the aid of water.

[0007] Both methods are currently used to produce sodium borohydride NaBH4 and utilize fossil borax obtained by mining. A disadvantage of the use of NaBH4 in widely used applications is the formation of sodium metaborate NaBO2, or metal metaborates, which are generally waste products, since there is currently no major use for NaBO2. Another disadvantage relates to the waste products generated during the synthesis of borohydride salts in the case of the Brown-Schlesinger process, such as sodium sulfate and chlorine gas Cl2 due to the use of sulfuric acid H2SO4. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] US 2,461,661 [Non-patent literature]

[0009] [Non-Patent Document 1] SS Muir, Sodium Borohydride Production and Utilization for Improved Hydrogen Storage, The University of Queensland, Australia, 2013 [Non-Patent Document 2] Blasdale, WC; Slansky, CMJ Am. Chem. Soc. 1939, 61 (4), 917~920 Summary of the Invention [Problem to be solved by the invention]

[0010] It is an object of the present invention to provide a process for producing a metal borohydride, such as sodium borohydride, using a metal metaborate or a hydrate thereof, such as sodium metaborate, as a boron source.

[0011] Another or alternative object of the present invention is to provide a cyclic process for producing metal borohydride, such as sodium borohydride.

[0012] It is yet another or alternative object of the present invention to provide a process for producing boric acid from a metal metaborate, e.g., sodium metaborate, which can be further used, for example, to produce metal borohydrides.

[0013] It is yet another or alternative object of the present invention to provide a non-polluting, non-waste producing process for producing boric acid, which can be further used, for example, to produce metal borohydrides.

[0014] It is yet another or alternative object of the present invention to provide a non-polluting, non-waste producing, circular method for chemically storing renewable energy, in particular renewable electricity, for use at a future time and / or at another location. [Means for solving the problem]

[0015] In one aspect, the present invention provides a method for preparing a zeolite comprising the steps of: n , or its hydrate M(BO2) n Metal borohydride M (BH4) from one of xH2O n wherein M is a metal, e.g., a metallic metal, an alkali metal, an alkaline earth metal, a transition metal, or a compound behaving as a metal, n is the valence value of the metal, and x is the number of water molecules bound to the metal metaborate in each hydrate, and the metal borohydride is a metal hydride MH n and trimethyl borate B(OMe)3, which is formed by the reaction of boric acid H3BO3 with methanol MeOH under dehydration H2O, The electrochemical cell (100) is used for the conversion of metal metaborate and water HO to boric acid in an electrochemical cell according to an overall reaction at least substantially according to the following equation: 4M(BO2) n +10nH2O → 4nH3BO3 + 4M(OH) n +nO2+2nH2, The electrochemical cell comprises an anode half-cell with an anode and at least substantially water as a liquid in the anode half-cell, a cathode half-cell with a cathode and at least substantially only water as a liquid in the cathode half-cell, and a cation exchange membrane separating the anode half-cell and the cathode half-cell; The positive and negative poles of the potential source are connected to the anode and cathode, respectively; At least substantially, a metal metaborate is provided to the 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, the H+ From electrolysis to acidic ions H + , and electron e - is produced at the anode and reacts with metal metaborate and water according to the following reaction: 2nH2O → 4nH + +nO2+4ne - 4M(BO2) n +4nH + +4nH2O → 4nH3BO3 + 4M n+ having an overall reaction in the anode half-cell at least substantially according to the following reaction: 4M(BO2) n +6nH2O→4nH3BO3+nO2+4M n+ +4ne - The cation exchange membrane transports metal ions M from the anode half-cell to the cathode half-cell. n+ Through In the cathode half-cell, electrons e from water and the cathode - from hydroxide ion OH - is produced at the cathode, and metal hydroxide M(OH) is converted from metal ions and water according to the following reaction: n Forming 4nH2O+4ne - →2nH2+4nOH - 4M n+ +4nOH - →4M(OH) n We have an overall reaction within the cathode half-cell that is at least substantially according to the following reaction: 4M n+ +4nH2O+4ne - →4M(OH) n +2nH2 The reactions defined by the reaction schemes are intended to be understood as the main reactions that should occur. The phrase "at least substantially" can be understood as "mainly". These reactions should be understood to occur at least substantially in that some other reactions may occur as minor reactions as well. The main reactions that occur are those as described above. Additional solvents and / or materials can be employed as well, provided they do not interfere with the main reactions that should occur according to the present invention.

[0016] In one embodiment, metal hydrides are produced by converting metal hydroxides to metallic metals in an electrochemical cell and then reacting with hydrogen, H2.

[0017] In one embodiment, the electrochemical cell is a Castner cell.

[0018] In one embodiment, hydrogen for reaction with metallic metals is generated by electrolysis of water.

[0019] In one embodiment, in the cathode half-cell of an electrochemical cell, the hydrogen produced is used to react with the metallic metal to convert metal metaborate and water HO to boric acid.

[0020] In one embodiment, the starting material is a metal metaborate M(BO2). n , or its hydrate M(BO2) n xH2O, in which M is a metal, for example a metallic, alkali, alkaline earth or transition metal or a compound acting as a metal, n is the valence value of the metal, and x is the number of water molecules bound to the metal metaborate in the respective hydrate, The electrochemical cell (100) is used for the conversion of metal metaborate and water HO to boric acid in an electrochemical cell according to an overall reaction at least substantially according to the following equation: 4M(BO2) n +10nH2O → 4nH3BO3 + 4M(OH)n +nO2+2nH2, The electrochemical cell comprises an anode half-cell with an anode and at least substantially water as a liquid in the anode half-cell, a cathode half-cell with a cathode and at least substantially only water as a liquid in the cathode half-cell, and a cation exchange membrane separating the anode half-cell and the cathode half-cell; The positive and negative poles of the potential source are connected to the anode and cathode, respectively; At least substantially, a metal metaborate is provided to the 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, the H + From electrolysis to acidic ions H + , and electron e - is produced at the anode and reacts with metal metaborate and water according to the following reaction: 2nH2O → 4nH + +nO2+4ne - 4M(BO2) n +4nH + +4nH2O → 4nH3BO3 + 4M n+ having an overall reaction in the anode half-cell at least substantially according to the following reaction: 4M(BO2) n +6nH2O→4nH3BO3+nO2+4M n+ +4ne - The cation exchange membrane transports metal ions M from the anode half-cell to the cathode half-cell. n+ Through In the cathode half-cell, electrons e from water and the cathode - from hydroxide ion OH - is produced at the cathode, and metal hydroxide M(OH) is converted from metal ions and water according to the following reaction: n Forming 4nH2O+4ne - →2nH2+4nOH - 4M n+ +4nOH -→4M(OH) n We have an overall reaction within the cathode half-cell that is at least substantially according to the following reaction: 4M n+ +4nH2O+4ne - →4M(OH) n +2nH2 The reactions defined by the reaction schemes are intended to be understood as the main reactions that should occur. The phrase "at least substantially" can be understood as "mainly". These reactions should be understood to occur at least substantially in that some other reactions may occur as minor reactions as well. The main reactions that occur are those as described above. Additional solvents and / or materials can be employed as well, provided they do not interfere with the main reactions that should occur according to the present invention.

[0021] In one embodiment, the metal M is selected from at least one of lithium Li, sodium Na, potassium K, magnesium Mg, calcium Ca, and aluminum Al.

[0022] In one embodiment, the concentration of metal metaborate in water ranges from 0.2M to 8M.

[0023] In one embodiment, a metal hydroxide is added to at least one of the anode and cathode half-cells to enhance electrical conductivity.

[0024] In one embodiment, the concentration of the metal hydroxide in the water ranges from 0M to 3M.

[0025] In one embodiment, the source of electrical potential is provided by, for example, a potentiostat, a galvanostat, or a battery.

[0026] In one embodiment, the potential supplied by the potential source between the anode and the cathode is in the range of 2V to 12V.

[0027] In one 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 small amounts of other metals.

[0028] In one embodiment, the material of the cathode is selected from at least one of DSA platinized titanium and any other type of platinum based material.

[0029] In one embodiment, the electrochemical cell for converting metal metaborate and water HO to boric acid is an electrochemical flow cell or a batch electrochemical cell.

[0030] In one embodiment, the boric acid provided by the electrochemical cell is available as a solution of boric acid dissolved in water, and the solution of boric acid dissolved in water is at least one of cooled and concentrated to produce boric acid by precipitation.

[0031] Further features and advantages of the present invention will become apparent from the description of the invention by non-limiting and non-exclusive embodiments. These embodiments should not be interpreted as limiting the scope of protection. Those skilled in the art will recognize that other alternatives and equivalent embodiments of the invention can be conceived and implemented without departing from the scope of the present invention. The embodiments of the present invention will be described with reference to the accompanying drawings, in which similar or identical reference symbols indicate similar, identical or corresponding parts. [Brief description of the drawings]

[0032] [Figure 1] FIG. 1 is a schematic diagram of the prior art Brown-Schlesinger process for the production of sodium borohydride. [Diagram 2] FIG. 1 is a schematic diagram of an electrochemical cell for producing boric acid from metal metaborate, according to one embodiment of the present invention. [Diagram 3] FIG. 1 is a schematic diagram of a cyclic process for producing sodium borohydride, according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] FIG. 2 shows a schematic diagram of an electrochemical cell 100 employed in a process for converting sodium metaborate NaBO2 to boric acid H3BO3, in accordance with one embodiment of the present invention. The electrochemical cell 100 is embodied as an electrochemical flow cell in the illustrated embodiment. In another embodiment, for example, the electrochemical cell may be a batch electrochemical cell. The electrochemical flow cell 100 includes an anode half-cell 110 with an anode 115 and a cathode half-cell 120 with a cathode 125. The anode 115 and the cathode 125 are connected by a potential source 130 having a positive electrode 131 connected to the anode 115 and a negative electrode 132 connected to the cathode 125, which generates electrons e - The anode half-cell 110 and the cathode half-cell 120 are separated by a cation exchange membrane 140 that allows cations to pass from one half-cell to the other. Water, HO, is supplied in flow to both the anode half-cell 110 and the cathode half-cell 120. Water serves as both a solvent and a reactant in the various reactions that take place. Water is primarily used in both half-cells, although one or more other solvents may also be employed.

[0034] Along with water, H2O, sodium metaborate, NaBO2, is also supplied to the anode half-cell. In practice, the sodium metaborate is supplied as a solution in water to act as the electrolyte for the anode half-cell 110. A potential source 130 provides a sufficient potential to the anode 115 and cathode 125 to cause the electrolysis of water in the anode half-cell according to the following reaction: 2H2O→4H + +O2+4e - This reaction generates acid in situ from the water in the anode electrolyte solution, which together with the water subsequently converts sodium metaborate, NaBO2, to boric acid, H3BO3, according to the following reaction: 4NaBO2+4H + +4H2O→4H3BO3+4Na + The above two equations are fairly formal approaches to the reaction mechanism. The latter reaction has a balance of atomic numbers between metaborate, tetraborate, and boric acid, and possibly other intermediates. In reality, these reactions occur simultaneously in the anode half-cell 110, resulting in the overall reaction: 4NaBO2+6H2O→4H3BO3+O2+4Na + +4e - Sodium metaborate is provided in aqueous solution at a selected concentration as the anode electrolyte to the anode half-cell 110, while boric acid in aqueous solution leaves the anode half-cell with oxygen, O2 gas. In the illustrated electrochemical flow cell 100, a water flow is provided that fills the anode half-cell 110 with sodium metaborate and evacuates the anode half-cell 110 of boric acid and oxygen. In one embodiment, the concentration of sodium metaborate in the water of the anode half-cell is 0.2M (mol / dm 3 ) to 8 M. The concentration used should be selected based, for example, on the solubility of the starting materials, intermediates, and products at the operating temperature.

[0035] Similarly, water is supplied in flowing form (preferably an aqueous solution of sodium hydroxide) to the cathode half-cell 120 of the electrochemical flow cell 100. In the cathode half-cell 120, water is reduced at the cathode 125 in a hydrogen evolution reaction, thereby producing hydrogen H gas and hydroxide ions OH - is formed according to the following reaction: 4H2O+4e - →2H2+4OH - 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 +is allowed to pass from the anode half-cell to the cathode half-cell. In the cathode half-cell, sodium ions and hydroxide ions form a solution of sodium hydroxide in water, which can be represented by the following reaction: 4Na + +4OH - →4NaOH The above two equations are a fairly formal approach to the reaction mechanism. In reality, both reactions occur simultaneously in the cathode half-cell 120, resulting in the overall reaction: 4Na + +4H2O+4e - →4NaOH+2H2 A stream of water is supplied to and discharged from the cathode half-cell 120 of the electrochemical flow cell 100 , carrying sodium hydroxide in solution and hydrogen gas formed from the cathode half-cell 120 .

[0036] The cation exchange membrane 140 transfers sodium ions Na from the anode electrolyte solution to the cathode electrolyte solution. + Suitable cation exchange membranes for this purpose are, for example, Nafion™ 324, 424, or 551 membranes, which are fluorinated polymer membranes, or NaSICON (Sodium Na, Super Ionic CONductor) membranes.

[0037] The reactions in both the anode half-cell 110 and the cathode half-cell 120 all occur simultaneously, balancing the number of atoms on both sides to result in the overall reaction in the electrochemical cell 100 as follows: 4NaBO2+10H2O→4H3BO3+4NaOH+O2+2H2

[0038] Generally, it is advantageous to heat the electrochemical cell for operation, for example to 80° C. The actual operating temperature selected will depend on the concentration and solubility of the materials (reactants, intermediates, and products) in solution, the properties of the cation exchange membrane employed, the flow rate of the electrolyte solution, etc.

[0039] Preferably, a concentration of sodium hydroxide is provided in the influent water of the cathode half-cell 120 to provide sufficient conductivity to the cathode electrolyte solution of the electrochemical cell 100. In one embodiment, the concentration of sodium hydroxide in the water of the cathode half-cell can range from 0M to 3M. At the lower end of the concentration range, the concentration differential across the membrane is more favorable, while higher concentrations provide higher conductivity and require lower potentials. The influent anode electrolyte solution of the anode half-cell 110 may be heated to provide sufficient solubility for the sodium metaborate, intermediates, and products in the anode electrolyte solution.

[0040] The exiting anode stream can be cooled to crystallize (precipitate) boric acid from the solution exiting the anode half-cell 110. Various conditions, such as flow rate and temperature, can be selected to crystallize most of the boric acid from the stream exiting the anode half-cell, after which the stream is circulated back to the inlet side of the anode half-cell, along with additional sodium metaborate added to any sodium metaborate that may have remained in the stream exiting the anode half-cell. The solubility of any intermediates, such as, for example, tetraborate, should be taken into consideration as well. The solubilities of sodium metaborate and boric acid at different temperatures are as follows, and these should be considered at the selected temperature:

[0041] [Table 1]

[0042] Similar considerations apply to the streams exiting and entering the cathode half-cell 120. Although the sodium hydroxide formed in the cathode half-cell should be removed from the stream, some remains as the stream circulates back to the cathode half-cell 120 to provide sufficient conductivity for the electrochemical cell 100.

[0043] Additional solvents may also be employed in the water in the half-cells, and more than one solvent may be used. Additional electrolytes and soluble materials, such as salts, may be added to one or both of the half-cells to improve conductivity or other considerations. However, such additional solvents and materials should not interfere with the primary reaction as described; they should be added to enhance the primary reaction.

[0044] The potential source 130 is embodied as a so-called potentiostat, which generates a cell voltage between the anode 115 and the cathode 125 in the range of 2V to 12V. In another embodiment, the potential source is a galvanostat. Theoretically, a minimum voltage of 1.23V is required, but due to electrode overpotentials and the resistance of the electrolyte solution, in practice it will be higher. The distance between the anode and the cathode can be selected, for example, according to the flow rates and concentrations used. The anode and cathode can be made of various suitable materials, for example, the anode can be made of stainless steel, mild steel, nickel or Raney nickel (porous nickel metal, possibly impure with small amounts of other metals), and the cathode can be made of, for example, DSA platinized titanium, or any other type of platinum-based material.

[0045] The production of boric acid and the respective reactions in the electrochemical cell for the production of boric acid are described above with respect to sodium. However, other metals M can be used as well in addition to or in place of sodium Na in the various compounds used. In the various reactions and in the compounds disclosed above, where n is the value of the valence of the metal M, the borohydride metal M(BH4) n , Metal Metaborate M(BO2) n , and metal hydroxide M(OH) nIn the above, metallic metals, such as magnesium Mg or aluminum Al, alkali metals or alkaline earth metals, such as lithium Li, calcium Ca, and potassium K, transition metals, or compounds behaving as metals, can be used as metal M. The exchange membrane should be selected according to the cation of the selected material. The overall reaction of the electrochemical cell is described as follows: 4M(BO2) n +10nH2O → 4nH3BO3 + 4M(OH) n +nO2+2nH2 The reaction equation for the anode half-cell is written as follows: 2nH2O → 4nH + +nO2+4ne - 4M(BO2) n +4nH + +4nH2O → 4nH3BO3 + 4M n+ While having an overall reaction in the anode half-cell according to the following reaction equation: 4M(BO2) n +6nH2O→4nH3BO3+nO2+4M n+ +4ne - The reaction in the cathode half-cell is written as follows: 4nH2O+4ne - →2nH2+4nOH - 4M n+ +4nOH - →4M(OH) n The overall reaction in the cathode half-cell is according to the following reaction equation: 4M n+ +4nH2O+4ne - →4M(OH) n +2nH2

[0046] FIG. 3 shows by way of example a schematic diagram of a cyclic process for producing sodium borohydride NaBH4 according to one embodiment of the present invention, although the underlying principle is the same as for any metal borohydride M(BH4). nStep 90 in the schematic diagram of FIG. 3 does not actually relate to the production of sodium borohydride, but rather to the reaction scheme described in the "Background Art" section and reproduced below. NaBH4+2H2O→NaBO2+4H2 Or the following reaction scheme for the general conversion of metal borohydrides: M(BH4) n +2nH2O→M(BO2) n +4nH2 This application relates to the use of sodium borohydride to produce hydrogen gas H2. Rather than using metal borohydrides to generate hydrogen gas, metal borohydrides can also be used as reducing agents, e.g., after quenching with water or any acid, the corresponding metal metaborate salts are also obtained.

[0047] A by-product of the conversion of sodium borohydride to hydrogen is sodium metaborate (or generally metal metaborates, M(BO2) n ). In the sodium example, the conversion reaction results in a hydrate of sodium metaborate, generally NaBO2·xH2O, also called sodium tetrahydroxyborate, NaB(OH)4. Sodium metaborate, a by-product of the hydrogen formation in step 90, is used as an input material for process step 10 of FIG. 3. Process step 10 is described with reference to FIG. 2 and includes an electrochemical cell 100 for converting sodium metaborate to boric acid, H3BO3. The fact that any hydrate of sodium metaborate may result from the hydrogen production step 90 does not adversely affect the process of step 10, since sodium metaborate dissolves in water, and water is also a reactant in the process of process step 10.

[0048] Process step 20 is known from the prior art Brown-Schlesinger process described above with respect to Figure 1 and includes the addition of methanol, MeOH, and dehydration from the boric acid formed in step 10 to form trimethyl borate, B(OMe)3, where Me represents a methyl group. The trimethyl borate and sodium hydride of step 20 are reacted to finally obtain sodium borohydride in process step 60. In the illustrated embodiment, sodium methoxide, NaOMe, a by-product of step 60, is reacted with water in process step 70 to recover methanol and sodium hydroxide, NaOH, which are added again in process step 20.

[0049] Overall metal borohydride M(BH4) in the embodiment of FIG. n The process for the production of presents a modification of boric acid formation step 10 with respect to the Brown-Schlesinger process of FIG. 1, but also presents some other modifications. Instead of sodium chloride NaCl, sodium hydroxide formed in process steps 10 and 70 is used as the sodium source in the sodium metal conversion process step 30, which can be done by the Castner process using an electrochemical cell, a Castner-type electrolytic cell (disclosed in US 2,461,661 to SF Skala, entitled "Electrolytic anolyte dehydration of Castner cells"). The sodium metal formed in process step 30 is used in process step 50 together with hydrogen formed in process steps 10 and / or possibly step 40, instead of using hydrogen gas from methane, to obtain sodium hydride NaH, which is used in process step 60 for the final production of sodium borohydride.

[0050] These modifications avoid the formation of various kinds of waste materials; the production of hydrogen H2 releases the greenhouse gas carbon dioxide CO2, the production of metallic sodium forms the toxic chloride gas Cl2, and the conversion of borax Na2B4O7 to boric acid H3BO3 produces sodium sulfate Na2SO4, which cannot be used in any other steps of the process. Furthermore, the use of the irritating reactant sulfuric acid H2SO4, required in step 4 of the original Brown-Schlesinger process, is avoided. Finally, the need to extract the raw borax is eliminated. The proposed metal borohydride production process, together with the hydrogen production process from metal borohydride, is atom-efficient, produces no waste materials, is inherently gentler, is cyclical, and the electrochemical processes (i.e. H2O electrolysis, boric acid production, and the Kastner process) can be carried out with renewable energy. This makes the new process highly sustainable and promising. [Explanation of symbols]

[0051] 100 Electrochemical Cells, Electrochemical Flow Cells 110 Anode half cell 115 Anode 120 Cathode half cell 125 Cathode 130 Potential source 131 Positive electrode 132 Negative electrode 140 Cation exchange membrane

Claims

1. As a starting material, metal metaborate M(BO 2 ) n , or its hydrate M(BO 2 ) n ・xH 2 Metal borohydrides M(BH 4 ) n wherein M is a metal, e.g., a metallic metal, an alkali metal, an alkaline earth metal, a transition metal, or a compound behaving as a metal, n is the valence value of the metal, and x is the number of water molecules bound to the metal metaborate in each hydrate, and the metal borohydride is a metal hydride MH n and trimethyl borate B(OMe) 3 is formed by the reaction of trimethyl borate with boric acid H 3 BO 3 Dehydration by reaction of methanol (MeOH) with H 2 Formed under O The electrochemical cell (100) comprises a metal metaborate and water, H, in an electrochemical cell, the overall reaction of which is at least substantially according to the following reaction: 2 It is used to convert O to boronic acid, 4M(BO 2 ) n +10nH 2 O→4nH 3 B.O. 3 +4M(OH) n +nO 2 +2nH 2 、 The electrochemical cell comprises an anode half-cell (110) with an anode (115) and, at least substantially, water as a liquid in the anode half-cell, a cathode half-cell (120) with a cathode (125) and, at least substantially, water as a liquid in the cathode half-cell, and a cation exchange membrane separating the anode half-cell and the cathode half-cell; The positive and negative poles of a potential source are connected to the anode and cathode, respectively; At least substantially, a metal metaborate is provided to the 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, the H + From electrolysis to acidic ions H + , and electron e - is produced at the anode and reacts with metal metaborate and water according to the following reaction: 2nH 2 O→4nH + +nO 2 +4ne - 4M(BO 2 ) n +4nH + +4nH 2 O→4nH 3 BO 3 +4M n+ having an overall reaction in the anode half-cell at least substantially according to the following reaction: 4M(BO 2 ) n +6nH 2 O→4nH 3 BO 3 +nO 2 +4M n+ +4ne - The cation exchange membrane transports metal ions M from the anode half-cell to the cathode half-cell. n+ Through In the cathode half-cell, electrons e from water and the cathode - from hydroxide ion OH - is produced at the cathode, and metal hydroxide M(OH) is converted from metal ions and water according to the following reaction: n Forming 4nH 2 O+4ne - →2nH 2 +4nOH - 4M n+ +4nOH - →4M(OH) n having an overall reaction in the cathode half-cell at least substantially according to the following reaction: 4M n+ +4nH 2 O+4ne - →4M(OH) n +2nH 2 method.

2. Metal hydrides convert metal hydroxides in an electrochemical cell to metallic metals, which then produce hydrogen, H 2 2. The method of claim 1 , wherein the compound is produced by reacting

3. The method of claim 2, wherein the electrochemical cell is a Castner-type electrolytic cell.

4. 4. The method according to claim 2 or 3, wherein hydrogen for reaction with the metallic metal is generated by electrolysis of water.

5. In the cathode half-cell of the electrochemical cell, metal metaborate and water H 2 5. The method according to claim 2, wherein the hydrogen produced to convert O to boronic acid is used to react with a metallic metal.

6. As a starting material, metal metaborate M(BO 2 ) n , or its hydrate M(BO 2 ) n ・xH 2 From one of the O to boric acid H 3 BO 3 wherein M is a metal, e.g., a metallic, alkali, alkaline earth, or transition metal or a compound acting as a metal, n is the valence value of the metal, and x is the number of water molecules bound to the metal metaborate in each hydrate; The electrochemical cell (100) comprises a reaction system in which metal metaborate and water, H, are reacted in an electrochemical cell according to an overall reaction scheme at least substantially as follows: 2 It is used to convert O to boronic acid, 4M(BO 2 ) n +10nH 2 O→4nH 3 B.O. 3 +4M(OH) n +nO 2 +2nH 2 、 The electrochemical cell comprises an anode half-cell (110) with an anode (115) and at least substantially water as the liquid in the anode half-cell, a cathode half-cell (120) with a cathode (125) and at least substantially only water as the liquid in the cathode half-cell, and a cation exchange membrane separating the anode half-cell and the cathode half-cell; The positive and negative poles of a potential source are connected to the anode and cathode, respectively; At least substantially, a metal metaborate is provided to the 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, the H + From electrolysis to acidic ions H + , and electron e - is produced at the anode and reacts with metal metaborate and water according to the following reaction: 2nH 2 O→4nH + +nO 2 +4ne - 4M(BO 2 ) n +4nH + +4nH 2 O→4nH 3 BO 3 +4M n+ having an overall reaction in the anode half-cell at least substantially according to the following reaction: 4M(BO 2 ) n +6nH 2 O→4nH 3 BO 3 +nO 2 +4M n+ +4ne - The cation exchange membrane transports metal ions M from the anode half-cell to the cathode half-cell. n+ Through In the cathode half-cell, electrons e from water and the cathode - from hydroxide ion OH - is produced at the cathode, and metal hydroxide M(OH) is converted from metal ions and water according to the following reaction: n Forming 4nH 2 O+4ne - →2nH 2 +4nOH - 4M n+ +4nOH - →4M(OH) n having an overall reaction in the cathode half-cell at least substantially according to the following reaction: 4M n+ +4nH 2 O+4ne - →4M(OH) n +2nH 2 method.

7. 7. The method according to claim 1, 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. 8. The method of any one of claims 1 to 7, wherein the concentration of metal metaborate in water is in the range of 0.2M to 8M.

9. 9. The method of claim 1, wherein a metal hydroxide is added to the cathode half-cell to increase electrical conductivity.

10. 10. The method according to claim 1, wherein the concentration of the metal hydroxide in the water is in the range of 0M to 3M.

11. 11. The method of claim 1, wherein the potential source is provided by a potentiostat, a galvanostat or a battery.

12. 12. The method according to any one of claims 1 to 11, wherein the potential supplied by the potential source between the anode and the cathode is in the range of 2V to 12V.

13. 13. The method according to any one of claims 1 to 12, wherein the material of the anode is selected from at least one of stainless steel, mild steel, nickel, Raney nickel or Raney nickel contaminated with small amounts of other metals.

14. 14. The method according to any one of claims 1 to 13, wherein the material of the cathode is selected from at least one of DSA platinized titanium and any other kind of platinum-based material.

15. Metal metaborate and water H 2 15. The method of any one of claims 1 to 14, wherein the electrochemical cell for converting O to boric acid is an electrochemical flow cell or a batch electrochemical cell.

16. 16. The method of claim 1, wherein the boric acid provided by the electrochemical cell is available as a solution of boric acid dissolved in water, and the solution of boric acid dissolved in water is at least one of cooled and concentrated to produce boric acid by precipitation.

Images