Method for producing periodate by anodic oxidation in a stationary reactor

Abstract

The present invention relates to a method for producing metal paraperiodates by anodizing iodine compounds having oxidation states from -I to +V in an electrolytic cell under specified conditions, and to an apparatus for carrying out this reaction.

Description

[Technical field]

[0001] The present invention relates to a method for producing metal paraperiodates by the anodic oxidation of iodine compounds having oxidation states from -I to +V in an electrolytic cell under specified conditions, and to an apparatus for carrying out this reaction. [Background technology]

[0002] Periodates are strong oxidizing agents that are widely used in chemical synthesis. When periodates are used at any stage in the synthesis of products, especially in the pharmaceutical, cosmetic and nutritional sectors, there is always a demand for economical and compliant production methods.

[0003] Periodate or periodic acid can be generated electrochemically by anodic oxidation from elemental iodine or salts of iodine where the oxidation state of iodine is less than +VII.

[0004] A common challenge in the preparation of periodate salts is the different solubilities of iodine species, which significantly impedes the performance of electrolysis. Iodine is dissolved in water as iodide (I - ) and hypoiodite (HIO), which disproportionates to it, making it soluble in alkaline media, but insoluble in neutral to acidic media. In contrast, periodate is soluble in aqueous acids and orthoperiodic acid (H 5 IO 6 ) is formed, but is insoluble in alkaline media and is converted to paraperiodate (Na 3 H 2 IO 6 ) is formed. The precipitation of iodine and paraperiodate will coat the anode surface and the separator, reducing the efficiency of the electrolysis. In addition, clogging of the flow electrolysis cell may occur, which will immediately interrupt the electrolysis and may damage the electrolysis cell.

[0005] International Publication No. WO2021 / 110928 relates to a method for preparing metal periodates by anodizing metal iodides with a carbon-based anode. The method is preferably carried out under basic conditions. Similarly, S. Arndt et al. in Angew.Chem.2020,132,8112-8118 describe the electrochemical synthesis of sodium periodate by anodizing sodium iodide under basic conditions with a boron-doped diamond (BDD) electrode. In these documents, paraperiodate is obtained in high yield and purity. However, the inventors have found that scaling up the reaction under the conditions of these documents can lead to an undesirable degree of clogging due to the formation of solid periodate precipitates in the electrolysis cell. Clogging is not only a maintenance issue requiring disassembly and cleaning of the cell, but can also cause high backpressure and even damage to the anode.

[0006] U.S. Pat. No. 4,687,565 relates to an electrolytic cell for producing periodate comprising a plurality of open anode chamber boxes with a plurality of cathodes mounted vertically and equally spaced apart parallel to the long sides of the cell body and plate separators adapted to maintain equal spacing between the cathodes, one or more anodes inserted into the anode chamber boxes, a plurality of polyvinyl chloride (PVC) diaphragms mounted parallel to the cathodes on both sides of the anode chamber boxes, an anolyte inlet attached to the bottom of the anode chamber boxes and an anolyte outlet attached to the top of the opposite side of the boxes, a cell cover attached to the cell body with an air inlet and cell gas exhaust, and a perforated PVC lid for the cathode chamber positioned between the cell cover and the upper level of the catholyte.

[0007] No. 5,074,975 relates to a method for the simultaneous electrosynthesis of alkali peroxides and oxygenated halogen salts of alkali metals, and a reactor for carrying out said reactions, comprising an oxygen-reducing cathode (preferably porous) and a halogen-generating anode, separated by an anion-permeable wall (preferably an anion exchange membrane).

[0008] The object of the present invention was to provide a method for the preparation of paraperiodate that is easy to scale up, can be carried out continuously or semi-continuously, and avoids or at least reduces clogging. Moreover, the method is not limited to the oxidation of metal iodides, but should be applicable to any kind of iodine starting material. In certain embodiments, the method should allow the use of starting materials in a dispersed (e.g. dissolved or suspended) or solid state, the separation of the desired product in-line, and / or the recycling of the electrolyte. Summary of the Invention

[0009] The inventors have discovered that during the anodization of iodide to the desired (para)periodate, clogging can be avoided or at least significantly reduced if the anolyte, which comprises a metal periodate and an iodide with an oxidation state between -I and +V, is recirculated to the anode chamber through an anolyte circuit, the anolyte circuit comprising a continuous stirred tank reactor operated in stationary mode with respect to the total molar ratio of metal periodate to iodide with an oxidation state between -I and +V in the anolyte. In particular, the anolyte recirculated through the anode chamber is not completely depleted of the target paraperiodate or periodate (i.e., an iodide with an oxidation state of the iodine atom +VII, a more detailed definition of which is given below) when reintroduced into the anode chamber, but rather a significant amount remains.

[0010] The present invention therefore relates to a method for the production of metal paraperiodates by anodizing iodine compounds with oxidation states from -I to +V in an electrolytic cell comprising an anolyte chamber with one or more anodes, a catholyte chamber with one or more cathodes and a separator arranged between the anolyte chamber and the catholyte chamber, the method comprising: recycling catholyte through a catholyte circuit to the catholyte chamber, recycling anolyte through an anolyte circuit to the anolyte chamber comprising a metal periodate and an iodine compound with an oxidation state from -I to +V selected from an iodine salt (obviously with oxidation states from -I to +V), elemental iodine, a mixture of different iodine salts (obviously with oxidation states from -I to +V) or a mixture of iodine and one or more iodine salts (obviously with oxidation states from -I to +V), and carrying out the anodic oxidation of the iodine compound at a pH of at least 10. The anolyte circuit comprises at least one continuous stirred tank reactor operated in a stationary mode with respect to the total molar ratio of metal periodates to iodine compounds having oxidation states −I to +V in the anolyte, the continuous stirred tank reactor being operated in a “stationary” mode by continuously or periodically feeding the iodine compounds having oxidation states −I to +V to the continuous stirred tank reactor and continuously or periodically removing metal periodates from the continuous stirred tank reactor.

[0011] The invention further relates to an apparatus configured for producing metal paraperiodate by the method of the invention, i.e., for producing metal paraperiodate by continuous anodic oxidation of an iodine compound, comprising an electrolysis cell including an anode chamber having one or more anodes, a cathode chamber having one or more cathodes, and a separator disposed between the anode chamber and the cathode chamber, a catholyte circuit for recirculating catholyte through the cathode chamber, the catholyte circuit comprising a catholyte reservoir, and an anolyte circuit for circulating anolyte through the anode chamber, the anolyte circuit comprising at least one continuous stirred tank reactor. The at least one continuous stirred tank reactor is provided with a supply means for supplying iodine compounds having an oxidation state of -I to +V selected from iodine salts (naturally with oxidation states of -I to +V), elemental iodine, a mixture of different iodine salts (naturally with oxidation states of -I to +V) or a mixture of iodine and one or more iodine salts (naturally with oxidation states of -I to +V) to the at least one continuous stirred tank reactor, and a withdrawal means for removing metal periodate reaction product from the at least one continuous stirred tank reactor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] definition Metal periodates are the metal salts of various periodic acids. In periodic acid, the corresponding anion consists of iodine in the oxidation state +VII and oxygen (oxygen in the oxidation state -II). Periodates include orthoperiodates (IO 6 5- , metal orthoperiodate has the formula M 5 IO 6 ), metaperiodate (IO 4 - , metal metaperiodate has the formula MIO 4 ), dimesoperiodate (I 2 O 9 4- , metal dimesoperiodate has the formula M 4 I 2 O 9 ), mesoperiodate (IO5 3- , metal mesoperiodates have the formula M 3 IO 5 Paraperiodate has the formula M 3 H 2 IO 6 and the corresponding double salt MIO 4 Also known as 2MOH. In the above formula, M is the metal equivalent [(M n+ ) 1 / n , n is the charge number]. For example, in the case of alkali metal periodates, M is the alkali metal cation, and in the case of alkaline earth metal periodates, M is (M 2+ ) 1 / 2 In periodates with multiple negative charges, the metal equivalents M may have the same or different meanings. For example, M in paraperiodate 3 H 2 IO 6 or MIO 4 In 2MOH, all three metal equivalents M may have the same meaning or may be derived from different metals. This is the situation that can arise, for example, when the starting material is an iodide salt (such as an iodide or iodate) whose countercation is different from that of the base present during anodization or that of the base used during workup of the reaction products. See below for further details.

[0013] In the present invention, an iodine compound having an oxidation state of -I to +V is an inorganic iodine compound in which the iodine atom has a specified oxidation state, i.e., an iodine salt having an oxidation state (of iodine) of -I to +V or elemental iodine. Inorganic iodine salts in which the iodine atom has an oxidation state of -I to +V include, for example, iodide [(M n+ ) 1 / n (I - iodine atom in the oxidation state -I], hypoiodite [(M n+ ) 1 / n (IO - iodine atom in the +I oxidation state], iodite [(M n+ ) 1 / n (IO 2 - )- iodine atom in the +III oxidation state], and iodate [(M n+ ) 1 / n (IO 3 - ) - ; an iodine atom in the +V oxidation state], where M is a cation, usually a metal cation or an ammonium cation, and n is the number of charges.

[0014] The anolyte is the liquid medium in the anode chamber and the catholyte is the liquid medium in the cathode chamber.

[0015] In the present invention, a dispersion is a solution or a suspension. Similarly, "dispersion" means dissolved or suspended.

[0016] Operating a continuous stirred tank reactor in a "steady-state mode" with respect to the total molar ratio of metal periodate to iodine compounds in the oxidation states -I to +V in the anolyte means that a predetermined molar ratio is selected and that during operation the actual molar ratio of metal periodate to iodine compounds is maintained at or near the predetermined molar ratio (range). Here, "near" means that the actual molar ratio (range) deviates from the predetermined molar ratio (range) by up to ±20%, preferably up to ±10%. Since metal periodate is continuously produced during the anodic oxidation of iodine compounds in the electrolytic cell, decreasing the amount of iodine compounds in lower oxidation states (i.e. -I to +V) and increasing the amount of metal periodate in the anolyte, the steady-state mode of operation can only be maintained by adding iodine compounds in lower oxidation states (i.e. -I to +V) and / or removing metal periodate. In order to maintain the actual ratio within the above range, more or less, up to 20 mole %, preferably up to 10 mole %, of a lower oxidation state iodine compound may be added to the anolyte when removing the metal periodate, the given molar ratio being conveniently defined for a particular point in the electrolysis, for example, the anolyte prior to entering the anode chamber.

[0017] The descriptions given below with respect to preferred embodiments of the invention are valid on their own but preferably also in combination with one another: wherever applicable, descriptions made in relation to preferred embodiments of the method of the invention also apply to the apparatus of the invention and vice versa, unless expressly specified otherwise.

[0018] Embodiments of the invention (Ex) Typical and preferred embodiments Ex are summarized in the following non-exhaustive list: Further preferred embodiments will become apparent from the paragraphs following this list.

[0019] A method for producing metal paraperiodates by anodizing iodine compounds having oxidation states of -I to +V in an electrolytic cell, the electrolytic cell comprising an anolyte chamber having one or more anodes, a catholyte chamber having one or more cathodes, and a separator disposed between the anolyte chamber and the catholyte chamber, the method comprising: recycling catholyte through a catholyte circuit to the catholyte chamber; recycling anolyte through an anolyte circuit to the anolyte chamber, the anolyte containing metal periodates and iodine compounds having oxidation states of -I to +V selected from iodine salts (obviously having oxidation states of -I to +V), elemental iodine, mixtures of different iodine salts (obviously having oxidation states of -I to +V), or mixtures of iodine and one or more iodine salts (obviously having oxidation states of -I to +V); and recycling the anodization of the iodine compounds. and performing anodic oxidation at a pH of at least 10, the anolyte circuit comprising at least one continuous stirred tank reactor operated in a stationary mode with respect to the total molar ratio of metal periodates and iodine compounds having oxidation states from -I to +V in the anolyte, the continuous stirred tank reactor being operated in a "stationary" mode by continuously or periodically supplying the iodine compounds having oxidation states from -I to +V to the continuous stirred tank reactor and continuously or periodically removing metal periodates from the continuous stirred tank reactor.

[0020] E.2. The method of embodiment E.1, wherein the metal periodate contained in the recycled anolyte is primarily metal paraperiodate.

[0021] E.3. The method of any one of the preceding embodiments, wherein for operating the continuous stirred tank reactor in stationary mode for the total molar ratio of metal periodate to iodine compound having oxidation states from -I to +V in the anolyte, a molar ratio or molar ratio range is defined, and during operation, the actual molar ratio or molar ratio range of metal periodate to iodine compound is maintained at or near the defined molar ratio or molar ratio range, where "near" means that the actual molar ratio or molar ratio range may deviate from the defined molar ratio or molar ratio range by up to ±20%, and the molar ratio is calculated based on the iodine atoms present in the metal periodate and the iodine compound.

[0022] E.4. The method according to embodiment E.3, wherein the defined molar ratio or molar ratio range relates to the molar ratio or molar ratio range in the anolyte before it enters the anode chamber.

[0023] E.5. The method of any one of the preceding embodiments, wherein the total molar ratio of metal periodate to iodine compounds having oxidation states -I to +V in the recycled anolyte is 1:>0 to 1:5 (i.e., some iodine compounds having oxidation states -I to +V should be present, but the total amount of iodine compounds having oxidation states -I to +V should not exceed 5 times the amount of metal periodate), and the iodine compounds have oxidation states -I to +III, is from 1:0 to 8:1 (meaning that the metal periodate exceeds the total amount of iodine compounds having oxidation states -I to +III by at least 8 times, if the latter are present), and if the oxidation state of the iodine compounds is +V, the total molar ratio of metal periodate to iodine compounds having oxidation state +V is from 1:0 to 1:5 (i.e. the total amount of iodine compounds having oxidation state +V, if present, must not exceed 5 times the amount of metal periodate).

[0024] E.6. The method of embodiment E.5, wherein the total molar ratio of metal periodate to iodine compounds having oxidation states -I to +V is 1:>0 to 1:4, and when the oxidation state of the iodine compounds is -I to +III, the total molar ratio of metal periodate to iodine compounds having oxidation states -I to +III is 1:0 to 10:1, and when the oxidation state of the iodine compounds is +V, the total molar ratio of metal periodate to iodine compounds having oxidation state +V is 1:0 to 1:4.

[0025] E.7. The method of embodiment E.6, wherein the total molar ratio of metal periodate to iodine compounds having oxidation states -I to +V is 200:1 to 1:4, where when the iodine compounds have oxidation states -I to +III, the total molar ratio of metal periodate to iodine compounds having oxidation states -I to +III is 1:0 to 10:1, and when the iodine compounds have an oxidation state of +V, the total molar ratio of metal periodate to iodine compounds having an oxidation state of +V is 200:1 to 1:4.

[0026] E.8. The method of any one of embodiments E.1 to E.4, wherein when the recycled anolyte is fed to the anolyte chamber, the total molar ratio of metal periodate to iodine compounds having oxidation states -I to +V is 1:>0 to 1:5 (i.e., some iodine compounds having oxidation states -I to +V should be present, but the total amount of iodine compounds having oxidation states -I to +V should not exceed 5 times the amount of metal periodate), and wherein when the iodine compounds have oxidation states -I to +III, the metal periodate is present. The total molar ratio of metal periodate to iodine compounds having oxidation states -I to +III is 1:0 to 8:1 (meaning that the metal periodate exceeds the total amount of iodine compounds having oxidation states -I to +III by at least 8 times), and if the oxidation state of the iodine compounds is +V, the total molar ratio of metal periodate to iodine compounds having an oxidation state of +V is 1:0 to 1:5 (i.e. the total amount of iodine compounds having an oxidation state of +V, if present, must not exceed 5 times the amount of metal periodate).

[0027] E.9. The method of embodiment E.8, wherein the total molar ratio of metal periodate to iodine compounds having oxidation states -I to +V is 1:>0 to 1:4, where if the iodine compounds have oxidation states -I to +III, the total molar ratio of metal periodate to iodine compounds having oxidation states -I to +III is 1:0 to 10:1, and where if the iodine compounds have an oxidation state of +V, the total molar ratio of metal periodate to iodine compounds having an oxidation state of +V is 1:0 to 1:4.

[0028] E.10. The method of embodiment E.9, wherein the total molar ratio of metal periodate to iodine compounds having oxidation states -I to +V is 200:1 to 1:4, where when the iodine compounds have oxidation states -I to +III, the total molar ratio of metal periodate to iodine compounds having oxidation states -I to +III is 1:0 to 10:1, and when the iodine compounds have an oxidation state of +V, the total molar ratio of metal periodate to iodine compounds having an oxidation state of +V is 200:1 to 1:4.

[0029] E.11. The method according to any one of embodiments E.1 to E.4 and E.8 to E.10, wherein for operating the continuous stirred tank reactor in a stationary mode, a molar ratio or molar ratio range is defined for the anolyte before entering the anode chamber with respect to the total molar ratio of metal periodate and iodine compounds having an oxidation state from -I to +V, and during operation, the actual molar ratio or molar ratio range of metal periodate and iodine compounds in the anolyte before entering the anode chamber is maintained within the defined molar ratio or molar ratio range ±20%, wherein said defined molar ratio or molar ratio range is the actual molar ratio or molar ratio range of metal periodate and iodine compounds in the anolyte before entering the anode chamber (i.e. , when fed to the anode chamber), the total molar ratio of the metal periodate to the iodine compound having an oxidation state of -I to +V is selected to be 1:>0 to 1:5, and when the oxidation state of the iodine compound is -I to +III, the total molar ratio of the metal periodate to the iodine compound having an oxidation state of -I to +III is 1:0 to 8:1, and when the oxidation state of the iodine compound is +V, the total molar ratio of the metal periodate to the iodine compound having an oxidation state of +V is 1:0 to 1:5, where the molar ratios are calculated based on the iodine atoms present in the metal periodate and the iodine compound.

[0030] E.12. The method of embodiment E.11, wherein the total molar ratio of metal periodate to iodine compounds having oxidation states -I to +V is 1:>0 to 1:4, where if the iodine compounds have oxidation states -I to +III, the total molar ratio of metal periodate to iodine compounds having oxidation states -I to +III is 1:0 to 10:1, and where if the iodine compounds have an oxidation state of +V, the total molar ratio of metal periodate to iodine compounds having an oxidation state of +V is 1:0 to 1:4.

[0031] E.13. The method of embodiment E.12, wherein the total molar ratio of the metal periodate to the iodine compounds having an oxidation state of -I to +V is 200:1 to 1:4, wherein when the iodine compounds have an oxidation state of -I to +III, the total molar ratio of the metal periodate to the iodine compounds having an oxidation state of -I to +III is 1:0 to 10:1, and when the iodine compounds have an oxidation state of +V, the total molar ratio of the metal periodate to the iodine compounds having an oxidation state of +V is 200:1 to 1:4.

[0032] E.14. The method according to any one of the preceding embodiments, wherein the method for preparing an alkali metal paraperiodate is an alkali metal iodide, an alkali metal iodate, iodine, or a mixture thereof, wherein the iodine compound having an oxidation state of -I to +V is an alkali metal iodide, an alkali metal iodate, iodine, or a mixture thereof.

[0033] E.15. The method according to embodiment E.14, which prepares sodium paraperiodate or potassium paraperiodate, wherein the iodine compound having an oxidation state of -I to +V is sodium iodide, potassium iodide, sodium iodate, potassium iodate, iodine, or a mixture thereof.

[0034] E.16. A method according to any of the previous embodiments, wherein anodization is carried out at a pH of at least 11.

[0035] E.17. The method of embodiment E.16, wherein the anodization is carried out at a pH of at least 12.

[0036] E.18. The method of embodiment E.17, wherein the anodization is carried out at a pH of at least 13.

[0037] E.19. A method according to any of the previous embodiments, wherein the anodization is carried out in the presence of a base, the base being selected from the group consisting of metal hydroxides, metal oxides and metal carbonates.

[0038] E.20. The method of embodiment E.19, wherein the anodization is carried out in the presence of a metal hydroxide, and wherein, when the iodine compound having an oxidation state of -I to +V is an alkali metal iodine salt, the metal of the base corresponds to the metal in the metal iodine salt.

[0039] E.21. The method according to any of the previous embodiments, wherein the catholyte comprises an aqueous medium with a pH of at least 10.

[0040] E.22. The method of embodiment E.21, wherein the catholyte comprises an aqueous medium with a pH of at least 11.

[0041] E.23. The method of embodiment E.22, wherein the catholyte comprises an aqueous medium with a pH of at least 12.

[0042] E.24. The method of embodiment E.23, wherein the catholyte comprises an aqueous medium with a pH of at least 13.

[0043] E.25. The method according to any of the previous embodiments, wherein the anodization is performed at 10-1000 mA / cm 2 The current density is in the range of

[0044] E.26. The method of embodiment E.25, wherein the anodization is performed at 100 to 750 mA / cm 2 The current density is in the range of

[0045] E.27. The method of embodiment E.26, wherein the anodization is performed at 250-500 mA / cm 2 The current density is in the range of

[0046] E.28. The method of embodiment E.27, wherein the anodization is performed at 400-430 mA / cm 2 The current density is

[0047] E.29. A process according to any of the preceding embodiments, wherein said iodine compound having an oxidation state ranging from -I to +V is continuously or periodically introduced into the continuous stirred tank reactor at substantially the same rate that metal periodate is continuously or periodically removed from the anode chamber, "substantially the same rate" meaning that the molar ratio of metal periodate to iodine compound is maintained within the above-specified range.

[0048] E.30. A method according to any of the preceding embodiments, wherein metal periodate produced in the anode chamber is separated from anolyte removed from the anode chamber, and the remainder of the anolyte is transferred to the continuous stirred tank reactor.

[0049] E.31. The method of embodiment E.30, wherein if the isolated periodate does not consist of metal paraperiodate or does not consist entirely of metal paraperiodate, periodates other than paraperiodate are converted to paraperiodate (e.g., by adding a base that converts periodates other than paraperiodate to paraperiodate).

[0050] E.32. The method according to any of the previous embodiments, wherein the separator disposed between the cathode chamber and the anode chamber is selected from a semi-permeable membrane, a diaphragm, and a frit.

[0051] E.33. The method of embodiment E.32, wherein the separator disposed between the cathode and anode compartments is an ion exchange membrane.

[0052] E.34. A method according to any of the previous embodiments, wherein one or more anodes comprises a carbon-based active layer.

[0053] E.35. The method of embodiment E.34, wherein the one or more anodes comprise a diamond layer doped with one or more elements from IUPAC groups 13, 15, or 16 of the periodic table.

[0054] E.36. The method of embodiment E.35, wherein the one or more anodes comprise a boron-doped diamond layer.

[0055] E.37. The method of any one of the preceding embodiments, wherein the iodine compound having an oxidation state of -I to +V is fed to the continuous stirred tank reactor in the form of an aqueous dispersion or in the form of a solid.

[0056] E.38. An apparatus for producing metal periodates, in particular metal paraperiodates, by successive anodic oxidation of iodine compounds in oxidation states -I to +V, in particular configured to carry out a method according to any of the embodiments E.1 to E.37, comprising an electrolysis cell including an anode chamber having one or more anodes, a cathode chamber having one or more cathodes, and a separator disposed between the anode chamber and the cathode chamber, a catholyte circuit for recirculating catholyte through the cathode chamber, the catholyte circuit comprising a catholyte reservoir, and an anolyte circuit for circulating anolyte through the anode chamber; The anolyte circuit comprises at least one continuous stirred tank reactor provided with supply means for supplying iodine compounds having an oxidation state from −I to +V selected from an iodine salt, elemental iodine, a mixture of different iodine salts, or a mixture of iodine and one or more iodine salts to the at least one continuous stirred tank reactor, and withdrawal means for removing a metal periodate reaction product from the at least one continuous stirred tank reactor.

[0057] E.39. The apparatus of embodiment E.38, wherein the supply means for supplying iodine compounds having oxidation states from -I to +V includes a starting material tank containing a solution of iodine compounds having oxidation states from -I to +V connected to the continuous stirred tank reactor.

[0058] E.40. The apparatus according to any of embodiments E.38 and E.39, wherein the removal means includes a collection vessel connected to the continuous stirred tank reactor via a discharge line.

[0059] E.41. The apparatus of embodiment E.40, wherein the supplying means for supplying an iodine compound includes a supply of solid iodine compound connected to the continuous stirred tank reactor.

[0060] E.42. The apparatus of embodiment E.41, wherein the removal means includes a collection vessel connected to the continuous stirred tank reactor via a discharge line and a recirculation line.

[0061] E.43. An apparatus according to any of embodiments E.38 to E.42, wherein the catholyte circuit comprises a catholyte tank, the catholyte tank being connected to the anolyte circuit via a transfer line for transferring a portion of the catholyte to the anolyte circuit.

[0062] E.44. The apparatus according to any of embodiments E.38 to E.43, wherein the electrolysis cell comprises a cooling water system for controlling the temperature of the anode chamber and / or the cathode chamber of the electrolysis cell.

[0063] E.45. An apparatus according to any of embodiments E.38 to E.44, comprising a measurement system for determining the ratio of metal periodates to iodine compounds of oxidation states -I to +V in the anolyte.

[0064] E.46. The apparatus of embodiment E.45, wherein the measurement system includes a potentiometer, an ammeter, a pH probe, or a combination thereof.

[0065] The substances to be anodized are iodine compounds with oxidation states -I to +V. Iodine compounds with oxidation states -I to +V are in fact iodine compounds with oxidation states -I, 0 (elemental iodine), +I, +III, or +V. Iodine compounds with oxidation states -I to +V are selected from iodine salts, elemental iodine, mixtures of different iodine salts, or mixtures of iodine with one or more iodine salts.

[0066] As explained above, iodine salts are inorganic iodine salts. Examples of suitable inorganic iodine salts with oxidation states (iodine atom) from -I to +V include iodide [(M n+ ) 1 / n (I - iodine atom in oxidation state -I], hypoiodite [(M n+ ) 1 / n (IO - iodine atom in oxidation state +I], iodite [(M n+ ) 1 / n (IO 2 - ) - iodine atom in oxidation state +III], and iodate [(M n+ ) 1 / n (IO 3 - ) - iodine atom in oxidation state +V], where M is a cation (usually a metal cation or ammonium cation) and n is the number of charges. Of these, metal salts are preferred, namely metal iodides, hypoiodites, iodates and iodates. Ideally, the metal countercation matches that required for the target metal paraperiodate, thus avoiding cation exchange.

[0067] Suitable metal countercations for the iodide salts and target metal paraperiodates are alkali metal cations, alkaline earth metal cations, and transition metal cations.

[0068] Suitable alkali metal countercations include, for example, lithium, sodium, potassium, and cesium cations.

[0069] Suitable alkaline earth metal countercations include, for example, magnesium or calcium cations.

[0070] Suitable transition metal iodine salts to be used as starting materials in the method of the present invention are those that are stable under atmospheric conditions (air, moisture) and at least partially soluble in the reaction medium at the desired concentration. In general, the reaction medium for anodization is aqueous. However, low solubility in pure water does not necessarily mean that the transition metal iodine salt is unsuitable, since the reaction (anodization) is carried out under basic conditions that may significantly increase the solubility in the reaction medium. For example, CuI is essentially insoluble in water at a pH of about 7, but is a suitable starting compound in a basic reaction medium, especially when the reaction medium contains an inorganic base salt as the base, the cation of which forms a water-soluble iodide, for example NaOH or KOH.

[0071] Suitable transition metal countercations include Sc(III), Y(III), La(III), Co(II), Ni(II), Cu(I), and Zn(II) cations, of which Cu(I) and Zn(II) cations are preferred due to their economical and readily available nature.

[0072] Among the starting iodine compounds listed above, in which the oxidation state of the iodine atom is between -I and +V, iodides, iodates, elemental iodine and mixtures thereof are preferred, more preferred are alkali metal iodides, alkali metal iodates, alkaline earth metal iodides, alkaline earth metal iodates, Sc(III) iodide, Sc(III) iodate, Y(III) iodide, Y(III) iodate, La(III) iodide, La(III) iodate, Co(II) iodide, Co(II) iodate, Ni(II) iodide, Ni(II) iodate, Cu(I) iodide, Cu(I) iodate, Zn(II) iodide, Zn(II) iodate, elemental iodine and mixtures thereof. Further preferred are alkali metal iodides, especially LiI, NaI, KI and CsI, alkali metal iodates, especially Li(IO 3 ), Na(IO 3 ), K(IO 3 ) and Cs(IO 3 ), alkaline earth metal iodides, especially MgI 2 and CaI 2, alkaline earth metal iodates, especially Mg(IO 3 ) 2 and Ca(IO 3 ) 2 , CuI, Cu(IO 3 ), ZnI 2 , Zn(IO 3 ) 2 , elemental iodine and mixtures thereof. Particularly preferred are alkali metal iodides, especially LiI, NaI, KI and CsI, alkali metal iodates, especially Li(IO 3 ), Na(IO 3 ), K(IO 3 ) and Cs(IO 3 ), alkaline earth metal iodides, especially MgI 2 and CaI 2 , alkaline earth metal iodates, especially Mg(IO 3 ) 2 and Ca(IO 3 ) 2 , elemental iodine and mixtures thereof. More particularly preferred are alkali metal iodides, especially LiI, NaI, KI and CsI, alkali metal iodates, especially Li(IO 3 ), Na(IO 3 ), K(IO 3 ) and Cs(IO 3 ), elemental iodine and mixtures thereof. 3 ), K(IO 3 ), iodine or a mixture thereof is used.

[0073] Therefore, the method of the present invention is preferably used to prepare alkali metal paraperiodates, alkaline earth metal paraperiodates, or Sc(III), Y(III), La(III), Co(II), Ni(II), Cu(I) or Zn(II) paraperiodates, or mixtures thereof. More preferably, the method of the present invention is used to produce alkali metal paraperiodates, in particular lithium, sodium or potassium paraperiodates, alkaline earth metal paraperiodates, in particular magnesium or calcium paraperiodates, Cu(I) paraperiodate, Zn(II) paraperiodate, or mixtures thereof. Even more preferably, the method of the present invention is used to prepare alkali metal paraperiodates, in particular lithium, sodium or potassium paraperiodates, or alkaline earth metal paraperiodates, in particular magnesium or calcium paraperiodates, or mixtures thereof. In particular, the process of the present invention is used to prepare an alkali metal paraperiodate, particularly sodium or potassium paraperiodate, especially sodium paraperiodate.

[0074] In the method of the invention, the anolyte is recycled to the anode chamber through an anolyte circuit. According to the invention, the anolyte comprises a metal periodate and an iodine compound with an oxidation state between -I and +V selected from an iodine salt, elemental iodine, a mixture of different iodine salts, or a mixture of iodine and one or more iodine salts.

[0075] In the method of the invention, the continuous stirred tank reactor is operated in a stationary mode with respect to the total molar ratio of metal periodate to iodine compounds with oxidation states of -I to +V in the anolyte by continuously or periodically feeding iodine compounds with oxidation states of -I to +V to the continuous stirred tank reactor and continuously or periodically removing metal periodate from the continuous stirred tank reactor. Operating in a stationary mode with respect to said total molar ratio means that a suitable molar ratio, or more generally a suitable molar ratio range, is specified and that during operation the actual molar ratio or molar ratio range of metal periodate to iodine compounds is maintained at said specified molar ratio or within said molar ratio range or in the vicinity of the specified molar ratio or molar ratio range. Here, "in the vicinity" means that the (limits of) the actual molar ratio or molar ratio range may deviate from the specified molar ratio or molar ratio range by up to ±20%. In this context, the molar ratio (range) is calculated based on the iodine atoms present in the metal periodate and the iodine compounds. Suitable and preferred values ​​of molar ratios or molar ratio ranges are defined below. It is convenient to define said molar ratios or molar ratio ranges for a particular point in the electrolysis. One suitable point in the electrolysis is the composition of the anolyte before it is fed to the anode chamber. Thus, in a preferred embodiment, said molar ratios or molar ratio ranges relate to the molar ratios or molar ratio ranges in the anolyte before it enters the anode chamber. Thus, preferably, operating in stationary mode with respect to said total molar ratio means that a suitable total molar ratio (range) for iodine compounds with metal periodate oxidation states -I to +V is defined for the anolyte before it enters the anode chamber, and during operation, the actual molar ratio (range) of metal periodate to iodine compounds in the anolyte before it enters the anode chamber is maintained at said defined molar ratio or within said defined molar ratio range or in the vicinity of the defined molar ratio or molar ratio range. Here, "in the vicinity" means that the actual molar ratio or molar ratio range may deviate from the specified molar ratio or molar ratio range by up to ±20%.

[0076] It has been found that clogging is mitigated or inhibited if there is a significant amount of metal periodate in the anolyte. Clogging is primarily to be avoided in the anode chamber, so it is important that metal periodate is present in sufficient amounts in the anolyte before it enters the anode chamber (it is of course also important in the anode chamber, but the amount of periodate is adjusted before feeding the anolyte to the anode chamber). Thus, in a preferred embodiment, in the recycled anolyte, when it is fed to the anode chamber, the total molar ratio of metal periodate to iodine compounds with oxidation states -I to +V is 1:>0 to 1:5 (i.e., some iodine compounds with oxidation states -I to +V should be present, but the total amount of iodine compounds with oxidation states -I to +V should not exceed 5 times the amount of metal periodate). Wherein, when the oxidation state of the iodine compound is -I to +III, the total molar ratio of the metal periodate to the iodine compound with the oxidation state -I to +III is 1:0 to 8:1 (i.e., the metal periodate exceeds the total amount of the iodine compound with the oxidation state -I to +III by at least 8 times, if the latter is present). Wherein, when the oxidation state of the iodine compound is +V, the total molar ratio of the metal periodate to the iodine compound with the oxidation state +V is 1:0 to 1:5 (i.e., the total amount of the iodine compound with the oxidation state +V, if present, should not exceed the amount of the metal periodate by more than 5 times). More preferably, the total molar ratio of the metal periodate to the iodine compound with the oxidation state -I to +V is 1:>0 to 1:4, and even more preferably 200:1 to 1:4. Wherein, when the iodine compound has an oxidation state of -I to +III, the total molar ratio of the metal periodate to the iodine compound having an oxidation state of -I to +III is 1:0 to 10:1, and when the iodine compound has an oxidation state of +V, the total molar ratio of the metal periodate to the iodine compound having an oxidation state of +V is 1:0 to 1:4, preferably 200:1 to 1:4.

[0077] Preferably, the above total molar ratio is not limited to the anolyte before entering the anode chamber, but is applied to the (re)circulated anolyte in general. Therefore, preferably, the total molar ratio of metal periodate and iodine compounds having oxidation states of -I to +V in the (re)circulated anolyte is 1:>0 to 1:5. Here, when the iodine compounds have oxidation states of -I to +III, the total molar ratio of metal periodate and iodine compounds having oxidation states of -I to +III is 1:0 to 8:1. Also, when the iodine compounds have an oxidation state of +V, the total molar ratio of metal periodate and iodine compounds having oxidation state of +V is 1:0 to 1:5. More preferably, the total molar ratio of metal periodate and iodine compounds having oxidation states of -I to +V is 1:>0 to 1:4, and even more preferably 200:1 to 1:4. Here, when the iodine compound has an oxidation state of -I to +III, the total molar ratio of the metal periodate to the iodine compound having an oxidation state of -I to +III is 1:0 to 10:1, and when the iodine compound has an oxidation state of +V, the total molar ratio of the metal periodate to the iodine compound having an oxidation state of +V is 1:0 to 1:4, preferably 200:1 to 1:4.

[0078] The molar ratio of metal periodate to iodine compounds with oxidation states -I to +V will vary depending on the location of the anolyte (by way of example only, the anolyte will contain more periodate after it leaves the anode chamber than before it enters the anode chamber), but the molar ratio conditions given preferably apply regardless of the location of the anolyte. As indicated above, the molar ratios given apply specifically to the anolyte before it enters the anode chamber. The molar ratio at this location of the anolyte can be adjusted, for example, by the amount of iodine compounds with oxidation states -I to +V added to the stirred tank reactor and / or the amount of periodate removed after passing through the anode chamber.

[0079] This method allows some deviation from the above molar ratios, especially during the initial period when the electrolysis is initiated, since steady state is usually reached only after a certain start-up time.

[0080] A molar ratio of 1:>0 means that there is a minimum amount of iodine compounds with oxidation states -I to +V.

[0081] Elemental iodine in the context of the above molar ratios is calculated as containing 2 moles of I (i.e., 1 mole of I 2 (is calculated as 2 moles for the purpose of determining the molar ratios above). Indeed, in the basic medium of the anolyte, at a pH of at least 10, used in the process of the present invention, elemental iodine disproportionates to iodide and hypoiodite to produce two iodine species. I 2 +2OH - →I - +IO - +H 2 O

[0082] Periodates containing x iodine atoms in the salt (e.g., dimesoperiodate (I 2 O 9 4- ) contains two iodine atoms per dimethoperiodate anion) is calculated in this context as containing x moles of I (e.g., 1 mole of I 2 O 9 4- is calculated as 2 moles to determine the molar ratio of the metal periodate and the lower oxidation state iodine compound.

[0083] The total molar ratio of metal periodates and iodine compounds with oxidation states -I to +V can be determined and adjusted, for example, by continuously or periodically analyzing the composition of the anolyte and supplying such an amount of iodine compounds with oxidation states -I to +V that the desired ratio of periodate / iodine (-I to +V) species is obtained. The anolyte can be quantitatively analyzed, for example, by LC-PDA or titration. When using LC-PDA, it is necessary to determine the influence coefficient of the iodine species analyzed, taking into account the different sensitivity of the method for different iodine species. In practice, it is usually sufficient to determine the ratio of periodate to iodate by analyzing the anolyte in the anolyte chamber or by analyzing the anolyte draining from the anolyte chamber. As explained below, the oxidation of iodine species with oxidation states -I to +III to periodate proceeds via iodate, either by stepwise anodic oxidation or by proportionation. This intermediate reaction to iodate is fast compared to the oxidation of iodate to periodate, so that in many cases iodine species with oxidation states -I to +III are present in the anolyte in amounts below the detection threshold. To analyze the anolyte with LC-PDA, the basic anolyte is appropriately neutralized or acidified to convert the paraperiodate present in the anolyte (low solubility in water) to the water-soluble metaperiodate, ensuring proper quantitative detection of all periodate species formed. Alternatively, the composition can be calculated. Once the electrolysis is started, the composition of the anolyte is known. By separating and weighing the continuously or periodically removed periodate, the amount of iodine compounds with oxidation states -I to +V consumed can be calculated from it. The amount required for the desired ratio is then replenished. Of course, it is also possible to combine these methods.

[0084] The compositional analysis / calculation is suitably carried out at suitable time intervals, for example several minutes or about an hour, from at least the start of the electrolysis until a steady state is obtained.

[0085] The metal periodate contained in the recycled anolyte can be any periodate in which the iodine atom has an oxidation state of +VII.

[0086] As explained above, metal periodates are the metal salts of various periodic acids. In periodic acid, the corresponding anion consists of iodine in the oxidation state +VII and oxygen. Periodates include orthoperiodates (IO 6 5- , metal orthoperiodate has the formula M 5 IO 6 ), metaperiodate (IO 4 - , metal metaperiodate has the formula MIO 4 ), dimesoperiodate (I 2 O 9 4- , metal dimesoperiodate has the formula M 4 I 2 O 9 ), mesoperiodate (IO 5 3- , metal mesoperiodates have the formula M 3 IO 5 Paraperiodate has the chemical formula M 3 H 2 IO 6 and the corresponding double salt MIO 4 Also known as 2MOH. In the above formula, M is the metal equivalent [(M n+ ) 1 / n , where n is the number of charges]. For example, in the case of alkali metal periodates, M is the alkali metal cation. In the case of alkaline earth metal periodates, M is (M 2+ ) 1 / 2 In periodates with multiple negative charges, the metal equivalents M may have the same or different meanings. For example, M in paraperiodate 3 H 2 IO 6 or MIO 4 In 2MOH, all three metal equivalents M may have the same meaning or may be derived from different metals, a situation that can arise, for example, when the countercation of the iodide salt used as a starting material is different from the countercation present in the base present during anodization or in the base used during workup of the reaction product.

[0087] Preferably, the metal periodate contained in the recycled anolyte is orthoperiodate, metaperiodate, paraperiodate, or a mixture thereof. More preferably, the metal periodate contained in the recycled anolyte comprises metal paraperiodate. Even more preferably, the metal periodate is the predominant metal periodate species in said anolyte, i.e., is present in a higher (molar) amount than other metal periodate species. Preferably, at least 50 mol %, more preferably at least 70 mol %, of the metal periodate contained in the recycled anolyte is metal paraperiodate.

[0088] The anodization is carried out at a pH of at least 10, such as 10 to 14 or 10 to 13, preferably at least 11, such as 11 to 14 or more, in particular at least 12, such as 12 to 14 or more, in particular at least 13, such as 13 to 14 or more. That is to say, the anolyte has a pH of at least 10, such as 10 to 14 or more, preferably at least 11, such as 11 to 14 or more, in particular at least 12, such as 12 to 14 or more, in particular at least 13, such as 13 to 14 or more.

[0089] Therefore, it is preferred that the anodization is carried out in the presence of a base. Since an aqueous medium is generally used for the anodization, suitable bases are those that are water-soluble and form hydroxyl ions in the aqueous phase. Preferred are inorganic bases such as metal hydroxides, metal oxides, metal carbonates, etc.

[0090] In order to avoid separation problems, in these bases the countercation preferably corresponds to the metal cation of the iodine salt used. If elemental iodine is used as starting material, of course, such a restriction is not necessary. However, the countercation of the base preferably corresponds to the countercation of the desired paraperiodic acid. Since aqueous media are generally used for the anodization, an exception to this priority is necessary if the base with the cation corresponding to the metal cation of the iodine salt is not (sufficiently) water-soluble. For example, CuO, Cu(OH) 2 , CuCO 3is essentially insoluble in water. Therefore, if CuI or other Cu iodine salts are used as the starting iodine salt, it is recommended to use a water-soluble base that is not Cu-based, such as NaOH or KOH. Certain alkaline earth metal iodine salts, especially MgI 2 and CaI 2 The same is true when using other iodide salts of Mg or Ca as starting materials, since the corresponding hydroxides, oxides and carbonates are barely soluble in water. In this case too, it is recommended to use a water-soluble base that is not Mg- or Ca-based, such as NaOH or KOH. "Not sufficiently water-soluble" means that the base does not dissolve in the concentration required to obtain the pH.

[0091] Preferably, the base is a metal hydroxide. More preferably, the base is a metal hydroxide, and the metal of the base corresponds to the metal in the metal iodine salt when a metal iodine salt (not elemental iodine) is used as the starting material, except in the above cases where the corresponding base is not (sufficiently) water-soluble. Alkali metal iodine salts, alkaline earth metal iodine salts and certain transition metal iodine salts are preferably used as starting materials, and taking into account the solubility of the corresponding hydroxides in the aqueous reaction medium, it is preferred to use an alkali metal hydroxide as the base. When an alkali metal iodine salt is used as the starting material, the metal of the base preferably corresponds to the metal in the alkali metal iodine salt used.

[0092] The method of the invention preferably comprises subjecting to anodization an aqueous dispersion of an iodine compound having an oxidation state of -I to +V and a base as anolyte. With regard to suitable and preferred iodine compounds and suitable and preferred bases, reference is made to what has been stated above. More precisely, the method of the invention preferably comprises subjecting to anodization an anolyte which is an aqueous dispersion of an iodine compound having an oxidation state of -I to +V mixed with a metal periodate and a base, in which the total molar ratio of the metal periodate and the iodine compound having an oxidation state of -I to +V is between 1:>0 and 1:5, where the iodine compound has an oxidation state of -I to +III, the total molar ratio of the metal periodate and the iodine compound having an oxidation state of -I to +III is between 1:0 and 8:1. Also, when the iodine compound has an oxidation state of +V, the total molar ratio of the metal periodate to the iodine compound having an oxidation state of +V is 1:0 to 1:5. More preferably, the total molar ratio of the metal periodate to the iodine compound having an oxidation state of -I to +V is 1:>0 to 1:4, even more preferably 200:1 to 1:4, when the iodine compound has an oxidation state of -I to +III, the total molar ratio of the metal periodate to the iodine compound having an oxidation state of -I to +III is 1:0 to 10:1, when the iodine compound has an oxidation state of +V, the total molar ratio of the metal periodate to the iodine compound having an oxidation state of +V is 1:0 to 1:4, preferably 200:1 to 1:4. As mentioned above, this molar ratio is present in the anolyte at least before it enters the anolyte chamber.

[0093] The processes in the anode chamber depend on the starting materials, are partly interconnected and complex. In theory, in a simplified mode, the following processes occur under basic conditions, depending on the type of iodine being oxidized:

[0094] I - +8OH - →IO 4 - +4H 2 O+8e - I + +8OH - →IO 4- +4H 2 O+6e - I 2 +16OH - →2IO 4 - +8H 2 O+14e - IO - +6OH - →IO 4 - +3H 2 O+6e - IO 3 - +2OH - →IO 4 - +H 2 O+2e -

[0095] Typically, the first four starting iodine species are converted stepwise to periodate, via subsequent more highly oxidized species.

[0096] Additionally, as explained above, elemental iodine disproportionates under basic conditions to iodide and hypoiodite, resulting in the production of two iodine species: I 2 +2OH - →I - +IO - +H 2 O Therefore, instead of the third reaction scheme above, the first and forty-third reaction schemes occur, at least in part.

[0097] Additionally, the iodine species may also be proportional to the periodate present. As an example, the reaction of iodide with elemental iodine is shown below: 3I 2 +6OH - →IO 3 - +5I - +3H 2 O I - +3IO 4 - →4IO3 - That is, at least a portion of the iodine or iodide starting material is not oxidized as such, but is oxidized in proportion to the periodate that is also present, such that iodate is the actual species that is oxidized.

[0098] Orthoperiodate IO 4 - can further react with hydroxyl ions to form paraperiodate. IO 4 - +2OH - →H 2 IO 6 3-

[0099] The total concentration of metal periodates and iodine compounds with oxidation states -I to +V in the anolyte is preferably 0.01 to 12 mol / L, more preferably 0.05 to 5 mol / L, even more preferably 0.1 to 2 mol / L, in particular 0.1 to 1 mol / L, specifically 0.1 to 0.5 mol / L, very specifically 0.1 to 0.3 mol / L, where the concentration refers to the amount of iodine atoms, for example iodide anion when using metal iodides as starting material, iodate anion when using metal iodates as starting material, two I atoms (due to disproportionation to iodide and hypoiodite in basic medium) when using elemental iodine as starting material.

[0100] The base is used at a concentration to provide the desired pH value.

[0101] The catholyte is generally an aqueous solution comprising an electrolyte. Preferably, the electrolyte is a base. Preferably, the base corresponds to the base used in the anolyte. If the electrolyte is a base, the pH is preferably at least 8, more preferably at least 10, even more preferably at least 11, in particular at least 12. Suitably, an inorganic base is used to make the pH of the aqueous medium in the catholyte chamber basic. Suitable and preferred inorganic bases have already been described above in connection with the anolyte, and therefore they are preferably selected from metal hydroxides, metal oxides and metal carbonates. Hydroxides are preferred. Alkali metal hydroxides, in particular sodium hydroxide and potassium hydroxide, are more preferred. Preferably, the base used in the catholyte is the same as the base used in the anolyte.

[0102] Naturally, the reaction at the cathode depends on the catholyte present in the cathode chamber. As mentioned before, the catholyte is generally an aqueous medium. In this case, the reaction taking place at the cathode is the reduction of water to hydrogen (with the formation of hydroxyl anions). 2H 2 O+2e - →H 2 +2OH -

[0103] The anolyte circuit includes at least one continuous stirred tank reactor operated in a steady state mode with respect to the total molar ratio of metal periodates to iodine compounds in the anolyte having oxidation states of −I to +V. As mentioned above, “steady state” in the present invention includes deviations of up to 20% from the absolute definition.

[0104] The anolyte is circulated between the anode chamber and the stirred tank reactor.

[0105] The stirred tank reactor is fed with materials to obtain the desired composition and concentration of the anolyte fed to the anode chamber. For this purpose, it is necessary to replenish the iodine compounds with oxidation states -I to +V, which are converted to periodates in the anodization process, and to replenish the water and / or base if they are depleted during the reaction or the product separation process (see below), and, if necessary, to add further additives or accelerators (the use of which is not preferred). In addition, the anolyte, from which a part of the periodates produced has been removed (see below for details), is of course also returned to the stirred tank reactor.

[0106] At the start of the electrolysis, the stirred tank reactor is also fed with a metal periodate, preferably a metal paraperiodate. The amount of metal (para)periodate is such that the desired ratio of metal (para)periodate to iodine compounds having oxidation states -I to +V is obtained at the desired concentration. However, once the electrolysis has started, no metal (para)periodate needs to be added unless it is necessary to adjust the desired ratio of metal (para)periodate to iodine compounds having oxidation states -I to +V, for example, because too much (para)periodate has been separated from the anolyte returned from the anode chamber.

[0107] When electrolysis is started, metal periodates are formed at the anode from iodine compounds with oxidation states -I to +V and are transported via the circulating anolyte to the stirred tank reactor where they are partially removed. Under the given conditions, especially with a basic pH of at least 10, the periodates consist at least partially of the desired paraperiodate. Generally, paraperiodate is the predominant periodate species in the recirculating anolyte, especially at higher pH values. Due to the rather low water solubility of metal paraperiodates, a significant amount of them is generally suspended in the anolyte in solid form and can be removed from the anolyte simply by precipitation after concentration, if necessary. Concentration can be carried out by conventional means, such as evaporation of part of the solvent, optionally under reduced pressure, partial freeze-drying, partial reverse osmosis, etc.

[0108] For this purpose, preferably, a portion of the anolyte that is recycled to the stirred tank reactor is removed from the stirred tank reactor and at least a portion of the metal paraperiodate is removed from this anolyte. If at least a portion of the paraperiodate is already present in solid form in the removed anolyte, its separation can be carried out by conventional means such as filtration or decantation of the supernatant. If it is necessary to first concentrate the anolyte to produce sufficient solids for separation, the anolyte is generally transferred to a suitable device in which part of the solvent is removed, for example by evaporation, if necessary under reduced pressure, or the anolyte is subjected to partial freeze-drying, partial reverse osmosis, etc. The precipitate obtained is then separated as described above.

[0109] If the anolyte is not basic enough and paraperiodate is not the predominant periodate species, then more base can be added to obtain paraperiodate, which will convert metaperiodate and other periodate species to the desired paraperiodate and force precipitation. Subsequent removal and testing can be performed as described above.

[0110] Alternatively, to isolate paraperiodate, the water can be more or less completely removed from the anolyte, for example by evaporation of the solvent, freeze-drying, reverse osmosis, evaporation of the residual water if necessary, optionally under reduced pressure, and the residue can be purified if desired.

[0111] If necessary, the isolated paraperiodate can be subjected to further purification steps, such as washing with water or a solvent mixture containing water, decomposition with water or a solvent mixture containing water, or recrystallization, in order to remove unreacted iodine starting compounds, excess base, undesired by-products, if any. However, depending on the application of paraperiodate, it is not mandatory to carry out a purification procedure. In many cases, especially when paraperiodate is used as an oxidizing agent, it is sufficient to evaporate the water from the aqueous medium obtained after neutralization. In some cases, it is not even necessary to evaporate the residual water (i.e. the aqueous medium obtained from the anode chamber can be used as it is in the subsequent oxidation process), or at least not to evaporate it to dryness.

[0112] The (para)periodate-depleted anolyte is then returned to the stirred tank reactor. Before, during or after the spent anolyte is returned to the stirred tank reactor, it is replenished with an iodine compound having an oxidation state of -I to +V. The latter is added in an essentially equimolar amount to the amount of paraperiodate removed. Preferably, an iodine compound having an oxidation state of -I to +V is fed to the stirred tank reactor.

[0113] Iodine compounds with oxidation states from -I to +V can be added in dispersed (usually aqueous dispersions) or in solid form. If the iodine compounds are added in dispersed form (usually in water), the possible water losses that occur during the removal of (para)periodate are at least partially compensated at the same time. If the iodine compounds are added in solid form, the possible water losses are usually compensated by additional addition of water, preferably also to the stirred tank reactor. This can be done simultaneously with the addition of the solid iodine compounds or independent of time.

[0114] The removal of (para)periodate can also lead to base depletion. This is also compensated for by adding base, which can be carried out simultaneously with the addition of solid iodine compounds or independent of time. The added base can be "fresh" material. However, in certain embodiments, the base is added in the form of a portion of the catholyte from the cathode chamber. Since hydroxyl ions are generated at the cathode during electrolysis (by reduction of water), it is not necessarily necessary to replenish the catholyte with fresh base to compensate for the amount transferred. Only the water transferred to the stirred tank reactor needs to be replenished in the cathode chamber.

[0115] Removal of anolyte from the anode chamber and stirred tank reactor, and addition of iodine compounds with oxidation states -I to +V to the (para)periodate-depleted anolyte, can be carried out continuously or periodically.

[0116] It is preferred that the removal of anolyte from the anode chamber and the stirred tank reactor, and the addition of iodine compounds having oxidation states from -I to +V to the paraperiodate-depleted anolyte, are carried out at essentially the same rate, so that the electrolysis occurs essentially in a steady-state mode. This can be achieved by simultaneously adding the iodine compounds of low oxidation states and removing the metal periodate, or intermittently, i.e., adding iodine compounds at certain time intervals and removing the metal periodate at other time intervals, as long as the molar ratio is maintained within a predetermined range.

[0117] The addition of iodine compounds with oxidation states -I to +V is preferably carried out at a rate and concentration such that the main iodine species in the anolyte present in the stirred tank reactor and, of course, in the anode chamber, is periodate. Preferably, the addition is carried out at a rate and concentration such that the total molar ratio of all metal periodates in the stirred tank reactor to all iodine compounds with oxidation states -I to +V is 1:>0 to 1:5, where the iodine compounds have oxidation states -I to +III, the total molar ratio of metal periodates to iodine compounds with oxidation states -I to +III is 1:0 to 8:1, and where the iodine compounds have oxidation state +V, the total molar ratio of metal periodates to iodine compounds with oxidation state +V is 1:0 to 1:5. More preferably, the total molar ratio of metal periodate to iodine compounds having an oxidation state of -I to +V is 1:>0 to 1:4, and even more preferably 200:1 to 1:4. In the case where the iodine compounds have an oxidation state of -I to +III, the total molar ratio of metal periodate to iodine compounds having an oxidation state of -I to +III is 1:0 to 10:1. In the case where the iodine compounds have an oxidation state of +V, the total molar ratio of metal periodate to iodine compounds having an oxidation state of +V is 1:0 to 1:4, and preferably 200:1 to 1:4. As mentioned above, this molar ratio is present in the anolyte at least before it enters the anolyte chamber.

[0118] In the method of the present invention, the anodization is preferably carried out in the absence of promoters and additives. In the present invention, promoters refer to anti-reducing and pro-oxidizing agents, such as polarizing substances. Additives are understood to refer to substances other than the starting compounds, the products produced in the course of the reaction, the acid, the base, the electrolyte medium (usually water), and the promoter. In conventional methods, the presence of promoters or additives is often necessary to obtain periodate in satisfactory yield. For example, the method of Nam et al., described in Journal of the Korean Chemical Society 1974,18,373, requires the presence of potassium dichromate as a reduction inhibitor. It is clear that chromium should be avoided in certain applications, such as health, personal care, and nutrition. Fluorides such as lithium fluoride and silicon fluoride are also often used, which are said to increase the overvoltage of oxygen at the anode and improve the oxidation efficiency. In particular, in the method of the present invention, the anodization is preferably carried out in the absence of promoters, especially in the absence of chromium salts and fluorides such as lithium fluoride and silicon fluoride.

[0119] The anode material can be essentially any material known in the art for this type of oxidation. However, when the desired product is used for a specific purpose that does not tolerate certain impurities such as heavy metals, especially lead, as in the case of pharmaceutical processes, the anode material is preferably free of such materials. Thus, in a preferred embodiment, the anode comprises a carbon-based active layer. Carbon-containing anodes (or, more generally, electrodes) or carbon-based anodes / electrodes, also referred to below, are well known in the art and include, for example, graphite electrodes, vitreous carbon (glassy carbon) electrodes, reticulated vitreous carbon electrodes, carbon fiber electrodes, electrodes based on carbonized composites, electrodes based on carbon-silicon composites, graphene-based electrodes, and diamond-based electrodes.

[0120] Carbon-containing anodes are not necessarily composed entirely of carbonaceous materials. Graphite electrodes are often composed solely or primarily of graphite, although other carbonaceous materials may be present as part of or as the outer layer of the electrode, i.e., the part that is in direct contact with the electrolyte. More details are provided below.

[0121] Of the above anodes, diamond-based electrodes are preferred: such electrodes are characterized by very high overpotentials for both oxygen and hydrogen evolution, resulting in a wide potential window.

[0122] Diamond has a large band gap of over 5 eV, so it is usually an electrical insulator by itself and is not suitable as an electrode material. However, diamond can be made conductive by doping with certain elements. Another method to make diamond conductive is to heat treat an undoped diamond film at temperatures above 1550 °C in a vacuum. These harsh conditions are thought to form a network of conductive carbon phases within the diamond film.

[0123] However, the former method is more practical and reliable, and therefore the diamond-based electrode is preferably an electrode comprising conductive doped diamond.

[0124] Suitable dopants are selected from elements in IUPAC groups 13, 15, or 16 of the periodic table.

[0125] Thus, in a preferred embodiment, the one or more anodes used in the methods of the present invention comprise diamond doped with one or more elements from IUPAC Groups 13, 15 or 16 of the Periodic Table.

[0126] A suitable Group 13 dopant is boron. Suitable Group 15 dopants are nitrogen and phosphorus. A suitable Group 16 dopant is sulfur. Boron doping results in p-type semiconductors, while nitrogen, phosphorus and sulfur doping results in n-type conductivity. Two or more different dopants can also be used, resulting in, for example, boron-nitrogen co-doping or boron-sulfur co-doping. In the case of co-doping, if the conductivities of the two or more dopants are different (such as in the case of BN or BS co-doping), the type of conductivity of the co-doped diamond depends in particular on the concentration of the single dopant and can be tailored to the desired type.

[0127] Among the above dopants, boron doping is preferred. Thus, in a more preferred embodiment, the one or more anodes used in the method of the present invention comprise boron doped diamond (BDD).

[0128] The boron doped diamond preferably comprises boron in an amount of from 0.02 to 1 wt% (200-10,000 ppm), more preferably from 0.04 to 0.2 wt%, especially from 0.06 to 0.09 wt%, based on the total weight of the doped diamond.

[0129] As already mentioned above, such electrodes generally do not consist of doped diamond alone. Rather, the doped diamond is attached to a substrate. In most cases, the doped diamond is present as a layer on a conductive substrate, but diamond particle electrodes in which the doped diamond particles are embedded in a conductive or non-conductive substrate are also suitable. However, anodes in which the doped diamond is present as a layer on a conductive substrate are preferred.

[0130] In particular, therefore, the one or more anodes used in the method of the present invention comprise a layer of boron doped diamond.

[0131] Suitable support materials for the electrode including the boron doped diamond layer are silicon, self-passivating metals, metal carbides, graphite, glassy carbon, carbon fibre and combinations thereof.

[0132] Suitable self-passivating metals include, for example, germanium, zirconium, niobium, titanium, tantalum, molybdenum, and tungsten.

[0133] Suitable combinations include, for example, metal carbide layers on the corresponding metals (such intermediate layers may be formed in situ when the diamond layer is applied to the metal support), composites of two or more of the support materials listed above, and combinations of carbon with one or more of the other elements listed above. Examples of composites include siliconized carbon fiber carbon composites (CFC) and partially carbonized composites.

[0134] Preferably, the support material is selected from the group consisting of elemental silicon, germanium, zirconium, niobium, titanium, tantalum, molybdenum, tungsten, carbides of the above eight metals, graphite, glassy carbon, carbon fibers, and combinations thereof (especially composite materials).

[0135] More preferred are the elements silicon, germanium, zirconium, niobium, titanium, tantalum, molybdenum, tungsten, and combinations of one of the above seven metals with the respective metal carbides.

[0136] Doped diamond electrodes and their manufacturing methods are known in the art, and are described, for example, in LJJ Janssen et al., Electrochimica Acta 2003,48,3959-3964, NL1013348C2 and the references cited therein.Suitable preparation methods include, for example, chemical vapor deposition (CVD), such as hot filament CVD and microwave plasma CVD, for preparing electrodes with doped diamond films, and high temperature and high pressure (HTHP) for preparing electrodes with doped diamond particles.Doped diamond electrodes are commercially available.

[0137] The cathode material is not critical and any commonly used material is suitable, such as stainless steel, chrome-nickel steel, platinum, nickel, bronze, tin, zirconium, or carbon, etc. In a particular embodiment, a stainless steel electrode is used as the cathode.

[0138] The separation of the anode and cathode compartments can be achieved by conventional dividing means (separators), such as semi-permeable membranes, diaphragms, frits, etc. In other words, the electrolytic cell is a divided cell. The separator separates the anolyte (liquid medium of the anode compartment) and the catholyte (liquid medium of the cathode compartment), but allows the equalization of the charges. The diaphragm is a separator that comprises a porous structure of an oxide material, such as a silicate, for example in the form of a porcelain or ceramic. However, since the diaphragm material is sensitive to harsh conditions, a semi-permeable membrane is generally preferred, especially when the reaction is carried out at a basic pH, which is preferred. The semi-permeable membrane is preferably one that can withstand such conditions, especially at a basic pH. Suitable semi-permeable membranes are, for example, ion exchange membranes, especially cation exchange membranes, i.e. membranes made of materials that allow the passage of cations (and the fluid, usually water) but not anions. More specifically, the semi-permeable membrane is a proton exchange membrane (PEM). Membrane materials that can withstand more severe conditions, especially basic pH, are based on fluorinated polymers. Examples of suitable materials for this type of membrane include sulfonated tetrafluoroethylene-based fluoropolymer copolymers, such as Nafion® brand from DuPont de Nemours and Gore-Select® brand from WL Gore & Associates, Inc. However, when using iodides with divalent or higher countercations, it is recommended to use a different semipermeable separator that is permeable only to monovalent cations. In this case, a diaphragm is preferred.

[0139] The electrolytic cell in which the process of the present invention is carried out comprises one or more anodes in one or more anodic chambers and one or more cathodes in one or more cathodic chambers, the anode chambers being separated from the cathode chambers.

[0140] When multiple anodes are used, the two or more anodes can be located in the same anode chamber or in separate compartments. When two or more anodes are in the same chamber, they can be located next to each other or stacked on top of each other. When more than one anode chamber is used, they can also be located next to each other or stacked on top of each other.

[0141] The same is true when more than one cathode is used.

[0142] Alternatively, when the electrolysis device includes a plurality of anodes and a plurality of cathodes, the electrolysis device can include a plurality of electrolysis cells, each cell including an anode chamber and a cathode chamber. The electrolysis cells can be positioned adjacent to each other or stacked on top of each other.

[0143] Suitable shapes and configurations of electrolysers containing multiple anodes and / or cathodes are known to those skilled in the art.

[0144] The method of the present invention is suitable for laboratory as well as industrial scale reactions.

[0145] The process of the present invention can be carried out as a semi-continuous or continuous process.

[0146] In a continuous process design, electrolyte is passed continuously through the cell; that is, electrolyte containing the iodine compound to be oxidized is continuously added, reacted, and the resulting reaction mixture is continuously removed from the process. A semi-continuous process design contains elements of both batch and continuous formats; the process is essentially continuous, but anolyte containing the iodine compound to be oxidized is added at specific times and the resulting reaction mixture is removed at specific times.

[0147] In the case of semi-continuous or continuous process designs, the anode and cathode compartments are usually designed as flow cells.

[0148] A variety of designs and shapes of flow cells are known in the art and can be applied to the methods of the present invention.

[0149] Typically, the electrolysis unit is equipped with a heat exchanger, a thermometer, mixing means, and gas outlets from the cathode and anode chambers. In addition, means for continuous feeding and removal are provided, for example in the form of a recirculation loop with a pump. The stirred tank reactor is part of the anolyte circuit, which usually also includes a loop to a device for removing a portion of the products formed and returning the remaining anolyte, as well as a connection to a feeding system for replenishing depleted starting materials, water, base, and other necessary components of the anolyte. As already explained above, the starting materials can be fed to the stirred tank reactor in dispersed form or as solids. In the latter case, a suitable solids feeding system, such as a screw conveyor, is required.

[0150] The apparatus according to the invention is a preferred form of electrolysis apparatus suitable for carrying out the method of the invention. Thus, an apparatus configured for preparing metal paraperiodate by the method of the invention, i.e. for preparing metal paraperiodate by continuous anodic oxidation of an iodine compound, comprises an electrolysis cell including an anode chamber having one or more anodes, a cathode chamber having one or more cathodes, a separator disposed between the anode chamber and the cathode chamber, a catholyte circuit for recirculating catholyte through the cathode chamber, the catholyte circuit including a catholyte reservoir, and a separator for recirculating anolyte through the anode chamber. and an anode circuit comprising at least one continuous stirred tank reactor having a supply means for supplying iodine compounds having an oxidation state from -I to +V selected from an iodine salt, elemental iodine, a mixture of different iodine salts, or a mixture of iodine and one or more iodine salts to the at least one continuous stirred tank reactor, and a withdrawal means for withdrawing a metal periodate reaction product from the at least one continuous stirred tank reactor.

[0151] For a given installation according to the invention, for example by using LC-PDA data or data obtained by other analytical or computational methods, calibration tests can be performed to determine the operating conditions under which the reactor is operated in a steady mode, with respect to the molar ratio of metal periodate to iodide in the anolyte with oxidation states of -I to +V. The reactor can thus be maintained in a steady state by choosing appropriate operating conditions, in particular with respect to the concentration of iodide (feed rate), the concentration of metal periodate (removal rate), the temperature, the flow rate of anolyte through the electrolytic cell, the pH of the anolyte, and the operating current density of the electrolytic cell.

[0152] Preferably, the device of the present invention is equipped with a suitable measurement system for determining and / or controlling the operating conditions of the device. The measurement system usually consists of a potentiometer and / or ammeter, a pH meter (usually an in-line pH meter), a temperature sensor, and a flow sensor. Usually, there is a linear relationship between flow rate and current density, i.e., if the flow rate increases by a certain factor, the current density increases as well while maintaining a steady state.

[0153] Electrolysis can be carried out under galvanostatic control (applied current is controlled and voltage is measured but not controlled) or potentiostatic control (applied voltage is controlled and current is measured but not controlled), the former being preferred.

[0154] Measuring the voltage under constant current control allows the reaction conditions to be adjusted so that the voltage is essentially maintained at the desired value, thus ensuring that the reactor operates in a stationary mode. Similarly, maintaining the current at the desired value under potentiostatic control can also ensure that the reactor operates in a stationary mode. The electrolysis system can be calibrated by measuring the current / voltage relationship of various electrolytes with known compositions, particularly known compositions of metal periodates and iodine compounds with oxidation states from -I to +V. Based on the calibration data, the electrolysis can be performed with the desired ratio of metal periodates and iodine compounds with oxidation states from -I to +V by establishing and maintaining appropriate current / voltage values ​​during electrolysis.

[0155] Under galvanostatic control, an increase in cell voltage indicates the production of more metal periodate and therefore the need to add more iodide with oxidation states -I to +V to maintain steady state in the reactor. Similarly, under potentiostatic control, a decrease in current density indicates an increase in the production of metal periodate and therefore also the need to add more iodide with oxidation states -I to +V to maintain steady state.

[0156] For the preferred constant current control, the observed voltage will typically be in the range 0 to 30V, more typically 1 to 20V, especially 1 to 10V.

[0157] In the case of potentiostatic control, the applied voltage is generally in the same range, namely from 1 to 30 V, preferably from 1 to 20 V, in particular from 2 to 10 V. The voltage can be precisely adjusted to the redox potential of the iodine species to be oxidized.

[0158] The anodization is preferably performed at a current of 10 to 1000 mA / cm 2 , more preferably 100 to 750 mA / cm 2 , especially 250 to 500 mA / cm 2 , specifically 400 to 430 mA / cm 2 These values ​​apply to a flow rate of approximately 7.5 L / h. If the flow rate is reduced or increased by a certain factor, the current density may also be reduced or increased by the same factor.

[0159] The anodization is preferably carried out at a temperature of from 5 to 80°C, more preferably from 10 to 60°C, especially from 20 to 45°C, particularly from 30 to 40°C.

[0160] The reaction pressure is not critical; therefore, anodization is generally carried out at atmospheric pressure, although higher pressures may be required if the reaction is carried out at temperatures above the normal boiling point of the aqueous medium to avoid boiling.

[0161] The invention further relates to an apparatus for producing metal paraperiodates by continuous anodic oxidation of iodine compounds, more precisely an apparatus adapted to produce metal paraperiodates by the method of the invention, the apparatus comprising an electrolytic cell comprising an anolyte chamber having one or more anodes, a catholyte chamber having one or more cathodes, a separator arranged between said anode chamber and said cathode chamber, a catholyte circuit for recirculating catholyte through said cathode chamber, said catholyte circuit comprising a catholyte reservoir, and an anolyte circuit for circulating anolyte through said anode chamber. a circuit, the anolyte circuit comprising at least one continuous stirred tank reactor provided with supply means for supplying iodine compounds having an oxidation state from −I to +V selected from an iodine salt, elemental iodine, a mixture of different iodine salts, or a mixture of iodine and one or more iodine salts to the at least one continuous stirred tank reactor, and withdrawal means for withdrawing a metal periodate reaction product from the at least one continuous stirred tank reactor.

[0162] Preferably, the supply means comprises a starting material tank containing a solution of iodine compounds with oxidation states -I to +V, connected to the continuous stirred tank reactor. The withdrawal means preferably comprises a collection vessel connected to the continuous stirred tank reactor via a discharge line. In a particular embodiment, the supply means for supplying iodine compounds with oxidation states -I to +V comprises a supply of solid starting material, here in particular solid iodine compounds with oxidation states -I to +V, connected to the continuous stirred tank reactor. In another particular embodiment, the withdrawal means comprises a collection vessel connected to the continuous stirred tank reactor via a discharge line and a recirculation line. In particular, this apparatus comprises a supply of solid starting material connected to the continuous stirred tank reactor and a collection vessel connected to the continuous stirred tank reactor via a discharge line and a circulation line. The catholyte circuit preferably comprises a catholyte tank, which is connected to the anolyte circuit via a transfer line for transferring a portion of the catholyte to the anolyte circuit. Specifically, the apparatus comprises a supply of solid starting material connected to the continuous stirred tank reactor, a collection vessel connected to the continuous stirred tank reactor via a discharge line and a recirculation line, and a catholyte tank connected to the anolyte circuit via a transfer line for transferring a portion of the catholyte to the anolyte circuit. The electrolytic cell is preferably equipped with a cooling water system for controlling the temperature of the anode and / or cathode compartments of the electrolytic cell.

[0163] Further preferred embodiments of the device of the invention will become apparent in the context of the following description of the figures.

[0164] The method of the invention combines the concepts of circulating flow electrolysis and continuous stirred tank reactors (e-CSTR), operating in stationary mode and allowing fully continuous operation if required. The products can be separated in-line and the remaining anolyte can be recycled to the process. This method allows the production of paraperiodate in a quality suitable for demanding applications such as pharmaceuticals, cosmetics and nutrition. The method is versatile with regard to the starting material, accepting any inorganic iodine compound as starting compound, including starting in a single step from iodide, which is readily available, economical, problem-free and easy to handle, but can also start from other iodine species such as iodate (a species commonly provided for recycling from oxidation processes where periodate is used as oxidant and therefore easily available) or iodine. The method is also versatile with regard to the physical form in which the starting material is added, allowing it to be fed in dispersed but also in solid form. The high conversion and space-time yield, as well as the high atom economy and the lack of need for promoters or additives, make this method particularly attractive. But most importantly, clogging can be significantly reduced. Moreover, the method can be easily extended to industrial design.

[0165] The method will now be further explained with reference to the schematic embodiments shown in the accompanying drawings and the examples described below.

[0166] In the drawings: FIG. 1 shows a first embodiment of an apparatus for carrying out the invention. FIG. 2 shows a second embodiment of an apparatus for carrying out the invention.

[0167] In FIG. 1, a first embodiment of an apparatus for producing metal periodates according to the method of the invention is generally indicated with the reference number 10. The apparatus 10 comprises an electrolytic cell 11 having an anode chamber 12 in which an anode 13 is arranged, and a cathode chamber 14 in which a cathode 15 is arranged. Between the anode chamber 12 and the cathode chamber 14, a separator 16, for example a semipermeable membrane, a diaphragm or a frit, is arranged. Both compartments are provided with an anode cooling water system 17 and a cathode cooling water system 18, respectively, to allow temperature regulation of the respective cells. The cathode chamber 14 is part of a catholyte circuit 19, which comprises a catholyte tank 20 and a catholyte recirculation pump 21. The anode chamber is part of an anolyte circuit 22, which comprises a continuous stirred tank reactor 23 serving as an anolyte tank and an anolyte circulation pump 24. In the continuous stirred tank reactor 23, a predetermined molar ratio of metal periodates and iodine compounds in the aggregation state -I to +V is maintained. To this end, the continuous stirred tank reactor 23 is supplied with a feed solution from a feed tank 25 via a feed pump 26 and a feed line 27. The anolyte can be removed from the continuous stirred tank reactor 23 via a discharge line 28 and a discharge pump 29, which discharges a portion of the anolyte into a product collection vessel 30. In this embodiment, the rate at which the iodine compound is fed from the starting material tank 25 to the continuous stirred tank reactor 23 corresponds to the rate at which metal periodate is produced by electrolysis in the anode chamber 12, which in turn determines the rate at which the metal periodate is removed from the continuous stirred tank reactor 23 via a discharge line 28 into the product collection vessel 30.

[0168] Figure 2 shows a second embodiment of the device according to the invention, in which elements identical or similar to those described in relation to figure 1 are designated by the same reference numbers increased by 100.

[0169] Thus, the apparatus for preparing metal periodates is designated by the reference numeral 110 and comprises an electrolytic cell 111 having an anode chamber 112 with an anode 113 and a cathode chamber 114 with a cathode 115. A separator 116 is also arranged between the anode chamber 112 and the cathode chamber 114. Both chambers are provided with an anode cooling water system 117 and a cathode cooling water system 118, respectively. The cathode chamber 114 is part of a catholyte circuit 119 which comprises a catholyte tank 120 and a catholyte recirculation pump 121. The anode chamber 112 is part of an anolyte circuit 122 which comprises a continuous stirred tank reactor 123 and an anolyte recirculation pump 124.

[0170] The apparatus of FIG. 2 differs from that of FIG. 1 in that the starting materials, in particular the iodine compounds, are fed as solids directly to the continuous stirred tank reactor 123. For this purpose, a vessel 131 and a feed line 132 for the solid starting material are provided. The vessel 131 may be provided with a motorized feed, such as a screw conveyor 133 driven by a motor 134. In this embodiment, the collection tank 130 is not a batch collection tank, but a collection tank in which metal periodates can be removed from the anolyte fed to the collection vessel 130 via the discharge line 128 and the discharge pump 129. The spent anolyte is recycled to the continuous stirred tank reactor 123 via the recirculation line 135 and the recirculation pump 136. As a further variation compared to the embodiment of FIG. 1, the apparatus 110 of FIG. 2 is provided with a transfer line 137 and a transfer pump 138, by which a certain amount of catholyte can be transferred to the continuous steel tank reactor 123 to adjust the pH of the anolyte during long-term operation. When a certain amount of catholyte is transferred to the anolyte circuit, water (H 2 O) needs to be replenished. EXAMPLES

[0171] Example 1 Formation of Sodium Paraperiodate by Anodic Oxidation of Sodium Iodide - Supply of Solid Sodium Iodide

[0172] In an apparatus 110 for producing metal periodate as shown in FIG. 2, a flow electrolysis cell 111 is provided with an anode chamber 112 and a cathode chamber 114 each having a capacity of 48 cm 2 The cell is equipped with electrodes 113, 115 of 1000 kcal / L. The cell is divided (anolyte and catholyte chambers are separated from each other via a cation exchange membrane 116 (Nafion® N 324 from DuPont)) and fixed with a 1 mm EPDM spacer. A boron-doped diamond electrode (DIACHEM® electrodes from Condias GmbH, 10 μm BDD (thickness 3 mm) on a silicon support, boron content about 800 ppm) was used as the anode 113. Stainless steel was used as the cathode 115. Each chamber was part of a respective electrolyte circuit 119, 122, which contained reservoirs for the anolyte (V=5 L) and catholyte (V=2.5 L), each circuit driven by a membrane pump 121, 124 (Ritmo R033 from Fink). The anolyte circuit included a continuous stirred tank reactor (CSTR) 123, which served as the anolyte reservoir and was stirred at 350 rpm, and was further connected to a collection vessel 130 via a discharge line 128 in order to separate a portion of the produced periodate from the anolyte by precipitation and decantation. The supernatant anolyte from the collection vessel 130 was returned to the CSTR 123 via a recirculation line 135. The discharge line 128 and the recirculation line 135 were driven by peristaltic pumps 129, 136 (RegloICC from Ismatec), respectively. Furthermore, the CSTR 123 was connected to a source of solid starting material to replenish the consumed iodide (here sodium iodide), indicated by references 131-134 in Fig. 2, and to the catholyte reservoir 120 to replenish the consumed base. Additionally, the catholyte reservoir 120 was connected to a supply 139 to replenish water lost during catholyte transfer and consumed during electrolysis at the cathode. During aqueous electrolysis, the cell was cooled by a thermostatically controlled anode cooling water system 117, 118.

[0173] For electrolysis, paraperiodate obtained from the previous electrolysis was suspended in caustic soda (4 M NaOH) and added to the anolyte reservoir. The pH of the anolyte was >12. The catholyte consisted of caustic soda of the same concentration. In addition, solid NaI was continuously fed to the anolyte at an addition rate of 3.5 g / h NaI. The anolyte and catholyte were sent to the electrolytic cell 111 at a flow rate of fr(an / cat) = 7.5 L / h. The suspension was removed from the anolyte by decantation in the second cycle (fr(dec) = various). The composition of the anolyte was frequently controlled by LC-PDA analysis. The removed suspension was filtered after electrolysis, the filter residue was washed with acetone and dried under reduced pressure, and the mass of the product was quantified to determine the productivity.

[0174] After 29 h of electrolysis, a total of 103 g (0.68 mol) of NaI was added, the precipitated paraperiodate in a collection vessel was filtered, the filter residue was washed with water and acetone, and dried under reduced pressure to give the product in 94% yield (497 g, 1.69 mol, purity 99.1% by LC-PDA), considering the initial amount of paraperiodate of 309 g (1.05 mol). The productivity was 6.5 g / h and the current efficiency was 24%. The IR spectrum was in agreement with the literature.

[0175] The anolyte contained in the anolyte reservoir had a total molar ratio of sodium periodate to sodium iodate of approximately 1:2 to 1:3, as determined by LC-PDA analysis of the anolyte returned to the CSTR. The iodide content in the anolyte returned to the CSTR was below the detection threshold of the LC-PDA. The amount of iodide added was such that the total molar ratio of sodium periodate to sodium iodide (before entering the analysis laboratory) was at least 15:1.

[0176] No clogging occurred.

[0177] Example 2 Formation of Sodium Paraperiodate by Anodic Oxidation of Sodium Iodide - Supply of Solid Sodium Iodide

[0178] The procedure of Example 1 was repeated, but the NaI addition rate was increased to 14.2 g / h. This increased the productivity to 16.8 g / h and the current efficiency to 61%. However, after 29 hours of electrolysis, the yield of sodium paraperiodate after a total of 411 g of NaI was added dropped to 61%. However, for a stationary reaction, this yield is still very satisfactory. The purity was 98.7%.

[0179] Again, no clogging occurred.

[0180] Example 3 Formation of Sodium Paraperiodate by Anodic Oxidation of Sodium Iodide - Supply of Solid Sodium Iodide

[0181] The procedure of Example 1 was repeated, but the flow rate was increased from fr(an / cat) to 700 L / h (using a Fink Flujo 01 pump) and the NaI addition rate was 8.5 g / h. This resulted in an increase in productivity to 15.6 g / h and a current efficiency of 57%. After 29 hours of electrolysis and addition of a total of 247 g of NaI, the yield of sodium paraperiodate was 94% and the purity was 98.7%.

[0182] Again, no clogging occurred.

[0183] Example 4 Formation of Sodium Paraperiodate by Anodic Oxidation of Sodium Iodide - Supply of Solid Sodium Iodide

[0184] The procedure of Example 1 was repeated, but with only 1 M NaOH concentration. After 71 hours of electrolysis, the yield of sodium paraperiodate was 64% and the purity was 99.7% after a total of 245 g NaI was added at a feed rate of 24 mmol / h (3.45 g / h). The productivity was 4.3 g / h and the current efficiency was 16%.

[0185] No clogging occurred.

[0186] Example 5 Formation of Sodium Paraperiodate by Anodic Oxidation of Sodium Iodate - Supply of Solid Sodium Iodate

[0187] The procedure of Example 4 was repeated, except that sodium iodate was used as the starting material. After 44 hours of electrolysis, a total of 754 g of NaIO was obtained at a feed rate of 86 mmol / h (17 g / h). 3 After the addition of 10 mmol / h, the yield of sodium paraperiodate was 70% and the purity was 99.9%. The productivity was 17.9 g / h and the current efficiency was 16%. Similar results were obtained when the addition rate was increased to 168 mmol / h (33 g / h).

[0188] The total molar ratio of sodium periodate to sodium iodate in the anolyte reservoir was approximately 1:1 to 1:2, as measured by LC-PDA.

[0189] No clogging occurred.

[0190] Example 6 Formation of sodium paraperiodate by anodic oxidation of elemental iodine - Supply of solid iodine

[0191] The procedure of Example 4 was repeated except that iodine was used as the starting material. After 75 hours of electrolysis, a total of 283 g of iodine was obtained. 2 After the addition of 1000 mg of sodium paraperiodate, the yield was 44% and the purity was 99.6%. The productivity was 3.9 g / h and the current efficiency was 12%.

[0192] No clogging occurred.

[0193] The total molar ratio of sodium periodate to sodium iodate in the anolyte reservoir was approximately 1:1 to 1:2, as determined by LC-PDA. The amount of iodine added was such that the total molar ratio of sodium periodate to iodine (before entering the analysis laboratory) was at least 14:1.

[0194] Example 7 Formation of Sodium Paraperiodate by Anodic Oxidation of Sodium Iodide - Replenishment of Dissolved Sodium Iodide

[0195] The setup is simpler than in Examples 1-6, with no catholyte feed to the CSTR and no anolyte return from the collection vessel to the CSTR.

[0196] In the apparatus 10 for producing metal periodate shown in FIG. 1, a flow electrolysis cell 11 is provided with an anode chamber 12 and a cathode chamber 14 each having a capacity of 48 cm 2 The cells were equipped with electrodes 13, 15 of 10 ... The anolyte circuit included a continuous stirred tank reactor (CSTR) 23, which served as the anolyte reservoir, stirred at 300 rpm and further connected to the feed solution (starting material tank 25) via line 27 and to a collection vessel 30 via line 28. Both lines 27, 28 were driven by respective peristaltic pumps 26, 28 (RegloICC from Ismatec). During electrolysis with water, the cell was cooled by thermostatically controlled anode and cathode cooling water systems 17, 18.

[0197] For electrolysis, the anolyte vessel was filled with the paraperiodate suspension obtained from the previous electrolysis suspended in caustic soda (1M NaOH). The pH of the anolyte was above 10. The catholyte consisted of caustic soda of the same concentration. The anolyte and catholyte were fed to the electrolysis cell at a flow rate of fr(an / cat) = 7.5 L / h. The suspension was removed from the anolyte and the feed solution was added at the same flow rate (fr(in / out) = various). The composition was frequently controlled by LC-PDA analysis. The withdrawn suspension was filtered after electrolysis, the filter residue was washed with acetone and dried under reduced pressure, and the mass of the product was quantified to determine the productivity.

[0198] Electrolysis was performed at a current of 20 A. NaI was added as an aqueous solution at a rate of 24 mmol / h. After 101 h of electrolysis and a total addition of 375 g of NaI, the yield of sodium paraperiodate was 52% and the purity was 99.6%. The productivity was 3.8 g / h and the current efficiency was 14%.

[0199] No clogging occurred.

[0200] Example 8 Formation of Sodium Paraperiodate by Anodic Oxidation of Sodium Iodate - Replenishment of Dissolved Sodium Iodate

[0201] The procedure of Example 7 was repeated, except that sodium iodate was used as the starting material. After 109 hours of electrolysis, a total of 950 g of NaIO was added at an addition rate of 44 mmol / h. 3 After the addition of 1000 ml of sodium paraperiodate, the yield was 68% and the purity was 99.9%. The productivity was 8.8 g / h and the current efficiency was 8%.

[0202] No clogging occurred, nor did clogging occur when the sodium iodate addition rate was increased to 179 mmol / h under otherwise similar conditions. [Explanation of symbols]

[0203] 10,110: Apparatus for preparing metal periodates 11,111: Electrolytic cell 12,112:Anode chamber 13,113: Anode 14,114: Cathode chamber 15,115: Cathode 16,116:Separator 17,117: Anode cooling water system 18,118: Cathode cooling water system 19,119:Catholyte circuit 20,120: Catholyte tank 21,121: Catholyte Circulation Pump 22,122:Anolyte circuit 23,123: Continuously stirred tank reactor 24,124: Anolyte Circulation Pump 25: Raw material tank 26: Supply pump 27: Supply Line 28,128: Discharge line 29,129: Discharge pump 30,130: Product collection container 131: Starting material container 132: Supply Line 133: Screw conveyor 134: Motor 135:Circulation line 136: Circulation pump 137: Catholyte transfer line 138: Transfer pump 139: Water supply pipe

Claims

1. A method for producing metal paraperiodate by anodizing an iodine compound having an oxidation state of −I to +V in an electrolytic cell, the electrolytic cell comprising an anode chamber having one or more anodes, a cathode chamber having one or more cathodes, and a separator disposed between the anode chamber and the cathode chamber, the method comprising the steps of: recirculating catholyte through a catholyte circuit to said cathode chamber; recirculating anolyte to the anode chamber through an anolyte circuit, the anolyte comprising metal periodates and iodine compounds having oxidation states from −I to +V selected from iodine salts, elemental iodine, a mixture of different iodine salts, or a mixture of iodine and one or more iodine salts; and performing said anodic oxidation of said iodine compound at a pH of at least 10; the anolyte circuit comprises at least one continuous stirred tank reactor operated in a stationary mode with respect to the total molar ratio of metal periodates to iodine compounds having oxidation states from −I to +V in the anolyte; wherein the continuous stirred tank reactor is operated in a steady state mode by continuously or periodically feeding the iodine compounds having an oxidation state of −I to +V to the continuous stirred tank reactor and continuously or periodically removing metal periodates from the continuous stirred tank reactor.

2. 2. The method of claim 1, wherein the metal periodate contained in the recycled anolyte is primarily metal paraperiodate.

3. operating the continuous stirred tank reactor in a stationary mode with respect to the total molar ratio of metal periodate to iodine compounds having oxidation states −I to +V in the anolyte means that a predetermined molar ratio or range of molar ratios is selected and, during operation, the actual molar ratio or range of molar ratios of metal periodate to iodine compounds is maintained at or near the predetermined molar ratio or range of molar ratios; By "near" it is meant that the actual molar ratio or molar ratio range may deviate from the selected molar ratio or molar ratio range by up to ±20%; 3. The method of claim 1 or claim 2, wherein the molar ratio is calculated based on the iodine atoms present in the metal periodate and the iodine compound.

4. 4. The method of claim 3, wherein the predetermined molar ratio or molar ratio range relates to a molar ratio or molar ratio range in the anolyte prior to entering the anode chamber.

5. the total molar ratio of metal periodate to iodine compounds having oxidation states from −I to +V in the recycled anolyte is 1:>0 to 1:5, and when the iodine compounds have oxidation states from −I to +III, the total molar ratio of metal periodate to iodine compounds having oxidation states from −I to +III is 1:0 to 8:1, and when the iodine compounds have an oxidation state of +V, the total molar ratio of metal periodate to iodine compounds having an oxidation state of +V is 1:0-1:5; 4. The method according to any one of claims 1 to 3, wherein preferably the total molar ratio of metal periodate to iodine compounds having an oxidation state of -I to +V is from 1:>0 to 1:4, more preferably from 200:1 to 1:4, and when the iodine compounds have an oxidation state of -I to +III the total molar ratio of metal periodate to iodine compounds having an oxidation state of -I to +III is from 1:0 to 10:1, and when the iodine compounds have an oxidation state of +V the total molar ratio of metal periodate to iodine compounds having an oxidation state of +V is from 1:0 to 1:4, preferably from 200:1 to 1:

4.

6. in the recycled anolyte, when fed to the anolyte chamber, the total molar ratio of metal periodate to iodine compounds having an oxidation state of −I to +V is 1:>0 to 1:5, and when the oxidation state of the iodine compounds is −I to +III, the total molar ratio of metal periodate to iodine compounds having an oxidation state of −I to +III is 1:0 to 8:1, and when the oxidation state of the iodine compounds is +V, the total molar ratio of metal periodate to iodine compounds having an oxidation state of +V is 1:0 to 1:5; 5. The method according to any one of claims 1 to 4, wherein preferably the total molar ratio of metal periodate to iodine compounds having an oxidation state of -I to +V is from 1:>0 to 1:4, more preferably from 200:1 to 1:4, and when the iodine compounds have an oxidation state of -I to +III the total molar ratio of metal periodate to iodine compounds having an oxidation state of -I to +III is from 1:0 to 10:1, and when the iodine compounds have an oxidation state of +V the total molar ratio of metal periodate to iodine compounds having an oxidation state of +V is from 1:0 to 1:4, more preferably from 200:1 to 1:

4.

7. a predetermined molar ratio or range of molar ratios is selected for the anolyte prior to entering the anode chamber in order to operate the continuous stirred tank reactor in a stationary mode with respect to the total molar ratio of metal periodate and iodine compounds having oxidation states from −I to +V, and during operation, the actual molar ratio of metal periodate and iodine compounds in the anolyte prior to entering the anode chamber is maintained within the predetermined molar ratio or range of molar ratios ±20%; the predetermined molar ratio or molar ratio range is selected such that the anolyte has a total molar ratio of metal periodate to iodine compounds having oxidation states from −I to +V in the anolyte prior to entering the anolyte chamber (i.e., as it is provided to the anolyte chamber) of from 1:>0 to 1:5; When the oxidation state of the iodine compound is from −I to +III, the total molar ratio of metal periodate to iodine compound having an oxidation state from −I to +III is selected to be from 1:0 to 8:1; When the oxidation state of the iodine compound is +V, the total molar ratio of metal periodate to iodine compound having an oxidation state of +V is selected to be from 1:0 to 1:5; 7. The method of claim 1, wherein the molar ratio is calculated based on the iodine atoms present in the metal periodate and the iodine compound.

8. The iodine compound having an oxidation state of −I to +V is an alkali metal iodide, an alkali metal iodate, iodine, or a mixture thereof, preferably sodium iodide, potassium iodide, sodium iodate, potassium iodate, iodine, or a mixture thereof; 8. A method according to any one of claims 1 to 7 for preparing an alkali metal paraperiodate, preferably sodium paraperiodate or potassium paraperiodate.

9. 9. The method according to claim 1, wherein the anodization is carried out at a pH of at least 11, in particular at least 12.

10. 10. The method of claim 1, wherein the anodization is carried out in the presence of a base, said base being selected from the group consisting of metal hydroxides, metal oxides and metal carbonates.

11. 11. The method of claim 10, wherein the anodization is carried out in the presence of a metal hydroxide, and when the iodine compound having an oxidation state of −I to +V is an alkali metal iodine salt, the metal of the base corresponds to the metal in the metal iodine salt.

12. 12. The method according to any one of the preceding claims, wherein the catholyte comprises an aqueous medium having a pH of at least 10, preferably at least 11, in particular at least 12.

13. Anodization is performed at 10 to 1000 mA / cm ２ , preferably 100 to 750 mA / cm ２ , especially 250 to 500 mA / cm ２ , specifically 400 to 430 mA / cm ２ The method according to any one of claims 1 to 12, wherein the method is carried out at a current density in the range of

14. 14. The method according to any one of claims 1 to 13, wherein the separator arranged between the cathode chamber and the anode chamber is selected from a semi-permeable membrane, a diaphragm and a frit, in particular an ion exchange membrane.

15. 15. The method of claim 1, wherein the one or more anodes comprises a carbon-based active layer.

16. 16. The method of claim 15, wherein the one or more anodes comprise a diamond layer doped with one or more elements from IUPAC Groups 13, 15 or 16 of the Periodic Table.

17. The method of claim 16, wherein the one or more anodes comprise a layer of boron doped diamond.

18. 18. The process of any one of claims 1 to 17, wherein the iodine compound having an oxidation state of -I to +V is fed to the continuous stirred tank reactor in the form of an aqueous solution, an aqueous suspension or a solid.

19. 19. An apparatus configured for preparing metal paraperiodate by the method of any one of claims 1 to 18, comprising: The electrolytic cell comprises an anode chamber having one or more anodes, a cathode chamber having one or more cathodes, and a separator disposed between the anode chamber and the cathode chamber; the catholyte circuit recirculates catholyte through the cathode chamber, the catholyte circuit including a catholyte reservoir; the anolyte circuit circulates anolyte through the anode chamber, the anolyte circuit comprising at least one continuous stirred tank reactor having a supply means for supplying the iodine compound having an oxidation state from −I to +V selected from an iodine salt, elemental iodine, a mixture of different iodine salts, or a mixture of iodine and one or more iodine salts to the at least one continuous stirred tank reactor, and a withdrawal means for removing the metal periodate reaction product from the at least one continuous stirred tank reactor.

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