METHOD FOR PREPARING PERIODATES VIA ANODIC OXIDATION IN A STEADY STATE REACTOR

Abstract

The present invention relates to a method for preparing a metal para-periodate by anodic oxidation of an iodine compound with an oxidation state from I to +V in an electrolysis cell under specific conditions, and to a device for carrying out this reaction.

Claims

1. A method for preparing a metal para-periodate by anodic oxidation of an iodine compound with an oxidation state from I to +V in an electrolysis cell, said electrolysis cell comprising an anodic compartment having one or more anodes, a cathodic compartment having one or more cathodes, and a separator arranged between said anodic and cathodic compartments, said method comprising recirculating a catholyte through a catholyte circuit into said cathodic compartment, recirculating an anolyte through an anolyte circuit into said anodic compartment, said anolyte comprising a metal periodate and an iodine compound with an oxidation state from I to +V selected from an iodine salt, elementary iodine, a mixture of different iodine salts or a mixture of iodine with one or more iodine salts, carrying out said anodic oxidation of said iodine compound at a pH of at least 10, wherein said anolyte circuit comprises at least one continuous stirred tank reactor operated in a steady-state mode with respect to the overall molar ratio of metal periodate to iodine compound with an oxidation state from I to +V in said anolyte, wherein said continuous stirred tank reactor is operated in a steady-state mode by continuously or periodically feeding said iodine com-pound with an oxidation state from I to +V into said continuous stirred tank reactor and continuously or periodically removing metal periodate from said continuous stirred tank reactor.

2. The method according to claim 1, wherein said metal periodate comprised in said recirculated anolyte is predominantly a metal para-periodate.

3. The method according to claim 1, wherein operating the continuous stirred tank reactor in a steady-state mode with respect to the overall molar ratio of metal periodate to iodine compounds with an oxidation state from I to +V in said anolyte means that a predefined molar ratio or molar ratio range is selected and during operation, the actual molar ratio or molar ratio range of metal periodate to iodine compounds is kept at the predefined molar ratio or molar ratio range or in close vicinity of the preselected molar ratio or molar ratio range, wherein close vicinity means that the actual molar ratio or molar ratio range may deviate from the selected molar ratio or molar ratio range by at most 20%, where the molar ratio is calculated on the basis of iodine atoms present in the metal periodate and the iodine compound.

4. The method according to claim 3, wherein the predefined molar ratio or molar ratio range relates to the molar ratio or molar ratio range in the anolyte before entering the anodic compartment.

5. The method according to claim 1, wherein in said recirculated anolyte the overall molar ratio of the metal periodate and the iodine compound with an oxidation state from I to +V is of from 1:>0 to 1:5; where in case that the iodine compound has an oxidation state from I to +III, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state from I to +III is of from 1:0 to 8:1; and where in case that the iodine compound has an oxidation state of +V, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state of +V is of from 1:0 to 1:5; where preferably the overall molar ratio of the metal periodate and the iodine compound with an oxidation state from I to +V is of from 1:>0 to 1:4; more preferably from 200:1 to 1:4; where in case that the iodine compound has an oxidation state from I to +III, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state from I to +III is of from 1:0 to 10:1, and where in case that the iodine compound has an oxidation state of +V, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state of +V is of from 1:0 to 1:4, preferably from 200:1 to 1:4.

6. The method according to claim 1, wherein in said recirculated anolyte, when fed to the anodic compartment, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state from I to +V is of from 1:>0 to 1:5; where in case that the iodine compound has an oxidation state of from I to +III, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state of from I to +III is of from 1:0 to 8:1; and where in case that the iodine compound has an oxidation state of +V, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state of +V is of from 1:0 to 1:5; where preferably the overall molar ratio of the metal periodate and the iodine compound with an oxidation state from I to +V is of from 1:>0 to 1:4; more preferably from 200:1 to 1:4; where in case that the iodine compound has an oxidation state from I to +III, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state from I to +III is of from 1:0 to 10:1, and where in case that the iodine compound has an oxidation state of +V, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state of +V is of from 1:0 to 1:4, more preferably from 200:1 to 1:4.

7. The method according to claim 1, wherein for operating the continuous stirred tank reactor in a steady-state mode with respect to the overall molar ratio of metal periodate to iodine compounds with an oxidation state from I to +V, for the anolyte before entering the anodic compartment a predefined molar ratio or molar ratio range is selected, and during operation, the actual molar ratio of metal periodate to iodine compounds in the anolyte before entering the anodic compartment is kept at the predefined molar ratio or molar ratio range20%; wherein said predefined molar ratio or molar ratio range is selected thusly that in said anolyte, before entering the anodic compartment (i.e. when fed to the anodic compartment), the overall molar ratio of the metal periodate and the iodine compound with an oxidation state from I to +V is of from 1:>0 to 1:5; where in case that the iodine compound has an oxidation state of from I to +III, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state of from I to +III is of from 1:0 to 8:1; and where in case that the iodine compound has an oxidation state of +V, the overall molar ratio of the metal periodate and the iodine compound with an oxidation state of +V is of from 1:0 to 1:5; where the molar ratio is calculated on the basis of iodine atoms present in the metal periodate and the iodine compound.

8. The method according to claim 1, for preparing an alkali metal para-periodate, preferably sodium or potassium para-periodate, where the iodine compound with an oxidation state from I to +V is an alkali metal iodide, alkali metal iodate, iodine or a mixture thereof, preferably sodium iodide, potassium iodide, sodium iodate, potassium iodate, iodine or a mixture thereof.

9. The method according to claim 1, where the anodic oxidation is carried out at a pH of at least 11.

10. The method according to claim 1, where the anodic oxidation is carried out in the presence of a base, where the base is selected from the group consisting of metal hydroxides, metal oxides and metal carbonates.

11. The method according to claim 10, where the anodic oxidation is carried out in the presence of a metal hydroxide, where in case that said iodine compound with an oxidation state from I to +V is an alkali metal iodine salt, the metal of the base corresponds to the metal in the metal iodine salt.

12. The method according to claim 1, where the catholyte comprises an aqueous medium with a pH of at least 10, preferably of at least 11.

13. The method according to claim 1, where the anodic oxidation is carried out at a current density in the range of from 10 to 1000 mA/cm2, preferably from 100 to 750 mA/cm2, in particular from 250 to 500 mA/cm2 and specifically of 400 to 430 mA/cm2.

14. The method according to claim 1, where said separator arranged between said cathodic and anodic compartments is selected from semipermeable membranes, diaphragms and frits, and is in particular an ion-exchange membrane.

15. The method according to claim 1, where the one or more anodes comprise a carbon-based active layer.

16. The method according to claim 15, where the one or more anodes comprise a diamond layer doped with one or more IUPAC group 13, 15 or 16 elements of the periodic table.

17. The method according to claim 16, where the one or more anodes comprise a boron-doped diamond layer.

18. The method according to claim 1, where said iodine com-pound with an oxidation state from I to +V is fed into said continuous stirred tank reactor in form of an aqueous solution, aqueous suspension or in solid form.

19. A device configured for preparing a metal para-periodate by the method of claim 1, the device comprising said electrolysis cell comprising an anodic compartment having one or more anodes, a cathodic compartment having one or more cathodes, and a separator arranged between said anodic and cathodic compartments, said catholyte circuit for recirculating catholyte through said cathodic compartment, said catholyte circuit comprising a catholyte reservoir, said anolyte circuit for circulating anolyte through said anodic compartment, said anolyte circuit comprising at least one continuous stirred tank reactor, said at least one continuous stirred tank reactor being provided with feeding means for feeding said iodine compound with an oxidation state from I to +V selected from an iodine salt, elementary iodine, a mixture of different io-dine salts or a mixture of iodine with one or more iodine salts into said at least one continuous stirred tank reactor and withdrawing means for withdrawing said metal periodate reaction product from said at least one continuous stirred tank reactor.

Description

[0192] The method will now be further described with reference to schematic embodiments shown in the attached drawings and with reference to examples described below.

[0193] In the drawings:

[0194] FIG. 1 shows a first embodiment of a device for carrying out the present invention; and

[0195] FIG. 2 shows a second embodiment of a device for carrying out the present invention.

[0196] In FIG. 1, a first embodiment of a device for preparing metal periodate in accordance with the method of the present invention is generally designated by reference sign 10. The device 10 comprises an electrolysis cell 11 having an anodic compartment 12, where an anode 13 is arranged and a cathodic compartment 14, where a cathode 15 is arranged. A separator 16, for instance a semipermeable membrane, a diaphragm or a frit, is arranged between the anodic compartment 12 and the cathodic compartment 14. Both compartments are provided with an anodic cooling water system 17 and a cathodic cooling water system 18, respectively, to allow for temperature regulation of the respective cells. The cathodic compartment 14 is part of a catholyte circuit 19, which comprises a catholyte tank 20 and a catholyte recirculation pump 21. The anolyte compartment is part of an anolyte circuit 22, which comprises a continuous stirred tank reactor 23, which acts as an anolyte tank and an anolyte recirculation pump 24. In the continuous stirred tank reactor 23, the predefined molar ratio of metal periodate to iodine compounds with an aggregation state from I to +V is maintained. To this effect, the continuous stirred tank reactor 23 is fed with a starting material solution from starting material tank 25 via feed pump 26 and feed line 27. Anolyte can be withdrawn from the continuous stirred tank reactor 23 via discharge line 28 and discharge pump 29, which discharges a certain fraction of the anolyte into product collection vessel 30. In this embodiment, the rate at which iodine compounds are fed into the continuous stirred tank reactor 23 from starting material tank 25 corresponds to the rate at which metal periodate is generated via electrolysis in the anodic compartment 12, which in turn determines the rate at which metal periodate is removed from the continuous stirred tank reactor 23 via discharge line 28 into product collection vessel 30.

[0197] FIG. 2 shows a second embodiment of a device according to the present invention. In FIG. 2, elements which are identical or similar to elements described in connection with FIG. 1 are denoted by the same reference signs augmented by 100.

[0198] Accordingly, the device for preparing metal periodate is designated by reference sign 110 and comprises an electrolysis cell 111 having an anodic compartment 112 with an anode 113 and a cathodic compartment 114 with a cathode 115. Again, a separator 116 is arranged between the anodic compartment 112 and the cathodic compartment 114. Both compartments are provided with an anodic cooling water system 117 and a cathodic cooling water system 118, respectively. The cathodic compartment 114 is part of a catholyte circuit 119, which comprises a catholyte tank 120 and a catholyte recirculation pump 121. The anolyte compartment 112 is part of an anolyte circuit 122, which comprises a continuous stirred tank reactor 123 and an anolyte recirculation pump 124.

[0199] The device of FIG. 2 differs from the device of FIG. 1 in that the starting material, especially the iodine compounds, are fed as solids directly into the continuous stirred tank reactor 123. To this effect, a container 131 for the solid starting materials and a supply line 132 are provided. The container 131 can be provided with a motorized feeder, for instance 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 which allows removal of metal periodate from the anolyte fed into the collection vessel 130 via discharge line 128 and discharge pump 129. The depleted anolyte is recycled into the continuous stirred tank reactor 123 via recirculation line 135 and recirculation pump 136. As a further variation compared to the embodiment of FIG. 1, the device 110 of FIG. 2 is provided with a transfer line 137 and a transfer pump 138 which allows the transfer of certain amount of catholyte into the continuous steel tank reactor 123 to allow for a pH adjustment of the anolyte during prolonged operation. As a certain amount of catholyte is transferred to the anolyte circuit, the catholyte circuit has to be resupplied with water (H.sub.2O) via water supply line 139.

EXAMPLES

Example 1 Anodic Oxidation of Sodium Iodide to Sodium Para-PeriodateSupplementing of Sodium Iodide in Solid Form

[0200] In a device 110 for preparing metal periodate as schematically depicted in FIG. 2, a flow-electrolysis cell 111 was equipped with 48 cm.sup.2 electrodes 113, 115 in the anode and the cathode compartments 112, 114, respectively. The cell was divided (anode and the cathode compartment separated from each other through a cation exchange membrane 116 (Nafion N 324 from DuPont)) and tethered by 1 mm EPDM spacers. A boron-doped diamond electrode (DIACHEM electrode from Condias GmbH; 10 m BDD on silicium support (3 mm thickness); ca. 800 ppm of boron) was used as anode 113. Stainless steel was used as cathode 115. Each compartment was part of a respective electrolyte circuit 119, 122 which included respective reservoirs for the anolyte (V=5 L) and catholyte (V=2.5 L) and each circuit was powered 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 which was stirred at 350 rpm and was further connected to a collection vessel 130 via discharge line 128 for separation of a part of the formed periodate by sedimentation and decantation from the anolyte. Supernatant anolyte from the collection vessel 130 was returned to the CSTR 123 via recirculation line 135. The discharge line 128 and the recirculation line 135 were powered by peristaltic pumps 129, 136, respectively (RegloICC from Ismatec). Moreover, the CSTR 123 was connected to a feed for solid starting material to supplement the consumed iodine compound (here sodium iodide), denoted by reference signs 131-134 in FIG. 2, as well as to the catholyte reservoir 120 to supplement consumed base. The catholyte reservoir 120 was moreover connected to a feed 139 to supplement water lost in the transfer of catholyte and consumed in electrolysis at the cathode. The cell was cooled by a thermostatically controlled anodic and cathodic cooling water system 117, 118 during the electrolysis using water.

[0201] For the electrolysis, para-periodate from previous electrolysis was suspended in caustic soda (4M NaOH) and added to the anolyte reservoir. pH of the anolyte was >12. The catholyte consisted of caustic soda of the same concentration. The anolyte was moreover fed continuously with solid NaI at an addition rate of 3.5 g/h NaI. The anolyte and catholyte were pumped through the electrolysis cell 111 with a flow rate of fr(an/cat)=7.5 L/h. The suspension was removed from the anolyte by decantation in a secondary 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, dried under reduced pressure, and the mass of the product was determined to obtain the productivity.

[0202] After 29 h of electrolysis and after addition of a total amount of 103 g of NaI (0.68 mol), the para-periodate precipitated in the collector was filtered off, the filter residue was washed with water and acetone, and was dried under reduced pressure to obtain the product in 94% yield (497 g, 1.69 mol, 99.1% purity by LC-PDA) considering the initial amount of para-periodate of 309 g (1.05 mol). The productivity accounted to 6.5 g/h and the current efficiency to 24%. The IR spectra was in accordance with literature.

[0203] In the anolyte contained in the anolyte reservoir, the overall molar ratio of sodium periodate to sodium iodate was ca. 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 added iodide was such that the overall molar ratio of sodium periodate to sodium iodide (before entering the analytic compartment) was at least 15:1.

[0204] No clogging occurred.

Example 2 Anodic Oxidation of Sodium Iodide to Sodium Para-PeriodateSupplementing of Sodium Iodide in Solid Form

[0205] The proceeding of example 1 was repeated; the addition rate of NaI was however increased to 14.2 g/h. This increased the productivity to 16.8 g/h and the current efficiency to 61%. However, the yield of sodium para-periodate after 29 h of electrolysis and after addition of a total amount of 411 g of NaI dropped to 61%. For steady state reaction, this yield is however still very satisfactory. Purity was 98.7%.

[0206] No clogging occurred here, either.

Example 3 Anodic Oxidation of Sodium Iodide to Sodium Para-PeriodateSupplementing of Sodium Iodide in Solid Form

[0207] The proceeding of example 1 was repeated; the flow rate was however increased to fr(an/cat) to 700 L/h (using Flujo01 pumps from Fink), and the addition rate of NaI was 8.5 g/h. This increased the productivity to 15.6 g/h and the current efficiency to 57%. The yield of sodium para-periodate after 29 h of electrolysis and after addition of a total amount of 247 g of NaI was 94%, purity 98.7%.

[0208] No clogging occurred here, either.

Example 4 Anodic Oxidation of Sodium Iodide to Sodium Para-PeriodateSupplementing of Sodium Iodide in Solid Form

[0209] The proceeding of example 1 was repeated, using however NaOH in a concentration of only 1M. After 71 h of electrolysis and after addition of a total amount of 245 g of NaI at a feeding rate of 24 mmol/h (3.45 g/h) the yield of sodium para-periodate was 64% with a purity of 99.7%. Productivity was 4.3 g/h and the current efficiency was 16%.

[0210] No clogging occurred.

Example 5 Anodic Oxidation of Sodium Iodate to Sodium Para-PeriodateSupplementing of Sodium Iodate in Solid Form

[0211] The proceeding of example 4 was repeated, using however sodium iodate as starting material. After 44 h of electrolysis and after addition of a total amount of 754 g of NaIO.sub.3 at a feeding rate of 86 mmol/h (17 g/h) the yield of sodium para-periodate was 70% with a purity of 99.9%. Productivity was 17.9 g/h and the current efficiency was 16%. Similar results were obtained when increasing the addition rate of to 168 mmol/h (33 g/h).

[0212] In the anolyte contained in the anolyte reservoir, the overall molar ratio of sodium periodate to sodium iodate was ca. 1:1 to 1:2, as determined by LC-PDA.

[0213] No clogging occurred.

Example 6 Anodic Oxidation of Elementary Iodine to Sodium Para-PeriodateSupplementing of Iodine in Solid Form

[0214] The proceeding of example 4 was repeated, using however iodine as starting material. After 75 h of electrolysis and after addition of a total amount of 283 g of 12 the yield of sodium para-periodate was 44% with a purity of 99.6%. Productivity was 3.9 g/h and the current efficiency was 12%.

[0215] No clogging occurred.

[0216] In the anolyte contained in the anolyte reservoir, the overall molar ratio of sodium periodate to sodium iodate was ca. 1:1 to 1:2, as determined by LC-PDA. The amount of added iodine was such that the overall molar ratio of sodium periodate to iodine (before entering the analytic compartment) was at least 14:1.

Example 7 Anodic Oxidation of Sodium Iodide to Sodium Para-PeriodateSupplementing of Sodium Iodide in Dissolved Form

[0217] The set-up was simpler than in examples 1-6, containing no catholyte feed to the CSTR and not returning anolyte from the collector to the CSTR:

[0218] In a device 10 for preparing metal periodate as schematically depicted in FIG. 1, a flow-electrolysis cell 11 was equipped with 48 cm.sup.2 electrodes 13, 15 in the anode and the cathode compartments 12, 14, respectively. The cell was divided (anode and the cathode compartment separated from each other through a cation exchange membrane 16 (Nafion N324 from DuPont)) and tethered by 1 mm EPDM spacers. A boron-doped diamond electrode (DIACHEM electrode from Condias GmbH; 10 m BDD on silicium support (3 mm thickness); ca. 800 ppm of boron) was used as anode 13. Stainless steel was used as cathode 14. Each compartment was part of a respective electrolyte circuit 19, 22 which included respective reservoirs for the anolyte (V=5 L) and catholyte (V=2.5 L) and each circuit was powered by respective membrane pumps 21, 24 (Ritmo R033 from Fink). The anolyte circuit included a continuous stirred tank reactor (CSTR) 23, which served as an anolyte reservoir and which was stirred at 300 rpm and was further connected to feedstock solution (starting material tank 25) via line 27 and to a collection vessel 30 via line 28. Both lines 27, 28 were powered by respective peristaltic pumps 26, 28 (RegloICC from Ismatec). The cell was cooled by a thermostatically controlled anodic and cathodic cooling water system 17, 18 during the electrolysis using water.

[0219] For the electrolysis, the anolyte vessel was loaded with a para-periodate suspension from previous electrolysis suspended in caustic soda (1M NaOH). pH of the anolyte was >10. The catholyte consisted of caustic soda of the same concentration. The anolyte and catholyte were pumped through the electrolysis cell with a flow rate of fr(an/cat)=7.5 L/h. The suspension was removed from the anolyte, while the feedstock solution was added at the same flow rate (fr(in/out)=various). The composition was frequently controlled by LC-PDA analysis. The removed suspension was filtered after electrolysis, the filter residue was washed with acetone, dried under reduced pressure, and the mass of the product was determined to obtain the productivity.

[0220] Electrolysis was carried out at a current of 20 A. NaI was added as an aqueous solution with an addition rate of 24 mmol/h. After 101 h of electrolysis and after addition of a total amount of 375 g of NaI the yield of sodium para-periodate was 52% with a purity of 99.6%. Productivity was 3.8 g/h and the current efficiency was 14%.

[0221] No clogging occurred.

Example 8 Anodic Oxidation of Sodium Iodate to Sodium Para-PeriodateSupplementing of Sodium Iodate in Dissolved Form

[0222] The proceeding of example 7 was repeated, using however sodium iodate as starting material. After 109 h of electrolysis and after addition of a total amount of 950 g of NaIO.sub.3 at an addition rate of 44 mmol/h the yield of sodium para-periodate was 68% with a purity of 99.9%. Productivity was 8.8 g/h and the current efficiency was 8%.

[0223] No clogging occurred. Nor did clogging occur when the addition rate of sodium iodate was increased to 179 mmol/h under otherwise analogous conditions.

LIST OF REFERENCE SIGNS

[0224] 10, 110 device of preparing metal periodate [0225] 11, 111 electrolysis cell [0226] 12, 112 anodic compartment [0227] 13, 113 anode [0228] 14, 114 cathodic compartment [0229] 15, 115 cathode [0230] 16, 116 separator [0231] 17, 117 anodic cooling water system [0232] 18, 118 cathodic cooling water system [0233] 19, 119 catholyte circuit [0234] 20, 120 catholyte tank [0235] 21, 121 catholyte recirculation pump [0236] 22, 122 anolyte circuit [0237] 23, 123 continuous stirred tank reactor [0238] 24, 124 anolyte recirculation pump [0239] 25 starting material tank [0240] 26 feed pump [0241] 27 feed line [0242] 28, 128 discharge line [0243] 29, 129 discharge pump [0244] 30, 130 product collection vessel [0245] 131 starting materials container [0246] 132 supply line [0247] 133 screw conveyor [0248] 134 motor [0249] 135 recirculation line [0250] 136 recirculation pump [0251] 137 catholyte transfer line [0252] 138 transfer pump [0253] 139 water supply line