Synthesis of hydriodic acid and electrodialysis cell

Abstract

To provide a method for synthesizing hydroiodic acid that can improve yield and reduce the amount of waste liquid generated, the amount of sulfate ions transferred to a product chamber liquid, and the amount of iodide ions transferred to an electrode chamber.SOLUTION: A method for synthesizing hydroiodic acid by a double displacement electrodialysis process, which is characterized in that, between a positive electrode and a negative electrode, from the positive electrode side, a positive electrode chamber, a cation exchange membrane, and a first sub-material chamber, and subsequently thereto a plurality of sets, each of the sets constituted of four membranes and four chambers consisting of a cation exchange membrane, a product chamber, a first anion exchange membrane, a first material chamber, a second anion exchange membrane, a second material chamber, a third anion exchange membrane, and a second sub-material chamber, are arranged, and by using an electrodialysis tank with the cation exchange membrane and a negative electrode chamber arranged therein, a raw material solution is passed through the first material chamber and the liquid passed through the first material chamber in the previous batch is passed through the second material chamber.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for synthesizing hydroiodic acid by electrodialysis and an electrodialysis cell. [Background technology]

[0002] A known method for producing hydroiodic acid is to suspend or dissolve iodine in water or hydroiodic acid, reduce the iodine using phosphorus, hypophosphorous acid, or the like, and then distill the hydroiodic acid from the reaction solution obtained after the reaction (for example, Patent Document 1).

[0003] Although this method is industrially advantageous, it requires highly pure iodine and a relatively expensive reducing agent as raw materials, produces a large amount of phosphoric acid as waste liquid, and is economically disadvantageous because the disposal cost of the mixed liquid of phosphoric acid, phosphorous acid, hypophosphorous acid, and hydroiodic acid, which is generated as the bottom liquid after distillation, is expensive.

[0004] Patent Documents 2 and 3 describe a method for directly producing hydroiodic acid from an iodine absorption solution, which is an intermediate product when iodine is produced from brine associated with natural gas by the blowing-out method, by double displacement electrodialysis.

[0005] Patent Documents 2 and 3 disclose an electrodialysis method (four-chamber method) using an electrodialysis cell in which multiple membrane chamber sets, each consisting of four membranes and four chambers, are arranged in the following order from the positive electrode side to the negative electrode side: a positive electrode chamber, a first cation exchange membrane which is a cation exchange membrane, a first auxiliary salt chamber, a first anion exchange membrane which is an anion exchange membrane, an auxiliary raw material chamber, a second cation exchange membrane which is a cation exchange membrane, a product chamber, a second anion exchange membrane which is a monovalent anion selective permeable membrane, a raw material chamber, a third cation exchange membrane which is a cation exchange membrane, and a second auxiliary salt chamber, followed by a cation exchange membrane and an anode chamber in that order.

[0006] This method is superior from the viewpoints of both economics and environmental protection because it uses an intermediate product of iodine production as the main raw material instead of highly purified iodine, thereby eliminating the need for several oxidation-reduction reactions and generating only small amounts of waste products such as phosphoric acid. However, there are still some areas that need improvement.

[0007] First, since an iodine absorbing solution with a high sulfate ion concentration is used as the raw material solution (specifically, the iodine absorbing solution contains sulfate ions at a molar ratio of approximately half that of iodide ions), a small amount of sulfate ions in the raw material solution is mixed into the product solution obtained by this method.

[0008] In particular, at the end of electrodialysis, when the iodide ion concentration in the raw solution decreases, the rate of sulfate ion migration from the raw material chamber to the product chamber increases. Therefore, if an attempt is made to increase the yield of iodide ions in the raw material solution, the amount of sulfate ions mixed into the product solution (crude hydroiodic acid aqueous solution) increases.

[0009] If sulfate ions are present in the crude hydroiodic acid aqueous solution, when the solution is heated in the subsequent distillation step, which is a purification step, the sulfate ions oxidize the iodide ions and produce free iodine. Therefore, it is necessary to add barium carbonate before the distillation step and remove the sulfate ions as a barium sulfate precipitate.

[0010] The cost of the barium carbonate used in this process, the cost of disposing of the barium sulfate precipitate that is generated, and the loss of hydroiodic acid that adheres to the barium sulfate precipitate all contribute to the manufacturing cost. Therefore, it is economically advantageous to produce a product solution with as little sulfate ion contamination as possible.

[0011] Second, in this method, some of the iodide ions in the product liquid pass through the cation exchange membrane on the positive electrode side of the product chamber and move to the auxiliary raw material chamber.

[0012] The iodide ions that have moved to the auxiliary raw material chamber pass through the anion exchange membrane on the positive electrode side of the auxiliary raw material chamber and move to the auxiliary salt chamber. Since the iodide ions that have moved to the auxiliary salt chamber remain there, the iodide ion concentration in the auxiliary salt chamber increases cumulatively during electrodialysis operation.

[0013] The residual liquid in the secondary salt chamber at the end of dialysis is an aqueous solution mainly composed of sodium hydrogen sulfate, containing approximately 0.1 to 1% iodide ions. Since sodium hydrogen sulfate has little industrial value, the residual liquid in the secondary salt chamber is disposed of as waste acid. The iodide ions contained in the residual liquid in the secondary salt chamber are lost. 0.5 to 10% of the iodide ions in the raw solution are lost.

[0014] Third, the movement of anions through an anion exchange membrane in electrodialysis can be electrical or diffusional. The rate of electrical movement is determined by the current density, while the rate of diffusional movement is proportional to the concentration difference on both sides of the membrane. At the start of electrodialysis, the concentration in the raw material chamber is higher than that in the product chamber, so diffusional movement occurs from the raw material chamber to the product chamber. In the latter half of dialysis, the concentration in the product chamber increases and the concentration in the raw material chamber decreases, so the direction of diffusional movement is from the product chamber to the raw material chamber. Toward the end of dialysis, the concentration difference between the product and raw material chambers increases, and the rate of diffusional movement also increases proportionally. The apparent (actual) rate of movement of iodide ions, which is the combination of electrical and diffusional movement, decreases significantly toward the end of dialysis.

[0015] The decrease in apparent migration rate can be avoided by lowering the final iodide ion concentration in the product chamber, but this is not an appropriate method because it places a heavy burden on the subsequent concentration process. In other words, to increase the final iodide ion concentration in the product liquid, iodide ions must be left in the raw material chamber. Therefore, the four-chamber method cannot achieve both high yield and high concentration ratio. In addition, a decrease in apparent migration rate from the raw material chamber to the product chamber at the end of the process is unavoidable.

[0016] Fourth, in the membrane chamber assemblies described in Patent Documents 2 and 3, the adjacent chamber, separated from the positive electrode chamber by a cation exchange membrane, serves as a secondary salt chamber. The secondary salt chamber solution contains approximately 0.1% hydroiodic acid, so some of the hydroiodic acid passes through the cation exchange membrane and reaches the positive electrode chamber. This can corrode the electrode or be oxidized at the positive electrode to form free iodine, which can corrode peripheral equipment. In particular, electrodes made of materials that are corrosion-resistant by forming an oxide film on their surfaces, such as stainless steel or titanium, can easily corrode when exposed to a strongly acidic aqueous solution containing iodide ions because the oxide film is reduced and removed by the iodide ions.

[0017] As described above, the methods described in Patent Documents 2 and 3 use an iodine absorption solution or an iodine-containing industrial waste liquid, which are intermediates in iodine production, as iodine raw materials, and use a very small amount of phosphorus compounds, and are therefore economically advantageous methods compared to the method described in Patent Document 1.

[0018] However, the yield is still not sufficient, and the amount of waste liquid generated, the amount of sulfate ions transferred to the product chamber liquid, and the amount of iodide ions transferred to the electrode chamber have not been sufficiently suppressed.

[0019] As described above, the use of electrodialysis for the synthesis of hydroiodic acid is considered to be rational, but there are still problems that need to be solved. [Prior art documents] [Patent documents]

[0020] [Patent Document 1] Japanese Patent Application Publication No. 8-59205 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-58896 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-272602 Summary of the Invention [Problem to be solved by the invention]

[0021] An object of the present invention is to provide a method for synthesizing hydroiodic acid, which can further improve the yield and reduce the amount of waste liquid generated, the amount of sulfate ions transferred to the product chamber liquid, and the amount of iodide ions transferred to the electrode chamber, and to provide an electrodialysis cell that can be suitably used in the above-mentioned method for synthesizing hydroiodic acid. [Means for solving the problem]

[0022] Such an object can be achieved by the present invention described below. A first aspect of the present invention provides a method for synthesizing hydroiodic acid, which comprises synthesizing hydroiodic acid from a raw material solution that is an aqueous solution containing iodide ions and a secondary raw material solution that contains hydrogen ions by a double displacement electrodialysis method, Between the positive electrode and the negative electrode, from the positive electrode side, a positive electrode chamber, a bipolar membrane or a cation exchange membrane, and a first auxiliary raw material chamber are successively provided, A plurality of membrane chamber sets, each consisting of four membranes and four chambers, are arranged in the following order: a cation exchange membrane, a product chamber, a first anion exchange membrane which is an anion exchange membrane, a first raw material chamber, a second anion exchange membrane which is an anion exchange membrane, a second raw material chamber, a third anion exchange membrane which is an anion exchange membrane, and a second auxiliary raw material chamber; The method is characterized by using an electrodialysis cell in which a cation exchange membrane and an anode chamber are subsequently arranged.

[0023] In the method for synthesizing hydroiodic acid according to the first aspect of the present invention, it is preferable that the auxiliary raw material liquid is circulated through the first and second auxiliary raw material chambers, dilute hydroiodic acid is circulated through the product chamber, the raw material liquid is circulated through the first raw material chamber, and a residual liquid of the raw material liquid circulated through the first raw material chamber in a previous batch or a liquid obtained by adding the residual liquid of the raw material liquid circulated through the first raw material chamber in a previous batch to the raw material liquid is circulated through the second raw material chamber.

[0024] A second aspect of the present invention provides a method for synthesizing hydroiodic acid, which comprises synthesizing hydroiodic acid from a raw material solution that is an aqueous solution containing iodide ions by bipolar membrane electrodialysis, and Between the positive electrode and the negative electrode, from the positive electrode side, a positive electrode chamber, a first bipolar membrane, and A plurality of chamber membrane sets, each consisting of three chambers and three membranes, are arranged in the following order: a product chamber, a first anion exchange membrane which is an anion exchange membrane, a first raw material chamber, a second anion exchange membrane which is an anion exchange membrane, a second raw material chamber, and a second bipolar membrane; The method is characterized in that an electrodialysis cell in which a negative electrode chamber is disposed is used.

[0025] In the method for synthesizing hydroiodic acid according to the second aspect of the present invention, it is preferable that dilute hydroiodic acid is passed through the product chamber in a circulating manner, the raw material liquid is passed through the first raw material chamber in a circulating manner, and a residual liquid of the raw material liquid passed through the first raw material chamber in a previous batch in a circulating manner or a liquid obtained by adding the raw material liquid to the residual liquid of the raw material liquid passed through the first raw material chamber in a circulating manner in a previous batch is passed through the second raw material chamber in a circulating manner.

[0026] In the method for synthesizing hydroiodic acid of the present invention, it is preferable that the raw material solution is prepared to have a pH of 4 or higher, and that the raw material solution is maintained at a pH of 4 or higher during the synthesis of hydroiodic acid.

[0027] In the method for synthesizing hydroiodic acid of the present invention, it is preferable that the first anion exchange membrane and the second anion exchange membrane are monovalent anion permselective membranes having monovalent anion selectivity.

[0028] In the method for synthesizing hydroiodic acid of the present invention, it is preferable to use, as the raw material liquid, any one of an iodine-absorbed liquid obtained by a blowing-out method, an iodine-released liquid obtained by an ion-exchange resin method, an iodine-concentrated liquid obtained by an electrodialysis method, an industrial waste liquid containing iodide ions, and an aqueous solution of iodide ions and sulfate ions mixed in a molar ratio of iodide ions to sulfate ions of 1:1 to 3:1.

[0029] The electrodialysis cell of the first aspect of the present invention comprises: To synthesize hydroiodic acid from a raw material solution that is an aqueous solution containing iodide ions, In the electrodialysis cell used for 、 Between the positive electrode and the negative electrode, from the positive electrode side, a positive electrode chamber, a bipolar membrane or a cation exchange membrane, and a first auxiliary raw material chamber are successively provided, A plurality of membrane chamber sets, each consisting of four membranes and four chambers, are arranged in the following order: a cation exchange membrane, a product chamber, a first anion exchange membrane which is an anion exchange membrane, a first raw material chamber, a second anion exchange membrane which is an anion exchange membrane, a second raw material chamber, a third anion exchange membrane which is an anion exchange membrane, and a second auxiliary raw material chamber; Next, the cation exchange membrane and the negative electrode chamber were placed. It is characterized by:

[0030] The electrodialysis cell of the second aspect of the present invention comprises: To synthesize hydroiodic acid from a raw material solution that is an aqueous solution containing iodide ions, In the electrodialysis cell used for 、 Between the positive electrode and the negative electrode, from the positive electrode side, a positive electrode chamber, a first bipolar membrane, and A plurality of chamber membrane sets, each consisting of three chambers and three membranes, are arranged in the following order: a product chamber, a first anion exchange membrane which is an anion exchange membrane, a first raw material chamber, a second anion exchange membrane which is an anion exchange membrane, a second raw material chamber, and a second bipolar membrane; Next, the cation exchange membrane and the negative electrode chamber were placed. It is characterized by: [Effects of the Invention]

[0031] According to the present invention, there is provided a method for synthesizing hydroiodic acid, which can further improve the yield and reduce the amount of waste liquid generated, the amount of sulfate ions transferred to the product chamber liquid, and the amount of iodide ions transferred to the electrode chamber, and there is also provided an electrodialysis cell that can be suitably used in the above-mentioned method for synthesizing hydroiodic acid. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of an electrodialysis cell used in the method for synthesizing hydroiodic acid according to the first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an example of the configuration of an electrodialysis cell used in the method for synthesizing hydroiodic acid according to the second embodiment of the present invention. [Figure 3] FIG. 3 is a graph showing the change in sulfate ion concentration over time in the product chamber in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0033] Preferred embodiments of the present invention will be described in detail below. [1] First embodiment First, a method for synthesizing hydroiodic acid according to the first embodiment of the present invention will be described.

[0034] FIG. 1 is a schematic diagram showing an example of the configuration of an electrodialysis cell used in the method for synthesizing hydroiodic acid according to the first embodiment of the present invention.

[0035] The method for synthesizing hydroiodic acid according to this embodiment is a method for synthesizing hydroiodic acid from a raw material liquid that is an aqueous solution containing iodide ions and a secondary raw material liquid that is an aqueous solution containing hydrogen ions by double displacement electrodialysis. In the electrodialysis, an electrodialysis cell 1 shown in FIG. 1 is used.

[0036] In the electrodialysis cell 1 shown in FIG. 1, a plurality of membrane chamber sets, each consisting of four membranes and four chambers, are arranged between the positive electrode 2 and the negative electrode 3 in the following order from the positive electrode side: a positive electrode chamber 10, a bipolar membrane or cation exchange membrane 4c, a first auxiliary raw material chamber 11, a cation exchange membrane 5c, a product chamber 12, a first anion exchange membrane 6s which is an anion exchange membrane, a first raw material chamber 13, a second anion exchange membrane 7s which is an anion exchange membrane, a second raw material chamber 14, a third anion exchange membrane 8a which is an anion exchange membrane, and a second auxiliary raw material chamber 15, followed by a cation exchange membrane 9c and a negative electrode chamber 16.

[0037] In the method for synthesizing hydroiodic acid in this embodiment, for example, an acid aqueous solution is circulated as auxiliary raw material chamber liquids 24, 25 through the first and second auxiliary raw material chambers 11, 15, respectively; dilute hydroiodic acid is circulated as product chamber liquid 21 through the product chamber 12; a raw material liquid is circulated as first raw material chamber liquid 22 through the first raw material chamber 13; and a liquid obtained by adding a raw material liquid to the residual liquid of the raw material liquid circulated through the first raw material chamber 13 in the previous batch or the residual liquid of the raw material liquid circulated through the first raw material chamber 13 in the previous batch is circulated through the second raw material chamber 14, as second raw material chamber liquid 23.

[0038] This makes it possible to provide a method for synthesizing hydroiodic acid that can further improve the yield and reduce the amount of waste liquid generated, the amount of sulfate ions transferred to the product chamber liquid, and the amount of iodide ions transferred to the electrode chamber.

[0039] The acid used in the auxiliary raw material solution is preferably a strong acid with a high degree of ionization and does not contain metal ions or ammonium ions. Furthermore, any acid may be used as long as it does not react with substances in the raw material solution, such as iodide ions. Examples include sulfuric acid and hydrochloric acid. The sulfate ions that migrate to the product chamber 12 migrate from the raw material chamber, and there is no problem if the auxiliary raw material solution contains sulfate ions. However, if a monovalent anion permselective membrane is used for the third anion exchange membrane, hydrochloric acid is preferred, but sulfuric acid is not preferred. Furthermore, if the raw material solution contains barium ions, which are acidic and form insoluble matters with sulfate ions, hydrochloric acid is preferred, but sulfuric acid is not preferred.

[0040] In the following description, the case where the cation exchange membrane 4c is used as the membrane separating the cathode chamber 10 and the first auxiliary raw material chamber 11 in the electrodialysis cell 1 will be mainly described.

[0041] In the electrodialysis cells used in the conventional multiple displacement electrodialysis method (four-compartment method), if the monovalent anion permselective membrane could completely suppress the migration of sulfate ions, which are divalent anions, there should be no migration of sulfate ions from the raw material chamber to the product chamber. However, the use of a monovalent anion permselective membrane alone is not sufficient to suppress the migration of sulfate ions, and some sulfate ions do migrate from the raw material chamber to the product chamber.

[0042] In other words, if the monovalent anion permselective membrane could completely suppress the movement of sulfate ions in a conventional four-compartment electrodialysis cell, it would be possible to eliminate the auxiliary salt chamber and operate it with three compartments, but a three-compartment multiple displacement electrodialysis cell has not yet been put to practical use.

[0043] The primary reason why the monovalent anion permselective membrane cannot completely suppress the movement of sulfate ions is that in aqueous solutions with a pH of 4 or less, sulfate ions (SO4 2- ), but exists as a monovalent ion, hydrogen sulfate ion (HSO4 - ), the monovalent ion iodide ion (I -) cannot be completely separated from the absorbent. Unfortunately, the absorption liquid is strongly acidic with a pH of about 1, and in the four-compartment electrodialysis method, all compartments except the feed compartment are strongly acidic, so even if the feed solution is adjusted to neutral, it will become strongly acidic during operation. Therefore, it is difficult to maintain the pH of the feed compartment at 4 or higher. Furthermore, if the feed compartment is made neutral or basic, the current efficiency will decrease. To improve current efficiency, it is better for the feed compartment to be acidic. Whether to adjust and maintain the pH at 4 or higher should be determined based on economic considerations, etc.

[0044] However, there is still some merit in using a monovalent anion permselective membrane. Even at pH 4 or below, the movement of sulfate ions (hydrogen sulfate ions) is suppressed to some extent, so although not completely, using one will reduce the amount of sulfate ions that move.

[0045] The second reason is that when the concentration ratio of sulfate ions to iodide ions in the raw material compartment increases near the end of the dialysis run, the rate at which sulfate ions move from the raw material compartment to the product compartment increases. The second reason is solved by the present invention.

[0046] In the electrodialysis cell 1 shown in FIG. 1 , the raw material chamber is divided into two consecutive chambers by a second anion exchange membrane 7s, which is a selectively permeable anion membrane. These chambers are designated, in order from the side adjacent to the product chamber 12, as the first raw material chamber 13 and the second raw material chamber 14. When two raw material chambers are arranged consecutively, the first raw material chamber 13 adjacent to the product chamber 12 receives approximately the same amount of iodide ions as those transferred to the product chamber 12 from the second raw material chamber 14, which is located on the opposite side of the product chamber 12. Therefore, the sulfate ion:iodide ion concentration ratio remains almost constant. This allows the sulfate ion:iodide ion concentration ratio in the first raw material chamber 13 to be maintained substantially constant until the end of the dialysis operation. As a result, the increase in the amount of sulfate ions transferring from the first raw material chamber 13 to the product chamber 12 immediately before the end of dialysis can be suppressed.

[0047] At the end of dialysis, the sulfate ion:iodide ion concentration ratio increases in the second raw material chamber 14 due to an increase in sulfate ion concentration caused by the migration of sulfate ions from the second auxiliary raw material chamber 15 and a decrease in iodide ion concentration caused by the migration of iodide ions to the first raw material chamber 13.

[0048] Therefore, at the end of dialysis, the migration rate of sulfate ions from the second raw material chamber 14 to the first raw material chamber 13 increases. However, because a sufficient amount of iodide ions is still present in the first raw material chamber 13, the sulfate ion:iodide ion concentration ratio increases slightly, but the effect on the migration rate of sulfate ions is limited and negligible. Therefore, the migration rate of sulfate ions from the first raw material chamber 13 to the product chamber 12 hardly increases. In other words, the increase in the migration rate of sulfate ions from the second raw material chamber 14, which occurs due to the increase in the sulfate ion:iodide ion molar ratio at the end of dialysis, can be captured by the first raw material chamber.

[0049] In the configuration shown in Figure 1, by dividing the raw material chamber into two in this way, it is possible to eliminate the auxiliary salt chamber that was necessary in conventional four-chamber electrodialysis cells. This eliminates the need to prepare an auxiliary salt chamber solution. Furthermore, by using the residual liquid from the first raw material chamber 13 as the chamber solution to be supplied to the second raw material chamber 14, the only waste liquid after the dialysis operation is the residual liquid from the second raw material chamber 14, thereby reducing the overall amount of waste liquid.

[0050] In addition, the loss that occurs when iodide ions move to the sub-salt chamber in the conventional four-chamber method is eliminated, thereby improving the yield.

[0051] The movement of iodide ions through an anion exchange membrane occurs not only through electrical migration but also through diffusion. The rate of electrical migration is proportional to the transmembrane voltage and current density. The rate of diffusion migration is proportional to the concentration difference. Therefore, the total (apparent) migration rate, which is the sum of the electrical migration rate and the diffusion migration rate, is affected by the difference in ion concentration between two adjacent chambers.

[0052] In the conventional four-chamber method, the difference in iodide ion concentration between the product chamber and the raw material chamber becomes large toward the end of dialysis, so the rate at which iodide ions return from the product chamber to the raw material chamber due to diffusion increases, causing the overall (apparent) rate of movement to decrease and eventually stop. In other words, iodide ions always remain in the raw material chamber at the end of dialysis.

[0053] However, by using the electrodialysis cell 1 shown in FIG. 1, the iodide ion concentration in first raw material chamber 13 is kept substantially constant, and therefore the difference in iodide ion concentration between two adjacent chambers, i.e., between product chamber 12 and first raw material chamber 13, and between first raw material chamber 13 and second raw material chamber 14, is smaller than the difference in iodide ion concentration between the product chamber and raw material chamber in the conventional four-chamber method.

[0054] This makes it possible to suitably suppress the rate of movement due to diffusion returning from the product chamber 12 to the first ingredient chamber 13, and to maintain the apparent rate of movement at a state close to the initial rate.

[0055] Furthermore, the speed of movement due to diffusion returning from the first raw material chamber 13 to the second raw material chamber 14 can be suitably suppressed, and the apparent speed of movement can be increased.

[0056] As a result, the loss of iodide ions remaining in the second raw material chamber 14 at the end of dialysis can be reduced more effectively than the loss of iodide ions remaining in the raw material chambers in the conventional four-chamber method, thereby more effectively improving the yield.

[0057] In other words, by leaving a certain amount of iodide ions in the first raw material compartment, the yield in the second raw material compartment can be improved and the increase in sulfate ions from the second raw material compartment toward the end of dialysis can be compensated for. The iodide ions left in the first raw material compartment are separated and recovered from the second raw material compartment to the first raw material compartment in the next batch, so they are not lost.

[0058] In the electrodialysis cell 1 shown in FIG. 1, a first auxiliary raw material chamber 11 is disposed on the negative electrode side of the positive electrode chamber 10 via a cation exchange membrane 4c.

[0059] If iodide ions are present in a chamber adjacent to the positive electrode chamber via a cation exchange membrane, the iodide ions are electrically attracted toward the positive electrode chamber, resulting in the generation of iodide ions that pass through the cation exchange membrane. Therefore, in the first embodiment of the present invention, the chamber adjacent to the positive electrode chamber is designated as the first auxiliary raw material chamber 11, which is the chamber other than the positive electrode chamber that has the lowest iodide ion concentration.

[0060] In Patent Documents 2 and 3, an auxiliary salt chamber with a relatively low iodide ion concentration is provided, but it is considered more reasonable to provide an auxiliary raw material chamber with an even lower iodide ion concentration than the auxiliary salt chamber.

[0061] In the electrodialysis cell 1 shown in FIG. 1, a second auxiliary raw material chamber 15 is disposed on the positive electrode side of the negative electrode chamber 16 via a cation exchange membrane 9c.

[0062] This is because there are anions (specifically, sulfate ions) in the anode compartment liquid that migrate from the anode compartment through the cation exchange membrane to the adjacent compartment on the cathode side. When these anions get mixed in, the auxiliary raw material compartment is least affected.

[0063] Although some iodide ions leak from the product chamber 12 through the cation exchange membrane 5c into the second auxiliary raw material chambers 15 other than the first auxiliary raw material chamber 11 and the second auxiliary raw material chamber 15 installed next to the anode chamber 16, the iodide ions in the auxiliary raw material chamber liquid 25 migrate preferentially over sulfate ions from the second auxiliary raw material chamber 15 to the adjacent second raw material chamber 14 through the third anion exchange membrane 8a, and therefore almost no iodide ions remain. As a result, the iodide ion concentration in the first auxiliary raw material chamber 11 is always the lowest among the four chambers other than the anode chamber.

[0064] The electrodialysis cell shown in FIG. 1 does not have an auxiliary salt chamber, as in Patent Documents 2 and 3. This means that there is no residual liquid in the auxiliary salt chamber after dialysis to be disposed of as waste acid, reducing the amount of waste liquid generated. In the four-chamber method shown in Patent Documents 2 and 3, iodide ions travel from the product chamber to the cathode side via the auxiliary raw material chamber and reach the auxiliary salt chamber. In this embodiment, however, iodide ions are captured in the liquid in the second raw material chamber and concentrated in the first raw material chamber. Only a portion of the iodide ions is lost during the transfer process at the end of dialysis, thereby increasing the yield.

[0065] [1-1] About the electrodialysis cell A pair of electrodes is arranged on both sides of the electrodialysis cell 1, one of which is a positive electrode 2 (anode) and the other is a negative electrode 3 (cathode).

[0066] Examples of materials constituting the positive electrode 2 include platinum (Pt), carbon (C), nickel (Ni), and composite materials (e.g., alloys, plating, etc.) such as titanium (Ti) / platinum, ruthenium (Ru) / titanium, iridium (Ir) / titanium, and titanium / palladium (Pd).

[0067] Examples of materials that can be used to form the negative electrode 3 include iron (Fe), nickel, platinum, titanium / platinum, carbon, and chromium (Cr) steel as stainless steel.

[0068] The electrodialysis cell 1 is provided with a chamber frame serving as a frame body having a rectangular shape in plan view and a notched portion (not shown).

[0069] A positive electrode 2 and a negative electrode 3 are attached to the inside of both ends along the longitudinal direction of this chamber frame, and a positive electrode chamber (positive electrode chamber 10) is formed by a cation exchange membrane 4c arranged on the negative electrode side of the positive electrode 2 of this electrodialysis cell 1, and a negative electrode chamber (negative electrode chamber 16) is formed by a cation exchange membrane 9c arranged on the positive electrode side of the negative electrode 3.

[0070] Between the positive electrode chamber 10 and the negative electrode chamber 16, a cation exchange membrane 4c, a cation exchange membrane 5c, a first anion exchange membrane 6s, a second anion exchange membrane 7s, a third anion exchange membrane 8a, and a cation exchange membrane 9c are sequentially arranged from the positive electrode side to the negative electrode side. These ion exchange membranes partition the positive electrode chamber 10 toward the negative electrode chamber 16 into a first auxiliary raw material chamber 11, a product chamber 12, a first raw material chamber 13, a second raw material chamber 14, and a second auxiliary raw material chamber 15.

[0071] A set of four chambers and four membranes, consisting of the first auxiliary raw material chamber 11, cation exchange membrane 5c, product chamber 12, first anion exchange membrane 6s, first raw material chamber 13, second anion exchange membrane 7s, second raw material chamber 14, and third anion exchange membrane 8a, is repeatedly arranged in several to several hundred sets (n sets). The number of repetitions n is not particularly limited, but is preferably, for example, several to several hundred sets, more specifically, 4 to 1800 sets.

[0072] In the following description, the cation exchange membranes 4c, 5c, and 9c may be collectively referred to as "cation exchange membranes."

[0073] In the following description, the first anion exchange membrane 6s, the second anion exchange membrane 7s, and the third anion exchange membrane 8a may be collectively referred to as "anion exchange membranes."

[0074] In the following description, the positive electrode chamber 10, the first auxiliary raw material chamber 11, the product chamber 12, the first raw material chamber 13, the second raw material chamber 14, the second auxiliary raw material chamber 15, and the negative electrode chamber 16 may be collectively referred to as the "liquid chamber."

[0075] The inner surface of the chamber frame of each liquid chamber separated by each ion exchange membrane is provided with a liquid supply port and a liquid discharge port (not shown) that communicate with the interior of the chamber frame. Also, a spacer (not shown) is provided within the chamber frame to distribute the flow and make the thickness of the chamber frame uniform.

[0076] The cathode chamber 10, the first auxiliary raw material chamber 11, the product chamber 12, the first raw material chamber 13, the second raw material chamber 14, the second auxiliary raw material chamber 15, and the anode chamber 16 are individually circulated with chamber solutions prepared to predetermined concentrations and amounts according to their respective purposes.

[0077] Alternatively, an external tank (not shown) may be provided to supply these chamber liquids, and these chamber liquids may be circulated between the liquid chambers and the external tank.

[0078] (anion exchange membrane) As the anion exchange membrane, a membrane with enhanced anion selective permeability can be suitably used, such as a strongly acidic styrene-divinylbenzene homogeneous anion exchange membrane.

[0079] However, the raw material solution used contains sulfate ions (SO4 2- When the anion exchange membrane contains divalent anions such as ammonium nitrate, ...

[0080] By using monovalent anion permselective membranes for the first anion exchange membrane 6s and the second anion exchange membrane 7s of the electrodialysis cell 1, the migration of sulfate ions into the product chamber 12 can be reduced.

[0081] In addition, to fully utilize the monovalent ion selectivity and separate and remove sulfate ions, sulfate ions must be separated from hydrogen sulfate ions (HSO4 - ) and avoid the pH range below 4, where sulfate ions exist as divalent anions, sulfate ions (SO4 2- It is preferable to prepare the raw material solution in a pH range of 4 or higher where the dialysis solution exists as a dialysis solution, and maintain the pH range during the dialysis operation.

[0082] This makes it possible to suppress the migration of sulfate ions contained in the raw material liquid supplied to the first raw material chamber 13 to the product chamber 12, and to improve the selective permeability of iodide ions, thereby further improving the yield of hydroiodic acid.

[0083] When a monovalent acid such as dilute hydrochloric acid is used as the auxiliary raw material liquid, either an anion exchange membrane or a monovalent anion selective permeable membrane may be used as the third anion exchange membrane 8a separating the second raw material chamber 14 and the second auxiliary raw material chamber 15. When a polyvalent acid such as dilute sulfuric acid is used as the auxiliary raw material liquid, it is preferable to use an anion exchange membrane.

[0084] Examples of such monovalent anion permselective membranes include strongly acidic styrene-divinylbenzene homogeneous anion exchange membranes, and more specific examples include Selemion ASV-N membrane (manufactured by AGC Corporation) and Neocepta ASE membrane (manufactured by Astom Corporation).

[0085] Specific examples of anion exchange membranes that do not have monovalent anion selectivity include Selemion AMV-N membrane (manufactured by AGC Corporation) and Neocepta ACS membrane (manufactured by Astom Corporation).

[0086] [1-2] About the raw material liquid As the raw material liquid, which is an aqueous solution containing iodide ions, any of the following can be suitably used: an iodine-absorbed solution obtained by the blowing-out method, an iodine-released solution obtained by the ion exchange resin method, an iodine-concentrated solution obtained by the electrodialysis method, an industrial waste liquid containing iodide ions, and an aqueous solution of iodide ions and sulfate ions mixed in a molar ratio of iodide ions to sulfate ions of 1:1 to 3:1.

[0087] The electrodialysis cell used in the first embodiment of the present invention is an electrodialysis cell having a structure in which cations in the raw material chamber do not move to the product chamber, as shown in JP 2018-94525 A, and therefore can also be used in a method of adding aluminum ions or the like to a raw material liquid to remove fluorine from the raw material liquid.

[0088] In the electrodialysis cell 1 shown in Figure 1, the first raw material chamber 13 and the second raw material chamber 14 are configured adjacent to each other in the same membrane chamber set, but this is not limited to this. When viewing the multiple membrane chamber sets that make up the electrodialysis cell as a whole, it is sufficient that the first raw material chamber and the second raw material chamber are configured adjacent to each other. For example, the first raw material chamber in the mth membrane chamber set (m is an integer greater than or equal to 1 and less than or equal to (n-1)) and the second raw material chamber in the (m+1)th membrane chamber set may be configured adjacent to each other.

[0089] [2] Second embodiment Next, a method for synthesizing hydroiodic acid according to the second embodiment of the present invention will be described.

[0090] FIG. 2 is a schematic diagram showing an example of the configuration of an electrodialysis cell used in the method for synthesizing hydroiodic acid according to the second embodiment of the present invention.

[0091] Hereinafter, the method for synthesizing hydroiodic acid according to the second embodiment of the present invention will be described with reference to this figure, but the differences from the above-described embodiment will be mainly described, and a description of similar points will be omitted.

[0092] The method for synthesizing hydroiodic acid according to this embodiment is a method for synthesizing hydroiodic acid from a raw material solution that is an aqueous solution containing iodide ions by bipolar membrane electrodialysis. In the electrodialysis, an electrodialysis cell 31A shown in FIG. 2 is used.

[0093] That is, the electrodialysis cell 31A shown in FIG. 2 has, between the positive electrode 32 and the negative electrode 33, a positive electrode chamber 40, a first bipolar membrane 34b, a product chamber 41, a first anion exchange membrane 35s which is an anion exchange membrane, a first raw material chamber 42, a second anion exchange membrane 36s which is an anion exchange membrane, a second raw material chamber 43, and a second bipolar membrane 37b′, each of which has three chambers and three membranes, arranged in this order from the positive electrode side, followed by a negative electrode chamber 44.

[0094] In this electrodialysis cell 31A, when a direct current of 0.83 V or more, which is the theoretical splitting voltage of water, but less than the maximum operating voltage specified by the ion exchange membrane manufacturer is supplied between the positive electrode 32 (anode) and the negative electrode 33 (cathode), the water is split into hydrogen ions and hydroxide ions in the first bipolar membrane 34b, and the hydrogen ions are discharged into the product chamber 41 on the negative electrode side, and the hydroxide ions are discharged into the positive electrode chamber 40 on the positive electrode side.

[0095] The hydrogen ions discharged into the product chamber 41 combine with the iodide ions that have migrated from the first raw material chamber 42 to produce hydroiodic acid. This allows hydroiodic acid to be produced more efficiently.

[0096] For example, in Japanese Patent Application Laid-Open No. 2009-023847, an alkaline compartment containing no iodide ions is installed adjacent to the positive electrode compartment in a bipolar membrane electrodialysis cell. The bipolar membrane electrodialysis cell used in the present invention not only lacks an alkaline compartment, but also has high iodide ion concentrations in all compartments except the positive electrode compartment. Therefore, even if the compartment with the lowest iodide ion concentration (the second raw material compartment) is selected and installed adjacent to the positive electrode compartment, the migration of iodide ions to the positive electrode compartment cannot be sufficiently reduced.

[0097] In the present invention, a bipolar membrane is used as the ion exchange membrane forming the polar compartment, thereby suppressing the migration of iodide ions into the polar compartment.

[0098] In this embodiment, by using the first bipolar membrane 34b as the membrane that separates the positive electrode chamber 40, the migration of iodide ions into the positive electrode chamber 40 can be more effectively suppressed.

[0099] According to the method of the present embodiment as described above, in the bipolar membrane electrodialysis method, the yield of hydroiodic acid can be further improved, and the amount of sulfate ions transferred to the product chamber liquid and the amount of iodide ions transferred to the electrode chamber can be reduced.

[0100] In the method for synthesizing hydroiodic acid of this embodiment, for example, dilute hydroiodic acid is circulated as product chamber liquid 51 through product chamber 41, a raw material liquid is circulated as first raw material chamber liquid 52 through first raw material chamber 42, and a liquid obtained by adding a raw material liquid to the residual liquid of the raw material liquid circulated through first raw material chamber 42 in the previous batch or the residual liquid of the raw material liquid circulated through first raw material chamber 42 in the previous batch is circulated through second raw material chamber 43 as second raw material chamber liquid 53.

[0101] [2-1] About the electrodialysis cell (anion exchange membrane) As the anion exchange membrane, a membrane with enhanced selective permeability for anions can be suitably used.

[0102] However, the raw material solution used contains sulfate ions (SO4 2- When the anion exchange membrane contains divalent anions such as ammonium nitrate, ...

[0103] In addition, to fully utilize the monovalent anion selectivity and separate and remove sulfate ions, sulfate ions must be separated from hydrogen sulfate ions (HSO4 - ) and avoid the pH range below 4, where sulfate ions exist as divalent anions, sulfate ions (SO4 2- It is preferable to prepare the raw material solution in a pH range of 4 or higher, where the pH is present as a dialysis solution, and maintain this pH during dialysis operation. Unlike double displacement dialysis, it is easy to maintain the pH of the raw material compartment at 4 or higher. This is particularly easy in the second raw material compartment, as the pH rises during operation.

[0104] The second reason why sulfate ions reach the product chamber is the increase in sulfate ion migration rate through the monovalent anion permselective membrane when the sulfate ion:iodide ion ratio in the feed chamber increases. To address this issue, the second embodiment of the present invention provides a first and second feed chamber adjacent to each other and separated by a monovalent anion permselective membrane. The first feed chamber, located adjacent to the product chamber, simultaneously sends iodide ions to the product chamber and receives them from the second feed chamber, maintaining a high iodide ion concentration even at the end of dialysis. Therefore, the sulfate ion:iodide ion ratio remains almost constant. As the iodide ion concentration in the second feed chamber decreases toward the end of a dialysis run, the sulfate ion migration rate from the second feed chamber to the first feed chamber increases. However, since there is still a sufficient amount of iodide ion in the first feed chamber at this time, sulfate ion migration from the first feed chamber to the product chamber is still suppressed. As a result, sulfate ions that migrate from the second raw material compartment due to an increase in the sulfate:iodide ratio in the second raw material compartment are captured in the first raw material compartment and do not reach the product compartment.

[0105] The movement of iodide ions through an anion exchange membrane occurs not only through electrical migration but also through diffusion. The rate of electrical migration is proportional to the transmembrane voltage and current density. The rate of diffusion migration is proportional to the concentration difference. Therefore, the total (apparent) migration rate, which is the sum of the electrical migration rate and the diffusion migration rate, is affected by the difference in ion concentration between two adjacent chambers.

[0106] In the case of conventional bipolar membrane electrodialysis, the difference in iodide ion concentration between the product chamber and the raw material chamber becomes large toward the end of dialysis, so the migration rate of iodide ions returning from the product chamber to the raw material chamber due to diffusion increases, causing the overall (apparent) migration rate to decrease and eventually stop. In other words, iodide ions always remain in the raw material chamber at the end of dialysis.

[0107] However, by using the electrodialysis cell 1 shown in FIG. 1, the iodide ion concentration in first raw material chamber 13 is kept substantially constant, and therefore the difference in iodide ion concentration between two adjacent chambers, i.e., between product chamber 12 and first raw material chamber 13, and between first raw material chamber 13 and second raw material chamber 14, is smaller than the difference in iodide ion concentration between the product chamber and raw material chamber in the conventional four-chamber method.

[0108] This makes it possible to suitably suppress the rate of movement due to diffusion returning from the product chamber 12 to the first ingredient chamber 13, and to maintain the apparent rate of movement at a state close to the initial rate.

[0109] Furthermore, the speed of movement due to diffusion returning from the first raw material chamber 13 to the second raw material chamber 14 can be suitably suppressed, and the apparent speed of movement can be increased.

[0110] As a result, the loss of iodide ions remaining in the second raw material chamber 14 at the end of dialysis can be reduced more effectively than the loss of iodide ions remaining in the raw material chamber in the conventional bipolar membrane electrodialysis method, thereby more effectively improving the yield.

[0111] In other words, by leaving a certain amount of iodide ions in the first raw material compartment, the yield in the second raw material compartment can be improved and the increase in sulfate ions from the second raw material compartment toward the end of dialysis can be compensated for. The iodide ions left in the first raw material compartment are separated and recovered in the second raw material compartment and are therefore not lost.

[0112] (bipolar membrane) The second bipolar membrane 37b' is a laminate of a cation exchange membrane and an anion exchange membrane, with the cation exchange membrane on the negative electrode side and the anion exchange membrane on the positive electrode side. One side of the second bipolar membrane 37b' acts as a cation exchange membrane and the other side acts as an anion exchange membrane.

[0113] As such a second bipolar membrane 37b', for example, NeoSepta Bipolar (Astrom Corporation) or the like is used.

[0114] The electrodialysis cell 31A shown in FIG. 2 is arranged between the positive electrode 32 and the negative electrode 33, with a plurality of membrane chamber sets, each set consisting of three chambers and three membranes, including, from the positive electrode side, a positive electrode chamber 40, a first bipolar membrane 34b, a product chamber 41, a first anion exchange membrane 35s which is an anion exchange membrane, a first raw material chamber 42, a second anion exchange membrane 36s which is an anion exchange membrane, a second raw material chamber 43, and a second bipolar membrane 37b′, and then an anode chamber 44.

[0115] In this electrodialysis cell 31A, when a direct current of 0.83 V or more, which is the theoretical splitting voltage of water, but less than the maximum operating voltage specified by the ion exchange membrane manufacturer is supplied between the positive electrode 32 (anode) and the negative electrode 33 (cathode), the water is split into hydrogen ions and hydroxide ions in the first bipolar membrane 34b, and the hydrogen ions are discharged into the product chamber 41 on the negative electrode side, and the hydroxide ions are discharged into the positive electrode chamber 40 on the positive electrode side.

[0116] The hydrogen ions discharged into the product chamber 41 combine with the iodide ions that have migrated from the first raw material chamber 42 to produce hydroiodic acid. This allows hydroiodic acid to be produced more efficiently.

[0117] Furthermore, by using the first bipolar membrane 34b as the membrane that separates the positive electrode chamber 40, the migration of iodide ions into the positive electrode chamber 40 can be more effectively suppressed.

[0118] The electrodialysis cell used in the second embodiment of the present invention is an electrodialysis cell having a structure in which cations in the raw material chamber do not move to the product chamber, as shown in JP 2018-94525 A, and therefore can also be used in a method of adding aluminum ions or the like to the raw material liquid to remove fluorine from the raw material liquid.

[0119] According to the method of this embodiment as described above, in the bipolar membrane electrodialysis method, the yield of hydroiodic acid can be further improved, and the amount of waste liquid generated, the amount of sulfate ions transferred to the product chamber liquid, and the amount of iodide ions transferred to the electrode chamber can be reduced.

[0120] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these. For example, modifications such as changing conditions or adding other steps may be made within the scope of the spirit of the present invention.

[0121] Finally, the features of the present invention will be described. First, we focused on minor migration of iodide ions other than the electrical migration from the raw material compartment to the product compartment, which is the main cause of electrodialysis, and developed a method to suppress it. Specifically, iodide ions migrate from the product compartment to the raw material compartment due to diffusion, driven by the difference in iodide ion concentration between the raw material compartment and the product compartment. This problem was solved by configuring the raw material compartments as two adjacent compartments and maintaining a certain level of iodide ion concentration in the raw material compartment on the product side until the end of dialysis. Additionally, to minimize the migration of iodide ions to the positive electrode compartment, which occurs due to the electrical migration of iodide ions through the cation exchange membrane, we either positioned the auxiliary raw material compartment, which has the lowest iodide ion concentration, next to the positive electrode compartment, or replaced the cation exchange membrane with a bipolar membrane, which is the least permeable to iodide ions.

[0122] Second, we focused on the fact that the rate at which sulfate ions move from the raw material chamber to the product chamber increases toward the end of dialysis. This problem was resolved, and the auxiliary salt chamber, which was previously required in multiple-displacement dialysis, was eliminated, leading to improved yield and product quality. Specifically, the raw material chambers were arranged as two consecutive chambers, and the iodide ion concentration in the raw material chamber closest to the product chamber was kept at a certain level until the end of dialysis, eliminating the increase in the rate at which sulfate ions move. Furthermore, the raw material chamber farthest from the product chamber was designated as the destination for sulfate ions from the auxiliary raw material chamber, eliminating the auxiliary salt chamber.

[0123] Third, electrodialysis cells prior to the present invention were configured with alternating cation-exchange membranes and anion-exchange membranes, or with bipolar membranes, cation-exchange membranes, and anion-exchange membranes in that order, whereas the present invention uses a positive-negative-negative-negative arrangement or a bipolar-negative-negative arrangement.

[0124] Fourth, the raw material solution can be used for multiple purposes. Specifically, the raw material solution is used as a raw material in the first raw material compartment, and by maintaining the iodide ion concentration until the end of dialysis, it reduces the return from the product compartment and facilitates the acceptance from the second raw material compartment. It also suppresses the increase in the rate of sulfate ion migration to the product compartment at the end of the process. Next, in the second raw material compartment, it is used as a raw material solution and also serves as a recipient for sulfate ions from the auxiliary raw material compartment. [Example]

[0125] The present invention will be described in more detail below using examples. In the following Examples 1 and 2 and Comparative Example 1, an electrodialysis cell (manufactured by Asahi Kasei Corporation, G4 type: effective membrane area 2 dm 2 Electrodialysis was performed using an electrodialysis device containing a cation exchange membrane (Selemion CSO, manufactured by AGC Corporation), a monovalent anion permselective membrane (Selemion ASV-N, manufactured by AGC Corporation), and an anion exchange membrane (Selemion AMV-N, manufactured by AGC Corporation). Sodium iodide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), sodium hydrogen sulfate monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), anhydrous sodium sulfate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 75% by mass sulfuric acid (manufactured by Toshin Corporation), and distilled water were used to prepare the feed solutions for each chamber. Hydroiodic acid, which was manufactured in-house, was used to prepare the product chamber solution.

[0126] For the analysis, the sample was diluted with pure water and measured using an ion chromatograph (Metrohm 883 Professional with chemical suppressor and carbon dioxide gas suppressor). All operations are 4A constant current operation (2A / dm 2 ) was performed.

[0127] (Comparative Example 1) <Configuration of electrodialysis cell> The electrodialysis cell was arranged between the positive and negative electrodes, with four sets of four membranes and four chambers in the following order from the positive electrode side: a positive electrode chamber, a cation exchange membrane, an auxiliary salt chamber, a second anion exchange membrane which is an anion exchange membrane, an auxiliary raw material chamber, a first cation exchange membrane which is a cation exchange membrane, a product chamber, a first anion exchange membrane which is a monovalent anion selective permeable membrane, a first raw material chamber, a second cation exchange membrane which is a cation exchange membrane, and an auxiliary salt chamber, followed by a cation exchange membrane and a negative electrode chamber.

[0128] <Preparation of the stock solution> The following liquids were prepared for each chamber: Electrode chamber solution: 2000 mL of 5% sodium hydrogen sulfate aqueous solution Sub-salt chamber solution: 1000 mL of 1.7% by mass sodium hydrogen sulfate aqueous solution Raw material chamber liquid: 1500 mL of aqueous solution containing 1.0 mol of sodium iodide and 0.5 mol of sulfuric acid Auxiliary raw material compartment liquid: 1000 mL of aqueous solution containing 0.6 moles of sulfuric acid Product liquid: 1 mass% hydroiodic acid aqueous solution 1000mL

[0129] <Electrodialysis> 2000 mL of electrode chamber liquid was circulated through each of the electrode chambers (positive electrode chamber and negative electrode chamber), 1000 mL of secondary salt chamber liquid was circulated through the secondary salt chamber, raw material chamber liquid was circulated through the raw material chamber, secondary raw material chamber liquid was circulated through the secondary raw material chamber, and product chamber liquid was circulated through the product chamber at 0.2 L / min.

[0130] <Ion concentration analysis> The operation was carried out for 2.3 hours, and the discharged liquids from the raw material chamber, auxiliary salt chamber, and product chamber were collected. The iodide ion (I - ) and sulfate ions (SO4 2- ) concentrations were analyzed.

[0131] The iodide ion (I - ) and sulfate ions (SO4 2- The results of the ion amount and ion concentration of each of the above are shown in Tables 1 and 2, respectively.

[0132] FIG. 3 also shows the change in the ion concentration of sulfate ions in the product chamber over time, along with that in Example 1.

[0133] [Table 1]

[0134] [Table 2]

[0135] result Approximately 87% of the difference between the amount of iodide ions in the raw material compartment and the amount of iodide ions in the collected solution was transferred from the raw material compartment, of which 0.5% of the iodide ions in the raw material compartment were transferred to the auxiliary salt compartment.

[0136] Furthermore, as shown in Figure 3, the rate of increase in sulfate ion concentration in the product chamber, i.e., the rate of sulfate ion migration to the product chamber, increased toward the end of dialysis.

[0137] The polar compartment solution was colored due to free iodine. After dialysis, a reducing agent was added to the polar compartment solution and the iodide ion concentration was measured, which confirmed 100 mg / L and 180 mg of iodide ions.

[0138] Example 1 <Configuration of electrodialysis cell> The electrodialysis cell was arranged between the positive and negative electrodes, with four sets of four membranes and four chambers in the following order from the positive electrode side: a positive electrode chamber, a cation exchange membrane, a second raw material chamber, a third anion exchange membrane which is an anion exchange membrane, an auxiliary raw material chamber, a cation exchange membrane, a product chamber, a first anion exchange membrane which is a monovalent anion selectively permeable membrane, a first raw material chamber, a second anion exchange membrane which is also a monovalent anion selectively permeable membrane, and a second raw material chamber, followed by a cation exchange membrane and a negative electrode chamber.

[0139] <Preparation of the stock solution> The following liquids were prepared for each chamber: Electrode chamber solution: 2000 mL of 5% sodium hydrogen sulfate aqueous solution First raw material compartment liquid: 1500 mL of aqueous solution containing 1.0 mol of sodium iodide ion and 0.5 mol of sulfuric acid Second raw material chamber liquid: 1400 mL of an aqueous solution containing 0.825 moles of iodide ions, 0.825 moles of sodium ions, and 0.83 moles of sulfate ions (residual liquid from the first raw material chamber from the previous run) Auxiliary raw material compartment liquid: 1000 mL of aqueous solution containing 0.6 moles of sulfuric acid Product liquid: 1 mass% hydroiodic acid aqueous solution 1000mL

[0140] <Electrodialysis> The electrode chamber liquid was circulated through the electrode chambers (positive electrode chamber and negative electrode chamber) at a rate of 1.5 L / min, the first raw material chamber liquid was circulated through the first raw material chamber, the second raw material chamber liquid was circulated through the second raw material chamber, the auxiliary raw material chamber liquid was circulated through the auxiliary raw material chamber, and the product chamber liquid was circulated through the product chamber at a rate of 0.2 L / min.

[0141] <Ion concentration analysis> The operation was carried out for 2.5 hours, and the discharged liquids from the first raw material chamber, the second raw material chamber, and the product chamber were collected. The iodide ions (I - ) and sulfate ions (SO4 2- ) concentrations were analyzed.

[0142] The results are shown in Tables 3 and 4, respectively. FIG. 3 also shows the change over time in the ion concentration of sulfate ions in the product chamber, along with Comparative Example 1.

[0143] [Table 3]

[0144] [Table 4]

[0145] result From the difference between the amount of iodide ions charged into the first raw material chamber and the amount of iodide ions collected from the second raw material chamber, 93% of the iodide ions in the raw material solution were obtained. Furthermore, in Example 1, the iodide ions in the raw material solution were obtained in the product chamber liquid at a higher yield than in Comparative Example 1.

[0146] As is clear from Figure 3, the rate of increase in sulfate ion concentration in the product chamber, i.e., the rate of sulfate ion migration to the product chamber, increases toward the end of dialysis in Comparative Example 1, whereas it remains constant in Example 1. In Example 1, the increase in sulfate ion concentration was reduced by approximately 40% compared to Comparative Example 1.

[0147] However, the polar compartment solution was strongly colored by free iodine. After the dialysis, a reducing agent was added to the polar compartment solution and the iodide ion concentration was measured, which confirmed 4000 mg / L and 7200 mg of iodide ions.

[0148] Example 2 <Configuration of electrodialysis cell> The electrodialysis cell was arranged between the positive and negative electrodes, with four sets of four membranes and four chambers in the following order from the positive electrode side: a positive electrode chamber, a cation exchange membrane, and an auxiliary raw material chamber, followed by a cation exchange membrane, a product chamber, a first anion exchange membrane which is a monovalent anion selectively permeable membrane, a first raw material chamber, a second anion exchange membrane which is a monovalent anion selectively permeable membrane, a second raw material chamber, a third anion exchange membrane which is an anion exchange membrane, and an auxiliary raw material chamber, followed by a cation exchange membrane and an anode chamber.

[0149] <Preparation of the stock solution> The following liquids were prepared for each chamber: Electrode chamber solution: 2000 mL of 5% sodium hydrogen sulfate aqueous solution First raw material compartment liquid: 1500 mL of aqueous solution containing 1.0 mol of sodium iodide and 0.5 mol of sulfuric acid Second raw material chamber liquid: 1400 mL of an aqueous solution containing 0.77 mol of iodide ion, 1.0 mol of sodium ion, and 0.80 mol of sulfate ion (residual liquid from the first raw material chamber from the previous run) Auxiliary raw material compartment liquid: 1000 mL of aqueous solution containing 0.6 moles of sulfuric acid Product liquid: 1 mass% hydroiodic acid aqueous solution 1000mL

[0150] <Electrodialysis> The electrode chamber liquid was circulated through the electrode chambers (positive electrode chamber and negative electrode chamber) at a rate of 1.5 L / min, the first raw material chamber liquid was circulated through the first raw material chamber, the second raw material chamber liquid was circulated through the second raw material chamber, the auxiliary raw material chamber liquid was circulated through the auxiliary raw material chamber, and the product chamber liquid was circulated through the product chamber at a rate of 0.2 L / min.

[0151] <Ion concentration analysis> The operation was carried out for 3.5 hours, and the discharged liquids from the first raw material chamber, the second raw material chamber, and the product chamber were collected. The iodide ion (I - ) and sulfate ions (SO4 2- ) concentrations were analyzed. The results are shown in Tables 5 and 6, respectively.

[0152] [Table 5]

[0153] [Table 6]

[0154] result Based on the difference between the amount of iodide ions charged into the first raw material chamber and the amount of iodide ions collected from the second raw material chamber, 95.8% of the iodide ions in the raw material solution were obtained. Furthermore, compared to Example 1 and Comparative Example 1, the iodide ions in the raw material solution were obtained in a higher yield in the product chamber solution.

[0155] During dialysis, no coloring due to free iodine was observed in the electrode solution. After dialysis was completed, a reducing agent was added to the electrode solution and the iodide ion concentration was measured, but no iodide ions were detected above the detection limit of 10 mg / L.

[0156] That is, in Example 2, it was confirmed that the migration of iodide ions to the electrode chamber was effectively suppressed by using the liquid chamber adjacent to the electrode chamber as the auxiliary raw material chamber. Furthermore, since the loss due to the iodide ions migrating to the electrode chamber was suppressed, the yield was further improved compared to Example 1.

[0157] An electrodialysis cell was used in which four membrane chamber sets, each consisting of three chambers and three membranes, were arranged between the positive and negative electrodes in the following order from the positive electrode side: a positive electrode chamber, a bipolar membrane, a product chamber, a first anion exchange membrane which is an anion exchange membrane, a first raw material chamber, a second anion exchange membrane which is an anion exchange membrane, a second raw material chamber, and a bipolar membrane, followed by an anode chamber. Electrodialysis was performed in the same manner as in the above examples, except that dilute hydroiodic acid was circulated through the product chamber, the raw material liquid was circulated through the first raw material chamber, and the residual liquid from the raw material liquid circulated through the first raw material chamber in the previous batch was circulated through the second raw material chamber. As a result, excellent results similar to those described above were obtained. [Industrial Applicability]

[0158] The method for synthesizing hydroiodic acid of the present invention is a method for synthesizing hydroiodic acid by double displacement electrodialysis from a raw material solution that is an aqueous solution containing iodide ions and an auxiliary raw material solution that is an aqueous solution containing hydrogen ions. The method uses an electrodialysis cell in which, between a positive electrode and a negative electrode, a plurality of membrane chamber sets, each consisting of four membranes and four chambers, are arranged in the following order from the positive electrode side: a positive electrode chamber, a bipolar membrane or a cation exchange membrane, a first auxiliary raw material chamber, a cation exchange membrane, a product chamber, a first anion exchange membrane that is an anion exchange membrane, a first raw material chamber, a second anion exchange membrane that is an anion exchange membrane, a second raw material chamber, a third anion exchange membrane that is an anion exchange membrane, and a second auxiliary raw material chamber, followed by a cation exchange membrane and an anode chamber.

[0159] Another embodiment of the method for synthesizing hydroiodic acid of the present invention is a method for synthesizing hydroiodic acid from a raw material solution that is an aqueous solution containing iodide ions by bipolar membrane electrodialysis, in which an electrodialysis cell is used in which, between a positive electrode and a negative electrode, a plurality of chamber membrane sets, each consisting of three chambers and three membranes, are arranged in the following order from the positive electrode side: a positive electrode chamber, a first bipolar membrane, a product chamber, a first anion exchange membrane which is an anion exchange membrane, a first raw material chamber, a second anion exchange membrane which is an anion exchange membrane, a second raw material chamber, and a second bipolar membrane, followed by a negative electrode chamber.

[0160] According to the method for synthesizing hydroiodic acid of the present invention, the yield can be further improved, the amount of waste liquid generated can be reduced, and the amount of sulfate ions transferred to the product chamber liquid and the amount of iodide ions transferred to the electrode chamber can be reduced.

[0161] Therefore, the method for synthesizing hydroiodic acid of the present invention has industrial applicability. The hydroiodic acid synthesized by the present invention is an important industrial product, and is used, for example, in the production of iodine compounds, as a reducing agent, a pharmaceutical raw material, an etching agent, an analytical reagent, etc. [Explanation of symbols]

[0162] 1. Electrodialysis cell 2 Positive electrode 3 negative electrode 4c Cation exchange membrane 5c Cation exchange membrane 6s First anion exchange membrane 7s Second anion exchange membrane 8a Third anion exchange membrane 9c Cation exchange membrane 10 Positive electrode chamber 11 First auxiliary raw material room 12 Product room 13 First raw material room 14 Second raw material room 15 Second auxiliary raw material room 16 Anode chamber 21 Product room liquid 22 First raw material chamber liquid 23 Second raw material chamber liquid 24 Sub-raw material room liquid 25 Sub-raw material room liquid 26 Positive electrolyte 27 Negative electrolyte 31A Electrodialysis Cell 32 Positive electrode 33 Negative electrode 34b First bipolar membrane 35s First anion exchange membrane 36s Second Anion Exchange Membrane 37b' Second bipolar membrane 40 Positive electrode chamber 41 Product room 42 First raw material room 43 Second raw material room 44 Anode chamber 51 Product room liquid 52 First raw material chamber liquid 53 Second raw material chamber liquid 54 Positive electrolyte 55 Negative electrolyte

Claims

1. A method for synthesizing hydroiodic acid by double displacement electrodialysis from a raw material solution that is an aqueous solution containing iodide ions and a secondary raw material solution that contains hydrogen ions, comprising: Between the positive electrode and the negative electrode, a positive electrode chamber, a bipolar membrane or a cation exchange membrane, a first auxiliary raw material chamber, and the like are provided in this order from the positive electrode side. a plurality of membrane chamber sets, each consisting of four membranes and four chambers, are arranged in the following order: a cation exchange membrane, a product chamber, a first anion exchange membrane which is an anion exchange membrane, a first raw material chamber, a second anion exchange membrane which is an anion exchange membrane, a second raw material chamber, a third anion exchange membrane which is an anion exchange membrane, and a second auxiliary raw material chamber; Subsequently, an electrodialysis cell equipped with a cation exchange membrane and an anode chamber is used to synthesize hydroiodic acid.

2. 2. The method for synthesizing hydroiodic acid according to claim 1, wherein the auxiliary raw material liquid is circulated through the first and second auxiliary raw material chambers, dilute hydroiodic acid is circulated through the product chamber, the raw material liquid is circulated through the first raw material chamber, and a residual liquid of the raw material liquid circulated through the first raw material chamber in a previous batch or a liquid obtained by adding the residual liquid of the raw material liquid circulated through the first raw material chamber in a previous batch to the raw material liquid is circulated through the second raw material chamber.

3. A method for synthesizing hydroiodic acid by bipolar membrane electrodialysis from a raw material solution that is an aqueous solution containing iodide ions, comprising: Between the positive electrode and the negative electrode, from the positive electrode side, a positive electrode chamber, a first bipolar membrane, and A plurality of chamber membrane sets, each consisting of three chambers and three membranes, are arranged in the following order: a product chamber, a first anion exchange membrane which is an anion exchange membrane, a first raw material chamber, a second anion exchange membrane which is an anion exchange membrane, a second raw material chamber, and a second bipolar membrane; A method for synthesizing hydroiodic acid, characterized by using an electrodialysis cell equipped with a negative electrode chamber.

4. 4. The method for synthesizing hydroiodic acid according to claim 3, wherein dilute hydroiodic acid is passed through the product chamber in a circulating manner, the raw material liquid is passed through the first raw material chamber in a circulating manner, and a residual liquid of the raw material liquid passed through the first raw material chamber in a previous batch in a circulating manner or a liquid obtained by adding the raw material liquid to the residual liquid of the raw material liquid passed through the first raw material chamber in a circulating manner in a previous batch is passed through the second raw material chamber in a circulating manner.

5. 5. The method for synthesizing hydroiodic acid according to claim 1, wherein the raw material solution is adjusted to have a pH of 4 or higher, and the raw material solution is maintained at a pH of 4 or higher during the synthesis of hydroiodic acid.

6. 6. The method for synthesizing hydroiodic acid according to claim 1, wherein the first anion exchange membrane and the second anion exchange membrane are monovalent anion-selective permeable membranes having monovalent anion selectivity.

7. 7. The method for synthesizing hydriodic acid according to claim 1, wherein the raw material liquid is any one of an iodine-absorbed solution obtained by a blowing-out method, an iodine-desorbed solution obtained by an ion-exchange resin method, an iodine-concentrated solution obtained by electrodialysis, an industrial waste liquid containing iodide ions, and an aqueous solution of iodide ions and sulfate ions mixed in a molar ratio of iodide ions to sulfate ions of 1:1 to 3:

1.

8. An electrodialysis cell used to synthesize hydroiodic acid from a raw material solution that is an aqueous solution containing iodide ions, comprising: Between the positive electrode and the negative electrode, a positive electrode chamber, a bipolar membrane or a cation exchange membrane, a first auxiliary raw material chamber, and the like are provided in this order from the positive electrode side. a plurality of membrane chamber sets, each consisting of four membranes and four chambers, are arranged in the following order: a cation exchange membrane, a product chamber, a first anion exchange membrane which is an anion exchange membrane, a first raw material chamber, a second anion exchange membrane which is an anion exchange membrane, a second raw material chamber, a third anion exchange membrane which is an anion exchange membrane, and a second auxiliary raw material chamber; An electrodialysis cell characterized in that a cation exchange membrane and a negative electrode chamber are arranged successively.

9. An electrodialysis cell used to synthesize hydroiodic acid from a raw material solution that is an aqueous solution containing iodide ions, comprising: Between the positive electrode and the negative electrode, from the positive electrode side, a positive electrode chamber, a first bipolar membrane, and A plurality of chamber membrane sets, each consisting of three chambers and three membranes, are arranged in the following order: a product chamber, a first anion exchange membrane which is an anion exchange membrane, a first raw material chamber, a second anion exchange membrane which is an anion exchange membrane, a second raw material chamber, and a second bipolar membrane; An electrodialysis cell characterized in that a cation exchange membrane and a negative electrode chamber are arranged successively.

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