JP2023012960A - Method for synthesizing hydroiodic acid and electrodialysis tank - Google Patents

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

The present invention relates to a method for synthesizing hydroiodic acid by electrodialysis and an electrodialysis cell.

As a method for producing hydroiodic acid, after suspending or dissolving iodine in water or hydroiodic acid, iodine is reduced using phosphorus or hypophosphorous acid, etc., and from the reaction solution obtained after the reaction A method of distilling hydroiodic acid by distillation is known (for example, Patent Document 1).

Although this method is industrially excellent, it requires high-purity iodine as raw materials and a relatively expensive reducing agent, and generates a large amount of phosphoric acid as a waste liquid. In addition, it is economically disadvantageous because the cost of disposing of the mixed solution of phosphoric acid, phosphorous acid, hypophosphorous acid, hydroiodic acid, etc., generated as a still residue after distillation is expensive.

Patent Documents 2 and 3 disclose a method of directly producing hydroiodic acid from an iodine-absorbing liquid, which is an intermediate in the production of iodine from brackish water accompanied by natural gas by the blowing-out method, by double displacement electrodialysis. It is written.

In Patent Documents 2 and 3, from the positive electrode side to the negative electrode side, a positive electrode chamber, a first cation exchange membrane that is a cation exchange membrane, a first sub-salt chamber, and then an anion exchange membrane. 1 anion exchange membrane, auxiliary raw material chamber, second cation exchange membrane that is a cation exchange membrane, product chamber, second anion exchange membrane that is a monovalent anion permselective membrane, raw material chamber, cation A plurality of sets of membrane chambers each having 4 membranes and 4 chambers are arranged in this order of the third cation exchange membrane, which is an exchange membrane, and the second sub-salt chamber, followed by the cation exchange membrane and the negative electrode chamber in this order. An electrodialysis method using an arrayed electrodialysis bath (four-chamber method) is disclosed.

Compared to the method of Patent Document 1, this method can omit several oxidation-reduction reactions by using an intermediate in the production of iodine instead of highly purified iodine as the main raw material, resulting in a small amount of waste such as phosphoric acid. It is excellent from the viewpoint of economy and environmental protection. However, there are still some points to be improved.

First, an iodine-absorbing solution with a high sulfate ion concentration (specifically, the iodine-absorbing solution contains sulfate ions that are about half the amount of iodide ions) is used as the raw material solution. Therefore, the product liquid obtained by this method contains a small amount of sulfate ions in the raw material liquid.

Especially at the end of electrodialysis, when the concentration of iodide ions in the raw material solution decreases, the transfer rate of sulfate ions from the raw material chamber to the product chamber increases, so the yield of iodide ions in the raw material solution is increased. If this is attempted, the amount of sulfate ions mixed into the product liquid (crude hydroiodic acid aqueous solution) increases.

If sulfate ions are present in the crude hydroiodic acid aqueous solution, the sulfate ions will oxidize the iodide ions and produce free iodine when heated in the distillation step, which is the subsequent refining step. Barium must be added to remove sulfate ions as a barium sulfate precipitate.

The cost of the barium carbonate used at this time, the cost of disposal of the generated barium sulfate precipitate, and the loss of hydroiodic acid adhering to the barium sulfate precipitate put pressure on the production cost. It is economically advantageous to use a product solution containing as little sulfate ions as possible.

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 compartment and move to the auxiliary material compartment.

The iodide ions that have moved to the auxiliary raw material chamber further 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 sub-salt compartment remain as they are in the sub-salt compartment, the iodide ion concentration in the sub-salt compartment increases cumulatively during the electrodialysis operation.

The sub-salt chamber residual liquid at the end of dialysis is an aqueous solution mainly composed of sodium hydrogensulfate containing about 0.1 to 1% of iodide ions. Since the industrial value of sodium hydrogensulfate is not high, the sub-salt chamber residual liquid is disposed of as waste acid. The iodide ions contained in the sub-salt chamber residual liquid are lost. 0.5 to 10% of the iodide ions in the raw material solution are lost.

Thirdly, in electrodialysis, the movement of anions through an anion exchange membrane includes movement by electrical movement and movement by diffusion. Of these, the speed of electrical migration is determined by the current density, and the speed of migration by diffusion is proportional to the concentration difference on both sides of the membrane. At the start of electrodialysis, the concentration is higher in the raw material chamber than in the product chamber, so diffusive movement is 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 movement direction due to diffusion is from the product chamber to the raw material chamber. At the end of dialysis, the concentration difference between the product chamber and the raw material chamber increases, and the movement speed due to diffusion increases proportionally. The apparent (actual) speed of iodide ion migration, which is the sum of the electrical migration and the diffusional migration, significantly decreases at the end of dialysis.

Lowering the finished iodide ion concentration in the product room can avoid a decrease in the apparent transfer rate, but this is not an appropriate method because it increases the load in the subsequent concentration step. In other words, in order to increase the finished iodide ion concentration of the product liquid, it is necessary to leave iodide ions in the raw material chamber. Therefore, the four-chamber method cannot achieve both a high yield and a high concentration ratio. In addition, it is unavoidable that the apparent moving speed from the raw material chamber to the product chamber decreases in the final stage.

Fourthly, in the membrane chamber sets described in Patent Documents 2 and 3, etc., the electrode chamber and the chamber adjacent to the cation exchange membrane are sub-salt chambers. Since the sub salt compartment liquid contains about 0.1% of hydroiodic acid, part of the hydroiodic acid passes through the cation exchange membrane and reaches the positive electrode compartment. It may corrode the electrodes or be oxidized at the positive electrode to form free iodine, which may corrode peripheral equipment. In particular, when using electrodes made of stainless steel, titanium, or other materials that provide corrosion resistance by forming an oxide film on the surface, iodide ions may , the oxide film is reduced and disappears, so it is easily corroded.

As described above, in the methods described in Patent Documents 2 and 3, the iodine-absorbing liquid and the iodine-containing industrial waste liquid, which are iodine production intermediates, are used as iodine raw materials, and the amount of phosphorus compounds used is very small. It is an economically advantageous method compared with the method described in .

However, the yield is still unsatisfactory, and the amount of waste liquid generated, the amount of sulfate ions transferred to the product chamber liquid, the amount of iodide ions transferred to the electrode chamber, etc. cannot be sufficiently suppressed. not

As described above, the use of electrodialysis for synthesis of hydroiodic acid is considered rational, but there are still problems to be solved.

JP-A-8-59205 JP 2005-58896 A Japanese Patent Application Laid-Open No. 2008-272602

An object of the present invention is to 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. It is another object of the present invention to provide a method for synthesizing hydroiodic acid, and to provide an electrodialysis cell that can be suitably used for the method for synthesizing hydroiodic acid as described above.

Such objects are achieved by the present invention described below.
In the method for synthesizing hydroiodic acid according to the first aspect of the present invention, hydroiodic acid is produced from a raw material liquid, which is an aqueous solution containing iodide ions, and an auxiliary raw material liquid containing hydrogen ions by a double displacement electrodialysis method. A method for synthesizing hydroiodic acid, comprising:
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,
Cation exchange membrane, product chamber, first anion exchange membrane that is an anion exchange membrane, first raw material chamber, second anion exchange membrane that is an anion exchange membrane, second raw material chamber, anion exchange membrane A plurality of membrane chamber sets each including 4 membranes and 4 chambers are arranged in order of the third anion exchange membrane and the second auxiliary raw material chamber,
The method is characterized by using an electrodialysis tank in which a cation exchange membrane and a negative electrode chamber are subsequently arranged.

In the method for synthesizing hydroiodic acid according to the first aspect of the present invention, the sub-raw material liquid is circulated through the first and second sub-raw material chambers, and dilute hydroiodic acid is passed through the product chamber. is circulated through the first raw material chamber, the raw material liquid is circulated through the first raw material chamber, and the remaining liquid of the raw material liquid circulated through the first raw material chamber in the previous batch is passed through the second raw material chamber, or It is preferable to circulate through a liquid obtained by adding the raw material liquid to the residual liquid of the raw material liquid that has been circulated through the first raw material chamber in the previous batch.

The method for synthesizing hydroiodic acid according to the second aspect 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. There is
Between the positive electrode and the negative electrode, from the positive electrode side, following the positive electrode chamber and the first bipolar film,
The product chamber, the first anion exchange membrane that is an anion exchange membrane, the first raw material chamber, the second anion exchange membrane that is an anion exchange membrane, the second raw material chamber, and the second bipolar membrane in that order, arranging a plurality of chamber-membrane sets each consisting of 3 chambers and 3-membrane sets,
The method is characterized by using an electrodialyzer in which a negative electrode chamber is continuously arranged.

In the method for synthesizing hydroiodic acid according to the second aspect of the present invention, dilute hydroiodic acid is circulated through the product chamber, the raw material liquid is circulated through the first raw material chamber, and In the second raw material chamber, the residual liquid of the raw material liquid circulated through the first raw material chamber in the previous batch or the residual liquid of the raw material liquid circulated through the first raw material chamber in the previous batch is filled with the raw material. It is preferable to circulate the liquid to which the liquid has been added.

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

In the method for synthesizing hydroiodic acid of the present invention, a monovalent anion permselective membrane having monovalent anion selectivity is used for the first anion exchange membrane and the second anion exchange membrane, is preferred.

In the method for synthesizing hydroiodic acid of the present invention, the raw material solutions include an iodine-absorbing solution obtained by a blowing-out method, an iodine-desorbing solution obtained by an ion exchange resin method, and an iodine solution obtained by an electrodialysis method. It is preferable to use any one of a concentrated liquid, an industrial waste liquid containing iodide ions, and an iodide ion/sulfate ion mixed aqueous solution having a molar ratio of iodide ions:sulfate ions of 1:1 to 3:1.

An electrodialysis cell according to a first aspect of the present invention is an electrodialysis cell used for double displacement electrodialysis, in which an auxiliary raw material chamber is arranged on the negative electrode side of the positive electrode chamber, and an auxiliary raw material chamber is arranged on the positive electrode side of the negative electrode chamber. characterized by

The electrodialysis cell of the second aspect of the present invention is an electrodialysis cell used for electrodialysis, wherein the ion exchange membrane that partitions the negative electrode side of the positive electrode chamber and/or the ion exchange membrane that partitions the positive electrode side of the negative electrode chamber is a bipolar membrane. characterized by

According to the present invention, the yield 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. It is also possible to provide an electrodialysis cell that can be suitably used for the synthesis method of hydroiodic acid as described above.

FIG. 1 is a schematic diagram showing a configuration example of an electrodialysis tank used in the method for synthesizing hydroiodic acid according to the first embodiment of the present invention. FIG. 2 is a schematic diagram showing a configuration example of an electrodialysis tank used in the method for synthesizing hydroiodic acid according to the second embodiment of the present invention. FIG. 3 is a graph showing temporal changes in sulfate ion concentration in the product room in Example 1 and Comparative Example 1. FIG.

Preferred embodiments of the present invention are 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.

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

In the method for synthesizing hydroiodic acid according to the present embodiment, hydroiodic acid is synthesized from a raw material liquid, which is an aqueous solution containing iodide ions, and an auxiliary raw material liquid, which is an aqueous solution containing hydrogen ions, by double displacement electrodialysis. This is a method for synthesizing hydroiodic acid.
In electrodialysis, the electrodialysis tank 1 shown in FIG. 1 is used.

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

In the method for synthesizing hydroiodic acid of the present embodiment, for example, acid aqueous solutions are circulated through the first and second auxiliary raw material chambers 11 and 15 as the auxiliary raw material chamber liquids 24 and 25, respectively, to produce a product. Dilute hydroiodic acid is circulated through the chamber 12 as the product chamber liquid 21 , and the raw material liquid is circulated through the first raw material chamber 13 as the first raw material chamber liquid 22 . The second raw material chamber liquid 23 is 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. The liquid to which the raw material liquid is added is circulated.

As a result, the yield 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. can provide the law.

The acid used in the auxiliary raw material liquid is a strong acid with a high degree of ionization, and preferably does not contain metal ions or ammonium ions. Any substance 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 move into the product chamber 12 are those that move from the raw material chamber, and there is no problem even if the auxiliary raw material liquid contains sulfate ions. However, when a monovalent anion permselective membrane is used as the third anion exchange membrane, hydrochloric acid is preferable and sulfuric acid is not preferable. Moreover, when the raw material liquid contains barium ions that are acidic and form insoluble matter with sulfate ions, hydrochloric acid is preferable, and sulfuric acid is not preferable.

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

In the electrodialysis tank used in the conventional double displacement electrodialysis method (four-chamber method), if the monovalent anion permselective membrane can completely suppress the migration of sulfate ions, which are divalent anions. For example, there should be no movement of sulfate ions from the raw material room to the product room, but the use of a monovalent anion permselective membrane alone cannot sufficiently suppress the movement of sulfate ions. , the sulfate ions move from the raw material chamber to the product chamber.

In other words, in the conventional four-chamber electrodialysis tank, if the monovalent anion permselective membrane can completely suppress the movement of sulfate ions, the operation in three chambers without the sub-salt chamber is possible. was put into practical use, but the three-chamber double-displacement electrodialyzer has not yet been put into practical use.

The first reason why the monovalent anion selective permeable membrane cannot completely suppress the movement of sulfate ions is that in an aqueous solution with a pH of 4 or less, sulfuric acid does not exist as a divalent sulfate ion (SO ₄ ²⁻ ). However, since it exists as monovalent ions, hydrogen sulfate ions (HSO ₄ ⁻ ), it cannot be completely separated from monovalent ions such as iodide ions (I ⁻ ) in the monovalent anion permselective membrane. . Unfortunately, the absorption liquid is strongly acidic with a pH of about 1, and in the four-chamber electrodialysis method, all the chambers other than the raw material chamber are strongly acidic. It becomes strongly acidic inside. Therefore, it is difficult to keep the raw material chamber at pH 4 or higher. Further, when the raw material chamber is made neutral or basic, the current efficiency is lowered. In order to improve the current efficiency, the raw material chamber should be acidic. It is preferable to determine whether or not to prepare and maintain the pH at 4 or higher, taking into account economic efficiency and the like.

However, there is no meaning in using a monovalent anion permselective membrane. Since the migration of sulfate ions (hydrogen sulfate ions) is suppressed to some extent even at pH 4 or less, the amount of sulfate ions that move is reduced, although not completely.

The second reason is that when the concentration ratio of sulfate ions to iodide ions increases in the raw material chamber just before the end of the dialysis operation, the rate of movement of sulfate ions from the raw material chamber to the product chamber increases. . The second cause is resolved by the present invention.

In the electrodialysis tank 1 shown in FIG. 1, the raw material chamber is separated by the second anion exchange membrane 7s, which is an anion selective permeable membrane, into two continuous chambers, and the first raw material is placed in order from the side adjacent to the product chamber 12. A chamber 13 and a second raw material chamber 14 are provided. When two raw material chambers are arranged in succession, in the first raw material chamber 13 adjacent to the product chamber 12, almost the same amount of iodide ions as the iodide ions that have moved to the product chamber 12 are transferred to the opposite side of the product chamber 12. , the sulfate ion:iodide ion concentration ratio remains almost unchanged. As a result, the sulfate ion:iodide ion concentration ratio in the first raw material chamber 13 can be kept substantially constant until the end of the dialysis operation. As a result, it is possible to suppress an increase in the amount of sulfate ions that move from the first raw material chamber 13 to the product chamber 12 just before the end of dialysis.

At the end of dialysis, in the second raw material chamber 14, the concentration of sulfate ions increases due to the movement of sulfate ions from the second auxiliary raw material chamber 15, and the iodide ions move into the first raw material chamber 13. A decrease in the iodide ion concentration due to the increase in the sulfate ion:iodide ion concentration ratio.

Therefore, in the final stage of dialysis, the speed of movement of sulfate ions from the second raw material chamber 14 to the first raw material chamber 13 increases. However, since a sufficient amount of iodide ions still exist in the first raw material chamber 13, the sulfate ion:iodide ion concentration ratio slightly increases, but the effect on the migration speed of sulfate ions is limited. Yes, and negligible. Therefore, the moving speed of sulfate ions moving from the first raw material chamber 13 to the product chamber 12 hardly increases. In other words, the first raw material chamber can capture an increase in the speed of movement of sulfate ions from the second raw material chamber 14 due to an increase in the molar ratio of sulfate ions to iodide ions at the end of dialysis.

In the configuration shown in FIG. 1, by partitioning the raw material chamber into two in this way, it is possible to eliminate the sub-salt chamber that is required in the conventional electrodialysis cell using the four-chamber method. This eliminates the need to prepare a sub-salt compartment solution. In addition, by using the residual liquid in the first raw material chamber 13 as the chamber liquid to be supplied to the second raw material chamber 14, the waste liquid after the dialysis operation is only the residual liquid from the second raw material chamber 14. As a result, the amount of waste liquid can be reduced.

In addition, since the conventional four-chamber method eliminates the loss caused by the movement of iodide ions to the sub-salt chamber, the yield can be improved.

The movement of iodide ions through an anion exchange membrane is not only electrical movement but also movement by diffusion. The speed of electrical transfer is proportional to the transmembrane voltage and current density. The speed of migration by diffusion is proportional to the concentration difference. Therefore, the overall (apparent) migration speed, which is the sum of the electrical migration speed and the migration speed due to diffusion, is affected by the ion concentration difference between the two adjacent chambers.

In the case of the conventional four-chamber method, at the end of dialysis, the difference in iodide ion concentration between the product chamber and the raw material chamber increases. Appearance) movement speed decreases, and eventually stops moving. That is, iodide ions always remain in the raw material chamber at the end of dialysis.

However, by using the electrodialysis tank 1 shown in FIG. 1, the iodide ion concentration in the first raw material chamber 13 is almost constant. The iodide ion concentration difference and the iodide ion concentration difference between the first source chamber 13 and the second source chamber 14 are smaller than the iodide ion concentration difference between the product chamber and the source chamber in the conventional four-chamber method.

As a result, the movement speed due to diffusion returning from the product chamber 12 to the first raw material chamber 13 can be suitably suppressed, and the apparent movement speed can be maintained close to the initial state.

In addition, the movement speed due to diffusion returning from the first raw material chamber 13 to the second raw material chamber 14 can be suppressed appropriately, and the apparent movement speed can be increased.

As a result, the loss of iodide ions remaining in the second source chamber 14 at the end of dialysis can be reduced more effectively than the loss of iodide ions remaining in the source chamber in the conventional four-chamber method. That is, the yield can be improved more effectively.

In other words, by leaving a certain amount of iodide ions in the first raw material chamber, the yield in the second raw material chamber is improved to compensate for the increased amount of sulfate ions from the second raw material chamber which increases at the end of dialysis. can be done. The iodide ions left in the first raw material chamber are separated and recovered from the second raw material chamber to the first raw material chamber in the next batch, so that there is no loss.

In addition, in the electrodialysis tank 1 shown in FIG. 1, the first auxiliary material chamber 11 is arranged on the negative electrode side of the positive electrode chamber 10 with the cation exchange membrane 4c interposed therebetween.

If iodide ions are present in the chamber that is in contact with the positive electrode chamber through the cation exchange membrane, the iodide ions are electrically pulled toward the positive electrode chamber, generating iodide ions that move through the cation exchange membrane. . Therefore, in the first embodiment of the present invention, the chamber adjacent to the positive electrode chamber is the first sub-raw material chamber 11 having the lowest iodide ion concentration other than the electrode chamber.

In Patent Documents 2 and 3, etc., a sub-salt chamber with a relatively low iodide ion concentration is arranged, but it is rational to make the sub-raw material chamber with a lower iodide ion concentration than the sub-salt chamber. Conceivable.

In addition, in the electrodialysis tank 1 shown in FIG. 1, the second auxiliary material chamber 15 is arranged on the positive electrode side of the negative electrode chamber 16 with the cation exchange membrane 9c interposed therebetween.

This is because there are anions (specifically, sulfate ions) in the negative electrode chamber liquid that migrate from the negative electrode chamber through the cation exchange membrane to the adjacent chamber on the positive electrode side. This is because the sub-raw material chamber is least affected by the contamination of the anions.

In the second sub-raw material chambers 15 other than the second sub-raw material chamber 15 installed next to the first sub-raw material chamber 11 and the negative electrode chamber 16, the product chamber 12 is connected through the cation exchange membrane 5c to the second sub-raw material chambers 15. However, the iodide ions in the auxiliary raw material chamber liquid 25 are transferred from the second auxiliary raw material chamber 15 to the adjacent second raw material chamber 14 via the third anion exchange membrane 8a. preferentially over sulfate ions, so little remains. As a result, the iodide ion concentration in the first sub-material chamber 11 is always the lowest among the four chambers other than the pole chamber.

The electrodialysis tank shown in FIG. 1 does not have a sub-salt chamber as in Patent Documents 2 and 3. That is, since there is no residual liquid in the sub-salt chamber to be disposed of as waste acid after dialysis is completed, the amount of waste liquid generated can be reduced. In the four-chamber method disclosed in Patent Documents 2 and 3, the iodide ions that have reached the sub-salt chamber from the product chamber to the positive electrode side via the sub-raw material chamber are removed from the second raw material chamber liquid in the present embodiment. trapped inside and condensed in the first ingredient compartment. Only part of the transfer is lost at the end of dialysis, which increases the yield.

[1-1] Electrodialysis tank In the electrodialysis tank 1, a pair of electrodes are arranged on both sides, one of the pair of electrodes being a positive electrode 2 (anode) and the other being a negative electrode 3 (cathode). be.

Materials constituting the positive electrode 2 include, for example, platinum (Pt), carbon (C), nickel (Ni), titanium (Ti)/platinum, ruthenium (Ru)/titanium, iridium (Ir)/titanium, titanium/ Composite materials such as palladium (Pd) (for example, alloys, plating, etc.) can be used.

Examples of materials that constitute the negative electrode 3 include iron (Fe), nickel, platinum, titanium/platinum, carbon, and chromium (Cr) steel as stainless steel.

The electrodialysis tank 1 has a chamber frame as a rectangular frame in a plan view having a cutout portion (not shown).

The positive electrode 2 and the negative electrode 3 are attached to the inside of both ends along the longitudinal direction of the chamber frame, and the positive electrode chamber ( The positive electrode chamber 10) is configured, and the cation exchange membrane 9c disposed on the positive electrode side of the negative electrode 3 configures the negative electrode chamber (negative electrode chamber 16).

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, and a second anion exchange membrane are provided from the positive electrode side to the negative electrode side. A membrane 7s, a third anion exchange membrane 8a and a cation exchange membrane 9c are arranged in sequence. By these ion exchange membranes, from the positive electrode chamber 10 toward the negative electrode chamber 16, the first sub-raw material chamber 11, the product chamber 12, the first raw material chamber 13, the second raw material chamber 14, and the second auxiliary raw material chamber are formed. It is divided into 15.

Then, the first auxiliary raw material chamber 11, the cation exchange membrane 5c, the product chamber 12, the first anion exchange membrane 6s, the first raw material chamber 13, the second anion exchange membrane 7s, the second raw material chamber 14 and Several sets to several hundreds of sets (n sets) are repeatedly arranged with four membranes in four chambers of the third anion exchange membrane 8a as one set. The number of repetitions n is not particularly limited.

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

Further, 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 membrane".

Further, 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 are collectively referred to. It may be described as a "liquid chamber".

A liquid supply port and a liquid discharge port (not shown) communicating with the inside of the chamber frame are provided on the inner surface of the chamber frame in each liquid chamber partitioned by each ion exchange membrane. Further, a spacer (not shown) is provided in the chamber frame and has a flow distributing function to make the thickness of the chamber frame uniform.

The positive electrode chamber 10, the first sub-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 are respectively filled with liquids according to the purpose. are prepared to have a predetermined concentration and a predetermined liquid volume, and are individually passed through circulation.

Further, an external tank (not shown) for supplying these chamber liquids may be provided, and these chamber liquids may be circulated between the liquid chamber and the external tank.

(anion exchange membrane)
As the anion exchange membrane, a membrane with enhanced anion selective permeability can be suitably used. As such an anion selective permeation membrane, for example, a strongly acidic styrene-divinylbenzene-based homogeneous anion exchange membrane or the like is used.

However, if the raw material liquid to be used contains divalent anions such as sulfate ions (SO ₄ ^2- ), use a monovalent anion permselective membrane with monovalent anion selectivity as the anion exchange membrane. preferably.

By using a monovalent anion permselective membrane for the first anion exchange membrane 6s and the second anion exchange membrane 7s of the electrodialysis tank 1, the transfer of sulfate ions to the product chamber 12 can be reduced. .

In order to fully exhibit monovalent ion selectivity and separate and remove sulfate ions, a region of pH 4 or less where sulfate ions exist as monovalent anion hydrogen sulfate ions (HSO ₄ ⁻ ) should be avoided. It is preferable to prepare the raw material solution in a pH range of 4 or higher where sulfate ions are present as sulfate ions (SO ₄ ²⁻ ), which are divalent anions, and maintain the pH during the dialysis operation.

As a result, the sulfate ions contained in the raw material liquid supplied to the first raw material chamber 13 can be suppressed from moving to the product chamber 12, and the selective permeability of iodide ions can be improved. . As a result, the yield of hydroiodic acid can be further improved.

The third anion exchange membrane 8a that separates the second raw material chamber 14 and the second auxiliary raw material chamber 15 may be an anion exchange membrane, one Any of the anion-selective membranes may be used. 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.

As such a monovalent anion permselective membrane, for example, a strongly acidic styrene-divinylbenzene-based homogeneous anion exchange membrane or the like is used. ), Neosepta ASE membrane (manufactured by Astom Co., Ltd.), and the like.

Further, specific examples of anion exchange membranes having no monovalent anion selectivity include Selemion AMV-N membrane (manufactured by AGC Corporation) and Neosepta ACS membrane (manufactured by Astom Corporation). .

[1-2] Raw material liquid The raw material liquid, which is an aqueous solution containing iodide ions, includes an iodine-absorbing liquid obtained by a blowing-out method, an iodine-desorbing liquid obtained by an ion-exchange resin method, and an iodine-releasing liquid obtained by an electrodialysis method. Any of the obtained iodine concentrate, industrial waste liquid containing iodide ions, and mixed aqueous solution of iodide ions and sulfate ions having a molar ratio of iodide ions to sulfate ions of 1:1 to 3:1 is preferably used. be able to.

In addition, the electrodialysis tank used in the first embodiment of the present invention is an electrodialysis tank having a structure in which cations in the raw material chamber shown in Japanese Patent Application Laid-Open No. 2018-94525 do not move to the product chamber, so the raw material liquid It can also be used in a method of adding aluminum ions or the like to remove fluorine in the raw material liquid.

In the electrodialysis tank 1 shown in FIG. 1, the first raw material chamber 13 and the second raw material chamber 14 are arranged adjacent to each other in the same membrane chamber set. It is only necessary that the first source chamber and the second source chamber are adjacent to each other when viewed as a whole of the plurality of constituting membrane chamber sets. An integer of 1 or more and (n−1) or less} and the second source chamber in the (m+1)-th membrane chamber set may be adjacent to each other.

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

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

Hereinafter, the method for synthesizing hydroiodic acid of the present invention according to the second embodiment will be described with reference to this figure, but the description will focus on the differences from the above-described embodiment, and the same items will not be described. omitted.

The method for synthesizing hydroiodic acid according to the present embodiment is a method for synthesizing hydroiodic acid from a raw material liquid, which is an aqueous solution containing iodide ions, by bipolar membrane electrodialysis.
In electrodialysis, an electrodialysis tank 31A shown in FIG. 2 is used.

That is, the electrodialysis tank 31A shown in FIG. 2 is between the positive electrode 32 and the negative electrode 33, from the positive electrode side, the positive electrode chamber 40, the first bipolar membrane 34b, the product chamber 41, and the anion exchange membrane. The first anion exchange membrane 35s, the first raw material chamber 42, the second anion exchange membrane 36s which is an anion exchange membrane, the second raw material chamber 43, and the second bipolar membrane 37b', three chambers and three membranes A plurality of membrane chamber sets are arranged as one set, followed by the negative electrode chamber 44 .

In this electrodialysis tank 31A, between the positive electrode 32 (anode) and the negative electrode 33 (cathode), a DC current of 0.83 V or higher, which is the theoretical splitting voltage of water, and lower than the maximum working voltage specified by the ion exchange membrane manufacturer is supplied. Then, the water is decomposed into hydrogen ions and hydroxide ions in the first bipolar membrane 34b, 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. Dispensed.

The hydrogen ions discharged into the product chamber 41 combine with the iodide ions transferred from the first raw material chamber 42 to produce hydroiodic acid.
Thereby, hydroiodic acid can be produced more efficiently.

For example, in Japanese Unexamined Patent Application Publication No. 2009-023847, a bipolar membrane electrodialysis tank is provided with an alkaline chamber in which iodide ions do not exist, adjacent to a positive electrode chamber. The bipolar membrane electrodialysis cell used in the present invention not only has no alkaline chamber, but also has a high iodide ion concentration in all chambers except for the pole chamber. Therefore, even if the chamber with the lowest iodide ion concentration (second raw material chamber) is selected and installed next to the positive electrode chamber, the movement of iodide ions to the electrode chamber cannot be sufficiently reduced.

In the present invention, a bipolar membrane is used as the ion-exchange membrane forming the electrode compartment to suppress migration of iodide ions to the electrode compartment.

In the present embodiment, by using the first bipolar film 34b as the film that partitions the positive electrode chamber 40, movement of iodide ions to the positive electrode chamber 40 can be more effectively suppressed.

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 ion transferred to the product chamber liquid and the amount of iodine transferred to the electrode chamber can be reduced. It is possible to reduce the movement amount of compound ions.

In the method for synthesizing hydroiodic acid of the present embodiment, for example, dilute hydroiodic acid is circulated as the product chamber liquid 51 through the product chamber 41, and the first raw material is passed through the first raw material chamber 42. The raw material liquid is circulated as the chamber liquid 52, and in the second raw material chamber 43, the residual liquid of the raw material liquid circulated through the first raw material chamber 42 in the previous batch or the previous batch is stored as the second raw material chamber liquid 53. , a liquid obtained by adding the raw material liquid to the residual liquid of the raw material liquid that has been circulated through the first raw material chamber 42 is circulated through.

[2-1] Electrodialysis tank (anion exchange membrane)
As the anion exchange membrane, a membrane with enhanced anion selective permeability can be suitably used.

However, if the raw material liquid to be used contains divalent anions such as sulfate ions (SO ₄ ^2- ), use a monovalent anion permselective membrane with monovalent anion selectivity as the anion exchange membrane. preferably.

In addition, in order to sufficiently exhibit monovalent anion selectivity and separate and remove sulfate ions, a region of pH 4 or less where sulfate ions exist as monovalent anion hydrogen sulfate ions (HSO ₄ ⁻ ) should be avoided. , Sulfate ions are present as sulfate ions (SO ₄ ²⁻ ), which are divalent anions. Unlike the double displacement dialysis method, it is easy to maintain the pH of the raw material chamber at 4 or higher. Especially, the second raw material chamber is easy because the pH rises during operation.

In addition, when the ratio of sulfate ions to iodide ions in the raw material chamber increases, which is the second cause of sulfate ions reaching the product chamber, the rate of movement of sulfate ions increases through the monovalent anion selective permeable membrane. In the second embodiment of the present invention, this is dealt with by providing a first raw material chamber and a second raw material chamber which are separated by a monovalent anion selective permeable membrane and exist side by side. In the first raw material chamber located next to the product chamber, iodide ions are sent to the product chamber and received from the second raw material chamber at the same time, so a high iodide ion concentration is maintained even at the end of dialysis. Therefore, the sulfate ion:iodide ion ratio hardly changes. At the end of the dialysis run, when the iodide ions in the second raw material chamber decrease and the sulfate ion:iodide ion ratio in the second raw material chamber increases, the sulfate ions move from the second raw material chamber to the first raw material chamber. Although the velocity increases, there is still a sufficient amount of iodide ions in the first source chamber at that time to continue to inhibit the transfer of sulfate ions from the first source chamber to the product chamber. As a result, sulfate ions migrating from the second source chamber caused by an increase in the sulfate:iodide ion ratio in the second source chamber are captured in the first source chamber and do not reach the product chamber.

The movement of iodide ions through an anion exchange membrane is not only electrical movement but also movement by diffusion. The speed of electrical transfer is proportional to the transmembrane voltage and current density. The speed of migration by diffusion is proportional to the concentration difference. Therefore, the overall (apparent) migration speed, which is the sum of the electrical migration speed and the migration speed due to diffusion, is affected by the ion concentration difference between the two adjacent chambers.

In the case of conventional bipolar membrane electrodialysis, the difference in iodide ion concentration between the product chamber and the raw material chamber increases at the end of dialysis. Overall (apparent) movement speed decreases, and eventually stops moving. That is, at the end of dialysis, iodide ions always remain in the raw material chamber.

However, by using the electrodialysis tank 1 shown in FIG. 1, the iodide ion concentration in the first raw material chamber 13 is almost constant. The iodide ion concentration difference and the iodide ion concentration difference between the first source chamber 13 and the second source chamber 14 are smaller than the iodide ion concentration difference between the product chamber and the source chamber in the conventional four-chamber method.

As a result, the movement speed due to diffusion returning from the product chamber 12 to the first raw material chamber 13 can be suitably suppressed, and the apparent movement speed can be maintained close to the initial state.

In addition, the movement speed due to diffusion returning from the first raw material chamber 13 to the second raw material chamber 14 can be suppressed appropriately, and the apparent movement speed can be increased.

As a result, the loss of iodide ions remaining in the second source chamber 14 at the end of dialysis can be reduced more effectively than the loss of iodide ions remaining in the source chamber in the conventional bipolar membrane electrodialysis method. That is, the yield can be improved more effectively.

In other words, by leaving a certain amount of iodide ions in the first raw material chamber, the yield in the second raw material chamber is improved to compensate for the increased amount of sulfate ions from the second raw material chamber which increases at the end of dialysis. can be done. The iodide ions left in the first raw material chamber are separated and recovered in the second raw material chamber into the first raw material chamber, so that they are not lost.

(bipolar membrane)
The second bipolar membrane 37b' is a laminate of a cation exchange membrane and an anion exchange membrane, and is arranged so that the cation exchange membrane is on the negative electrode side and the anion exchange membrane is on the positive electrode side. In the second bipolar membrane 37b', one side acts as a cation exchange membrane and the other side acts as an anion exchange membrane.

As such a second bipolar film 37b', for example, Neosepta Bipolar (ASTOM Co., Ltd.) or the like is used.

The electrodialysis tank 31A shown in FIG. 2 includes, from the positive electrode side, a positive electrode chamber 40, a first bipolar membrane 34b, a product chamber 41, and a first anion exchange membrane between the positive electrode 32 and the negative electrode 33. An anion exchange membrane 35s, 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'. A plurality of membrane chamber sets are arranged, followed by the negative electrode chamber 44 .

In this electrodialysis tank 31A, between the positive electrode 32 (anode) and the negative electrode 33 (cathode), a DC current of 0.83 V or higher, which is the theoretical splitting voltage of water, and lower than the maximum working voltage specified by the ion exchange membrane manufacturer is supplied. Then, the water is decomposed into hydrogen ions and hydroxide ions in the first bipolar membrane 34b, 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. Dispensed.

The hydrogen ions discharged into the product chamber 41 combine with the iodide ions transferred from the first raw material chamber 42 to produce hydroiodic acid.
Thereby, hydroiodic acid can be produced more efficiently.

Further, by using the first bipolar film 34b as the film that partitions the positive electrode chamber 40, the movement of iodide ions to the positive electrode chamber 40 can be more effectively suppressed.

Note that the electrodialysis tank used in the second embodiment of the present invention is an electrodialysis tank having a structure in which the cations in the raw material chamber shown in Japanese Unexamined Patent Application Publication No. 2018-94525 do not move to the product chamber. It can also be used in a method of adding aluminum ions or the like to remove fluorine in the raw material liquid.

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 waste liquid generated, the amount of sulfate ions transferred to the product chamber liquid, and The migration of iodide ions to the electrode chamber can be reduced.

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 gist of the present invention.

Finally, the features of the present invention will be described.
First, we focused on the minor movement of iodide ions other than the electrical movement of iodide ions from the raw material room to the product room, which is the main part in electrodialysis, and developed a method to suppress it. Specifically, there is movement from the product chamber to the raw material chamber by diffusion driven by the concentration difference of iodide ions between the raw material chamber and the product chamber. This problem was solved by making two raw material chambers continuous and increasing the iodide ion concentration in the raw material chamber on the product chamber side by a certain level or higher until the end of dialysis. In addition, as a method of minimizing the movement of iodide ions to the positive electrode chamber caused by the electrical movement of iodide ions through the cation exchange membrane, the secondary raw material chamber with the lowest iodide ion concentration is placed next to the positive electrode chamber. Alternatively, the cation exchange membrane was replaced with a bipolar membrane through which iodide ions are most difficult to pass.

Secondly, we focused on the fact that the transfer rate of sulfate ions moving from the raw material chamber to the product chamber increases at the end of dialysis. This led to improvements in yield and product liquid quality. Specifically, two raw material chambers were arranged in succession, and the concentration of iodide ions in the raw material chamber on the product chamber side was maintained at a certain level or higher until the end of dialysis, thereby eliminating an increase in the moving speed of sulfate ions. In addition, the secondary salt chamber is eliminated by making the raw material chamber farther from the product chamber the transfer destination of the sulfate ions from the secondary raw material chamber.

Thirdly, electrodialyzers prior to the present invention had cation exchange membranes and anion exchange membranes alternately arranged, or bipolar membranes, cation exchange membranes, and anion exchange membranes arranged in this order. In the invention it is a yang, yin, yin, yin arrangement or a bipolar, yin, yin arrangement.

Fourthly, multi-purpose use of the raw material liquid can be mentioned. Specifically, the raw material solution is used as a raw material in the first raw material chamber, and by maintaining the iodide ion concentration until the end of dialysis, the return from the product chamber is reduced and the acceptance from the second raw material chamber is reduced. made easy. In addition, it suppressed the increase in the moving speed of sulfate ions to the product room in the final stage. Then, in the second raw material chamber, it is used not only as a raw material liquid, but also as a recipient of sulfate ions from the auxiliary raw material chamber.

EXAMPLES The present invention will be described in more detail below using examples.
Hereinafter, in Examples 1 and 2 and Comparative Example 1, electrodialysis was performed using an electrodialysis apparatus including an electrodialysis tank (manufactured by Asahi Kasei Corporation, model G4: effective membrane area: 2 dm ² ). The cation exchange membrane is Celemion CSO (manufactured by AGC Corporation), the monovalent anion permselective membrane is Celemion ASV-N (manufactured by AGC Corporation), and the anion exchange membrane is Celemion AMV-N (AGC Corporation). company) was used. For preparation of each chamber liquid, sodium iodide manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., sodium hydrogen sulfate monohydrate manufactured by the same company, anhydrous sodium sulfate manufactured by the same company, 75% by mass sulfuric acid manufactured by Toshin Co., Ltd., and distilled water. Using. Self-manufactured hydroiodic acid was used for charging the product room liquid.

For the analysis, the sample was diluted with pure water and measured using an ion chromatograph (with 883 professional chemical suppressor manufactured by Metrohm, with carbon dioxide gas suppressor).
All operations were performed at 4A constant current operation (2A/dm ² ).

(Comparative example 1)
<Configuration of electrodialysis tank>
The electrodialyzer is located between the positive electrode and the negative electrode, from the positive electrode side, to the positive electrode chamber, the cation exchange membrane, the sub-salt chamber, followed by the second anion exchange membrane, which is an anion exchange membrane, the auxiliary raw material chamber, and the cation exchange membrane. The first cation exchange membrane, the product chamber, the first anion exchange membrane that is a monovalent anion permselective membrane, the first raw material chamber, the second cation exchange membrane that is a cation exchange membrane, the secondary 4 sets of 4 membranes and 4 chambers were arranged in order of the salt chamber, followed by the cation exchange membrane and the negative electrode chamber.

<Preparation of charging solution>
A charge solution for each of the following chambers was prepared.
Electrode chamber liquid: 2000 mL of 5% by mass sodium hydrogen sulfate aqueous solution
Sub-salt chamber liquid: 1000 mL of 1.7% by mass sodium hydrogen sulfate aqueous solution
Raw material chamber liquid: 1500 mL of an aqueous solution containing 1.0 mol of sodium iodide and 0.5 mol of sulfuric acid
Auxiliary material chamber liquid: 1000 mL of an aqueous solution containing 0.6 mol of sulfuric acid
Product room liquid: 1000 mL of 1% by mass hydroiodic acid aqueous solution

<Electrodialysis>
2000 mL of the electrode chamber liquid is circulated through the electrode chambers (positive electrode chamber and negative electrode chamber), 1000 mL of the sub-salt chamber liquid is passed through the sub-salt chamber, the raw material chamber liquid is passed through the raw material chamber, and the auxiliary raw material chamber is fed with the auxiliary raw material chamber. The raw material chamber liquid and the product chamber liquid were circulated through the product chamber at a rate of 0.2 L/min.

<Ion concentration analysis>
The operation was carried out for 2.3 hours, and the effluents from the raw material chamber, sub-salt chamber, and product chamber were collected, and the iodide ion (I ⁻ ) and sulfate ion (SO ₄ ²⁻ ) concentrations in each collected liquid were measured. analyzed.

Tables 1 and 2 show the ion amounts and ion concentrations of iodide ions (I ⁻ ) and sulfate ions (SO ₄ ²⁻ ) for the feed solution and the capture solution in each chamber, respectively.

In addition, FIG.

Results Approximately 87% of the difference in the amount of iodide ions in the feed chamber charge and the capture liquid was transferred from the feed chamber. Among them, 0.5% of the iodide ions in the raw material compartment moved to the sub-salt compartment.

Further, as shown in FIG. 3, the rate of increase in sulfate ion concentration in the product chamber, ie, the rate of migration of sulfate ions to the product chamber, increased at the end of dialysis.

Coloration due to free iodine was observed in the polar fluid. After the dialysis was completed, a reducing agent was added to the extreme compartment fluid, and the iodide ion concentration was measured.

(Example 1)
<Configuration of electrodialysis tank>
The electrodialyzer is between the positive electrode and the negative electrode, from the positive electrode side, the positive electrode chamber, the cation exchange membrane, the second raw material chamber, followed by the third anion exchange membrane, which is an anion exchange membrane, the auxiliary raw material chamber, and the cation exchange. Membrane, product chamber, first anion exchange membrane that is a monovalent anion permselective membrane, first raw material chamber, second anion exchange membrane that is a monovalent anion permselective membrane, and second raw material chamber in this order. Four sets of four membranes and four chambers were arranged, followed by a cation exchange membrane and a negative electrode chamber.

<Preparation of charging solution>
A charge solution for each of the following chambers was prepared.
Electrode chamber liquid: 2000 mL of 5% by mass sodium hydrogen sulfate aqueous solution
First raw material chamber liquid: 1500 mL of an 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 mol of iodide ions, 0.825 mol of sodium ions, and 0.83 mol of sulfate ions (remaining liquid from the previous first raw material chamber)
Auxiliary material chamber liquid: 1000 mL of an aqueous solution containing 0.6 mol of sulfuric acid
Product room liquid: 1000 mL of 1% by mass hydroiodic acid aqueous solution

<Electrodialysis>
Electrode chambers (positive electrode chamber and negative electrode chamber) are each circulated with the electrode chamber liquid at 1.5 L/min, the first raw material chamber liquid is passed through the first raw material chamber, and the second raw material is passed through the second raw material chamber. The chamber liquid was circulated at a rate of 0.2 L/min to the sub-raw material chamber and the product chamber liquid to the product chamber.

<Ion concentration analysis>
The operation was carried out for 2.5 hours, the effluents from the first raw material chamber, the second raw material chamber and the product chamber were collected, and iodide ions (I ⁻ ) and sulfate ions (SO ₄ ²⁻ ) concentrations were analyzed.

The results are shown in Tables 3 and 4, respectively.
In addition, FIG.

Result 93% of the iodide ions in the raw material solution could be obtained from the difference between the charge in the first raw material chamber and the acquisition in the second raw material chamber. Moreover, in Example 1, compared with Comparative Example 1, iodide ions in the raw material liquid could be obtained in the product chamber liquid at a higher yield.

As is clear from FIG. 3, the rate of increase in the concentration of sulfate ions in the product chamber, that is, the rate of migration of sulfate ions to the product chamber, increases at the end of dialysis in Comparative Example 1, whereas in Example 1, Constant speed. In Example 1, compared with Comparative Example 1, the increase in sulfate ions could be reduced by about 40%.

However, the polar fluid was strongly colored by free iodine. After the dialysis was completed, a reducing agent was added to the extreme compartment fluid, and the iodide ion concentration was measured.

(Example 2)
<Configuration of electrodialysis tank>
The electrodialysis tank is placed between the positive electrode and the negative electrode, from the positive electrode side, the positive electrode chamber, the cation exchange membrane, the auxiliary material chamber, followed by the cation exchange membrane, the product chamber, and the first anion which is the monovalent anion selective permeation membrane. An exchange membrane, a first raw material chamber, a second anion exchange membrane that is a monovalent anion selective permeable membrane, a second raw material chamber, a third anion exchange membrane that is an anion exchange membrane, and an auxiliary raw material chamber in this order 4 Four sets of four membrane chambers were arranged, followed by a cation exchange membrane and a negative electrode chamber.

<Preparation of charging solution>
A charge solution for each of the following chambers was prepared.
Electrode chamber liquid: 2000 mL of 5% by mass sodium hydrogen sulfate aqueous solution
First raw material chamber liquid: 1500 mL of an 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 ions, 1.0 mol of sodium ions, and 0.80 mol of sulfate ions (remaining liquid from the previous first raw material chamber)
Auxiliary material chamber liquid: 1000 mL of an aqueous solution containing 0.6 mol of sulfuric acid
Product room liquid: 1000 mL of 1% by mass hydroiodic acid aqueous solution

<Electrodialysis>
Electrode chambers (positive electrode chamber and negative electrode chamber) are each circulated with the electrode chamber liquid at 1.5 L/min, the first raw material chamber liquid is passed through the first raw material chamber, and the second raw material is passed through the second raw material chamber. The chamber liquid was circulated at a rate of 0.2 L/min to the sub-raw material chamber and the product chamber liquid to the product chamber.

<Ion concentration analysis>
The operation was carried out for _3.5 hours, ^and the ^effluents from the first raw material chamber, the second raw material chamber and the product chamber were collected. ) concentrations were analyzed.
The results are shown in Tables 5 and 6, respectively.

Result 95.8% of the iodide ions in the raw material solution could be obtained from the difference between the charge in the first raw material chamber and the acquisition in the second raw material chamber. Moreover, compared with Example 1 and Comparative Example 1, the iodide ions in the raw material liquid could be obtained in the product chamber liquid at a higher yield.

No coloration due to free iodine was observed in the anolyte during dialysis. After the dialysis was completed, a reducing agent was added to the extreme chamber fluid and the iodide ion concentration was measured. No iodide ion exceeding the detection limit of 10 mg/L was detected.

That is, in Example 2, it was confirmed that the movement of iodide ions to the electrode chamber was suitably suppressed by using the liquid chamber adjacent to the electrode chamber as the auxiliary material chamber. Moreover, the yield was further improved as compared with Example 1 because the loss due to the iodide ions that migrated to the electrode chamber was suppressed.

As an electrodialysis tank, between the positive electrode and the negative electrode, from the positive electrode side, the positive electrode chamber, the bipolar membrane, the product chamber, the first anion exchange membrane that is an anion exchange membrane, the first raw material chamber, anions An electrodialysis cell in which four sets of membrane chambers, each consisting of three chambers and three membranes, are arranged in the order of a second anion exchange membrane, a second raw material chamber, and a bipolar membrane, followed by a negative electrode chamber. , dilute hydroiodic acid is circulated through the product chamber, the raw material liquid is circulated through the first raw material chamber, and the first raw material chamber is circulated through the second raw material chamber in the previous batch. Electrodialysis was carried out in the same manner as in the above example, except that the remaining raw material solution was circulated, and the same excellent results were obtained.

In the method for synthesizing hydroiodic acid of the present invention, hydroiodic acid is synthesized from a raw material liquid that is an aqueous solution containing iodide ions and an auxiliary raw material liquid that is an aqueous solution containing hydrogen ions by double displacement electrodialysis. A method for synthesizing hydrogen acid, wherein, 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, and a product chamber are placed between the positive electrode and the negative electrode. , 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, and a third anion that is an anion exchange membrane A method of using an electrodialysis cell in which a plurality of membrane chamber sets each consisting of 4 membranes and 4 chambers are arranged in order of an exchange membrane and a second auxiliary raw material chamber, followed by a cation exchange membrane and a negative electrode chamber. be.

Another embodiment of the method for synthesizing hydroiodic acid of the present invention is to synthesize hydroiodic acid from a raw material solution that is an aqueous solution containing iodide ions by bipolar membrane electrodialysis. In this method, between the positive electrode and the negative electrode, from the positive electrode side, the positive electrode chamber, the first bipolar membrane, the product chamber, the first anion exchange membrane that is an anion exchange membrane, the first A plurality of chamber membrane sets with three chambers and three membranes are arranged in this order of one raw material chamber, a second anion exchange membrane that is an anion exchange membrane, a second raw material chamber, and a second bipolar membrane, and This is a method using an electrodialysis cell in which a negative electrode chamber is arranged at the bottom.

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

Therefore, the method for synthesizing hydroiodic acid of the present invention has industrial applicability.
The hydroiodic acid synthesized by the present invention is used, for example, in the production of iodine compounds, reducing agents, pharmaceutical raw materials, etching agents, analytical reagents, and is an important industrial product.

1 Electrodialyzer 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 sub-raw material chamber 12 product chamber 13 first raw material chamber 14 second raw material chamber 15 second auxiliary raw material chamber 16 negative electrode chamber 21 product chamber liquid 22 first raw material chamber liquid 23 second raw material chamber liquid 24 auxiliary raw material chamber liquid 25 auxiliary raw material chamber liquid 26 positive electrode liquid 27 negative electrode liquid 31A electrodialysis tank 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 chamber 42 First raw material chamber 43 Second raw material chamber 44 Negative electrode chamber 51 Product chamber liquid 52 First raw material chamber liquid 53 Second raw material chamber liquid 54 Cathode liquid 55 Anode liquid

Claims (9)

A method for synthesizing hydroiodic acid by synthesizing hydroiodic acid from a raw material liquid that is an aqueous solution containing iodide ions and an auxiliary raw material liquid containing 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,
Cation exchange membrane, product chamber, first anion exchange membrane that is an anion exchange membrane, first raw material chamber, second anion exchange membrane that is an anion exchange membrane, second raw material chamber, anion exchange membrane A plurality of membrane chamber sets each including 4 membranes and 4 chambers are arranged in order of the third anion exchange membrane and the second auxiliary raw material chamber,
A method for synthesizing hydroiodic acid, characterized by using an electrodialysis tank in which a cation exchange membrane and a negative electrode chamber are subsequently arranged. 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, and the raw material liquid is passed through the first raw material chamber. The remaining liquid of the raw material liquid circulated through the first raw material chamber in the previous batch or the raw material liquid circulated through the first raw material chamber in the previous batch is stored in the second raw material chamber. 2. The method for synthesizing hydroiodic acid according to claim 1, wherein the liquid obtained by adding the raw material liquid to the residual liquid of (1) is circulated. A method for synthesizing hydroiodic acid by synthesizing hydroiodic acid from a raw material solution, which is an aqueous solution containing iodide ions, by bipolar membrane electrodialysis,
Between the positive electrode and the negative electrode, from the positive electrode side, following the positive electrode chamber and the first bipolar film,
The product chamber, the first anion exchange membrane that is an anion exchange membrane, the first raw material chamber, the second anion exchange membrane that is an anion exchange membrane, the second raw material chamber, and the second bipolar membrane in that order, arranging a plurality of chamber-membrane sets each consisting of 3 chambers and 3-membrane sets,
A method for synthesizing hydroiodic acid, characterized by using an electrodialysis tank continuously arranged with a negative electrode chamber. Dilute hydroiodic acid is circulated through the product chamber, the raw material liquid is circulated through the first raw material chamber, and the first raw material chamber is circulated through the second raw material chamber in a pre-batch. 4. The method according to claim 3, wherein the residual liquid of the raw material liquid passed through or the 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 the previous batch is circulated. Synthesis of hydroiodic acid. 5. The hydrogen iodide according to any one of claims 1 to 4, wherein the raw material solution is prepared so as 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 the hydroiodic acid. Method for synthesizing acids. 6. The method according to any one of claims 1 to 5, wherein a monovalent anion permselective membrane having monovalent anion selectivity is used for the first anion exchange membrane and the second anion exchange membrane. of hydroiodic acid. Examples of the raw material liquid include an iodine-absorbing liquid obtained by a blowing-out method, an iodine-desorbed liquid obtained by an ion-exchange resin method, an iodine-concentrated liquid obtained by an electrodialysis method, an industrial waste liquid containing iodide ions, an iodine 7. Hydroiodic acid according to any one of claims 1 to 6, wherein any one of a mixed aqueous solution of iodide ions and sulfate ions having a molar ratio of iodide ions: sulfate ions of 1:1 to 3:1 is used. Synthetic method. 1. An electrodialysis cell for use in double displacement electrodialysis, characterized in that an auxiliary raw material chamber is arranged on the negative electrode side of a positive electrode chamber, and an auxiliary raw material chamber is arranged on the positive electrode side of the negative electrode chamber. 1. An electrodialysis cell for electrodialysis, characterized in that an ion-exchange membrane for partitioning the negative electrode side of the positive electrode chamber and/or an ion-exchange membrane for partitioning the positive electrode side of the negative electrode chamber is a bipolar membrane.

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