JP2023014952A - Recovery method of iodine from aromatic iodine compound - Google Patents

Abstract

To provide a technique capable of recovering iodine at a higher recovery rate from aromatic iodine compounds having an iodine group by a desorption and purification method.SOLUTION: An aromatic iodine compound is deiodinated in the presence of a platinum group element-supported fiber catalyst, an alkali and a reducing agent under mild conditions at ambient temperature and pressure, and then the fibrous catalyst is rapidly removed to separate and recover iodine from the deiodinated liquid. The catalyst support is an anion-exchange fiber that can be quickly taken out of a reaction system. In the separation and recovery of iodine from the deiodinated liquid, high purity iodine can be recovered at a higher recovery rate by using a technique such as an iodine vaporization and absorption method.SELECTED DRAWING: Figure 2

Description

Detailed description of the invention

The present invention relates to a method for recovering iodine from aromatic iodine compounds.

Chile is the world's largest producer of iodine, followed by Japan. As for the applications, X-ray contrast agents account for the most, with more than 20%, followed by catalysts, antibacterial agents, and polarizing films. Since iodine is used in a wide range of fields from the medical field to the industrial field, it is expected that the amount of iodine used will increase more and more in the future.

In Chile, iodate is produced by eluting iodate from Chilean saltpeter, but there are concerns about a stable supply due to the fact that the political situation is not necessarily stable and it exists in the desert. In Japan, it is produced from salt water called underground brine that is pumped up during the production of natural gas. The pumping volume is limited in consideration of ground subsidence caused by pumping brackish water. Under such circumstances, it is difficult to rapidly increase the production of iodine, and recycling is an urgent matter. In particular, it is important to recover iodine from X-ray contrast agents that use a large amount of iodine and their manufacturing processes.

Iodine-based contrast agents, which are representative compounds among aromatic iodine compounds, all have a basic structure in which iodine is bound to an aromatic ring as shown in the general formula on the left side of the reaction formula in FIG. In order to recover , it is necessary to eliminate iodine from the aromatic ring and separate it.

As a known technique, Patent Document 1 discloses a technique of heating a contrast agent-containing liquid at a pH of 0.5 or lower, preferably at 100° C. or higher (Patent Document 1, Japanese Patent Application Laid-Open No. 2020-522456).

Patent Document 2 proposes a method of recovering iodine by adding Cu ⁺⁺ or fine powder copper and an alkaline solution to a liquid containing a contrast agent and heating to form an inorganic compound, which is then subjected to oxidation, extraction, or the like. (Patent document 2, EP0106934).

In Patent Document 3, conversion of iodine in a contrast agent to iodide ions is carried out under reflux under alkaline high-temperature conditions in the presence of a reducing substance selected from copper powder, zinc powder, iron powder, and the like. . After that, a technique of converting iodide ions to iodine molecules using a H ₂ O ₂ —FeCl ₃ composite oxidizing agent and extracting and purifying them with an organic solvent has been disclosed (Patent Document 3, CN103508421).

However, in these known techniques, in order to eliminate iodine from an aromatic ring having an iodine group, a chemical solution such as an acid or an alkali and a metal such as copper must be added and heated at 100° C. or higher. In addition, desorbed iodine is separated and recovered under strongly acidic conditions. In addition to requiring a heat- and chemical-resistant reaction vessel, it was also necessary to use chemicals that have a large environmental impact. In addition, there is a danger to the work environment due to vaporization of hydroiodic acid. Therefore, in order to employ these known techniques, it is necessary to design and operate a chemical plant that takes safety into consideration, and it cannot be said that the amount of iodine that is worth the cost can be recovered.

JP 2020-522456 EP 0106934 CN103508421

Problems to be Solved by the Invention

Until now, the recovery of iodine from aromatic iodine compounds has required complex chemical plants at high temperatures in order to desorb iodine from aromatic rings having iodine groups and to separate the desorbed iodine from coexisting components. It had a big impact on the load. Therefore, it is an object to provide a technique capable of separating and recovering iodine from an aromatic iodine compound under mild conditions or from a deiodinated liquid.

Means to solve problems

The present invention is a method for recovering iodine from aromatic iodine compounds having the following features.
(1) A first step of deiodinating a liquid containing an aromatic iodine compound in the presence of a platinum group element-supported catalyst, a reducing agent and an alkali, a second step of separating the catalyst from the deiodinated liquid, and desorbing A method for recovering iodine from an aromatic iodine compound, comprising a third step of separating and recovering iodine from the deiodinated liquid (2) The third step includes an iodine vaporization absorption method, an ion exchange resin adsorption method, electrodialysis, A method for recovering iodine from an aromatic iodine compound according to item (1), which is at least one selected from solid-liquid separation methods (3), item (1) or (2), wherein the platinum group element is palladium (4) The iodine system according to any one of (1) to (3), wherein the carrier for supporting the platinum group element is an anion exchanger. (5) A method for recovering iodine from a contrast agent (5) The shape of the anion exchanger according to claim 4 is a molded body containing fibers, twisted yarns that are aggregates of fibers, woven fabrics, non-woven fabrics, or cut bodies thereof ( 1) A method for recovering iodine from the aromatic iodine compound according to any one of items 1 to 4); The method for recovering iodine from the aromatic iodine compound according to any one of items (1) to (5), which contains an iodine group of

The aromatic iodine compound in the present invention includes an iodine compound having a benzene ring, an iodine compound having a condensed ring such as naphthalene, and an iodine compound having a heterocyclic ring such as pyridine, and the number of bonded iodine is 1. It is a general term for the compounds described above.

In order to briefly describe the present invention, deiodination of an aromatic iodine compound uses a catalyst in which palladium is supported on an anion exchange fiber as a catalyst, and an alkali and a reducing agent are added to perform a deiodination reaction at room temperature. A method for separating and recovering desorbed iodine will be described.

For an aromatic iodine compound, a hydrodeiodination reaction occurs even at normal temperature and normal pressure when reacted in the presence of a palladium-supported catalyst, a reducing agent and an alkali. It is important in terms of facility simplification and safety measures, and is extremely important in order to smoothly and promptly recover iodine from the deiodinated liquid in the next step.

The deiodination reaction formula can be considered as shown in FIG. As the aromatic iodine compound, triiodobenzene in which three iodine atoms are bonded to the benzene ring is described, but the range is not limited to this.

Here, there are homogeneous and heterogeneous palladium catalysts, and it is preferable to use a heterogeneous catalyst in consideration of the subsequent separation step. As a palladium-based heterogeneous catalyst, a catalyst in which palladium is supported on activated carbon is commercially available and can be used. However, since activated carbon is pulverized even in the form of granules, solid-liquid separation operation between the catalyst and the deiodinating liquid is required after the reaction. For example, operations such as filtration and sedimentation separation are required, which increases the number of facilities for iodine recovery and the installation area. Palladium-supported activated carbon is improved and molded into granules or pellets on the market. It is necessary to pay attention to the adsorption of organic substances to the activated carbon micropores.

A palladium-supported catalyst in which palladium is supported on an anion exchanger can be preferably used. Ordinary ion-exchange resins can also be used, but fibrous anion-exchangers are preferable as palladium carriers because they have a large surface area and are easily molded into short fibers, twisted yarns, woven fabrics, non-woven fabrics, and the like. In the case of short fibers, an operation such as adding an alkali and a reducing agent at the same time and stirring them is also possible. Separation from the deiodized solution can also be carried out by means of catching with a net. Therefore, as a palladium-based heterogeneous catalyst, a catalyst in which palladium is supported on anion-exchange fibers is preferable.

In the method of supporting palladium on an anion exchanger, palladium chloride [(PdCl ₄ ) ²⁻ ] is adsorbed on the anion exchanger, and then Pd ²⁺ is converted to Pd ⁰ using a reducing agent. can be carried on. During this reaction process, palladium is strongly retained and rarely lost. This is because palladium chloride is adsorbed by ion exchange not only on the surface of anion exchange fibers but also on the inside thereof, and ^PdO after reduction is entangled with polymer chains. Therefore, solid-liquid separation and handling of the catalyst and the deiodinating liquid are easy, which is preferable for the present invention.

Iodide ions are present in the deiodinated liquid of the iodine-based contrast agent. In order to recover this, the catalyst is taken out from the liquid, and depending on the purity, further separation and purification steps are required. FIG. 2 is a flowchart showing an example of the method for recovering iodine from the contrast medium of the present invention. All steps from the deiodination step to the separation and recovery step of desorbed iodine through the step of catalyst separation can be carried out under mild conditions of normal temperature and normal pressure. Although several kinds of processes seem to be combined, the main equipment is the deiodination reaction equipment and the iodine separation and recovery equipment because the separation of the catalyst can be carried out quickly in the present invention.

There are various methods for producing anion-exchange fibers, but as a method for producing the palladium catalyst support of the present invention, existing fibers are irradiated with radiation and then contacted with a monomer having an anion-exchange group to form grafted side chains. A grown radiation graft polymerization method is preferred. When existing fibers are functionalized by radiation graft polymerization, twisted yarns can be handled in the form of bobbins as shown in FIG. It has a shape in which twisted yarn 2 is wound around a core 1 with holes, and is easy to handle. Palladium-supported catalysts are also manufactured in bobbin form and provided for subsequent molding. In the case of a sheet-like nonwoven fabric, the polymerization process is different because it is a reaction of cloth, but it can be used.

The method of recovery of the palladium catalyst is closely related to the method of use and form. In the case of short fibers, it is possible to stir them together with other chemicals, and the contact efficiency between the catalyst and the liquid is high. The palladium catalyst can be separated from the deiodination liquid by attaching it to the deiodination reaction tank or by installing a mesh wire mesh capable of capturing short fibers in the middle of the piping from the deiodination reaction tank to the iodine separation and recovery tank. good too.

Twisted yarn can be unwound from bobbins and processed into other molded products. It can also be processed into the shape of a wind filter shown in FIG. 4 or the shape of a molding shown in FIG. The wound filter-like catalyst can be molded by winding the catalyst twisted yarn 3 around the perforated core 4 . It can be accommodated in existing housings and can be contacted by pumped circulation. The braided catalyst is a type of braid having a structure in which the catalyst twisted yarns 5 are radially protruded from the core 6 . Suspension in the deiodination bath enables contact with the liquid. Alternatively, the fiber assembly can be placed in a basket or bag and brought into contact with the liquid. The deiodination reaction can be carried out under mild conditions.

After the deiodination is completed, the palladium-supported fibers are removed from the deiodination solution, so that the next iodine separation and recovery step can be started immediately. Organic matter having an aromatic ring, sodium hydroxide, sodium iodide, and a reducing agent remain in the liquid from which the catalyst was removed. Several methods are conceivable for recovering iodine from this liquid, but a method selected from the iodine vaporization absorption method, ion exchange resin adsorption method, electrodialysis, and solid-liquid separation method can safely obtain iodine of high purity. preferred because

Palladium is a representative catalyst belonging to the platinum group elements, but other platinum group elements, platinum (Pt), rhodium (Rh), iridium (Ir), ruthenium (Ru), and osmium (Os) can also be used. can. As a reducing agent, hydrazine, formic acid, sodium borohydride (NaBH ₄ ), etc. can be used.

The invention's effect

INDUSTRIAL APPLICABILITY According to the present invention, the deiodination reaction, the separation of the catalyst, and the recovery of iodine from the deiodized liquid can be carried out gently at normal temperature and normal pressure, and facilities and environmental measures are easy to handle. Moreover, the purity of the obtained iodine is also high. This is an extremely effective technique for reusing iodine resources.

Deiodination reaction of iodine-based contrast agents in the presence of palladium-supported fibers, reducing agents, and alkali A diagram showing the flow of a method for recovering iodine from a contrast medium Bobbin, which is a reaction form of twisted yarn Wind filter type catalyst Mole-like catalyst Method for producing palladium-supported anion-exchange fiber by radiation graft polymerization method Method of using short fibrous catalyst (one example) How to use wind filter type catalyst (one example) How to use a mall-like catalyst (one example) Conceptual diagram of the iodine vaporization and absorption method Conceptual diagram of the ion-exchange resin adsorption method Conceptual diagram of the electrodialysis method Conceptual diagram of solid-liquid separation method Chemical structure of iopamidol

In the following, iodine-based contrast agents, which are typical aromatic iodine compounds, are deiodinated using a catalyst in which palladium is supported on anion-exchange fibers manufactured using radiation graft polymerization, and then further deiodinated. An embodiment of the present invention will be described in more detail by taking a method for recovering iodine from a liquid as an example.

FIG. 6 shows an example of a synthesis route of palladium-supported anion-exchange fibers using a radiation graft polymerization method. In FIG. 6, a commercially available polyolefin fiber as a substrate is irradiated with gamma rays and then contacted with dimethylaminoethyl methacrylate (DMAEMA) having a tertiary amine to grow graft side chains of DMAEMA from the substrate. This tertiary amine is utilized to adsorb palladium chloride, which is then reduced with sodium formate to deposit Pd ⁰ on the fibers.

One of the advantages of radiation-induced graft polymerization is that existing polymers of various shapes can be used. For example, single fibers, twisted yarns that are aggregates of single fibers, woven fabrics and nonwoven fabrics that are processed into sheets from single fibers, cut strips of these, films, porous films, porous hollow fibers, particles, etc. can all be used. However, the present invention prefers fibers. This is because the surface area is large, a high reaction rate can be obtained, and molding is easy and handling is easy.

Examples of fiber materials include synthetic fibers, natural fibers such as cellulose fibers such as cotton, animal fibers such as silk and wool, regenerated fibers, and mixed fibers thereof. Synthetic fibers include polyester, polyamide, acrylic, polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, polyurethane, polyvinyl alcohol, fluorine, and the like. Cellulose fibers include natural cellulosic fibers such as cotton and linen, viscose rayon, cuprammonium rayon, regenerated cellulose fibers such as Polynosic, refined cellulose fibers such as Tencel, and semi-synthetic fibers such as acetate and diacetate. be Among these, polyolefin-based materials such as polyethylene, polyamide-based materials such as nylon, and cellulose-based fiber polymers are particularly preferable. Among these materials, the material can be appropriately determined in consideration of radiation resistance, graft polymerizability, chemical resistance, and the like.

The ionizing radiation irradiated to the base material includes α rays, β rays, gamma rays, electron beams, neutron beams, ultraviolet rays, etc., but gamma rays and electrons that have the ability to penetrate deep from the surface of the fiber that is the base material It is preferred to use lines. The radiation irradiation conditions are not particularly limited, but in order to obtain sufficient grafting efficiency, it is preferably 5 to 200 kGy, particularly 15 to 100 kGy in a deoxygenated state. At this time, the oxygen concentration may be any concentration that achieves graft polymerization at a required polymerization rate, preferably 1% or less, more preferably 100 ppm or less. Gamma rays are used in FIG.

When fibers are irradiated with ionizing radiation, radicals are generated on the surface and inside of the fibers. When a monomer having an ion-exchange group or a monomer convertible to an ion-exchange group is brought into contact here, the monomer polymerizes with the generated radical as a starting point. Graft polymerization is classified into a pre-irradiation graft polymerization method and a simultaneous irradiation graft polymerization method depending on the timing of irradiation with radiation. The pre-irradiation graft polymerization method is a polymerization method in which the base material is exposed to radiation in advance, and then the base material and the monomer are brought into contact with each other. It's a good way. The simultaneous irradiation graft polymerization method is a graft polymerization method in which radiation is irradiated in the coexistence of a base material and a monomer. Although either irradiation method can be employed in the present invention, it is more preferable to use the pre-irradiation graft polymerization method, which produces a small amount of homopolymer, as a method for producing the separating material, which is the application of the present invention. FIG. 6 shows an example of graft polymerization by the pre-irradiation graft polymerization method.

In graft polymerization, when the monomer to be brought into contact is liquid, it is called a liquid-phase graft polymerization method, and when it is a gas, it is called a gas-phase graft polymerization method. When an emulsion monomer solution is used in the liquid-phase graft polymerization method, the method is called an emulsion graft polymerization method. Furthermore, there is an impregnation graft polymerization method positioned between the liquid phase graft polymerization method and the gas phase graft polymerization method. The impregnation graft polymerization method is a graft polymerization method in which the amount of monomer is calculated in advance so as to obtain a predetermined graft ratio, and the required amount of monomer is previously impregnated into the organic polymer molded article. Either method can be applied in the present invention.

Radicals are generated by irradiation and then brought into contact with a monomer having an anion-exchange group to grow a graft side chain having an anion-exchange group. Anion exchange groups can be introduced into the fiber in this way. Vinylbenzyltrimethylammonium chloride, arylamine, N,N-dimethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylate (DMAEMA), N,N-diethylaminoethyl methacrylate, N,N-dimethyl as monomers having anion exchange groups Examples include acrylamide, N,N-dimethylaminopropylacrylamide, quaternary ammonium salts of N,N-dimethylaminopropylacrylamide, and the like.

Monomers that do not have anion-exchange groups in themselves but can be converted to anion-exchange groups by a secondary reaction can also be used, such as glycidyl methacrylate (GMA), styrene, and chloromethylstyrene. After graft polymerization of these monomers, for example, in the case of GMA, a tertiary amino group can be introduced by reacting with an amine having a secondary amine such as dimethylamine, diethylamine and diethanolamine. A quaternary ammonium group can be introduced by reacting a polyamine such as trimethylamine, triethylamine or a salt thereof, or triethylenediamine, which can be used as a carrier for supporting a platinum group element of the present invention.

Adsorption of palladium chloride on anion-exchange fibers and subsequent reduction to Pd ⁰ with sodium formate can be performed in batch or column mode. Since the platinum group element becomes an anion as a chloro complex, it can be easily adsorbed on the anion exchange fiber. Platinum group elements other than palladium can also be used, but palladium can be preferably used in consideration of catalyst performance, price, and the like. As the reducing agent, not only hydrazine (hydrate or salt) but also reducing agents such as sodium borohydride can be used. The amount of Pd ⁰ supported can be easily controlled by the graft ratio and the amount of palladium chloride used, but can be appropriately set by the amount and concentration of the iodine-based contrast medium to be treated and the decomposition treatment conditions. Since palladium chloride is an expensive chemical, it is not necessary to add an amount corresponding to the anion exchange groups. Almost no precipitated Pd ⁰ falls off from the fibers.

In the deiodination treatment of the iodine-based contrast agent, the Pd ⁰ -supporting fiber is added to the mixed solution of the iodine-based contrast agent, the reducing agent, and the alkali, and the reaction is performed at normal temperature and pressure for a predetermined time to deiodine. can. After deiodination is completed, solid-liquid separation can be performed by removing the fibers. The necessary amount of Pd ⁰ -supported catalyst fiber and processing conditions can be determined in advance by preliminary tests, taking into consideration the type and amount of the iodine-based contrast agent to be processed, the processing conditions, and the like.

When radiation graft polymerization is carried out on base fibers, the reaction is likely to take place in the form of twisted yarn or non-woven fabric, and the catalyst can be produced in that form. In the case of twisted yarn, it can be processed into a sheet such as a rope, non-woven fabric, or woven fabric in addition to the shape of short fibers, wind filters, and malls, and various usages can be considered depending on the shape of the catalyst.

The cut fibrous catalyst can be packed in a packed tower and used in a flow system, and can also be used in a fluidized system shown in FIG. In the fluidization method, a contrast medium 8 is charged in a deiodination reaction tank 7, a cut fibrous catalyst 9 is added together with an alkali and a reducing agent from a chemical tank 10, and after stirring for a predetermined period of time, a mesh wire mesh 11 capable of capturing fibers is added. It can be separated from the deiodinated liquid by filtering with .

As shown in FIG. 8, the wound filter-like catalyst is often housed in a housing 12 of an existing cartridge filter and used, and can be installed in the circulation line of the deiodination reaction tank 7 . Cartridge filters originally have a filtering function, and it is possible to combine both filtering and catalytic decomposition functions.

As a method of using the mall-like catalyst, as shown in FIG. 9, it is suitable to use the mall-like catalyst 13 by immersing it in the liquid of the contrast agent 8 . When the molding is immersed for a certain period of time and the prescribed treatment is completed, it can be easily recovered by winding it up using the suspension device 14 at the upper end of the molding.

In the step of separating and recovering iodine from the deiodized liquid after catalyst separation, one or more of the iodine vaporization absorption method, ion exchange resin adsorption method, electrodialysis method, and solid-liquid separation method are selected to improve the purity. High iodine can be recovered with high recovery.

A suitable oxidizing agent in the step of separating and recovering iodine is selected from one or more mixtures of hypohalite, halogen oxoacid, molecular chlorine, nitrite, hydrogen peroxide. The pH adjusting liquid is selected from one or more mixtures of sulfuric acid, hydrochloric acid, nitric acid. The reducing agent is selected from one or more mixtures of sulfites, bisulfites, thiosulfates. Both are composed of inorganic compounds that do not contain organic substances or metal elements.

The iodine vaporization and absorption method is also called a blowout method, and is a method that is commercially used to recover iodine from brackish water (underground seawater). As shown in FIG. 10, the deiodinated and catalyst-separated separated liquid is stored in a separated liquid tank 15, added with an oxidizing agent 16 to convert iodide ions into iodine, and then sent to an iodine vaporization tank 17. Here, iodine is vaporized by a method such as bubbling or showering to the filler 19 using the air from the blower 18 . Vaporized iodine is put into practical use by absorbing it with reducing agent-containing absorbent 21 in iodine absorption tank 20 . Since the liquid property is quite different from that of brackish water, it is possible to optimize the vaporization conditions of iodine from the deiodized liquid in advance through small-scale preliminary experiments.

In the ion-exchange resin adsorption method, as shown in FIG. 11, an oxidizing agent is added to the separation liquid tank 15, and ions that have become triiodide ions (I ₃ ⁻ ) are sent to the ion-exchange adsorption tower 22 and then to the anion-exchange resin 23. Absorb. Here, triiodide ions are adsorbed, and the liquid mainly composed of organic substances is stored in the treatment liquid tank 24 . After adsorption, the anion exchange resin 23 elutes iodine with an eluent 25 containing a reducing agent, and stores the iodine in an iodine eluent tank 26 . The chemical formula of the triiodide ion may also be written as I -.I ₂ , and I ₅ ^- (I ^- .(I ₂ ) ₂ ) ^and I ₇ ^- (I ^- .(I ₂ ) ₃ ) Existing. Therefore, it is possible to adsorb iodine many times the ion exchange capacity. This technology is also a technology that has been put into practical use by iodine manufacturers. If necessary, column experiments can be performed to optimize the selection of anion exchange resin, flow rate, adsorption capacity, elution conditions, etc., and to create a basic design.

Since I ⁻ has a high ion selectivity, a method of adsorbing I ⁻ as it is to an ion exchange resin without adding an oxidizing agent can also be employed. In this case, the elution must use other agents, such as sodium chloride solution, rather than reducing agents.

Since the electrodialysis method moves ions by electricity as shown in FIG. 12, it is not necessary to use an oxidizing agent or a reducing agent unlike the iodine vaporization absorption method and the ion exchange resin adsorption method. A normal electrodialysis apparatus 27 has cation exchange membranes 30 and anion exchange membranes 31 alternately installed between an anode 28 and a cathode 29, and desalination compartments 32 and concentration compartments 33 are alternately formed. FIG. 12 is a diagram of a simplified electrodialysis apparatus for explaining the basic principle. The deiodinated and catalyst-separated separated liquid is introduced from the separated liquid tank 15 into the desalting chamber 32, where iodide ions permeate the anion exchange membrane 31 toward the anode 28, and sodium ions flow toward the cathode 29 as cations. It permeates the exchange membrane 30 . Both of the permeated ions become sodium iodide again in the concentrating chamber 33 , circulate between the iodine concentrated liquid tank 34 and the concentrating chamber, and are recovered in the iodine recovery tank 35 . Since the deiodinated organic matter having a benzene ring cannot permeate the ion exchange membrane, it passes through the desalting chamber and is returned to the separated liquid, which is discharged to the waste liquid tank 36 after desalting. Since the electrodialyzer has a small experimental device, it is possible to study the optimum conditions in advance through preliminary experiments, such as the electrical characteristics, the composition of the concentrate to be charged first, and the influence of organic matter.

In the solid-phase separation method, as shown in FIG. 13, the deiodinated and catalyst-separated separated liquid is stored in a crystallization tank 37, and a pH adjusting liquid 38 is added to adjust the pH from neutral to weakly acidic. An oxidizing agent 16 is added and stirred for a predetermined period of time to precipitate iodide ions as solid iodine and prepare slurry. This is separated into a solid phase and a liquid phase in a solid-liquid separation tank 39 using sedimentation separation, a solid-liquid separation membrane, or the like. Solid iodine is recovered in a solid tank 40 , and aqueous solution containing organic substances and inorganic salts is recovered in a liquid tank 41 . If the separation of the liquid phase is insufficient, solid iodine washing with pure water and a drying step may be added. Optimum conditions such as crystallization process conditions and solid-liquid separation conditions can be studied in advance by small-scale preliminary experiments.

As described above, the method of recovering iodine from the contrast agent of the present invention is mainly deiodinated with an alkali reducing agent using palladium-supported anion exchange fibers as a catalyst, and the recovery of iodine from the deiodinated liquid is performed by the iodine vaporization absorption method, It was explained that the method can be selected from the ion exchange resin adsorption method, the electrodialysis method and the solid-liquid separation method. The treatment can be consistently carried out under mild conditions of normal temperature and normal pressure, and the obtained iodine has a very high purity.

Hereinafter, the present invention will be described in more detail with reference to examples, using iopamidol shown in FIG. .

<Production of palladium-supported anion-exchange fiber>

(1) Production of Weakly Basic Anion-exchange Fiber 500 g of polyethylene fiber having a diameter of about 25 μm was placed in a plastic bag with a zipper, and then subjected to nitrogen substitution, and then irradiated with 100 kGy of gamma rays. The irradiated fibers were immersed in a 10% aqueous solution of dimethylaminoethyl methacrylate (DMAEMA) previously bubbled with nitrogen for 30 minutes, and reacted at 40° C. for 5 hours. After the reaction, the fibers were taken out and batch-washed five times with pure water at 40°C. When the weight after drying was measured, the weight increase rate was 58%, that is, the graft rate was 58%. This fiber was a weakly basic anion exchange fiber with 2.8 mmol/g of tertiary amine.

(2) Supporting Pd ⁰ 1.4 g of palladium chloride (PdCl ₂ ) was dissolved in 1 M hydrochloric acid to make a total volume of 1000 ml. The weakly basic anion exchange fiber produced in (1) was immersed in 500 ml of this liquid and stirred for 1 hour. After 1 hour, the anion-exchange fiber turned yellow and the liquid became transparent, thus adsorbing palladium chloride ions ((PdCl ₄ ) ²⁻ ). Next, it was immersed in a 2% aqueous solution of sodium formate to reduce and support Pd ²⁺ to Pd ⁰ . Reduction changed the fiber from yellow to black. The Pd ⁰ loaded fibers had a weight gain of 4.5% relative to the weakly basic anion exchange fibers.

(3) Deiodination experiment 1 of iodine contrast agent
Iopamidol (Iopamiron 370 Note) was used as an iodine-based contrast agent. This liquid contains 370 mg of iodine per ml. The chemical structure is as shown in FIG. 14, and three iodine bonds are attached to the benzene ring. To 1 ml of iopamidol, 20 ml of 1 M sodium hydroxide and 1 g of hydrazine (N ₂ H ₄ .H ₂ O) were added, and 0.3 g of palladium-supported fibers produced in (2) were added, followed by shaking at 25° C. for 2 hours. The iodide ion concentration of this liquid was measured by ion chromatography. From this value, the iodide ion was 315 mg. About 80% of the iodine in iopamidol was detected as iodide ions. No iodide ions were detected in the iopamidol solution prior to the deiodination reaction. Therefore, the iodide ion is obtained by the deiodination reaction of iopamidol.

(4) Recovery of iodine (ion exchange resin adsorption method)
The same experiment as in (3) was performed to prepare 300 ml of deiodinated liquid. The pH of this solution was adjusted to neutral with 10% sulfuric acid, and the solution was passed through a glass column with a diameter of 20 mm filled with 30 ml of a strongly basic anion exchange resin in Cl form at SV10. When the iodide ion concentration in the treatment liquid was measured, it was 1 mg/L or less, and most of it was adsorbed on the ion exchange resin. In this ion _- exchange resin adsorption test ^, iodide ions were adsorbed without using an oxidizing agent. It is clear that the iodine can be recovered with the ion exchange resin, since .

(1) Deiodination experiment 2 of iodine contrast agent
Palladium produced by increasing the amount of iodine-based contrast agent from Example 1, adding 1000 ml of sodium hydroxide and 50 g of hydrazine (N2H4.H2O) to 50 ml of iopamidol (Iopamiron 370 Note), and further by the same method as in (2). 15 g of supporting fiber (the weight increase rate after supporting palladium was 6.2%) was added, and the mixture was shaken at 25° C. for 3 hours. From the iodide ion concentration of 16700 mg/L in this liquid, about 90% of the iodine in iopamidol was deiodinated.

(2) Recovery of iodine (electrodialysis method)
Microacylizer EX3B manufactured by Astom Co., Ltd. was used as an electrodialyzer. As the ion exchange membrane, a strongly acidic cation exchange membrane (trade name: Neosepta CSE) and a monovalent anion selective membrane (trade name: Neosepta CSE) manufactured by Astom Co., Ltd. are used as one unit, and 10 units of two-chamber method electric A dialysis machine was used. The effective membrane area is 550 cm ² . The palladium catalyst was removed from the deiodinated solution (1) with tweezers and introduced into the desalting chamber of the electrodialyzer. Electrodialysis was carried out for 3 hours under operating conditions of 1.1 A average current and 10 V voltage. In addition, 700 ml of 0.1 M NaCl was used as an electrolytic solution in the concentration chamber. 16000 mg of iodine were recovered from the concentration compartment iodide ion measurement after 3 hours of operation. The recovery rate was about 95% with respect to the deiodinated liquid.

Comparative example 1

(1) Deiodination experiment 3 of iodine contrast agent
Iopamidol (Iopamiron 370 Note) was used as an iodine-based contrast agent. 20 ml of 1 M sodium hydroxide and 1 g of hydrazine (N2H4.H2O) were added to 1 ml of iopamidol, and the mixture was shaken at 25°C for 2 hours. About 4% of iodine in iopamidol was deiodinated from 16 mg of iodide ions in this liquid.

(2) Recovery of iodine (solvent extraction method)
The same experiment as in (1) was performed to prepare 10 ml of deiodinated liquid. The pH of this solution was adjusted to neutral with 10% sulfuric acid, and 1 ml of 0.5% sodium nitrite was added as an oxidizing agent to convert iodide ions to iodine. In order to extract iodine into the organic layer, 10 ml of n-hexane was added, mixed for 2 minutes, and separated by standing. After the extraction, the water layer was discharged, and 10 ml of pure water and 1 ml of 5 mM sodium thiosulfate as a reducing agent were added and permeated for 2 minutes to back-extract iodine into the water layer. Measurement of iodide ions in the aqueous layer indicated a recovery of about 65% for the deiodinated liquor.

本発明によるヨウ素系造影剤からのヨウ素回収率が非常に高いことが分かる。Table 1 summarizes the iodine desorption rate, the recovery rate from the iodine desorption liquid, and the total recovery rate from Examples 1 and 2 and Comparative Example 1.

It can be seen that the iodine recovery from the iodine-based contrast agent according to the invention is very high.

INDUSTRIAL APPLICABILITY In the present invention, the deiodination reaction, the separation of the catalyst, and the recovery of iodine from the deiodinated liquid can be carried out gently at normal temperature and normal pressure, and the installation area and equipment cost are small. In addition, there are also advantages that environmental measures are easy and the purity of the obtained iodine is high. Aromatic iodine compounds are used in a wide range of applications, from materials for synthetic organic chemistry to pharmaceuticals such as thyroid hormones. In particular, the amount of X-ray contrast medium used is increasing more and more along with medical and industrial development. In resource-poor Japan, iodine recycling technology is extremely effective as one of the few self-sufficient resources.

1 perforated core (for bobbin)
2 twisted yarn 3 catalyst twisted yarn (for wind filter)
4 perforated core (for wind filter)
5 Catalyst twisted yarn (for mall)
6 Wick 7 Deiodination reaction tank 8 Contrast agent 9 Cut fibrous catalyst 10 Chemical liquid tank 11 Mesh wire mesh 12 Cartridge filter housing 13 Mall catalyst 14 Suspension device 15 Separation liquid tank 16 Oxidizing agent 17 Iodine vaporization tank 18 Blower 19 Filling Agent 20 Iodine absorption tank 21 Reducing agent-containing absorbing liquid 22 Ion exchange adsorption tower 23 Anion exchange resin 24 Treated liquid tank 25 Eluent containing reducing agent 26 Iodine eluent tank 27 Electrodialyzer 28 Anode 29 Cathode 30 Cation exchange membrane 31 Anion Exchange membrane 32 Desalination chamber 33 Concentration chamber 34 Concentrated iodine tank 35 Iodine recovery tank 36 Desalted waste liquid tank 37 Crystallization tank 38 pH adjustment liquid 39 Solid-liquid separation tank 40 Solid tank 41 Liquid tank

Claims (6)

A first step of deiodinating a liquid containing an aromatic iodine compound in the presence of a platinum group element-supported catalyst, a reducing agent and an alkali, a second step of separating the catalyst from the deiodinated liquid, and desorbing the desorbed iodine. A method for recovering iodine from an aromatic iodine compound, comprising a third step of separating and recovering from the iodinated liquid The method for recovering iodine from an aromatic iodine compound according to claim 1, wherein the third step is at least one selected from an iodine vaporization absorption method, an ion exchange resin adsorption method, an electrodialysis method, and a solid-liquid separation method. 3. The method for recovering iodine from an aromatic iodine compound according to claim 1 or 2, wherein said platinum group element is palladium. The method for recovering iodine from an aromatic iodine compound according to any one of claims 1 to 3, wherein the carrier for supporting a platinum group element is an anion exchanger. The anion exchanger according to any one of claims 1 to 4, wherein the shape of the anion exchanger according to claim 4 is a fiber, a twisted yarn that is an aggregate of fibers, a woven fabric, a nonwoven fabric, or a molded body containing a cut body thereof. Method for recovering iodine from aromatic iodine compounds The method for recovering iodine from an aromatic iodine compound according to any one of claims 1 to 5, wherein the aromatic iodine compound contains one or more iodine groups bonded with a single bond to an unsaturated cyclic compound.

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