JP2569111B2 - Method for recovering iodine from waste liquid containing organic iodine compound - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for recovering iodine from a waste liquid containing an organic iodine compound.

Iodine is industrially a radiographic contrast agent, industrial bactericide,
Widely used as a raw material for agricultural and horticultural herbicides,
As a catalyst for dehydrogenation, isomerization and condensation of organic compounds,
It is often used and is an extremely valuable resource in industry.

[Prior Art] Various proposals have been made for recovery of iodine. For example, Japanese Patent Publication No. 64-5814 and Japanese Patent Publication No. 46-35244 are disclosed.
No. 48-4235 describes an adsorbent for removing radioactive iodine present as alkyl iodide.
No. 7 In a gas phase dehydrogenation reaction of an organic substance using iodine as a catalyst, the reaction mixture gas discharged from the reaction system is brought into contact with copper oxide at a high temperature, and then the partially iodinated copper oxide is oxidized with an oxidizing agent, and There is a description of a method for releasing and recovering the compound. JP-A-51-34896 discloses that waste containing iodine or an iodine compound is introduced into an incinerator and burned, and iodine contained in the combustion gas is converted to an aqueous solution of alkaline sodium thiosulfate or sodium sulfite. To recover iodine. As a method for recovering iodine from an aromatic organic iodine compound, EP 106934
No. 1 describes that iodine is recovered by heat treatment with a strong alkali in the presence of a copper-based catalyst.

[Problems to be Solved by the Invention] In recent years, the growth of organic iodine compounds, particularly radiographic contrast agents and industrial germicides, has been remarkable, and iodine has been in a tight state. On the other hand, since these organic iodine compounds have an extremely complicated structure, they are produced through many steps.

Naturally, a waste liquid is generated in each step, and expensive iodine is lost in the waste liquid as various organic compounds such as by-products and intermediates. Such iodine loss increases as the structure of the target X-ray contrast agent or bactericide becomes more complicated, and some compounds lose 50 to 70% of iodine used as a raw material.

An object of the present invention is to provide a method for industrially recovering and recycling iodine from a generated waste liquid in the production of an organic iodine compound.

[Means and Actions for Solving the Problems] The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, a waste liquid containing an organic iodine compound is deiodinated by a reduction reaction and then oxidized. After liberating iodine, found that the object of the present invention can be achieved by introducing air to drive out the liberated iodine and absorbing it into an alkaline aqueous solution or a specific reducing aqueous solution.
The present invention has been completed.

That is, the present invention is characterized in that after the organic iodine compound in the waste liquid containing the organic iodine compound is reduced and deiodinated, the oxidized and released iodine is expelled by air and absorbed in an alkaline aqueous solution or a reducing aqueous solution. This is a method for recovering iodine.

It is well known that organic iodine compounds generally undergo a deiodination reaction by various reduction reactions. However, there is no known technique applied to the recovery of iodine by reductive deiodination of an organic iodine compound in a waste liquid as in the present invention.

The waste liquid used in the present invention includes diatrizoic acid (3,5-diacetylamino-2,4,6-triiodobenzoic acid), acetolizoic acid (3-acetylamino-2,4,6-triiodobenzoic acid), iopamidol and the like. X-ray contrast agent, 3,5-diamino-2,4,6-triiodobenzoic acid, 5-amino-2,
An intermediate of an X-ray contrast agent such as 4,6-triiodoisophthalic acid or an agricultural and horticultural herbicide ioxinil, an industrial germicide tridiiodomethylsulfone, etc. Acidic waste liquid and the like, or a mixture thereof, but are not necessarily limited thereto. These waste liquids are used after pH adjustment as appropriate.

 Hereinafter, the present invention will be described in detail.

Examples of the reduction reaction used in the present invention include a catalytic hydrogenolysis reaction, a metal zinc, metal tin, metal aluminum or metallic reduction reaction, an electrolytic reduction reaction, and the like.

The hydrogenation catalyst used in the catalytic hydrocracking reaction is metal,
There are numerous types depending on the combination of carriers, additives, activation methods, etc., nickel-based catalysts, cobalt-based catalysts,
There are platinum group catalysts, chromium oxide based catalysts, copper based catalysts, osmium based catalysts, iridium based catalysts, molybdenum based catalysts and the like, and particularly nickel based catalysts, cobalt based catalysts and palladium-carbon catalysts give good results.

The hydrocracking temperature is from 10 to 150C, preferably from 30 to 80C. If the decomposition temperature is too low, the reaction does not proceed, while if it is too high, a large amount of waste liquid needs to be heated, which is not preferable from an economic viewpoint.

The hydrogen pressure may be normal pressure to 50 kg / cm ² . The reaction proceeds faster as the reaction is carried out at a high pressure, but the hydrogenolysis reactor is also required to be robust and the cost is enormous, which is not preferable.

The reaction time varies depending on the hydrocracking temperature, the amount of the catalyst, the hydrogen pressure, and the temperature of the organic iodine compound in the waste liquid. In general, the reaction may be performed with stirring for 1 to 15 hours. In addition, this reaction is preferably performed at PH 7-14 because the generated iodide ions are stabilized when the reaction is performed under alkaline conditions.

Since the reduction reaction with metal zinc, metal tin, metal aluminum or metal iron is considered to be due to electron transfer from the metal to the organic iodine compound, the reduction proceeds more smoothly as the surface area of the metal is larger. Therefore, the metal used is powdery, sandy,
It is desirable to use it in the form of granules or flowers.

The reduction temperature is in the range of 10 to 100C, preferably 20 to 60C. The reaction is performed under acidic conditions. When the pH is 0.5 to 5, the deiodination reaction proceeds very smoothly. When the pH is lower than 0.5, the metal is not used for deiodination and is used for generating hydrogen gas as a side reaction, which is not economical. If the pH is higher than 5, the reaction becomes extremely slow. Although the treatment time varies depending on the treatment temperature, the amount of metal used, the pH of the treatment solution, and the concentration of the organic iodine compound in the waste solution, the reaction may generally be performed with stirring for 1 to 15 hours.

The electrolytic reduction reaction is usually performed in an electrolytic cell including an anode chamber and a cathode chamber each having a diaphragm provided at the center.

As the diaphragm, asbestos, ceramics and the like can be used in addition to the cation exchange membrane, but the cation exchange membrane is preferable. The anode compartment is usually composed of a sulfuric acid solution and an anode, and the cathode compartment is composed of a target processing solution and a cathode. In the cathode chamber, if necessary, a considerable amount of salts, acids or bases may be dissolved as a supporting electrolyte to increase the conductivity of the waste liquid, but in general, the waste liquid itself already contains a sufficient amount of salts. In many cases, the addition of a supporting electrolyte is unnecessary.

The concentration of the sulfuric acid solution in the anode chamber is not particularly limited and can be appropriately selected from a wide range.
It is preferable to use a 10% by weight sulfuric acid aqueous solution or a sulfuric acid alcohol solution.

Any known anode can be used as long as it is not dissolved in a sulfuric acid solution. For example, examples of the anode include lead, lead alloy, platinum, gold, silver, nickel, nickel alloy, zinc, zinc alloy, cadmium, graphite, and carbon. Among them, it is preferable to use lead or platinum.

As the anode, lead, zinc, nickel, platinum, graphite, carbon, lead oxide, nickel oxide, manganese oxide, iron oxide,
Metals coated with a noble metal such as gold, ruthenium or iridium or rubidium can be mentioned, but lead, zinc, nickel and the like are particularly preferable.

As a reduction method of the electrolytic reduction of the present invention, any of a constant voltage method and a constant current method is possible, but the constant current method is preferable.

In the case of the constant current method, the current density is usually 0.1 to 10 A / d
m ² , preferably 0.5 to 3 A / dm ² . The amount of electricity required for the electrolysis reaction is not fixed depending on the shape of the electrolytic cell, the type of electrode, the reactivity of the substrate, and the like. The potential of the reductive deiodination reaction by electrolysis of an organic iodine compound is lower than the reduction potential of most of the other functional groups. Therefore, even if a mixture of various organic compounds is subjected to the reduction reaction, it is the earliest that the compound undergoes the reduction reaction. This is an iodination reaction, and as a result, high current efficiency is obtained.

After the completion of the deiodination reaction, the pH of the treatment liquid is appropriately adjusted, and then the treatment liquid is oxidized with an oxidizing agent such as hydrogen peroxide, sodium hypochlorite, chlorine, chlorine water, sodium sulfite, etc., to release iodine.

The free iodine is expelled from the processing solution by passing the processing solution through an air introduction tube, and is easily collected and concentrated by leading to the absorbing solution.

In order to perform the above operation more efficiently, it is appropriate to use a method in which the treatment liquid is lengthened from the upper part of the driving tower, and the iodine is collected in the air through the lower part. It is preferable to use a packing such as a magnetic ring or the like in order to improve the contact in the removal tower, or to introduce the filler in a shower state from the upper part of the removal tower.

The iodine thus expelled is sent to an absorption tower. As the absorbing solution, an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide or a reducing aqueous solution such as an aqueous solution of sulfurous acid, sodium thiosulfate, or sodium sulfite is used.

The solution that has absorbed free iodine contains sodium iodide, potassium iodide or an excess of a reducing agent such as sodium thiosulfate and sodium sulfite, sodium sulfate, and sodium carbonate. Therefore, when recovering iodine from the absorbing solution, the absorbing solution is acidified and then blown with chlorine to precipitate free iodine.

Iodine is an extremely corrosive element, and therefore, it is generally very difficult to select and design a constituent material of an iodine recovery apparatus. However, in the present invention, the recovery is performed under a low-temperature and reducing condition, and the corrosive action of iodine is extremely suppressed. Since free iodine or iodide salt is not treated at high temperature or under acidic conditions as in the prior art, there is a great advantage that the selection and design of the constituent materials is much easier than other known iodine recovery apparatuses.

〔Example〕

Next, the method of the present invention will be specifically described with reference to examples.

Example 1 As a sample waste liquid, a waste liquid generated in the production of 5-amino-2,4,6-triiodoisophthalic acid was used.

 The adjustment of the sample waste liquid was as follows.

4800 ml of water and 182 g of 5-aminoisophthalic acid were charged into a reactor, and the temperature was raised to 90 ° C. while stirring. Next, iodine monochloride
536 g was dripped in about 1 hour. Then, after stirring at the same temperature for about 5 hours, the mixture was cooled to room temperature. The crystals are filtered off and 1000 ml
And washed with water. The filtrate and the washing solution were combined to obtain 5500 ml of sample waste liquid.

This waste liquid contains 5-amino-2-iodoisophthalic acid, 5-amino-4-iodoisophthalic acid, 5-amino-2,4-diiodoisophthalic acid, 5-amino-4,6-diiodoisophthalic acid. Acid, various organic iodine compounds such as 5-amino-2,4,6-triiodoisophthalic acid and unreacted iodine monochloride, inorganic iodine compounds such as free iodine are contained,
The amount of iodine contained in 100 ml of the waste liquid was 1.156 g, of which 0.693 g was contained in the organic iodine compound.

500 ml of the waste liquid obtained above was charged into a reactor, and the pH was adjusted to 13 with a 30% by weight aqueous sodium hydroxide solution.
0 mg of 5% by weight palladium-carbon catalyst was added. 50
C., and hydrogen gas was introduced at a flow rate of 50 ml / min while stirring. After continuing the introduction of hydrogen under normal pressure for 5 hours,
The introduction of hydrogen was stopped, and the mixture was cooled to room temperature.

The palladium-carbon catalyst was filtered off, and the filtrate was transferred to a reactor equipped with an air introduction pipe and an exhaust pipe, and the pH was adjusted to 3 with concentrated sulfuric acid. The treatment liquid was oxidized with an aqueous solution of sodium hypochlorite having an effective chlorine amount of 5% to release iodine. Subsequently, air was introduced and the exhaust pipe was absorbed in a 10% by weight aqueous sodium hydroxide solution. This absorption liquid contained 5.528 g of iodine, and the recovery rate of iodine from the waste liquid was 95.6%.

Example 2 500 ml of the waste liquid obtained in Example 1 was charged into a reactor, and the pH was adjusted to 2.5 with a 30% by weight aqueous sodium hydroxide solution.
3.75 g of sandy zinc was added and the mixture was stirred at 50 ° C. for 4 hours. After filtering off unreacted zinc, chlorine gas is blown into the filtrate,
Iodine was liberated. The filtrate was transferred to a reactor equipped with an air introduction pipe and an exhaust pipe, air was introduced, and the iodine released was absorbed by the alkaline solution by introducing the exhaust pipe to a 10% by weight aqueous sodium hydroxide solution. The absorption solution contained 5.465 g of iodine, and the recovery rate of iodine from the waste solution was 9%.
4.5%.

Example 3 A waste liquid generated during purification of diatrizoic acid was used as a sample waste liquid.

100 g of the crude sodium salt of diatrizoic acid was recrystallized from 400 ml of a mixed solvent of water: isopropanol = 40: 60. The obtained filtrate and washing solution were combined, isopropanol was distilled off under reduced pressure, and the remainder was diluted to 500 ml with water to obtain a sample waste liquid. The amount of iodine contained in this waste liquid was 1.840 g per 100 ml.

After adjusting the pH to 1 with sulfuric acid, 500 ml of the waste liquid obtained above is put into a cathode compartment of an electrolytic cell separated by a diaphragm (cation exchange membrane, Selemion CMV, manufactured by Asahi Glass), and 10
500 ml by weight of a sulfuric acid aqueous solution was added. Constant current electrolysis (0.5 A / dm ² ) was performed at 30 ° C. using nickel as a cathode material and platinum as an anode material, and a current of 6 F / mol was applied to perform reductive deiodination.

The electrolyte was post-treated as in Example 1. The absorption liquid contained 8.74 g as iodine, and the recovery rate of iodine from the waste liquid was 95.0%.

Example 4 Hydrocracking was performed under the same conditions as in Example 1 using 500 ml of the waste liquid obtained in Example 1 and 2.0 g of Raney nickel as a hydrocracking catalyst. After the decomposition, the catalyst was allowed to settle for a while and the supernatant liquid was separated by decantation. 500 ml of the waste liquid was added to the catalyst again, and hydrogenolysis was performed. This operation was repeated five times to treat a total of 2500 ml of the waste liquid, then the pH of the treated liquid was adjusted to 3 with concentrated sulfuric acid, and chlorine gas was introduced to release iodine.

The following apparatus was prepared as an apparatus for recovering iodine from this processing solution.

A glass column with a length of 800 mm and an inner diameter of 30 mm was used as a drive-out tower, with a liquid inlet at the center and an air inlet at the bottom. 5 mm inside diameter between air inlet and liquid inlet
300mm high glass ring cut at 7mm intervals
mm.

As an absorption tower, a glass column having a length of 600 mm and an inner diameter of 30 mm was used, a liquid inlet was provided at an upper part thereof, and an air inlet was provided at a lower part thereof.

The upper end of the column of the discharge tower was connected to the air inlet of the lower part of the absorption tower by a vinyl tube, and the absorption liquid was transported from the receiver to the liquid inlet of the upper part of the absorption tower by a metering pump for recycling.

The iodine-free liquid was sent to the above apparatus at a flow rate of 10 ml / min from the liquid inlet at the center of the drive-out tower. Air was supplied from the lower air inlet at a flow rate of 50 ml / min. 10 as absorbent
Weight percent sodium sulfite aqueous solution
It was supplied at a flow rate of 10 ml / min.

Treat 2500 ml of iodine free solution, and add 2
6.85 g was recovered. The recovery rate was 92.9%.

[Effect of the Invention] According to the method of the present invention, iodine can be recovered from a waste liquid containing an organic iodine compound in an extremely high yield. Further, the selection and design of the constituent materials of the recovery device are easier than conventionally known recovery methods, and are extremely industrially useful as a method for recovering iodine from a waste liquid containing an organic iodine compound.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location C02F 1/72 CDV C02F 1/46 101C (56) References JP-A-48-72109 (JP, A JP-A-63-1448 (JP, A) JP-B-57-20037 (JP, B2) Irrigation Wastewater Handbook Handbook, edited by the Editing Committee for Irrigation Wastewater Handbook, published October 30, 1973 by Maruzen Co., Ltd. 576-577 Page 7.11.4, Nozaki and Fujishiro, "Iodine and Its Industry" Published by Tokyo Denki University Press, April 1, 1962, page 29, 9 lines to 30 pages, 9 lines, 232 pages [3] 234 pages [ 1]

Claims (4)

(57) [Claims] An organic iodine compound in a waste liquid containing an organic iodine compound is reduced and deiodinated, and then oxidized and released iodine is expelled by air and absorbed in an alkaline aqueous solution or a reducing aqueous solution. How to recover iodine. 2. The method according to claim 1, wherein the deiodination is a catalytic hydrocracking reaction. 3. The method according to claim 1, wherein the deiodination is a reduction reaction with metallic zinc, metallic tin, metallic aluminum or metallic iron. 4. The method according to claim 1, wherein the deiodination is an electrolytic reduction reaction.