JP2569104B2 - 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 widely used as a raw material for radiographic contrast agents, industrial fungicides, agricultural and horticultural herbicides,
It is often used as a catalyst for dehydrogenation, isomerization, condensation reactions and the like of organic compounds, and is an extremely valuable industrial resource.

[Prior Art] Various proposals have been made for recovery of iodine. For example, Japanese Patent Publication Nos. 46-5814 and 46-35244 disclose a method for removing radioactive iodine existing as alkyl iodide. There is a description about the adsorbent, JP-B-48-42357
In the gas-phase dehydrogenation of organic substances 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. There is a description of a method for releasing and recovering iodine. JP-A-51-34896 discloses that waste containing iodine or an iodine compound is introduced into a combustion furnace 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 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, in particular, radiographic contrast agents and industrial germicides has been remarkable, and iodine is in a tight situation. On the other hand, since these organic iodine compounds have an extremely complicated structure, they are produced through many steps. Naturally, wastewater is generated in each process, and expensive iodine is a by-product,
It is lost in wastewater as various organic compounds such as intermediates. Such iodine loss increases as the structure of the target radiographic contrast agent or bactericide becomes more complex, 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 reusing iodine from waste liquid generated in the production of an organic iodine compound.

Means and Action for Solving the Problems The present inventors have conducted intensive studies to solve the above problems, and as a result, reacted a waste liquid containing an organic iodine compound in the presence of a hydrocracking catalyst to obtain an organic iodine. The inventors have found that the object of the present invention can be achieved by converting iodine in the compound into inorganic iodide ions, oxidizing the compound with an oxidizing agent, and releasing and recovering iodine, thereby completing the present invention.

That is, the present invention is a method for recovering iodine, which comprises hydrolyzing a waste liquid containing an organic iodine compound in the presence of a hydrocracking catalyst and releasing iodine with an oxidizing agent.

Generally, an organic iodine compound is used in the presence of a hydrocracking catalyst.
Although hydrogenolysis is easily performed, a technique for recovering iodine by hydrocracking an organic iodine compound in a waste liquid as in the present invention is not known.

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,
Reaction waste solution, washing solution, recrystallization waste solution, acid generated in the production of intermediates of X-ray contrast agents such as 4,6-triiodoisophthalic acid or the herbicide ioxinil for agricultural and horticultural use, tolyl diiodomethyl sulfone for industrial use, etc. It is, but not limited to, a precipitation waste liquid or a mixture thereof.

There are very many types of hydrogenation catalysts to use, depending on the combination of the metal used, the carrier, the additive, the activation method, etc., but nickel-cobalt catalysts, platinum catalysts, chromium oxide catalysts, copper catalysts , An osmium-based catalyst, an iridium-based catalyst, a molybdenum-based catalyst, and the like. In particular, 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 to a high temperature, which is not preferable from an economic viewpoint.

The hydrogenation pressure is preferably 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 hydrogenation pressure, and the concentration of the organic iodine compound in the waste liquid. In general, the reaction may be performed for 1 to 15 hours with stirring.

In addition, this reaction is desirably performed at PH 7-14 because the generated iodide ion is stabilized as a salt when the reaction is performed under alkaline conditions. This hydrocracking reaction can be carried out either batchwise or continuously.

After the completion of the hydrocracking reaction, the catalyst is separated from the processing solution, and the catalyst is returned to the reaction system. When the treatment liquid is oxidized with an oxidizing agent such as hydrogen peroxide, sodium hypochlorite, chlorine or the like, iodine is released.

The free iodine thus obtained is expelled from the treatment solution by introducing air, and absorbed in an aqueous alkali solution such as sodium hydroxide or potassium hydroxide or an aqueous reducing solution such as alkaline sodium thiosulfate or sodium sulfite ( Blowing out method).

In addition, it is possible to recover the iodine by a known method such as a method of adsorbing and fixing free iodine on activated carbon (activated carbon method) or a method of adsorbing and fixing it on ion exchange resin (ion exchange resin method), and reuse it as iodine. It is.

Since iodine is an extremely corrosive element, it is generally very difficult to select and design the constituent materials of the iodine recovery apparatus. However, in the present invention, recovery is performed under alkaline and reducing conditions, and the corrosive action of iodine is extremely suppressed.

Since free iodine or iodide salt is not treated at a high temperature as in the prior art, there is a great advantage that the selection and design of the constituent materials is extremely easy as compared with other known iodine recovery apparatuses.

〔Example〕

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

Example 1 A waste liquid generated in the production of 5-amino-2,4,6-triiodoisophthalic acid was used as a sample. The preparation of the sample 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, 536 g of iodine monochloride was added dropwise in about 1 hour. afterwards,
After stirring at the same temperature for about 5 hours, the mixture was cooled to room temperature. The crystals were separated by filtration and washed with 1000 ml of water, and the reaction 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. It contains various organic iodine compounds such as acid, 5-amino-2,4,6-triiodoisophthalic acid and inorganic iodine compounds such as unreacted iodine monochloride and free iodine, and is contained in 100 ml of waste liquid. The amount of iodine was 1.156 g, of which 0.693 g was contained in the organic iodine compound.

500 ml of the obtained waste liquid was charged into a reactor, and the pH was adjusted to 13 with a 30% by weight aqueous sodium hydroxide solution.
A 100% by weight palladium-carbon catalyst was added, the temperature was raised to 50 ° C. while stirring, and hydrogen gas was introduced at a flow rate of 50 ml / min.

After the introduction of hydrogen gas was continued for 5 hours, the introduction of hydrogen gas was stopped, and the mixture was cooled to room temperature.

The palladium-carbon 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 5 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.

Then, air was introduced, and the exhaust pipe was led to a 10% by weight aqueous solution of sodium hydroxide, so that the released iodine was absorbed into the alkaline solution. 5.52 as iodine in this absorbent
It contained 8 g, and the recovery rate of iodine from the waste liquid was 95.6%.

Example 2 A waste liquid generated during purification of diatrizoic acid was used as a sample.

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 crystals were collected by filtration and washed with 100 ml of water-isopropanol. 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.

500 ml of the obtained waste liquid was charged into a reactor, the pH was adjusted to 13, and 2.0 g of commercially available Raney Nickel was added in a water-containing state. The temperature was raised to 50 ° C. while stirring, and hydrogen gas was introduced at a flow rate of 50 ml / min.

After the introduction of hydrogen gas was continued for 5 hours, the introduction of hydrogen was stopped, and the mixture was cooled to room temperature.

After the Raney nickel was filtered off, the filtrate was treated in the same manner as in Example 1 to obtain 8.67 g of iodine. The iodine recovery was 95.3%.

Example 3 Hydrocracking was carried out in the same manner as in Example 1 using 500 ml of the waste liquid obtained in Example 1 and 2.0 g of commercially available Raney nickel as a hydrocracking catalyst. After the completion of the hydrocracking, Raney nickel was allowed to settle for a while, and the supernatant was separated.

500 ml of the waste liquid was added again to Raney nickel, and hydrogenolysis was performed. This operation was repeated 5 times, and after a total of 2500 ml of waste liquid was treated, post-treatment was performed in the same manner as in Example 1,
28.23 g were recovered. The recovery was 97.7%.

[Effects 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.
In addition, the selection and design of the constituent materials of the recovery device are easier than the recovery methods of the prior art, and the method of the present invention is industrially extremely useful as a method for recovering iodine from a waste liquid containing an organic iodine compound.

 ──────────────────────────────────────────────────続 き Continued on the front page (56) References JP-B-57-20037 (JP, B2) Irrigation Wastewater Handbook, edited by the Editing Committee for Irrigation Wastewater Handbook, published October 30, 1973 by Maruzen Co., Ltd. 576-577 Section 7.11.4 Iodine and its industry by Nozaki and Fujishiro Published on April 1, 1962 Published by Tokyo Denki University Press, 9 lines at the end of page 29 to 9 lines at page 30

Claims (6)

(57) [Claims] 1. A method for recovering iodine, comprising hydrolyzing a waste liquid containing an organic iodine compound in the presence of a hydrocracking catalyst and releasing iodine with an oxidizing agent. 2. The method according to claim 1, wherein the hydrocracking catalyst is a palladium-based catalyst. 3. The method according to claim 1, wherein the hydrocracking catalyst is a nickel-based catalyst or a cobalt-based catalyst. 4. The method according to claim 2, wherein the palladium-based catalyst is a palladium-carbon catalyst. 5. The method according to claim 3, wherein the nickel-based catalyst is a Raney nickel catalyst. 6. The method according to claim 3, wherein the cobalt-based catalyst is a Raney cobalt catalyst.