JPH06157007A - Method for recovering iodine from waste liquor containing organic iodine compound - Google Patents

Abstract

PURPOSE:To produce a purified iodine product of high purity by economically deiodinating an organic iodine compound in a waste liquor containing the organic iodine compound in high yield and then separating and purifying the iodine using a well-known steam distillation method. CONSTITUTION:An organic iodine compound in a waste liquor containing the organic iodine compound is strongly alkalified with at least one of sodium hydroxide or potassium hydroxide and then deiodinated according to the thermal decomposing reaction to provide iodide ions. The pH is then regulated to <=6 with sulfuric acid and the resultant iodide ions are oxidized with at least one of chlorine gas or a solution of sodium hypochlorite to distill the liberated iodine with steam. The steam distilled iodine is subsequently absorbed with at least one of a sodium bisulfite, a sodium sulfite and a sodium hydroxide solutions to afford a solution of hydriodic acid. The oxidized and liberated iodine is then purified by a pressurizing melting method to produce the purified iodine product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering iodine from a waste liquid containing an organic iodine compound generated during a process for producing an iodine roentgen contrast agent.

[0002]

2. Description of the Related Art Regarding the method for recovering iodine from an organic iodine compound, Japanese Unexamined Patent Publication No. 1-201002 discloses that a waste liquid containing an organic iodine compound is deiodinated in the presence of a hydrocracking catalyst and then iodine is removed with an oxidizing agent. There is a description of a method for recovering iodine, which is characterized by being liberated. Japanese Patent Laid-Open No. 1-20100
No. 3 is characterized in that a waste liquid containing an organic iodine compound is subjected to deiodination treatment with at least one of metallic zinc, metallic tin, metallic aluminum and metallic iron under acidic condition, and then iodine is liberated with an oxidizing agent. There is a description about a method of recovering iodine. Japanese Unexamined Patent Publication (Kokai) No. 1-224202 describes a method for recovering iodine, which is characterized in that a waste liquid containing an organic iodine compound is deiodinated by electrolytic reduction under acidic conditions and then oxidized to liberate iodine. Japanese Patent Application Laid-Open No. 1-224203 discloses that an organic iodine compound in a waste liquid containing an organic iodine compound is reduced and deiodinated under acidic conditions, and then oxidized and liberated iodine is expelled by air and absorbed in an alkaline aqueous solution or a reducing aqueous solution. There is a description of a method for recovering iodine, which is characterized by JP-A-1-108102 discloses a compound selected from the group consisting of (a) organic compound (b) iodine and / or iodine compound and (c) alkali metal, alkali metal compound, alkaline earth metal and alkaline earth metal compound. The method is characterized in that a waste liquid or mud containing at least one kind is dried and then heat-treated at a temperature of 300 to 1300 ° C. to recover an alkali metal iodide and / or an alkaline earth metal iodide. There is a description of a method for separating and recovering iodine.

Conventionally, various methods for recovering iodine have been proposed from natural gas brackish water. Iodine ions are converted to free iodine with an oxidizing agent such as chlorine and then expelled with air, and a reducing solution such as an aqueous solution of sulfurous acid gas is proposed. Method (blowout method), or a method of adsorbing and fixing free iodine on activated carbon (activated carbon method), or a method of adsorbing and fixing iodine ions and free iodine on an ion exchange resin (ion exchange resin method), or copper Methods such as a method of reacting with ions to separate copper iodide as a precipitate (copper method) are known, and these methods have an iodine concentration of 50 to 150 mg / min in natural gas brine.
at very low concentrations and l, moreover cans water to be treated is in the condition to say that a very large amount of the thousands to tens of thousands m ^{3 /} day. The iodine concentration in the waste liquid containing the organic iodine compound in the present invention is several g / l to several hundred g / l,
The amount of waste liquid to be treated is also several m ³ / day to several tens m ³ at most.
It is about / day. In addition to other organic iodine compounds,
Inorganic salts such as salt and organic compounds such as organic solvents are contained in large amounts. After deiodination, when crystals of iodine are directly precipitated from such waste liquid, the iodine crystals are dissolved or bound to an organic compound such as an organic solvent contained in the waste liquid and separated into two layers due to the difference in specific gravity to form crystals. Of the iodine, even if crystals are deposited, the purity decreases due to the coprecipitation phenomenon of organic compounds and inorganic salts, and the recovery rate decreases due to the re-refining operation. It is difficult to recover. Further, in order to recover iodine by the known method as described above, the waste liquid having a high iodine concentration must be diluted with a large amount of water up to a concentration of brine, which causes an increase in the size of the apparatus and is not economical. .

[0004]

Iodine in natural gas brackish water exists in a form called iodine ion, and if PH is made acidic, free iodine can be easily produced by an oxidizing agent. However, since iodine in the organic iodine compound treated in the present invention is bonded to carbon, it is impossible to generate free iodine with an oxidizing agent under the same acidity as brine. Therefore, in order to recover iodine from such an organic iodine compound, the bond cannot be recovered by a known method unless the bond between iodine and carbon is cut off and iodine is made into an inorganic iodine compound such as iodine ion.

The present invention provides a method for recovering iodine, which comprises economically producing a high yield of an organic iodine compound in a waste liquid containing the organic iodine compound, deiodifying the iodine, reducing it under acidic conditions, and separating and purifying the liberated iodine. The task is to do.

[0006]

Means and Actions for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that the organic iodine compound in the waste liquid containing the organic iodine compound is decomposed by a thermal decomposition reaction under strong alkaline. It was found that the object of the present invention can be achieved by deiodifying and converting into iodine ions, and then separating and refining iodine liberated by oxidation under acidic conditions by a known steam distillation method, and completed the present invention. .

That is, according to the present invention, the organic iodine compound in the waste liquid containing the organic iodine compound is made strongly alkaline with at least one of sodium hydroxide and potassium hydroxide, and deiodinated by a thermal decomposition reaction to form iodine ions. Then P with sulfuric acid
H6 or less, oxidized by at least one of chlorine gas or sodium hypochlorite solution, free iodine is distilled by steam, absorbed by at least one of sodium bisulfite, sodium sulfite and sodium hydroxide solution, and iodized. This is a method of recovering iodine, which comprises producing a purified iodine product by refining the iodine liberated by oxidation under acidic conditions after the solution is made into a hydrogen acid solution by a pressure melting method.

The organic iodine compound in the waste liquid used in the present invention is iohexol (5- (N-2-hydroxypropylacetamide) -2,4,6-triiodo).
-N, N'-bis (2,3-dihydroxypropyl)
-Isophthalamide), iovamidol, retogen contrast agents such as iodoamide, 5-amino-
2,4,6-triiodo-N, N'-bis (2,3.
-Dihydroxypropyl) -isophthalamide
And 5-aceamido-2,4,6-triiodo-N, N'-bis (2,3, -dihydroxypropyl) -isophthalamide, which are intermediates of retogen contrast agents and the like, which are eliminated by the method of the present invention. Any iodizable organic iodine compound (various iodinated aryls and iodinated alkyls) may be used and is not particularly limited. Further, any impurities such as inorganic salts and organic compounds such as organic solvents may be mixed as long as the impurities mixed in the waste liquid do not form a compound by reacting with free iodine under acidic conditions.

Generally, there are many unclear points as to what kind of manufacturing process such a waste liquid is generated in, and what kind of use it is, and impurities contained in the waste liquid. Since there are various miscellaneous substances, there is no particular limitation as long as they are waste liquids having the above-mentioned properties, and all of them are treated waste liquids.

The present invention will be described in detail below. Deiodination of the organic iodine compound used in the present invention is considered to be electron transfer of the OH ⁻ group to the organic iodine compound under conditions of high temperature and high base.

Solid or 40 wt% sodium hydroxide or potassium hydroxide solution is added to the waste liquid containing the organic iodine compound to adjust the alkaline concentration in the waste liquid to 20 to 35 wt%.
In between. The reaction temperature varies depending on the alkaline concentration, but is 100 ° C. or higher. The reaction time varies depending on the alkaline concentration and the reaction temperature, but the reaction may be performed for about 1 to 5 hours. The deiodination rate is 95% or more, although it varies depending on the type of organic iodine compound, the type and amount of impurities mixed in the waste liquid, the above reaction conditions and the like.

After the completion of the deiodination reaction, water is added in an amount of 3 times the amount of the waste liquid so that the liquid temperature becomes 40 ° C. or lower. Next, this waste liquid is adjusted to pH 6 or less with sulfuric acid, put into a steam distillation apparatus, and at least one kind of chlorine gas or sodium hypochlorite solution is added to bring the oxidation-reduction potential to +580 to +650 mv to release all iodine ions. To Steam is introduced into this waste liquid to distill free iodine, and iodine is absorbed and dissolved in at least one of sodium bisulfite, sodium sulfite, and sodium hydroxide solution to obtain a hydroiodic acid solution.

The hydroiodic acid solution was placed in a pressure melting vessel, chlorine gas was blown into it to cause iodine crystals to break out, and the pressure was adjusted to 2-3.
After melting at kg / cm ² and a temperature of 120 to 150 ° C. for several hours, it can be cooled to obtain a purified iodine product.

Free iodine is a substance that is extremely corrosive, and in general, a very expensive material such as glass lining is used as the constituent material of the iodine recovery device. In the deiodination reactor of the present invention, since all deiodinated iodine is in the form of iodine ions, there is no concern about corrosion in free iodine, and the material of the apparatus is determined by the reaction temperature and the alkali concentration, and generally this Under such conditions, stainless steel products are often used, which is very economical.

As described above, according to the present invention, the organic iodine compound in the waste liquid containing the organic iodine compound can be deiodinated easily, with high yield and economically, and iodine can be recovered by the known steam distillation method. This has a great advantage.

[0016]

EXAMPLES Next, the method of the present invention will be specifically described by way of examples.

Example 1 As a sample waste liquid, a purified waste liquid generated during the process for producing iohexol having the following composition was used.

[0018]

[Table 1]

The organic iodine compound in this waste liquid is iohexol (5- (N-2-hydroxypropylacedamide) -2,4,6-triiodo-N,
N'-bis (2,3-dihydroxypropyl)
-Isophthalamide) and the organic solvent is 2-
Methoxyethanol and isopropyl alcohol.

100 g of this waste liquid, 32 g of iodine and 200 ml of city water were charged into a reactor and mixed well. Next, 294 ml of 50 wt% sodium hydroxide solution was added to adjust the sodium hydroxide concentration in the treatment waste liquid to 30 wt%. While stirring this treatment liquid, heat it from the outside to keep the liquid temperature at 120 ° C.
And reacted for 5 hours. The deiodination rate of the organic iodine compound after the reaction was 99%. After the completion of the deiodination reaction, 1,500 ml of city water was added to bring the liquid temperature to 40 ° C. and 70% by weight.
The pH was adjusted to 3.5 by adding sulfuric acid. This waste liquid was charged into a steam distillation apparatus, and a 12 wt% sodium hypochlorite solution was added until the oxidation-reduction potential reached +650 mv to make all iodine ions free iodine. 12% by weight sodium hypochlorite solution addition amount (effective chlorine concentration: 138 g /
1) was 70 ml. After adding 12 wt% sodium hypozincate solution, add 70 wt% sulfuric acid again
Adjusted to 3.5. Next, while heating the steam distillation apparatus, steam having a pressure of 1 kg / cm ² and a temperature of 100 ° C. was introduced to distill free iodine. The amount of water vapor required for distilling iodine was 60 g, which was 1.59 times the theoretical amount.
The amount of iodine in the waste liquid after distillation was 0.31 g, and the distillation rate was 99%. The distilled iodine was dissolved and absorbed with 525 ml of a 3 wt% sodium bisulfite solution to obtain a hydroiodic acid solution.

Chlorine gas was blown into the hydroiodic acid solution to cause crystals of iodine to break out, and the crystals were placed in a pressure kettle equipped with a jacket and melted at a pressure of 2 kg / cm ² and a temperature of 130 ° C. for 5 hours. Then, 31.37 g of iodine crystals were taken out by air cooling to obtain a purified iodine product. The iodine recovery rate in the treated waste liquid was 98.0%.

[0022]

Industrial Applicability According to the method of the present invention, the organic iodine compound of the waste liquid containing the organic iodine compound can be deiodinated with iodine economically in high yield, and separated and purified by using the steam distillation method. It is possible to manufacture high-purity refined iodine products.

Claims (1)

[Claims] 1. An organic iodine compound in a waste liquid containing an organic iodine compound is deiodinated by a thermal decomposition reaction under strong alkalinity to form iodine ions, which are then oxidized under acidic conditions to separate and purify the liberated iodine. Iodine recovery method.