JP2001247989A - Method for electrolyzing alkali chloride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preventing the deterioration of electrolytic performance with time to the utmost at the time of electrolyzing an aqueous alkali chloride solution mixed with recovered hydrochloric acid by an ion- exchange membrane process and/or an aqueous solution of by-produced alkali chloride recovered from a reaction solution subjected to the dehydrochlorination reaction of an organochlorine compound by detecting an index of organic impurity concentration in an aqueous alkali chloride solution correlated to the deterioration of electrolytic performance with time and imparting the tolerance indicated by the index. SOLUTION: The organic impurity concentration, expressed in terms of tetrachlorobutane, quantitatively analyzed by ECD-GC in the aqueous alkali chloride solution is controlled to <100 ppb, prefrably to <10 ppb, and the solution is electrolyzed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for electrolyzing alkali chloride using an ion exchange membrane. More specifically, the present invention relates to a method for preparing an organic chlorine compound using an aqueous alkali chloride solution to which hydrochloric acid recovered from a synthesis reaction and / or a decomposition reaction of an organic chlorine compound is added and / or an alkali hydroxide as a dehydrochlorinating agent. The present invention relates to a method for electrolyzing alkali chloride using an aqueous solution of by-produced alkali chloride recovered from a reaction solution having undergone a dehydrochlorination reaction.

[0002]

2. Description of the Related Art The ion exchange membrane method as a method for producing chlorine and alkali hydroxide by electrolyzing alkali chloride is more effective than the mercury method and the diaphragm method from the viewpoints of pollution prevention and energy saving, and furthermore, the alkali chloride content is reduced. It is currently the mainstream in Japan because of its ability to obtain low quality alkali hydroxide. When performing alkali chloride electrolysis using an ion exchange membrane, an alkali chloride aqueous solution having a high purity is required.

However, as for the organic impurities contained in the aqueous alkali chloride solution, Japanese Unexamined Patent Publication No. Sho 53-5099 discloses a method for removing organic impurities from an aqueous alkali chloride solution using activated carbon. With respect to the concentration of organic impurities in the aqueous alkali chloride solution, only the change in COD (chemical oxygen demand) before and after the treatment is described, and no description is given of the allowable range. Indeed, judging from the examples of JP-A-53-5099, one criterion is that the concentration of organic impurities in the aqueous alkali chloride solution in the diaphragm method is not more than 5 mg / L of COD. Although the use of an ion exchange membrane, which is an organic substance, is considered to have a greater adverse effect on the electrolysis performance of organic impurities in an alkali chloride aqueous solution, the allowable range of the ion exchange membrane method is limited. It was not clear.

[0004] During the electrolysis of alkali chloride, hydrochloric acid is often added to adjust the pH of the aqueous alkali chloride solution. As the hydrochloric acid, there may be used hydrochloric acid produced as a by-product during a synthesis reaction of an organic chlorine compound or hydrochloric acid generated by a decomposition reaction of an organic chlorine compound. Since such hydrochloric acid often contains organic impurities, when performing electrolysis of alkali chloride by an ion-exchange membrane method using an alkali chloride aqueous solution to which such recovered hydrochloric acid is added, particularly, an aqueous solution of an alkali chloride is used. It was necessary to clarify the allowable range of the concentration of the organic impurities therein.

On the other hand, vinylidene chloride, epoxy resin and the like, which are raw materials of vinylidene chloride resin, which are consumed in large quantities as useful materials, are produced using alkali hydroxide as a dehydrochlorinating agent. In this case, an alkali chloride in an equimolar amount to the alkali hydroxide used is produced as a by-product. From the viewpoint of resource saving,
It is very beneficial to recover these by-produced alkali chlorides in the form of an aqueous alkali chloride solution for electrolysis.

Using alkali hydroxide as a dehydrochlorinating agent,
Several studies have been made on a method for recovering an aqueous solution of alkali chloride produced as a by-product when performing a dehydrochlorination reaction of organic substances for electrolysis. For example, Japanese Patent Application Laid-Open No. 57-51101
Japanese Unexamined Patent Application Publication No. HEI 9-133, discloses an aqueous solution of by-produced alkali chloride for performing a dehydrochlorination reaction of 1,1,2-trichloroethane with an alkali hydroxide solution and recovering an aqueous solution of alkali chloride by-produced when producing vinylidene chloride for electrolysis. Has been proposed. In this proposal, COD is also mentioned as an index of the amount of organic impurities in the aqueous alkali chloride solution for electrolysis, and in the case of the diaphragm method, the COD in the generally used aqueous alkali chloride solution is 15 ppm or less. Have been.

Further, in order to carry out a dehydrochlorination reaction of 1,1,2-trichloroethane with an alkali hydroxide solution and to recover an alkali chloride aqueous solution by-produced when vinylidene chloride is produced, it is necessary to use chlorinated carbonic acid. After the hydrogen is removed by distillation, a special treatment is required as a secondary treatment in which the hydrogen is brought into contact with an alkali hypochlorite solution in the presence of nickel oxide. It is described that by performing this treatment, the COD in the aqueous alkali chloride solution can be reduced to 15 ppm or less, and this can also be used for electrolysis by an ion exchange membrane method. However, the causative substance of COD is not completely known, and COD cannot be reduced to 15 ppm or less. Therefore, as secondary treatment of aqueous by-product alkali chloride, activated carbon or the like that is often used for secondary treatment of organic substances is usually used. It is described that the use of an adsorbent is not appropriate.

Further, the examples and comparative examples of the Japanese Patent Application Laid-Open No. 57-51101 describe the CO 2 in the aqueous alkali chloride solution when the secondary treatment as described above is performed.
This is only the D value, and there is no description indicating what the electrolysis performance will be when the by-product alkali chloride aqueous solution actually subjected to such secondary treatment is used for electrolysis by the ion exchange membrane method. . Therefore, when performing electrolysis of alkali chloride using an ion-exchange membrane, if the concentration of organic impurities in the alkali chloride aqueous solution is set to 15 ppm or less of COD, it is possible to prevent reduction in electrolysis performance as much as possible. At present, it has not been clarified whether or not it is truly appropriate to use COD as an index indicating the allowable range of the organic impurity concentration in order to prevent the reduction of the concentration as much as possible.

[0009]

SUMMARY OF THE INVENTION The present invention relates to an alkali chloride aqueous solution to which hydrochloric acid recovered from a synthesis reaction and / or a decomposition reaction of an organic chlorine compound is added by an ion exchange membrane method.
And / or when performing the electrolysis of the by-product alkali chloride aqueous solution recovered from the reaction solution after performing the dehydrochlorination reaction of the organic chlorine compound using alkali hydroxide as the dehydrochlorinating agent, Using the concentration of organic impurities detected by gas chromatography (GC) as an index,
An object of the present invention is to provide a method capable of preventing a decrease in electrolytic performance as much as possible by setting the allowable range.

[0010]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors first examined the relationship between the COD value of an aqueous alkali chloride solution and the electrolytic performance of alkali chloride by an ion exchange membrane method. As a result, the phenomenon that the COD value of the alkali chloride aqueous solution is increased despite the fact that the current efficiency during the alkali chloride electrolysis is suppressed by treating the alkali chloride aqueous solution with activated carbon is recognized. Was done. For an aqueous solution of alkali chloride having a COD value of 1 mg / L or less, CO
It has also proven difficult to measure D. Therefore, in the electrolysis of alkali chloride by the ion-exchange membrane method, it was found that COD was not suitable as an index of organic impurities in the aqueous alkali chloride solution that adversely affected the electrolytic performance. We decided to investigate a method for quantitatively analyzing organic impurities in the sample with higher precision.

[0011] Therefore, the reaction solution after the vinylidene chloride formation reaction by the dehydrochlorination reaction of 1,1,2-trichloroethane is performed by using alkali hydroxide as a dehydrochlorinating agent, and the resulting by-product is subjected to steam distillation. The trace organic impurities contained in the aqueous alkali chloride solution were analyzed by GC or the like. As a result, trace organic impurities in the by-product aqueous alkali chloride solution are mainly composed of tetrachlorobutane, which is considered to be caused by impurities in the raw material 1,1,2-trichloroethane, and have various types of carbon atoms of 2 to 2. It has been found that it consists of six chlorine compounds and the like.

Furthermore, gas chromatography (ECD) with an electron capture detector having high detection sensitivity to chlorine compounds
-GC), the concentration of trace organic substances in the aqueous alkali chloride solution in terms of tetrachlorobutane as the main component was calculated as ppb
A method for quantitative analysis with high precision on the order was established. As a result of measurement by this quantitative analysis method, it was confirmed that although depending on the conditions of steam distillation, the by-product aqueous alkali chloride solution after steam distillation contained 1,000 to 6,000 ppb of organic impurities in terms of tetrachlorobutane.

On the other hand, the reaction liquid after the reaction of producing vinylidene chloride by dehydrochlorination of 1,1,2-trichloroethane using alkali hydroxide as a dehydrochlorinating agent was separated into an organic phase and an aqueous phase. . A low-boiling substance such as 1,1,2-trichloroethane is distilled off from the unreacted organic phase containing 1,1,2-trichloroethane as a main component by using an evaporator, so that tetrachlorobutane is used as a bottom liquid. A sample having substantially the same composition as the trace organic impurities in the recovered aqueous alkali chloride solution was obtained. The thus obtained sample containing tetrachlorobutane as a main component was added to and dissolved in an aqueous alkali chloride solution prepared by dissolving a reagent-grade alkali chloride, and then passed through a chelate resin. Was carried out to examine the effect of the concentration of organic impurities in terms of tetrachlorobutane detected by ECD-GC in an aqueous solution of alkali chloride on electrolysis performance. Further, by using alkali hydroxide as a dehydrochlorinating agent and performing a reaction for producing vinylidene chloride by a dehydrochlorination reaction of 1,1,2-trichloroethane, a by-product aqueous alkali chloride solution obtained by steam distillation of a reaction solution obtained by steam distillation of the reaction solution. Was further subjected to activated carbon treatment or distillation to reduce the concentration of organic impurities detected by the contained ECD-GC, and then an electrolysis confirmation experiment of alkali chloride using an ion exchange membrane was performed.

As a result of the above-mentioned detailed studies, the present inventors have found that, when the electrolysis of alkali chloride is carried out by the ion-exchange membrane method, an organic compound in an aqueous solution of alkali chloride which adversely affects the electrolytic performance of the ion-exchange membrane is used. As an index of the impurity concentration, it was found that an organic impurity concentration in terms of tetrachlorobutane, which was quantitatively analyzed by ECD-GC, was effective. Furthermore, a correlation between the concentration of organic impurities when using this index present in an aqueous alkali chloride solution and the time-dependent decrease in the current efficiency of an ion exchange membrane, which is one of the indexes of electrolytic performance, was found. The present invention has been made.

That is, the present invention provides an aqueous solution of an alkali chloride to which recovered hydrochloric acid is added from a synthesis reaction and / or a decomposition reaction of an organic chlorine compound, and / or an alkali chloride is used as a dehydrochlorinating agent. Using a by-product alkali chloride aqueous solution recovered from the reaction solution after performing the dehydrochlorination reaction, by performing electrolysis of alkali chloride with an ion exchange membrane, in a method of obtaining chlorine and alkali hydroxide, GC
Wherein the concentration of the organic impurities detected in step (a) is less than 100 ppb. In particular, using sodium hydroxide as a dehydrochlorinating agent,
This is an effective method for electrolyzing alkali chloride when using a by-product salt solution (by-product sodium chloride aqueous solution) recovered from the reaction solution after the vinylidene chloride generation reaction by dehydrochlorination of 1,1,2-trichloroethane. .

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. As the ion exchange membrane used in the present invention, any fluorocarbon cation exchange membrane having a carboxylic acid group and / or a sulfonic acid group usable for electrolysis of alkali chloride can be used. It is preferred to use a perfluorocation exchange membrane that shares sulfonic acid and sulfonic acid groups. The ion exchange membrane used in the present invention has a total thickness of 80 to 350 μm, preferably 100 to 300 μm. Also, if necessary,
Preferably, it can be reinforced with a reinforcing woven fabric such as a cloth or a net made of polytetrafluoroethylene or the like, a nonwoven fabric or a metal mesh, a porous body, or the like.

Further, as is well known, the gas generated by electrolysis adheres to the film surface, which causes an increase in electrolysis voltage. As a method for preventing the gas from adhering to the film surface to prevent this, a method of roughening the film surface or a layer composed of inorganic particles and a binder component on the film surface (hereinafter referred to as an inorganic layer) Is preferable in the present invention since the effect of preventing gas adhesion is remarkable.

As the electrolysis conditions of the present invention, known electrolysis conditions of alkali chloride can be employed. Specifically, an alkali hydroxide aqueous solution having a concentration of 140 to 300 g / L is supplied to the anode side, and water is added to the cathode side to make the alkali hydroxide concentration 23 to 40%, and 5 to 60 A /
It can be performed at a current density of dm ² and an electrolysis temperature of 50 to 110 ° C. The term “recovered hydrochloric acid from the synthesis reaction of an organic chlorine compound” as used in the present invention may be any one as long as hydrochloric acid by-produced when synthesizing the organic chlorine compound is recovered. Examples thereof include those obtained by recovering hydrochloric acid by-produced in reacting chlorine and isobutylene to synthesize methallyl chloride.

The term "recovered hydrochloric acid from the decomposition reaction of an organochlorine compound" as used in the present invention refers to a solution obtained by recovering hydrochloric acid generated by a decomposition reaction of an organochlorine compound caused by the presence of an organochlorine compound at a high temperature. Anything is fine. Examples thereof include those in which hydrochloric acid generated by decomposition during incineration of an organic chlorine compound is recovered. These recovered hydrochloric acid may be added to the alkali chloride aqueous solution in order to adjust the pH of the alkali chloride aqueous solution in any of the steps of the alkali chloride electrolysis. For example, when recycling an alkali chloride aqueous solution having a reduced alkali chloride concentration due to electrolysis leaving the electrolytic cell and using it again for electrolysis, it may be added to release chlorine dissolved in the alkali chloride aqueous solution. is there. As described above, the present invention is applied in any case where the recovered hydrochloric acid is added to the aqueous alkali chloride solution used for the electrolysis of the alkali chloride.

The "alkali hydroxide" in the present invention includes sodium hydroxide and potassium hydroxide.
As an example of the term "aqueous by-product aqueous alkali chloride solution recovered from the reaction solution after performing a dehydrochlorination reaction of an organic chlorine compound using alkali hydroxide as a dehydrochlorinating agent" in the present invention, a chlorohydrin group is reacted with an alkali hydroxide. By-product alkali chloride aqueous solution recovered in the reaction to produce an epoxy group,
More specifically, a by-product salt solution and the like recovered in the reaction of forming an epoxy resin by the reaction of bisphenol A, epichlorohydrin and sodium hydroxide can be mentioned. Preferred is a by-product saline solution that is recovered in the reaction of 1,1,2-trichloroethane with sodium hydroxide to produce vinylidene chloride.

In the present invention, "G in aqueous solution of alkali chloride"
The “concentration of the organic impurities detected in C” is a value measured by the following quantitative analysis. First, 550 g of an aqueous alkali chloride solution for measuring the concentration of an organic impurity detected by GC is sampled. To this, 15 g of hexane (grade for high performance liquid chromatography) is added, and the mixture is shaken with a shaker for 30 minutes to perform hexane extraction. Inject 2 μL of this hexane extract and add ECD-G
Perform C analysis.

The ECD-GC analysis conditions were as follows: detector temperature: 230 ° C., injection (In)
Jection temperature: 230 ° C, Column (Col)
temperature) 60 ° C. → 100 ° C. Heating rate + 2 ° C. /
After the temperature is raised for one minute, the temperature is held at 100 ° C., and the analysis time is 60 minutes. The column (Collum) is a sintered silica capillary column (Bonded Fused Silica Cap).
illary Collumn), 0.53 mmI.
D. × 25m × 1.0μm methyl silicone (Met
yl Silicone: manufactured by Tokyo Chemical Industry Co., Ltd.).

[0023] Among the peaks recorded in the obtained GC chart, the retention time is 2.5 minutes or more, and the hexane observed in the GC chart when the ECD-GC analysis of only hexane was performed as a reference under the same conditions. The peak area of the remaining peaks excluding the derived peak is determined. By multiplying the peak area by a factor obtained from an absolute calibration curve of tetrachlorobutane prepared in advance, the concentration of organic impurities detected by GC in the hexane extract in terms of tetrachlorobutane is obtained. This concentration is multiplied by the amount of hexane added at the time of hexane extraction and divided by the weight of the aqueous alkali chloride solution to obtain the concentration of organic impurities detected by GC in the aqueous alkali chloride solution in terms of tetrachlorobutane. Find the value. That is, the “concentration of organic impurities detected by GC in the aqueous alkali chloride solution” referred to in the present invention is defined under the above-mentioned certain conditions.
It is the concentration of the organic substance contained in the aqueous solution of alkali chloride in terms of tetrachlorobutane obtained from the peak area of the organic substance detected by ECD-GC.

In the present invention, when chlorine and alkali hydroxide are obtained by electrolysis of alkali chloride using an ion exchange membrane, the concentration of organic impurities detected by GC in the aqueous alkali chloride solution is less than 100 ppb, preferably 10 ppb.
By limiting the value to less than b, it is possible to prevent the current efficiency of the ion exchange membrane from decreasing with time during alkali chloride electrolysis as much as possible. In this case, if the concentration of the organic impurities detected by GC in the aqueous alkali chloride solution is 100 ppb or more, the current efficiency of the ion exchange membrane during the electrolysis of alkaline chloride is greatly reduced. The reason for this is not clear, but the organic impurities in the aqueous alkali chloride solution are adsorbed to the ion exchange membrane, and this is accumulated, leading to a reduction in the current efficiency of the ion exchange membrane during electrolysis with time. It is considered to be. On the other hand, when the concentration of organic impurities detected by GC in the aqueous alkali chloride solution is 100
At less than ppb, adsorption of organic impurities in the aqueous alkali chloride solution onto the ion-exchange membrane hardly occurs, so that it is considered that the temporal reduction in current efficiency of the ion-exchange membrane during alkali chloride electrolysis is significantly suppressed. .

In the present invention, in obtaining chlorine and alkali hydroxide by electrolysis of alkali chloride using an ion exchange membrane, the lower limit of the concentration of organic impurities detected by GC in the aqueous alkali chloride solution is as follows. There is no particular limitation from the viewpoint of suppressing a temporal decrease in the current efficiency of the ion exchange membrane in the above. However, in order to significantly reduce the concentration of organic impurities detected by GC in the aqueous alkali chloride solution, a great deal of cost is required. Considering the economic feasibility of balancing the cost of removing the detected organic impurities,
It is preferably at least 0.1 ppb.

As a method for reducing the concentration of organic impurities detected by GC in an aqueous alkali chloride solution, inorganic impurities such as magnesium ions, calcium ions, and sulfate ions in the aqueous alkali chloride solution are reduced by using an alkali agent such as sodium hydroxide or the like. When an inorganic coagulant such as polyaluminum chloride or a polymer coagulant such as polyacrylamide is used to precipitate a hardly soluble hydroxide or carbonate by adding a carbonate such as barium carbonate, alkali chloride is added. A coagulation sedimentation method by adding a drug, which can co-precipitate an organic impurity detected by GC in an aqueous solution, may be mentioned.

When an alkali hydroxide is used as a dehydrochlorinating agent and an aqueous solution of by-produced alkali chloride is recovered from the reaction solution after the dechlorination reaction of the organic chlorine compound, the reaction solution is usually treated with an organic phase. After decantation to an aqueous phase, an operation such as steam distillation of the aqueous phase is performed.
Organic impurities detected by GC of 000 ppb or more are included. As described above, when the alkali chloride aqueous solution contains a large amount of organic impurities detected by GC, activated carbon removes organic substances detected by GC and further removes organic substances detected by GC. By distilling the organic impurities, the concentration of the organic impurities detected by GC in the aqueous alkali chloride solution can be reduced. The conditions of these operations are appropriately set, and if necessary, by combining these operations, the concentration of organic impurities detected by GC in the aqueous alkali chloride solution can be reduced to 100 pp.
A reduction to the required level of less than b is achieved.

[0028]

The present invention will be described more specifically below with reference to examples and comparative examples. [Preparation of tetrachlorobutane (sample A)] A volume of 9 L equipped with an overflow tube and a reflux condenser
1 in a continuous flow reactor with a stirring blade (retention volume 6 L)
1,2-trichloroethane (synthesized by reacting vinyl chloride monomer with chlorine using ferric chloride as a catalyst)
Was introduced at a rate of 140 g / min from a 125 g / min, 3.2 mol / L aqueous sodium hydroxide solution (reagent grade: prepared by dissolving sodium hydroxide manufactured by Wako Pure Chemical Industries, Ltd. in distilled water). The temperature was brought to 75 ° C. by heating, hot water of about 55 ° C. was passed through a reflux condenser, and the reaction was carried out while stirring the reaction vessel at a stirring rotation speed of 450 rpm.
Vinylidene chloride, a reaction product distilled off from the top of the reflux condenser, was liquefied in a condenser and collected in an externally cooled tank. The reaction solution overflowing from the continuous flow reactor was separated into an upper aqueous phase and a lower organic phase by a decanter, and each was collected. The collected organic phase was subjected to evaporator pressure: 125 mmHg, temperature:
After concentration under reduced pressure at 100 ° C., distillation under reduced pressure was carried out with an Alder-Show distillation apparatus. Pressure: 100mmH
g, bottom temperature 149.6 ° C, top temperature 134.7 ° C
By collecting the fraction distilled in the above step, the purity is 98.
11% of tetrachlorobutane (sample A) was obtained.

[Preparation of Model Sample of Organic Impurity in Alkaline Chloride Aqueous Solution (Sample B)] A 1,2,1 L continuous flow reactor (retention volume 6 L) equipped with an overflow tube and a reflux condenser and having a volume of 9 L with stirring blades was installed. 125 g of trichloroethane (synthesized by reacting vinyl chloride monomer with chlorine using ferric chloride as a catalyst)
/ Minute, 3.2 mol / L aqueous sodium hydroxide solution (special grade reagent: prepared by dissolving sodium hydroxide manufactured by Wako Pure Chemical Industries, Ltd. in distilled water) at 140 g / minute, and the reaction temperature was increased by external heating. 75 ° C, hot water of about 55 ° C is passed through the reflux condenser, and the stirring rotation speed is 450r.
The reaction was carried out while stirring the reactor at pm. Vinylidene chloride, a reaction product distilled off from the top of the reflux condenser, was liquefied in a condenser and collected in an externally cooled tank. The reaction solution overflowing from the continuous flow reactor was separated into an upper aqueous phase and a lower organic phase by a decanter, and each was collected. The collected organic phase was concentrated under reduced pressure using an evaporator under the conditions of a pressure of 125 mmHg and a temperature of 125 ° C. until no distillate remained. According to the ECD-GC analysis, the composition of the thus obtained concentrated liquid (sample B) was almost the same as that of the trace organic impurities contained in the by-product saline solution of Comparative Example 2 described later.

[Method of Measuring Organic Impurity Concentration Detected by GC in Aqueous Alkali Chloride Solution] In the following Examples and Comparative Examples, “the concentration of organic impurities detected by GC in an aqueous alkali chloride solution” was determined by the following method. This is a value obtained as a result of measurement by an analytical method. 550 g (0.0%) of an aqueous alkali chloride solution for measuring the concentration of organic impurities detected by GC.
(Measured in units of 1 g). To this, 15 g (weighed in units of 0.01 g) of hexane (grade for high performance liquid chromatography: manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the mixture was shaken with a shaker for 30 minutes.
Hexane extraction was performed. 2 μL of this hexane extract was injected, and ECD-GC (GAS CHROMATOGRA
PH G2800: manufactured by Yanaco).

The ECD-GC analysis conditions were as follows: detector temperature: 230 ° C., injection (In)
Jection temperature: 230 ° C, Column (Col)
temperature) 60 ° C. → 100 ° C. Heating rate + 2 ° C. /
Min After the temperature was raised, the temperature was held at 100 ° C., and the analysis time was 60 minutes. The column is a sintered silica capillary column (Bonde
d Fused SilicaCapillary C
ollum), 0.53 mm D. × 25m
− × 1.0 μm methyl silicone (Metyl S
ilicone): manufactured by Tokyo Chemical Industry.

Among the peaks recorded in the obtained GC chart, the retention time was 2.5 minutes or more, and ECD-GC of hexane alone was used as a reference under the same conditions.
The peak area of the peak other than the peak derived from hexane observed in the GC chart when the analysis was performed was determined. By multiplying this peak area by a factor obtained from an absolute calibration curve of tetrachlorobutane prepared in advance (using sample A obtained by the above-described method), organic impurities detected by GC in the hexane extract are multiplied. Was calculated in terms of tetrachlorobutane. This concentration is multiplied by the amount of hexane added at the time of hexane extraction and divided by the weight of the aqueous alkali chloride solution to obtain the concentration of organic impurities detected by GC in the aqueous alkali chloride solution in terms of tetrachlorobutane. The value was determined.

[Analytical Method of Metal Ions in Alkali Chloride Aqueous Solution] In the following Examples and Comparative Examples, analysis of metal elements such as Ba, Fe, Ca and Mg in an alkali chloride aqueous solution was carried out by I
CP (Inductive coupled plus)
ma) Using an apparatus (ICP-1000III).

[Electrolytic Experiment of Alkali Chloride] The alkaline chloride electrolysis experiment in the following Examples and Comparative Examples was carried out by the following method. ACIPLE as the ion exchange membrane
X (trademark) F4202 (manufactured by Asahi Kasei Corporation) was used. A low hydrogen overvoltage cathode is disposed on the carboxylic acid layer side of the ion exchange resin membrane, and a low chlorine overvoltage anode is disposed on the sulfonic acid layer side. The current density is 40 A / L while adjusting the concentration of the aqueous alkali chloride solution on the anode side to 205 g / L. Electrolysis was performed at dm ² , a temperature of 90 ° C., and an alkali concentration of 33 wt%. For the aqueous alkali chloride solution, electrolysis was performed using the aqueous alkali chloride solution of Reference Example 1 described later for the first 14 days, and the current efficiency after 14 days was measured. Initial current efficiency (current efficiency after 14 days) is 97.
After confirming that it was 5% ± 0.5%, the current efficiency after 120 days was measured using the alkaline chloride aqueous solution described in each Example and Comparative Example, and the current efficiency was compared with the initial current efficiency in each experiment. The difference was defined as a decrease in current efficiency.

Reference Example 1 Salt (special grade of reagent: Wako Pure Chemical Industries, Ltd.) was dissolved in distilled water to prepare a salt solution having a salt concentration of 310 g / L. Ba, F after passing this salt solution through a chelating resin (Duolite C467: manufactured by Sumitomo Chemical)
Each of the concentrations of e, Ca, and Mg was 5 ppb or less. Using the saline solution passed through the chelating resin, the initial current efficiency in the following Examples and Comparative Examples was confirmed.

Example 1 To a saline solution prepared in the same manner as in Reference Example 1, 100 ppb of Sample B was added and dissolved by stirring. This salt solution was passed through B after passing through the chelating resin.
Each concentration of a, Fe, Ca, and Mg was 5 ppb or less. The concentration of the organic impurities detected by GC was 95 ppb. It is considered that the reason why the concentration of the organic impurities was decreased by passing through the chelate resin was that the organic impurities in the saline solution were adsorbed by the chelate resin. Using the saline solution passed through the chelate resin, an electrolysis experiment of sodium chloride was performed. Table 1 shows the results.

Comparative Example 1 To a saline solution prepared in the same manner as in Reference Example 1, 1000 ppb of Sample B was added and dissolved by stirring. This salt solution was passed through B after passing through the chelating resin.
Each concentration of a, Fe, Ca, and Mg was 5 ppb or less. The concentration of the organic impurities detected by GC was 850 ppb. An electrolysis experiment of salt was carried out using the saline solution passed through the chelate resin. Table 1 shows the results.

(Comparative Example 2) A 1,1,2-trichloroethane (ferric chloride as a catalyst) was used in a 9 L continuous flow reactor equipped with a stirring blade equipped with an overflow tube and a reflux condenser (retention volume: 6 L). 125 g / synthesized by reacting vinyl monomer with chlorine)
Aqueous solution of sodium hydroxide (reagent grade: prepared by dissolving sodium hydroxide manufactured by Wako Pure Chemical Industries in distilled water) at 140 g / min, and the reaction temperature was increased to 75 by external heating. ° C, circulate hot water of about 55 ° C through the reflux condenser and stir at 450 rpm.
The reaction was carried out while stirring the reaction vessel at m. Vinylidene chloride, a reaction product distilled off from the top of the reflux condenser, was liquefied in a condenser and collected in an externally cooled tank. The reaction solution overflowing from the continuous flow reactor was separated into an upper aqueous phase and a lower organic phase by a decanter, and each was collected.

The collected aqueous phase was subjected to a steam distillation apparatus (height: 1).
650 mm, inner diameter: 50 mm, filler: Raschig ring)
While blowing ² kg / cm ² steam,
After performing continuous steam distillation while controlling the bottom temperature at 104 ° C. and the top temperature at 98 ° C., the distillate from the bottom was filtered with a 1 μm mesh filter. The salt concentration of the by-product saline solution thus obtained is 130 g / L.
Met. This salt solution contains salt (special grade reagent: Wako Pure Chemical Industries)
Was added and dissolved to prepare a salt solution having a salt concentration of 310 g / L. Each of the concentrations of Ba, Fe, Ca, and Mg after passing the salt solution through the chelating resin was 5 p.
pb or less. The concentration of the organic impurity detected by GC was 1100 ppb. An electrolysis experiment of salt was carried out using the saline solution passed through the chelate resin. Table 1 shows the results.

(Example 2) The adjusted saline solution was activated carbon (C
W-130: manufactured by Nimura Chemical Co., Ltd.), and the same procedure as in Comparative Example 2 was carried out except that the organic impurities in the saline solution were removed by adsorption. Ba, F in saline solution after passing through chelating resin
Each of the concentrations of e, Ca, and Mg was 5 ppb or less. The concentration of organic impurities detected by GC is 9 p.
pb. An electrolysis experiment of salt was carried out using the saline solution passed through the chelate resin. Table 1 shows the results.
Shown in

Example 3 By-product salt solution was obtained in the same manner as in Comparative Example 2. The salt solution was further subjected to continuous distillation in an Alder-Show type distillation apparatus while controlling the bottom temperature at 103 ° C. and the amount of distillate from the top to 30% of the feed liquid, and trapped the effluent from the bottom. Gathered. The salt concentration of the obtained secondary purified saline was 186 g / L. Salt (special grade of reagent: manufactured by Wako Pure Chemical Industries, Ltd.) was added and dissolved in this saline to prepare a salt water having a salt concentration of 310 g / L. Ba, Fe, C after passing the salt solution through the chelating resin.
Each of the concentrations of a and Mg was 5 ppb or less. The concentration of organic impurities detected by GC is 23 ppb
Met. An electrolysis experiment of salt was carried out using the saline solution passed through the chelate resin. Table 1 shows the results.

[0042]

[Table 1] As is clear from Table 1, when the electrolysis of alkali chloride is carried out using an ion exchange membrane, when the concentration of organic impurities detected by GC in the aqueous alkali chloride solution is 100 ppb or more, the current efficiency after 3 months When the concentration of organic impurities detected by GC in the aqueous alkali chloride solution is less than 100 ppb, the decrease in current efficiency after three months can be considerably suppressed. In particular, when the concentration of organic impurities detected by GC in the alkali chloride aqueous solution is less than 10 ppb, the current efficiency hardly decreases after three months.

[0043]

As described above, according to the method of the present invention, when electrolyzing alkali chloride using an ion exchange membrane,
Since the concentration of organic impurities detected by GC in the aqueous alkali chloride solution is less than 100 ppb, it is possible to prevent the electrolytic performance of the ion exchange membrane from decreasing over time as much as possible, which is extremely useful industrially. In particular, in the method of the present invention, sodium hydroxide is used as a dehydrochlorinating agent, and a by-product salt solution recovered from a reaction solution after a vinylidene chloride generation reaction is performed by a dehydrochlorination reaction of 1,1,2-trichloroethane. It is extremely useful when used, and is also preferable from the viewpoint of resource saving.

[Brief description of the drawings]

FIG. 1 is a graph showing an ECD-value obtained by measuring an organic impurity concentration detected by GC in a saline solution used in an electrolysis experiment in Example 2.
It is a GC chart.

FIG. 2 is a graph showing an ECD-value obtained by measuring an organic impurity concentration detected by GC in a saline solution used in the electrolysis experiment of Comparative Example 2.
It is a GC chart.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hiroyoshi Takarada 6-4100 Asahicho, Nobeoka-shi, Miyazaki F-term in Asahi Kasei Kogyo Co., Ltd. 4K021 AA03 AB01 BA03 BC01 DB31

Claims (2)

[Claims] An alkali chloride aqueous solution to which recovered hydrochloric acid is added from a synthesis reaction and / or a decomposition reaction of an organic chlorine compound and / or an alkali hydroxide is used as a dehydrochlorinating agent to carry out a dehydrochlorination reaction of the organic chlorine compound. In a method of obtaining chlorine and alkali hydroxide by performing electrolysis of alkali chloride by an ion exchange membrane using a by-product alkali chloride aqueous solution recovered from the reaction solution after the reaction, gas chromatography in an alkali chloride aqueous solution is performed by gas chromatography. An electrolysis method of an alkali chloride, wherein a concentration of an organic impurity to be detected is less than 100 ppb. 2. An aqueous solution of sodium chloride as a by-product recovered from a reaction solution after a reaction for producing vinylidene chloride by a dehydrochlorination reaction of 1,1,2-trichloroethane using sodium hydroxide as a dehydrochlorinating agent. 2. The method for electrolyzing alkali chloride according to claim 1, wherein: