JPS6313933B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a purified aqueous alkali chloride solution from an aqueous alkali chloride solution obtained by the dehydrochlorination reaction of 1,1,2-trichloroethane. The purpose is to produce an alkaline aqueous solution. In recent years, there has been a remarkable progress in the production of chlorinated hydrocarbons, and the use of chlorinated organic solvents such as 1,1,1-trichloroethane, trichlorethylene, and perchlorethylene, and resins such as polyvinyl chloride and polyvinylidene chloride has become extremely difficult. It is becoming abundant. Vinylidene chloride, a chlorinated hydrocarbon, is also being produced in increasing quantities. Vinylidene chloride is also used as a raw material for polyvinylidene chloride resin.
It is produced in large quantities as an intermediate raw material for trichloroethane. The method for producing vinylidene chloride is generally a method of dehydrochlorinating 1,1,2-trichloroethane with an aqueous alkali solution, and usually an aqueous calcium hydroxide solution is used as the aqueous alkali solution. The reaction using calcium hydroxide in the production of vinylidene chloride proceeds as shown in the following formula: CH ₂ C・CHC ₂ + 1/2Ca(OH) ₂ → CH ₂ = CC ₂ + 1/2CaC ₂ + H ₂ O −(1) The target vinylidene chloride can be obtained with almost 100% selectivity. However, the released hydrogen chloride is neutralized with calcium hydroxide and is discarded as calcium chloride as shown in equation (1). The reality is that in exchange for selectively obtaining vinylidene chloride, equimolar amounts of hydrochloric acid are lost. From the viewpoint of resource conservation, this hydrochloric acid content needs to be effectively recovered. For example, if the dehydrochloric acid reaction is performed using sodium hydroxide instead of calcium hydroxide, the released hydrochloric acid becomes sodium chloride as shown in equation (2). CH ₂ C・CHC ₂ +NaOH→ CH ₂ = CC ₂ + NaC + H ₂ O −(2) Also, if the dehydrochlorination reaction is performed using potassium hydroxide instead of calcium hydroxide, potassium chloride will be produced as shown in the following equation (3). can get. CH ₂ C・CHC ₂ +KOH→ CH ₂ =CC ₂ +KC+H ₂ O −(3) If vinylidene chloride is removed from the reaction solution generated after the dehydrochloric acid reaction, an aqueous sodium chloride solution (saline solution) or an aqueous potassium chloride solution can be obtained. For example, by subjecting these to electrolysis of sodium chloride and electrolysis of potassium chloride, they can be recovered and utilized as effective chlorine. However, such a method has not yet been put into practical use. One of the reasons for this is that after performing the dehydrochlorination reaction using a caustic alkali aqueous solution, the alkali chloride aqueous solution recovered cannot be purified to a high enough degree that it can be used, for example, for electrolysis of an aqueous alkali chloride solution. be. In particular, since caustic soda is usually more expensive than calcium hydroxide, it has no industrial value unless the aqueous sodium chloride solution (saline solution) produced after the dehydrochlorination reaction is recovered and reused. When vinylidene chloride is obtained by dehydrochlorinating 1,1,2-trichloroethane with an aqueous caustic alkali solution, chlorinated hydrocarbons such as vinylidene chloride and 1,1,2-trichloroethane are present in the aqueous solution after the reaction. Since it is dissolved, it cannot be used as is. In order to perform a reaction using a caustic alkali aqueous solution and use the recovered alkali chloride aqueous solution for, for example, electrolysis, chlorinated hydrocarbons as described above must be removed. These have a negative effect on electrolytic reactions. Therefore, in order to use this recovered aqueous alkali chloride solution in electrolytic reactions, it is necessary to make it as clean as the aqueous alkali chloride solution normally used for electrolysis. The present inventors carried out intensive studies to purify the aqueous alkali chloride solution recovered when vinylidene chloride is obtained through the above-mentioned dehydrochlorination reaction using a caustic alkaline solution, and found that there were additional problems as follows. did. That is, in order to remove the chlorinated hydrocarbons in an aqueous alkali chloride solution obtained by dehydrochlorinating 1,1,2-trichloroethane with a caustic alkaline solution, the aqueous alkali chloride solution is used in the same manner as the commonly used steam distillation. There is a method of simple distillation. That is, if the alkali chloride aqueous solution is distilled and 3 to 10 wt% of its weight is distilled out, the dissolved chlorinated hydrocarbons will be distilled out together with the water, and there will be almost no remaining alkali chloride aqueous solution. . However, when we measured the COD in the aqueous alkali chloride solution after such distillation, it was found to be 50 to 100 ppm.
It turns out that it exists. This COD value differs slightly depending on the distillation rate of steam distillation, but when the distillation amount is 10
% or more, for example, 20 to 50%, and it does not decrease to the extent that dissolved alkali chloride precipitates even if it is distilled.
It is currently unknown what substance causes this COD, but the COD in the salt water used in diaphragm salt electrolysis plants is usually 15 ppm.
Therefore, in order to recover and utilize the aqueous alkali chloride solution, it is necessary to reduce the COD to 15 ppm or less. In order to reduce COD in the amount of several ppm, high-level treatment is generally performed in wastewater treatment. For example, physical treatment such as activated carbon adsorption, biological treatment such as activated sludge, or chemical treatment such as ozonolysis. However, these are not suitable for purifying the recovered aqueous alkali chloride solution obtained by this reaction. A method for purifying an aqueous alkali chloride solution not only needs to reduce COD, but also needs to be economically practicable and be able to be used for purposes such as electrolytic reactions after treatment. In this case, biological treatment is unsuitable for this purpose. Adsorbents such as activated carbon and molecular sheep were ineffective and did not reduce COD. Chemical treatments such as ozone, hydrogen peroxide and sodium hypochlorite are only slightly reduced.
For example, it is not suitable for use in the above-mentioned diaphragm method salt electrolysis. The present inventors have devoted their efforts to solving these problems, and have completed the present invention by discovering a method that can practically and economically reduce the COD in the aqueous alkali chloride solution. That is, the present invention involves removing chlorinated hydrocarbons by distillation from an aqueous alkali chloride solution obtained by dehydrochlorinating 1,1,2-trichloroethane with a caustic alkaline solution, and then removing the aqueous alkali chloride solution obtained. , a method for producing a purified aqueous alkali chloride solution, which comprises bringing the method into contact with an alkaline hypochlorite solution in the presence of nickel oxide. Describing preferred embodiments of the present invention, 1.
A reaction solution obtained by dehydrochlorinating 1,2-trichloroethane with a caustic alkaline solution is separated into an organic layer and an aqueous layer in a separation tank. The aqueous layer is an aqueous alkali chloride solution, and the recovered aqueous alkali chloride solution (containing COD 60 to 100 ppm) is obtained by performing simple distillation on this as-is, preferably to remove trace amounts of dissolved chlorinated hydrocarbons. By contacting with alkali hypochlorite in the presence of nickel oxide, a highly purified aqueous alkali chloride solution can be produced. The nickel oxide may be in the form of itself or may be supported on an inert porous material such as diatomaceous earth.
The state of the oxide may be both Ni ₂ O ₃ and NiO ₂ , but either may be used. It is thought that Ni ₂ O ₃ and NiO ₂ are alternately changed due to the presence of COD causative substances and alkali hypochlorite. As the nickel oxide, commonly available products such as those available under the trade name Panion (manufactured by Ariko Metal Co., Ltd.) can be used. Examples of alkali hypochlorite to be used in the presence of nickel oxide include sodium hypochlorite, potassium hypochlorite, etc., and the amount used is the same as the amount of oxygen indicated by COD. The amount of alkali hypochlorite that can supply the above amount of oxygen to the system may be added. In addition, as a method for contacting an aqueous alkali chloride solution with an alkali hypochlorite solution in the presence of nickel oxide, a method is to add nickel oxide and an alkali hypochlorite solution to an aqueous alkali chloride solution, and stir and mix. Another method is to fill a packed tower with nickel oxide and pass an aqueous alkali chloride solution to which an alkaline hypochlorite solution has been added through the packed tower, but other methods may also be used. When contacting with an alkaline hypochlorite solution in the presence of nickel oxide, the temperature is preferably in the range from room temperature to 80°C, and the contact time is from several minutes to several hours (in the case of a packed column type, the average residence time is 0.5 to 5 time), and the amount of nickel oxide added is preferably 1 g or more per 100 ml of recovered aqueous alkali chloride solution (in the case of a packed column type, the amount that gives a space velocity of 0.5 to 5 Hr ^-1 ). According to the present invention, a purified aqueous alkali chloride solution with a COD concentration of 15 ppm or less can be easily and smoothly obtained, and the obtained purified aqueous alkali chloride solution can be used for electrolysis such as asbestos diaphragm method, ion exchange membrane method, mercury method, and various other uses. It can be used for. Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Example 1, Comparative Example 1, and Comparative Example 2 When vinylidene chloride was produced by contacting 1,1,2-trichloroethane with a caustic soda solution to carry out a dehydrochlorination reaction, the reaction solution containing the obtained common salt was first Organic substances were separated in a separation tank, and then heated simple distillation was performed to distill out the dissolved organic substances together with water. The reaction solution was cloudy at first, but after about 3% of the total amount was distilled off, the remaining solution became clear and colorless. When this liquid was analyzed, the concentration of common salt was 303 g/, caustic soda 6 g/, and COD 65 ppm. This liquid is hereinafter referred to as recovered saline solution. Take 200 ml of this recovered saline solution into a 500 ml beaker and add a nickel peroxide-containing substance (Panion: trade name of Ariko Metal Co., Ltd., 5 mm diameter x 5 mm columnar, component: Ni ₂ O ₃ .
4.0 g of 3H ₂ O (70% by weight, the balance being cement) and 2.0 ml of sodium hypochlorite (12% solution) were added, stirred at room temperature for 3 hours, and after conventional filtration, COD was analyzed. For comparison, the case of only panion (Comparative Example 1) and the case of only sodium hypochlorite (Comparative Example 2)
The same procedure was carried out for . The results were as shown in the table below.

[Table] For reference, the COD in the brine supplied to the diaphragm salt electrolysis plant was 10 to 14 ppm, and the COD in the electrolytic solution leaving the electrolytic cell was 10 to 12 ppm. Example 2 100 ml of the same recovered saline solution as in Example 1 (specific gravity 1205)
Each time, 1 ml of sodium hypochlorite (12% solution) was added to serve as the liquid to be treated. The same panion as in Example 1 (5 mm containing nickel peroxide) was placed in a glass double tube with an inner diameter of 44 mm.
The container was filled with 150 ml of 5 mm diameter column (column shape) and maintained at 60°C by passing hot water to the outside. The above-mentioned liquid to be treated was supplied using a metering pump at a rate of 118 g/Hr. (Average residence time approximately 1.5 hours) Salt water passed through the panion packed bed
When I measured the COD, it had dropped to 9pm. Comparative Example 3 The same apparatus as in Example 2 was filled with commercially available granular activated carbon instead of panions, and the same recovered saline solution as in Example 1 was supplied. Thereafter, the same operations as in Example 2 were performed. However, COD hardly decreased to 60-65 ppm. Comparative Example 4 5.0 ml of 3% hydrogen peroxide solution was added to 200 ml of the same recovered saline solution as in Example 1 and left at 80 to 90°C for 1 hour, but there was almost no change in COD. Comparative Example 5 Ozone was added to 400 ml of the same recovered saline solution as in Example 1.
Air containing 5100 ppm was blown for 10 minutes at a flow rate of 1/min. The COD of the recovered saline solution was measured and found to be 44 ppm. Example 3 A reaction solution containing potassium chloride obtained by reacting 1,1,2-trichloroethane with a caustic potassium solution,
The organic matter and the potassium chloride aqueous solution were separated, and the potassium chloride aqueous solution was subjected to simple distillation to remove the dissolved organic matter. When this liquid was analyzed, the concentration of potassium chloride was 297 g/, caustic potassium 7 g/, and COD 68 ppm. Thereafter, this solution was treated in the same manner as in Example 1 except that potassium hypochlorite was used instead of sodium hypochlorite, and the COD was analyzed and found to be 13 ppm.

Claims (1)

[Claims] 1. Chlorinated hydrocarbons are removed by distillation from an aqueous alkali chloride solution obtained by dehydrochlorinating 1,1,2-trichloroethane with a caustic alkaline solution, and then the aqueous alkali chloride solution obtained is treated with nickel oxide. 1. A method for producing a purified aqueous alkali chloride solution, which comprises bringing it into contact with an alkaline hypochlorite solution in the presence of.