JPS5910924B2 - Manufacturing method of sodium hypochlorite - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing sodium hypochlorite by removing trace amounts of heavy metals contained in caustic soda produced by diaphragm salt electrolysis.

Sodium hypochlorite has a strong oxidizing effect and is used in large quantities for bleaching, disinfection, deodorization, and as a raw material for the chemical industry.

The method for producing such sodium hypochlorite includes adjusting the concentration of concentrated caustic soda with pure water, etc., and then absorbing and reacting chlorine gas to obtain sodium hypochlorite with a concentration of about -2%, or Highly concentrated sodium hypochlorite with a concentration of about 25% is produced, precipitated salt is separated, and the product is diluted to sodium hypochlorite with a concentration of about 12% and sold commercially.

In general, caustic soda obtained by diaphragm method electrolysis contains more impurities such as nickel, chromium, and iron than caustic soda obtained by mercury method salt electrolysis because nickel and stainless steel are used as materials for the evaporator used in the concentration process. include.

Sodium hypochlorite manufactured using caustic soda containing these heavy metals as a raw material is highly degradable, and not only does the effective chloric acid concentration easily decrease, but also the hypochlorous acid that contains many of these impurities. This has an adverse effect on the production of various products using soda as a raw material, and is a cause of lowering the commercial value of the final product.

Therefore, in the past, caustic soda produced by mercury-method salt electrolysis was used exclusively as a raw material, but now that a switch to mercury-method salt electrolysis has been promoted, it is now possible to obtain high-quality sodium hypochlorite from caustic soda produced by diaphragm-method salt electrolysis. is coveted.

Under these circumstances, the inventors of the present invention conducted tax-conscious research and discovered a method for producing high-quality sodium hypochlorite using the diaphragm-method caustic soda that had undergone the removal of heavy metals and the heavy metals removed. The present invention has now been completed.

The present invention uses caustic soda obtained by diaphragm method salt electrolysis,
It is characterized by partially chlorinating the sodium hypochlorite concentration in the range of 0.001 to 5% to precipitate the contained heavy metals, and then reacting the partially chlorinated liquid from which the heavy metals have been removed by filtration with chlorine gas. This is a method for producing sodium hypochlorite.

In the process of partially chlorinating and filtering caustic soda in the method of the present invention, there is no limit to the concentration of caustic soda, but especially when partially chlorinating caustic soda with a high concentration, the concentration of caustic soda is hardly diluted, This is advantageous because the nickel compounds in the caustic soda can be selectively removed.

The chlorination rate is determined by the concentration of sodium hypochlorite o. oo1. Excessive chlorination is meaningless from the purpose of removing heavy metals, and the upper limit is preferably 5%.

Generally, when producing sodium hypochlorite, if heavy metals are contained in the raw materials, the decomposition of the sodium hypochlorite will be accelerated when chlorine is absorbed and reacted with caustic soda, and the decomposition during the manufacturing process and product damage will occur. Stability deteriorates and the amount of chlorine per product increases.

The above phenomenon is particularly noticeable when crushing sodium hypochlorite using diaphragm method caustic soda.

Therefore, in order to eliminate these drawbacks, the present inventors partially chlorinated caustic soda using a diaphragm method to remove heavy metals, especially nickel compounds, thereby eliminating the decomposition described above and reducing the amount of chlorine used per product from mercury. I learned that results comparable to those obtained by electrolyzing caustic soda can be obtained.

In addition, when producing high-concentration sodium hypochlorite, the precipitated salt has a small particle size when the diaphragm method caustic soda is used without partial chlorination, and the amount of adhering mother liquor is large for the separation of salt crystals. The decomposition of sodium hypochlorite is also significant, but when using the separated method purified caustic soda that has been partially chlorinated and filtered by the method of the present invention, the particle size of the precipitated common salt is large and the decomposition is small. The present invention will be explained with reference to and comparative examples.

In these, "department" and "department" are both based on weight.

Examples 1 and 2 and Comparative Example 1 and Reference Example 1 After partially chlorinating chlorine by blowing chlorine into caustic soda (concentration: 48 sq.), this was mixed with 15% of the weight of diatoms based on the weight of the solution. The solution was filtered under pressure using Shitazawa Cloth Parein (manufactured by Nakao Filter Engineering), and the heavy metal concentration and hypochlorous acid concentration of the resulting solution were measured.

Next, these Oki liquids were adjusted with pure water to make a caustic soda solution with a concentration of 19070, and 277 parts of chlorine gas was added to 1953 parts of the solution.
222 parts of a 12.9% sodium hypochlorite solution were obtained.

Further, 260 parts of 48% caustic soda was added to this solution, and 99.6 parts of chlorine gas was gradually added to react. After the reaction, precipitated salt was separated to obtain a 25.2% sodium hypochlorite solution. The reaction temperature was maintained at 20°C.

These results are shown in Table 1.

In addition, when sodium hypochlorite was produced by filtrating caustic soda without partial chlorination and reacting with chlorine in the same manner as above (Comparative Example 1), and when using mercury method caustic soda, the same results were obtained. Table 1 also shows the results for the case where sodium hypochlorite was produced by reaction with offshore chlorine without partial chlorination (Reference Example 1).

Claims (1)

[Claims] 1 Caustic soda obtained by diaphragm method salt electrolysis is partially chlorinated to a concentration of sodium hypochlorite in the range of 0.001 to 5 parts to precipitate the heavy metals contained, and the heavy metals are removed by filtration.Partial chlorination A method for producing sodium hypochlorite, which is characterized by reacting a chemical solution with chlorine gas.