JPH0159961B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an aqueous solution containing sodium hydroxide;
The present invention relates to a method for producing an aqueous sodium hypochlorite solution by reacting with chlorine through gas-liquid contact.

Specifically, the main objective is to easily and efficiently produce a highly concentrated aqueous solution of sodium hypochlorite using a normal reaction tank used in the production of sodium hypochlorite.

When sodium hydroxide and chlorine are reacted, equivalent amounts of sodium hypochlorite and sodium chloride are produced according to the following formula: 2NaOH + Cl ₂ →NaClO + NaCl + H ₂ O. However, in order to suppress the decomposition of sodium hypochlorite, some unused amount is generated. It is necessary to dissolve the reactive sodium hydroxide, and a normal aqueous solution of sodium hypochlorite has sodium hypochlorite, sodium chloride, and sodium hydroxide as its main components, and the composition varies depending on the solubility of these components in water. It is determined. That is, the concentration of sodium hypochlorite produced and the composition of the aqueous solution are approximately determined by the concentration of the sodium hydroxide aqueous solution of the raw material. However, beyond the range where these three can coexist in the liquid phase, crystals of sodium chloride, which has the lowest solubility, precipitate.

To explain this specifically, when producing sodium hypochlorite by introducing chlorine into a 20% aqueous sodium hydroxide solution, the reaction is carried out to the extent that 2 to 3% of unreacted sodium hydroxide remains. If stopped, a sodium hypochlorite aqueous solution containing approximately 16% sodium hypochlorite and approximately 13% sodium chloride will be produced. This composition is within the melting range at room temperature, and a uniform reaction mass can be obtained. However, when the concentration of the raw material sodium hydroxide exceeds 25%, sodium chloride crystals precipitate at room temperature, and the reaction mass becomes a slurry.

For example, when introducing chlorine into a 30% sodium hydroxide aqueous solution to obtain high concentration sodium hypochlorite, if the reaction is stopped when 2 to 3% of unreacted sodium hydroxide remains, the sodium hypochlorite is about 25%, and sodium chloride is about 20%, which is outside the range of dissolution at room temperature, so some of the sodium chloride precipitates, and the sodium chloride concentration in the reaction solution becomes about 7%.

In this way, when producing high-concentration sodium hypochlorite, precipitation of sodium chloride crystals during the reaction cannot be avoided, and over-separation is required after the reaction is completed. Sodium chloride crystals precipitate in the chlorine injection pipe introduced into the system, causing blockage of the introduction pipe. This requires cumbersome work such as interrupting the reaction and cleaning the tubes.
If there is a tendency for blockage, the introduction of chlorine may cause local contact with the reaction solution, and prolongation of the reaction time due to interruption of the reaction may result in the decomposition of the sodium hypochlorite produced and the by-product of chlorate. , resulting in a decrease in yield. Furthermore, the crystal grain size of the precipitated sodium chloride is also adversely affected, and the over-separation operation after the reaction is completed becomes difficult, thereby affecting the yield of the desired product.

As described above, when producing a highly concentrated sodium hypochlorite aqueous solution, it is necessary to devise a chlorine introduction method. In general, this method involves dissolving sodium chloride with water, removing attached sodium chloride using mechanical methods, and installing a double chlorine introduction pipe that opens along the flow direction of the reaction solution. A method of reacting while circulating the liquid at high speed (Japanese Patent Application Laid-open No. 56-114807), in which a chlorine-containing gas is supplied from the inner tube using a double-tube cyclone reactor, and a circulating reaction liquid containing a fresh sodium hydroxide aqueous solution is generated. A method has been proposed (Japanese Unexamined Patent Publication No. 58-20703) in which the liquid is supplied to the outer tube from a tangential direction, and the two are brought into contact and reacted at the bottom of the cyclone while flowing downward.
These methods are not only quite complicated, but also cannot completely prevent adhesion, and are not only expensive in terms of equipment and power costs, but also troublesome to operate.

For example, in JP-A-56-114807, a double reaction tube is installed in the upper part of the reactor, and a circulation pump controls the flow rate of the circulating reaction liquid flowing outside the inner tube and the flow rate of chlorine gas introduced from the inner tube. By adjusting this method, a space is created at the tip of the chlorine introduction tube under a hydraulic pressure state, and the process is carried out while preventing the adhesion of sodium chloride crystals, but there is a problem in controlling the flow rate of the reaction solution and the flow rate of the chlorine gas.

As a result of intensive research to improve these points, the present inventor discovered a simple method that does not cause any adhesion or blockage of sodium chloride crystals and uses a commonly used reaction tank, and completed the present invention. Ta.

That is, in the method of the present invention, when producing a high concentration sodium hypochlorite aqueous solution by reacting an aqueous sodium hydroxide solution with chlorine, the opening position of the chlorine introduction pipe is provided above the final liquid level of the reaction solution in the reaction tank. hand,
Production of a highly concentrated sodium hypochlorite aqueous solution characterized by supplying chlorine above the liquid surface of a reaction tank and reacting 25 to 42% by weight aqueous sodium hydroxide with chlorine while sufficiently stirring the reaction liquid. is a method,
This eliminated clogging of the pipes and made it possible to flow chlorine for a predetermined period of time without fluctuations in the flow rate. For this reason, the reaction proceeded smoothly, and the crystallinity of the precipitated sodium chloride also improved, resulting in improved so-called liquid drainage. As a result, the yield of sodium hypochlorite in the liquid is also improved by 6 to 7%.

Since the present invention is a gas-liquid contact reaction, stirring is a necessary condition during the reaction. If the stirring is insufficient, the reaction liquid will be in contact with chlorine locally for a long time, which will accelerate the decomposition reaction of the generated sodium hypochlorite, resulting in undesirable side production of sodium chlorate. A certain level of stirring is required. However, this reaction occurs quickly, so
Vigorous stirring is not required. Specifically, the stirring speed is about 60 rpm in a 10 m ³ reaction tank, which is not much different from normal reaction stirring. As long as the stirring speed is fast, there will be no adverse effect on the reaction itself, but if the stirring speed is too fast, droplets of the reaction liquid will adhere to the upper part of the reaction tank, and extra power costs will be required, so there is no advantage. The optimum stirring speed may be set as appropriate based on the design of the reaction liquid volume, the shape of the stirring blade, etc.

The concentration of the sodium hydroxide aqueous solution used in the method of the present invention is preferably 25 to 42% by weight. If it is less than 25% by weight, a highly concentrated aqueous sodium hypochlorite solution cannot be obtained, and the reaction solution becomes a homogeneous solution, so there is no need to apply the method of the present invention. Furthermore, if the concentration of the aqueous sodium hydroxide solution exceeds 42% by weight, a large amount of NaCl will precipitate as a reaction product, making stirring difficult. Alternatively, even if the reaction solution is allowed to stand after the reaction is completed, it becomes fine NaCl crystals with a slow sedimentation rate and poor filterability, and it takes a long time to filter and separate the precipitated NaCl. Furthermore, during filtration, there are problems such as poor liquid drainage and a sodium hypochlorite aqueous solution remaining in the NaCl crystal filtrate, resulting in a decrease in yield, which is undesirable.

There is no particular limitation on the shape of the chlorine introduction tube, and the opening may be perpendicular or perpendicular to the reaction liquid surface. The distance from the liquid surface to the introduction tube is not particularly limited either, but if they are too close, droplets of reaction liquid will adhere, so it is preferable to keep the distance at least about 1 cm. As mentioned above, this reaction is rapid, and even if the chlorine is blown above the liquid level, almost no unreacted chlorine escapes out of the system.

According to the present invention, there is no clogging of the chlorine introduction pipe, and the chlorination reaction can be carried out smoothly and easily over a long period of time. Effective for producing concentrated sodium hypochlorite. It is also useful for saving equipment and reducing labor.

Examples and comparative examples of the present invention are listed below.
Although a specific explanation will be given, the present invention is of course not limited to this in any way. Note that % indicates weight %.

Example 1 A separable four-necked flask with a diameter of 105 mm and a height of 110 mm was equipped with a stirring bar with a semicircular stirring blade of 60 mm in diameter, a thermometer, and a chlorine introduction tube with a diameter of 8 mm (with the hole opening perpendicular to the liquid level). , installed 1 cm above the liquid surface at the end of the reaction.)
A waste gas exhaust pipe (the exhaust pipe led to a 15% sodium hydroxide suction tank) was installed and used as a reactor.

After adding 700g of 40% sodium hydroxide,
Chlorine was introduced at 57g/hr for 4.1hrs. During this time, the reaction mass was maintained at 30° C. and stirring was at 500 rpm. During this time, no sodium chloride crystals were observed in the chlorine introduction tube, and the reaction was completed smoothly. Also, no increase in the number of exhaust gas absorption tanks was observed. After filtering out the formed sodium chloride crystals, 715 g of a solution with a sodium hypochlorite concentration of 29.5% was obtained. The yield based on chlorine was 86%.

Example 2 Example 1 except that the temperature of the reaction mass was changed to 20°C
I did the same thing.

The obtained liquid has a sodium hypochlorite concentration of 30.5
It was 710g in percent. The yield based on chlorine was 88%.

Example 3 Except for changing the concentration of sodium hydroxide as a raw material to 35% and changing the chlorine introduction rate to 50 g/hr.
The same procedure as in Example 1 was carried out.

A solution of 700 g of 29% sodium hypochlorite was obtained. The yield based on chlorine was 94%.

Example 4 The same procedure as in Example 1 was carried out except that the concentration of sodium hydroxide as a raw material was changed to 42%.

A filtrate of 720 g of 29.9% sodium hypochlorite was obtained. The yield based on chlorine was 87.8%.

Comparative Example 1 The same procedure as in Example 1 was carried out, except that the chlorine inlet tube was immersed in the sodium hydroxide solution as the raw material. During the reaction, the chlorine introduction tube was often clogged with sodium chloride crystals, so the reaction was carried out while removing the attached crystals every 10 to 20 minutes. It took 8 hours from the start to the end of the reaction.

A liquid containing 680 g of 29% sodium hypochlorite was obtained. The yield based on chlorine was 80%.

Comparative Example 2 This was carried out in the same manner as in Example 3, except that the chlorine inlet tube was immersed in the raw material sodium hydroxide solution. During the reaction, the chlorine introduction tube was often clogged with sodium chloride crystals, so the reaction was carried out while removing the attached crystals every 10 to 20 minutes. It took 8 hours from the start to the end of the reaction.

A liquid containing 670 g of 28% sodium hypochlorite was obtained. The yield based on chlorine was 87%.

Comparative example 3 The rotation speed of stirring was changed to 500 rpm as in Example 1.
The same method as in Example 1 was carried out except that the speed was reduced to 300 rpm. As a result, 670g of 29% sodium hypochlorite solution was obtained, and the yield relative to chlorine was
It was 79%. Also stirring speed 300, 400, 500rpm
The relationship between the yield and the sodium hypochlorite yield when carried out at 300 rpm is as shown in FIG. 1, and it can be seen that stirring is insufficient at 300 rpm.

Comparative Example 4 The same procedure as in Example 1 was carried out except that the concentration of sodium hydroxide as a raw material was changed to 45% and the chlorine introduction rate was changed to 60 g/hr.

After the reaction was completed, it was allowed to stand still, but the precipitation of NaCl was slow.
Furthermore, time was required for filtration and separation. After filtering the produced sodium chloride crystals, 600 g of a filtrate with a sodium hypochlorite concentration of 30.5% was obtained. The yield based on chlorine was 71%.

[Brief explanation of drawings]

Figure 1 shows the relationship between the stirring speed of the reaction solution and the yield of sodium hypochlorite in the solution with respect to the introduced chlorine when carrying out Example 1 of the present invention.

Claims (1)

[Claims] 1. When producing a high-concentration sodium hypochlorite aqueous solution by reacting a sodium hydroxide aqueous solution with chlorine, the opening position of the chlorine introduction pipe is set above the final liquid level of the reaction liquid in the reaction tank, and the liquid in the reaction tank is A method for producing a highly concentrated aqueous sodium hypochlorite solution, which comprises supplying chlorine onto the surface and reacting the chlorine with a 25 to 42% by weight aqueous sodium hydroxide solution while sufficiently stirring the reaction solution.