JPS5910932B2 - Manufacturing method of carbonated soda water salt - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for obtaining sodium carbonate hydrate from an electrolytic solution obtained from a diaphragm method salt electrolytic cell (hereinafter simply referred to as diaphragm method electrolyte).

Conventionally, the method for producing soda carbonate has been to use sodium bicarbonate as a method (1) absorb ammonia into purified brine, react it with carbon dioxide gas to form sodium bicarbonate and ammonium chloride, separate the crystallized sodium bicarbonate, and then (1) ) The mother liquor containing ammonium chloride obtained by separating out the bicarbonate of soda is reacted with milk of lime and decomposed into ammonia and calcium chloride solution, and the ammonia is recovered and recycled. The so-called ammonia soda method used (hereinafter simply referred to as method A), or (2) refined solid salt is added to the ammonium chloride-containing mother liquor after separation of sodium bicarbonate to crystallize and separate the ammonium chloride, and the oral fluid is again subjected to the ammonia absorption process. There is a so-called ammonium salt and soda co-production method.

Both methods (1) and (2) yield bicarbonate of soda, so in order to produce soda ash, it must be calcined and decomposed using equation (1).

The soda ash obtained by decomposing the sintered ash is called light ash and has a low bulk density.In order to make dense ash with a high bulk density, it is monohydrated as shown in equation (2) and then converted to monohydrate. Then, it must be calcined and dehydrated as shown in equation (3) (hereinafter, the process shown in equation (2) + (3) will be referred to as the dense ashing step).

The disadvantages of these above-mentioned methods are that the method A requires a large amount of energy in the calcining decomposition step and the dense ashing step because it uses bicarbonate of soda, and it requires a nuammonia recovery step, which requires a large amount of milk of lime and steam. Not only is this method necessary, but also all the coexisting chlorine ions are discarded, which is not a preferable method from the viewpoint of resource conservation.

Furthermore, the ammonium chloride/soda co-production method has a major drawback in that the amount of production depends on the demand for ammonium chloride produced as a by-product.

As a method that does not involve sodium bicarbonate, there is a method of reacting caustic soda liquid with carbon dioxide gas to obtain sodium carbonate aqueous salt.

In this method, monohydrate is directly obtained, and if it is calcined and dehydrated, it can be obtained as dense ash.

However, this force method requires a concentrated caustic soda solution in terms of ice balance, and when a diaphragm method electrolyte with a relatively dilute caustic soda concentration is used as a raw material for soda ash production, a step of concentrating the electrolyte is necessary. It is.

Therefore, this method also requires a large amount of energy, and is not necessarily a preferable force method.

To a caustic soda solution with a concentration of 40 parts or more, add bicarbonate of soda to produce carbonate of soda, and then add anhydrous carbonate of soda in an amount that can fix all the water produced at that time and the water entrained from the caustic soda solution as water of crystallization. A method has been proposed (BP979378) in which the ash is reacted using a paddle mixer or the like, and then directly calcined and dehydrated to produce dense ash.

However, this method still requires a concentrated caustic soda solution, and all impurities contained in the caustic soda solution are entrained in the dense ash. It cannot be used unless it is a caustic soda solution.

Also, the growth of monohydrate crystals is insufficient.

Therefore, even if the diaphragm electrolyte is used as it is in this method, a large amount of salt and other impurities contained in the diaphragm electrolyte will be completely entrained in the dense ash and a high-quality product will not be obtained. I can think of things that I can't do.

As described above, it is extremely difficult to use the diaphragm method electrolyte as a raw material for a carbonate noder in its natural state without concentrating and purifying it.

To carbonate the diaphragm electrolyte without concentrating it, the diaphragm electrolyte is reacted with carbon dioxide gas and separated as sodium bicarbonate.The mother liquor is then dissolved in the raw material salt, further purified, and then subjected to diaphragm electrolysis. A method is disclosed (Japanese Patent Publication No. 51-30879) in which bicarbonate of soda is obtained, so a calcining decomposition process is necessary, and a dense ashing process is also required to produce dense ash. be.

A method is disclosed in which the electrolyte of the diaphragm method is mixed and supplied with the process solution of the A method or the ammonium chloride soda co-production method to indirectly produce bicarbonate of soda.
-41236, JP-A-49-511.99).

However, all of these methods are aimed at producing sodium bicarbonate, and as will be described later, are different in technical concept from the present invention.

The present inventors conducted various studies on a method for producing soda carbonate using a diaphragm electrolyte as a raw material in a process that minimizes energy consumption, and arrived at the present invention.

The technical idea of the present invention is (1) to use the diaphragm method electrolyte without concentrating it.

(2) Do not use steam for concentration during the soda carbonation process.

(3) The method is not a method for producing sodium bicarbonate that requires a calcining decomposition step and a dense ashing step, but a method for directly producing sodium carbonate hydrate for dense ash.

(4) The alkali yield is sufficiently high.

(5) That is, the manufacturing method must minimize energy consumption.

etc. (There is this.

However, in order to completely satisfy the above technical idea, (1)
Even when carbon dioxide gas is blown into the diaphragm electrolyte, sodium carbonate hydrate does not precipitate, or even if it precipitates, it is very small.

(2) Since a large amount of sodium carbonate is still dissolved in the mother liquor from which the sodium carbonate aqueous salt is separated, purging it as it is will result in a large alkali loss.

In other words, the alkali yield is extremely low.

(3) Growing crystals cannot be obtained because the carbonate slurry concentration is low and it is difficult to maintain a long residence time for the crystals.

There are problems such as these, and it has become clear that it is necessary to solve these problems in order to establish an effective method for producing soda carbonate.

The present inventors have arrived at the present invention as a result of further research.

That is, in the present invention, when reacting the diaphragm method electrolyte, Lie I ash, and sodium bicarbonate obtained in the third step described below to obtain sodium carbonate hydrate, Lie 1 ash is supplied at a temperature of 60°C or higher, and the crystallization tank temperature is If there is an excess of caustic soda in the reaction solution, reduce the concentration of caustic soda to 1 wt.
%, and in the case of a shortage of caustic soda, the bicarbonate soda concentration is reduced to less than 2 wt %.The slurry obtained in the first step is separated into crystals and mother liquor, and as necessary. The gist is a method for producing sodium carbonate hydrate, which comprises a second step of washing, a third step of reacting the mother liquor obtained in the second step with carbon dioxide gas to crystallize sodium bicarbonate, and supplying the crystals to the first step. It is something.

The present invention will be explained in more detail.

The diaphragm electrolyte usually has a sodium hydroxide concentration of 5 to 15 wt% and contains 10 to 20 wt% of common salt.

The higher the concentration of caustic soda and the higher the concentration of common salt, the greater the amount of sodium carbonate aqueous salt crystallized when carbonated.

It is desirable to use a sodium bicarbonate separated mother liquor in the Nua method or the diaphragm method for chlorination electrolysis.The higher the salt concentration is, the better.

Even the electrolyte composition described above can be effectively used in the present invention.

The light ash used in the present invention may be obtained by calcining and decomposing sodium bicarbonate produced by the ammonium chloride soda co-production method in method A and/or method].The temperature at which the ash is supplied to the reaction system must be 60°C or higher. is necessary.

When the temperature is below 60°C, when light ash is introduced into the crystallization tank, the degree of supersaturation near the crystal surface increases rapidly and more nuclei are generated, making it difficult to obtain large grown crystals. Otherwise, a sodium carbonate aqueous salt with the light ash particles left intact is generated, making it impossible to obtain good dense ash.

The optimal amount of lye 1 to ash to be supplied to the reaction system varies depending on the concentration of caustic soda and salt in the diaphragm electrolyte, but it should be 70 to 95% of the caustic soda in the diaphragm electrolyte (monohydrate yield). ) is preferably added in an amount that can precipitate the sodium carbonate aqueous salt.

More preferably, the amount is such that the monohydrate yield is 85 to 95%.

If the light ash is in an amount where the AiTi flow rate is -F from 70, a large amount of sodium bicarbonate will be surplus in the third step described below, and if the amount is above 95φ, it will be needed in the second step. Soda bicarbonate cannot be supplied from the third process.

As a result of various studies, the present inventors found that when the caustic soda concentration of the diaphragm method electrolyte is taken as a function of xwt, Lie 1. It has been found that by determining the amount of ash supplied, sodium carbonate hydrate can be obtained with a desired monohydrate yield, and at the same time, there is no shortage of sodium bicarbonate required in the first step.

Further, when the amount of light ash supplied is less than 1.00 kg, the crystal form of the crystallized sodium carbonate hydrate becomes slightly smaller.

The amount of bicarbonate of soda supplied from the third step described below is equivalent to the amount of caustic soda in the diaphragm electrolyte to be supplied (
1 mole to 1 mole), but the reaction solution composition in the sodium carbonate crystallization tank should be less than 1 wt % in terms of caustic soda concentration if there is an excess of caustic soda, and the sodium bicarbonate concentration should be less than 1 wt % if there is a shortage of caustic soda. It must be less than 2wt.

When the concentration of caustic soda exceeds 1 wt%, the crystalline form of the crystallized sodium carbonate hydrate deteriorates, and the physical properties when formed into dense ash deteriorate.

The reason is not clear, but the salt concentration is between 13 and 20.
This is thought to be due to the unique crystallization mechanism as the reaction involves crystallization of solid sodium bicarbonate and caustic soda solution in a crystallization tank with a high wt%.

If the concentration of sodium bicarbonate exceeds 2 wt%, sodium sesquicarbonate will precipitate in addition to monohydrate, which is not preferable.

The temperature of the crystallization tank is 60°C to l. It is preferably within the range of 0 0°C.

If the temperature is lower than 60℃, good crystals cannot be obtained, and if the temperature is lower than 100℃.
When the temperature rises above °C, anhydrous carbonate soda begins to crystallize.

The slurry concentration in the crystallization tank is preferably 20 to 40 wt%, but it may exceed this range depending on the amount of light ash supplied. It is sometimes effective to reduce the slurry concentration by using a method such as classification, static settling, etc. to increase the slurry concentration.

When separating the sodium carbonate aqueous salt from the mother liquor in the second step, since the mother liquor with a high salt concentration adheres to the crystals, it is preferable to wash the crystals with water or an aqueous sodium carbonate solution as necessary.

The amount of cleaning solution used at this time is 10 to 1.5 wt per crystal.
% is sufficient.

The third step of reacting carbon dioxide gas with the separated mother liquor of sodium carbonate and salt to obtain sodium bicarbonate can be carried out using the usual method, but from the point of view of reducing alkali loss, the temperature should ultimately be set at 20 to 20°C.
It is preferable to separate the bicarbonate of soda after the temperature is lowered to 40°C.

The carbon dioxide gas used is not particularly limited, and is used in an amount sufficient to produce bicarbonate of soda.

Sodium bicarbonate does not require washing or drying, and can be used in the form of a dog with attached mother liquor.

Separation C In this case, normal separation such as centrifugal filtration, pressure filtration, or vacuum filtration may be used, but it is also possible to cycle bicarbonate soda slurry concentrated in a static tank or liquid cyclone to the first step. It is.

The mother liquor obtained in the third step contains 1 to 5 wt% of bicarbonate of soda.
However, since the salt concentration is 14 to 24 wt higher, it can also be used as a salt water for electrolysis using the A method or the diaphragm method.

Next, the features of the present invention are listed as follows: (1) By circulating sodium bicarbonate, monohydrate can be crystallized without concentration, and the yield of monohydrate is also extremely high compared to the carbon dioxide gas blowing method. .

(2) By using light ash, water is consumed and the crystallization rate of sodium carbonate water salt further increases.

(3) That is, more than 80% (monohydrate yield) of caustic soda in the diaphragm electrolyte can be recovered as sodium carbonate hydrate.

If only carbon dioxide gas is blown in, the yield is between 0 and 10, although it depends on the composition of the diaphragm electrolyte.

(4) By using light ash from the A method or the ammonium chloride soda co-production method, the dense ashing process is no longer necessary.

(5) By circulating sodium bicarbonate and using light ash, the slurry concentration in the crystallization tank is increased and the residence time of the crystals is sufficiently long, so that crystal growth is slowed down.

(6) A simple tank-type crystallization tank for complete mixing is sufficient.

(7) As the monohydrate for dense ash, it is desired that the monohydrate has sufficient hardness so that it will not become pulverized when it is made into soda ash. As shown in the examples, the hardness test results were better than those of dense ash obtained by converting light ash into light ash and then passing through a dense ashing process, or dense ash obtained by carbonating concentrated strength soda liquid.

(8) Since the sodium bicarbonate separated mother liquor in the third step is purged, alkali loss is small.

(9) Since the sodium bicarbonate separated mother liquor in the third step has a high salt concentration, it can be used in method A or diaphragm method brine electrolysis.

(10) The amount of sodium bicarbonate used in the first step is approximately equivalent to the amount of caustic soda in the diaphragm electrolyte (1 mole to 1 mole), but there is a difference between the amount of sodium bicarbonate produced in the third step, or the excess amount. It is desirable that there is no shortage.

If it is in excess, it is necessary to purge with bicarbonate of soda, and if it is insufficient, it is necessary to supply it from outside the system.

However, in the present invention, by adjusting the amount of light ash supplied depending on the composition of the diaphragm electrolyte, it is possible to control excess or deficiency, so the operation is extremely simple.

As detailed above, the present invention not only has economical advantages such as reduction of energy cost l. Obtainable.

This is because the diaphragm method electrolyte is used as the raw material, the crystallization tank conditions are limited as mentioned above, the light ash containing some ammonium salt is used, and the salt concentration in the crystallization tank is 13 to 20 wt%. This seems to be due to the complex interaction of factors such as being highly respected and cycling the bicarbonate of soda in the process.

This will be explained below using examples.

Example 1 The first step was carried out as follows.

Caustic soda concentration 9. 6 wt section, salt concentration 16.8
wt% diaphragm electrolyte 20509/H, salt 0.
8239/H of light ash containing 4 wt %, and 3. salt from the third step described below. 2 liters of bicarbonate soda cake containing 12.0 wt% water at a feed rate of 486 F/H.
The mixture was supplied to a glass container (effective volume: .4 liters) and reacted with stirring to crystallize carbonate under hydrate.

The temperature of the supplied diaphragm electrolyte, the temperature of the bicarbonate soda cake was 25°C, the temperature of the light ash was 80°C, and the crystallization tank was heated to 95°C (maintained at this temperature).

The slurry produced in the second step was extracted at 3359 g\H and passed through a centrifugal port.

The conditions for centrifugal filtration were 750 G, and 1243 g/h of monohydrate crystal cake with an attached mother liquor of 3 wt % was obtained.

Furthermore, the monohydrate crystal cake was washed with 15 wt% of water, and the carbonate soda water salt was dried. It contained 1 wt% of salt, and the results of the hardness test were very good with a crush rate of 6.0.

The crushing rate of the soda water salt obtained by the method A was 10 to 12, and that of the monohydrate obtained by carbonating the diaphragm method soda water solution (48 wt%) by the conventional method was 1.3.0%.

The third step was carried out as follows.

The mother liquor from which the sodium carbonate aqueous salt was separated is 14.
It included 4wt and 1.6.8wt of good salt.

This mother liquor was continuously supplied to a glass container having an effective volume of 54, and carbon dioxide gas was blown into the container.

The temperature inside the container was 600C.

Pour the obtained slurry in batches into 5 liter glass containers.35
While cooling to ℃, carbon dioxide gas was further blown in for 1 hour.

This slurry was vacuum filtered using a glass filter, and 3. Owt staff, water 1 2. Owt staff, bicarbonate of soda 8 5. Ow t% cake 5 3 3 9/
Obtained from H.

In addition, the monohydrate yield was 84%. Example 2 The temperature of the monohydrate crystallization bath in the first step was changed to 80°C and 60°C, and the other conditions were the same as in Example 1.

The crushing rate is 7.5 and 11.0, respectively, as shown in Table 1.
I was on good terms with the person in charge.

Comparative Example 1 The crystallization tank temperature in the first step was changed to 50°C, and the other conditions were the same as in Example 1.

The crystal form of the sodium carbonate water salt was poor, and the crushing rate was also poor at 140.

Comparative Example 2 The temperature of the crystallization tank in the first step was 80°C, the temperature of the light ash supplied was changed to 50°C, and the other conditions were as in Example 1. L
- The same procedure was carried out.8 The crystal shape of the sodium carbonate hydrate was slightly poor, and the crushing rate was 13.
．． It was poor at 5%.

Example 3 and Comparative Example 3 The same conditions as in Example 1 were carried out except that the amount of bicarbonate soda cake introduced in the first step was varied to adjust the caustic soda concentration or bicarbonate soda concentration in the crystallization tank.

As shown in Table 1, unfavorable results were obtained when the caustic soda concentration was 1 wt % or more or the sodium bicarbonate concentration was 2 wt % or more.

Example 4 The same conditions as in Example 1 were carried out except that the amount of light ash added was changed.

The results are shown in Table 1. All were good.

=74- Example 5 Caustic soda concentration 10.7w. Section t, salt concentration 15.7w
t % diaphragm electrolyte at 2000 g/H, bicarbonate soda cake from the third step 52'l/H, light ash input amount 9049/H, 602 g/H, 20]. ．． I did it instead of 9/H.

The crystallization tank was the same as in Example 1, the temperature of the supplied diaphragm electrolyte was 50°C, and the temperature of the light ash was 1.5°C. The crystallization tank was maintained at 90°C.

The resulting slurry was treated in the same manner as in Example 1 to obtain sodium carbonate hydrate crystals and a bicarbonate soda cake.

The results are shown in Table 1. Good results were obtained in both cases.

Example 6 The amount of light ash introduced in the first step was 1"00.9/Hr.
, 1105 g/Hr, and the other conditions were the same as in Example 5.

The results are shown in Table 1. Light ash input amount is 1009/H
When the amount is as low as r, the resulting monohydrate crystals are somewhat poor, with a crushing rate of 13, and the excess rate of sodium bicarbonate is 17%, with a large amount of sodium bicarbonate remaining.

On the other hand, the input amount of light ash is (1 3 6 0-80x
)is more than]. 1 0 5. ! In the case of i'/Hr,
There was a large shortage of bicarbonate of soda from the third step.

Claims (1)

[Claims] 1. Electrolyte and light ash from a diaphragm method salt water electrolyzer
When reacting sodium bicarbonate obtained in the third step described below to obtain sodium carbonate hydrate, (1) supply light ash maintained at 608C or higher, and keep the reaction liquid content at 60°C to 100°C.
If the mother liquor contains excess caustic soda, the caustic soda concentration should be maintained within the range of 1. (2) The reaction solution obtained in the first step is separated into crystals and mother liquor, and the reaction solution obtained in the first step is separated into crystals and mother liquor, (a second step in which the crystals are washed accordingly; and (3) a third step in which the mother liquor obtained in the second step is reacted with carbon dioxide gas to crystallize sodium bicarbonate and the crystals are supplied to the first step. Method for producing aqueous salt. 2 In the method according to claim 1, when the caustic soda concentration in the electrolyte from the diaphragm method salt water electrolytic cell is xwt%, .OOkg for 1 ton of the electrolyte. that's all(
1 3 6 0-80x) A method of supplying light ash of less than 0-80x kg.