JPS6265924A - Production of chlorine and caustic soda - Google Patents

Abstract

PURPOSE:To remarkably save the energy and to produce chlorine and caustic soda by using sodium chloride as the a material and mainly utilizing thermochemical reaction. CONSTITUTION:Sodium chloride is allowed to react with nitric acid to form chlorine, nitrosyl chloride and sodium nitrate. The obtained nitrosyl chloride is oxidized to form chlorine. Meanwhile, the sodium nitrate obtained along with chlorine and nitrosyl chloride is allowed to react with calcium fluoride and silicon tetrafluoride to form sodium hexafluorosilicate which is heated and decomposed to form sodium fluoride. Then the obtained sodium fluoride is allowed to react with calcium oxide and water and caustic soda is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] This invention relates to a method for producing chlorine by reacting sodium chloride with nitric acid, and simultaneously treating the produced sodium nitrate with a sootide to produce caustic soda.

[Conventional technology]

Generally, when producing chlorine and caustic soda using sodium chloride as a raw material, electrolysis methods such as the diaphragm method, mercury method, and ion exchange membrane method have a practical power generation efficiency of 3.
It is about 5%, and it cannot be said that energy is necessarily used effectively.

For this reason, it is estimated that if there was a method to produce chlorine and caustic soda from sodium chloride using heat directly without converting it into electricity, energy consumption would be greatly reduced. Therefore, there is a strong demand for the development of such technology.

Conventionally, chlorine has been produced from sodium chloride by a thermochemical reaction, and the nitrosyl chloride method has been carried out industrially. However, this process is no longer practiced due to limited demand for sodium nitrate, which co-produces with chlorine. In addition, as methods for producing caustic soda using a thermochemical reaction, the nitrate-lime method using sodium carbonate as a raw material, the Lgwig method, and the fluoride method have been used in the past, but all of these methods have been used since the advent of electrolysis. The main reason for this is that electrolysis can produce both chlorine and caustic soda from sodium chloride; This is because they could only produce chlorine or only sodium carbonate from sodium chloride, and were unable to produce both chlorine and caustic soda.

Known methods for producing sodium carbonate using sodium chloride as a raw material include the Le Plan method, the ammonia soda method, and the ammonium chloride method, but none of these methods can produce chlorine.

[Problem that the invention seeks to solve]

For this reason, there is currently no technology for producing both chlorine and caustic soda using IIum chloride as a raw material and using exclusively thermochemical reactions.

The present invention is intended to provide a new method for producing chlorine and caustic soda that meets the needs of the technical field as described above and overcomes the drawbacks of conventional methods.

[Means for solving problems]

This invention thermochemically decomposes sodium chloride (by reacting the sodium chloride with nitric acid to produce chlorine, nitrosyl chloride, and sodium nitrate, and oxidizing the obtained nitrosyl chloride to produce chlorine). On the other hand, sodium hexafluorosilicate is produced by reacting sodium nitrate obtained with chlorine and nitrosyl chloride with calcium fluoride and silicon tetrafluoride, and the obtained sodium hexafluorosilicate is thermally decomposed to produce fluorinated This is a method of obtaining chlorine and caustic soda from sodium chloride by first producing sodium and then reacting the resulting sodium fluoride (calcium dioxide) with water to produce caustic soda.

In the first step of reacting sodium chloride with nitric acid to produce chlorine, nitrosyl chloride and sodium nitrate, if the concentration of the nitric acid aqueous solution is below 58%, the temperature will drop to 1.
Even at 40°C, the reaction rate is 75% or less. However, when the concentration of the nitric acid aqueous solution is 60% by weight or more, the reaction proceeds almost 100% even at 130°C. Furthermore, in a 64% by weight aqueous nitric acid solution, the reaction proceeds 100% even at 110°C, and the reaction rate becomes faster.

Therefore, the reaction temperature in the first stage is determined in relation to the concentration of the nitric acid aqueous solution, but preferably the reaction temperature is 8
The concentration of the nitric acid aqueous solution at this time is maintained within the range of 60% by weight or more and 65% by weight or less. The reaction in this case is as follows.

The separation of the products in the first stage (-) is as follows. Since chlorine and nitrosyl chloride are gases at the reaction temperature, they naturally separate from the sodium nitrate produced in the nitric acid aqueous solution. Since the condensation temperatures of chlorine and nitrosyl chloride are -34.1°C for chlorine and -5.5°C for nitrosyl chloride, these differences are used to separate them by cooling. The resulting nitrosyl chloride is then oxidized with air or oxygen, or nitric acid. In the case of oxidation with air and oxygen, the reaction temperature is relatively high, about 200°C.

On the other hand, when nitrosyl chloride is oxidized with nitric acid, the temperature may be above room temperature, but the higher the temperature, the higher the reaction rate. However, in this case, the reaction rate is also affected by the concentration of the nitric acid aqueous solution as the oxidizing agent. For example, when the reaction temperature is 100°C and the reaction time is the same, the reaction rate is about 41% for a 57% by weight nitric acid aqueous solution (= about 66% by weight).
In a nitric acid aqueous solution of % by weight, the reaction rate is 100%.

Therefore, the oxidation reaction of nitrosyl chloride with nitric acid (=
The reaction conditions are determined by the relationship between the reaction temperature and the concentration of the nitric acid aqueous solution, but preferably the reaction temperature is 80°C or higher,
At a temperature below 120°C, the concentration of the nitric acid aqueous solution at this time is 57
% by weight or more. The reaction in this case is as follows.

/NOCt-141N0.4NO, +/C4+, (H,
O(2) Nitrogen dioxide produced together with chlorine in reaction (2) is dissolved and absorbed in water to produce nitric acid, which is recycled again in reactions (1) and (2).

Next, in the second step, the sodium nitrate produced in the first step is reacted with calcium fluoride and silicon tetrafluoride. The reaction in this case is as follows.

NaNα+4CaFt+ 4S+ Fa→rkS'
Fa+ 4Ca(Na), (3) This reaction (3) is carried out in an aqueous solution. The reaction temperature may be room temperature, and the produced sodium hexafluorosilicate precipitates as crystals.

However, since this sodium hexafluorosilicate is difficult to dissolve in cold water but dissolves in hot water, it is preferable to cool the aqueous solution in order to efficiently separate and recover it. Sodium hexafluorosilicate thus precipitated is subjected to f-superpartitioning by conventional means and then thermally decomposed.

The reaction in this case is as follows.

/Na, S+F, -+ NaF + i+Ft (4
) This reaction (4) starts at about 500°C,
Preferably, the temperature is maintained in a temperature range of 600°C or higher and 950°C or lower (-).While the sodium fluoride produced by reaction (4) f2 is solid, the silicon tetrafluoride produced at the same time is a gas. Therefore, there is no need to take special measures to separate the product.The silicon tetrafluoride produced at this time is recycled and used again in the reaction (3).The obtained sodium fluoride is lucicum and water.

The reaction in this case is as follows.

NaF+4CaOjupeki0 → NaoH+4CaF, (5)
This reaction (5) is actually carried out by adding sodium fluoride to an aqueous suspension of calcium hydroxide produced by adding calcium oxide to water, or by adding sodium fluoride to water. This is carried out by adding oxidizing lucicum or calcium hydroxide to the solution after dissolution, but the quality of the caustic soda obtained is the same in either case. In this case, the reaction proceeds at room temperature, but is preferably maintained at a temperature range of 70°C or higher and lower than the boiling point of the aqueous solution. Caustic soda produced by reaction (5) is obtained as an aqueous solution,
Since calcium fluoride is produced together with caustic soda and precipitated as crystals, it is recirculated and used in the reaction (3) after being overperformed by a conventional means.

On the other hand, calcium nitrate produced together with sodium hexafluorosilicate in reaction (3) and dissolved in the aqueous solution is recovered as a solid by normal means (secondary evaporation of water). The reaction in this case is as follows.

4Ca (Na), -) 4CaO+NO++iO,
(6) This reaction (6) starts at about 561°C, but is preferably maintained at a temperature range of 600°C or higher and 950°C or lower. Reaction (6) (=The calcium oxide thus produced is recycled again in the reaction (5).

In addition, nitrogen dioxide and oxygen produced together with calcium oxide are both dissolved and absorbed in water to produce nitric acid, and the above reaction (
It is used cyclically in 1) and (2).

The reaction in this case is as follows.

2Nα+1−(, O+/α→2HNO, (force) In this way, chlorine and caustic soda can be efficiently produced from sodium chloride.

〔Effect of the invention〕

The effects of this invention are listed below.

1) In power generation, heat is used as it is without using electricity, which has a low heat-to-electricity conversion efficiency, as an energy source, so it can save a lot of energy.

2) All intermediate products, except for chlorine and caustic soda, are recycled, so not only do industrial wastes not be generated, but the substances consumed, in addition to sodium chloride as a raw material, exist naturally in inexhaustible quantities. Only water and air (oxygen). Therefore, there is no need for environmental and resource concerns.

3) Not only naturally occurring salt, but also Chilean saltpetre and calice, which is a mixture of Chilean saltpetre and salt, naturally occurring in Chile and Peru in South America can be effectively used. In other words, if the method of the present invention is applied to saltpetre and calice as raw materials, it is possible to produce caustic soda and nitric acid in the case of saltpeter, and chlorine, caustic soda, and nitric acid in the case of calice, and the ingredients contained in the raw materials are Every bit of it is used effectively, and there are no waste components. Moreover, the substances consumed in each case are water and air (
(oxygen) only.

4) Since no special corrosive substances are generated during the reaction at high temperatures, special corrosion-resistant materials are not required for the high-temperature equipment.

5) The silicon tetrafluoride gas generated by the thermal decomposition of sodium hexafluorosilicate is completely absorbed into the aqueous solution containing sodium nitrate and calcium fluoride and reacts with it, posing a health and safety problem. There is no risk that waste gas containing fluorine will be released.

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples.

Example 300m/In a glass reactor, sodium chloride 5.8
Add 5S' and 20vtl of 64% by weight nitric acid aqueous solution and
By reacting for 10 minutes at 0C, chlorine, nitrosyl chloride and sodium nitrate are produced.

The nitrosyl chloride generated at this time was cooled and separated, and the chlorine was introduced as a gas into a 0.18ON sodium hydroxide aqueous solution, absorbed, reacted, and quantified.
It was 341. On the other hand, the cooled and separated nitrosyl chloride was passed through a 66% by weight aqueous nitric acid solution at 100°C while being heated and vaporized. At this time, a nitric acid aqueous solution is poured into a glass cylindrical tube to a depth of approximately 18 cm, and gaseous nitrosyl chloride is blown in from the bottom of the tube together with oxygen so that the gas comes into contact with the nitric acid aqueous solution, passes through it, and escapes to the top. After passing through the nitric acid aqueous solution, the gas was reduced to 0.
The amount of chlorine generated was 1.101 when introduced into an 18ON sodium hydroxide aqueous solution, absorbed, reacted, and quantitatively determined. The overall yield of chlorine was 97.2%.

Next, the sodium nitrate produced with chlorine is separated, and all of the sodium nitrate dissolved in the liquid f is evaporated to dryness and collected, and all of them are dissolved in water again to make a total of 100m/bin. In this, calcium fluoride (24.07) was suspended. This suspension was then placed in a 300 m/glass cracked absorption bottle, and silicon tetrafluoride gas was blown in at room temperature for about 20 minutes while stirring. , to produce sodium hexafluorosilicate.Next, the crystals of sodium hexafluorosilicate precipitated in the aqueous solution were collected by filtration, placed in a platinum boat, and heated in an electric furnace.Approximately 750°
After thermal decomposition at C for 1 hour, the mixture was naturally cooled to room temperature. The sodium fluoride produced in the platinum boat was added to a 100° C. hydroxide suspension aqueous solution and allowed to react for about 20 minutes. Thereafter, the solution was naturally cooled to room temperature, and the calcium fluoride crystals formed and clouded in the aqueous solution were separated by filtration using R paper. When the caustic soda concentration in the F solution was examined, it was found to be 166% by weight. Also, at this time, r
The separated calcium fluoride crystals were completely washed with water, the amount of caustic soda contained in the water after washing was determined, and the amount of caustic soda in the liquid F was added to determine the total amount of the generated caustic soda. The place is 3.70? Met. Therefore, the yield of caustic soda was 92.7% based on sodium chloride.

Claims (1)

[Claims] (1) In thermochemically decomposing sodium chloride,
The sodium chloride is reacted with nitric acid to produce chlorine, nitrosyl chloride, and sodium nitrate, the obtained nitrosyl chloride is oxidized to produce chlorine, and the sodium nitrate obtained together with chlorine and nitrosyl chloride is reacted with calcium fluoride. Silicon tetrafluoride is reacted to produce sodium hexafluorosilicate, the obtained sodium hexafluorosilicate is thermally decomposed to produce sodium fluoride, and then calcium oxide and water are added to the obtained sodium fluoride. A method for producing chlorine and caustic soda, the method comprising reacting chlorine and caustic soda to produce caustic soda.