JPH0251843B2 - - Google Patents

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 sodium metaborate to produce caustic soda. .

[Conventional technology]

Generally, when producing chlorine and caustic soda using sodium chloride as a raw material, diaphragm method, mercury method,
Electrolytic methods such as ion exchange membrane methods are widely used. By the way, the electrolysis method is defined by the power generation efficiency of heat to electricity conversion as an energy source. As is well known, the actual power generation efficiency is currently around 35%, and it cannot be said that energy is necessarily used effectively. Therefore, without converting heat into electricity,
If there was a way to produce chlorine and caustic soda from sodium chloride using heat directly,
It is estimated that energy consumption will be significantly reduced. Therefore, there is a strong demand for the development of such technology.

BACKGROUND ART Conventionally, as a method for producing chlorine from sodium chloride by a thermochemical reaction, the nitrosyl chloride method has been carried out industrially. However, this method is no longer practiced due to limited demand for sodium nitrate, which is a by-product along with chlorine. In addition, as methods for producing caustic soda through thermochemical reactions, the slaked lime method using sodium carbonate as a raw material, the Lo¨wig method, and the fluoride method have been used in the past, but all of these methods disappeared with the advent of electrolysis. I deleted it. The main reason for this is that electrolysis can produce both chlorine and caustic soda from sodium chloride, whereas methods using thermochemical reactions produce only chlorine or sodium carbonate from sodium chloride. This is because it was not possible to produce both chlorine and caustic soda. Known methods for producing sodium carbonate using sodium chloride as a raw material include the Le Blanc method, the ammonia-soda method, and the ammonium chloride method, but none of them 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 sodium chloride as a raw material and exclusively using 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]

In thermochemically decomposing sodium chloride, this invention reacts the sodium chloride with nitric acid to produce chlorine, nitrosyl chloride, and sodium nitrate, oxidizes the obtained nitrosyl chloride to produce chlorine, and , reacting the obtained sodium nitrate with chlorine and nitrosyl chloride with sodium metaborate to produce a boron compound, and then hydrolyzing the boron compound to produce a mixed aqueous solution of caustic soda and sodium metaborate,
This is a method for obtaining caustic soda by precipitating and separating crystals of sodium metaborate from the resulting mixed aqueous solution.

In this method, the boron compound produced as an intermediate is a white powdery solid having the general formula Na ₄ B ₂ O ₅ .

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 less than 58% by weight, the reaction rate is less than 75% even at a reaction temperature of 140°C. However, when the concentration of the nitric acid aqueous solution exceeds 60% by weight, 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 step is determined in relation to the concentration of the nitric acid aqueous solution, but preferably the reaction temperature is 80°C or higher and 140°C or lower, and the concentration of the nitric acid aqueous solution at this time is 60% by weight or higher. , kept within a range of 65% by weight or less. The reaction in this case is as follows.

NaCl + 4/3HNO ₃ →NaNO ₃ +1/3NOCl + 1/3Cl ₂ +2/3H ₂ O (1) 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. Chlorine and nitrosyl chloride, which are generated as gases, have respective condensation temperatures of −34.1°C for chlorine and −34.1°C for nitrosyl chloride.
Since the temperature is 5.5℃, these differences are used for cooling and separation. The nitrosyl chloride thus cold-separated is then oxidized with air, oxygen, or nitric acid. In the case of oxidation with air and oxygen, the reaction temperature is relatively high at 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, if the reaction temperature is 100°C and the reaction time is the same, the reaction rate is approximately 41% with a 57% by weight nitric acid aqueous solution.
%, whereas in a 66% by weight nitric acid aqueous solution, the reaction rate is 100%. Therefore, the reaction conditions for the oxidation reaction of nitrosyl chloride with nitric acid 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℃, the concentration of nitric acid aqueous solution at this time is 57
% by weight or more. The reaction in this case is as follows.

1/3NOCl + 2/3HNO ₃ →NO ₂ + 1/6Cl ₂ + 1/3H ₂ O (2) Nitrogen dioxide produced along with chlorine in this reaction (2) is dissolved and absorbed in water to produce nitric acid.
It is recycled again in the reactions (1) and (2).

Next, in the second step, sodium metaborate is reacted with the sodium nitrate produced in the first step. The reaction in this case is as follows.

NaNO ₃ +NaBO ₂ →1/2Na ₄ B ₂ O ₅ +NO ₂ +1/4O ₂ (3) This reaction (3) starts at about 500°C, but is preferably maintained at a temperature range of 600°C or higher and 900°C or lower. drooping While the boron compound produced by reaction (3) is solid, nitrogen dioxide and oxygen produced simultaneously are gases, so there is no need to take any special measures to separate the products. Further, both nitrogen dioxide and oxygen produced at this time are dissolved and absorbed in water to produce nitric acid, which is recycled and used again in the reactions (1) and (2). The reaction in this case is as follows.

2NO ₂ +H ₂ O+1/2O ₂ →2HNO ₃ (4) The obtained boron compound is then hydrolyzed. The reaction in this case is as follows.

1/2Na ₄ B ₂ O ₅ + 1/2H ₂ O→NaOH + NaBO ₂ (5) This reaction (5) proceeds even at room temperature, but in order to efficiently obtain a higher concentration caustic soda aqueous solution, The temperature is preferably kept at 60°C or higher and lower than the boiling point of the aqueous solution. The mixed aqueous solution of caustic soda and sodium metaborate produced in reaction (5) is then cooled. The cooling temperature in this case is preferably in the range of 0° C. or higher and room temperature or lower. When the mixed aqueous solution is cooled to such a temperature range, the dihydrate or tetrahydrate of sodium metaborate is precipitated as crystals from the aqueous solution. When the sodium metaborate crystals thus precipitated are separated by conventional means, caustic soda is obtained as an aqueous solution. The sodium metaborate crystals separated at this time were then heated,
Dehydrates the water contained in the crystals. The reaction in this case is as follows.

NaBO ₂ xH ₂ O→NaBO ₂ +xH ₂ O (6) (However, x is 2 or 4) This reaction (6) starts at about 300°C, but preferably at a temperature of 400°C or higher and 900°C or lower. Temperature range maintained. The sodium metaborate produced in reaction (6) is recycled and used again in the reaction (3).

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, resulting in significant energy savings.

(2) Intermediate products, excluding chlorine and caustic soda,
Since everything is recycled, not only does it not produce industrial waste, but the only substances consumed are water and air (oxygen), which naturally exist in inexhaustible quantities, in addition to sodium chloride as a raw material. Therefore, no environmental and resource concerns are necessary.

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

〔Example〕

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

Example In a 300ml glass reactor, sodium chloride
Add 5.85g and 20ml of 64% by weight nitric acid aqueous solution and heat at 130℃.
A 10 minute reaction produces chlorine, nitrosyl chloride and sodium nitrate. The nitrosyl chloride generated at this time was cooled and separated, and the chlorine was introduced as a gas into a 0.18N aqueous sodium hydroxide solution for an absorption reaction and quantified, and the amount of chlorine generated was 2.34 g. On the other hand, the cooled and separated nitrosyl chloride was heated and vaporized at 100°C.
was passed through a 66% by weight aqueous nitric acid solution. At this time, a nitric acid aqueous solution was placed in a glass cylindrical tube to a depth of approximately 18 cm, and gaseous nitrosyl chloride was blown into the bottom of the tube along with oxygen so that the gas came into contact with the nitric acid aqueous solution, passed through it, and escaped to the top. . After passing through the nitric acid aqueous solution, the gas was introduced into a 0.180N sodium hydroxide aqueous solution, absorbed and reacted, and the amount of chlorine generated was 1.10 g. The overall yield of chlorine was 97.2%. Next, the sodium nitrate produced along with chlorine is separated, and all the sodium nitrate dissolved in the liquid is evaporated to dryness and collected. They are placed in a platinum boat, and then sodium metaborate is placed on top of the sodium nitrate crystals. 10 g of crystals were added and heated in an electric furnace. about
After reacting at 700°C for 40 minutes, it was naturally cooled to room temperature. Next, when the boron compound produced in the platinum boat was poured into water at 100°C, the solid boron compound completely dissolved. Excess water was evaporated while maintaining the temperature of the resulting aqueous solution at about 100°C until the total solute concentration in the aqueous solution was 38.1% by weight.
Thereafter, this aqueous solution was naturally cooled to room temperature. Next, when this aqueous solution was cooled to about 7°C in a low-temperature thermostat, crystals of sodium metaborate hydrate began to form, so after keeping it as it was for about 10 minutes,
It was returned to room temperature. The resulting crystals were separated using paper, and the concentration of the resulting caustic soda aqueous solution was measured and found to be 22.7% by weight. In addition, after completely washing the separated sodium metaborate crystals with water, the amount of caustic soda in the washing water was measured.
The total amount of caustic soda in the caustic soda aqueous solution as the liquid was 3.64 g.

The yield of this caustic soda was 91.0% 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, and the obtained nitrosyl chloride is oxidized to produce chlorine. and on the other hand, reacting sodium metaborate with sodium nitrate obtained together with chlorine and nitrosyl chloride to produce a boron compound, and then hydrolyzing this boron compound to produce a mixed aqueous solution of caustic soda and sodium metaborate, 1. A method for thermochemically producing chlorine and caustic soda, characterized in that caustic soda is obtained by precipitating and separating crystals of sodium metaborate from the resulting mixed aqueous solution. 2. The manufacturing method according to claim 1, wherein the intermediate boron compound is a compound represented by the general formula Na ₄ B ₂ O ₅ .