JPS6265923A - Thermochemical 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 a raw material and mainly utilizing thermochemical reaction. CONSTITUTION:Sodium chloride is allowed to react with nitric acid to form chlorine, nitrosyl chloride and sodium nitrate and 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 sodium metaborate to form a boron compd. Then the boron compd. is hydrolyzed to form an aq. mixed soln. of caustic soda and sodium metaborate. The crystal of the sodium metaborate is deposited from the aq. mixed soln. and separated and caustic soda is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is a method for producing caustic soda by reacting sodium chloride with nitric acid to completely produce chlorine, and simultaneously treating the produced sodium nitrate with sodium metaborate. Regarding.

[Conventional technology]

Generally, #A pieces, which produce chlorine and caustic soda from sodium chloride, are widely used by electrolysis methods such as the diaphragm method, the mercury method, and the ion exchange method. By the way, the electrolysis method is defined by the power generation efficiency of heat → electricity exchange as an energy source. As is well known, the actual power generation efficiency at present is about 35 cm, and it cannot be said that energy is necessarily used effectively. Therefore, if there was a way to directly use heat to produce chlorine and caustic soda from sodium chloride without converting heat to electricity, it is estimated that a large amount of energy would be saved. .

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 because demand for sodium nitrate, which is a by-product along with chlorine, is limited. In addition, as methods for producing caustic soda through thermochemical reactions, there were the 0 method, the slaked lime method using sodium carbonate as a raw material, the L6w1i method, and the fluoride method, but all of them 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 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 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 and demands of the technical field as described above and overcomes the drawbacks of conventional methods.

[Means for solving problems]

In thermochemically decomposing sodium chloride, the present invention involves reacting the sodium chloride with nitric acid to produce chlorine, nitrosyl chloride, and sodium nitrate, oxidizing the obtained ichnitrosyl salt to produce chlorine, and , Sodium metaborate was reacted with sodium nitrate obtained together with chlorine and nitrosyl chloride to produce a boron compound, and then this boron compound was hydrolyzed 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 a mixed aqueous solution.

In this method, the boron compound produced as an intermediate is a white powdery solid represented by the general formula %.

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 58% by weight or less, the reaction temperature is 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 80°C or more and 140°C or less, and the concentration of the nitric acid aqueous solution at this time is 60% by weight or more, It is kept within a range of 65% by weight or less.The reaction in this case is as follows.

NaC1+/HNO,→NaN0. +Le N0C1+/,
, C12+”/, HzO (11 The separation of the products in the first stage is as follows. Since chlorine and nitrosyl chloride are gases at the reaction temperature, the sodium nitrate produced in the aqueous solution of nitrate is naturally Chlorine and nitrosyl chloride, which occur as gases, have respective condensation temperatures of -34,1°C for chlorine and -3 for nitrosyl salt.
Since the temperature is 5.5°C, these differences are utilized for cooling and separation. The nitrosyl chloride thus cold-separated is then oxidized with air, oxygen, or nitric acid. For oxidation with air and oxygen, the reaction temperature is approximately 2
The temperature is relatively high at 00'C. On the other hand, when oxidizing ichnitrosyl salt with nitric acid, the temperature may be above room temperature, but the higher the temperature, the higher the reaction rate.
The reaction rate is also influenced 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, a 57% by weight nitric acid aqueous solution has a reaction rate of about 41L%, whereas a 66% by weight nitric acid aqueous solution has a reaction rate of 100L%. 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.
Preferably, the reaction temperature is 80°C or higher and 120°C or lower,
At this time, the concentration of the nitric acid aqueous solution is maintained at 57% by weight or more. The reaction in this case is as follows.

ShiNOCI+/Ding〕3→No2+ //6C42+ruH
2O(2) Nitrogen dioxide produced along with chlorine in this reaction (2) is dissolved and absorbed by 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.

l NaNO3+ NaBO2→/ Na4B20s +N
02+ / 02 (3) This reaction (3) is about 5
Starting at 00°C, preferably in a temperature range of 600°C or higher and 900°C or lower. boron compound produced by reaction (3)].

is a solid, whereas nitrogen dioxide and oxygen produced at the same time are gases, so there is no need to take special measures to separate the products. Further, both the nitrogen dioxide and oxygen produced at this time are dissolved and absorbed in water to produce nitrate r1k, which is recycled and used again in the reactions fl) and (2). The reaction in this case is as follows.

2NO2+H20+'/102→2HN03The obtained boron compound is then hydrolyzed.

The reaction in this case is as follows.

'/Na4B205 + '7' H2O→NaOH
+NaBO2151 This reaction (5) proceeds even at room temperature, but in order to efficiently obtain a higher-strength caustic soda aqueous solution, it is preferably maintained at a temperature range of 60°C or higher and below the boiling point of the aqueous solution. . The mixed aqueous solution of caustic soda and sodium metaborate produced by 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.

The mixed aqueous solution is cooled to such a temperature range.
' Hydrate or tetrahydrate precipitates as crystals.

When the sodium metaborate crystals thus precipitated are separated by filtration by a conventional means, caustic soda is obtained as an aqueous solution. The sodium metaborate crystals separated at this time are then heated to dehydrate the water contained in the crystals. The reaction in this case is as follows.

NaBO2,xl-(20→NaBO2+ xH2O
f6) (wherein X is 2 or 4) This reaction f61 tf'i starts at about 300'C, but is preferably maintained at a temperature range of 400°C or more and 900°C or less. The sodium metabolite produced in reaction (6) is recycled 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.

1j3i) 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 is possible to save a large amount of energy.

(2) Since all intermediate products, except for chlorine and caustic soda, are recycled, not only no industrial waste is generated, but the consumed substances are chlorinated as raw materials.
Outside of Jum, water and air exist naturally in inexhaustible quantities (r!!
only). Therefore, there is no need for environmental and resource concerns.

(3) Not only naturally occurring salt, but also Chilean saltpeter and karinyu, which is naturally present in Chile and Peru in South America as a mixture of Chilean saltpeter and salt, can be effectively used. In other words, if the method of the present invention is applied to Chilean saltpetre and Karinyu as raw materials, it is possible to produce caustic soda and nitric acid in the case of Chilean saltpeter, and chlorine, caustic soda, and nitric acid in the case of Karinyu, and the ingredients contained in the raw materials are Every bit of it is 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 3 In a 00 ml glass reactor, 5.5 ml of sodium chloride was added.
85.9 and 64% by weight nitric acid aqueous solution 20 pouches 130℃
Chlorine, nitrosyl chloride and sodium nitrate are produced by reacting for 10 minutes.

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, followed by an absorption reaction and quantitatively determined.
It was 34g. On the other hand, while heating and vaporizing the cooled and separated nitrosyl chloride, 66% by weight at 100°C was heated.
It was passed through a nitric acid aqueous solution.

At this time, approximately 18 crrL of nitric acid aqueous solution was added to the all-glass pear cylindrical tube.
Gaseous nitrochloride and nitrogen were blown into the tank from the bottom of the tank, and the gas came into contact with the aqueous nitric acid solution, passed through it, and escaped to the top. The gas that had completely passed through the nitric acid aqueous solution was introduced into a 0.18ON sodium hydroxide aqueous solution, absorbed, reacted, and quantified, and the amount of chlorine generated was 1.10. ! It was 9. The overall yield of chlorine was 97.2%.

Next, the sodium nitrate produced with chlorine is collected from door to door, and all of the sodium nitrate dissolved in the P solution is evaporated to dryness.Then is then placed in a platinum boat, and then the sodium nitrate crystals are placed on top of the sodium nitrate crystals. Sodium metaborate crystal 10
! ? Q was added and heated in an electric furnace. 40 at about 700℃
After reacting for a minute, the mixture 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. While maintaining the temperature If of the resulting aqueous solution at about 100° C., excess water was evaporated until the total solute concentration in the aqueous solution was 38.1% by weight. After that, this aqueous solution was naturally cooled to room temperature.7Next, this aqueous solution was cooled to about 7℃ in a low-temperature constant temperature bath, and soon crystals of hydrated sodium metahousate were formed, so after keeping it as it was for about 10 minutes, it was again cooled. Returned to room temperature. The formed crystals are filtered and separated using two pieces of paper.
When the concentration of the obtained caustic soda aqueous solution was measured, it was found that 2
It was 2.7% 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, and the sum of this amount and the amount of caustic soda in the aqueous solution of caustic soda as the P solution was 3.64.
．． The yield of this caustic soda was 91.0% based on sodium chloride.

Claims (2)

[Claims] (1) In thermochemically decomposing sodium chloride,
The sodium chloride is reacted with nitric acid to produce chlorine, nitrosyl chloride and sodium nitrate, the resulting nitrosyl chloride is oxidized to produce chlorine, while the resulting sodium nitrate along with chlorine and nitrosyl chloride is reacted with sodium metaborate. react to produce a boron compound, then hydrolyze this boron compound to produce a mixed aqueous solution of caustic soda and sodium metaborate, and precipitate and separate crystals of sodium metaborate from the resulting mixed aqueous solution. A method for thermochemically producing chlorine and caustic soda, the method comprising obtaining caustic soda by: (2) The boron compound formed in the middle has the general formula Na_4B
The manufacturing method according to claim 1, which is a compound represented by _2O_5.