JPH0621005B2 - Chlorine dioxide manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing chlorine dioxide by reacting sodium chlorate with a reducing agent.

(Prior art) The methods of chlorine dioxide production currently industrially implemented are roughly divided into i) a method of reducing sodium chlorate with sulfurous acid gas with an acidic sulfuric acid solution, and ii) sodium chloride with an acidic sulfuric acid solution and hydrogen chloride. Reduction method iii) Reduction method of sodium chlorate or calcium chlorate with hydrochloric acid In any of these methods, a reaction waste liquid is produced together with chlorine dioxide (and chlorine). In the case of each of the above methods i) and ii), sulfuric acid and Glauber's salt are the main components and a small amount of sodium chlorate is contained, but in many cases, the Glauber's salt is effectively used by mixing it with the cooking black liquor for papermaking pulp. is doing. It may also be used for the production of sulphate soil.

However, there is a limit to the amount of waste liquid that can be used, and if the amount of waste liquid exceeds that amount, it must be abandoned, and in that case, neutralizing chemicals etc. are required, which requires a large amount of expense. . In particular, the method ii) has been adopted by many factories recently because it is easier to operate than i), but the amount of reaction waste liquid generated is extremely large (about 1.1 tons of Glauber's salt per ton of chlorine dioxide generated). , About 7 tons including about 2 tons of sulfuric acid are by-produced) The treatment method is often problematic. Although the amount of waste liquid in the method i) is smaller than that, a sulfurous acid gas generator is required, and in that respect, the operation operation becomes complicated and there is a possibility that pollution problems due to sulfurous acid gas may occur.
Further, as a method for improving the methods i) and ii), there is a method of recovering neutral Glauber's salt or acidic Glauber's salt from the reaction waste liquid and reusing sulfuric acid, which is convenient for solving the above-mentioned waste liquid problem. Alternatively, there is a drawback in that an equipment such as an evaporator is required and the equipment cost is extremely high and the operation is complicated. Also, ii
The method i) produces a small amount of chlorate and salt or dilute hydrochloric acid solution of calcium chloride as waste liquid, but these are not useful as paper-making chemicals and are abandoned after neutralization with a small amount of alkali. It is economically disadvantageous as compared with the method of effectively utilizing. There is also a method of electrolyzing this waste liquid (in the case of a salt solution) and returning it to sodium chlorate again.
It is economically disadvantageous because the salt concentration is low, so concentration is required and equipment costs are high. If salt is added without concentration, an unnecessarily large amount of concentrated salt solution will be generated because the amount of waste liquid will be large, which will be extremely irrational on the whole plant scale including the electrolysis process. become.

Further, the method i) is a method in which only chlorine dioxide is generated, whereas the method ii) and iii) is characterized in that chlorine is simultaneously generated. Usually, this by-product chlorine is separated from chlorine dioxide in the absorption stage, then absorbed by caustic alkali and consumed as sodium hypochlorite in the pulp bleaching process. However, when the amount of sodium hypochlorite used is small in the bleaching step, its excess becomes a problem. Most of the methods currently used industrially are i) and ii), and the method most often used is the method of ii). The advantage of this method is that it does not require complicated auxiliary equipment such as a sulfurous acid gas generator and a sodium sulfate recovery device as described above, therefore the equipment cost is low and the operation is simple. Is also the best. On the other hand, as a drawback, the amount of waste liquid generated is larger than that in i), and chlorine gas is a byproduct, which often causes a problem when the scale of the generator increases.

As for the generated waste liquid, in the method of reducing sodium chlorate with hydrogen chloride under sulfuric acid acidity, there are cases where hydrochloric acid is used as a hydrogen chloride source and where salt and sulfuric acid are used. In the past, common salt and sulfuric acid were often used, but since this increases the amount of sodium ions in the system, resulting in an increase in the amount of waste liquid due to the solubility, hydrochloric acid has recently been often used. Although the amount of waste liquid was certainly reduced by this, about 1.3 times as much waste liquid was produced as compared with the method i) because of the water entering the system with hydrochloric acid. As described above, by-product chlorine may be a problem.

(Problems to be Solved by the Invention) The present invention is capable of reducing the amount of by-product chlorine and the amount of waste liquid in the method of generating chlorine dioxide using hydrochloric acid as a reducing agent, which is industrially possible. The aim is to provide an advantageous method.

(Means for Solving the Problems) The present invention is to divide a reaction zone into two in the production of chlorine dioxide by reacting a reducing agent with sodium chlorate.
(I) Sodium chlorate, methanol, and sulfuric acid are added and reacted in the reaction zone A, and (II) Hydrogen peroxide or hydrogen peroxide and sulfuric acid are added and reacted with the waste liquid from A in the reaction zone B and left. It is a method for producing chlorine dioxide, which is characterized by decomposing sodium chlorate and separating and obtaining chlorine dioxide generated from each reaction zone.

Next, the method of the present invention will be described with reference to the drawings.

To the chlorine dioxide generation tank (1) (reaction zone A), add sulfuric acid (4) together with sodium chlorate (3) from the storage tank (2), and introduce methanol (5) together with the inert gas (9) described below. To do. Further, to the chlorine dioxide generation tank (6) (reaction zone B), lead the waste liquid (7) from the chlorine dioxide generation tank (1) that has been reacted so that sodium chlorate remains, and add hydrogen peroxide (8). . Chlorine dioxide gas (10) generated by inhaling an inert gas (9) such as air is taken out from the bottom of each tank (1) (6), led to a chlorine dioxide absorption tower (11) and cooled with cold water (12). Chlorine dioxide is absorbed to produce chlorine dioxide water (13). Waste liquid from chlorine dioxide generation tank (6)
(14) has sulfuric acid and Glauber's salt as main components and is used for pulp cooking. The chlorine dioxide gas absorption part generated in each chlorine dioxide generation tank may be common. The decomposition rates of sodium chlorate in reaction zones A and B are methanol,
It can be arbitrarily adjusted by the addition amount of sulfuric acid and hydrogen peroxide. The required amount of sulfuric acid may be added to the reaction zone A or a part thereof may be added to the reaction zone B.

The main reaction equation in reaction zone A (chlorine dioxide generation tank 1) is shown by the following equation: NaClO ₃ + 1 / 2H ₂ SO ₄ + 1 / 2CH ₃ OH → ClO ₂ + 1 / 2Na ₂ SO ₄ + 1 / 2HCHO + H ₂ O ... (1) The main reaction equation in the reaction zone B (chlorine dioxide generation tank 6) is shown by the following equation.

NaClO ₃ + 1 / 2H ₂ SO ₂ + 1 / 2CH ₂ SO ₄ → ClO ₂ + 1 / 2Na ₂ SO ₄ + H ₂ O + 1 / 2O ₂ (2) (Action) Sodium chlorate acidified with sulfuric acid by methanol A method for producing chlorine dioxide by reducing an aqueous solution is known as a "Solvay method". However, this reaction has a very good reaction yield, but is very slow. Even if a large number of large-capacity reactors are used, a large amount of waste liquid containing unreacted sodium chlorate, etc. is discharged, and this reaction rate It was considered that the raw material soda chlorate was inferior in unit consumption due to its low value.

In the method of the present invention, since the reaction with methanol is carried out only in the reaction zone A, even if the unreacted sodium chlorate is contained in the reaction waste liquid from the reaction zone A, it is more efficiently decomposed in the reaction zone B into chlorine dioxide. Therefore, the basic unit of sodium chlorate is good as a whole.

Further, since methanol is inexpensive, its amount used is small, and the amount of sulfuric acid used is relatively reduced, it does not increase the production cost of chlorine dioxide. On the other hand, a method of reducing by-product chlorine accompanying the generation of chlorine dioxide gas with hydrogen peroxide is disclosed in JP-A-53-53.
As described in JP-A-66892 and JP-A-63-8203, hydrogen peroxide is expensive and causes an increase in production cost of chlorine dioxide. However, in the method of the present invention, since the use thereof is limited to the reaction zone B, the use amount thereof can be relatively reduced with respect to the chlorine dioxide generation amount and the cost is not increased.

(Effects of the Invention) Various advantages of the method of the present invention are listed below.

1) Since hydrochloric acid or a chloride serving as a hydrogen chloride generation source is not used in the reaction zones A and B, the amount of by-product chlorine can be reduced or substantially reduced to zero, so that the problem due to excess by-product chlorine can be solved. It is also possible to deal with the decrease in the amount of sodium hypochlorite or chlorine used in the bleaching process.

2) Since the amount of water entering the system is reduced, the conventional method ii)
It is possible to further reduce the amount of waste liquid as compared with the method of i). Therefore, the problem due to excess waste liquid can be avoided.

3) In addition to the above advantages, the economically expensive hydrogen peroxide and the inexpensive methanol are used in combination to keep the balance, and the production cost of chlorine dioxide is not increased as compared with the conventional method.

4) The conventional method does not require auxiliary equipment such as a sulfurous acid gas generator, waste liquid concentration equipment, crystallization equipment, etc., and the operation is simple and automatic operation can be carried out easily. Costs and operating costs can be reduced, and conversion from existing equipment can be done easily.

(Examples) The method of the present invention will be described below with reference to Examples and Comparative Examples.

Example 1 Using the apparatus shown in the drawings, 639 g of NaClO _{3 was} added to reaction zone A.
Aqueous solution of 31 / hr, concentrated sulfuric acid 14.9 / hr
At a rate of 40 ° C., and methanol was blown in from the bottom at a rate of 2.5 / hr and air was blown at a rate of 28 Nm ³ / hr. The flow rate of the waste liquid discharged from the reaction zone A is 41
/ Hr, composition: NaClO ₃ 90 g /, H ₂ SO ₄ 483 g /
, Na ₂ SO ₄ 267 g /, methanol trace, while introducing this into the reaction zone B, hydrogen peroxide solution (H ₂ O ₂ 35
%) At a ratio of 1.4 / hr, and the liquid is 50-60.
After heating to ℃, air was blown in from the bottom at a rate of 5.7 m ³ / hr. Gas evolved from reaction zone A (ClO ₂ 10.
1 kg / hr) and the gas generated from the reaction zone B (ClO ₂ 2
(kg / hr) is absorbed in cold water at 5 ° C. in the same chlorine dioxide absorption tower to give 172 chlorine dioxide water (ClO ₂ 7 g /).
Obtained at a rate of 0 / hr. On the other hand, the flow rate of the waste liquid flowing out from the reaction zone B is 40 / hr, the composition is NaClO ₃ 10 g /, Na
₂ SO ₄ 324 g /, H ₂ SO ₄ 450 g /, H ₂ O ₂ trace, and each substance basic unit per ton of chlorine dioxide generated was as follows.

1,650 kg of NaClO ₃ , 140 kg of 35% H ₂ O ₂ , 2,290 kg of H ₂ SO ₄ , 167 kg of methanol, 1,500 kg of waste sulfuric acid Comparative Example 1 In reaction zone A, an aqueous solution of 639 g of NaClO ₃ 25.8.
/ Hr, concentrated sulfuric acid 14.2 / hr, 35% hydrogen peroxide solution 7 / hr, and the mixture is heated to 40 to 60 ° C.
Further, air is blown from the bottom at a rate of 28 Nm ³ / hr.
Generated gas (ClO ₂ 10.1 kg / hr) is absorbed in cold water at 5 ° C. to make chlorine dioxide water (ClO ₂ 7 g /) 1430
/ Hr. On the other hand, the flow rate of the waste liquid flowing out from the reaction zone A is 38 / hr, the composition is NaClO ₃ 8 g /, Na ₂ SO ₄
It was 289 g /, H ₂ SO ₄ 465 g /, H ₂ O ₂ trace, and the basic unit of each substance per ton of chlorine dioxide generated was as follows.

NaClO _3, 1,650 kg, 35% H ₂ O ₂ 850 kg, H ₂
SO _4, 2,560 kg, waste sulfuric acid 1,770 kg In this example, sodium chlorate is reduced with hydrogen peroxide using chlorine ion as a medium in a sulfuric acid acidic solution to generate chlorine dioxide. It requires much expensive hydrogen peroxide and is inferior in economic efficiency (By the way, the market price of 35% hydrogen peroxide is about three times that of methanol).

Comparative Example 2 In reaction zone A, an aqueous solution of NaClO ₃ 639 g / 31 /
hr and concentrated sulfuric acid 14.9 / hr were added at a ratio of 40-
Warm up to 50 ° C and methanol 25.2 / h from the bottom
r and air were blown in at a rate of 28 Nm ³ / hr. on the other hand,
The flow rate of waste liquid flowing out from the reaction zone A is 40.3 / hr,
The composition is 90 g of NaClO ₃ /, 267 g of Na ₂ SO ₄ /, H ₂
SO _{4 was} 483 g /, and the basic unit of each substance per ton of chlorine dioxide generated was as follows.

NaClO _3, 1,980 kg, methanol 200 kg, H ₂ SO
₄ 2,740Kg, waste sulfuric acid 1,950kg This example is the so-called Solvay Process for reducing the chlorine sodium in methanol with sulfuric acid acidic solution, although byproduct chlorine than in Example is almost zero, the waste sulfuric acid number It can be seen that the basic unit of sodium chlorate is also poor and the economy is poor.

[Brief description of drawings]

The drawing is a schematic diagram showing an apparatus for carrying out the method of the present invention. 1 ... Chlorine dioxide generation tank (reaction zone A), 6 ... Same (reaction zone B), 3 ... Sodium chlorate aqueous solution injection path, 4 ... Sulfuric acid injection path, 5 ... Methanol injection path, 7 ... Waste liquid path from reaction zone A to B, 8 ... Hydrogen peroxide water injection path, 11 ... Chlorine dioxide absorption tower.

Claims (1)

[Claims] 1. To produce chlorine dioxide by reacting sodium chlorate with a reducing agent, the reaction zone is divided into two parts, and (I) reaction zone A is reacted with sodium chlorate, methanol and sulfuric acid. (II) In the reaction zone B, hydrogen peroxide, or hydrogen peroxide and sulfuric acid are added to the waste liquid from A to react with each other to decompose the residual sodium chlorate and to obtain chlorine dioxide generated from each reaction zone. Characteristic chlorine dioxide production method.