JPH0621004B2 - 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 chlorine dioxide production methods that are currently used industrially are roughly divided into i) a method of reducing sodium chlorate with sulfurous acid gas with a sulfuric acid acidic solution ii) sodium chlorate with hydrogen chloride with an acidic sulfuric acid solution Method of reduction iii) Method of reducing 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 cases of i) and ii) above, both contain sulfuric acid and Glauber's salt as main components and a small amount of sodium chlorate, but in many cases, they are mixed with cooking black liquor for papermaking pulp to effectively utilize Glauber's salt. is doing. It may also be used for the production of sulphate soil.

However, there is a limit to the absolute amount of waste liquid that can be used, and if a waste liquid that exceeds that amount is generated, it must be discarded, and in that case, a neutralizing agent or the like is 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 of the method i) is smaller than this, a sulfurous acid gas generator is required, which may complicate the operation and cause pollution problems due to sulfurous acid gas. 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,
Although it is convenient for solving the above-mentioned waste liquid problem, it has a drawback that a refrigerator or an evaporator is required, but the facility cost is extremely high and the operation is complicated. In addition, the method iii) produces a small amount of chlorate and dilute hydrochloric acid solution of salt or calcium chloride as waste liquid, but these are not useful as paper-making agents and are abandoned after neutralization with a small amount of alkali. However, it is economically disadvantageous as compared with the method of effectively utilizing the waste liquid. Further, there is a method of electrolyzing this waste liquid (in the case of a salt solution) and returning it to sodium chlorate again, but since the salt concentration is thin, concentration is required and the equipment cost is large, which is economically disadvantageous. 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.

In addition, the method i) produces only chlorine dioxide, while the method ii) iii) is characterized by the simultaneous production of chlorine. 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), but the method most often used is the method of ii). As described above, 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. Therefore, the equipment cost is low and the operation is simple. The basic unit is also the best. On the other hand, the drawback is that the amount of waste liquid generated is
Compared to i), there are more, and chlorine gas as a by-product often causes problems as 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. This certainly reduced the amount of waste liquid, but since it enters the system with hydrochloric acid, about 1.3 times as much waste liquid is produced as compared with the method of i). 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 chlorine dioxide generation method using hydrochloric acid as a reducing agent. It is an object to provide an industrially advantageous method in which these amounts can be adjusted according to the needs of the house.

(Means for Solving the Problems) The present invention is to divide a reaction zone into two in the production of chlorine dioxide by reacting sodium chlorate with a reducing agent, and (I)
Sodium chlorate, methanol and sulfuric acid are added and reacted in the reaction zone A, and (II) In the reaction zone B, hydrochloric acid is added and reacted with the waste liquid from A to decompose the residual sodium chlorate, which is generated from each reaction zone. This is a chlorine dioxide production method characterized in that chlorine dioxide is obtained separately from a mixed gas of chlorine dioxide and chlorine.

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 sodium chlorate (3) and sulfuric acid (4) from the storage tank (2), and introduce methanol (5) together with the inert gas (10) described below. To do. Further, to the chlorine dioxide generation tank (7) (reaction zone B), the waste liquid (8) from the chlorine dioxide generation tank (1) reacted so that the sodium chlorate remains, is introduced and hydrochloric acid (9) is added. A mixed gas (11) of chlorine dioxide and chlorine generated by sucking an inert gas (10) such as air is taken out from the bottom of each tank (1) (7), and introduced into a chlorine dioxide absorption tower (12) to cool water ( Chlorine dioxide gas is absorbed by 13) to produce chlorine dioxide water (14). Chlorine gas that is not absorbed by water is guided to the chlorine absorption tower (15) and absorbed by caustic alkali or lime milk (16), hypochlorite solution (17)
And The waste liquid (18) from the chlorine dioxide generation tank (7) contains sulfuric acid and Glauber's salt as main components, and is used for black liquor for pulp cooking. Although the ratio of chlorine dioxide and chlorine generated in each chlorine dioxide generation tank is different, the gas absorption part can be common. The separation method of chlorine dioxide and chlorine is not limited to the method exemplified here, and various known chemical and physical separation methods can be applied.

In the reaction zone A, only chlorine dioxide gas is generated. The decomposition rate of each sodium chlorate in the reaction zones A and B can be arbitrarily adjusted by the addition amounts of methanol, hydrochloric acid and sulfuric acid. 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 equations in the reaction zone A (chlorine dioxide generation tank 1) are shown by the following equations (1) and (2).

NaClO ₃ + 1 / 2H ₂ SO ₄ + 1 / 2CH ₃ OH → ClO ₂ + 1 / 2Na ₂ SO ₄ + 1 / 2HCHO + H ₂ O… (1) Also in reaction zone B (chlorine dioxide generation tank 7) The reaction formula is shown by the following formula (2).

2NaClO ₃ + 4HCl → 2ClO ₂ + Cl ₂ + 2NaCl + 2H ₂ O (2) (Action and effect of the invention) In the method of the present invention, the reaction zone is divided into AB as described above, and different reducing agents are used respectively. In addition, the following effects are produced by adjusting the reaction rates of the above two zones.

1) As a result of replacing hydrochloric acid used as a reducing agent in the reaction zone A with methanol, the amount of water entering the system is reduced. Problems of waste liquid treatment are avoided.

2) Similarly, by using methanol in the reaction zone A, the amount of by-product chlorine can be reduced, and the problem due to excess by-product chlorine can be solved.

That is, when chlorine (for example, sodium hypochlorite as a bleaching agent) is not required at the demand destination, the reaction rate in the reaction zone A may be increased. On the contrary, when chlorine does not meet the required amount of the demand destination, the reaction rate in the reaction zone B may be increased. As described above, it is a great feature of the method of the present invention that the production amount of the by-product can be arbitrarily adjusted depending on the demand of the customer.

3) The use of methanol as a reducing agent is known per se as the “Solvay method”. However, this reaction has a good reaction yield from the beginning, 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 is discharged and the reaction rate is low. As a result, the raw material soda chlorate is inferior in the basic unit, which has been regarded as a drawback.

In the method of the present invention, the reaction with methanol is carried out only in the reaction zone A. Therefore, if the unreacted sodium chlorate is left in the waste liquid from A, the reaction is carried out in the reaction zone B.
In the above, since it is efficiently decomposed into hydrochloric acid by hydrochloric acid and becomes chlorine dioxide, the drawbacks of the methanol method are covered, and the basic unit of sodium chlorate is improved as a whole.

4) It does not require complicated auxiliary equipment such as a sulfurous acid gas generator, waste liquid concentration equipment or crystallization equipment like the method of i) above, and the operation is simple and automatic operation can be performed easily. . Therefore, it is easy to convert existing equipment to reduce the amount of chlorine by-product and the amount of waste liquid generated. Further, methanol is inexpensive and can be used in a small amount, and the amount of sulfuric acid used is relatively reduced, so that the cost of chlorine dioxide is not increased.

(Example) Hereinafter, the present invention will be described with reference to Examples and Comparative Examples.

Example 1 In reaction zone A, an aqueous solution of 639 g / g NaClO _{3 was} added at 31 / hr.
And at the same time with concentrated sulfuric acid at a ratio of 14.9 / hr. This is heated to 40 to 50 ° C. and blown with methanol at a rate of 2.5 / hr and air at a rate of 28 Nm ³ / hr from the lower part.
The flow rate of the waste liquid discharged from the reaction zone A is 40 / hr, and the composition is NaClO ₃ 90 g /, Na ₂ SO ₄ 267 g /, H ₂ SO ₄
482 g /, methanol 1 g /, HCHO trace, and while introducing this into the reaction zone B, 35% hydrochloric acid was added to 2.
It is poured at a rate of 9 / hr and the liquid is heated to 50-60 ° C,
Air was blown from the bottom at a rate of 5.7 Nm ³ / hr. Gas evolved from reaction zone A (ClO ₂ 10.1 kg / hr) and gas evolved from reaction zone B (ClO ₂ 2 kg / hr, Cl ₂ 1.2 k
(g / hr) is absorbed in cold water at 5 ° C. in the same chlorine dioxide absorption tower, and chlorine dioxide water (ClO ₂ 7 g /, Cl ₂ 0.3 g /
) Was obtained at a rate of 1720 / hr. Further, the exhaust gas from the absorption tower is absorbed in 40 g of NaOH / water solution to give a sodium hypochlorite solution (effective chlorine of 31.6 g /) at 22 / hr.
Obtained in proportion. On the other hand, the flow rate of the waste liquid from the reaction zone B is 4
0.7 / hr, composition: NaClO ₃ 10 g /, HCl ₂ g /
, Na ₂ SO ₄ 318 g /, H ₂ SO ₄ 441 g /,
The basic unit of each substance per ton of chlorine dioxide generated was as follows.

1,650 kg of NaClO ₃ , 285 kg of 35% hydrochloric acid, 2,290 kg of H ₂ SO ₄ , 167 kg of methanol, 1,500 kg of waste sulfuric acid, 100 kg of by-product Cl ₂ Comparative Example 1 In reaction zone A, an aqueous solution of 639 g of NaClO ₃ of 25.8 was used.
/ Hr, concentrated sulfuric acid 14.9 / hr, 35% hydrochloric acid 14.5 /
Pour at each rate of hr and heat to 40-50 ° C. Air is blown from the bottom at a rate of 28 Nm ³ / h8. Generated gas (ClO ₂ 10.1 kg / hr, Cl ₂ 5.8 kg / hr is absorbed in cold water at 5 ° C to give chlorine dioxide water (ClO ₂ 7 g /, Cl ₂ 1 g
/) Was obtained at a rate of 1430 / hr. Further, the exhaust gas from the absorption tower is absorbed in 40 g of NaOH / water solution to give 139 of sodium hypochlorite solution (effective chlorine: 31.6 g /).
/ Hr. On the other hand, the flow rate of the waste liquid flowing out from the reaction zone B is 43.0 / hr, and the composition is NClO ₃ 8 g /, HCl.
_{3g /, Na 2 SO 4 251g} /, H 2 SO 4 453g /
The basic unit of each substance per ton of chlorine dioxide generated was as follows.

NaClO ₃ 1,650 kg, 35% hydrochloric acid 1710 kg, H ₂ SO ₄ 2,745 kg, waste sulfuric acid 1,950 kg, by-product Cl ₂ 580 kg This example is a method of reducing sodium chlorate with hydrochloric acid in a sulfuric acid acidic solution. In comparison, it can be seen that the amount of waste sulfuric acid and chlorine by-product is large.

Comparative Example 2 In reaction zone A, an aqueous solution of NaClO ₃ 639 g / 31 /
hr, concentrated sulfuric acid 14.9 / hr, methanol 25.2 / hr
And the mixture is heated to 40 to 50 ° C. Air is blown from the bottom at a rate of 28 Nm ³ / hr. Generated gas (ClO ₂
10.1 kg / hr) was absorbed with cold water at 5 ° C. to obtain chlorine dioxide water (ClO ₂ 7 g /) at a rate of 1430 / hr. On the other hand, the flow rate of the waste liquid flowing out of the reaction zone is 40.3.
/ Hr, NaClO ₃ 90 g /, Na ₂ SO ₄ 267 g /, methanol 1 g /, HCHO trace, and each substance basic unit per ton of chlorine dioxide generated is as follows.

NaClO ₃ 1980kg, Methanol 200kg, H ₂ SO ₄ 2,745kg, Waste sulfuric acid 1,950kg, No by-product Cl ₂ This example is a method of reducing sodium chlorate with methanol in an acidic sulfuric acid solution. Is almost zero and small, but the amount of waste sulfuric acid is large, the basic unit of sodium chlorate is also bad, 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 generating tank (reaction zone A), 7 ... Same (reaction zone B), 6 ... Hydrochloric acid injection route, 8 ... Waste liquid route from reaction zone A to B, 11 ... Evolved gas route 12 ... Chlorine dioxide absorption tower, 15 ... Chlorine 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, hydrochloric acid is added to the waste liquid from A to react to decompose residual sodium chlorate, and chlorine dioxide is separated and obtained from a mixed gas of chlorine dioxide and chlorine generated in each reaction zone. Chlorine dioxide production method.