JPH0383802A - Production of chlorine dioxide - Google Patents

Abstract

PURPOSE:To decrease the amounts of by-produced chlorine and waste liquid in the conventional process for the production of chlorine dioxide by the reaction of sodium chlorate with hydrochloric acid as a reducing agent by dividing the reaction zone into two zones and using different reducing agents in each reaction zone. CONSTITUTION:In the production of chlorine dioxide by the reaction of sodium chlorate with a reducing agent, the reaction zone is divided into two zones A and B. Sodium chlorate 3, methanol 5, hydrochloric acid 6 and sulfuric acid 4 are supplied to the reaction zone A (ClO2 generation tank 1) and made to react with each other. Hydrochloric acid 9 is added to the waste liquid 8 of the zone A in the reaction zone B (ClO2 generation tank 7) and reacted to decompose the residual sodium chlorate. The objective chlorine dioxide is separated from the mixed gas 11 consisting of chlorine dioxide and chlorine generated from the reaction zones A and B. For example, the mixed gas 11 is introduced into an absorption column 12, chlorine dioxide is absorbed in cold water 13 and recovered as ClO2 water 14 and the residual chlorine is absorbed in an alkali 16 in the absorption column 15 and recovered as a hypochlorite solution 17. The waste liquid 18 is composed mainly of sulfuric acid and sodium sulfate and is used as a black liquor for pulp digestion.

Description

[Detailed description of the invention] (Industrial application field) The present invention involves reacting sodium chlorate with a cyclic agent (2) (1) The present invention relates to a method for producing chlorine dioxide.

(Prior technology) The methods of producing chlorine dioxide that are currently being industrially implemented can be roughly divided into 1) A method in which sodium chlorate is reduced with sulfur dioxide gas in a sulfuric acid solution ■) A method in which sodium chlorate is reduced with hydrogen chloride in a sulfuric acid solution Reduction Method I) Method of Reducing Sodium Chlorate or Calcium Chlorate with Hydrochloric Acid In either of these methods, a reaction waste liquid is produced together with chlorine dioxide (and chlorine). In the case of methods 1) and 1) above, the main ingredients are sulfuric acid and mirabilite, and some sodium chlorate is also included, but in many cases, the mirabilite content is mixed into the cooking black liquor for paper pulp to effectively utilize the mirabilite content. are doing. In some cases, it is also used in the production of sulfate clay.

However, there is a limit to the absolute amount of waste liquid that can be used, and if waste liquid exceeds that limit, it will have to be abandoned, and in that case, patents featuring neutralizing agents, etc. will require a large amount of expense. . In particular, method 0 has been recently adopted by many factories because it has a simpler operation method than method 1), but it produces an extremely large amount of reaction waste liquid (1.1 tons of mirabilite per ton of chlorine dioxide generated). (about 7 tons, including about 2 tons of sulfuric acid, are produced as by-products).The treatment method is often a problem. Although the amount of waste liquid in method 1) is smaller than this, it requires a sulfur dioxide gas generator, which complicates operation and may cause pollution problems due to sulfur dioxide gas.

In addition, as an improvement method of methods I) and (ii), there is a method of recovering neutral sodium sulfate or acidic sodium sulfate from the reaction waste liquid and reusing sulfuric acid. Another disadvantage is that it requires an evaporator or the like, resulting in extremely high equipment costs and complicated operation. Also,■
) method produces a small amount of chlorate and common salt or a dilute hydrochloric acid solution of calcium chloride as waste liquid, but these are of no use as papermaking chemicals and are discarded after being neutralized with a small amount of alkali. It is economically disadvantageous compared to methods that utilize it effectively.

Furthermore, 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 low, concentration is required and equipment costs are high, which is economically disadvantageous. Furthermore, if salt is added without concentrating, the amount of waste liquid will be large and an unnecessarily large amount of crushed salt solution will be produced, which is extremely unreasonable on the scale of the entire plant including the electrolysis process. become.

Further, method 1) generates only chlorine dioxide, whereas method I)l) is characterized in that chlorine is generated at the same time. Normally, this by-product chlorine is separated from chlorine dioxide in the absorption stage, then absorbed with caustic alkali and consumed as sodium hypochlorite in the pulp bleaching process. However, if the amount of sodium hypochlorite used in the bleaching process is small, its excess becomes a problem. Most of the methods currently used industrially are 1) and -), of which method 2) is the most widely used. As already mentioned, the advantages of this method are that it does not require complicated incidental equipment such as a sulfur dioxide gas generator or a mirabilite recovery device, so the equipment cost is low, operation is simple, and the raw material sodium chlorate is The basic unit is also the best. On the other hand, the drawbacks are that the amount of waste liquid generated is larger than in 1), and chlorine gas is produced as a by-product, which often becomes a problem as the scale of the generator increases.

Regarding the generated waste liquid, in the method of reducing sodium chlorate with hydrogen chloride using sulfuric acid, there are cases where hydrochloric acid is used as the hydrogen chloride source, and there are cases where common salt and sulfuric acid are used. In the past, common salt and sulfuric acid were often used7, but these tend to increase the amount of sodium ions in the system (due to solubility, resulting in an increase in the amount of waste liquid), so recently hydrochloric acid is often used. This certainly reduced the amount of waste liquid, but since it entered the system together with hydrochloric acid, the amount of waste liquid was about 1.8 times that of method I). Furthermore, as mentioned above, by-product chlorine can be a problem.

(Problem N to be solved by the invention) The present invention solves the above problems, that is, it is possible to reduce the amount of by-product chlorine and the amount of waste liquid in a method for generating chlorine dioxide using hydrochloric acid as a reducing agent, and furthermore, it is possible to reduce the amount of by-product chlorine and the amount of waste liquid. It is an object of the present invention to provide an industrially advantageous method that can adjust these stores according to the needs of consumers.

(Means for solving al
) In reaction zone A, sodium chlorate, methanol, hydrochloric acid and sulfuric acid are added and reacted, or each of the above components except hydrochloric acid is added and reacted, and (I) in reaction zone B, hydrochloric acid is added to the waste liquid from the mu. This method of producing chlorine dioxide is characterized by carrying out an addition reaction to decompose residual sodium chlorate, and then separating and obtaining chlorine dioxide from a mixed gas of chlorine dioxide and chlorine generated from each reaction zone.

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

The chlorine dioxide generation tank (1) (reaction zone) has a storage tank (2).
With sodium chlorate (3), sulfuric acid (4) and hydrochloric acid (6
), and methanol (6) is introduced together with an inert gas (10) described later. Also, chlorine dioxide generating tank (a)
In (reaction zone B), the waste liquid (8) from the chlorine dioxide generation tank (1), which has been reacted so that sodium chlorate remains, is led and hydrochloric acid (9) is added. From the bottom of each type (1) and (7), a mixed gas of chlorine dioxide and chlorine (11) generated by blowing in an inert gas such as air (10) is taken out and led to a chlorine dioxide absorption tower (12) where it is filled with cold water (13). ) to absorb chlorine dioxide gas to produce chlorine dioxide water (14).

Chlorine gas that is not absorbed by water is led to a chlorine absorption tower (15) and absorbed into caustic alkali or milk of lime (16) to form a hypochlorite solution ('ty). The waste liquid (18) from the chlorine dioxide generating tank (7) contains sulfuric acid and sodium sulfate as main components, and is used as black liquor for pulp cooking. Although the ratio of chlorine dioxide and chlorine generated in each chlorine dioxide generating tank is different, the gas absorption part can be shared. Furthermore, the method for separating chlorine dioxide and chlorine is not limited to the method exemplified here, and various known chemical and physical separation methods can be applied.

Alternatively, hydrochloric acid may be omitted from the chlorine dioxide generation tank (1), and sodium chlorate, sulfuric acid, and methanol may be added for reaction. In this case, only chlorine dioxide gas is generated in reaction zone A. Also, reaction zone A.

The decomposition rate of each sodium chlorate in B can be arbitrarily adjusted by adjusting the amounts of methanol, hydrochloric acid, and sulfuric acid added. Note that the entire required amount of sulfuric acid may be added to reaction zone A, or a portion thereof may be added to reaction zone B.

The main reaction equations in the reaction zone (chlorine dioxide generation tank 1) are shown by the following equations (1) and (2).

Na0NO, + 1/2H, 804+ 1/20H, O
TI −+(!10. +1/72Na, So, +1
/2H(IO+H,0-(1)NaOIOl+'1
/2Ht804 + Hog →CeO, + 1/20
11t+ 1/2Na, 80. +H, O"' (2)
Further, the main reaction formula in reaction zone B (chlorine dioxide generation tank 7) is shown by the above formula (2) or the following formula (3).

2Na(JO, + 411(J → 2ceo, +Of
! , +2NaCJ + 2H,0-(5) (Function and Effects of the Invention) As described above, the method of the present invention divides the reaction zone into AB, uses different reducing agents in each zone, and further reduces the reaction rate in the above two zones. By adjusting , the following effects are produced.

1) By replacing part or all of the hydrochloric acid used as a reducing agent in the reaction zone with methanol, the amount of water entering the system is reduced, making it possible to further reduce the amount of waste liquid compared to method I) above. This avoids the problem of excessive waste liquid disposal.

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

That is, if chlorine (for example, sodium hypochlorite as a bleaching agent) is not required at the customer, the addition of hydrochloric acid in the reaction zone may be set to zero. Conversely, if the amount of chlorine does not meet the requirements of the demand, the amount of hydrochloric acid added in reaction zone A may be increased until the required amount is met. A major feature of the method of the present invention is that the production amount of by-products can be arbitrarily adjusted according to the needs of the customers.

3) The use of methanol as a reducing agent is itself known as the "Trubey method". However, although this reaction originally has a good reaction yield, it is very slow, and even if a large number of large-capacity reactors are used, a large amount of waste liquid containing unreacted sodium chlorate is discharged, resulting in a low reaction rate. As a result, the disadvantage was that the basic unit of sodium chlorate as a raw material was inferior.

In the method of the present invention, the reaction with methanol is carried out only in reaction zone A, so the Nislever is used to ensure that unreacted sodium chlorate remains in the waste liquid from A.
Since it is efficiently decomposed into chlorine dioxide by hydrochloric acid in the process, the drawbacks of the methanol method are covered, and the basic unit of sodium chlorate is improved overall.

4) Unlike method I) above, there is no need for complicated incidental equipment such as a sulfur dioxide gas generator, waste liquid concentration equipment, or crystallization equipment, and the operation is simple and automatic operation can be carried out easily. . Therefore, it is easy to convert existing equipment to reduce the amount of chlorine by-product and waste liquid generated. Furthermore, methanol is inexpensive and only needs to be used in a small amount, and the amount of sulfuric acid used is also relatively reduced, so the cost of chlorine dioxide does not increase.

(Example) The present invention will be explained below with reference to Examples and Comparative Examples.

Example 1 Using the apparatus shown in the drawing, Na (40g8
An aqueous solution of S 9 f/l was added at a rate of 37 (!/hr), concentrated sulfuric acid 18.61/hr, S 6% hydrochloric acid 2.81/hr, heated to 40-50°C, and methanol was added from the bottom. 2.51/hr, air at 34 N m/hrcD
Injected in proportion. The flow rate of waste liquid discharged from reaction zone A is 51//hr, and the composition is NaIO185,8f//
l-HC11101/1. H,80,4799/1
．． Na, 804255f/l, methanol 1f/l
l+HOHOtrace.

While introducing this waste liquid into reaction zone B, add 35% hydrochloric acid to
Note 6: The added solution was heated to 50 to 60°C at a rate of sl/hr, and air was blown from the bottom at a rate of 8.8 Nml/hr. Generated gas from reaction zone A (CeO!1
2, 1 kg/hr, C (1ffi1.2 kg/
hr) and gas generated from reaction zone B (C!NO,
2.4 kg/hr, (J, 1.4 kg/hr) was absorbed into 6°C cold water in the same chlorine dioxide absorption tower,
Chlorine dioxide water CClO271/e.

C1tO, S f/I) was obtained at a rate of 2.0801/hr.

Furthermore, the exhaust gas from the absorption tower was absorbed into a NaOH401/l aqueous solution and a sodium hypochlorite solution (available chlorine 31.6
'l/l') was obtained at a rate of 501/hr. On the other hand, the flow rate of the waste liquid flowing out from the reaction zone B is 51.01/hi, NaCe0 9 f/l for the reaction zone, and 2 f/l for the HOI.
1. Na0IO1 5051/l, E[,804442f/II Thea t
), and the basic units of each substance per ton of chlorine dioxide generated were as follows.

Na0e0. 1,650kg, 36% hydrochloric acid 6
23kg.

H, 80,2458kg, methanol 130
kg.

Waste sulfuric acid 1.670kg, by-product C#, 177k
g Example 2 An aqueous solution of 0.639 t/l of NaCl was poured into the reaction zone at a rate of 31//hr, and at the same time 14.8 t/l of concentrated sulfuric acid was poured into the reaction zone.
Inject at a rate of 1/hr. This was heated to 40 to 60'C, and methanol 2.51/hr and air 28/hr were added from the bottom.
Blow in at a rate of N m"/hr. The flow rate of waste liquid discharged from reaction zone A is 40 (t/hr, its composition is Na
0IO1s O'I/e, Na, 80.2871/l
.

II, 80448! 9/l, methanol 197g
.

HC! While introducing this into reaction zone B, 55% hydrochloric acid was added at a rate of 2 J#/hr, the solution was heated to 50-60°C, and air was introduced from the bottom at 5.7 N.
It was blown in at a rate of m',,'hr. Gas generated from the reaction zone ((J'0.10.1 kg/hr)
and gas generated from reaction zone B (CIo, 2 kg/
hr, O#, t, tkg/hr) in 5°C cold water in the same chlorine dioxide absorption tower, and
! 0.7 fl/l.

agffio, g IIl) 172011/hr
obtained at a rate of

Furthermore, the exhaust gas from the absorption tower is absorbed into a NaOH401/l aqueous solution to form a sodium hypochlorite solution (available chlorine! 1.
6 f/l') was obtained at a rate of 22 (1/hr).

- The flow rate of waste liquid from reaction zone B is 40.1 e/hr
.

Composition: NaCeOs 10 fl/l -HCII
2f/II-Na0IO1S 18 f/11-H
t80+ 441 t/(l), and the basic unit of each substance per ton of generated chlorine dioxide was as follows.

Na010g 1-1-6601C35% hydrochloric acid 28
5kg.

H,80,2◆290kg, methanol 167
kg.

Waste sulfur 1M! 1.500kg, by-product CI, 10
0kg Comparative Example 1 In reaction zone A, an aqueous solution of Na C110s 639 f/l was added at 25 fJ l/hr, concentrated sulfuric acid 14.9
e/hr. 35% hydrochloric acid was added at a rate of 14 and 511 times per hour, and the mixture was heated to 40 to 50°C. Also, air is pumped in from the bottom.
Blow at a rate of 8 Nm/hr. Generated gas (C1ot
10.1 kg/hr.

0 (It 5.8 kg/hr) was absorbed into 5°C cold water to make chlorine dioxide water (010.7 fl/e, C
1 l, 1 g/l') at a rate of 14301/hr. Furthermore, the exhaust gas from the absorption tower is treated with NaOH401/
11 was absorbed into an aqueous solution to obtain a sodium hypochlorite solution (available chlorine 31.69/(1) at a rate of IS 91/hr. On the other hand, the flow rate of the waste liquid flowing out from reaction zone B was 48.
0 #/hr, composition is Na OJOi 8 II
(!,)! Ol 39/ l -Nag Bo42
51 f/11. H,8044659/11 Thea F
), and the basic unit of each substance per ton of chlorine dioxide generated was as follows.

N a OI Os 1 = 650 kg. 36% hydrochloric acid 1,710 kg.

H, 80, 2,745 kg, waste sulfuric acid 1,85
0kg.

By-product (J, 580 kg) This example is a method of reducing sodium chlorate with hydrochloric acid using a sulfuric acid solution, and it can be seen that there are more waste sulfuric acid and by-product JIji compared to the examples.

Comparative Example 2 Naclo, 859 fil (D water soluble, V
of! 1/l/hr, concentrated sulfuric acid 14.91/hr, J
Added at a rate of 25, 2 g/hr, 40~
Warm to 60°C. Also, air is pumped out from the bottom by 28NKIm/
Insert at the rate of hr. Generated gas (110, 10, 1kg
/hr) was absorbed with cold water at 6°C to obtain chlorine dioxide water (ago, rf/l') at a rate of 1430 g/hr. On the other hand, the flow rate of waste liquid flowing out from the reaction zone is 40
．． 3 (j/hr.

NaCJOi 901/1. Na, 804267 f
i(1,Jri/-k j f//l, ECHO1
race, and the basic unit of each substance per ton of generated chlorine dioxide is as follows.

Na01Oa 1 saokg, fi tanur 200kg.

Ht 804 2,745kg - Waste sulfuric acid 1.116
0kg.

By-product OJ, none This example is a method of reducing sodium chlorate with metamer in a sulfuric acid solution, and the amount of by-product chlorine is almost zero compared to the example, but the amount of waste sulfuric acid is large (and the amount of sodium chlorate It can be seen that the basic unit is also poor and the economical efficiency is inferior.

[Brief explanation of drawings]

The drawing is a schematic illustration of an apparatus for carrying out the method of the invention. 1... Chlorine dioxide generation tank (reaction zone A), 7... Threshold (reaction zone B), 6.8... Hydrochloric acid injection route, 8... Waste liquid route from reaction zone B to B. 11... Generated gas route 12... Chlorine dioxide absorption tower, 15... Chlorine absorption tower

Claims (2)

[Claims] (1) In producing chlorine dioxide by reacting sodium chlorate with a reducing agent, the reaction zone is divided into two. (I) In reaction zone A, sodium chlorate, methanol, hydrochloric acid, and sulfuric acid are added and reacted. II) Reaction zone B
The production of chlorine dioxide is characterized in that hydrochloric acid is added to the waste liquid from A to cause a reaction to decompose residual sodium chlorate, and chlorine dioxide is separated and obtained from a mixed gas of chlorine dioxide and chlorine generated from each reaction zone. Law. (2) In the method according to claim 1, in the reaction zone A,
A method for producing chlorine dioxide by adding and reacting sodium chlorate, methanol, and sulfuric acid.