JPH03115102A - Production of chlorine dioxide - Google Patents

Abstract

PURPOSE:To industrially and advantageously obtain chlorine dioxide without generating by-product chlorine by reducing an aq. sodium chlorate soln. acidified with sulfuric acid with methanol to produce chlorine dioxide and allowing hydrogen peroxide to react with the waste soln. to decompose the remaining sodium chlorate into chlorine dioxide. CONSTITUTION:Sodium chlorate 3 and sulfuric acid 4 are added to a chlorine dioxide generating vessel 1, methanol 5 is further introduced along with an inert gas 9, and a reduction reaction is carried out so that sodium chlorate is left to generate chlorine dioxide 10. The chlorine dioxide 10 is discharged by the inert gas 9, introduced into an absorption tower 11 and absorbed in cold water 12. The waste soln. 7 from the vessel 1 is introduced into a chlorine dioxide generating vessel 6, hydrogen peroxide 8 is added to cause a reaction, and the remaining sodium chlorate is decomposed into chlorine dioxide 10. The inert gas 9 is blown in to discharge the chlorine dioxide 10, which is introduced into the absorption tower 11 and absorbed in cold water 12 to produce aq. chlorine dioxide 13. In addition, the waste soln. 14 from the vessel 6 is used for cooking pulp.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing chlorine dioxide by reacting sodium chlorate with a reducing agent.

(Prior art) The methods for producing chlorine dioxide that are currently being industrially implemented can be roughly divided into: i) a method in which sodium chlorate is reduced with sulfur dioxide gas in a sulfuric acid solution; ii) a method in which sodium chlorate is reduced with hydrogen chloride in a sulfuric acid solution; Reduction method iii) Method of reducing sodium chlorate or calcium chlorate with hydrochloric acid In both of these methods, a reaction waste liquid is produced together with chlorine dioxide (and chlorine). In the case of methods i) and ii) above, the main components are sulfuric acid and mirabilite, and some sodium chlorate is also included, but in many cases, the mirabilite needles are mixed into the cooking black liquor for paper pulp to effectively utilize the mirabilite needles. 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 this limit, it must be discarded, and in that case, neutralizing agents are required, which requires a large amount of expense. . In particular, method ii) has been recently adopted by many factories because it is simpler to operate than method 1), but the amount of reaction waste liquid produced is extremely large (approximately 1.1 tons of Glauber's sulfate 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 i) is smaller than this, it requires a sulfur dioxide gas generator, which complicates the operation.
Additionally, there is a risk of pollution problems caused by sulfur dioxide gas. In addition, as an improvement to methods i) and ii), there is a method of recovering neutral mirabilite or acidic mirabilite from the reaction waste liquid and reusing sulfuric acid, which is convenient for solving the above-mentioned waste liquid problem.
On the other hand, it requires a refrigerator or an evaporator, resulting in extremely high equipment costs and complicated operation.

In addition, the method of 111) produces a small amount of chlorate and common salt or a dilute hydrochloric acid solution of calcium chloride as waste liquid, but these have no utility value as papermaking chemicals (they are discarded after being neutralized with a small amount of alkali). This method is economically disadvantageous compared to methods that effectively utilize waste liquid.Furthermore, there is a method to electrolyze this waste liquid (in the case of a salt solution) and return it to sodium chlorate again, but the salt concentration is too high and concentration is required. This is economically disadvantageous due to high equipment costs.Furthermore, if salt is added without concentrating, the amount of waste liquid will be large, resulting in the production of an unnecessarily large amount of 4-salt solution, including the electrolytic process. This would be extremely unreasonable on the scale of the entire plant.

Further, method i) generates only chlorine dioxide, whereas methods 1i) and iii) are 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, excess poses a problem. Most of the methods currently used industrially are i) and ii), of which method ii) is the most commonly 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 equipment, so the equipment cost is low, the operation is done using an hour wheel, and the raw material for sodium chlorate is The units are also the best. On the other hand, the drawbacks are that the amount of waste liquid generated is larger than in (i), 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 used, but because these increase the amount of sodium ions in the system and result in an increase in the amount of waste liquid due to solubility, recently hydrochloric acid has been used more often. This method certainly reduced the amount of waste liquid, but due to water entering the system along with the hydrochloric acid, the amount of waste liquid was about 1.3 times that of method i). Furthermore, as mentioned above, by-product chlorine can be a problem.

(Problems 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 that uses hydrochloric acid as a reducing agent, and it is possible to do so industrially. The purpose is to provide an advantageous method.

(Means for Solving the Problems) In other words, in producing chlorine dioxide by reacting sodium chlorate with a reducing agent, the reaction zone is divided into two, and the opening →
In reaction zone A, sodium chlorate, methanol, and sulfuric acid are added and reacted, and in reaction zone B, hydrogen peroxide or hydrogen peroxide and sulfuric acid are added and reacted with the waste liquid from A to remove residual sodium chlorate. This is a method for producing chlorine dioxide, which is characterized by decomposing chlorine dioxide and separating and obtaining chlorine dioxide 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 A) has a storage tank (2).
Add sulfuric acid (4) together with sodium chlorate (3),
Further, methanol (5) is introduced together with an inert gas (9) described later. Also, chlorine dioxide generation tank (6) (reaction zone B)
The waste liquid (7) from the chlorine dioxide generation tank (1), which has been reacted so that sodium chlorate remains, is introduced into hydrogen peroxide (8).
) is added. From the bottom of each tank (1) (6), chlorine dioxide gas (10) generated by blowing in an inert gas (9) such as air is taken out and led to a chlorine dioxide absorption tower (11) where it is oxidized with cold water (12). Chlorine gas is absorbed to produce chlorine dioxide water (13). The waste liquid (14) from the chlorine dioxide generating tank (6) contains sulfuric acid and sodium sulfate as main components, and is used for pulp cooking. The chlorine dioxide gas absorption unit generated in each chlorine dioxide generating tank may be shared. Further, the decomposition rate of sodium chlorate in reaction zones A and B can be arbitrarily adjusted by adding methanol, sulfuric acid, and hydrogen peroxide. 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 formula in reaction zone A (chlorine dioxide generation tank 1) is shown by the following formula: NaCl 03 + 1/21LtSOt + 1/2
CI+3011-ClO,+ 1/2NatSO,+
1/211CIIO+ 1lzo (1) The main reaction formula in reaction zone B (chlorine dioxide generating tank 6) is shown by the following formula.

NaCI O, + 1/211tOi +1/2112
5Oa →Cl (h + 1/2NazSO4+ 2
HzO+ Ot·(2) (Function) A method for producing chlorine dioxide by reducing a sulfuric acid acidic sodium chlorate aqueous solution with methanol is known as the "Tsurubay 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 etc. is discharged, and the reaction rate is low. The disadvantage was that the basic unit of raw material sodium chlorate was inferior due to the low value of sodium chlorate.

In the method of the present invention, the reaction with methanol is carried out only in reaction zone A, so even if the reaction waste liquid from reaction zone A contains unreacted sodium chlorate, it is more efficiently decomposed into chlorine dioxide in reaction zone B. Therefore, the overall consumption of sodium chlorate is good.

Furthermore, since methanol is cheap and the amount used is small, and the amount of sulfuric acid used is also relatively reduced, the production cost of chlorine dioxide does not increase. On the other hand, a method for reducing by-product chlorine due to the generation of chlorine dioxide gas using hydrogen peroxide was disclosed in Japanese Patent Application Laid-Open No.
However, hydrogen peroxide is expensive and causes an increase in the production cost of chlorine dioxide. However, in the method of the present invention, its use is limited to reaction zone B, so the amount used can be reduced relative to the amount of chlorine dioxide generated, and the cost will not increase.

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

l) Since chloride, which is a source of hydrochloric acid or hydrogen chloride, is not used in the reaction zone A-B, the amount of by-product chlorine can be reduced or made substantially zero, thereby eliminating the problem of excessive by-product chlorine. It is also possible to reduce the amount of sodium hypochlorite or chlorine used in the bleaching process.

2) Because the amount of water entering the system is reduced, the conventional method 1i
It has become possible to further reduce the amount of waste liquid compared to method (i) as well as method (iii)). Therefore, problems caused by excess waste liquid can be avoided.

3) In addition to the above advantages, the combination of economically expensive hydrogen peroxide and inexpensive methanol maintains a balance and does not increase the production cost of chlorine dioxide compared to conventional methods.

4) There is no need for incidental equipment such as a sulfur dioxide gas generator, waste liquid concentration equipment, or crystallization equipment in the case of conventional methods, and operation is simple and automatic operation can be carried out easily. In addition to reducing costs and operating costs, it is also easy to convert from existing equipment.

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

Example 1 Using the apparatus shown in the drawing, NaC4 (h6
39 g/l aqueous solution at 311/hr, concentrated sulfuric acid 14,9
Mix at a rate of 1/hr, heat to about 40°C, and pour methanol from the bottom at a rate of 2.51/hr and air at a rate of 28
It was blown in at a rate of Nm3/hr. The flow rate of waste liquid discharged from reaction zone A is 411/hr, and the composition is NaCA'Oz
90 g/l, HzSOa 483 g/11
NazSOa 267 g/1, methanol tra
ce, and while introducing it into reaction zone B, hydrogen peroxide solution (1120235%) was added at a rate of 1.4 E/hr, the liquid was heated to 50 to 60 °C, and the mixture was poured from the bottom. Air was blown in at a rate of 5.7 m3/hr. Generated gas from reaction zone A (Cj!Oz 10.1 k
g/hr) and gas generated from reaction zone B (C1o
z 2 kg/hr) into 5°C cold water in the same chlorine dioxide absorption tower to obtain chlorine dioxide water (010□
7 g/1) to 1720! /hr. On the other hand, the flow rate of waste liquid flowing out from reaction zone B is 4 Q l
/ hr, composition is NaC120310g/1%
NazSOa 324 g/Il, 1IzsO
a 450g/Il, 1Izo, trace
The basic unit of each substance per ton of generated chlorine dioxide was as follows.

NaC7031,650kg-35%1120214
0 kg -1+2SO, 2,290 kg, methanol 167 kg.

1.500 kg of waste sulfuric acid Comparative example 1 Aqueous solution 2 of Na2SO4639 g/l in reaction zone A
5,81/hr, ? H sulfuric acid 14.21 /
hr, 35% hydrogen peroxide solution 7 (! / hr) and warm to 40 to 60°C. Also, blow air from the bottom at a rate of 28 Nm3/hr until 0 generated gas <CIo
.

10.1 kg/hr) was absorbed with cold water at 5°C, and chlorine dioxide water (CI 0□ 1 g/l) was dissolved in
It was obtained at a rate of 1/hr. On the other hand, the flow rate of waste liquid flowing out from reaction zone A is 381/hr, and the composition is NaC7!0:
+ ag/l, NatSOa 289g/11Hz
SO4465g/l, )1.0. trace, and the basic unit of each substance per ton of generated chlorine dioxide was as follows.

NaClO31,650kg-35%1Izoz
850kg SHHzSO42,560kg-waste sulfuric acid 1
, 770g In this example, chlorine dioxide is generated by reducing sodium chlorate in a sulfuric acid solution with hydrogen peroxide using chlorine ions as a medium, but compared to the example, a large amount of expensive hydrogen peroxide is required. However, it is found to be less economical (by the way, the market price of 35% hydrogen peroxide is about three times that of methanol).

Comparative Example 2 NaCff0: + 639 g/1 in reaction zone A
An aqueous solution of 311/hr, ? W sulfuric acid 14.9
12/hr, heated to 40-50°C, and poured methanol from the bottom at 25.21/hr,
Air was blown in at a rate of 28 Nm3/hr. On the other hand, the waste liquid meteor flowing out from reaction zone A has a composition of 40.31/hrll, NaC10°90 g/E, Na2SO4267
g/l, 112504483 g/l, and the basic unit of each substance per ton of chlorine dioxide generated was as follows.

NaClO3 1,980 kg - methanol 200 kg
, 11□so, 2,740 kg, waste sulfuric acid 1.9
50g This example is the so-called Solvay method in which sodium chlorate is reduced with methanol using a sulfuric acid solution, and the by-product chlorine is almost zero compared to the example, but there is a lot of waste sulfuric acid and the sodium chlorate consumption rate is poor, making it less economical. It turns out that it is inferior to

[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), 6... Same (reaction zone B), 3... Sodium chlorate aqueous solution injection route, 4... Sulfuric acid injection route, 5... Methanol injection route, 7... Waste liquid route from reaction zone A to B, 8... Hydrogen peroxide solution injection route, 11... Chlorine dioxide absorption tower.

Claims (1)

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