JPS638203A - Production of high-purity chlorine dioxide - Google Patents

Abstract

PURPOSE:To readily, efficiently and continuously produce high-purity ClO2 at a low cost, by reducing an alkali metal chlorate with H2O2 in presence of a specific amount of a chloride in an acidic aqueous solution of sulfuric acid. CONSTITUTION:(A) An alkali metal chlorate, e.g. NaClO3, is dissolved in (B) a strong acidic aqueous solution of sulfuric acid in 8-11 N acid concentration to give 0.03-0.2mol/l concentration of the above-mentioned alkali metal chlorate. (D) H2O2 in an amount of 5-10% excess of the theoretical amount based on the component (A) is as a reducing agent added to the resultant solution to carry out reductive reaction in the presence of (C) a chloride, e.g. NaCl, in a concentration as low as 0.02-0.1mol/l at 30-50 deg.C.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing chlorine dioxide by reducing an alkali metal chlorate in an acidic sulfuric acid solution using a continuous reaction tank. The present invention relates to a method for easily and inexpensively producing high-purity chlorine dioxide using hydrogen as a reducing agent.

(Prior Art) In recent years, high-purity chlorine dioxide has been used in fields such as pulp bleaching, sterilization of water and sewage systems, and denitrification. Chlorine dioxide is particularly indispensable as a pulp bleaching agent and is produced in large quantities, and is primarily used for bleaching bleached kraft pulp.

Conventionally, R has been widely used as a method for producing chlorine dioxide.
Method 2 is a method in which chlorate is reduced in an aqueous sulfuric acid solution using chloride as a reducing agent. Taking hydrochloric acid as an example of the reducing agent, the main reaction is shown by the following formula.

N a CI O1+ HCl + 1/2 H2
SO--CI02+1/2CI2+1/2Na2S○
4+H20... (1) This method is extremely popular because it uses simple equipment and has a good yield, but it cannot avoid producing chlorine that is half the amount of chlorine dioxide in terms of molar ratio. This by-product chlorine is normally absorbed by alkali and used as hypochlorite (hypo), and chlorine has been used effectively.

(Problem to be solved by the invention) However, recently in Japan, the bleaching series has changed from chlorine treatment (E stage) - alkaline extraction (E stage) - hypo treatment (H stage) - alkaline extraction (E stage). stage) - chlorine dioxide treatment (stage D), that is, there is a tendency to transition from CEHED to CEDED. If the bleaching series becomes CEDED,
There is no H stage, making it impossible to use by-product chlorine as hypo. Although it is possible to absorb the by-product chlorine in water and use it in the zero stage, it is not necessarily a preferable method of use since only dilute chlorine water can be obtained.

A method has been proposed in which hydrogen peroxide is added to generate chlorine dioxide using hydrogen chloride as a reducing agent (Japanese Patent Laid-Open No. 53-66892). Although the composition of the reaction solution in this method has not been clarified, it is a reaction in the coexistence of a large amount of chloride, and it is possible to reduce the amount of by-product chlorine and produce high-purity chlorine dioxide, but it is possible to produce high-purity chlorine dioxide. It is not an efficient method because it consumes a large amount of chlorate and also requires a large amount of hydrogen peroxide.

Therefore, there has been a demand for the development of a method for easily and efficiently producing high-purity chlorine dioxide without producing chlorine as a by-product.

(Means for Solving the Problems) The present inventors have conducted extensive research to solve the above problems, and as a result, by adding hydrogen peroxide as a reducing agent under specific reaction conditions, high purity It has been discovered that chlorine dioxide can be produced easily and inexpensively. That is, the present invention provides a method for continuously producing chlorine dioxide by reducing an alkali metal chlorate in an acidic aqueous solution of sulfuric acid, in which the acid concentration is reduced in the presence of 0.02 to 0.1 mol/l of chloride. 8 to 11N, alkali metal chlorate 0.03 to 0.2
This is a method for producing high-purity chlorine dioxide, which is characterized by reducing the chlorine dioxide with hydrogen peroxide while adjusting the reaction temperature to 30 to 50°C.

Regarding the mechanism of reducing chlorate under strong acidity to generate chlorine dioxide, see 'vV, H, Rapson
The theory [Tappi Vol. 39, No. 8, p. 554, 1956, 1] is widely supported. According to this theory, when sodium chlorate is used as an example of an alkali metal chlorate, the reaction content of the present invention can be considered as follows.

2NaC1○, +H2So, == 2HCIOs+Na25O-' (2) HCIO+
HCI;: HCIO2+HCl0...(3) HC103+HCl02== 2CI02+820...(4) HCIO+H2O2=: HC1+820+02...(5) By adding various equations (2) to (5), the main reaction formula of the present invention, (
6) Equation is obtained.

2NaC1○, +H2O2+H2SO4→2C1○2+
Na25O, +2H20+02...(6) Various conditions are required to allow this reaction to proceed under favorable conditions. That is, the sulfuric acid concentration in the reaction tank is 8 to IIN, and the alkali metal chlorate is 0.03 mol/
l to 0.2 mol/l and the reaction temperature to 30 to 50 mol/l.
C), it is necessary to react with hydrogen peroxide as a reducing agent in the presence of chloride in an amount of 0.02 mol/l to 0.1 mol/l.

To make it easier to understand the present invention, the following terms and phrases are defined,
As the alkali metal chlorate, sodium chlorate will be explained as an example.

Chlorine dioxide purity (%): Sodium chlorate consumption: Sodium chlorate supply (kg) Chlorine dioxide generation (kg) Hydrogen peroxide consumption: Chlorine dioxide generation (kg) First, let's talk about sulfuric acid concentration: It is lower than 8N. Concentrations are not preferable because many side reactions occur and the sodium chlorate consumption rate increases. In addition, low acid concentration is not preferable because if an attempt is made to obtain highly pure chlorine dioxide, the hydrogen peroxide basic unit increases, and conversely, if the hydrogen peroxide basic unit is lowered, the chlorine dioxide purity decreases. Conversely, even if the sulfuric acid concentration is higher than IIN, there is almost no reduction in the sodium chlorate or hydrogen peroxide consumption, so not only is there no particular advantage, but the sulfuric acid consumption also increases, and the liquid temperature decreases when the operation is stopped. The industrial value decreases due to problems due to sulfur precipitation.

As the alkali metal chlorate, potassium salt or sodium salt is used, or mainly sodium chlorate is used, and its concentration can be used in a wide range, but the preferred concentration is 0.03 mol/l to 0.2 mol/l. be. In this case, only one reaction tank may be used, but considering the basic unit of sodium chlorate, a second reaction tank, which is widely used in the conventional SC2 method and R2 method, may be used as an auxiliary means. . The sodium chlorate concentration mentioned above is the concentration in the first reaction tank (main reaction tank). When the sodium chlorate concentration is less than 0.03 mol/l, the basic unit of sodium chlorate increases due to a decrease in the main reaction rate for generating chlorine dioxide. On the other hand, if the concentration is higher than 0.2 mol/l, the reaction will be with chloric acid)
The ratio of produced chlorine dioxide to +7 um is high, and the conversion rate to chlorine dioxide is sufficient, but the amount of chloric acid in the exhaust acid is high.
There is a large loss of +7 um, and even if the second reaction tank is used auxiliary, the basic unit of sodium chlorate becomes high as a result, which is not preferred industrially.

The reaction temperature is preferably 30 to 50°C. Even if the temperature is lower than 30°C, there is no problem with the reaction itself, except that the reaction rate is slow. However, since the reaction is generally an exothermic reaction, cooling is necessary to keep the reaction solution at a constant temperature, but keeping it below 30°C requires special equipment and is not a good idea for industrial production. . reaction temperature is 50
At temperatures higher than °C, the unit consumption rate increases due to the ineffective decomposition of hydrogen peroxide, and for industrial production, chlorine dioxide decomposition (puffing) is likely to occur, making safe operation impossible.

In order to carry out the process of the invention very effectively, it is necessary to maintain a low chloride concentration in the reaction vessel. As mentioned above, JP-A-53-66892 describes a method of supplying sodium chlorate and sodium chloride in approximately equal moles, but when hydrogen peroxide is added, the corresponding chloride is always produced, so this When treated under these conditions, the basic unit of Fium chlorate is poor, and not only is it not possible to obtain favorable results, but the high chloride concentration in scarlet acid imposes restrictions on how the waste acid can be used. . Since the chloride concentration in the present invention is as low as 0.02 mol/l to 0.1 mol/l, the reaction can proceed smoothly, and since the chloride concentration in hydrochloric acid is low, , in black liquor)
It is extremely preferable when mixed with sulfuric acid or when used in the production of sulfuric acid bread clay.

In order to maintain the chloride concentration within this range, 0.5 to 10 mol% of Ylium chloride is mixed into the chlorate, or 0.5 to 10 mol% of the chlorate is mixed.
Hydrochloric acid can easily be supplied in the form of 35% hydrochloric acid.
This can be done.

Hydrogen peroxide used as a reducing agent is expressed by the above-mentioned formula (6) (
According to 2, the molar ratio of sodium chlorate should be 1/2, but since it may be used in a partial reaction, it is better to add 5 to 10% more than the theoretical amount. Using an excess amount is not only disadvantageous in terms of cost, but also has many undesirable points such as remaining in the exhaust acid. Adding a small amount of hydrogen peroxide to the second reactor to ensure sufficient chlorate utilization is also a means of increasing the utilization rate, with the amount being 3-5% of the amount added to the main reactor. is sufficient.

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

(Example 1) 0.14 mol/l (approximately 15 g/l) of sodium chlorate and 9 mol/l of sulfuric acid were placed in 21 continuous glass reaction vessels each having an overflow port.
．． Filled with an aqueous solution consisting of 5N and 0.05 mol/l chloride (approximately 3 g/l as sodium chloride).
The temperature was kept at °C. A sodium chlorate aqueous solution containing a small amount of sodium chloride (sodium chlorate 5.6 mol/l, sodium chloride 0.15 mol/l) was added at 68 ml/hr, 98
% sulfuric acid at 36 ml/hr and 60% hydrogen peroxide at 9 ml/hr.
．． It was supplied at a rate of 2 ml/hr. 120On+ air
When blown in at a rate of 1/min, chlorine dioxide gas was 24.
It was continuously generated at 9 g/hr and its purity was 98.2%. From the second result, sodium chlorate and hydrogen peroxide (
60%) are 1.63 and 0.63, respectively.
It was 46. The composition of the reaction solution remained almost the same as the initial composition.

(Example 2) Using the same reaction tank as in Example 1, sodium chlorate 0.11 mol/l (approximately 12 g/l), sulfuric acid 10, ON
and 0.03 moles of chloride per month (approx. 2 g of sodium chloride/
It was filled with an aqueous solution having the composition of I) and kept at 45°C. 83ml of an aqueous solution of 5.6mol/l sodium chlorate
1/hr, 98% sulfuric acid at 43 ml/hr, 60% hydrogen peroxide at 11.0 ml/hr, and a small amount of 35% hydrochloric acid at 1.1 ml/hr. 1400 air
When the gas was injected at a rate of +ml/min, equilibrium was reached in about 30 minutes, and an analysis was performed after 1 hour.
), and the purity of the chlorine dioxide gas was 98.0%. From these results, the basic units of sodium chlorate and hydrogen peroxide were 1.62 and 0.46 (as 60% hydrogen peroxide), respectively. The reaction solution composition remained almost as it was at the beginning.

(Comparative Example 1) Chloric acid was added using the same reaction tank as in Example 1. l) Rum 0.11 mol/l (approximately 12 g/l), sulfuric acid 7. ON and chloride 0.05 mol/l (about 3 g sodium chloride/
It was filled with an aqueous solution having the composition of I) and kept at 45°C. 83ml of an aqueous solution of 5.6mol/l sodium chlorate
1/hr, 98% sulfuric acid at 34ml/hr, 60% hydrogen peroxide at 11. Oml/hr and a small amount of 35% hydrogen chloride were fed at a rate of 14.3 ml/hr. 140 air
When the gas was blown at a rate of 0 + + + 1/min, equilibrium was reached in about 1 hour, and gas analysis revealed that chlorine dioxide gas was 2
It was generated at 6.8 g/hr (0,397 mol/hr), and the chlorine dioxide purity was 81.9%. From this result, the basic unit of sodium chlorate is 1.758, hydrogen peroxide (60
(as %) was 0.509. The equilibrium concentration of the reaction solution was 0.19 mol/l of sodium chlorate and 7 mol/l of sulfuric acid.
．． ON and chloride were 0.223 mol/l.

(Comparative Example 2) Using the same reaction tank as in Example 1, sodium chlorate/
122 m of sodium chloride mixed solution (3.10 mol of sodium chlorate/3.13 mol of sodium chloride/l)
l/hr, 98% sulfuric acid at 67ml/hr.

60% hydrogen peroxide was supplied at a rate of 9.2 ml/hr, and the liquid temperature was kept at 35°C. The operation was carried out while blowing air at a rate of 1200 wl/min. Equilibrium was reached in 30 minutes, so analysis was performed and the amount of chlorine dioxide was 22.5 g/h.
The purity of chlorine dioxide gas was 75.6%. As a result, sodium chlorate and hydrogen peroxide (
60%) are 1.76 and 0.0%, respectively.
It was 50.

(Example 3) Using the same reaction tank as in Example 1, 0.0% sodium chlorate was added.
10 mol/l, (approximately 10.6 g/l), sulfuric acid 10.9N
and chloride 0.027 mol/l (sodium chloride approx.
．． 6 g/l) and heated at 35°C.
It was kept warm. 33+ al/hr of 5.6 mol/l aqueous solution of sodium chlorate, 46 ml/hr of 98% sulfuric acid,
11. 60% hydrogen peroxide. Oml/hr and small quantity 3
5% hydrochloric acid was supplied at a rate of 1.1 ml/hr. When air was blown at a rate of 1400+++ l/min, the result was approximately 30
Equilibrium was reached after minutes. An analysis was conducted 1 hour after the start of the reaction, and 30.5 g/hr of chlorine dioxide gas was generated.
The purity of chlorine dioxide was 98.2%. From this result, the basic units of sodium chlorate and hydrogen peroxide (as a 60% product) were 1.62 and 0.46, respectively, and almost the same results as in Example 2 were obtained.

(Example 4) Using the same reaction tank as in Example 1, the reaction temperature was 45°C and the sulfuric acid concentration was 8.5N. 81 ml/hr of an aqueous solution of 5.6 mol/l of sodium chlorate
, 98% sulfuric acid 33.5ml/hr, 60% hydrogen peroxide 11,7 +nl/hr and 35% hydrochloric acid 1.8
The solution was supplied at a rate of ml/hr, and analysis was performed when equilibrium was reached. The amount of chlorine dioxide generated is 29.5g/hr (
0,438 mol/hr), and the purity of chlorine dioxide is 97
．． It was 0%. From this result, the basic units of sodium chlorate and hydrogen peroxide (as 60%) are each 1,640.
and 0.494 (Comparative Example 3) Using the same reaction tank as in Example 1, the reaction temperature was 35°C, and the sulfuric acid concentration was 12. It was turned on. Sodium chlorate 5
．． 6 mol/l aqueous solution at 83 ml/hr, 98% sulfuric acid at 50 ml/hr, 60% hydrogen peroxide at 11. Oml/h
r and 35% hydrochloric acid were supplied at a rate of 1.1 ml/hr. When equilibrium was reached, analysis showed that the amount of chlorine dioxide generated was 30.4 g/hr, and the purity of chlorine dioxide gas was 98.1%. From this result, the basic units of sodium chlorate and hydrogen peroxide (as a 60% product) are each 1.
62 and 0.46, but the sulfuric acid consumption rate increased,
After the reaction was stopped, the mixture was allowed to stand at room temperature (20'C), and precipitation of sulfur was observed.

(Comparative Example 4) In the same reaction tank as in Example 1, an aqueous solution of 5.6 mol/l of sodium chlorate was added at 82 mL, 5'ml/hr, and 98% sulfuric acid was added at 41 mL, 1 ml/hr, 60% hydrogen peroxide. 13
, 7 ml/hr and 35% hydrochloric acid 1.8 ml/hr
The liquid temperature was maintained at 45°C. 140 air
When the mixture was blown at a rate of 0 ml/min, equilibrium was reached with 0.02 mol/l of sodium chlorate, 9.5 N of sulfuric acid, and 0.10 mol/l (about 5.8 g/l) of chloride (sodium chloride). As a result of gas analysis, chlorine dioxide gas was 29. O
g/hr (0,430 mol/hr), and its chlorine dioxide purity was 97.3%. From this result, the basic units of sodium chlorate and hydrogen peroxide (as a 60% product) were 1.697 and 0.586, respectively.

(Effects of the Invention) According to the method of the present invention, high purity chlorine dioxide can be easily produced without requiring a complicated reaction device. Mainly, since the basic units of alkali metal chlorate and hydrogen peroxide can be minimized, high-purity chlorine dioxide can be produced at low cost and efficiently.

Claims (1)

[Claims] In a method for continuously producing chlorine dioxide by reducing an alkali metal chlorate in an acidic aqueous solution of sulfuric acid, the acid concentration is reduced to 8 to 11N in the presence of 0.02 to 0.1 mol/l of chloride, and the alkali Metal chlorate at 0.03 to 0.
A method for producing high-purity chlorine dioxide, which is characterized by reducing the amount of chlorine dioxide with hydrogen peroxide at a concentration of 2 mol/l and adjusting the reaction temperature within the range of 30 to 50°C.