A kind of preparation method of chlorine dioxide

Abstract

The invention discloses a method for preparing chlorine dioxide, comprising the following steps: uniformly mixing chlorate solid, formamide and acid to form a reaction liquid, performing an oxidation-reduction reaction at 50-80°C to obtain chlorine dioxide; the molar ratio of formamide to chlorate is 0.1-1.5:1; and the acid concentration in the reaction liquid is 5-8 mol / L. The preparation method of the invention adopts a new reducing agent to prepare high-purity chlorine dioxide, overcoming the technical problems of low purity of chlorine dioxide, low raw material reaction rate, and long reaction time in the traditional technology.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a method for preparing chlorine dioxide. Background Art

[0002] Chlorine gas is the most commonly used chlorine oxidant in urban sewage treatment plants because of its easy operation and low cost. However, chlorine gas will produce organic byproducts such as trihalomethanes during the reaction, which can cause cancer and various diseases and cannot meet the requirements of healthy drinking water. Therefore, it is imperative to find an efficient and non-toxic chlorine oxidant.

[0003] Chlorine dioxide is recognized as the most ideal alternative to chlorine preparations internationally because of its broad-spectrum, commercially effective and safe sterilization characteristics. Many countries have adopted chlorine dioxide to treat factory wastewater. At the same time, chlorine dioxide is a strong oxidant. Chlorine dioxide is active in nature. Its effective chlorine is 2.6 times that of chlorine. It can react violently with many substances. Its solubility is about 5 times that of chlorine. Chlorine dioxide is soluble in water and basically does not undergo hydrolysis reaction. It can better treat complex and diverse organic matter in wastewater and does not produce halogenated hydrocarbon organic disinfection by-products.

[0004] The preparation of chlorine dioxide can be divided into electrolytic method and chemical method. Due to the high production cost and maintenance cost of electrolytic method, most of the chlorine dioxide is prepared by chemical method in actual production. According to the main raw materials, the chemical method of preparing chlorine dioxide can be divided into chlorite method and chlorate method. Because the price of sodium chlorate is much cheaper than that of sodium chlorite, sodium chlorate is often used as the main raw material for the generation of chlorine dioxide in large-scale production.

[0005] The sodium chlorate reduction method for preparing chlorine dioxide is based on the redox reaction of sodium chlorate with a reducing agent under strong acid conditions. The commonly used processes in my country's industrial production include the R1 method with sulfur dioxide as a reducing agent, the R2 and R5 methods with hydrochloric acid as a reducing agent, the R8 method with methanol as a reducing agent, and the R11 method with hydrogen peroxide as a reducing agent.

[0006] In the R1 method, chlorine dioxide is not easy to source, the conversion rate is not high, and there are many by-products. The R2 and R5 methods have high conversion rates, but they carry one-third of chlorine gas, and they will still produce a large amount of halogenated hydrocarbons when used for drinking water disinfection. In the R8 method, methanol is volatile and is a high-risk chemical. It will cause secondary pollution of methanol in drinking water disinfection. In the R11 method, hydrogen peroxide has a low stability and is a high-risk chemical with a high price.

[0007] The chlorine dioxide obtained by the existing chlorine dioxide preparation method has low purity (reference: Lu Yun, Qiao Chengzhong, Chen Tianlang, etc. Research progress of chlorine dioxide preparation methods and related products in my country [J]. Chemical Research and Application, 2008 (04): 367-373.). For example, the R5 method of producing chlorine dioxide using hydrochloric acid as a reducing agent generates at least one-half chlorine gas while producing a certain amount of chlorine dioxide. The purity of chlorine dioxide is below 66%, the product is seriously impure, and the raw material conversion rate is generally not high, which will cause secondary pollution of water quality.

[0008] Therefore, it is particularly important to find a new reducing agent and a new method for preparing pure chlorine dioxide using sodium chlorate as raw material. Summary of the invention

[0009] The invention provides a method for preparing chlorine dioxide, adopts a new reducing agent to prepare high-purity chlorine dioxide, and overcomes the technical problems of low purity of chlorine dioxide, low raw material utilization rate, long reaction time and the like in the traditional technology.

[0010] The technical solution of the present invention is as follows:

[0011] A method for preparing chlorine dioxide comprises the following steps:

[0012] The chlorate solid, formamide and acid are uniformly mixed to form a reaction liquid, and an oxidation-reduction reaction is carried out at 50-80° C. to obtain chlorine dioxide;

[0013] The molar ratio of formamide to chlorate is 0.1-1.5:1;

[0014] The acid concentration in the reaction liquid is 5-8 mol / L.

[0015] The reaction equation of the present invention is formula (1) or formula (2):

[0016] (1)6NaClO3+2CH3NO+3H2SO4→5ClO2+1 / 2Cl2+N2+2CO2+3Na2SO4+6H2O

[0017] (2)6NaClO3+2CH3NO+6H2SO4→5ClO2+1 / 2Cl2+N2+2CO2+6NaHSO4+6H2O.

[0018] Preferably, the concentration of chlorate in the reaction solution is 1.5-2.5 mol / L.

[0019] Preferably, the chlorate is an alkali metal or alkaline earth metal chlorate; more preferably, it is sodium chlorate.

[0020] Preferably, the molar ratio of formamide to chlorate is 0.5-1.3:1.

[0021] Within this molar ratio range, the utilization rate of chlorate is high and the purity of the obtained chlorine dioxide is high.

[0022] Preferably, the acid concentration in the reaction liquid is 5-6 mol / L.

[0023] The higher the acid concentration, the more thorough the reaction. The reaction will not occur at low acidity. When the acid concentration in the reaction liquid is 5-6 mol / L, the reaction can be carried out thoroughly.

[0024] Preferably, the acid is sulfuric acid.

[0025] The increase of reaction temperature is conducive to the reaction and the utilization rate of sodium chlorate is improved. When the reaction temperature is too low, the reaction is not thorough. When the reaction temperature is too high, it has no promoting effect on the reaction and also causes the cost to increase.

[0026] Preferably, the reaction temperature is 60-75° C., and the reaction time is 20-40 min. Preferably, the chlorine dioxide obtained by the redox reaction is collected by a three-stage gas absorption device to obtain a chlorine dioxide solution.

[0027] The three-stage absorption device can fully absorb the chlorine dioxide gas without leakage, thus improving the safety of the reaction and the yield of chlorine dioxide.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The preparation method of the present invention creatively uses formamide as a reducing agent, so that the redox reaction rate is fast and the utilization rate of the raw materials is high. When preparing concentrated chlorine dioxide, a small amount of byproduct chlorine gas is produced, and the purity of chlorine dioxide is relatively high.

[0030] (2) The preparation method of the present invention has a short reaction time and is simple to operate, which is conducive to the rapid preparation of chlorine dioxide solution, reduces the preparation time, and ensures the timeliness of on-site preparation of chlorine dioxide solution.

[0031] (3) The experimental equipment of the preparation method of the present invention is basically closed to prevent leakage of chlorine dioxide gas, which not only improves the safety of the experiment, but also facilitates the absorption of chlorine dioxide gas.

[0032] (4) The inert gas N2 produced during the reaction can reduce the concentration of chlorine dioxide in the system, thereby increasing the safety of the reaction system. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below in conjunction with the examples. It should be pointed out that the examples described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0034] In the following examples, the concentration of sodium chlorate was determined by ion chromatography, and the concentration of chlorine dioxide was determined by a five-step iodine titration method. Three sets of parallel samples were measured and the results were obtained within the allowable error range.

[0035] The purity of chlorine dioxide is the ratio of the mass of chlorine dioxide to the total mass of chlorine.

[0036] The calculation formula is: chlorine dioxide purity = chlorine dioxide mass / (chlorine dioxide mass + chlorine mass).

[0037] Example 1

[0038] 1.06g sodium chlorate, 0.5ml formamide and 5ml 6mol / L sulfuric acid solution (water bath to 60°C) were added to the reactor respectively to make the overall reaction liquid acidity 5mol / L (5ml sulfuric acid was diluted by 0.5ml formamide). The reactor was placed in a water bath at 60°C. The air pump was turned on to allow the generated gas to enter the three-stage collection device. After the reaction for 30 minutes, the water bath heating was stopped after the experiment was completed, and the exhaust device was turned off. The absorption bottle contained the prepared chlorine dioxide solution.

[0039] The three-stage collection device consists of three gas collection bottles connected in series, each of which contains deionized water.

[0040] The utilization rate of sodium chlorate was 13.52%. The results of the five-step iodine titration method are shown in Table 1:

[0041] Table 1 Example 1 Sample measurement results

[0042]

[0043] From Table 1, it can be concluded that the chlorine dioxide output in the reaction is 66.78 mg / L, and the purity of chlorine dioxide gas is 99.48%.

[0044] Example 2

[0045] Add 1.06g sodium chlorate, 0.5ml formamide, and 5ml 6mol / L sulfuric acid solution (water bath to 75°C) to the reactor to make the overall reaction liquid acidity 5mol / L. Put the reactor into a water bath at 75°C, turn on the air pump, and let the generated gas enter the three-stage collection device. After the reaction for 30 minutes, stop the water bath heating, turn off the exhaust device, and the absorption bottle is the prepared chlorine dioxide solution.

[0046] The utilization rate of sodium chlorate was measured to be 84.93%; the results of the five-step iodine titration method are shown in Table 2:

[0047] Table 2 Example 2 Sample measurement results

[0048]

[0049] From Table 2, it can be concluded that the chlorine dioxide output in the reaction is 296.79 mg / L, and the purity of chlorine dioxide gas is 85.67% (the reduction in purity may be due to the decomposition of chlorine dioxide, which produces some chlorine gas).

[0050] Example 3

[0051] Add 1.06g sodium chlorate, 0.2ml formamide, and 5ml 7mol / L sulfuric acid solution (water bath to 60°C) to the reactor to make the overall reaction liquid acidity 6mol / L. Put the reactor into a water bath at 60°C, turn on the air pump, and let the generated gas enter the three-stage collection device. After 30 minutes of reaction, stop the water bath heating, turn off the exhaust device, and the absorption bottle is the prepared chlorine dioxide solution.

[0052] The utilization rate of sodium chlorate was measured to be 40.79%; the results of the five-step iodine titration method are shown in Table 3:

[0053] Table 3 Example 3 Sample measurement results

[0054]

[0055] From Table 3, it can be concluded that the chlorine dioxide production in the reaction is 178.75 mg / L, and the purity of the chlorine dioxide gas is 93.48%.

[0056] Example 4

[0057] Add 1.06g sodium chlorate, 0.5ml formamide, and 5ml 7mol / L sulfuric acid solution (water bath to 60°C) to the reactor to make the overall reaction liquid acidity 6mol / L. Put the reactor into a water bath at 60°C, turn on the air pump, and let the generated gas enter the three-stage collection device. After 30 minutes of reaction, stop the water bath heating, turn off the exhaust device, and the absorption bottle is the prepared chlorine dioxide solution.

[0058] The utilization rate of sodium chlorate was measured to be 96.92%; the results of the five-step iodine titration method are shown in Table 4:

[0059] Table 4 Example 4 Sample measurement results

[0060]

[0061] From Table 4, it can be concluded that the chlorine dioxide production in the reaction is 357.50 mg / L, and the purity of the chlorine dioxide gas is 87.43%.

[0062] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing chlorine dioxide, characterized in that: The following steps are involved: The chlorate solid, formamide and acid are uniformly mixed to form a reaction liquid, and an oxidation-reduction reaction is carried out at 60-75° C. for 20-40 minutes to obtain chlorine dioxide; The molar ratio of formamide to chlorate is 0.1-1.5:1; The acid concentration in the reaction liquid is 5-8 mol / L.

2. The method for preparing chlorine dioxide according to claim 1, characterized in that: The concentration of chlorate in the reaction liquid is 1.5-2.5 mol / L.

3. The method for preparing chlorine dioxide according to claim 1 or 2, characterized in that: The chlorate is an alkali metal or alkaline earth metal chlorate.

4. The method for preparing chlorine dioxide according to claim 1, characterized in that: The molar ratio of formamide to chlorate is 0.5-1.3:

1.

5. The method for preparing chlorine dioxide according to claim 1, characterized in that: The acid concentration in the reaction liquid is 5-6 mol / L.

6. The method for preparing chlorine dioxide according to claim 1 or 5, characterized in that: The acid is sulfuric acid.

7. The method for preparing chlorine dioxide according to claim 1, characterized in that: The chlorine dioxide obtained by the redox reaction is collected by a three-stage gas absorption device to obtain a chlorine dioxide solution.

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