METHOD FOR PREPARING HIGH-PURITY CHLORINE DIOXIDE BY USING METHANOL AND HYDROGEN PEROXIDE AS REDUCING AGENT

Abstract

The invention discloses a method for preparing high-purity chlorine dioxide by using methanol and hydrogen peroxide as reducing agent. The method comprises: concentrated sulfuric acid and sodium chlorate solution are injected into the generator to form the reaction mother liquid. The reaction mother liquid shall be maintained a certain acidity, temperature and sodium chlorate content, and then it is reacted with the reducing agent (methanol and hydrogen peroxide) to produce chlorine dioxide gas and by-product sodium sulfate. The chlorine dioxide gas is cooled and absorbed by low temperature chilled water to obtain an aqueous solution of chlorine dioxide, and by-products are recycled. The chlorine dioxide solution produced by the aforementioned method has a 60-70% reduction in the Cl2 content and 14-20% reduction in sulfuric acid consumption than that of the chlorine dioxide produced by using a single methanol reducing agent, and the by-product produced is sodium sulfate, not sodium hydrogen sulfate, so neutralization reaction treatment is not required.

Claims

1. A method for preparing high-purity chlorine dioxide by using methanol and hydrogen peroxide as reducing agent, characterized in that, it comprises the following steps: First step, the concentrated sulfuric acid and sodium chlorate solution are injected into the generator system to form a reaction mother liquid. The reaction mother liquid is maintained at an acidity of 5.8-6.2N, sodium chlorate content is 234-266 g/l, and temperature is maintained at 69-73 C.; the aforesaid generator system consists of a reactor and a reboiler connected by a circulation pipe; Second step, the reducing agent is added into the reaction mother liquid to produce chlorine dioxide gas and by-product sodium sulfate. The reducing agent is composed of methanol and hydrogen peroxide. The ratio of methanol to hydrogen peroxide by mass percentage is: 60-70% of methanol:30-40% of hydrogen peroxide; Third step, the generated chlorine dioxide gas is cooled and absorbed by 4-10 C. chilled water to obtain the chlorine dioxide aqueous solution, and the by-product sodium sulfate is filtered, washed and recycled.

2. A method for preparing high-purity chlorine dioxide by using methanol and hydrogen peroxide as reducing agent according to claim 1, wherein in the second step, the methanol is first diluted with demineralized water to a volume concentration of 20% and then added to the reaction mother liquid from the venturi pipe at the reboiler outlet.

3. A method for preparing high-purity chlorine dioxide by using methanol and hydrogen peroxide as reducing agent according to claim 2, wherein in the second step, the hydrogen peroxide is first prepared as hydrogen peroxide solution with a mass concentration of 30% and then mixed with the sodium chlorate solution, and added to the reaction mother liquid from the reboiler inlet.

4. A method for producing high-purity chlorine dioxide by using methanol and hydrogen peroxide as reducing agent according to claim 2, wherein in the first step, the reactor is maintained vacuum and pressure is 78 to 82 kPa.

5. A method for preparing high-purity chlorine dioxide by using methanol and hydrogen peroxide as reducing agent according to claim 2, wherein in the third step, the chlorine dioxide gas is discharged from the top of the reactor, and the mixed gas temperature of the chlorine dioxide gas and the steam generated by the reactor is 57-68 C. and is gradually cooled to 38-45 C. by the intercooler, and then enters the chlorine dioxide absorption tower, the chlorine dioxide aqueous solution is formed by spraying and absorption of chilled water.

6. A method for preparing high-purity chlorine dioxide by using methanol and hydrogen peroxide as reducing agent according to claim 2, wherein in the second step, the preferred ratio of the methanol to hydrogen peroxide is: 66% of methanol:34% of hydrogen peroxide.

Description

SPECIFIC EMBODIMENTS

[0020] The method of the present invention will be further described below with reference to the accompanying drawings and examples:

[0021] The process of the method of the invention is as shown in FIG. 1: concentrated sulfuric acid enters the generator from one side of the venturi pipe of the reboiler outlet, and methanol is diluted with demineralized water and then enters the generator from the other side of the venturi pipe. The hydrogen peroxide is mixed with the sodium chlorate solution and then enters the reboiler from the outlet pipe of the circulation pump, and enters the generator through the reboiler. The reaction liquid continuously circulates between the generator and the circulation pipe under the action of the circulation pump, and the reaction mother liquid is heated by the reboiler to maintain the temperature required for the reaction, and the generator and the reboiler are connected through the circulation pipe to form a circulation circuit.

[0022] With the addition of methanol and hydrogen peroxide, chlorine dioxide is continuously generated in the generator. The chlorine dioxide and the evaporated water vapor are discharged from the top of the generator into the intercooler, after cooled by the intercooler, they enter the chlorine dioxide absorption tower (the intercooler and the chlorine dioxide absorption tower are combined to form a cooling and absorption device). Chilled water is filled into the absorption tower to absorb chlorine dioxide to form the chlorine dioxide aqueous solution.

[0023] The solid content in the generator is controlled to a certain concentration range, and the produced sodium sulfate is pumped out together with the mother liquid from the bottom of the generator by the sodium sulfate feed pump, and sent to the sodium sulfate filter device for filtration and recycle, and the filtered mother liquid is returned to the generator.

[0024] In the present invention, the addition point of methanol is at the venturi pipe of the reboiler outlet, and the addition point of hydrogen peroxide is between the inlet of the reboiler and the outlet of the circulation pump.

Example 1

[0025] 186 kg of 98% mass concentrated sulfuric acid and 547 kg of 30% mass concentration sodium chlorate solution are injected into the generator to form a reaction mother liquid, which is circulating in the circulation pipe of the generator under the action of a circulation pump, and maintains at an acidity of 5.8-6.2N and a sodium chlorate content of 158-266 g/l. The heat is transferred to the mother liquid by a reboiler to maintain a temperature of 69-73 C. 20% (v/v) methanol with a weight of 44.8 kg and 30% (w/w) hydrogen peroxide with a weight of 16.3 kg are continuously and uniformly injected into the generator to produce chlorine dioxide. The generator maintains vacuum, pressure is 78 to 82 kPa(g). Under the negative pressure condition, the temperature of the mixed gas of chlorine dioxide and water vapor discharged from the generator is 57-68 C., and is preliminarily lowered to 38-45 C. by the intercooler, the gas enters the chlorine dioxide absorption tower and is sprayed with 4-10 C. chilled water to produce chlorine dioxide solution. By-products are generated and continue to form precipitated crystals in the mother liquor as the reaction progresses. To maintain the volume percentage of the solids in the reaction liquid is 18-23%, the mother liquid containing sodium sulfate is pumped out from the bottom of the generator, and the by-product sodium sulfate is filtered out by a filter, and the filtrate is returned to the generator. The concentration of the chlorine dioxide solution produced is 9.4 g/l, the Cl.sub.2 content of the solution is 0.08 g/l, and the sulfuric acid consumption is 0.86 t/tClO.sub.2.

Example 2

[0026] 186 kg of 98% mass concentration sulfuric acid and 547 kg of 30% mass concentration sodium chlorate solution are injected into the generator to form a reaction mother liquid, which is circulating in the circulation pipe of the generator under the action of a circulation pump, and maintains at an acidity of 5.8-6.2N and a sodium chlorate content of 158-266 g/l. The heat is transferred to the mother liquid by a reboiler to maintain a temperature of 69-73 C. 20% (v/v) methanol with a weight of 46.5 kg and 30% (w/w) hydrogen peroxide with a weight of 14.3 kg are continuously and uniformly injected into the generator to produce chlorine dioxide. The generator maintains vacuum, pressure is 78 to 82 kPa(g). Under the negative pressure condition, the temperature of the mixed gas of chlorine dioxide and water vapor discharged from the generator is 57-68 C., and is preliminarily lowered to 38-45 C. by the intercooler, the gas enters the chlorine dioxide absorption tower and is sprayed with 4-10 C. chilled water to produce chlorine dioxide solution. By-products are generated and continue to form precipitated crystals in the mother liquor as the reaction progresses. To maintain the volume percentage of the solids in the reaction liquid is 18-23%, the mother liquid containing sodium sulfate is pumped out from the bottom of the generator, and by-product sodium sulfate is filtered out by a filter, and the filtrate is returned to the generator. The concentration of the chlorine dioxide solution produced is 9.5 g/l, the Cl.sub.2 content of the solution is 0.09 g/l, and the sulfuric acid consumption is 0.87 t/tClO.sub.2.