JPS62270404A - Production of chlorine - Google Patents

Abstract

PURPOSE:To prevent reduction in catalytic life and vaporization of chromium content in a catalyst, by reducing a CO amount in an exhaust gas containing hydrogen chloride into a fixed range and carrying out oxidation reaction in the presence of the catalyst comprising chromium oxide as a main component. CONSTITUTION:A hydrogen chloride-containing exhaust gas prepared in a reaction process of organic compound as a by-product is treated by an ordinary method and CO content in the exhaust gas is reduced to 10vol%. Then, hydrogen chloride is oxidized in the presence of a catalyst comprising chromium oxide as a main component so hydrogen chloride is converted into chlorine. Chromium oxide which is obtained by precipitating a chromic salt with a basic compound to give chromium oxide and by calcining the chromium hydroxide is used as the catalyst.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a method for producing chlorine, and more specifically, to a method for producing chlorine, which is a method for producing chlorine, and more specifically, a method for producing chlorine, which is produced as a by-product in processes such as chlorination reaction and phosgenation reaction of organic compounds. This invention relates to an industrial method for producing chlorine by oxidizing hydrogen gas with an oxygen-containing gas.

[Technical background of the invention]

Chlorine is produced on a large scale by salt electrolysis, and although the demand for chlorine increases year by year, the demand for caustic soda, which is simultaneously produced during salt electrolysis, is less than that of chlorine, so the imbalance between each On the other hand, a large amount of hydrogen chloride is produced as a by-product during the chlorination or phosgenation reaction of organic compounds, and the amount of by-product hydrogen chloride is proportional to the demand for hydrochloric acid. Because it is more common,
Large amounts of hydrogen chloride remain unused and wastefully disposed of as exhaust gas. Moreover, the processing costs for this disposal amount to a considerable amount.

If chlorine can be efficiently recovered from large amounts of discarded hydrogen chloride as described above, the demand for chlorine can be met in the chemical industry without creating an imbalance with the production of caustic soda.

[Problems to be solved by the prior art and the invention] The reaction of oxidizing hydrogen chloride to produce chlorine has been known since ancient times as Deac.
This is known as the ON reaction. 1868 DeacqH
The copper-based catalyst according to the invention is considered to be a catalyst that exhibits excellent activity even in conventional solutions, and many catalysts have been proposed in which various compounds are added as third components to copper chloride and potassium chloride. However, in order to oxidize hydrogen chloride with these catalysts at an industrially sufficient reaction rate, the reaction temperature must be at least 400°C.
It is necessary to do more than this, and problems such as a reduction in catalyst life due to scattering of catalyst components become a problem.

From the above point of view, as a non-copper-based catalyst, chromium oxide is more stable and durable at high temperatures than copper, etc., so a method using chromium oxide as an oxidation catalyst for hydrogen chloride is proposed in British Patent Nos. 584790 and 676667. No. 846
It has been proposed in No. 832, etc.

However, even these conventionally known methods require a relatively high reaction temperature and have low space velocities, so they are not industrially satisfactory.

The present inventors investigated various methods for producing chlorine by oxidizing hydrogen chloride with an oxygen-containing gas in the presence of a catalyst whose main component is chromium oxide, and found that a chromium oxide catalyst (CrzOa)
In the process, 1q of chromium hydroxide was prepared by using chromium nitrate or chromium chloride as a trivalent chromium salt and using ammonia as a basic compound as a neutralizing agent to obtain a precipitated catalyst at 800°C. They discovered that molded catalysts can maintain high activity and filed an application earlier.

However, as a result of further investigation and using a chromium oxide catalyst obtained by calcining chromium hydroxide synthesized by precipitation with trivalent chromium salts and basic compounds for long-term reactions, it was found that the catalyst had no activity. It has been found that if a large amount of carbon monoxide is contained in the hydrogen chloride gas as a raw material, the life of the catalyst is shortened and the amount of chromium, which is a catalyst component, volatilized increases.

This volatile chromium content flows out of the reactor together with the reaction product gas. If this volatile chromium is used as a raw material for salt without being removed, sufficient consideration must be given to its handling from the standpoint of occupational hygiene and pollution prevention.

From this point of view as well, it is necessary to prevent volatilization of chromium.

The purpose of the present invention is to prevent the life of the catalyst from decreasing and further to prevent the chromium content of the catalyst component from volatilizing.

[Means for solving problems]

As a result of careful frugality, the present inventors have discovered that the above object can be achieved by reducing the content of carbon monoxide contained in exhaust gas within a certain range, and have completed the present invention.

That is, the present invention provides a method for producing chlorine by oxidizing hydrogen chloride from exhaust gas containing hydrogen chloride, which is produced as a by-product in a reaction step in the reaction of organic compounds, using an oxygen-containing gas. This is a method for producing chlorine, which is characterized in that the carbon content is previously treated to be less than 10 parts by volume, and then trivalent chromium salt is subjected to an oxidation reaction with a basic compound.

The present invention will be explained in detail below.

If carbon monoxide in the exhaust gas is contained in a volume ratio of 10 or more, the life of the chromium oxide catalyst will be shortened, and the amount of chromium vaporized from the catalyst will increase.

This volatile chromium content flows out of the reactor together with the reaction product gas. If chlorine is separated without removing this volatile chromium, the chromium content in the product chlorine may pose a problem.

However, if the content of carbon monoxide in the exhaust gas is less than 10 parts by volume, a decrease in the life of the catalyst and volatilization of the chromium content can be prevented.

In order to reduce the carbon monoxide content, a method for treating hydrogen chloride gas is to burn carbon monoxide into carbon dioxide gas using a palladium catalyst supported on alumina. A method of liquefying and separating hydrogen chloride in exhaust gas and then evaporating the hydrogen chloride to use it as raw material gas. A method to reduce carbon monoxide by cleaning exhaust gas with a copper chloride solution. Although any method may be used, a method using a palladium catalyst on an alumina carrier is simple and effective.

A fixed-bed type oxidizer was filled with a 1-volume palladium catalyst supported by pelletized alumina, the temperature was set to approximately 300"C, and sufficient oxygen was added to reduce the carbon monoxide in the exhaust gas to less than 10 volume fractions. and send the exhaust gas to the oxidation tower at SV 2,0
OONl/ni9. The oxidation of carbon monoxide to carbon dioxide is carried out. Carbon dioxide in the exhaust gas is not involved in the conversion of hydrogen chloride to chlorine and is removed in subsequent purification steps.

In the present invention, prior to the oxidation reaction of hydrogen chloride to chlorine, the hydrogen chloride is treated in advance to reduce the content of carbon monoxide to a specific amount or less, and then subjected to the oxidation reaction to chlorine. The reaction temperature is maintained at 300 to 500°C, and usually preferably 350 to 450°C.

becomes large, which poses a problem when using the catalyst for a long time.

Furthermore, below 300°C, the rate of conversion of hydrogen chloride to chlorine is low, making it impossible to supply hydrogen chloride at an industrially sufficient space velocity.

In addition, in the present invention, the molar ratio of hydrogen chloride to be subjected to the reaction and oxygen in the oxygen-containing gas is preferably 0.25 to 10. If the amount of oxygen is less than the theoretical amount of 0.25, the conversion rate of hydrogen chloride to chlorine will decrease. It gets lower.

Furthermore, if more oxygen is used than necessary, high operating costs are required. Also, the amount of hydrogen chloride supplied to the catalyst bed is 20
0-180ONA7 to 9. Cat, hr ranges are suitable.

The catalyst used in the present invention is a chromium oxide catalyst (Cr20a
), chromium hydroxide obtained by using chromium nitrate or chromium chloride as a trivalent chromium salt and using ammonia as a basic compound as a neutralizing agent to obtain a precipitated catalyst,
It is a catalyst whose main component is chromium oxide obtained by firing at a temperature below OO°C, and in which case silicon oxide is preferably used as a binder.

Hereinafter, the present invention will be explained in detail with reference to Examples.

Example 1 Oxygen was added to the hydrogen chloride gas discharged from the phosgenation reaction process of 1-lylenediamine, which contained 10 parts by volume of carbon monoxide gas, so that the carbon monoxide content became 3 parts by volume. Ta.

The temperature of the Ni oxidizer filled with 1 ky of pellet-shaped catalyst with lqb palladium supported on an alumina carrier was set to 3
The temperature was maintained at 00°C, and exhaust gas containing oxygen was introduced to adjust the carbon monoxide gas content in the exhaust gas to 3 volumes.

On the other hand, the catalyst was prepared in the following manner as described in Japanese Patent Application No. 60-292880.

Chromium nitrate nonahydrate 3°Oky was dissolved in deionized water 301, and 9 was added dropwise to 28 parts ammonia water 2.9 parts over 30 minutes while stirring well.

Deionized water was added to the resulting precipitate slurry to dilute it to 2001, and after standing overnight, decantation was repeated to wash the precipitate. Colloidal silica corresponding to 10 parts of the total weight after firing was added. The granular powder obtained by drying this mixed slurry with a spray dryer was heated to 600°C in an air atmosphere.
It was baked for 3 hours.

Ta. This catalyst 1507& was packed into a N1 fluidized bed reactor with an inner diameter of 4 inches, the outside was heated to 370°C by a sand bath, and oxidized with the above palladium catalyst, and the exhaust gas containing 3 parts by volume of carbon monoxide gas was .3 Nl 1 min (HC112,
6Nl, Co O, 4Nl%C02B98Nl), oxygen gas 6.3Nj? /min(i(Cl base SV 50
0tJl/9. cat, hr oxygen excess rate + ool
) was introduced into a fluidized bed and reacted while the catalyst was fluidized.

The temperature of the catalyst layer rose to 400°C due to heat generation.

The reactor effluent gas was collected with a L-lap made by connecting an absorption bottle of an aqueous potassium iodide solution and an absorption bottle of an aqueous caustic soda solution in series, and titrated with sodium sulfate and hydrochloric acid to remove unreacted hydrogen chloride and the generated chlorine. was quantified.

The conversion rate of hydrogen chloride immediately after the start of the reaction was 68%, and 20%.
Even after 0 hours, the conversion rate was 66%.

The weight loss of the catalyst after 200 hours of reaction was 309, which was 2 times the amount of catalyst initially charged.

Comparison VA-1 Catalyst 15079 prepared in exactly the same manner as in Example-1 was packed into a Ni fluidized bed reactor with an inner diameter of 4 inches, and the outside was heated to 360° C. using a sand agitation bath.

Exhaust gas 14Nl/min (H1tz6N1.Co1.
4-Nl), oxygen gas 6.3 Nl 1 minute (HCl base, SV 500 Nil/kF1. cat,
An hr oxygen excess ratio of 91 was introduced into the fluidized bed, the catalyst was fluidized, and unreacted hydrogen chloride was produced in the same manner as in Example-1, and after 200 hours, the ratio decreased to 55%. The weight loss of the catalyst after 200 hours of reaction was 90.9, which was 6 times the amount of catalyst initially charged.

Claims (2)

[Claims] (1) In a method of producing chlorine by oxidizing hydrogen chloride using oxygen-containing gas from exhaust gas containing hydrogen chloride, which is a by-product in the reaction process of organic compound reaction, carbon monoxide contained in the exhaust gas is In the presence of a catalyst mainly composed of chromium oxide prepared by pre-treating the content to less than 10% by volume and then precipitating trivalent chromium salt with a basic compound and calcining the obtained chromium hydroxide, A method for producing chlorine, characterized by carrying out an oxidation reaction. (2) Claim No. 1, in which carbon monoxide contained in exhaust gas is previously treated to less than 10% by volume by converting carbon monoxide into carbon dioxide gas with oxygen using a 1% palladium catalyst with alumina as a carrier. The method described in section.