JPS6345102A - Production of chlorine - Google Patents

Abstract

PURPOSE:To produce high-purity chlorine in high yield of raw material, by oxidizing hydrogen chloride gas obtained as a by-product of a reaction process of an organic compound after decreasing the content of the organic compound existing in the hydrogen chloride gas below a specific level. CONSTITUTION:The content of benzene-group organic compounds existing as impurities in a hydrogen chloride gas by-produced in the chlorination reaction or phosgenation reaction of an organic compound is decreased to <=1wt% e.g. by liquefaction distillation, washing with high-boiling solvent, low-temperature separation, adsorption with activated carbon, etc. The treated hydrogen chloride gas is oxidized at 350-450 deg.C in the presence of an oxidation catalyst produced by treating a trivalent Cr salt such as Cr(NO3)3 with a basic compound such as ammonia water and supporting 20-80wt% Cr2O3 catalyst prepared by the above treatment on an SiO2 carrier. Chlorine gas having high purity can be produced in high efficiency by this process.

Description

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

(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. , it is difficult to adjust each imbalance properly.

On the other hand, a large amount of hydrogen chloride is produced as a by-product during the chlorination reaction or phosgenation reaction of organic compounds, and the amount of by-product hydrogen chloride is far greater than the required amount of hydrochloric acid, so a large amount of hydrogen chloride remains unused. It is wastefully disposed of as exhaust gas while still being used.

Moreover, the processing costs for this disposal amount to a considerable amount.

If chlorine can be efficiently recovered from hydrogen chloride, which is discarded in large quantities as described above, it will be possible to meet the demand for chlorine in the chemical industry without creating an imbalance with the production of caustic soda.

(Prior art and problems to be solved by the invention) The reaction of oxidizing hydrogen chloride to produce chlorine has been known since ancient times.
This is known as the ON reaction. 1868 DeacOn
The copper-based catalyst according to the invention is said to exhibit excellent activity even in conventional amounts, 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 at an industrially sufficient reaction rate with these catalysts, the reaction temperature must be kept low (both 400
℃ or higher, which poses problems such as a reduction in catalyst life due to scattering of catalyst components.

From the above points, 1, methods using chromium oxide as an oxidation catalyst for hydrogen chloride are also available, for example in British Patent Nos. 584790 and 67.
It has been proposed in No. 6667, No. 846832, etc.

However, even in these conventionally known methods, the reaction temperature must be relatively high, and therefore the activity is not decreased due to catalyst loss, and the space velocity is also extremely low, so that the conditions are not industrially satisfactory.

In addition, the present inventors have investigated various catalysts mainly composed of chromium oxide, which is highly active even at low temperatures. The main component is chromium oxide obtained by calcining chromium hydroxide obtained by using ammonia or the like as a basic compound as a neutralizing agent to obtain the precipitated catalyst at a temperature below 800°C. They discovered a catalyst molded using silicon oxide as a binder and a catalyst made by crushing 20 to 611% chromium oxide as chromia (crxos) on a silicon oxide carrier, and filed an application earlier.

However, when such a chromium oxide catalyst is used for a long-term reaction, organic compounds and
Particularly when benzene-based hydrocarbons are included, if even a trace amount of these impurities is present, these impurities may be chlorinated or partially oxidized in the reaction system to produce polychlorine compounds, which may deposit on the catalyst surface. It has been found that this causes inconvenient problems such as a decrease in the activity of the catalyst or blockage of piping in the process system for treating the product gas after the reaction.

In the exhaust gas discharged from the chlorination of organic compounds, for example, the production process of chlorobenzene through the chlorination reaction of benzene, in addition to by-product hydrogen chloride, unreacted benzene is usually 5 to 1.
Contains 11%. In addition, for example, a plant for producing isocyanate gA through the phosgenation reaction of tolylene diamine contains not only a large amount of hydrogen chloride but also a considerable amount of toluene used as a phosgenation reaction solvent, dichlorobenzene, etc. in the form of vapor. There is.

When exhaust gas containing organic compounds derived from reaction substrates or solvents discharged from such an organic chemical reaction process is directly reacted in the presence of the chromium oxide catalyst used in the present invention, an oxidation reaction also occurs at the same time, resulting in multiple reactions. Tar deposits from chlorine compounds are produced.

In particular, this tendency is remarkable when the reaction temperature is lowered to take advantage of the advantage of being able to carry out the reaction at a relatively low temperature, which is a feature of the present invention.

Furthermore, aromatic hydrocarbons such as benzene and toluene as mentioned above have relatively high pressure, so they are entrained in the reaction gas and contaminate the post-treatment system after the oxidation reaction.For example, chlorine produced by the oxidation reaction The reactant gas containing is usually cooled,
Chlorine is separated from the reaction gas through post-processing steps such as cleaning and compression, but if the above organic compounds are present in these steps where the temperature drops, they will precipitate and cause problems such as pipe blockage. stir up

(Means for Solving the Problems) From these viewpoints, the present inventors have conducted various studies and determined that it is necessary to reduce as much as possible the organic compounds in the exhaust gas containing hydrogen chloride that is subjected to the oxidation reaction. I found out.

That is, in the present invention, after the content of the arissubane compound contained in the exhaust gas is treated in advance to be less than 1% by weight, chromium oxide (e
Of chlorine, which is characterized by an oxidation reaction in the presence of a catalyst whose main component is rxos)! This is method A.

As described above, in the method of the present invention, it is necessary to reduce the content of organic compounds in the raw materials to at least 1% by weight or less before producing chlorine by oxidation reaction.

During the production of chlorine in the oxidation reaction, most of the organic compounds in the exhaust gas are burned or decomposed into polychlorine compounds, and some of them that adhere to the catalyst surface are entrained in the reaction gas and removed. The part is further chlorinated and partially oxidized on the catalyst, and deposits in the form of tar on the catalyst surface.

Therefore, the catalytic activity is determined by the balance between the amount of polychlorine compounds deposited on the catalyst surface and the amount of the part that adheres to the catalyst surface that is oxidized and burned and removed as carbon dioxide and other gases. Since the present invention is usually carried out at a relatively low temperature of about 350 to 400°C, in this temperature range, if the organic compound content is more than 1% by weight, the amount of deposition increases, resulting in a decrease in the catalyst activity of the present invention. In addition, it is desirable that organic compounds are not contained in the raw material gas, but in order to suppress the content to 10 ppm or less, the cost of refining the raw material gas increases, which is industrially disadvantageous. % or less, preferably to about 100 ρρ-.

Hydrogen chloride gas can be treated by any method such as liquefaction distillation, washing with a high boiling point solvent, cryogenic separation, or use of an adsorbent to reduce the organic compounds contained, but adsorption with activated carbon is simple and effective. It is true.

In the case of adsorption treatment using activated carbon, the activated carbon used may be fruit shell-based, wood-based, petroleum-based, etc., as long as it can adsorb organic compounds, and the usage conditions may be the same as normal activated carbon usage conditions. The amount depends on the amount of organic compounds contained in the hydrogen chloride and the number of times the activated carbon is regenerated.

Furthermore, thermal regeneration and reduced pressure regeneration methods can be applied to regenerate activated carbon, but desorption using steam, hot air regeneration using inert gas, etc. are effective. Of course, if the amount of activated carbon used is small, it can be disposed of without being recycled. The method is a fixed bed type adsorption system, but there is no problem in adopting the commonly used moving bed absorption system or fluidized bed absorption system.

In the present invention, prior to the oxidation reaction, the material is treated in advance to reduce the content of organic compounds to a certain level or below, and then subjected to the oxidation reaction.
The temperature is maintained at ~500°C, usually 350-450°C, more preferably 350-400°C.

The higher the temperature, the faster the conversion rate of hydrogen chloride, but the faster the rate of continuous loss of chromium components from the catalyst, which becomes a problem when using the catalyst for a long time. Furthermore, below 300'C, the conversion rate of hydrogen chloride is low, making it impossible to supply hydrogen chloride at an industrially sufficient space velocity, and the amount of polychlorine compounds deposited on the catalyst surface tends to increase. Become.

In addition, in the present invention, the molar ratio of hydrogen chloride used in the reaction to atom 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 will be low). In addition, polychlorine compounds tend to increase, which is undesirable. On the other hand, if more than the required amount of oxygen is used, high operational costs are required.

In addition, the amount of hydrogen chloride supplied to the catalyst bed is 200 to 180
ONj! /hour/Kg/catalyst range is suitable.

The present inventors have made many adjustments to the catalyst. 2, for example, Japanese Patent Application No. 60-292880, Japanese Patent Application No. 61-14
It can be adjusted by the method described in 8055.

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

Example 1 Raw material exhaust gas containing hydrogen chloride discharged from the chlorine/arsenic reaction process of benzene containing 1% by weight was treated with activated carbon 2k.
The benzene in the treated hydrogen chloride gas was reduced to about 1100 pp by passing it through a column packed with g.

On the other hand, the catalyst was prepared according to the method described in Japanese Patent Application No. 60-292880.

Chromium nitrate nonahydrate 3. Dissolve OKg in 30j2 of deionized water and add 2.9g of 28% ammonia water while stirring well.
Kg was injected dropwise over a period of 30 minutes.

Deionized water was added to the resulting precipitate slurry to dilute it to 200 μl, and after standing overnight, decantation was repeated to wash the precipitate. Colloidal silica was added in an amount of 10% of the total weight after firing. The granular powder obtained by drying this mixed slurry with a spray dryer was heated at 60'C in an air atmosphere.
It was baked for 3 hours.

Thereafter, the particulate catalyst was sieved using a JIS standard sieve to obtain a chromia catalyst having an average particle diameter (median diameter) of 50 to 60 μm.

375 g of this catalyst was packed into a Ni fluidized bed reactor with an inner diameter of 2 inches, and the outside was heated to 340°C with a sand bath, and the activated carbon treatment gas described above was 1.25 Ml/winS, and the oxygen gas was 0.
．． 63 Nl/u1n was introduced into the catalyst bed, and the oxidation reaction was carried out while the catalyst was fluidized.

The temperature of the catalyst bed reached 350℃ due to heat generation.The reactor effluent gas was collected in a trap consisting of an absorption bottle of an aqueous potassium iodide solution and an absorption bottle of an aqueous caustic soda solution connected in series, and titrated with sodium thiosulfate and hydrochloric acid. Then, unreacted hydrogen chloride and generated chlorine were quantified.

The conversion rate of hydrogen chloride immediately after the start of the reaction was 70%, and 20%
Even after 0 hours, the conversion rate was 69%. The carbon content of the catalyst after use was analyzed as an indicator of the organic matter content in the catalyst. The results were soppm as shown in Table-1.

Example 2 A raw material gas containing hydrogen chloride having the same raw material composition as in Example 1 was treated with activated carbon in the same manner as in Example 1 to reduce benzene to about 100 pp-. The reaction was carried out using hydrogen chloride gas in the presence of a catalyst according to the catalyst preparation method described below.

The catalyst has an average pore volume of 1.0 cc/g and an average particle size of 58
It was prepared by immersing μ silicon oxide powder in an aqueous chromic acid anhydride solution and then calcining it at 600° C., and 60% of Crt (h) was supported based on the total weight of the catalyst.

Using this catalyst, a reaction was carried out in the same reactor as in Example 1 under the same conditions.

The conversion rate of hydrogen chloride immediately after the start of the reaction was 69%, and 20%
Even after 0 hours, the conversion rate was 68%. The carbon content of the used catalyst was soppm as shown in Table-1.

Comparative Examples 1 and 2 Reactions were carried out using the same catalyst and reactor as in Example 1, except that hydrogen chloride gas containing 1% by weight of benzene was used without subjecting the raw material gas to activated carbon treatment.

The reaction was carried out under conditions where the oxygen excess rate was changed, resulting in a decrease in the conversion rate,
The results of examining the carbon content of the used catalyst are shown in Example 1.2.
They are shown in Table 1.

Table-1

Claims (6)

[Claims] (1) In a method for producing chlorine by oxidizing hydrogen chloride using an oxygen-containing gas from exhaust gas containing hydrogen chloride, which is a by-product in the reaction process of organic compound reaction, the amount of organic compounds contained in the exhaust gas is A method for producing chlorine, which comprises pre-treating the content to less than 1% by weight, and then carrying out an oxidation reaction in the presence of a catalyst containing chromium oxide (cr_2o_3) as a main component. (2) The method according to claim (1), wherein the treatment for removing organic compounds contained in the exhaust gas is treatment by activated carbon adsorption. (3) The method according to claim (1), wherein the organic compound contained in the exhaust gas is a benzene compound. (4) The method according to claim (1), wherein the oxidation reaction temperature is 350 to 450°C. (5) Claim 1, wherein the catalyst containing chromium oxide as a main component is a catalyst prepared by calcining chromium hydroxide obtained by precipitating a trivalent chromium salt with a basic compound. Method. (6) Claim 1, wherein the catalyst containing chromium oxide as a main component is a catalyst in which 20 to 80% by weight of chromium oxide is supported as chromia (cr_2o_3) on a silicon oxide carrier by dipping. the method of.