JPS62270405A - Production of chlorine - Google Patents

Abstract

PURPOSE:To recover and collect chlorine from a formed gas efficiently, by spray-drying chromia hydrogel-containing slurry by a fluidized bed reactor, calcining the dried material to give a fine spherical catalyst and using the catalyst. CONSTITUTION:A hydrogen chloride gas prepared as a by-product in a reaction process of organic compound is oxidized in a fluidized bed reactor to give chlorine. In the operation, slurry containing 2-20wt% chromia hydrogel is spray-dried and then calcined to give a fine spherical catalyst and the catalyst is used. The catalyst is usually used in a range of about 350-450 deg.C. Since the catalyst has high activity, high mechanical strength and especially improved wear resistance, chlorine gas is efficiently recovered from a formed gas.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing chlorine by oxidizing hydrogen chloride gas with an oxygen-containing gas. More specifically, a method for producing chlorine, which comprises using a suitably prepared microspherical catalyst to produce chlorine by oxidizing hydrogen chloride gas with an oxygen-containing gas using a fluidized bed reactor. It is related to.

(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 produced during salt electrolysis is less than that of chlorine. However, a situation has arisen in which it is difficult to adjust each imbalance properly.

On the other hand, large amounts of hydrogen chloride are produced as a by-product during chlorination reactions of organic compounds or reactions using phosgene. remains unused and wasted. Additionally, the processing costs for disposal can be considerable.

If chlorine can be efficiently recovered from large amounts of discarded hydrogen chloride as described above, the demand for chlorine can be met 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 conducted since ancient times using De
This is known as the acon reaction. 1868, Dea
The copper-based catalyst invented by John Con. has been shown 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, it is necessary to raise the reaction temperature to 400°C or higher, which poses problems such as shortened catalyst life due to scattering of catalyst components. becomes.

From the above viewpoint, as a non-copper-based catalyst, chromium oxide has been proposed to be used as a catalyst for the oxidation of hydrogen chloride because it has stability and durability against high temperatures compared to copper and the like. However, no results showing sufficient activity have been reported yet. For example, British Patent No. 584
．． No. 790 discloses that hydrogen chloride is passed at around 400°C over a thermally decomposed catalyst impregnated with an aqueous solution of chromic acid anhydride or chromium nitrate to generate chlorine, and when the catalyst is deactivated, hydrogen chloride is released. A discontinuous method is described in which the supply of hydrogen chloride is stopped, air is allowed to flow to regenerate the catalyst, and then the air flow is cut off and hydrogen chloride is allowed to flow again.

Furthermore, British Patent Nos. 676 and 667 disclose hydrogen chloride and oxygen-containing gas at 420 to 130°C using a catalyst in which dichromate or dark green chromium oxide is supported on a carrier.
The reaction was carried out at a reaction temperature of 380 Hr-' and a hydrogen chloride conversion rate of 67.4% of the equilibrium value, and a space velocity of 680 t.
lr'', a conversion rate of 63% of hydrogen chloride was obtained. At that time, the reaction was observed even at a reaction temperature of 340°C, but in this case, the space velocity was set to a low value of 6511+'', and a conversion rate of 52% was obtained. It's just that you're getting it.

Furthermore, as an improved method of these, British Patent No. 846,832
The reaction was carried out in the presence of a chromium oxide catalyst and in the presence of chromyl chloride in the gas phase of the reaction system. As a specific example, a hexavalent weight, ammonium monocomate, is calcined to produce hexavalent chromium oxide, and trivalent chromium oxide obtained by reducing this with hydrogen is used as a catalyst, and hydrogen chloride and oxygen are combined. molar mixture at a reaction temperature of 420°C and a space velocity of 1200
1-1r-', the conversion of hydrogen chloride was 92% of the equilibrium value, but it decreased to 46% after 185 hours, so chromyl chloride was added to the raw material hydrogen chloride to maintain the activity. A method of mixing is used.

However, hexavalent chromium, such as ammonium dichromate and chromyl chloride, is harmful to the human body, and this method requires steps such as hydrogen reduction during catalyst preparation and separation and purification of chromyl chloride after the reaction is completed. It becomes complicated.

For this reason, even if chromium oxide is used as a catalyst, unless a new reaction reagent is added as described in the above-mentioned British Patent No. 846,832, conventionally known methods have a high reaction temperature and a low space velocity. Due to its low temperature, it is not in a condition that can withstand industrial operations. That is, conventionally reported chromium oxide catalysts did not exhibit particularly superior performance compared to copper-based catalysts.

The present inventors have previously discovered a method for efficiently producing chlorine using a catalyst that has high activity and can process a large amount of hydrogen chloride.

In order to recover chlorine with high efficiency by oxidizing hydrochloric acid with molecular oxygen, it is necessary to increase the chlorine gas concentration in the absorption process. In order to provide high-concentration chlorine gas, it is necessary to increase the concentrations of hydrogen chloride gas and oxygen gas in the reactor inlet gas, and as a result, the calorific value based on the heat of reaction per unit volume of the reactor increases.

A fluidized bed reactor is more advantageous than a fixed bed reactor in order to efficiently remove the heat of reaction and enable the use of even a small reactor.

In order to employ a fluidized bed reactor, a microspherical fluidized bed catalyst with a particle size suitable for the fluidized bed reactor is required. However, there is still no known method for producing chlorine by oxidizing hydrogen chloride gas with an oxygen-containing gas in a fluidized bed reactor using a fluidized bed catalyst containing microspherical chromia as a main component.

An object of the present invention is to provide a method for producing chlorine using a chromia-based fluidized bed catalyst that has high activity, high mechanical strength, and particularly excellent wear resistance.

(Means for Solving the Problems) The present inventors oxidized hydrogen chloride gas with an oxygen-containing gas using a fluidized bed reactor, and discovered that a fluid containing Romia as a main component is suitable for use in producing chlorine. Various studies were conducted regarding the manufacturing method of bed catalysts. As a result, when spray-drying chromia hydrogel obtained by adding an alkaline substance to an aqueous chromium salt solution and granulating it into microspheres, a slurry containing chromia hydrogel with a concentration in the range of 2 to 20% by weight was sprayed. It was discovered that a microsphere catalyst suitable for a fluidized bed catalyst could be obtained by drying, and the present invention was completed.

That is, when producing chlorine by oxidizing hydrogen chloride gas with an oxygen-containing gas using a fluidized bed reactor, the present invention spray-dries a slurry containing chromia hydrogel at a concentration in the range of 2 to 20% by weight, and then calcinates it. This is a method for producing chlorine, which is characterized by using a microspherical catalyst obtained by.

The chromia hydrogel used in the method of the present invention is
It is usually manufactured by the following method. That is,
An alkaline substance (especially preferably ammonia water) is added to an aqueous solution containing a chromium salt to form a chromia hydrogel precipitate. The generated chromia hydrogel precipitate is washed with water using a conventional method, and either directly or with silica gel,
If necessary, add a third or even fourth additive,
The total slurry concentration is adjusted to 2 to 20% by weight.

To adjust the slurry concentration, commonly used methods such as filtration concentration or centrifugation can be applied.

The concentration of chromia is often in the range of 30 to 100% by weight in the fired catalyst, and the concentration of silica is in the range of 0 to 70% by weight.

The slurry thus adjusted to a range of 2 to 20% by weight is spray-dried and granulated into microspheres. The type of spray dryer used can be one with a disk type or nozzle type atomizer. The disk type is usually used to obtain particles with a relatively narrow particle size distribution, and the nozzle type is often used to obtain particles with a relatively wide particle size distribution. Even in the case of a nozzle type, one using a fluid nozzle is particularly preferred. The microspheres used as fluidized bed catalysts have a particle size of 5
-200μ, particularly those distributed over a wide range of about 10-150μ, and an average particle size in the range of 40-80μ are suitable. Usually, to produce microspheres with the above particle size distribution,
Nozzle-type atomizers are often used, and the nozzle hole diameter is 0.
A range of 5 to 2.0 m/lIlφ is often used, and a suitable pump pressure for injecting the slurry into the nozzle is a range of 5 to 31 Jg/cIA.

Hot air is used to dry the sprayed particles. The hot air temperature is often in the range of 100 to 500'C.

The slurry to be used is the one obtained by washing the precipitate of chromia hydrogel produced by reacting an aqueous solution of chromium salt with an alkaline substance such as aqueous ammonia or urea using a conventional method, and then concentrating the precipitate, or by adding silica sol to the precipitate of chromia hydrogel after washing. , and the third to fourth additives are used. It is necessary to maintain the concentration of the chromia hydrogel-containing slurry in the range of 2 to 20% by weight during spray drying. The viscosity of the slurry in this range varies depending on the composition of chromia hydrogel and silica sol, but is usually in the range of 10 to 2000 cp. By keeping the slurry concentration within the range described above, it is possible to produce chromia gel microspheres having a particle size distribution in the optimum range for the fluidized bed catalyst described above.

If the slurry IJ-41 degree is less than 2% by weight, the particle size distribution will be biased towards small particle sizes, and if the slurry concentration exceeds the above concentration, the particle size distribution will not only be biased towards large particle sizes, but the slurry viscosity will increase, causing nozzle It becomes difficult to spray from the ground.

After spray drying, the microspheres usually have a density of 400 to 80% in an air atmosphere.
The catalyst is calcined at a temperature of 0°C.

Microspheres produced using a slurry with a concentration in the above range,
The abrasion resistance of the subsequently calcined catalyst was good;
A catalyst suitable for fluidized beds is obtained.

In the method of the present invention, the catalyst produced as described below is used for producing chlorine by oxidizing hydrogen chloride gas with an oxygen-containing gas at a normal reaction temperature range of 350 to 450°C.

In the method of the present invention, the molar ratio of hydrogen chloride and oxygen is H
A range of Cfi 10□ of 110.25 to 1/1 is often used.

The linear velocity of the reaction gas is suitably 10 to 50 cm/sec.

(Functions and Effects) By the method of the present invention, highly concentrated hydrogen chloride gas can be oxidized with oxygen, and the concentration of produced chlorine in the reactor outlet gas can be maintained at a high level. Therefore, chlorine can be recovered and obtained from the generated gas extremely efficiently, and industrially advantageous chlorine recovery becomes possible.

(Example) The present invention will be explained below with reference to Examples.

Example 1 126 kg of 40% by weight chromium nitrate aqueous solution and 905 kg of pure water were added.
5Kg and then 25% by weight aqueous ammonia92.
3 kg was injected dropwise over 4 hours. During the dropwise addition, the mother liquor was sufficiently stirred, and the liquid temperature was adjusted to maintain the reaction temperature in the range of 45 to 50°C.

After aging the resulting precipitate at 50° C. for 3 hours, the precipitate was washed, filtered and concentrated. Then 25% by weight silica sol 28K
g was added and thoroughly stirred and mixed. The concentration of the resulting slurry was 6.5% by weight. Pour this slurry through a nozzle diameter of 1
, using a 2m#n pressurized nozzle type spray dryer, the slurry was sprayed at a pressure of 10Kg, and the inlet air temperature was 32
It was granulated into microspheres at 0°C. The obtained microspheres were heated to 550'c
The mixture was calcined for 5 hours to produce a fluidized bed catalyst. The average particle size of this catalyst is 67μ, and the particle size is distributed over a wide range of 10μ to 150μ, which is a desirable property as a fluidized bed catalyst. Wear loss measured by ACC method (accelerated test) is 0
．． 16χHr-' and exhibits sufficient wear resistance as a catalyst.

2 kg of this catalyst was taken and packed into a fluidized bed reactor with an inner diameter of 4 inches, and the catalyst bed temperature was set at 380'C to 390°C, IICI.
I102 was reacted at 1.10.5 gas linear velocity of 30 cm and 8 ec, and chlorine was recovered at a hydrogen chloride addition rate of 78%.

Examples 2 to 7 Using the same method and apparatus as in Example 1, catalysts were prepared by varying the concentration of the slurry used.

The average particle size of the catalyst obtained is shown in the table below. The average particle size of the fluidized bed catalyst used in this reaction is suitably in the range of 40 to 80 microns.

Claims (1)

[Claims] (1) When producing chlorine by oxidizing hydrogen chloride gas with oxygen-containing gas using a fluidized bed reactor, chromia hydrogel
A method for producing chlorine, which comprises using a microspherical catalyst obtained by spray-drying a slurry containing chlorine at a concentration in the range of 20% by weight and then calcination.