JPS61136902A - Manufacture of chlorine - Google Patents

Abstract

PURPOSE:To recover efficiently chlorine from hydrogen chloride by oxidizing hydrogen chloride with an oxygen-contg. gas in the presence of a specific catalyst. CONSTITUTION:The deposit obtained by the reaction of an aq. soln. contg. 3-30wt% Cr(NO3)3 or CrCl3 with aq. ammonia having 20-30wt% concn. is filtered, and dried. The dried deposit is then calcined at <=800 deg.C for from several hr to 20hr to obtain a catalyst. Subsequently, 1mol hydrogen chloride is allowed to react with an oxygen-contg. gas contg. about 1/4 molar equivalent of oxygen in the presence of the catalyst at 300-400 deg.C and at 700-1,200Hr<-1> space velocity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing chlorine, and more particularly to an improvement in a method for producing chlorine by oxidizing hydrogen chloride 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 greater than that of chlorine. Due to the small size, it is difficult to properly adjust the imbalance between the two.

On the other hand, a large amount of hydrogen chloride is produced as a by-product during the chlorination reaction of organic compounds or during the production of phosgene, and the amount of by-product hydrogen chloride is far greater than the demand for hydrochloric acid, so a large amount of hydrogen chloride remains unused. It is being used and wasted. Furthermore, the processing costs for disposal reach a staggering amount.

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

(Conventional methods and their problems) The reaction of oxidizing hydrogen chloride to produce chlorine has been carried out since ancient times using De
This is known as the acon reaction. 1868 Deac
The copper-based catalyst invented by On et al. is said to be the catalyst that has shown the most excellent activity to date, 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. Furthermore, in the oxidation reaction of hydrogen chloride,
There is an equilibrium, and as the temperature increases, the amount of chlorine produced decreases, so it is necessary to develop a catalyst that is active at as low a temperature as possible.

From the above point of view, iron-based catalysts and others have been proposed as catalysts other than copper-based catalysts, but catalysts that exhibit sufficient practical performance are still unknown. Since chromium oxide is more stable and durable at high temperatures than copper or the like, there have been proposals to use chromium oxide as a catalyst for the oxidation of hydrogen chloride, but no results have yet been reported showing sufficient activity. For example, in British Patent No. 584,790, hydrogen chloride is passed over a thermally decomposed catalyst impregnated with an aqueous solution of chromic acid anhydride or chromium nitrate at around 400°C to generate chlorine and decompose the catalyst. A method is described in which, after deactivation, the supply of hydrogen chloride is stopped, air is allowed to flow through the catalyst to regenerate the catalyst, the air flow is cut off, and hydrogen chloride is allowed to flow again. Also,
British Patent Nos. 676 and 667 use a catalyst containing dichromate or dark green chromium oxide on a carrier,
Hydrogen chloride and oxygen-containing gas are reacted at a reaction temperature of 420 to 430°C and a space velocity of 580 Hr-1, and the conversion rate of hydrogen chloride is 674 Hr-1, which is the equilibrium value, and the space velocity is 680 Hr-1.
A hydrogen chloride conversion of 5% was obtained. Reaction temperature 340℃
However, the reaction is observed, but in this case, the space velocity is reduced to 65
A conversion rate of only 52% was obtained with a low value of Hr~1.

As described above, even if chromium oxide is used as a catalyst, the conventionally known methods have high reaction temperatures and low space velocities, so they are not suitable for industrial operation. That is, conventionally reported chromium oxide catalysts do not exhibit particularly superior performance compared to copper-based catalysts.

(Objective of the Invention) The object of the present invention is to provide a method for efficiently recovering chlorine from hydrogen chloride using a catalyst that is active at low temperatures and can handle a large amount of hydrogen chloride (high space velocity). There is a particular thing.

(Means to Solve the Problems of Existing Methods) The present inventors have conducted various studies on methods for producing chlorine by oxidizing hydrogen chloride, and sometimes on catalysts used in the oxidation reaction. Using a chromium oxide catalyst prepared according to a previously unreported catalyst preparation method, the reaction temperature is lower than that of previously known catalysts, and hydrogen chloride can be produced at a much higher space velocity and conversion rate than conventional methods. They discovered that chlorine can be produced from chlorine and completed the present invention.

That is, the gist of the present invention is that when hydrogen chloride is oxidized with an oxygen-containing gas to produce chlorine, a compound obtained by reacting chromium nitrate or chromium chloride with ammonia is heated at a temperature below 800°C. The purpose is to carry out the reaction in the presence of a calcined catalyst.

Hydrogen chloride, which is a raw material used in the method of the present invention, is usually a tonnage of hydrogen chloride produced as a by-product during the chlorination reaction of an organic compound, or hydrochloric acid produced as a by-product, such as hydrogen chloride produced during the production of phosgene.

The oxidizing agent for hydrogen chloride is an oxygen-containing gas, and oxygen gas or air is often used. Oxygen gas is often used when the reactor is a fluidized bed type, and air is often used when the reactor is a fixed bed type. The molar ratio of hydrogen chloride to be subjected to the reaction and oxygen in the oxygen-containing gas is around 1 mole of hydrogen chloride to 1 mole of oxygen (equivalent), and usually, the molar ratio of oxygen to 1 mole of hydrogen chloride is around 5 to 5 moles of oxygen.
It is often used in excess of 0%. The amount of hydrochloric acid supplied to the catalyst bed is 200 to 800 Nt/Hr, KyCat,
range is suitable. The reaction temperature is 300-400℃,
In particular, a temperature of 630 to 670°C is often used.

The catalyst used in the method of the present invention is a compound obtained by reacting chromium nitrate or chromium chloride with ammonia.
It is fired at a temperature below 0°C. Usually, chromium nitrate or chromium chloride dissolved in water is reacted with aqueous ammonia to form a precipitate. The amount of chromium nitrate or chromium chloride dissolved in water is often in the range of 3 to 50 wt%. Ammonia water usually has 20 to 30
% NH, OH concentration is suitable. The generated precipitate is separated from P, washed, dried, and then calcined for several to 20 hours at a temperature below 800°C in an air atmosphere, in a vacuum, or in an inert gas atmosphere such as nitrogen to form a catalyst. . The fired catalyst is pressed into tablets and used in a fixed bed reactor. To prepare a catalyst for a fluidized bed, the resulting precipitate is washed with a decanterizer/funnel, made into a slurry of an appropriate concentration, shaped into granules and dried with a dryer, and then calcined at a temperature below 800°C to form a catalyst. shall be.

That is, it is essential to use chromium nitrate or chromium chloride as the starting material for the chromium compound used in the method of the present invention, and it is essential to use ammonia as the alkaline substance that generates the precipitate. Compounds that can generate ammonia, such as urea, can be used in the same way instead of ammonia.

As chromium compounds, chromium sulfate, basic chromium sulfate,
When chromic acid, dichromate, etc. are used, a highly active and high performance catalyst cannot be obtained even if ammonia is used as a precipitant.

In addition, even when chromium nitrate or chromium chloride is used, a highly active catalyst cannot be obtained if a caustic alkali such as caustic soda or caustic potassium or an alkali carbonate such as soda carbonate or bicarbonate is used as a precipitant in addition to anomonia. .

Similarly, chromium oxide obtained by thermally decomposing nitrates, chromic acid anhydride, or commercially available chromium hydroxide does not provide a high performance catalyst.

It is necessary to maintain the firing temperature of the catalyst at a temperature lower than 800°C, and if the catalyst is fired at a temperature of 800°C or higher, the catalytic activity decreases rapidly.

There is no particular restriction on the lower limit of the firing temperature, but it is usually preferably higher than the temperature at which the oxidation reaction of hydrogen chloride is carried out.

Calcination is often carried out by drying the precipitate in a separate calcining furnace, but it can also be filled into the reaction tube used for the reaction and calcined at the same time as the reaction.

(Operation and Effects of the Invention) According to the method of the present invention, a space velocity of 700 to 12
00 Hr-1, which is much higher than the conventional method, can be obtained, and the resulting conversion rate also reaches +aQ% of the equilibrium conversion rate. In other words, the present invention has a much lower temperature activity, a higher space velocity, and a higher conversion rate of hydrogen chloride than any conventionally known catalyst system, so it is an industrially advantageous method for efficiently producing chlorine from hydrogen chloride. The present invention provides a method.

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

Example-1 Chromium nitrate nonahydrate 300? was dissolved in 3 tons of deionized water, and 28 tons of ammonia water 2851 was injected dropwise over a period of 10 minutes while stirring well. Deionized water was added to the resulting precipitate slurry to dilute it to 20 tons, and after it was left to stand overnight, the precipitate was washed with repeated decanting and washing. The precipitate was separated and air-dried, then dried at 100-120°C for 6 hours, heated in an electric furnace to 100-600'C in an air atmosphere over 3 hours, and fired at 550°C for 4 hours.

The fired catalyst was crushed and the particles with a particle size of 1 to 1.5 m/iη were placed in a stainless steel reactor with an inner diameter of 1 inch.
The reactor was filled and heated to 340° C. from the outside of the reaction chamber using a moving sand bath.

Hydrogen chloride gas 100 me/min, air 180
rue/min(SV=1.120 Hr-
1) was preheated to 600°C, and then introduced into the catalyst layer and reacted. The catalyst bed temperature rose to 656°C due to the heat of reaction.

The reactor effluent gas was collected in a trap 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 thiosulfate and hydrochloric acid to quantify the amount of chlorine that produced unreacted hydrogen chloride. .

The conversion rate of hydrogen chloride was 81%, which corresponds to 100% of the equilibrium conversion rate at this reaction temperature.

Example-2 Chromium chloride hexahydrate 200? Dissolved in 3 t of deionized water,
While stirring well, add 28% ammonia water 290? was added dropwise and injected to produce a precipitate. The precipitate slurry was diluted to 20 t with deionized water, left overnight, and the precipitate was washed by decantation to separate the P.

After air-drying the separated precipitate at 110°C for 6 hours,
It took 5 hours to raise the temperature to 550°C, and then calcined at 550°C for 5 hours to prepare a catalyst. , This catalyst 152 was packed in the same apparatus as in Example-1, and the catalyst bed temperature was 555°C, and hydrogen chloride was heated at 100 rue/mi.
185 rug/min of air was introduced to cause a reaction. Chlorine was produced at a conversion rate of hydrogen chloride of 70 degrees. This value corresponded to 90% of the equilibrium conversion.

Example-3 After washing the precipitate slurry obtained from chromium nitrate and ammonia water by decantation in the same manner as in Example-1,
It was dried with a spray dryer to obtain a granular powder. This powder was heated in a fluidized state for 600 minutes while introducing air in a fluidized and calcined furnace.
It was baked at ℃ for 3 hours. Particle size of this catalyst: 100-150me
The sh portion was sieved, 60 g was charged into a fluidized bed reactor with an inner diameter of 40 mrnφ, and heated to 540° C. from the outside in an electric furnace.

Hydrogen chloride gas 400 wLll/min, oxygen gas 14a, me/min, nitrogen gas 100 me/mi
n was introduced into the catalyst bed, and the reaction was carried out while the catalyst was fluidized.

Chlorine gas was produced at a hydrogen chloride conversion rate of 76 degrees.

Example-4 After drying the precipitate obtained in the same manner as Example-1 at 110°C, the calcination temperature was changed to 400°C, 500°C, 600°C, and 700°C.
, 800°C, and 900°C to prepare six types of catalysts. The firing time was 3.5 hours each.

Table 1 shows the results of the reaction at 650°C using the same apparatus and method as in Example 1.

Table 1 Comparative Examples 1 to 5 Catalysts using various starting materials for chromium and precipitants were prepared and reacted using the same apparatus and method as in Example 1. The results obtained are shown in Table-2.

Table 2 Comparative Examples 6 to 10 Chromium nitrate, chromic anhydride, and commercially available chromium hydroxide were thermally decomposed to produce chromium oxide, and reacted with a catalyst calcined at 500°C in the same apparatus and reaction conditions as in Example 1. Ta. The results obtained are shown in Table-3.

In addition, the surface area of chromium chloride aqueous solution is 1so m2/S'
, impregnated with silica gel particles with an average pore diameter of 100X, and after drying,
Catalyst calcined at 400°C and commercially available chromium oxide catalyst (8
The results obtained by Volatile Chemistry X-421) are also listed.

Table-6

Claims (1)

[Claims] 1) When producing chlorine by oxidizing hydrogen chloride with an oxygen-containing gas, a compound obtained by reacting chromium nitrate or chromium chloride with ammonia is reacted in the presence of a catalyst calcined at a temperature below 800°C. A method for producing chlorine, characterized by: