JPH0568401B2 - - Google Patents

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 has increased dramatically in recent years, the increase in demand for caustic soda, which is simultaneously produced during salt electrolysis, is similar to that of chlorine. As the number of people living in Japan is smaller than that of Japan, a situation has arisen in which it is difficult to properly adjust the imbalance. On the other hand, large amounts of hydrogen chloride are generated during chlorination reactions of organic compounds or reactions using phosgene, and the amount of by-product hydrogen chloride is far greater than the amount of hydrochloric acid required. remains unused and wasted. Further, processing costs for disposal are also required. 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 producing chlorine by oxidizing hydrogen chloride has long been well-known as the Deacon reaction. 1868
The copper-based catalyst invented by Deacon is considered to be the catalyst with the most excellent activity to date, and many catalysts have been proposed in which various compounds are added as third components to copper chloride or potassium chloride. However, in order to oxidize hydrogen chloride at an industrially sufficient reaction temperature 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. . Furthermore, there is an equilibrium in the oxidation of hydrogen chloride,
Since the amount of chlorine produced decreases as the temperature increases, it is desirable to use a catalyst that is active at as low a temperature as possible, and lower temperatures are more advantageous in terms of corrosion of the equipment. 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-based catalysts, there have been proposals to use chromium oxide as an oxidation catalyst for hydrogen chloride, but no results showing sufficient activity have been reported yet. For example, UK patent
No. 584790 discloses that hydrogen chloride is passed at around 400℃ over a thermally decomposed catalyst impregnated with an aqueous solution of chromic acid anhydride or chromium nitrate to generate chlorine, and after the catalyst is deactivated, hydrogen chloride is released. A 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. British Patent No. 676667 also discloses that using a catalyst in which dichromate or dark green chromium oxide is supported on a carrier, hydrogen chloride and oxygen-containing gas are reacted at a reaction temperature of 420 to 430°C at a space velocity of 380 Hr ^-1. The conversion of hydrogen chloride was 67.4% of the equilibrium value, and the conversion of hydrogen chloride was 63% at a space velocity of 680 Hr ^-1.The reaction was observed even at a reaction temperature of 340°C, but in this case, By keeping the space velocity at a low value of 65 Hr ^-1 , a conversion rate of only 52% was obtained. And, this prior art discloses that all chromia cannot be an active catalyst for the oxidation of hydrochloric acid. In other words, chromia, which is active in the oxidation of hydrogen chloride, is amorphous, and to produce an amorphous chromia catalyst, it is necessary to heat treat chromia anhydride at a temperature below 400°C, and chromia heated above 500°C clearly shows that it crystallizes and loses HCl oxidation activity. Furthermore, British Patent No. 846852 proposes that the chromia catalyst has a short catalyst life for the oxidation of hydrogen chloride and cannot withstand industrial operation. This shows that the catalyst life can be extended by entraining ₂ Cl ₂ ). This also shows that the chromia catalyst has a short lifespan, so it cannot be used as is for long-term continuous operation. This patent also mentions about chromia catalyst when ammonium dichromate or chromic acid is heated below 500℃.
It is disclosed that amorphous chromia preferably calcined at 350 to 400°C exhibits high activity. 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. (Object of the invention) The object of the present invention is low temperature activity,
The object of the present invention is to provide a method for efficiently recovering chlorine from hydrogen chloride using a catalyst that can process a large amount of hydrogen chloride (high space velocity). (Means for Solving the Problems of Existing Methods) The present inventors have conducted various studies on methods for producing chlorine by oxidizing hydrogen chloride, particularly regarding catalysts using oxidation reactions. By using a chromium oxide catalyst produced according to a catalyst preparation method that has never been reported before, the reaction temperature is lower than that of previously known catalysts, and a high conversion rate can be achieved at a much higher space velocity than conventional methods. They discovered that chlorine can be produced from hydrogen chloride and completed the present invention. That is, the gist of the present invention is to oxidize hydrogen chloride with an oxygen-containing gas to produce chlorine, which is obtained by reacting a chromium salt such as chromium nitrate, chromium chloride, or a chromium salt of an organic acid with ammonia. Catalyst prepared from a compound obtained by firing a mixture of both compounds at a temperature below 800℃, and a compound obtained by reacting a chromium salt with ammonia at a temperature below 800℃. The purpose is to react in the presence of a catalyst prepared by mixing a silicon compound with a catalyst calcined at a high temperature, or a catalyst prepared by further calcining this mixed catalyst at a temperature below 800°C. The raw material hydrogen chloride used in the method of the present invention is
Typically, by-product hydrochloric acid such as hydrogen chloride, which is produced as a by-product during the chlorination reaction of an organic compound, or hydrogen chloride, which is produced as a by-product during the reaction between phosgene and an organic compound, is often used. 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 used for the reaction and oxygen in the oxygen-containing gas is around 1/4 mole (equivalent) of oxygen to 1 mole of hydrogen chloride,
Usually, oxygen is often used in excess of 5 to 50% of the equivalent amount. The amount of hydrochloric acid supplied to the catalyst bed is 200~
A range of 1800N/Hr・Kgcat. is suitable. The reaction temperature is often 300 to 400°C, particularly 330 to 380°C. The catalyst used in the process of the present invention is a mixture consisting of a reaction product of a chromium salt such as chromium nitrate, chromium chloride or a chromium salt of an organic acid with ammonia or an ammonia-releasing compound such as urea, and a silicon compound. It is fired at a temperature below ℃. Usually, a chromium compound is precipitated by reacting the above-mentioned chromium salt dissolved in water with aqueous ammonia. The amount of chromium salt dissolved in water is often in the range of 3 to 30 wt%, and aqueous ammonia is usually used in a range of 5 to 30 wt%.
The NH ₄ OH concentration is appropriate. In order to mix this chromium compound precipitate and a silicon compound, a silicon compound such as ethyl silicate is mixed with an aqueous solution of chromium salt, and the reaction with aqueous ammonia produces chromium hydroxide and silicon hydroxide. There is a method of coprecipitating the precipitate. Alternatively, a method is employed in which the precipitate of a chromium compound and a fine powder of silica sol or silica gel such as colloidal silica are kneaded with water. The kneaded material was air-dried at room temperature using a conventional method, then dried at 80 to 120°C, and then dried at 800°C.
It is made into a catalyst by calcining it at a temperature not exceeding that of the above. The slurry of the chromium precipitate and silicon compound mixture was dried into a spherical fine powder using a spray dryer, and then
The fluidized calcined product is suitable for use as a fluidized bed catalyst. A paste made of a mixture of chromium precipitate and a silicon compound is extruded, dried and calcined, and used as a catalyst for fixed beds. In addition, the compound obtained by the reaction of the above-mentioned chromium salt and ammonia is washed and dried by a conventional method, and then baked at a temperature below 800°C, and then a silicon compound such as silica gel, silica sol, silicate alkyl ester, etc. There is also a method of obtaining a catalyst by mixing and drying the catalyst, or by further calcining this at a temperature of less than 800°C. In this case as well, a slurry of a mixture of a chromium compound and a silicon compound obtained by calcination and dried with a spray dryer becomes a catalyst suitable for a fluidized bed, and an extruded catalyst becomes a catalyst suitable for a fixed bed. The mixing ratio of chromium and silica is usually not particularly limited, but if it is expressed as the weight ratio of Cr ₂ O ₃ and SiO ₂ , which are the forms obtained by final calcination of the catalyst,
A range of Cr ₂ O ₃ /SiO ₂ =30/70 to 95/5 is often used. That is, it is essential to use chromium nitrate, chromium chloride, or an organic acid salt of chromium 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 forms the precipitate. be. Compounds capable of generating ammonia, such as urea, can be used in the same manner instead of ammonia. As a chromium compound,
When chromium sulfate, basic chromium sulfate, chromic acid, dichromate, etc. are used, a highly active, high-performance catalyst cannot be obtained even if ammonia is used as a precipitant. Furthermore, even when chromium nitrate or chromium chloride is used, a highly active catalyst cannot be obtained when a caustic alkali such as caustic soda or caustic potash or an alkali carbonate such as soda carbonate or bicarbonate is used instead of ammonia as a precipitant. . Similarly, chromium oxide obtained by thermally decomposing nitrate, chromic acid anhydride, or commercially available chromium hydroxide does not provide a high-performance catalyst. The element used as the second component for chromium in the method of the invention is silicon, which is in the form of silica in the catalyst body. By containing silica as a second component, the mechanical strength and heat resistance of the catalyst are improved. The second component must be silica, and if alumina or titania is used as the second component, aluminum or titanium will be desorbed from the catalyst if the hydrogen chloride oxidation reaction is carried out for a long time. This causes problems such as a decrease in the mechanical strength of the 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 higher than 800°C, the catalyst activity will decrease 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, particularly 450°C or higher. The catalyst obtained is not amorphous but crystalline. (Operation and Effects of the Invention) According to the method of the present invention, the space velocity of hydrochloric acid is 700 to 1800 Hr ^-1 , which is much higher than that of the conventional method, at a temperature lower than that of the conventional method, that is, about 300 to 360°C. Throughput can be obtained, and the conversion rate achieved reaches 100% of the equilibrium conversion rate. In other words, the present invention provides an industrially advantageous method for producing chlorine that can efficiently produce chlorine from hydrogen chloride because it can obtain a much higher conversion rate of hydrogen chloride at a much higher space velocity than conventionally known catalyst systems. It provides: (Example) The present invention will be explained below with reference to Examples. Example 1 Dissolve 300 g of chromium nitrate nonahydrate in 3 parts of deionized water, and add 28% ammonia water while stirring well.
258 g was injected dropwise over 10 minutes. The resulting precipitate was washed by decantation, filtered, and air-dried.
After drying at 100-120℃ for half a day, 500℃ in air atmosphere
It was baked for 3 hours. The calcined chromium oxide was pulverized in a mortar, 28 g of silica sol (Snowtex-N, manufactured by Nissan Chemical) was added, and further 25 g of water was added and kneaded. The paste after kneading is extruded into a 3m/
Formed into mφ x 4m/m, dried at 100℃, then 550℃
A catalyst was prepared by calcining for 4 hours. The breaking strength of this catalyst in the circumferential direction was 3.5 to 3.8 kg, which is sufficient for use as an industrial catalyst. 50 g of this catalyst was taken and filled into a stainless steel tube with an inner diameter of 1 inch, and the outside was heated to 350°C in a sand fluidized bath. Hydrogen chloride gas 48N/Hr, air 90N/Hr
Hr was introduced into the catalyst bed for reaction. When the reaction gas was sampled and the amounts of unreacted hydrogen chloride and produced chlorine were determined, chlorine was produced at a hydrogen chloride conversion rate of 76%. After the reaction of this catalyst was continued for 45 days under the above reaction conditions, the conversion rate of hydrogen chloride was 72%. Example 2 300 g of chromium nitrate nonahydrate was dissolved in deionized water 3, 72 g of ethyl silicate solution was added, and aqueous ammonia was added dropwise with thorough stirring to obtain a coprecipitated compound of chromium hydroxide and silica hydrogel. This compound was dried with a pressure nozzle spray dryer to produce spherical microspheres, and fluidized calcined at 600°C to prepare a catalyst. 80 g of this catalyst was placed in a fluidized bed reactor with an inner diameter of 40 m/m and heated to 350° C. from the outside. Hydrogen chloride 55N/Hr and oxygen 25N/Hr were introduced into the catalyst bed and reacted. Chlorine was produced at a conversion rate of hydrogen chloride of 81%. Example 3 300 g of chromium nitrate nonahydrate was dissolved in deionized water 3 and 28% ammonia water was added dropwise to cause precipitation of chromium hydroxide. The obtained precipitate was filtered and 200 g of silica sol (Nissan Chemical, Snowtex-N) was added.
The slurry was thoroughly mixed and dried with a spray dryer to form spherical microspheres. This was fluidized and calcined at 500°C to prepare a catalyst. This catalyst was reacted under the same conditions as in Example 2, and a conversion rate of hydrochloric acid of 79% was obtained. Example 4 300 g of chromium nitrate nonahydrate was dissolved in deionized water 3, and 28% ammonia water was added dropwise to obtain a chromium hydroxide precipitate. After washing the precipitate, filtering it, and drying it,
After baking at 400℃ for 3 hours to form chromium oxide,
It was ground to 100mesh or less in a mortar. 50 g of silica sol (Nissan Chemical, Snowtex-N) and 15 g of water were added to the above powder, mixed well, and kneaded using a kneader. 3 of the obtained paste
After extrusion molding to m/mφ×4m/m, drying
It was calcined at ℃ for 4 hours and used as a catalyst. This catalyst was reacted under the same conditions as in Example 1, and chlorine was obtained with a conversion rate of hydrogen chloride of 79%. Comparative Examples 1 to 4 and Examples 5 to 7 Chromia-silica catalysts were prepared by the method of Example 1 with various starting materials for the catalyst, and
Table 1 shows the results of the reaction in the same manner as above.

[Table] Example 8 Catalysts were produced by varying the firing temperature of the chromia-silica catalyst obtained in the same manner as in Example 1, and their activities were measured. The reaction conditions are the same as in Example 1. The results obtained are shown in Table-2.

[Table] Example 9 A precipitate obtained by adding aqueous ammonia to an aqueous nitrate solution was filtered, dried, and then calcined at 500°C. The resulting chromium oxide was ground into fine powder. Silica sol was added to this fine powder at a weight ratio of 1:1, and stirring was continued overnight to obtain a uniform slurry. This slurry was dried with a spray dryer to prepare a microspherical fluidized bed catalyst. Using this catalyst, the catalytic activity was measured under the same reaction conditions as in Example 2. As a result, chlorine was produced at a conversion rate of hydrogen chloride of 73%. Comparative Example 5 A simple chromia catalyst without the addition of silica sol was prepared in the same manner as in Example 1. The chromia hydrogel paste after kneading is extruded, and 3
Form into m/mφ x 4m/m, dry at 100℃, and dry at 550℃.
It was calcined for 4 hours and used as a catalyst. The circumferential breaking strength of this catalyst was 2.0 to 2.4 kg, which was lower than the 3.5 to 3.8 kg obtained in Example 1 in which silica was added.

Claims (1)

[Claims] 1. When hydrogen chloride is oxidized with an oxygen-containing gas to produce chlorine, the reaction takes place in the presence of a catalyst prepared from a chromium compound obtained by reacting a chromium salt with ammonia and a silicon compound. A method for producing chlorine, which is characterized by: 2 Claims in which the catalyst is a mixture of chromium nitrate, chromium chloride, or a chromium compound obtained by reacting an organic acid chromium salt with ammonia and a silicon compound, which is calcined at a temperature below 800°C. The method described in paragraph 1. 3 Claims in which the catalyst is a mixture of chromium nitrate, chromium chloride, or a chromium compound obtained by reacting a chromium salt of an organic acid with ammonia, calcined at a temperature below 800°C, and a silicon compound. The method described in paragraph 1. 4 A mixture of a silicon compound and a chromium compound obtained by reacting chromium nitrate, chromium chloride, or a chromium salt of an organic acid with ammonia at a temperature of less than 800°C is further heated to 800°C.
2. The method according to claim 1, wherein the firing is performed at a temperature below .degree.