RU2287366C1 - Catalyst for dehydrogenation of c2-c5-hydrocarbons - Google Patents

Abstract

FIELD: organic chemistry, chemical technology, catalysts.

SUBSTANCE: invention describes a catalyst for dehydrogenation of (C₂-C₅)-hydrocarbons that comprises aluminum, chrome oxides, compound of modifying metal, alkaline and/or alkaline-earth metal. Catalyst comprises additionally silicon and/or boron compounds and as a modifying agent the proposed catalyst comprises at least one compound chosen from the following group: zirconium, titanium, iron, gallium, cobalt, molybdenum, manganese, tin. The catalyst is formed in the process of thermal treatment of aluminum compound of the formula Al₂O₃ ^. n H₂O wherein n = 0.3-1.5 and in common with compounds of abovementioned elements and shows the following composition, wt.-% (as measure for oxide): chrome oxide as measured for Cr₂O₃, 12-23; compound of a modifying metal from the group: Zr, Ti, Ga, Co, Sn, Mo and Mn, 0.1-1.5; silicon and/or boron compound, 0.1-10.0; alkaline and/or alkaline-earth metal compound, 0.5-3.5, and aluminum oxide, the balance. Catalyst shows the specific surface value 50-150 m²/g, the pore volume value 0.15-0.4 cm³/g and particles size 40-200 mcm. Also, invention describes a method for preparing this catalyst. Invention provides preparing the catalyst showing the enhanced strength and catalytic activity.

EFFECT: improved and valuable properties of catalyst.

12 cl, 2 tbl

Description

The invention relates to methods for preparing catalysts for the dehydrogenation of paraffin hydrocarbons, in particular for the dehydrogenation of C ₂ -C ₅ paraffins to the corresponding olefins.

Olefins are one of the most important products of organic synthesis. They are used in the production of polypropylene, synthetic rubber, antiknock high-octane gasolines and a number of other industries.

One way to obtain olefins is the dehydrogenation of paraffins. It is well known that from a thermodynamic point of view, the dehydrogenation of C ₂ -C ₅ hydrocarbons is not among the effective processes. Since the dehydrogenation reaction is endothermic, temperatures of 500-600 ° C are necessary to achieve a technically acceptable feed conversion. However, even at these temperatures, undesirable side reactions of cracking and isomerization proceed at a noticeable rate. This is because the carbon-carbon (CC) bond is significantly less strong than the carbon-hydrogen (CH) bond. Therefore, the catalyst for the dehydrogenation process should direct the process along an energetically disadvantageous path, i.e. to allow the process to be carried out at low temperatures, and to make the cracking reaction rate as low as possible. Moreover, it should minimize the inevitable formation of a certain amount of hydrocarbons of normal and cyclic structure. That is, the dehydrogenation catalyst should provide high selectivity to the desired olefin while reducing isomerization, side reactions leading to coking. The formation of coke on the catalyst requires periodic regeneration of the latter at elevated temperatures; therefore, the catalyst must be thermostable. Special requirements are imposed on the mechanical strength of the catalyst, since destruction causes environmental pollution problems.

Available literature describes many catalytic compositions based on noble metals or combined with other elements.

A known method (Patent EP N 637578, IPC C 07 C 5/333, 1995) with a catalytic system containing gallium, platinum, possibly one or more alkali or alkaline earth metals and a support that consists of alumina in the delta or theta phase or in a mixed delta + theta or theta + alpha or delta + theta + alpha phase, and modified with silica.

However, compositions containing noble metals have increased cracking ability at elevated temperatures. This leads to rapid coking of the catalyst and loss of activity and, consequently, a decrease in service life.

The disadvantage of the catalyst is its relatively low strength.

Despite the fact that catalysts based on precious metals and gallium are a new generation of dehydrogenation catalysts, most researchers have come to the conclusion that effective oxides of C ₂ -C ₅ paraffins are chromium oxides supported on alumina and have increased mechanical strength, although chromium compounds belong to harmful substances. Therefore, when creating new catalysts based on chromium compounds, the main task is to firmly fix chromium in the carrier, reduce wastewater when it is received, and increase activity and stability.

A known catalyst containing oxides of potassium, chromium, silicon on alumina (A.S. USSR N 1366200, IPC B 01 J 37/02, 23/26, 1988). The catalyst is obtained by impregnation of alumina, previously calcined at 1000-1150 ° C, first with solutions of chromium and potassium compounds, followed by drying, then re-impregnation with a solution of silicon compounds, followed by drying and calcination.

The disadvantage of the catalyst and method is the low mechanical strength and selectivity.

A known method of preparing an aluminum-chromium catalyst for dehydrogenation of paraffin hydrocarbons (RF Patent N 1736034, IPC B 01 J 37/02, 23/26, 21/04, 1995), which involves calcining aluminum hydroxide in a suspended layer at a temperature interaction of 450-800 ° C within 0.05-2.0 s with a further decrease in temperature to 280-400 ° C, peptization of aluminum hydroxide with nitric acid with the simultaneous introduction of chromium and potassium-containing compounds, molding by spray drying and calcination, annealing is carried out at 50-80 wt. .% hydroxide Luminos, the remaining 20-50 wt.% of aluminum hydroxide is calcined at 950-1200 ° C for 2-10 hours.

The catalyst has not enough high activity and stability, low mechanical strength. The method of its preparation is complex and multi-stage. The formation of the catalyst is carried out at the stage of spray drying.

A known method of producing a catalyst for the dehydrogenation process based on Al, Cr, K and Si for the dehydrogenation of C ₃ -C ₅ paraffin hydrocarbons (Japanese Patent N 7010350, IPC B 01 J 23/26, 1995), which includes firing at 500 700 ° C of alumina with particles in the form of microspheres, annealing at a temperature of> 1000 ° C for several hours, impregnation of the calcined product with a solution containing compounds of Cr and compound K, drying of the resulting product, treatment with impregnation of the drying product with a solution containing the compound silicon and followed by final processing by drying and firing at <700 ° C.

The disadvantage of the resulting catalyst is also the lack of strength and stability, as well as the complexity and multi-stage process.

The closest technical solution for the composition and method of producing the catalyst to the claimed catalyst is a catalyst for the dehydrogenation of hydrocarbons (RF Patent N 1836140, IPC B 01 J 23/26, 21/06; C 07 C 5/333, 1993). The catalyst contains chromium oxide, an alkali and / or alkaline earth metal compound and at least one modifying metal compound on an alumina support, it contains zirconia as a modifying metal compound in the following ratio, wt.%:

Chromium oxide calculated as Cr ₂ O ₃ 25 An alkali and / or alkaline earth metal compound calculated as oxide 0.7 - 4.7 Zirconium dioxide 0.9 Carrier Rest

For the preparation of the catalyst, a support is used - aluminum oxide in the form of tablets, the carrier is impregnated with a solution containing chromium and zirconium compounds, after the product is soaked, it is dried in vacuum, then heat treatment is carried out at 740 ° C, then the catalyst is impregnated with an alkali or alkaline earth metal compound and two-stage drying, first in a vacuum, then in an atmosphere of air, then the product is subjected to heat treatment at 740 ° C.

The catalyst has an increased service life by reducing coke formation, but insufficient activity at a very high content of chromium oxide (25%) and a complex manufacturing process.

The objective of the present invention is to obtain a catalyst with high strength, activity and method for its preparation.

The problem is solved by a catalyst for the dehydrogenation of C ₂ -C ₅ hydrocarbons containing aluminum oxides, chromium, a compound of a modifying metal, an alkali and / or alkaline earth metal, the catalyst additionally contains silicon and / or boron compounds in an amount of 0.1-10%, as a modifying metal, it contains at least one compound from the group: zirconium, titanium, iron, gallium, cobalt, molybdenum, manganese, tin, and a catalyst formed during the heat treatment of an aluminum compound of the formula Al ₂ O ₃ · n H ₂ O, where n = 0 , 3-1.5, together with the compounds of the above elements and has the following composition, wt.% (In terms of oxide):

Chromium oxide calculated as Cr ₂ O ₃ 12-23 A compound of a modifying metal from the group: Zr, Ti, Fe, Ga, Co, Sn, Mo, Mn 0.1-1.5 Compound of silicon and / or boron 0.1-10.0 Alkaline and / or alkaline earth metal compound 0.5-3.5 Aluminium oxide Rest

The catalyst has a specific surface area of 50-150 m ² / g, a pore volume of 0.15-0.4 cm ³ / g and a particle size of 40-200 μm.

The problem is also solved by obtaining a catalyst for the dehydrogenation of C ₂ -C ₅ hydrocarbons, which includes impregnating an alumina-based support with solutions of chromium compounds, an alkali and / or alkaline earth metal modifying metal, drying and calcining at 700-800 ° C, as of the support, an aluminum compound of the formula Al ₂ O ₃ · n H ₂ O, where n = 0.3-1.5, is used as the modifying metal compound, at least one compound from the group of zirconium, titanium, iron, gallium, cobalt, molybdenum , manganese, tin and additionally introduce compounds of silicon and / or boron in an amount of 0.1-10% wt. impregnation with a carrier, followed by drying and applying the remaining components of the catalyst or together with other components of the catalyst and the catalyst after calcination has the following composition, wt.% (in terms of oxide):

Chromium oxide calculated as Cr ₂ O ₃ 12-23 A compound of a modifying metal from the group: Zr, Ti, Fe, Ga, Co, Mo, Mn, Sn 0.1-1.5 Compound of silicon and / or boron 0.1-10.0 Alkaline and / or alkaline earth metal compound 0.5-3.5 Aluminium oxide Rest

To prepare the catalyst, an aluminum compound of the formula Al ₂ O ₃ · n H ₂ O is used, where n = 0.3-1.5, having an amorphous or poorly crystallized structure or partially crystalline structure obtained, for example, by fast dehydration of hydrargillite (applies to the catalyst )

The resulting catalyst has a specific surface area of 50-150 m ² / g, pore volume of 0.15-0.4 cm ³ / g

The impregnation of an aluminum compound of the formula Al ₂ O ₃ · n H ₂ O, where N = 0.3-1.5, is carried out in an aqueous solution of a silicon and / or boron compound with a pH of 6.5 - 12 and at a temperature of 70-100 ° C followed by drying and applying the remaining components in terms of moisture capacity, or they are simultaneously impregnated with compounds of boron and / or silicon, an alkali and / or alkaline earth metal, chromium, a modifying metal in terms of moisture capacity, at a temperature of 20-100 ° C. After impregnation, the catalyst was dried in vacuo.

As boron compounds, boric acid is used. As silicon compounds use a silicon hydrosol, tetraethoxysilane.

In the known solution for the preparation of the catalyst, a carrier is used having a formed crystalline structure (γ-Al ₂ O ₃ and others), onto which the active components of the catalyst are applied repeatedly by impregnation. To fix these components on the carrier, heat treatment is carried out in several stages. Nevertheless, a sufficiently strong fixation of the active component on the carrier does not occur. This is expressed in the fact that during operation of the catalyst, the active component is carried away.

In the proposed solution, the formation of the catalyst occurs during heat treatment from an aluminum compound of the formula Al ₂ O ₃ · n H ₂ O, where N = 0.3-1.5, having preferably an amorphous or poorly crystallized structure or partially crystalline structure, together with the active components of the catalyst, which leads to a strong connection of the carrier with the active components.

In addition, when all components are applied together, the support and the catalyst composition are simultaneously formed and modified, which allows the active components to be chemically dispersed in such a way that, after heat treatment at 700-800 ° C, the chromium, potassium and modifying compounds are in an X-ray amorphous state, which allows significantly increase the activity and selectivity of the catalyst.

The catalyst is prepared as follows.

To prepare the catalyst, an aluminum compound with the gross formula Al ₂ O ₃ · n H ₂ O (n = 0.3-1.5) is used. This compound can be obtained by any known method, for example, rapid dehydration of hydrargillite. An x-ray amorphous structure of this compound is preferred. The particle size of the aluminum compound is 40-200 microns.

By alumina of an amorphous structure is meant an X-ray analysis that does not reveal any lines characteristic of any crystalline phase. By a partially crystalline oxygen-containing aluminum compound is meant one whose analysis reveals lines characteristic of the crystalline phases of at least one of the compounds in the diffraction spectrum: bayerite, hydrargillite, boehmite, γ-, χ-, η-, δ-, θ-, κ-Al ₂ O ₃ .

In the proposed method, the impregnation is carried out simultaneously by all components of the catalyst or from solution, or by moisture capacity. The preferred option is a method of applying moisture capacity, because while there is no wastewater containing harmful chromium compounds.

When an aluminum compound is impregnated with boron and / or silicon connectors from a solution at pH 6.5-12 and a temperature of 70-100 ° C, favorable conditions are created for uniform distribution of boron and / or silicon in the aluminum compound structure, which increase the thermal stability of the catalyst. Drying fixes the resulting aluminum compound modified with boron and / or silicon. This allows you to separate in time and space the processes of obtaining a partially modified compound of aluminum and catalyst, which is sometimes necessary during the preparation of the catalyst in connection with the problems of providing raw materials, marketing of the finished catalyst, production ecology. In addition, in the case of preparing a tableted catalyst, this step is necessary, because the resulting modified aluminum compound serves in this case as a binder.

In the case of preparing a tableted catalyst, a catalyst composition is prepared from an aluminum compound modified with boron and / or silicon, which is obtained by impregnating an aluminum compound of the formula Al ₂ O ₃ · n H ₂ O in an aqueous solution of a boron and / or silicon compound at pH 6.5-12 and a temperature of 70-100 ° C and compounds of an alkali and / or alkaline earth metal, modifying metal, chromium. Then this composition is tabletted or granulated by any of the known methods (pressing, molding, extrusion, rolling, etc.), followed by heat treatment.

The proposed method allows to significantly simplify the technology for producing a paraffin dehydrogenation catalyst compared to existing methods by eliminating several stages of carrier preparation: precipitation of aluminum hydroxide, spray drying or molding of granules, heat treatment of the carrier in comparison with known solutions.

Determination of the phase composition of the materials used in the technology for producing a dehydrogenation catalyst is carried out by the X-ray diffraction method based on x-ray diffraction. The samples are taken in CuK _α radiation using differential discrimination of the monochromator. The range of angles on a 2θ scale is from 10 to 75 ° C, the angular velocity of the detector is 1/60 ° C.

The specific surface area is determined by the BET method, the pore volume by adsorption of water, the particle size by the sieve method.

The abrasion resistance is determined by the mass fraction of losses during abrasion of the catalyst. The method is based on the destruction of catalyst particles in a fluidized bed and measuring the mass of particles carried away by a stream of air whose speed is stabilized.

The invention is illustrated by the following examples.

Example 1. An aluminum compound of the formula Al ₂ O ₃ · n H ₂ O (n = 0.7) of an amorphous structure in the form of a microspherical powder with a particle size of 100 to 200 μm in an amount of 25 kg is loaded into a heat and agitator. A solution containing 5 kg of chromic anhydride, 460 g of potassium alkali, 570 g of zirconium oxynitrate and 150 g of tetraethoxysilane is poured there.

The impregnation is carried out at a temperature of 20 ° C for 1 hour. Then drying is carried out in vacuum. The dried catalyst is calcined at 700 ° C. for 6 hours in a fluidized bed furnace. The composition of the obtained catalyst are presented in table. N 1, and its physicochemical catalytic properties are given in table. N 2.

Examples 2 to 5. The catalyst is prepared analogously to example 1, differs in the temperature of impregnation, the structure of the aluminum compound and the composition of the introduced modifying elements. Data on the temperature, structure of the aluminum compound and on modifying additives are given in table. N 1. And the properties of the obtained catalysts are in table. N 2.

Example 6. In a reactor with a stirrer and heating, pour 80 l of chemically purified water, load 270 g of boric acid and heat to 70 ° C, then load 27 kg of aluminum compound of the formula Al ₂ O ₃ · n H ₂ O (n = 0.5 ) in the form of a microspherical powder of an amorphous structure. The pH of the suspension is adjusted to 6.5 with mineral acid. The process is carried out at 85 ° C for 2 hours, then the precipitate is filtered off, dried in a chamber dryer at a temperature of 100 ° C to remove free moisture. After drying, the partially modified aluminum compound is impregnated in a heating and stirrer, where a solution containing 250 g of potassium alkali and 180 g of cesium hydroxide, as well as 120 g of manganese hydroxide and 130 g of zirconium hydroxide and 5 kg of chromic anhydride is fed. The impregnation is carried out at 60 ° C for 1 hour, after which it is dried under vacuum and calcined at 750 ° C for 6 hours. The resulting catalyst has the properties and composition shown in table. NN 1 and 2.

Examples 7 and 8. The catalyst is prepared analogously to example 6, differs in the impregnation temperature and pH of the suspension, the composition of the used catalyst components. All data are presented in table. NN 1 and 2.

Example 9. In a reactor with a stirrer and heating, 18 liters of water are poured, then 30 g of silica sol and 3 kg of a small-spherical aluminum compound Al ₂ O ₃ · 0.9 H ₂ O are loaded, having a poorly crystallized structure and a particle size of predominantly 40 μm. Adjust the pH of the suspension to 7.2 with nitric acid. The processing of the aluminum compound with silicon is carried out for 2 hours at 85 ° C. Then the precipitate is filtered off and dried at 110 ° C in a chamber dryer. After drying, the resulting powder is impregnated at 85 ° C with a solution containing 900 g of chromic anhydride, 25 g of lithium nitrate, 28 g of barium nitrate and 68 g of zirconium oxynitrate. Moreover, the impregnation is carried out simultaneously with obtaining a paste-like mass of the catalyst, which is then formed into tablets, dried at 110 ° C and calcined at 730 ° C. Get a catalyst with the properties shown in table. NN 1 and 2.

Example 10 (prototype). 1200 g of alumina in the form of tablets are impregnated with a solution containing 532.8 g of chromium trioxide and 28.0 g of zirconium oxyacetate (respectively 52 wt.% Zirconium dioxide). After impregnation, the product is dried for 3 hours at a temperature of 140 ° C and for 16 hours at a temperature of 110 ° C in an air atmosphere, after which it is calcined for 2 hours at a temperature of 740 ° C in an air atmosphere. Then the catalyst is impregnated with potassium acetate and two-stage drying, first for 3 hours at a temperature of 140 ° C in vacuum, and then for 16 hours at a temperature of 110 ° C in air. Then the product is calcined for 2 hours at a temperature of 740 ° C in air. Get the catalyst on a carrier of the following composition: 72.1 wt.% Al ₂ O ₃ ; 25 wt.% Cr ₂ O ₃ ; 0.9 wt.% ZrO ₂ and 2 wt.% K ₂ O and the properties shown in table. N 2.

As can be seen from the presented examples, the catalyst of the proposed composition has high mechanical strength, which allows not to harm the environment, while the catalyst has high activity and selectivity in the process of dehydrogenation of hydrocarbons.

Claims (12)

1. The catalyst for the dehydrogenation of C ₂ -C ₅ hydrocarbons containing oxides of aluminum, chromium, a compound of a modifying metal, alkali and / or alkaline earth metal, characterized in that the catalyst further comprises silicon and / or boron compounds in an amount of 0.1 to 10 wt. %, as a modifying metal, contains at least one compound from the group: zirconium, titanium, iron, gallium, cobalt, molybdenum, manganese, tin, and the catalyst is formed during the heat treatment of an aluminum compound of the formula Al ₂ O ₃ · n H ₂ O where n = 0.3 - 1.5, joint naturally with compounds of the above elements, and has the following composition, wt.% (in terms of oxide): Chromium oxide calculated as Cr ₂ O ₃ 12 - 23 Modifier Metal Compound from the group: Zr, Ti, Fe, Ga, Co, Sn, Mo, Mn 0.1 - 1.5 Compound of silicon and / or boron 0.1 - 10.0 Alkaline and / or alkaline earth metal compound 0.5 - 3.5 Aluminium oxide Rest 2. The catalyst according to claim 1, characterized in that the aluminum compound of the formula Al ₂ O ₃ · n H ₂ O, where n = 0.3 - 1.5, has an amorphous or poorly crystallized structure or partially crystalline structure. 3. The catalyst according to claim 1, characterized in that it has a specific surface area of 50-150 m ² / g and a pore volume of 0.15-0.4 cm ³ / g. 4. The catalyst according to claim 1, characterized in that it has a particle size of 40 to 200 microns. 5. A method of producing a catalyst for the dehydrogenation of C ₂ -C ₅ hydrocarbons, comprising impregnating an alumina-based carrier with solutions of chromium compounds, an alkali and / or alkaline earth metal modifying metal, drying and calcining at 700 - 800 ° C, characterized in that as the carrier, an aluminum compound of the formula Al ₂ O ₃ · n H ₂ O, where n = 0.3 - 1.5, is used as the modifying metal compound, at least one compound from the group is used: zirconium, titanium, iron, gallium, cobalt , molybdenum, manganese, tin, and supplement Silicon and / or boron compounds are introduced in an amount of 0.1-10 wt.% by impregnation of the carrier, followed by drying and application of the remaining catalyst components or together with other catalyst components, and the catalyst after calcination has the following composition, wt.% (in terms of oxide): Chromium oxide calculated as Cr ₂ O ₃ 12 - 23 Modifier Metal Compound from the group: Zr, Ti, Fe, Ga, Co, Mo, Mn, Sn 0.1 - 1.5 Compound of silicon and / or boron 0.1 - 10.0 Alkaline and / or alkaline earth metal compound 0.5 - 3.5 Aluminium oxide Rest 6. The method according to claim 5, characterized in that the catalyst has a specific surface area of 50-150 m ² / g, a pore volume of 0.15-0.4 cm ³ / g. 7. The method according to claim 5, characterized in that the aluminum compound of the formula Al ₂ O ₃ · n H ₂ O, where n = 0.3 - 1.5, has an amorphous or poorly crystallized structure or partially crystalline structure obtained by rapid dehydration hydrargillite. 8. The method according to claim 5, characterized in that the impregnation of the aluminum compound of the formula Al ₂ O ₃ · n H ₂ O, where n = 0.3 to 1.5, is carried out in an aqueous solution of a silicon and / or boron compound with a pH of 6 , 5 - 12 and at a temperature of 70 - 100 ° C, followed by drying and application of the remaining components in terms of moisture capacity. 9. The method according to claim 5, characterized in that the aluminum compound of the formula Al ₂ O ₃ · n H ₂ O, where n = 0.3 to 1.5, is impregnated simultaneously with boron and / or silicon compounds, alkaline and / or alkaline earth metal, chromium, metal modifying moisture capacity at a temperature of 20 - 100 ° C. 10. The method according to claim 5, characterized in that after impregnation, the catalyst is dried in vacuum. 11. The method according to claim 5, characterized in that boric acid is used as boron compounds. 12. The method according to claim 5, characterized in that silicon compounds use a silicon hydrosol, tetraethoxysilane.