RU2735920C1 - Catalyst for dehydrogenation of paraffin hydrocarbons and method of preparation thereof - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to catalyst for dehydrogenation of paraffin hydrocarbons, including chromium oxide in amount of 8–16 wt. %, sodium and/or potassium compound in amount of 1–3.5 wt. %, aluminium oxide is the rest, the precursor of which is an oxygen-containing aluminium compound obtained by fast partial dehydration of hydrargillite. At that, precursor of aluminium oxide has formula Al₂O_3-x(OH)_x⋅nH₂O, where x = 0.3–0.5, n = 0.3–1.2, catalyst is formed during the heat treatment aluminium oxide precursor in conjunction with compounds of the abovementioned elements and has a surface area of 97–131 m²/g and a pore volume of 0.18–0.21 cm³/g. Invention also relates to a method of producing a catalyst.

EFFECT: technical result consists in development of dehydrogenation catalyst and method of its production with simplified composition, showing high activity, strength, selectivity and resistance to sintering.

7 cl, 2 tbl, 7 ex

Description

The invention relates to methods of preparing catalysts for the dehydrogenation of various 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, high-octane additives (methyl tertiary butyl ether) of gasolines and a number of other industries.

One of the ways 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 an efficient process. Since the dehydrogenation reaction is endothermic, temperatures of 500-600 ° C are required to achieve a technically acceptable conversion of the feedstock. However, even at these temperatures, undesirable side reactions of cracking and isomerization proceed at a noticeable rate. This is because the carbon-carbon (C-C) bond is much weaker than the carbon-hydrogen (CH) bond. Therefore, the catalyst for the dehydrogenation process must direct the process along an energetically unfavorable 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. At the same time, it should minimize the inevitable formation of a certain amount of hydrocarbons of normal and cyclic structure. The dehydrogenation catalyst should provide high selectivity for the desired olefin while reducing the rate of 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 thermally stable and have high mechanical strength.

Until now, effective catalysts for the dehydrogenation of C ₂ -C ₅ paraffins are chromium oxides deposited on aluminum oxide and possessing increased mechanical strength, although chromium compounds are harmful substances. Therefore, when creating new catalysts based on chromium compounds, the main task is to firmly fix chromium in the carrier, reduce wastewater during its production, and increase its activity and stability.

To increase the activity and selectivity (patent EP 0947247, IPC B01J 23/26, publ. 06.10.1999) it is proposed to increase the content of chromium oxide in the catalyst in a certain range of more than 30 wt. %, but not more than 40 wt. %. The catalyst contains aluminum oxide and promoting additives from the group: alkali and alkaline earth metal oxide, oxides of scandium, yttrium, zirconium, lanthanum, titanium, hafnium, cesium, potassium. The catalyst is obtained by double impregnation of the support with a solution of chromium compounds, drying and calcining.

With such a chromium content, the formation of coke decreases and there is a simultaneous increase in the activity and selectivity of the catalyst.

The disadvantage of the catalyst is its low strength and high content of chromium compounds, as well as a complicated method of its preparation.

Known catalyst for the dehydrogenation of hydrocarbons (WO 2010009076, IPC B01J 21/02, B01J 23/04, B01J 23/26, publ. 21.01.2010), including chromium oxide from 10 wt. % up to 30 wt. %, promoters - sodium oxide and potassium oxide from 0.1 to 5 wt. %. Aluminum oxide, alumina, silicates, zeolites, etc. are used as a carrier.

The catalyst may additionally contain oxides of zirconium and magnesium, or mixtures thereof.

The disadvantage of the catalyst is its low strength and insufficiently high activity and selectivity.

Known dehydrogenation catalyst for use in a stationary or fluidized bed (WO 2005040075, IPC B01J 21/04, B01J 23/26, publ. 06.05.2005), containing 10-30 wt. % chromium oxide, promoters - zirconium oxide in an amount from 0.1 to 15 wt. %), and magnesium oxide in an amount from 0.1 to 15 wt. %. The catalyst contains alumina, silicates, zeolites, etc. as a carrier.

The disadvantage of this catalyst is its low strength.

Known catalyst for the dehydrogenation of C ₃ -C ₅ paraffinic hydrocarbons to olefins (patent RU 2322290, IPC B01J 23/26, B01J 21/02, publ. 20.04.2008), containing chromium oxide, alkali metal oxide, transition metal oxides and a carrier, as a carrier, it contains a nanostructured oxygen-containing aluminum compound of the general formula: Al ₂ O _3-x (OH) _x ⋅nH ₂ O, where: x = 0-0.28, n = 0.03-1.8, consisting of nanostructured primary particles with a size of 2-5 nm and characterized by a disordered / defective layered structure close to the structure of bayerite.

The disadvantage of the catalyst is the introduction of cerium oxide additives into the catalyst, which increases the cost of the catalyst due to the high price of cerium compounds.

Known catalyst that contains chromium oxide in an amount of 12-23 wt. %, a compound of an alkali and / or alkaline earth metal in the amount of 0.5-3.5 wt. %), zirconium dioxide in an amount of 0.1-5.0 wt. % and at least one oxide promoter from the group: niobium, tantalum, hafnium in the amount of 0.001-2.0 wt. % on aluminum oxide (patent RU 2200143, IPC S07C 5/333, B01J 23/26, 37/02, publ. 03/10/2003). The catalyst is formed in the process of heat treatment of an aluminum compound of the formula Al ₂ O ₃ ⋅nH ₂ O, where: n = 0.3-1.5, X-ray amorphous structure together with the compounds of the above elements. To prepare the catalyst, an aluminum compound with a layered X-ray amorphous structure of the formula Al ₂ O ₃ ⋅nH ₂ O is used, where: n = 0.3-1.5, preferably with a surface of 50-250 m ² / g. This compound can be obtained by any known method, for example by rapid dehydration of hydrargillite.

The disadvantage of this catalyst is that it has no practical application due to the scarcity and high cost of the used compounds of hafnium, niobium, tantalum. Moreover, such a catalyst does not solve the problem of stability.

Known catalyst for the dehydrogenation of paraffinic hydrocarbons (patent RU 2148430, B01J 23/26, publ. 05/10/2000), which contains chromium oxides 12-23%), an alkali and / or alkaline earth metal compound in an amount of 0.5-3, 5% and a non-metal compound: boron and / or silicon in an amount of 0.1-10%. The catalyst also contains at least one compound of the modifying metal (Ti, Zr, Sn, Fe, Ga, Co, Mn, Mo) in the amount of 0.5-1.5%. The catalyst is formed as a result of heat treatment of an aluminum compound of the formula Al ₂ O ₃ ⋅nH ₂ O, where n = 0.3-1.5, together with the rest of the compounds.

The disadvantage of this catalyst is a rather complex chemical composition, which creates certain difficulties in reproducing its properties during preparation.

The closest in terms of the method for preparing the catalyst is the method used to obtain the catalyst for the dehydrogenation of C ₄ -C ₅ paraffinic hydrocarbons (patent RU 2705808, B01J 23/26, B01J 23/16, B01J 23/04, B01J 21/04, C07C 5/333 ). The catalyst is prepared by impregnating boehmite with solutions of chromium oxide precursors (chromic anhydride, potassium chromate, potassium dichromate, ammonium chromate, ammonium dichromate, chromium hydroxide, chromium nitrate, chromium acetate, chromium oxalate, chromium acetylacetonate, chromium alcoholates, organometallic complex compounds of chromium, etc.) , potassium oxide, taken from the calculation of the composition of the finished catalyst (chromium oxide - 8-20 wt.%, potassium oxide - 0.1-5 wt.%, aluminum oxide - the rest). Boehmite is placed in a vacuum mixer chamber and degassed. Then, an aqueous solution of the precursor of chromium oxide is metered at atmospheric pressure or in vacuum in an amount corresponding to the incipient capacity of the carrier. The carrier is impregnated for 0.5-2 hours. After impregnation, the catalyst is dried at atmospheric pressure or in vacuum for 1-12 hours and calcined in air at a temperature of 600-900 ° C for 4-6 hours. Then, an aqueous solution of the precursor of potassium oxide (potassium carbonate, potassium hydroxide, potassium nitrate, potassium nitrite, potassium sulfate, potassium permanganate, potassium oxalate, potassium acetate, or a mixture thereof) is metered under atmospheric pressure or in vacuum in an amount corresponding to the moisture capacity of the carrier. The carrier is impregnated for 0.5-2 hours. Boehmite of the composition Al ₂ O ₃ ⋅nH ₂ O is used as the alumina support, where n = 1.00-1.19 mol / mol Al ₂ O ₃ .

The disadvantage of the prototype is the complexity of the method of obtaining the carrier used for the preparation of the catalyst and the complex method of forming the catalyst, including the separate application of the catalyst components.

The problem of the proposed solution is the development of a catalyst for the dehydrogenation of hydrocarbons, having supported components in an active form, using an oxygen-containing aluminum compound obtained by rapid partial dehydration of hydrargillite and the development of a method for introducing active components into it that provide resistance to sintering, coking, and simplification of the catalyst composition while maintaining high activity.

The problem is solved using a catalyst for the dehydrogenation of paraffinic hydrocarbons, including chromium oxide in an amount of 8-16 wt. %, a compound of sodium and / or potassium in the amount of 1-3.5 wt. %, alumina, the precursor of which is an oxygen-containing aluminum compound obtained by rapid partial dehydration of hydrargillite. The precursor of alumina has the formula Al ₂ O _3-x (OH) _x ⋅nH ₂ O, where: x = 0.3-0.5, n = 0.3-1.2, the catalyst is formed during the heat treatment of the precursor of alumina together with the compounds of the above elements and has a specific surface area of 97-131 m ² / g and a pore volume of 0.18-0.21 cm ³ / g.

Preferably, the oxygen-containing aluminum compound is spheroidal particles consisting of hexagonal rods with a system of flat parallel pores corresponding to splitting along the (001) face in which the hydroxyl groups are located.

Preferably, the hydroxyl groups on the (001) face in the infrared spectrum have an absorption band of about 3300 cm ^-1 .

The problem is also solved using a method for producing a catalyst for the dehydrogenation of hydrocarbons, including impregnation of an oxygen-containing aluminum-containing compound obtained by rapid partial dehydration of hydrargillite, with solutions of chromium compounds, an alkali metal, drying and calcining at 700-800 ° C. For the preparation of the catalyst, an oxygen-containing aluminum compound is used, which has the formula Al ₂ O _3-x (OH) _x ⋅nH ₂ O, where: x = 0.3-0.5, n = 0.3-1.2, which is obtained quickly partial dehydration of hydrargillite in a flow reactor.

Preferably, the impregnation is carried out in a rotating drum with a controlled speed, which has a unit for introducing an impregnating solution and a thermoelement for drying.

Preferably, hydrargillite for the production of an oxygen-containing aluminum compound is obtained from nepheline raw materials by sintering with soda and limestone.

Preferably, the chromium and alkali metal compounds are introduced by contacting the aluminum compound with solutions of the corresponding active elements in sequence.

The proposed carrier is an oxygen-containing aluminum compound, obtained in a flow reactor by rapid dehydration of aluminum hydroxide, for the preparation of catalysts of the formula Al ₂ O _3-x (OH) _x ⋅nH ₂ O, where: x = 0.3-0.5, n = 0.3-1.2 has centers that activate the supported catalytic substances, characterized in the infrared spectrum by the absorption band of hydroxyl groups with a wavenumber of 3300 cm ^-1 .

The presence of such centers in the oxygen-containing aluminum compound makes it possible to obtain dehydrogenation catalysts that are stable at elevated operating temperatures for a long time (in the catalysts used for regeneration, there were no large crystallites indicating sintering of highly dispersed catalyst particles).

Hydroxyl groups on the (001) face in the infrared spectrum are characterized by an absorption band of ≈ 3300 cm ^-1 , which indicates the presence of OH groups in geometrically constrained conditions, that is, inside narrow interlayer spaces.

Active components introduced into interlayer spaces exhibit high catalytic activity, selectivity, and thermal stability.

This aluminum compound is an X-ray amorphous or poorly crystallized structure or a partially crystalline structure and has a minimal loss of water in the solid phase, thus avoiding the formation of inactive crystalline alumina. The use of an aluminum compound with such hydroxyl groups leads to the formation of catalysts with increased activity, selectivity, stability, and strength.

The proposed aluminum compound is obtained in a flow reactor at an excess pressure of water vapor, followed by rapid quenching (cooling) of the carrier leaving the reactor - an oxygen-containing aluminum compound.

Thus, to obtain the above-described oxygen-containing aluminum compound with the claimed structure, the following conditions must be observed:

- carrying out the dehydration of the initial hydrargillite in a flow reactor to create the same conditions in the moving particles in the gas stream;

- the presence of water vapor in the gas flow;

- a given short-term presence of particles in the gas flow;

- sharp cooling of thermally activated particles of aluminum hydroxide leaving the flow reactor.

The preferred aluminum hydroxide for the production of an oxygen-containing aluminum compound is hydrargillite, the particles of which consist of hexagonal rods with hexagonal sides of 1-10 μm. Such hydrargillite can be obtained, for example, from nepheline raw materials by sintering with soda and limestone.

Hydrargillite from nepheline raw materials, obtained by sintering with soda and limestone, has a spheroidal particle shape and a particle size of 20-300 microns, consisting of hexagonal rods with hexagonal sides of 1-10 microns.

The obtained oxygen-containing aluminum compound under the above-described conditions is spheroidal particles consisting of hexagonal rods with a system of flat parallel pores corresponding to splitting along the (001) face.

During the process of rapid partial dehydration of hydrargillite particles, consisting of a large number of hexagonal rods, favorable conditions are created for uniform heat transfer and the course of dehydration and amorphization processes - violation of structural order. During dehydration under the conditions described above, part of the water is removed from hydrargillite and hydroxyl groups are formed. At the same time, the shape and size of the hydrargillite particles are preserved in the carrier. The formed oxygen-containing aluminum compound has spheroidal particles with a size of 20-300 microns, consisting of a large number of hexagonal rods with a system of flat parallel pores corresponding to hydrargillite cleavage along the (001) face. The formation of flat parallel pores is explained by the layered structure of hydrargillite ("Carriers and Supported Catalysts", Theory and Practice / Alvin B. Styles, Moscow: Chemistry, 1991, pp. 27-29).

According to the data of scanning electron microscopy, an oxygen-containing aluminum compound of the general formula: Al ₂ O _3-x (OH) _x ⋅nH ₂ O, where: x = 0.3-0.5, n = 0.3-1.2, obtained in flow reactor, has a spherical particle shape.

The method of obtaining the proposed catalyst is carried out as follows.

To prepare the catalyst, an aluminum compound of the formula Al ₂ O _3-x (OH) _x nH ₂ O is used, where: x = 0.3-0.5, n = 0.3-1.2, preferably with a surface of 80-250 m ² / g. The proposed aluminum compound was obtained in a flow reactor, followed by rapid quenching (cooling) of the carrier leaving the reactor.

In the proposed method, impregnation is carried out simultaneously or sequentially with all the components of the catalyst by any known methods.

In order to accelerate the introduction of active components into the layered structure of the carrier, it is proposed to use the sequential introduction of the components.

When carrying out the impregnation in a rotating drum, preferably with an adjustable angle of inclination, it is possible to separately apply alkali metal compounds with drying and subsequent application of chromium compounds and also drying.

The abrasion strength is determined by the weight fraction of the catalyst abrasion loss. The method is based on the destruction of catalyst particles in a fluidized bed and measurement of the mass of particles carried away by a stream of air, the speed of which is stabilized.

Specific surface area and porous structure (pore size distribution, total pore volume, average pore diameter) were determined on a Quadrasorb evo QDS-30 apparatus from Quantachrome Instruments by nitrogen adsorption and desorption. The determination was carried out by measuring the amount of gas adsorbed or desorbed from the solid surface of the analyzed sample at a certain equilibrium gas pressure. The measurement range of the pore diameter is from 2 to 100 nm (N ₂ ), the specific pore volume is from 0.05 to 2.00 cm ³ / g (N ₂ ).

The TGA (TCA) phase compositions of the support and catalyst were determined by X-ray phase analysis based on X-ray diffraction. The measurements were carried out on a Shimadzu XRD-6100 apparatus in the range of angles from 10 to 85 degrees 20 each with computer recording of the results.

The morphology of the TGA (TCA) particles of the carrier and catalyst was studied by scanning electron microscopy on a VEGA3 SBH microscope.

The fractional composition of the TGA (TCA) of the support and catalyst was determined by laser scattering on diffraction analyzers Malvern Mastersizer 2000, Mastersizer 3000.

IR spectra of all investigated objects were recorded on a Shimadzu FTIR-8300 spectrometer in the range of 400-6000 cm ^-1 with a resolution of 4 cm ^-1 . The IRS method was used to test the state of OH groups and molecular water.

Obtaining an oxygen-containing aluminum compound.

Technical alumina hydrate is fed into the reactor by a belt auger. Gases with a temperature of 300-600 ° C and a speed of 15 m / s are fed into the lower part of the reactor from the furnace.

Dehydrated aluminum hydroxide is separated from the gas flow in cyclones (outlet gas temperature is 340 ° C), after which it is cooled in fluidization mode to 90 ° C for 5 min with cold air, while an oxygen-containing aluminum compound of composition Al ₂ O _3-x ( OH) _x ⋅nH ₂ O, where: x = 0.3-0.5, n = 0.3-1.2.

The composition of the obtained support is shown in Table 1 (oxygen-containing aluminum compound).

The following examples illustrate the preparation of dehydrogenation catalysts using the support shown in Table 1.

Example 1.

An aluminum compound of the formula Al ₂ O _3-x (OH) _x ⋅nH ₂ O, where: x = 0.4, n = 0.5, in the form of a microspherical powder with a particle size of 100 to 200 μm, with Ssp = 170 m ² / g is loaded into the impregnating agent. An impregnating solution containing chromium and potassium compounds is also poured there. The pressure in the impregnator is maintained at 1 atm. All components are taken in such amounts to provide, after calcination, the composition of the catalyst in terms of oxides, wt. %: chromium - 16.0, potassium - 1.5, aluminum oxide - the rest. After drying, the catalyst is calcined at 750 ° C. Table 2 shows the physicochemical and catalytic properties of the catalyst.

Example 2.

Similar to example 1, only use an aluminum compound of the formula Al ₂ O _3-x (OH) _x ⋅nH ₂ O, where: x = 0.32, n = 1.20 and the catalyst after calcination has the following composition in terms of oxides, wt ... %: chromium - 8.0, potassium - 1.6, aluminum oxide - the rest.

Example 3.

Similar to example 1, only an aluminum compound of the formula Al ₂ O _3-x (OH) x⋅nH ₂ O is used, where: x = 0.50, n = 0.30 and the catalyst after calcination has the following composition in terms of oxides, wt ... %: chromium - 16, potassium - 1.5, sodium - 2.0, aluminum oxide - the rest.

Impregnation is carried out with active components in a rotating drum at an angle of 10 ° to the horizon and through a nozzle fixed in the layer of an aluminum compound, solutions of potassium, chromium, sodium compounds are sequentially sprayed with drying at a temperature of 60 ° C after spraying each compound. The catalyst is calcined at 800 ° C.

Examples 4-6.

Similar to example 3, only they differ in the used aluminum compound and the composition of the catalyst, during impregnation, a solution of the chromium compound is first sprayed, the catalyst is calcined at a temperature of 700 ° C.

Example 7 (prototype for patent RU 2148430).

An aluminum compound of the formula Al ₂ O ₃ ⋅nH 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 the impregnator with heating and stirring. 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 carry out drying in vacuum. The dried catalyst is calcined at 700 ° C for 6 hours in a fluidized bed furnace. The composition of the obtained catalyst, its physicochemical and catalytic properties are presented in Table 2.

The technical result of the proposed solution is the development of a dehydrogenation catalyst and a method for its production with a simplified composition, showing high activity, strength, selectivity and resistance to sintering.

Claims (7)

1. A catalyst for the dehydrogenation of paraffinic hydrocarbons, including chromium oxide in an amount of 8-16 wt. %, a compound of sodium and / or potassium in the amount of 1-3.5 wt. %, aluminum oxide the rest, the precursor of which is an oxygen-containing aluminum compound obtained by rapid partial dehydration of hydrargillite, characterized in that the precursor of aluminum oxide has the formula Al ₂ O _3-x (OH) _x ⋅nH ₂ O, where x = 0.3- 0.5, n = 0.3-1.2, the catalyst was formed during the heat treatment of the precursor of aluminum oxide together with the compounds of the above elements and has a specific surface area of 97-131 m ² / g and a pore volume of 0.18-0.21 cm ³ / g. 2. Catalyst according to claim 1, characterized in that the oxygen-containing aluminum compound is spheroidal particles consisting of hexagonal rods with a system of flat parallel pores corresponding to splitting along the (001) face in which the hydroxyl groups are located. 3. The catalyst according to claim 1, characterized in that the hydroxyl groups on the (001) face in the infrared spectrum are characterized by an absorption band of about 3300 cm ^-1 . 4. A method of obtaining a catalyst for the dehydrogenation of hydrocarbons according to any one of claims. 1-3, including impregnation of an oxygen-containing aluminum-containing compound obtained by rapid partial dehydration of hydrargillite with solutions of chromium compounds, an alkali metal, drying and calcining at 700-800 ° C, characterized in that an oxygen-containing aluminum compound having the formula Al ₂ O is used to prepare the catalyst _3-x (OH) _x ⋅nH ₂ O, where x = 0.3-0.5, n = 0.3-1.2, which is obtained by rapid partial dehydration of hydrargillite in a flow reactor. 5. The method according to claim 4, characterized in that the impregnation is carried out in a rotating drum with a controlled speed, which has a unit for introducing an impregnating solution and a thermoelement for drying. 6. The method according to claim 4, characterized in that hydrargillite for producing oxygen-containing aluminum compounds is obtained from nepheline raw materials by sintering with soda and limestone. 7. A method according to any one of claims. 5, 6, characterized in that the chromium and alkali metal compounds are introduced by contacting the aluminum compound with solutions of the corresponding active elements in series.