RU2538960C1 - Catalyst of dehydration of c4-c5 paraffin hydrocarbons - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: dehydration catalyst represents aluminium oxide carrier, modified with silicon oxide, on which active component chrome oxide and promoter potassium oxide are distributed. Silicon oxide is fixed on aluminium oxide in form of silicon oxide structures Si(OSi)_n(O-)_4-n, where n is from 1 to 4, in which silicon in spectrum NMR MAS ²⁹Si is characterised by presence of lines with chemical shifts from -95 to -105 ppm (line Q³) and from -107 to -124 ppm (line Q⁴) with ratio of integral intensities Q³/Q⁴ from 0.5 to 1.5, with chrome in active component being characterized in UV-Vis-spectrum of diffuse reflection by band of absorption of d-d electronic transition of octahedral Cr(III) cation with wave number from 16500 to 17000 cm^-1. Catalyst has specific surface value from 10 to 250 m²/g, volume of pores not less than 0.15 cm³/g, and its composition is formed in the following ratio, wt %: chrome oxide - 8-20, potassium oxide- 0.1-5, silicon oxide - 0.1-5, aluminium oxide carrier - the remaining part.

EFFECT: claimed catalyst of paraffin hydrocarbons possesses high activity, selectivity and thermal stability.

3 cl, 2 dwg, 1 tbl, 17 ex

Description

The invention relates to the field of chemical technology and catalytic chemistry, in particular to catalysts, methods for producing catalysts for the dehydrogenation of C ₄ -C ₅ paraffinic hydrocarbons to the corresponding olefins in the presence of a catalyst containing chromium, potassium and silicon oxides supported on an alumina carrier. C ₄ -C ₅ olefins are widely used to produce synthetic rubbers, plastics, motor fuel components and other valuable petrochemical products. The growing demand for polyisoprene rubbers requires increasing production capacities of isobutylene and isopentenes, which is possible through the development and use of more efficient catalytic systems.

The dehydrogenation of C ₄ -C ₅ paraffin hydrocarbons is preferably carried out in fluidized bed reactors of a microspherical alumina-chromium catalyst at a temperature of more than 500 ° C. Coke deposits formed during the reaction are burned out during the periodic regeneration of the catalyst at temperatures above 600 ° C.

The performance characteristics of chromium-aluminum catalysts for the dehydrogenation of paraffin hydrocarbons are determined by the properties of the active component of chromium oxide and the characteristics of the alumina carrier. The concentration, state of chromium in the active component determines the yield of olefins, the selectivity of the catalytic action and thermal stability of the catalytic system. The structural stability of the catalyst is determined by the stability of its porous system and phase composition under the conditions of the dehydrogenation process. To improve the properties of chromium-chromium catalysts, a large number of compositions with silicon compounds obtained by drying catalyst suspensions, impregnating finished alumina supports with solutions of the active component, promoters, and modifiers have been proposed.

A known catalyst for the dehydrogenation of paraffin hydrocarbons (CCCS Authority Certificate No. 789151, IPC B01J 21/4, B01J 23/24, publ. 23.12.80), such as n-butane, isobutane, isopentane, in which natural aluminosilicate is used as a source of silicon oxide . The catalyst is prepared by drying the catalyst suspension. The composition of the catalyst, wt.%: Chromium oxide - 12.7-14.3; silicon oxide - 4-15; potassium oxide - 1.3-1.9; sodium oxide - 0.4-0.8; aluminum oxide - the rest. The catalyst has a high activity: in the sum of isoamylenes and isoprene per missed isopentane - 46.8 wt.%; the sum of n-butylenes and divinyl per missed n-butane - 47.5 wt.%; on isobutylene per missed isobutylene - 57.6 wt.%. The disadvantage of the catalyst is the low selectivity for the target olefins due to the high yield of cracking products.

A known catalyst for the dehydrogenation of C ₂ -C ₅ hydrocarbons (RF Patent No. 2287366, IPC B01J 23/26, B01J 37/02, C07C 5/333, publ. 09/28/99), containing oxides of aluminum, chromium, silicon compounds and / or boron , alkali or alkaline earth metal, at least one compound from the group: zirconium, titanium, iron, gallium, cobalt, molybdenum, manganese, tin. An aluminum compound of the formula Al ₂ O ₃ · nH ₂ O (n = 0.3-1.5) amorphous structure in the form of a microspherical powder is used as a carrier. The catalyst is prepared by impregnating the aluminum compound with solutions of the above elements, followed by drying and calcination at 700-800 ° C. As a source of silicon, tetraethoxysilane is used. The catalyst has a specific surface area of 50-150 m ² / g, a pore volume of 0.15-0.4 cm ³ / g, a particle size of 40-200 microns. The composition of the catalyst, wt.%: Chromium oxide - 12-23; a compound of a modifying metal from the group: Zr, Ti, Fe, Ga, Co, Mo, Mn, Sn - 0.1-1.5; a compound of silicon and / or boron - 0.1-10; the connection of an alkaline and / or alkaline earth metal is 0.5-3.5; aluminum oxide - the rest. The catalyst in the isobutane dehydrogenation reaction is characterized by high activity — the yield of unsaturated C ₄ hydrocarbons to the missed isobutane is 51.9%. The disadvantages of the catalyst are low selectivity - the yield of unsaturated C ₄ hydrocarbons on decomposed isobutane is not more than 86.6%, the complexity of the production technology, the complexity of the composition and reproduction of properties.

Known highly active, not containing silicon oxide, a dehydrogenation catalyst for C ₃ -C ₅ paraffin hydrocarbons (RF Patent No. 2350594, IPC C07C 5/333, B01J 23/26, B01J 21/04, B01J 23/04, B01J 37/02), such as propane, isobutane, isopentane, based on an alumina carrier of boehmite morphology with a specific surface area of 80-250 m ² / g, a pore volume of at least 0.2 cm ³ / g, microcrystallite sizes according to the values of coherent scattering regions from 500 to 3000 Å , with interlayer water in an amount corresponding to a molar ratio of water to alumina from 0.8 to 1.2. The catalyst is prepared by impregnating the support with solutions of the precursors of chromium oxide, potassium oxide and the promoter, which is at least one of the oxides selected from the group: copper oxide, zinc oxide, manganese oxide, tin oxide, boron oxide, zirconium oxide, followed by drying and calcination at a temperature of from 600 to 900 ° C. The composition of the catalyst, wt.%: Chromium oxide - 10-20, potassium oxide - 0.1-5, promoter - 0.1-5, alumina carrier - the rest. The catalyst is characterized by high activity in the reactions of dehydrogenation of propane, isobutane, isopentane. The propylene yield for the missed propane is 33.4%, the yield of isobutylene for the missed isobutane is 54.6%, the yield of isoamylene for the missed isopentane is 47.5%. The disadvantages of the catalyst are low selectivity for the target olefins and low thermal stability.

The closest technical solution to the present invention is a catalyst for the production of light olefins (US Patent No. 6362385, C07C 5/333, C07C 5/373, C07C 5/327, publ. 03/26/2002) by dehydrogenation of the corresponding paraffins, containing chromium oxide, tin oxide, alkali metal oxide, aluminosilicate, high temperature alumina. The catalyst is obtained by thermal decomposition of microspherical pseudoboehmite prepared by spray drying a sol of aluminum hydroxide and silica sol. Chromium, tin, alkali metal oxides are impregnated onto the prepared alumina, dried and calcined. The composition of the catalyst, wt.%: Cr ₂ O ₃ - 6-30, SnO - 0.1-3.5, alkali metal, expressed as M ₂ O - 0.4-3, SiO ₂ - 0.08-3, Al ₂ O ₃ - the rest. The catalyst is characterized by high selectivity for the target olefin. In the isobutane dehydrogenation reaction, isobutylene selectivity is 94 mol%. In the propane dehydrogenation reaction, the propylene selectivity is 89 mol. % The disadvantages of the catalyst are low activity and insufficient resistance of the granules to abrasion due to the formation of coagulation contacts between the particles of their components.

The objective of the invention is to increase the activity, selectivity and thermal stability of a dehydrogenation catalyst for C ₄ -C ₅ paraffin hydrocarbons by forming on its surface an active component of chromium (III) oxide in the form of clusters in the presence of a silicon modifier, fixed in the form of surface silicon-silicon structures Si (OSi ) _n (O-) _4-n , where n 1 to 4.

The problem is solved by the development of a dehydrogenation catalyst for C ₄ -C ₅ paraffin hydrocarbons, which is an alumina carrier modified with silicon oxide, on which the active component chromium oxide and the potassium oxide promoter are distributed. The catalyst has a specific surface area of from 10 to 250 m ² / g, a pore volume of at least 0.15 cm ³ / g.

The difference between the invention and the prototype is the following:

- in the catalyst, silicon oxide is fixed on alumina in the form of silicon oxide structures Si (OSi) _n (O-) _4-n , where n is from 1 to 4, in which silicon in the MAS ²⁹ Si NMR spectrum is characterized by the presence of lines with chemical shifts from - 95 to -105 ppm (line Q ³ ) and from -107 to -124 ppm. (line Q ⁴ ) with a ratio of integrated intensities Q ³ / Q ⁴ from 0.5 to 1.5;

- in the catalyst, chromium (III) oxide is placed and fixed in the form of clusters in which chromium is characterized in the UV-type diffuse reflection spectrum by the absorption band dd of the electronic transition of the octahedral Cr (III) cation with a wave number from 16,500 to 17,000 cm ^-1 ;

- alumina carrier in the catalyst contains χ-Al ₂ O ₃ in an amount of from 0.5 to 15 wt.%;

- in the catalyst, the concentration of strong acid sites characterized by a heat of desorption of ammonia of more than 150 kJ / mol is not more than 3 μmol NH ₃ / g.

- while the composition of the catalyst is formed in the following ratio, wt.%:

chromium oxide 8-20 potassium oxide 0.1-5 silica 0.1-5 alumina carrier rest

With the specified set of restrictive and distinctive features, the presence of the claimed lines in the NMR spectrum of MAS ²⁹ Si with chemical shifts from -95 to -105 ppm (line Q ³ ) and from -107 to -124 ppm. (line Q ⁴ ) provided that the ratio of the integrated intensities Q ³ / Q ⁴ from 0.5 to 1.5 indicates the formation of oligomeric structures from SiO ₄ tetrahedra attached to the surface of aluminum oxide (Figure 1, Table 1). The Q ⁴ line corresponds to a surface silicon atom connected to four SiO ₄ tetrahedra via Si — O — Si bonds. The Q ³ line corresponds to the surface silicon atom bonded to three SiO ₄ tetrahedra and one (OH-) or (AlO-) group (Sato S., Sodesawa T., Nozaki F., Shoji H. Solid-state NMR of silica-alumina prepared by chemical vapor deposition // Journal of Molecular Catalysis. - 1991. - V.66. - P.343-355). The ratio of the signal intensities Q ³ / Q ⁴ and the position of the resonance signals on the MAS ²⁹ Si NMR spectra indicates a high degree of coordination of silicon with an alumina support and free hydroxyl groups as a result of the formation of sections coated with amorphous silicon-oxide structures on the catalyst surface.

The formation on the surface of an alumina support of silicon oxide structures Si (OSi) _n (O-) _4-n (where n is from 1 to 4), characterized by a lower pH value of the hydrated surface compared to alumina, leads to an increase in the degree of oligomerization of surface particles Cr (VI) and the formation of polychromatic particles upon application of the precursor of the active component. Upon thermal activation of the catalyst, surface polychromats are reduced to highly active chromium (III) oxide clusters, characterized by an absorption band in the UV-Spectrum from 16,500 to 17,000 cm ^-1 (Figure 2), which indicates the presence of chromium (III) ions in the catalyst in octahedral coordination (Weckhuysen BM, Wachs IE, Schoonheydt RA Surface Chemistry and Spectroscopy of Chromium in Inorganic Oxides // Chemical Reviews. - 1996. - V.96. - P.3327-3349). The specified state of chromium on the surface of the catalyst in the presence of a silicon oxide modifier contributes to an increase in the activity of the catalyst in the dehydrogenation of C ₄ -C ₅ paraffins.

The introduction of silicon into the catalyst and the formation of surface silicon-oxide structures reduces the degree of interaction of chromium with the surface of aluminum oxide, which leads to a smaller amount of chromium incorporated into the structure of aluminum oxide during phase and structural transformations of the catalyst as a result of local overheating of the catalyst and contributes to its thermal stability during operation (Sanfilippo D ., Miracca I. Dehydrogenation of paraffins: synergies between catalyst design and reactor engineering // Catalysis Today. - 2006. - V.111. - P.133-139).

The aluminum-chromium catalyst for the dehydrogenation of C ₄ -C ₅ paraffins is characterized by a wide signal in the spectra of temperature-programmed ammonia desorption in the region of heats of ammonia desorption from 80 to 160 μmol / g. Acid sites having a desorption heat of more than 150 μmol / g are strong acid sites active in side reactions of hydrocarbon cracking. Modification of the surface of an alumina support with silicon oxide structures causes a decrease in the concentration of acid centers with a heat of desorption of ammonia of more than 150 kJ / mol to an amount of not more than 3 μmol / g, resulting in increased catalyst selectivity for target olefins (Egorova S.R., Kataev A.N., Bekmukhamedov G.E., Lamberov A.A., Gilmullin PP, Nesterov O.N. Development of a technology for the production of a microspherical alumina support for a paraffin dehydrogenation catalyst. (2) Effect of hydrothermal conditions rabotki on operational parameters of microspheroidal alumina support and isobutane dehydrogenation catalyst alyumohromovogo // Catalysis in Industry -. 2009. - №6 -. S.48-60).

As a result, the process of dehydrogenation of C ₄ -C ₅ paraffin hydrocarbons in the presence of a catalyst in accordance with this invention is carried out more efficiently, which is reflected in an increase in the yield of target hydrocarbons, a decrease in the yield of by-products, and an increase in thermal stability.

In contrast to the claimed invention, in the prototype, the light paraffin dehydrogenation catalyst is a composition consisting of alumina, silica, chromium oxide, alkaline oxide promoter and tin. The multicomponent composition of the catalyst in the prototype determines the complex reproducibility of the catalytic properties. As a result of the use of pseudoboehmite spray-drying product as a precursor of the carrier, the catalyst granules have low abrasion resistance during operation in the fluidized bed. In addition, treatment of a composition of pseudoboehmite with silicon oxide at a temperature of 1000 ° C leads to the formation of aluminosilicate structures with high surface acidity (Paukshtis E.A. Infrared spectroscopy in heterogeneous acid-base catalysis - Novosibirsk: Nauka, 1992. - 255 p.). Therefore, in the prototype, the catalyst has insufficient selectivity in the dehydrogenation of paraffins.

The catalyst according to the invention is prepared by impregnating an alumina carrier with solutions of the precursors of silicon oxide, chromium oxide, potassium oxide, taken from the calculation of the composition of the finished catalyst, wt.%:

chromium oxide 8-20 potassium oxide 0.1-5 silica 0.1-5 alumina carrier rest

The alumina carrier is placed in the chamber of the vacuum mixer and degassed. Then, the silica precursor solution is dosed in an amount corresponding to the moisture capacity of the carrier. The carrier is impregnated with a solution for 0.5-2 hours. After impregnation, the carrier is dried at atmospheric pressure, in vacuum at a residual pressure of 30-150 mm Hg. or in a stream of dried nitrogen for 1-12 hours and calcined in air or in a stream of dried nitrogen at a temperature of 300-600 ° C for 4-6 hours.

The silica-modified support is placed in a vacuum mixer chamber and degassed. Then, aqueous solutions of the precursors of chromium oxide and potassium oxide are dosed at atmospheric pressure or in vacuum at a residual pressure of about 30-150 mm Hg. in an amount corresponding to the moisture capacity of the carrier. The carrier is impregnated with solutions for 0.5-2 hours. After impregnation, the catalyst is dried at atmospheric pressure or in vacuum at a residual pressure of 30-150 mm Hg. for 1-12 hours and calcined in air at a temperature of 600-900 ° C for 4-6 hours.

As a source of chromium oxide, 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. are used.

As a source of potassium oxide, potassium carbonate, potassium hydroxide, potassium nitrate, potassium nitrite, potassium sulfate, potassium permanganate, potassium oxalate, potassium acetate or mixtures thereof are used.

As a source of silicon oxide use silica stabilized by sodium, potassium, aluminum, ammonium ions, as well as potassium silicate, sodium; organosilicon compounds: alkoxysilanes Si (OR ₁ ) _n (OR ₂ ) _4-n , where R ₁ , R ₂ = C ₆ H ₅ , C _m H _{2m + 1} , m = 1-5, oligoethoxysiloxanes.

As an alumina support, boehmite, pseudoboehmite, an aluminum compound of the X-ray amorphous structure of the formula Al ₂ O ₃ · nH ₂ O, where n = 0.5-1.5, aluminum oxides in the phases γ-Al ₂ O ₃ , δ-Al ₂ O are used ₃ , η-Al ₂ O ₃ , χ-Al ₂ O ₃ , θ-Al ₂ O ₃ , κ-Al ₂ O ₃ , α-Al ₂ O ₃ or in mixed phases (γ-Al ₂ O ₃ + δ- Al ₂ O ₃ , γ-Al ₂ O ₃ + η-Al ₂ O ₃ , γ-Al ₂ O ₃ + χ-Al ₂ O ₃ , γ-Al ₂ O ₃ + δ-Al ₂ O ₃ + θ-Al ₂ O ₃ , γ-Al ₂ O ₃ + δ-Al ₂ O ₃ + χ-Al ₂ O ₃ + κ-Al ₂ O ₃ , δ-Al ₂ O ₃ + θ-Al ₂ O ₃ + α-Al ₂ O ₃ , δ-Al ₂ O ₃ + θ-Al ₂ O ₃ + κ-Al ₂ O ₃ + α-Al ₂ O ₃ ).

The phase composition of the carrier is determined by x-ray diffraction. Radiographs are taken using long-wavelength radiation CuK _α and a graphite monochromator on a diffracting beam. The range of recording angles on a scale of 20 is from 5 to 95 degrees.

The particle size distribution of the carrier is determined by laser diffraction. The essence of the method for determining the fractional composition is described in ASTM D4464-10, Standard Test Method for Particle Size Distribution of Catalytic Material by Laser Light Scattering.

The specific surface area and pore volume are determined by low-temperature nitrogen adsorption. The essence of the method for determining the parameters of a porous system is described in ASTM D 3663-99, “Standard Method for Studying the Surface Area and Pore Volume of Catalysts and Catalyst Carriers”.

Recording of ²⁹ Si NMR spectra of the catalysts is carried out by rotating the samples at a magic angle with a frequency of 5 kHz. ²⁹ Si NMR spectra of the catalysts were recorded in the range from -650 to 650 ppm. at an operating frequency of 79.495 MHz, a spectral resolution of 48.83 Hz.

The UV-type spectra of the diffuse reflection of the catalysts are recorded on a scanning two-beam spectrophotometer connected to an integrating sphere with a diameter of 60 mm coated from the inside with BaSO ₄ . A BaSO ₄ plate is used as a standard. To take spectra, catalyst samples 40-100 μm in size are placed in a holder with a quartz window. The spectra are recorded in the range 200-800 nm (12500-50000 cm ^-1 ) with a spectral resolution of 2 nm. UV-spectra of the samples of the catalyst and chromium oxide are decomposed into Gaussian components to determine the position and intensity of the maxima of the absorption bands.

The surface acidity of the catalysts is determined by the method of thermoprogrammed desorption of ammonia on a flow-through device with a thermal conductivity detector. The adsorption step is carried out in an ammonia stream for 30 minutes at a temperature of 100 ° C. After adsorption, physically sorbed ammonia is blown off with helium at 100 ° C for 30 minutes. Then the sample is cooled to room temperature in a helium stream. Thermally programmed desorption of ammonia is carried out from room temperature to 700 ° C at a rate of 10 K / min. The calculations of the TPD of ammonia by the distribution of acid centers are carried out according to the methodology (Yushchenko V.V. Calculation of the spectra of the acidity of catalysts according to the thermoprogrammed desorption of ammonia // Journal of Physical Chemistry. - 1997. - T.71, No. 4. - P.628-632) .

The catalyst is tested in the processes of dehydrogenation of isobutane and isopentane at a dehydrogenation temperature of 530-570 ° C, a volumetric feed rate of 300-400 h ^-1 . Regeneration is carried out with air at a temperature of 650 ° C, keeping the catalyst for 30 minutes. The tests are carried out in a flow-through laboratory type apparatus with a quartz tube reactor in a fluidized bed of a catalyst. The volume of the loaded catalyst is 100 cm ³ . The process is carried out in cycles in the following sequence: dehydrogenation - 15 minutes, inert gas purge - 5 minutes, air regeneration - 30 minutes, inert gas purge - 5 minutes, then the cycles are repeated. After exposure of the catalyst at a temperature of 570 ° C for 2 hours, two idle cycles are carried out. In the third cycle, during the dehydrogenation reaction, contact gas is taken from 6 to 15 minutes inclusive in an amount of 1 liter. Contact gas is analyzed by gas chromatography. According to the results of chromatographic analysis, the yield of the target olefin on the passed and decomposed paraffin is calculated — the activity and selectivity of the catalyst, respectively.

The specific embodiment of the invention is illustrated by the following examples.

Example 1

200 g of the support — boehmite of the formula Al ₂ O ₃ · nH ₂ O, where n = 1, with a particle size of 20 to 250 μm are impregnated with 86 ml of silica with a concentration of SiO _{2 of} 5.6 wt.%, Stabilized by ammonium ions. The impregnation is carried out for 1 hour at room temperature and atmospheric pressure. The carrier is dried in vacuo at a residual pressure of 30 mm Hg. and a temperature of 80 ° C for 2 hours.

The catalyst is prepared by impregnating the support with a solution of chromium and potassium oxide precursors, for which the dried support is placed in a vacuum mixer chamber and 82 ml of an aqueous solution containing 24.1 g of chromic anhydride and 2.3 g of potassium hydroxide are dosed. The impregnation is carried out for 1 hour at room temperature. The impregnated carrier is dried in vacuo at a residual pressure of 30 mm Hg. and a temperature of 80 ° C for 2 hours, calcined in air at a temperature of 750 ° C for 4 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

Example 2

The catalyst carrier and the catalyst are obtained in the same manner as described in example 1, but carry out additional heat treatment at a temperature of 1100 ° C for 2 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

Example 3

The catalyst carrier and catalyst are obtained in the same manner as described in example 1, but pseudoboehmite of the formula Al ₂ O ₃ · nH ₂ O is used, where n = 1.5, impregnating 90 ml of a solution of tetraethoxysilane in ethanol with a silicon concentration of 1.1 mass. % for 0.5 hours at room temperature and atmospheric pressure. The carrier is dried in vacuo at a residual pressure of 30 mm Hg. and a temperature of 80 ° C for 1 hour, treated at a temperature of 550 ° C for 2 hours in a stream of dry air. The heat-treated carrier is impregnated with 172 ml of an aqueous solution containing 34.5 g of ammonium chromate, 2.8 g of potassium carbonate for 1 hour at room temperature and atmospheric pressure. The impregnated carrier is dried at atmospheric pressure and a temperature of 80 ° C for 12 hours, then calcined in air at a temperature of 750 ° C for 4 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

Example 4

The catalyst carrier and catalyst are obtained in the same manner as described in example 1, but they use an aluminum compound of an X-ray amorphous structure of the formula Al ₂ O ₃ · nH ₂ O, where n = 0.5, impregnating 94 ml of an aqueous solution of potassium metasilicate with a concentration of SiO ₂ 8, 2 wt.% For 1 hour in vacuum at a residual pressure of 100 mm Hg and at room temperature. The carrier is dried for 12 hours at atmospheric pressure and a temperature of 80 ° C. The dried support is impregnated with 180 ml of an aqueous solution containing 41.9 g of ammonium dichromate, 4.2 g of potassium carbonate for 1 hour at a residual pressure of 100 mm Hg, dried for 2 hours in vacuum at a residual pressure of 30 mm Hg. Art. and a temperature of 80 ° C, calcined in air at a temperature of 770 ° C for 4 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

Example 5

The catalyst carrier and catalyst are obtained in the same manner as described in example 1, but pseudoboehmite of the formula Al ₂ O ₃ · nH ₂ O is used, where n = 1.5, impregnating 90 ml of a tetramethoxysilane benzene solution with a silicon concentration of 5.0 wt.% for 1 hour at room temperature and atmospheric pressure. The carrier is dried in vacuo at a residual pressure of 30 mm Hg. and a temperature of 80 ° C for 2 hours. The dried support is impregnated with 172 ml of an aqueous solution containing 37.2 g of ammonium dichromate, 6.6 g of potassium chromate for 0.5 h in vacuum at a residual pressure of 80 mm Hg. and room temperature, dried for 2 hours in vacuum at a residual pressure of 30 mm RT.article and a temperature of 85 ° C, calcined in air at a temperature of 800 ° C for 5 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

Example 6

The catalyst carrier and the catalyst are obtained in the same manner as described in example 1, but they use an aluminum compound of an X-ray amorphous structure of the formula Al ₂ O ₃ · nH ₂ O, where n = 0.5, impregnating 94 ml of silica with a concentration of SiO _{2 of} 3.3 mass. % stabilized by aluminum ions for 1 hour at a temperature of 30 ° C and at a residual pressure of 150 mm Hg The carrier is dried for 2 hours in vacuo at a residual pressure of 30 mm Hg. and temperature 80 ° C. The carrier is impregnated with 90 ml of an aqueous solution containing 21.9 g of chromic anhydride, 2.2 g of potassium hydroxide for 0.5 hours at a temperature of 30 ° C and atmospheric pressure, dried for 12 hours at a temperature of 80 ° C and atmospheric pressure, calcined in air at 780 ° C for 4 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

Example 7

The catalyst carrier and the catalyst are obtained in the same manner as described in example 1, but using boehmite of the formula Al ₂ O ₃ · nH ₂ O, where n = 1, impregnating 86 ml of a benzene solution of tetramethoxysilane with a silicon concentration of 6.4 wt.% For 1 hours at room temperature and at atmospheric pressure. The carrier is dried for 2 hours in vacuo at a residual pressure of 30 mm Hg. and temperature 80 ° C. The dried support is impregnated with 82 ml of an aqueous solution containing 34.1 g of chromic anhydride, 4.9 g of potassium carbonate for 1 hour at room temperature and at a residual pressure of 150 mm Hg, dried for 2 hours in vacuum at a residual pressure 30 mmHg and a temperature of 85 ° C, calcined in air at a temperature of 800 ° C for 4 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

Example 8

The catalyst carrier and the catalyst are obtained in the same manner as described in example 1, but using boehmite of the formula Al ₂ O ₃ · nH ₂ O, where n = 1, impregnating 86 ml of a solution of methoxytriethoxysilane in ethanol with a silicon concentration of 2.5 wt.% In for 2 hours at room temperature and atmospheric pressure. The carrier is dried for 2 hours in vacuo at a residual pressure of 30 mm Hg. and a temperature of 80 ° C, then treated at a temperature of 450 ° C for 2 hours in a nitrogen atmosphere. The carrier is impregnated with 164 ml of an aqueous solution containing 27.4 g of ammonium dichromate, 2.8 g of potassium carbonate for 0.5 hours in vacuo at a residual pressure of 50 mm Hg. and a temperature of 30 ° C, dried for 12 hours at a temperature of 80 ° C and atmospheric pressure, calcined in air at a temperature of 740 ° C for 4 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

Example 9

The catalyst carrier and the catalyst are obtained as described in example 1, but using boehmite of the formula Al ₂ O ₃ · nH ₂ O, where n = 1, impregnating 86 ml of silica with a concentration of SiO _{2 of} 8.0 wt.%, Stabilized by sodium ions , for 2 hours in vacuum at a residual pressure of 150 mm Hg and room temperature. The carrier is dried for 2 hours in vacuo at a residual pressure of 30 mm Hg. and temperature 80 ° C. The dried support is impregnated with 82 ml of an aqueous solution containing 39.6 g of chromic anhydride, 5.0 g of potassium hydroxide for 0.5 hours at atmospheric pressure and room temperature, dried for 12 hours at atmospheric pressure and a temperature of 80 ° C, calcined in air at 700 ° C for 6 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

Example 10

The catalyst support and catalyst are prepared in the same manner as described in Example 1, but boehmite of the formula Al ₂ O ₃ · nH ₂ O is used, where n = 1, impregnating 86 ml of a ethyl silicate-32 benzene solution with a silicon concentration of 3.1 mass% in for 2 hours at room temperature and atmospheric pressure. The carrier is dried for 12 hours in a stream of dried nitrogen at a temperature of 90 ° C, calcined in an atmosphere of nitrogen at a temperature of 450 ° C for 5 hours. The heat-treated carrier is impregnated with 180 ml of an aqueous solution containing 35.4 g of ammonium chromate, 2.3 g of potassium hydroxide for 0.5 hours in vacuum at a residual pressure of 80 mm Hg. and a temperature of 30 ° C, dried for 2 hours in vacuum at a residual pressure of 30 mm Hg and a temperature of 80 ° C, calcined in air at a temperature of 800 ° C for 4 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

Example 11

The catalyst carrier and catalyst are prepared in the same manner as described in Example 1, but boehmite of the formula Al ₂ O ₃ · nH ₂ O, where n = 1, is used, impregnating 86 ml of a solution of dimethoxydiethoxysilane in ethanol with a silicon concentration of 2.3 wt.% In for 1 hour at room temperature and atmospheric pressure. The carrier is dried in a stream of dried nitrogen at a temperature of 90 ° C for 12 hours, then calcined in a stream of dried nitrogen at a temperature of 450 ° C for 5 hours. The calcined support is impregnated with 90 ml of an aqueous solution containing 28.2 g of chromic anhydride, 2.8 g of potassium hydroxide for 1 h in vacuum at a residual pressure of 150 mm Hg. and room temperature, dried for 2 hours in vacuum at a residual pressure of 30 mm RT.article and a temperature of 80 ° C, calcined in air at a temperature of 800 ° C for 4 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

Example 12

The catalyst carrier and catalyst are obtained in the same manner as described in example 1, but boehmite of the formula Al ₂ O ₃ · nH ₂ O is used, where n = 1, impregnating 86 ml of an aqueous solution of potassium metasilicate with a concentration of SiO _{2 of} 11.1 wt.% for 0.5 hours in vacuum at a residual pressure of 150 mm Hg and temperature 30 ° C. The carrier is dried for 2 hours in vacuo at a residual pressure of 30 mm Hg. and a temperature of 80 ° C, calcined in a stream of dried nitrogen at a temperature of 350 ° C for 2 hours. The calcined support is impregnated with 88 ml of an aqueous solution containing 26.7 g of chromic anhydride, 1.9 g of potassium hydroxide for 1 hour in vacuum at a residual pressure of 100 mm Hg. and room temperature, dried for 2 hours in vacuum at a residual pressure of 30 mm RT.article and a temperature of 80 ° C, calcined in air at a temperature of 780 ° C for 5 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

Example 13

The catalyst support and catalyst are prepared in the same manner as described in Example 1, but boehmite of the formula Al ₂ O ₃ · nH ₂ O, where n = 1, is used, impregnating 86 ml of a solution of trimethoxyethoxysilane in ethanol with a silicon concentration of 5.2 wt.% In for 1.5 hours at a temperature of 20 ° C and atmospheric pressure. The impregnated carrier is dried for 12 hours in a stream of dried nitrogen at a temperature of 90 ° C, calcined in a stream of dried nitrogen at a temperature of 400 ° C for 5 hours. The carrier is impregnated with 180 ml of an aqueous solution containing 52.9 g of ammonium chromate, 4.8 g of potassium carbonate for 1 h in vacuum at a residual pressure of 100 mm Hg. and room temperature, dried for 2 hours in vacuum at a residual pressure of 30 mm RT.article and a temperature of 80 ° C, calcined in air at a temperature of 800 ° C for 4 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

Example 14

The catalyst carrier and catalyst are obtained in the same manner as described in example 1, but boehmite of the formula Al ₂ O ₃ · nH ₂ O, where n = 1, is used, impregnating 86 ml of silica sol SiO ₂ 2.0 wt.%, Stabilized by ammonium ions, for 1 hour in vacuum at a residual pressure of 100 mm Hg and temperature 20 ° C. The impregnated carrier is dried for 2 hours in vacuo at a residual pressure of 30 mm Hg. and a temperature of 80 ° C, calcined in air at a temperature of 300 ° C for 5 hours. The carrier is impregnated in two stages with 180 ml of an aqueous solution containing 43.4 g of ammonium chromate, 3.7 g of potassium carbonate, dried for 2 hours in vacuum at a residual pressure of 30 mm Hg. and a temperature of 80 ° C, calcined in air at a temperature of 750 ° C for 6 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

Example 15

The catalyst carrier and the catalyst are obtained as described in example 1, but using boehmite of the formula Al ₂ O ₃ · nH ₂ O, where n = 1, impregnating 86 ml of silica with a concentration of SiO ₂ 5.0 wt.%, Stabilized by aluminum ions , for 0.5 hours at atmospheric pressure and room temperature. The dried support is calcined in air at 400 ° C. for 4 hours. The heat-treated carrier is impregnated with 90 ml of an aqueous solution containing 27.7 g of chromic anhydride, 2.1 g of potassium hydroxide for 1 hour at atmospheric pressure and a temperature of 30 ° C, dried for 2 hours in vacuum at a residual pressure of 30 mm Hg . and a temperature of 80 ° C, calcined in air at a temperature of 800 ° C for 2 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

Example 16 (comparisons)

A microspherical pseudoboehmite carrier with a particle size of 5-300 μm obtained by spray drying a hydrated alumina and silica sol containing 1.2 wt.% SiO ₂ is subjected to heat treatment at 450 ° C for 1 hour and then at 1030 ° C for 4 hours in a stream of dry air. The calcined support is impregnated for 2 hours at atmospheric pressure and a temperature of 85 ° C with 68 ml of an aqueous solution containing 48.6 g of chromic anhydride, 4.40 g of potassium hydroxide, 3.0 g of tin oxalate. The impregnated carrier was incubated for one hour at room temperature, then dried for 15 hours at atmospheric pressure and a temperature of 90 ° C, calcined in a stream of dry air at a temperature of 750 ° C for 4 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

Example 17 (comparisons)

The catalyst carrier and the catalyst are obtained in the same manner as described in example 16, but carry out additional processing at a temperature of 1100 ° C for 2 hours.

The composition, properties of the catalyst and the results of catalytic tests in the dehydrogenation reactions of isobutane and isopentane are shown in table 1.

As can be seen from the above examples, the proposed catalyst is superior in activity, selectivity and thermal stability in the dehydrogenation reactions of C ₄ -C ₅ paraffin hydrocarbons of the prototype catalysts.

The higher dehydrogenating activity of the catalyst samples in comparison with the prototype catalysts is due to the fixation of the active phase of chromium (III) oxide in the form of highly active clusters on the surface of the catalyst, in which chromium (III) ions are present in the octahedral coordination and are characterized by an absorption band in the UV View spectrum from 16500 to 17000 cm ^-1 . The formation of highly active clusters of chromium (III) oxide is ensured by the distribution on the surface of the alumina support of amorphous silicon-silicon structures Si (OSi) _n (O-) _4-n (where n is from 1 to 4), in which silicon in the MAS ²⁹ Si NMR spectrum is characterized the presence of lines with chemical shifts from -95 to -105 ppm (line Q ³ ) and from -107 to -124 ppm. (line Q ⁴ ). As follows from the ratio of the intensity of the Q ³ / Q ⁴ signals and the position of the resonant signals on the MAS ²⁹ Si NMR spectra, specific silicon-oxide structures with a greater degree of coordination of silicon with an alumina support and free hydroxyl groups are predominantly formed.

The increase in the target olefin selectivity of the catalyst samples of the present invention in dehydrogenation processes compared to the prototype catalysts is due to a change in the acid characteristics of the surface of the alumina carrier when modified with silicon oxide structures, accompanied by a decrease in the concentration of the strongest acid centers with an ammonia desorption energy of more than 150 kJ / mol, catalyzing undesired cracking reactions hydrocarbons, to a minimum amount of not more than 3 μmol / g.

The increase in thermal stability of the catalyst sample of this invention compared to the prototype catalyst is caused by a decrease in the number of chromium atoms introduced into the structure of the alumina carrier during phase and structural transformations caused by high temperatures during regeneration due to a decrease in the degree of interaction of chromium with the surface of the carrier in the presence of specific silicon-oxide structures.

Table 1 Example No. The composition of the catalyst, wt.% S _beats , m ² / g V _p , cm ³ / g N _s.c.c. μmol / g δ (Q ³ ), ppm δ (Q ⁴ ), ppm I (Q ³ ) / I (Q ⁴ ) υ ( ⁴ A _2g → ⁴ T _2g ), cm ² Dehydrogenation Cr ₂ O ₃ K ₂ O Al ₂ O ₃ SiO ₂ Isobutane Isopentane VP,% BP,% VP,% BP,% Total including χ-Al ₂ O ₃ one 2 3 four 5 6 7 8 9 10 eleven 12 13 fourteen fifteen 16 17 one 9.5 1,0 87.0 0 2,5 69 0.22 0.5 -102 -118 0.62 16850 54.3 94.7 47.8 86.7 2 9.5 1,0 87.0 0 2,5 42 0.18 0 -96 -110 0.94 16920 46.4 92.3 40.5 84.3 3 10.0 1,1 87.9 4,5 1,0 83 0.23 1,2 -104 -122 0.52 16910 52.1 92.3 45.6 85.9 four 11.5 1.3 83.7 10 3,5 124 0.21 2.6 -103 -115 0.75 16800 53.6 91.5 47.0 86.5 5 13.3 1.7 80.5 1,5 4,5 78 0.22 0.8 -101 -111 0.84 16770 54.1 94.2 47.2 85.7 6 8.1 0.9 89.5 0.2 1,5 72 0.21 0.3 -105 -121 0.54 16880 51.7 93.2 47.5 85,2 7 12.5 1,6 80.9 13.5 5,0 147 0.24 2.9 -99 -110 0.87 16730 53.9 90.8 47.1 84.5 8 8.7 1,0 88.4 4.3 1.9 86 0.21 1.3 -104 -118 0.58 16870 50.7 92.4 46.2 85.0 9 14,4 2.0 80.3 2,4 3.3 91 0.20 2.0 -102 -114 0.78 16810 53,4 93.7 47.3 84.8 10 9.2 1,0 87.2 7.0 2.6 105 0.18 2,3 -101 -117 0.66 16840 51.1 91.3 45.3 85.7 eleven 11.0 1,2 86.1 0 1.7 67 0.21 0.4 -105 -119 0.56 16890 53.8 94.5 47.5 86.3 12 10,2 0.8 84.2 0.6 4.8 96 0.24 0.8 -98 -110 0.91 16750 54.6 94.5 47.9 85.6 13 12.9 1,6 81.8 5,4 3,7 112 0.23 1.8 -102 -115 0.77 16790 52,5 90,4 46.4 85.7 fourteen 11,2 1.3 86.6 2,4 0.9 104 0.21 0.7 -106 -123 0.51 16930 53,4 94.6 47.5 86.5

Continuation of table 1 one 2 3 four 5 6 7 8 9 10 eleven 12 13 fourteen fifteen 16 17 fifteen 10.8 0.9 86.1 3,7 2.2 83 0.23 1.3 -103 -119 0.59 16820 54.0 93.9 46.3 85.7 16 (comparisons) 19.0 1.9 76.9 2,5 SiO ₂ = 1.2 SnO = 1.0 102 0.32 10,2 -101 -109 0.86 17220 51.7 92.6 40.3 85,2 17 (comparisons) 19.0 1.9 76.9 2,5 SiO ₂ = 1.2 SnO = 1.0 67 0.16 4.3 -95 -108 1,2 17430 31.3 87.4 28.7 81.0 VP - the olefin yield on the missed paraffin,%; BP — olefin yield on decomposed paraffin,%; N _{c.c.cc.EdesNH3} — content of acid centers with a heat of ammonia desorption of more than 150 kJ / mol, µmol / g; δ (Q ³ ) and δ (Q ⁴ ), ppm - the position of the signal of the oxide-silicon structures Q ³ and Q ⁴ on ²⁹ Si NMR spectra in parts per million; I (Q ³ ) / I (Q ⁴ ) is the ratio of the signal intensities of the oxide-silicon structures Q ³ and Q ⁴ on ²⁹ Si NMR spectra; υ ( ⁴ A _2g → ⁴ T _2g ), cm ^-1 - wave number of the electronic transition ⁴ A _2g → ⁴ T _2g in the octahedral Cr (III) cation, cm ^-1

Claims (3)

1. The catalyst for the dehydrogenation of C ₄ -C ₅ paraffin hydrocarbons, which is an alumina carrier, modified with silicon oxide, on which the active component of chromium oxide is distributed, the potassium oxide promoter, characterized in that silicon oxide is attached to alumina in the form of silicon oxide structures Si (OSi ) _n (O-) _4-n , where n is from 1 to 4, in which silicon in the MAS ²⁹ Si NMR spectrum is characterized by the presence of lines with chemical shifts from -95 to -105 ppm. (line Q ³ ) and from -107 to -124 ppm. (line Q ⁴ ) with a ratio of integrated intensities Q ³ / Q ⁴ from 0.5 to 1.5, in which chromium in the active component is characterized in the UV-type spectrum of diffuse reflection by the absorption band dd of the electronic transition of the octahedral Cr (III) cation with a wave number from 16500 to 17000 cm ^-1 , with a specific surface area of 10 to 250 m ² / g, a pore volume of at least 0.15 cm ³ / g, while the composition of the catalyst is formed in the following ratio, wt.%:
chromium oxide 8-20 potassium oxide 0.1-5 silica 0.1-5 alumina carrier rest 2. The catalyst according to claim 1, characterized in that the alumina carrier contains χ-Al ₂ O ₃ in an amount of from 0.5 to 15 wt.%. 3. The catalyst according to claim 1, characterized in that the concentration of strong acid sites characterized by a heat of desorption of ammonia of more than 150 kJ / mol is not more than 3 μmol NH ₃ / g

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