RU2256499C1 - Catalyst, method for preparation thereof, and a method for dehydration of hydrocarbons using this catalyst - Google Patents

Abstract

FIELD: hydrogenation-dehydrogenation catalysts.

SUBSTANCE: invention relates to production of olefin or diolefin hydrocarbons via dehydrogenation of corresponding paraffinic C₃-C₅-hydrocarbons carried out in presence of catalyst comprising chromium oxide and alkali metal deposited on composite material including alumina and aluminum wherein percentage of pores larger than 0.1 μm is 10.0-88.5% based on the total volume of open pores equal to 0.10-0.88 cm³/g. Preparation of catalyst involves treatment of carrier with chromium compound solution and solution of modifying metal, preferably sodium or sodium and cerium. Carrier is prepared by from product resulting from thermochemical activation of amorphous hydrargillite depicted by formula Al₂O₃·nH₂O, where 0.25<n<2.0, added to homogenous mass in amount 1.0 to 99.0% using, as additional material, powdered aluminum metal, which is partly oxidized in hydrothermal treatment and calcination stages. Hydrocarbon dehydrogenation process in presence of the above-defined catalyst is also described.

EFFECT: increased activity and selectivity of catalyst.

3 cl, 2 dwg, 4 tbl, 7 ex

Description

The invention relates to the field of production of olefin or diolefin hydrocarbons by dehydrogenation of the corresponding paraffinic C ₃ -C ₅ hydrocarbons and may find application in the chemical and petrochemical industries.

A known method of producing olefinic hydrocarbons by dehydrogenation in the presence of a catalyst composition, wt.%: Cr ₂ O ₃ - 10.0-30.0; ZnO - 30.0-45.0; Al ₂ O ₃ - the rest [Pat. RF №2178398, С 07 С 5/333, 1999]. As a carrier, microspherical granules based on aluzinc spinel are used. The maximum productivity in this process, determined by the product of the conversion to selectivity, is 52.4% of the initial isobutane at an isobutane space velocity of 400 h ^-1 and a temperature of 590 ° C.

The known process of dehydrogenation of paraffin hydrocarbons in the presence of a chromium-containing catalyst composition, wt.%: Cr ₂ About ₃ - 10.0-20.0; In ₂ About ₃ - 1.0-1.5; Me ₂ O - 0.5-2.5; SiO ₂ - 0.5-2.0; Al ₂ O ₃ - the rest, where: Me - alkali metal. As a carrier for the catalyst, microspherical alumina based on gamma, delta, theta modifications in various ratios is used. The maximum yield of the product (isobutene) is 51.7% at a space velocity of isobutane of 400 h ^-1 and a temperature of 574 ° C [Pat. RF №2156233, С 07 С 5/333, 2000].

The processes described above are carried out in a fluidized bed.

Closest to the proposed is a catalyst for the dehydrogenation process in a fixed bed of the composition, wt.%: Cr ₂ O ₃ - 15.0-25.0; Me (alkali metal) ≤ 0.5; Al ₂ O ₃ - the rest [Pat. UK No. 2162082, B 01 J 23/26, 21/04, 1985]. As a carrier for the catalyst, Al ₂ O ₃ granules with a size of ~ 3 mm, an apparent density of 1.36 g / cm ³ , a true density of 3.53 g / cm ³ , a bulk density of 0.836 g / cm ³ , and a total pore volume of 0.435 cm ^{3 are used} / g, an average pore size of 11 nm. The maximum productivity of isobutene is 59.5% at a volumetric speed of isobutene of 367 h ^-1 and a temperature of 620 ° C. A disadvantage of the known catalyst is the absence (or small amount) of pores of a large (> 100 nm) size in the carrier - 1.5% of the total the volume of open pores, determined from the difference between the reciprocal of the apparent and true density of the granules of the carrier [Kinetics and catalysis, 2000, v.41, v.6, s.904]. The absence of large pores is also reflected in a very low average pore size (table 1), which leads to diffusion inhibition of gaseous reactants and reaction products. The latter causes a decrease in catalyst productivity and a deterioration in the performance of the hydrocarbon dehydrogenation process as a whole. The absence of metal in the composition of the carrier can lead to local overheating and greater coking of the catalyst.

The increase in pores of large size in the granules of the carrier is possible by adding large particles or particles burned out during the calcination of additives in the extrudate paste or powder mixture. However, this, as a rule, leads to a significant decrease in mechanical strength and a decrease in the apparent density of the granules. The latter value usually correlates with the bulk density of the granules and determines the efficiency of a unit volume of the reaction space, which is fundamentally important when replacing one catalyst with another.

The invention solves the problem of increasing the efficiency of the process of dehydrogenation of olefinic hydrocarbons through the use of a catalyst based on a carrier having a sufficiently large fraction of pores of a large size while maintaining a high apparent strength of the granules. The task is also to maintain high catalyst activity due to the high specific surface of the carrier to increase the dispersion of the active component when applied by impregnation, as well as to increase the thermal conductivity of the catalyst granules due to the presence of metal particles in the carrier.

The problem is solved in that:

a) a ceramic matrix providing mechanical strength of the carrier has a high specific surface area;

b) the material dispersed along the ceramic matrix of the carrier does not have a high specific surface and is a metal aluminum. Moreover, with a total volume of open pores of the carrier of 0.10-0.88 cm ³ / g, the proportion of macropores larger than 0.1 μm is, vol.%: 10.0-88.5.

The catalyst prepared using the above support contains chromium oxide with additives of an alkali metal, preferably sodium or sodium and cerium oxide.

The problem is also solved by the method of preparation of the catalyst for the dehydrogenation process.

For the preparation of a catalyst containing chromium and aluminum oxides in the prototype [US Pat. UK No. 2162082, B 01 J 23/26, 21/04, 1985] the alumina-based support is impregnated with solutions containing chromium and alkali metal compounds, followed by drying and calcination.

In the proposed method, as a carrier, a composition containing aluminum oxide and aluminum is used with the parameters of the porous structure described above, which is impregnated with solutions of compounds of chromium and sodium or chromium, sodium and cerium. The carrier is synthesized from a powdered charge, including powdered aluminum and a bonding component, a product of thermochemical activation of aluminum trihydroxide (TXA) in an amount of 1.0-99.0 wt.%. The mixture is poured into a special mold, permeable to water vapor. The mold with the mixture is processed in hydrothermal conditions. After hydrothermal treatment, the obtained granular product is removed from the mold, dried and calcined. The resulting carrier contains both aluminum oxides of gamma, eta, theta and other modifications, as well as aluminum remaining unoxidized after hydrothermal treatment and calcination. The proportion of pores with a diameter of more than 0.1 μm is 11.0-87.5 vol.% Of the total pore volume of the carrier.

The TCA product used for the preparation of the mixture is obtained by dehydration under the conditions of pulsed heating of technical alumina hydrate - hydrargillite Al (OH) ₃ [Zolotovsky BP, Buyanov RA, Balashov VA, Krivoruchko O.P.// Scientific basis for the preparation of catalysts. Collection of scientific papers. Novosibirsk; Institute of Catalysis SB RAS. 1990. P.108]. The product TXA thus obtained is in an amorphous state and has the composition Al ₂ O ₃ · nH ₂ O, where 0.25 <n <2.0. The product has a high reactivity and is easily hydrated in the presence of an aqueous or vapor-phase medium with the formation of aluminum hydroxide pseudoboehmite structure AlOOH. The introduction of the TXA product into the charge provides additional strength and a high specific surface area of the granules. In partial oxidation under hydrothermal conditions, aluminum provides compaction of granules while maintaining a high proportion of macropores and increasing their thermal conductivity.

The properties of the obtained media are shown in table 1. The true density of the previously milled granules is determined by the pycnometric method. The pore volume of less than 100 nm and the specific surface area is determined from nitrogen isotherm adsorption. For comparison, the properties of the carrier based on aluminum oxide from the prototype [Pat. UK No. 2162082, B 01 J 23/26, 21/04, 1985]. As can be seen from table 1, in comparison with the pure TXA product and aluminum, the proportion of macropores in the carriers obtained by mixing is less. However, the specific surface area and apparent granule density of carriers obtained by mixing, as a rule, increase. This is reflected in a nonmonotonic change in the bulk density of the granules. Optimal in terms of specific surface area and apparent density are compositions containing 40-80 wt.% Product TCA in the initial charge. Qualitatively, the presence of a large number of pores with a size of 1-10 μm is illustrated in Figure 1.

Prepared according to the method described above, the support is calcined in a stream of air at temperatures of 600-1000 ° C, preferably 700-800 ° C, for 2-10 hours, preferably 4-6 hours, and is used to prepare a supported chromium oxide catalyst. The catalyst is prepared by impregnating the carrier granules with an aqueous CrO ₃ solution according to the moisture capacity of the carrier. The concentration of chromic acid in the solution is calculated from the need to obtain in the finished calcined catalyst 12-25 wt.%, Preferably 18-20 wt.%, Cr ₂ O ₃ . Simultaneously with chromic acid, soluble salts of modifying additives: sodium and cesium are introduced into the impregnating solution. The content of additives in terms of oxides is, wt.%: 0.2-1.0 Na ₂ O, 0.1-2.0 CeO ₂ .

After impregnation, the catalyst is dried in air at room temperature for 12 hours, then at 110 ° C for 6 hours and calcined in air at 600-800 ° C for 4-6 hours. The temperature is raised to the final calcination temperature with stepwise exposure for 1-2 hours at 400 ° C.

The invention is illustrated by the following examples.

Example 1. The catalyst is prepared by impregnating 70 g of support 46 (table 1) with an initial ratio of TXA: Al = 60: 40 (wt.%) 40 ml of an aqueous solution containing 20.1 g of CrO ₃ and 1.035 g of NaNO ₃ . The sample is dried in air at room temperature for 12 hours, then in an oven at 110 ° C for 6 hours and calcined at 400 ° C for 1 hour and at 700 ° C for 4 hours.

Example 2. The catalyst is prepared according to example 1, but in addition to the impregnation solution add 2.181 g of Ce (NO) ₃ · 6H ₂ O.

Example 3. The catalyst is prepared according to example 2, but using the carrier 2 (table 1) with an initial ratio of TXA: Al = 99: 1 (wt.%).

Example 4. The catalyst is prepared according to example 2, but using the carrier 3 (table 1) with an initial ratio of TXA: Al = 80: 20 (wt.%).

Example 5. The catalyst is prepared according to example 2, but using the carrier 4A (table 1) with an initial ratio of TXA: Al = 60: 40 (wt.%).

Example 6. The catalyst is prepared according to example 2, but using the carrier 5 (table 1) with an initial ratio of TXA: Al = 40: 60 (wt.%).

Example 7. The catalyst is prepared according to example 2, but using the carrier 7 (table 1) with an initial ratio of TXA: Al = 1: 99 (wt.%).

The catalyst is tested in dehydrogenation reactions of propane, isobutane and n-butane at a temperature of from 540 to 620 ° C. The dehydrogenation process is carried out in a flowing quartz reactor in a stationary catalyst layer with a fraction size of 2.5-3.5 mm. The granules of the catalyst are uniformly mixed with granules of quartz of the same size in the ratio of catalyst: quartz = 1: 1. The tests are carried out both at atmospheric and at a reduced partial pressure of a dehydrogenated hydrocarbon. The partial pressure of the hydrocarbon is reduced by diluting it with helium. The gas volumetric rate of hydrocarbon delivery varies from 150 to 1200 h ^-1 . The process is carried out in cycles in the following sequence: dehydrogenation - 12 minutes, inert gas purge - 10 minutes, air regeneration - 15 minutes, inert gas purge - 10 minutes, and then the cycle is repeated. The degree of conversion, the olefin yield on the passed and decomposed (selectivity) hydrocarbon is estimated by gas chromatographic analysis of a sample taken ten minutes after the start of dehydrogenation.

Figure 2 and tables 2-4 presents data on the catalytic properties of the catalysts prepared according to examples 1-7 in the dehydrogenation reactions of isobutane, propane and n-butane.

Figure 2 presents the dependence of the selectivity for isobutylene from the degree of conversion of isobutane for the inventive catalyst on a carrier of alumina keramet (1) and prototype (2). 1 - example 2 (carrier 4B, TXA: Al = 60: 40 wt.%, Table 1).

The test results show that in the isobutane dehydrogenation reaction at comparable temperatures (580-590 ° C), the catalyst of the present invention has significantly greater activity and selectivity compared to the catalyst taken as a prototype. The maximum yield of the proposed catalyst and the process based on it (67.7%) significantly exceeds the maximum yield of the prototype (59.5%). The yield of isobutene exceeds the yield of the product of the prototype in the entire investigated range of degrees of conversion of isobutane. In the propane dehydrogenation reaction under close test conditions, our catalyst has a propylene yield of 47.4% (610 ° C, 600 h ^-1 , table 3), while the closest analogue has a yield of 35.3% (620 ° C, 600 h ^-1 ) [Pat. RF №2178398, С 07 С 5/333, 1999].

Table 1.
Media specifications. No. The content of TCA in the mixture wt. % The apparent density of the granules, g / cm ³ The true density of the granules, g / cm ³ The total pore volume, cm ³ / g Pore volume less than 0.1 microns, cm ³ / g The proportion of macropores (more than 0.1 microns),% Specific surface, m ² / g The bulk density of the granules (2-3 mm), g / cm ³ The mechanical strength of the granules, MPa 1 100 0.84 3.57 0.91 0.31 65.9 74.6 0.5 1.4 2 99 0.85 3.56 0.88 0.30 65.9 74,2 0.5 1,6 3 80 1.10 3.20 0.61 0.29 52,5 111.8 0.6 2,3 4a 60 1.28 3.40 0.49 0.23 53.1 98.2 0.8 6.3 4b 1,60 * 3.00 * 0.33 * 0.22 * 33.3 * 135.7 * 5 40 1,60 3.25 0.32 0.15 53.1 88.3 0.8 10.1 6 twenty 1.89 2.93 0.10 0.09 10.0 51,2 1,1 8.8 7 1,0 1,60 2.73 0.26 0,03 88.5 34.5 0.9 4.8 8 0 1,59 2.72 0.26 0,03 88.5 28.6 0.9 4,5 nine Prototype 1.36 3.53 0.45 0.44 1,5 150 0.84 - * Hydrothermal treatment at 100 ° C, other examples 200 ° C.

Table 3.
Dehydrogenation of propane to a Cr ₂ O ₃ / Al ₂ O ₃ -Al catalyst (Example 2, carrier 4b, charge ratio TXA: Al = 60: 40 wt.%, Table 1) at various temperatures and dilutions with an inert gas. Dilution With ₃ H ₈ : He volume T ° C Catalytic performance V C ₃ H ₈ h ^-1 V (C ₃ H ₈ + H) h ^-1 The degree of conversion% Yield C ₃ H ₆ mol. % Selectivity C ₃ H ₆ mol. % 1-0 600 600 570 39.2 37.9 96.5 590 46.3 43.9 94.8 600 51.9 48.4 93.3 610 51.2 47.4 92.6 1: 2,8 600 2670 570 43.7 42.7 97.7 590 48.1 46.3 96.2 600 51.1 48.8 95.5 610 50.3 47.9 95.4 1: 2,8 160 600 570 54.9 51.8 94.4 590 54.5 50.9 93.4 600 65.8 58.4 88.6 610 50.3 58.8 85.6

Table 4.
Dehydrogenation of n-butane on a Cr ₂ O ₃ / Al ₂ O ₃ catalyst (example 2, carrier 4b, ratio in a TXA: Al mixture = 60: 40 wt.%, Table 1) at various temperatures. Dilution With ₃ H ₁₀ : He volume. Catalytic performance V C ₄ H ₁₀ h ^-1 V (C ₄ H ₁₀ + He) h ^-1 T ° C The degree of conversion% Output C ₄ H ₆ mol. % Yield (C ₄ H ₆ + C ₄ H ₈ ) mol. % Selectivity C ₄ H ₆ + C ₄ H ₈ mol. % 1: 2,8 600 2670 540 37.6 3.5 37.0 98.5 560 46.7 5.4 45.5 97.4 580 47.4 7.6 45.6 96.3 590 52.0 9.3 49.5 95.2 1: 2,8 160 600 540 48.1 3.6 46.6 96.9 560 63.4 5.6 59.7 94.2 580 69.1 7.7 63.4 91.7 590 71.7 9.4 64.0 89.3

Claims (3)

1. The catalyst for the process of dehydrogenation of hydrocarbons, containing in its composition chromium oxide, an alkali metal deposited on a carrier, characterized in that the carrier is a composite material comprising aluminum oxide and aluminum, while the proportion of pores larger than 0.1 μm in total the volume of open pores of the carrier, equal to 0.10-0.88 cm ³ / g of the carrier, is 10.0-88.5%. 2. A method of preparing a catalyst for a hydrocarbon dehydrogenation process containing chromium oxide, alumina and a modifying additive, comprising treating the support with a solution of chromium compounds and a solution of a modifying metal, preferably sodium or sodium and cerium, characterized in that the porous composite material is used as a support, comprising aluminum oxide and aluminum, obtained from hydrargillite thermochemical activation product is an amorphous compound of Al ₂ O ₃ · nH ₂ O, where 0,25 <n <2,0, to poured into a homogeneous mass in an amount of 1.0-99.0 wt.%, and powdered metal aluminum is used as an additional material, which is partially oxidized at the stages of hydrothermal treatment and calcination, while the proportion of pores larger than 0.1 microns in the total volume open pores of the carrier, equal to 0.10-0.88 cm ³ / g of the carrier, is 10.0-88.5%. 3. The process of dehydrogenation of hydrocarbons on an oxide-chromium-oxide-aluminum catalyst, characterized in that the catalyst according to any one of claims 1 and 2 is used.

Images