RU2391134C2 - Method of preparing catalyst for dehydrogenation of paraffin hydrocarbons - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the process of obtaining olefin or diolefin hydrocarbons C₃-C₄ through catalytic dehydrogenation of corresponding paraffin hydrocarbons, and specifically to preparation of a dehydrogenation catalyst, and can be used in chemical and petrochemical industry. The method of preparing a catalyst for dehydrogenating paraffin hydrocarbons C₃-C₄ by impregnating the γ-Al₂O₃ catalyst support with a solution of Cr and K salts with subsequent drying and tempering at high temperature is distinguished by that, before impregnation with salt solutions, the γ-Al₂O₃ catalyst support undergoes high temperature treatment with hydrogen at 300-500°C and impregnation of the support with the metal salts is carried out in 24-65 hours.

EFFECT: obtained catalyst surpasses known catalysts on activity and selectivity.

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Description

The invention relates to a process for the production of C ₃ -C ₄ olefin or diolefin hydrocarbons by catalytic dehydrogenation of the corresponding C ₃ -C ₄ paraffin hydrocarbons, namely, the production of a dehydrogenation catalyst, and can be used in the chemical and petrochemical industries.

A known method of producing isobutene by dehydrogenation of isobutane in a fluidized bed of a chromium-containing catalyst composition, wt.%:

Cr ₂ O ₃ - 10.0 ÷ 20.0

B ₂ O 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 is an alkali metal. As a carrier for the catalyst, microspherical alumina is used based on γ, δ, and θ modifications in various ratios. [one]

The maximum yield of isobutene on this catalyst is 51.7 wt.% At a volumetric feed rate of isobutane of 400 h ^-1 and a temperature of 574 ° C.

A known method of producing a catalyst for the dehydrogenation of paraffinic hydrocarbons, in which a composite material is used as a catalyst carrier, including aluminum oxide and powdered aluminum. [2] The product of thermochemical activation of aluminum trihydroxide (TXA) in the amount of 1.1–99.0% is used as a bonding component. The compressed carrier is then subjected to hydrothermal treatment, followed by impregnation with the salts of Cr, Na and cesium or cerium.

Obtaining such a catalyst involves a lot of technological operations, and the process is quite complicated and expensive. In addition, the indicators of the dehydrogenation process on this catalyst are presented in molar percent and the formation of products such as hydrogen, coke and cracking products is not taken into account. Given the full composition of the dehydrogenation products, the process indicators — activity and selectivity — are very low.

The activity of the catalyst strongly depends on the amount deposited on the carrier of the active phase in the form of a complex of metal oxides. Deep and complete impregnation of the carrier is hindered by the inhibitory effect of the air adsorbed in the pores of the carrier.

A known method of removing adsorbed in the pores of a carrier of air by vacuum. [3] The carrier is evacuated in order to improve the uniformity of the impregnation of the grains and a more complete deposition of the active components.

The process is very complex in an industrial environment.

Closest to the claimed is a method of preparing a dehydrogenation catalyst by impregnation of the carrier - γ-Al ₂ O ₃ with salts of Cr ⁺⁶ , alkali metals and a modifying metal from the group: Ir, Ti, Fe, Ga, Co, Sn, Mo, Mn, as well as Si and / or B. [4]

A method of producing a catalyst includes the steps of: 1 - impregnating a carrier with solutions of metal salts; 2 - drying and calcination of the impregnated carrier at 700 ÷ 800 ° C. The carrier is impregnated in an aqueous solution of a silicon and / or boron compound with pH = 6.5–12.0 at a temperature of 70–100 ° C, followed by drying and application of the remaining components in terms of moisture capacity or simultaneous impregnation with salts of components in terms of moisture capacity at a temperature of 20–100 ° C.

The disadvantages of this catalyst: low activity (42 ÷ 52 wt.%) And selectivity (84.5 ÷ 88.0 wt.%), With the conversion of isobutane 52.9 ÷ 60.4 wt.%; as well as multicomponent and complex composition.

The objective of the present invention is to simplify the composition of the catalyst and improve the performance of the main catalytic properties - activity and selectivity.

The problem is solved by a catalyst for the dehydrogenation of C ₃ -C ₄ hydrocarbons containing chromium and potassium oxides supported on γ-Al ₂ O ₃ .

The catalyst is prepared by impregnating γ-Al ₂ O _{3 with an} aqueous solution containing CrO ₃ , K ₂ CO ₃ .

A distinctive feature of the method is the preparation of the catalyst carrier γ-Al ₂ O ₃ and the conditions for its impregnation. To increase the degree of filling of the carrier pores with active components and improve the uniformity of impregnation, the carrier is preliminarily treated with hydrogen at an elevated temperature: 300–500 ° C for 3–5 hours in order to remove air adsorbed in the pores, then the carrier is cooled to 50–80 ° C and pour in an impregnating solution. The impregnation of the carrier is carried out for 24 ÷ 65 hours with periodic stirring. After which the catalyst is dried at 120 ° C for 3 hours and calcined at 600 ÷ 700 ° C for 4 hours. The resulting catalyst is tested in a flow through pilot plant for the dehydrogenation of C ₃ -C ₄ paraffin hydrocarbons.

A method of producing a catalyst is illustrated by the following examples.

Example 1

100 g of γ-Al ₂ O ₃ (80 cm ³ ) having the following physicochemical parameters:

d ₄ ²⁰ = 1.25 g / cm ³ ;

mass fraction of impurities,%:

- iron - 0.02,

- sodium in terms of Na ₂ O - 0.02;

strength coefficient, kg / mm - 1.05;

specific surface, m ² / g - 195;

total pore volume, cm ³ / g - 0.68;

fractional composition of granules:

from 100 to 200 microns - 90%;

fall asleep in a porcelain cup and dried at 100 ° C for 3 hours, then cooled to 50 ° C and fill in 100 cm ^{3 of an} aqueous solution containing 38.5 g of CrO ₃ and 5.5 g of K ₂ CO ₃ . The carrier is impregnated for 48 hours with periodic stirring. Then the residues of the impregnating solution are evaporated, the catalyst is dried at 120 ° C for 3 hours and subjected to thermal calcination at 650 ° C for 4 hours. After calcination, the cooled catalyst is loaded into a tubular quartz reactor (d × l = 25 × 500 mm).

The composition of the obtained catalyst are shown in table 1.

Isobutane is passed through the catalyst at a space velocity of V = 400 h ^-1 at an initial temperature in the reactor of 600 ° C. The obtained process indicators: average dehydrogenation temperature (t _cp ) and catalytic properties are presented in table 2.

Example 2

The preparation of the catalyst is carried out under conditions similar to those described in example 1. The catalyst carrier, before being impregnated with a salt solution, is treated with hydrogen (V = 100 h ⁻¹ ) at 500 ° C for 8 hours, then cooled in a stream of hydrogen to 50 ° C and filled with an impregnating solution. The impregnation of the media are within 48 hours. Then the residues of the impregnating solution are evaporated, the catalyst is dried and calcined at 650 ° C for 4 hours. The composition of the obtained catalyst are presented in table 1.

The isobutane dehydrogenation on the resulting catalyst is carried out under the conditions of example 1. The results are presented in table 2.

Example 3

The preparation of the catalyst is carried out under the conditions of example 2. The treatment of the carrier with hydrogen is carried out at 400 ° C and V = 200 h ^-1 for 3 hours. The carrier is impregnated for 36 hours. The composition of the catalyst are presented in table 1.

The isobutane dehydrogenation on the resulting catalyst is carried out under the conditions of example 1. The results are presented in table 2.

Example 4

The preparation of the catalyst is carried out by a method similar to that described in example 2. Thermostating of the carrier in a stream of hydrogen (V = 300 h ^-1 ) at 350 ° C is carried out for 4 hours. Impregnation of the carrier is carried out within 24 hours. The composition of the obtained catalyst are presented in table 1.

Isobutane dehydrogenation is carried out under the conditions of example 1. The results are presented in table 2.

Example 5

The preparation of the catalyst is carried out in a manner similar to that described in example 2. Thermostating of the carrier in a stream of hydrogen (V = 100 h ^-1 ) at 200 ° C. Spend within 8 hours. The media is impregnated for 15 hours. The composition of the obtained catalyst are presented in table 1.

Isobutane dehydrogenation is carried out under the conditions of example 1. The results are presented in table 2.

Example 6

The preparation of the catalyst is carried out by a method similar to that described in example 2. Thermostating of the carrier in a stream of hydrogen at V = 200 h ^-1 , t = 400 ° C is carried out for 3 hours. Impregnation is carried out for 65 hours. The composition of the obtained catalyst are presented in table 1.

Isobutane dehydrogenation is carried out under the conditions of example 1. The results are presented in table 2.

Example 7 (prototype)

The 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 a heat and agitator. A solution containing 5 kg of chromic anhydride (CrO ₃ ), 460 g of potassium alkali (KOH), 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 1.

The isobutane dehydrogenation on the resulting catalyst is carried out at a temperature of 580 ° C. The results are presented in table 2.

Example 8

On the catalyst obtained in example 6, dehydrogenation of n-butane is carried out at an average dehydrogenation temperature _tdeg = 520 ° C, V = 400 h ^-1 .

The results are presented in table 2.

Example 9

On the catalyst obtained in example 6, conduct propane dehydrogenation at an average dehydrogenation temperature t _de = 550 ° C, V = 400 h ^-1 .

The results are presented in table 2.

Table 1 The composition of the obtained catalysts Example No. The composition of the catalyst, wt.% CrO ₃ Cr ₂ O ₃ K ₂ O Al ₂ O ₃ one 2 3 four 5 one 2.0 12.5 1,5 rest 2 2.6 14.2 2.0 - // - 3 2,3 14.0 1.9 - // - four 2,3 14.0 1.7 - // - 5 2.5 12.8 1.7 - // - 6 3,7 14.5 2,3 - // - 7 p / p 15.0 ¹ 1,0 - // - Si - 0.1 Zr - 1.5 B - 1.5 Where: ¹ - total content of chromium oxides.

table 2 Catalytic properties of catalysts Example No. Dehydrogenation Temperature, ° С Indicators VP ¹ , wt.% BP ² , wt.% K ³ , wt.% The yield of coke, wt.% Consumption factor ⁴ , kg / kg one 521 56.83 93.92 60.63 0.52 1,07 2 551 65.22 90.44 72.43 1.13 1,11 3 531 63.60 92.80 68.60 0.72 1,08 four 535 69.28 91.41 75.79 1.24 1.09 5 550 55.04 83.53 69.90 2.13 1.20 6 547 69.24 92.36 75.00 1.25 1,08 7 p / p 580 51.9 85.9 60,4 - 1.16 8 520 48.39 85.28 56.74 1.93 1.17 9 550 41.48 84.46 49.11 2.22 1.18 Where: ¹ - VP - the yield of unsaturated hydrocarbons to the passed raw materials, wt.%; ² - BP - the output of unsaturated hydrocarbons to converted raw materials, wt.%; ³ - K - conversion of raw materials, wt.%; ⁴ - expenditure coefficient, equal to the ratio of K to VP and determines the consumption of raw materials in kg to obtain 1 kg of the target product.

As can be seen from the above examples, the catalysts obtained by the present method contain more active (CrO ₃ + Cr ₂ O ₃ ) and modifying (K ₂ O) components than the known one. And accordingly, their indices for catalytic activity and selectivity are higher. The catalyst impregnation time of less than 24 hours does not allow more complete application of active and modifying components to the carrier impregnation. And the impregnation of the carrier for more than 65 hours does not increase the content of active components on the catalyst and does not increase its activity and selectivity.

Treatment of the support with hydrogen at a temperature below 300 ° C does not allow to achieve the desired result, and the temperature of treatment with hydrogen support above 500 ° C is not energetically justified.

Due to the high activity and selectivity of the obtained catalyst, the consumption coefficient for isobutane decreases from 1.16 to 1.07-1.08, and the dehydrogenation temperature decreases from 580 ° C to 531 ° C.

References

1. P. RF №2156233, 2000 BI No. 14.

2. P. RF №2256499, 2005 07.20.

3. Technology of catalysts. / Ed. I.P. Mukhlenova. - L .: Chemistry, 1979, p. 139.

4. P. RF №2148430, 2000 BI No. 13.

Claims (1)

A method of obtaining a catalyst for the dehydrogenation of paraffin hydrocarbons With ₃ -C ₄ impregnation of a γ-Al ₂ O ₃ catalyst support with a solution of Cr and K salts, followed by drying and calcination at elevated temperature, characterized in that the γ-Al ₂ O ₃ catalyst support before impregnation with salt solutions subjected to high-temperature treatment with hydrogen at 300-500 ° C and the carrier is impregnated with metal salts for 24-65 hours