RU2026110C1 - Method for manufacture of chromo-alumina catalyst for dehydrating and dealkylating hydrocarbons - Google Patents

Abstract

FIELD: chemical engineering, manufacture of catalysts. SUBSTANCE: method in which chromic acid is fed to bead mill. Next water and aluminum oxide are added the latter at the rate of 2-3 percent by weight of the catalysis. Mixing for 10 min follows. The obtained solution is fed to a mixer along with water, aluminium oxide and aluminium hydroxide previously exposed to grinding and reprecipitation. Mixing for 30 min follows. The resulting compound is discharged from the mixer and subjected to molding drying and grinding so as to obtained particles less than 1 mm in size. The obtained powder is charged into a in which added are water and the mentioned chromic solution. The compound is plasticized formed into braided straps and dried. Heat treatment follows. It is effected at 650 C for 5 h in a gas-vapor medium having 10 % of steam contained in it. EFFECT: higher efficiency of process, between quality of product. 3 tbl

Description

 The invention relates to the production of catalysts, in particular an aluminum-chromium catalyst for the processes of dehydrogenation of paraffins and dealkylation of alkyl aromatic hydrocarbons.

A known method of producing an aluminum-chromium catalyst for the dehydrogenation of hydrocarbons by double impregnation of a combined carrier with chromic acid, namely, that a mixture of powdered alumina and reprecipitated aluminum hydroxide is impregnated with chromic acid, plasticized, molded, dried and ground. The resulting powder was again impregnated with chromic acid, kneaded, molded, dried and heat treated in a steam environment at 700 ^C for 10h (1). However, this catalyst is not sufficiently active in the processes of dehydrogenation of paraffins and dealkylation of alkyl aromatic hydrocarbons.

 The closest in technical essence and the achieved result is a method of preparing an aluminum-chromium catalyst for dealkylation and cyclization of hydrocarbons, which consists in multiple impregnation during plasticization of a combined support consisting of 10-15 wt.% Milled redeposited aluminum hydroxide and 90-50 wt.% Milled aluminum oxide (technical alumina) with an aqueous solution of chromic acid, followed by molding, drying after each impregnation and heat treatment. Alumina in an amount of 10-50 wt.% From entering the carrier is pre-milled to a fraction of 1-25 microns. (2).

 The method is complex technology, the resulting catalyst has insufficient activity.

 The purpose of the invention is the preparation of a catalyst with increased activity.

 This goal is achieved by the described method of preparing an aluminum-chromium catalyst for dehydrogenation and dealkylation of hydrocarbons by repeatedly impregnating a combined support, which is a mixture of reprecipitated aluminum hydroxide and alumina, with a chromic acid solution in which 2-3 wt.% Of alumina from the total mass of the catalyst are pre-dissolved, followed by molding, drying after each impregnation and heat treatment.

 The activation heat treatment of the catalyst obtained by the present method can be carried out in any medium, preferably in a steam-air one.

 The promoting effect of peptization with chromic acid, containing from 2 to 3% alumina in the form of lameness and sol of a finely dispersed oxide, is explained by the weak peptization of unrefined powdered alumina and, as a consequence, the insufficient formation of aluminum chromate on its surface, on the basis of which active centers are created.

PRI me R 1. 44.7 cm ^{3 of} chromic acid containing 1000 g / DM ^{3 of} chromic anhydride, loaded into a bead mill, add 15.7 cm ^{3 of} water and 4.3 g of alumina, which is 2.5% aluminum oxide based on the total weight of the catalyst. Then, 700 g of beads are loaded into the mill and mixed for 10 minutes.

 30.0 cm3 of the resulting solution is introduced into the mixer, where 92.8 g of commodity alumina (alumina) having a particle size of at least 30 μm, 71 g of reprecipitated aluminum hydroxide milled to 1-25 μm and 35 cm3 of water are preloaded. After stirring for 30 minutes, the mass is discharged from the mixer, molded and dried, then milled to particles less than 1 mm.

The resulting powder is re-loaded into the mixer, 30 cm ^{3 of} chromic acid obtained as described above and 22 cm ^{3 of} water are added. Mass plasticized for 30 minutes, formed into strands, dried and heat-treated at 650 ^{° C} for 5 hours vapor-medium containing 10% water vapor.

 The finished catalyst contains 18 wt.% Chromium oxide, 0.2 wt.%, Sodium oxide, the rest is aluminum oxide.

The resulting catalyst was tested in a butane dehydrogenation reaction in vacuo. Test conditions: temperature 575 ^{° C}
The residual pressure of 125 mm RT. Art.

Volumetric feed rate of 400 h ^-1 Raw material composition: butane-99.4-%,
isobutane 0.6%
The test results are given in table. 1.

PRI me R 2. The catalyst is prepared analogously to example 1, only 3 g of alumina (2% Al ₂ O ₃ ) is introduced into the bead mill. The test results are given in table. 1.

PRI me R 3. The catalyst is prepared analogously to example 1, only 5.7 g of alumina (3% Al ₂ O ₃ ) is introduced into the bead mill. The test results are given in table. 1.

 From comparing the data table. 1 it can be seen that the activity of the samples obtained by the described method increases, the most significant is the increase in the yield of valuable monomer - butadiene.

 The activity of the catalyst increases due to increased peptization of the surface and the formation of active centers.

PRI me R 4. The catalyst prepared as described in examples 1.3, is tested in the reaction of dealkylation of toluene at 620 ^about With a pressure of 6 MPa, a volumetric feed rate of toluene of 0.4 m ^-1 molar dilution of hydrogen toluene 5: 1 Catalyst loading 100 cm ³ , grain 3x4 mm. The test results are given in table. 2.

 As can be seen from the table. 2, the activity (benzene yield) of samples obtained by the present method increases.

PRI me R 5. The catalyst prepared according to example 1, is tested in the process of dealkylation of industrial benzene-toluene-xylene (BTK) fractions at a temperature of 620 ^about C, a pressure of 6 MPa, a volumetric feed rate of 0.4 h ^-1 molar dilution of hydrogen: feed 5: 1. The composition of the raw materials wt.% .: benzene 8.5; toluene 45.4; ethylbenzene 7.3; xylenes 38.0; hydrocarbons C ₉ , 0.7.

 The results are shown in table. 3.

 A comparison of the obtained data shows that the activity of the catalyst obtained by the present method increases.

Claims (1)

 METHOD FOR PREPARING ALUMINUM-CHROMIUM CATALYST FOR DEHYDROGENING AND DEALKYLATION OF HYDROCARBONS by repeatedly impregnating a combined support, which is a mixture of reprecipitated aluminum hydroxide and alumina, a solution of chromic acid followed by molding, drying after each impregnation and heat treatment, which gives rise to heat treatment that activity, in a solution of chromic acid previously dissolved 2 - 3% of aluminum oxide of the total mass of the catalyst and the resulting astvor used to impregnate the carrier.

Images