RU2594485C1 - Method of activating catalyst for producing fluorine-containing hydrocarbons - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to chemical industry, to a method of activating chromium-containing catalysts, which can be used in reactions of gas-phase fluorination of halogenated hydrocarbons. Described is a method of activating a catalyst for producing fluorine-containing hydrocarbons by gas-phase hydrofluorination of halohydrocarbons, containing chromium (III), aluminium compounds, metal compounds selected from a group comprising or iron, or nickel, or cobalt or zinc or magnesium, or any mixture thereof, which includes seven steps: drying catalyst precursor in air flow; catalyst calcination in inert gas flow; catalyst calcination in air flow; calcination of catalyst in gas mixture of hydrogen fluoride and nitrogen; raising temperature; stepwise increase in concentration of hydrogen fluoride in HF-N₂ gas mixture; raising temperature to 370-380 °C, stepwise raising of pressure of HF; raising temperature to 370-380 °C and stepwise raising of pressure of HF.

EFFECT: technical result consists in increase of low-temperature of catalyst activity.

8 cl, 1 dwg, 2 tbl, 7 ex

Description

The invention relates to the field of chemical industry, to a method for activating chromium-containing catalysts that can be used in gas-phase fluorination reactions of halogenated hydrocarbons, in particular, in the following processes:

- fluorination of tetrachlorethylene Cl ₂ C = CCl ₂ into pentafluoroethane CHF ₂ -CF ₃ ;

- fluorination of trichlorethylene Cl ₂ C = CHCl in 1,1,1,2-tetrafluoroethane CH ₂ F-CF ₃ .

Fluorinated hydrocarbons such as pentafluoroethane, commonly referred to as R-125, and 1,1,1,2-tetrafluoroethane, referred to as R-134a, are used as refrigerants, blowing agents, aerosol preparations, propellants, cleaning agents, and the like. The use of fully fluorinated hydrocarbons is a very urgent task, since in comparison with the currently widely used chlorohydrocarbons, they have a less destructive effect on the ozone layer.

Known methods for the fluorination of halogenated hydrocarbons, which include passing a gaseous mixture of hydrogen fluoride and halogenated hydrocarbons through a catalyst bed, the main catalytic component of which are chromium compounds in the form of oxides, oxyfluorides or fluorides, sometimes in combination with promoting and stabilizing additives of Al, Mg, Fe, Ni, Zn, Co, etc. ["Industrial organofluorine products." Directory. St. Petersburg, Chemistry, 1996, p. 65, 69. Kemnitz E., Winfield J.M. II Advanced Inorganic Fluorides. 2000. P. 367].

There are various methods for preparing and activating chromium-containing catalysts for fluorination of chlorine-containing organic compounds. They include the preparation of precursors containing the main and auxiliary catalytic components in the form of hydroxides, oxides, salts, and the subsequent activation of the precursors, i.e., the formation of active centers of the catalyst during heat treatment in various gaseous media, nitrogen, air, and hydrogen. Activation is completed during the treatment of calcination products with fluorine-containing compounds: gaseous HF or fluorine-containing halogenated hydrocarbons contained in the catalyzed gas mixture with the formation of active chromium oxyfluorides.

A high activity of catalysts based on chromium compounds is achieved if, upon activation, the optimal conditions for the transition from hydroxide or oxide precursors to oxyfluorides - partially fluorinated chromium oxides having a high specific surface and containing fluorine and oxygen in active form are realized.

A variety of methods are known for activating the initial precursors by varying the conditions for the stages of activating heat treatment. Thus, a known method for producing 1,1,1,2-tetrafluoroethane by the interaction of 1,1,1-trifluoro-2-chloroethane with hydrogen fluoride in the presence of a catalyst based on chromium oxide [US Pat. US No. 4158675. С07С 17/08, 01/19/1979]. The catalyst is prepared by precipitating chromium hydroxide with ammonia from aqueous solutions of Cr (III) salts. Then the chromium hydroxide paste is treated with water vapor at 50-180 ° C, dried, tabletted, calcined in air or oxygen and fluorinated in HF at 250-400 ° C for at least 30 minutes. The disadvantage of this method is the lack of selectivity.

In Pat. US No. 5475167, С07С 17/08, 12.12.96, in the process of hydrofluorination of freon 124 to freon 125, Cr ₂ O ₃ obtained by pyrolysis of (NH ₄ ) ₂ Cr ₂ O ₇ and subjected to activation consisting in preliminary calcination in one of the agents is used, selected from CO, H ₂ , H ₂ O, or mixtures thereof. Upon preliminary activation with hydrogen, the catalyst is first calcined in a stream of nitrogen at a temperature of 400 ° C for about 8 hours, then it is cooled to 175 ° C and treated at the same temperature with hydrogen for 1 hour. Then, the catalyst is activated in a mixture of nitrogen and hydrogen fluoride at a temperature of 275 ° C. The activated catalyst is used in the synthesis of R125 freon at a reaction temperature of 275 to 400 ° C. The yield of HFC 125 was 67%.

A known catalyst for producing fluorocarbons, in particular pentafluoroethane R-125, containing Cr (III) compounds and a carrier is magnesium fluoride, and additionally containing Fe (III) and optionally Zn (II) compounds in the following ratio of components in terms of metals, wt.%: Fe (III) 0.1-2.0, Zn (II) 0-2.0, Cr (III) 6.5-12.0, MgF - the rest [Pat. RF No. 2179885, B01J 23/26, C07C 17/20, 02.27.2002]. The catalyst is prepared by mixing preformed MgF ₂ with water-soluble salts of Cr (III), Fe (III), Zn (II) and extrusion granulation of the resulting paste. To activate, the catalyst is first dried in nitrogen at 250 ° C, then gaseous hydrogen fluoride is fed into the reactor at a flow rate of 0.1 kg / h and the temperature is raised to 450 ° C. The nitrogen supply is turned off and the catalyst is kept in a stream of hydrogen fluoride for 0.5 h. The reactor is cooled in a stream of hydrogen fluoride to 375 ° C, the flow rate of hydrogen fluoride is set to 98.5 g / h, and perchlorethylene is supplied in an amount of 64 g / h (molar ratio HF : C ₂ Cl ₄ = 8.0: l), creating an overpressure in the reactor equal to 0.3 MPa. Under these conditions, the conversion of perchlorethylene was 84.1%. A disadvantage of the known catalyst is the low activity and selectivity at low reaction temperatures.

A known process for the hydrofluorination of halogenated hydrocarbons in the presence of a catalyst comprising partially fluorinated chromium oxide having a specific surface area of 170-300 m ² / g [Pat. US No. 6300531. B01J 23/26, C07C 17/20, 09/10/2001]. The catalyst is obtained by ammonia precipitation from aqueous solutions of Cr (III) salts, dried in air at 70-300 ° C, granulated, calcined in nitrogen at a temperature of about 360-400 ° C for ~ 2 hours. The resulting product has S _beats = 170- 300 m ² / g (preferably 200-260 m ² / g) atomic ratio O / Cr not more than 3: 1, preferably from 2: 1 to 2.3: 1. The calcined catalyst is activated in HF in the temperature range from 150 to 400 ° C, in which there is no condensation of water and there is no danger of crystallization of chromium oxide at the stages of calcination and fluorination due to overheating of the catalyst in the exothermic crystallization process of α-Cr ₂ O ₃ and fluorination of chromium oxide. Partially fluorinated chromium oxides (oxyfluorides) are most active, therefore, fluorination is carried out to relatively low fluorine contents (from 8 to 15 wt.%), The upper limit of fluorine content is 48 wt.%. But the conditions for achieving such degrees of fluorination (pressure, gas composition) are not indicated.

The disadvantage of this method is the lack of reproducibility of the properties of the catalyst, possibly due to local overheating during an uncontrolled exothermic fluorination process.

A known catalyst, a method for its preparation and activation, and a method for fluorination of halogenated hydrocarbons with gaseous hydrogen fluoride, including chromium oxide (III) and aluminum compound (III), the content of which in terms of Al ₂ O ₃ is from 2 to 15 wt.% [Pat. RF №2322291. B01J 23/26, С07С 17/20, 04/20/2008], The catalyst is prepared by the co-precipitation of chromium (III) and aluminum (III) hydroxides from inorganic salts of chromium (III) and aluminum (III) and bases, followed by filtration, washing water, drying in air at 110-200 ° С and calcination of mixed aluminum and chromium hydroxides in an inert nitrogen or argon gas with a gradual increase in temperature from room temperature to 350 ± 20 ° С at a rate of not more than 100 ° С / h with isothermal exposure during 2-8 hours at temperatures 250 ± 20 ° С, 300 ± 20 ° С, 350 ± 20 ° С. The catalyst calcined in nitrogen has a specific surface area of 130-300 m ² / g, a pore volume of at least 0.3 cm ³ / g and a monomodal pore size distribution in the range of 70-300 Å.

The stage of fluorinating activation is carried out in gas mixtures containing 15-25 vol.% Hydrogen fluoride and 85-75 vol.% Inert gas at a temperature of 330-350 ° C and a pressure of 0.10 ± 0.02 MPa, while the fluorinated catalyst has a specific surface area of less than 60 m ² / g.

A disadvantage of the known activation method is the presence of a significant amount of residual water due to incomplete dehydration of the precursor in the selected range of temperatures of calcination in nitrogen - 330-350 ° C. Under the conditions of a catalytic reaction, it is possible to release residual water into the gas phase, which in the presence of hydrogen fluoride contributes to the corrosivity of the gas mixture.

Closest to the proposed invention is the method described [Pat. RF №2449832 "The method of activation of the catalyst for producing fluorine-containing hydrocarbons." B01J 23/26, B01J 21/0, C07C 17/20. 05/10/2012].

A method for activating a chromium-containing catalyst for fluorination of halogenated hydrocarbons is described, including chromium (III) oxide and an aluminum (III) compound, the content of which in terms of Al ₂ O ₃ is 2-15 wt.%, Additionally containing Me metal compounds selected from the group including or iron, or nickel, or cobalt, or zinc, or copper, or magnesium, or any mixture thereof in an amount of 0.1-1.5 wt.% in terms of oxides. The activation process is carried out in four stages, including: a) drying the catalyst in a stream of nitrogen at a temperature of 100-200 ° C and atmospheric pressure; b) treating the catalyst with difluorochloromethane (R-22) at a temperature of 300-370 ° C and atmospheric pressure; c) treating the catalyst with a mixture of hydrogen fluoride with nitrogen at a temperature of 340-370 ° C at atmospheric pressure, with a gradual increase in the concentration of hydrogen fluoride in a mixture with nitrogen to 100 mol. %; g) treatment of the catalyst with hydrogen fluoride at a temperature of 340-370 ° C and a pressure of up to 0.4 MPa. The result is a reduction in the total time of activation, avoiding local overheating in the catalyst grain, which leads to good reproducibility of activity.

The disadvantage of this method is the low activity in the low temperature region of catalytic hydrofluorination (280-380 ° C). At the same time, it is known that low temperatures for the catalytic hydrofluorination of halogenated hydrocarbons can reduce the occurrence of undesirable side processes, including coking, as well as reduce energy costs for the process.

Effective methods for improving the physicochemical and, consequently, catalytic properties of hydrofluorination catalysts of halocarbons are optimization of the composition of the catalyst and the method of its activation.

The invention solves the problem of increasing the low-temperature activity and selectivity of a chromium-containing catalyst for the gas-phase hydrofluorination of halogenated hydrocarbons, in particular, in the fluorination of perchlorethylene Cl ₂ C = CCl ₂ into pentafluoroethane CHF ₂ -CF ₃ (R-125), and 1,1,1-trifluorochloroethane (R-133a) in 1,1,1,2-tetrafluoroethane CH ₂ F-CF ₃ (R-134a).

The problem is solved in that in the method of fluorination of halogenated hydrocarbons with gaseous hydrogen fluoride, a catalyst is used comprising chromium (III) compounds, the amount of which in terms of Cr ₂ O ₃ is 98-85 wt.%, And aluminum (III) compounds, the amount of which in in terms of Al ₂ O ₃ is 2-15 wt.%, additionally containing metal compounds (Me) selected from the group comprising either iron, or nickel, or cobalt, or zinc, or magnesium, or any mixture thereof in an amount of from 0.1 -1.5 wt.% In terms of oxides, which after My activation method has a specific surface area of at least 60 m ² / g. On the surface of the catalyst, the atomic ratio of oxygen to chromium is O / Cr = 0.4-1.5, and the atomic ratio of fluorine to chromium is F / Cr = 1.3-2.8. Such ratios indicate the formation on the surface of the activated catalyst of oxyfluorides with the general formula CrO _x F _y (x = 0.6-1.5, y = 1.3-2.8), which, according to our and published data, are the most active compounds of chromium catalysts for the hydrofluorination of organochlorine compounds. Smaller F / Cr ratios indicate insufficient fluorination of the starting chromium oxide at the stage of preliminary fluorinating activation. Large relationships indicate the possibility of the formation of inactive coarsely dispersed CrF ₃ .

The problem is also solved due to the fact that the proposed activation method, i.e. conditions for the transition from hydroxide and oxide precursors to active chromium oxyfluorides. The proposed activation method includes 7 consecutive stages and the conditions for their implementation:

I. Drying the catalyst in a stream of air at a temperature of 70-200 ° C,

preferably 110-150 ° C, and atmospheric pressure (0.10 ± 0.02 MPa).

II. Calcination of the catalyst in an inert gas stream, such as nitrogen, argon, helium, at a temperature of 450-500 ° C, preferably 470-480 ° C, and atmospheric pressure.

III. Calcination of the catalyst in an air stream at a temperature of 290-340 ° C, preferably 300-330 ° C, and atmospheric pressure.

IV. Calcination of the catalyst in a gas mixture of 15-25 vol.% Hydrogen fluoride and 85-75 vol.% Nitrogen, preferably 20 vol.% HF, 80 vol.% N ₂ , at a temperature of 120-130 ° C and a pressure of 0.1 ± 0.02 MPa.

V. A stepwise increase in temperature from 120-130 ° C to 330-350 ° C, preferably up to 340-350 ° C, in increments of 20 ÷ 25 ° C and holding at each stage for 15-20 minutes in a 20% volume of gas mixture. % HF, 80 vol.% N ₂ at a pressure of 0.1 ± 0.02 MPa.

VI. A stepwise increase in the concentration of hydrogen fluoride in the HF-N ₂ gas mixture from 20 to 100 vol.% HF with a step of 20 vol.% HF and exposure at each stage for 15-20 minutes at a temperature of 340-360 ° C, preferably 340-350 ° С, and pressure 0.1 ± 0.02 MPa.

VII. An increase in temperature to 370-380 ° C and a stepwise increase in HF pressure from 0.1 to 0.4 MPa in increments of 0.1 MPa with exposure at each stage for 15-20 minutes.

The problem is also solved by the claimed properties of the products obtained in stages II, III and VII:

after stage II activation, the water content in the product is 2.5-3.5 wt%,

after stage II of activation, the specific surface area is at least 200 m ² / g.

after stage III of activation, the specific surface area of the product is at least 150 m ² / g and the atomic O / Cr ratio on the surface of the product is 1.8-2.0.

after the VII stage of activation, the specific surface area of the product is at least 60 m / g and on the catalyst surface the atomic ratio of oxygen to chromium is O / Cr = 0.6-1.5, the atomic ratio of fluorine to chromium F / Cr = 1.3-2.8.

The technical result is an increase in the low-temperature activity of the catalyst due to the formation of finely dispersed chromium oxyfluorides with the general formula CrO _x F _y (x = 0.6-1.5, y = 1.3-2.8).

The claimed properties of the catalyst are achieved due to the method of each stage and the properties of the products after stages II, III, VII. So, in the product obtained after stage I and II of activation (drying in an air stream at a temperature of 70-200 ° C and atmospheric pressure 0.10 ± 0.02 MPa and calcination in nitrogen at a temperature of 470-480 ° C and atmospheric pressure 0 , 10 ± 0.02 MPa), an X-ray amorphous, finely dispersed Cr (III) oxide is formed, containing 2.5-3.5 wt.% Water, which does not increase the corrosivity of the gas mixture.

In stage III, the catalyst is activated by calcining in an oxidizing medium (air) at a relatively low temperature of 290-340 ° C, preferably 300-330 ° C. This leads to the formation of chromium (III) oxide with superstoichiometric oxygen (atomic ratio 0 / Cr ~ 1.8-2.0), which, upon contact with fluorine-containing gases, is capable of forming highly active oxyfluorides. This occurs with preliminary fluorinating activation in stages IV-VII. In this case, the properties of oxide products obtained in the previous stages play an important role: dispersity, oxygen state (oxidation state and the presence of non-stoichiometric oxygen) in oxide products obtained in the previous stages.

In addition, the conditions for carrying out the stages of fluorination of oxide precursors at stages IV-VII play a significant role. It is known that fluorination of oxides is a highly exothermic process that can lead to local overheating, lower specific surface area and deep fluorination of chromium oxide with the formation of coarse stoichiometric fluorides CrF ₃ . To avoid this, the conditions for gradual phased fluorination in stages IV-VII with a controlled process temperature, the concentration of HF in a mixture of HF + N ₂ and the feed rate of the gas mixture are declared.

At the initial stage of chromium oxide fluorination (stage IV), the oxide precursor is carefully calcined in a gas mixture containing 15–25 vol% hydrogen fluoride and 85–75 vol% inert gas, preferably 20 vol% HF, 80 vol% N ₂ , at a relatively low temperature of 120-130 ° C and a pressure of 0.1 ± 0.02 MPa

At stage V, a stepwise increase in temperature is carried out from 120-130 ° C to 330-350 ° C, preferably up to 340-350 ° C, in increments of 20 ÷ 25 ° C and holding at each stage for 15-20 minutes in a gas mixture 20 vol.% HF, 80 vol.% N ₂ at a pressure of 0.1 ± 0.02 MPa.

At stage VI, a stepwise increase in the concentration of hydrogen fluoride in the HF-N ₂ gas mixture is carried out from 20 to 100 vol.% HF with a step of 20 vol.% HF and exposure at each stage for 15-20 minutes at a temperature of 340-360 ° C, preferably 340-350 ° C, and a pressure of 0.1 ± 0.02 MPa.

At stage VII, an increase in temperature is carried out to 380-390 ° C and a stepwise increase in pressure HF to 0.1 to 0.4 MPa with a step of 0.1 MPa and exposure at each stage for 15-20 minutes.

The claimed conditions of the fluorinating stages of activation prevent overheating and deactivation of the catalyst. The catalyst obtained after the VII stage of activation has a specific surface area of at least 60 m ² / g. On the surface, the atomic ratio of oxygen to chromium is O / Cr = 0.6-1.5, the atomic ratio of fluorine to chromium is F / Cr = 1.3-2.8. The rate constant of the hydrofluorination reaction of perchlorethylene is 1.5-1.6 s ^-1 .

Research Methods

The specific surface area (S _beats , m ² / g) is determined by the BET method by thermal desorption of argon.

The content (wt.%) Of chromium, aluminum, iron, nickel, cobalt, zinc and magnesium in the samples is determined by atomic emission spectroscopy with ionization-coupled plasma (ICP AES) on a Baird atomic emission spectrometer)

The contents of Cr, F, O and the atomic ratios O / Cr and F / Cr on the surface of the chromium-containing oxide precursor after stage III and the finished catalyst after stage VII of activation are determined by X-ray photoelectron spectroscopy (XPS). In accordance with published data, the position and intensity of photoelectron lines makes it possible to identify the qualitative and quantitative composition of the surface of samples of chromium-containing catalysts [L. Kolditz, G. Kauschka, W. Schmidt, Z. Anorg. Allg. Chem., 434, (1977) 41. D. Bechadergue, M. Blanchard, P. Canesson. Appl. Catal. 20 (1986) 179-187].

Before shooting, the samples are ground and applied to an indium substrate. Spectra were taken on a KRATOS ES 300 X-ray spectrometer from Kratos Analytical (Great Britain). Spectra are taken in the operating mode of the x-ray tube 15 kV × 13 mA, which corresponds to the dissipated power of the x-ray radiation 195 W. As the primary radiation using K _α -line of aluminum with a photon energy of 1486.6 eV. To determine the qualitative chemical composition and the presence of impurities, survey spectra of samples were taken in the range of binding energies of 0-1250 eV with an energy step of 1 eV, with a constant analyzer transmittance HV = 50.

To determine the quantitative chemical composition and electronic states of individual elements, the precision spectra of the main photoelectron lines of individual elements were taken with a binding energy step of 0.1 eV, with a constant transmission energy of the analyzer HV = 25. The spectra were excavated to averag the noise and increase accuracy. The Cls line carbon was used as the calibration standard, the binding energy of which was taken equal to 284.8 eV.

Further processing of the spectra was carried out using special WinCalc software.

From the spectra of the Cr2p line characterizing the state of chromium on the surface (drawing), it can be seen that chromium is represented mainly by two states. The low-energy state with a binding energy of the Cr2p line equal to 576.9-577.2 is referred to in the literature as chromium bound to oxygen. A state with a binding energy of 578.9-579.4 relates to chromium bound to fluorine. The position and intensity of these lines make it possible to estimate the ratio 0: Cr and F: Cr on the surface of oxide and fluorinated catalysts (drawing and table 1).

The catalytic activity of the catalyst samples is determined on a flow-through installation with a fixed catalyst bed in the kinetic region (grain size 0.25-0.5 mm). The catalytic activity in the fluorination reaction of tetrachlorethylene in R-125 is measured under the following conditions: temperature 320 ° C, pressure 0.4 MPa, molar ratio HF / tetrachlorethylene 10/1 ÷ 20/1, contact time 0.2 ÷ 2 s. The activity of the catalyst in the fluorination reaction of tertachlorethylene is judged by the rate constant of the first order conversion. K = -ln (1-X) / τ, where X is the degree of conversion of tetrachlorethylene (mole fractions) at contact time τ.

The invention is illustrated by the following examples, which describe methods of activation of the catalyst according to the claimed activation method (examples 1, 2, 3, 4), as well as activation methods outside of the claimed intervals (comparative examples 5, 6, 7).

Physico-chemical and catalytic properties of the samples according to examples 1-7 are shown in table 2.

Example 1

Describes the preparation of a catalyst in which the content of aluminum (III) in terms of oxide is 5 wt.% Al ₂ O ₃ and the content of chromium (III) in terms of oxide is 95 wt.% Cr ₂ O ₃ .

Prepare 1 l of a solution of mixed chlorides of Al (III) and Cr (III) with a concentration of 3.0 g of Al ₂ O ₃ / l and 57 g of Cr ₂ O ₃ / l and 1.3 l of a solution of ammonia with a concentration of 6.5%.

200 ml / water is poured into a reactor with a capacity of 2.5-3 l, heated to 70 ± 5 ° C and, with stirring, a solution of mixed Al (III) and Cr (III) chlorides is simultaneously added at a rate of W = 20 ml / min and an ammonia solution at a rate that provides a constant pH of 7.0 ± 0.2. At the end of the precipitation, the precipitate is allowed to age at a temperature and a precipitation pH of 1 h, then it is filtered and washed with water until there are no Cl ^- ions in the washing liquid (qualitative reaction with AgCl) and dried. The dried precipitate is ground to a powder with a grain size <0.1 mm. A 0.5% solution of polyethylene oxide (PEO) is added to the powder in an amount providing a paste moisture of 45%, mixed until a plastic paste is formed, and extruded into cylindrical granules with a diameter of 5 mm.

The obtained catalyst granules are activated as follows.

It is dried in air at 70-250 ° C and atmospheric pressure for at least 5 hours (stage I activation).

The dried granules are calcined in a stream of nitrogen at 470-480 ° C and atmospheric pressure. The water content in the product is 2.5-3.5 wt.%, The specific surface area of the product is not less than 200 m ² / g (stage II activation).

At stage III of activation, the sample is calcined in an air stream at a temperature of 290-340 ° C and atmospheric pressure for 4 hours. The specific surface area of the product is at least 150 m ² / g, and the atomic O / Cr ratio on the surface is 1.8-2.0.

Next, the catalyst is subjected to fluorination activation in a gaseous mixture of N ₂ + HF under the following conditions:

Stage IV - calcination in a gas mixture of 15-25 vol.% HF + 85-75 vol.% N ₂ at a temperature of 125 ± 5 ° C and a pressure of 0.1 ± 0.02 MPa. preferably 20 vol.% HF, 80 vol.% N ₂ .

Stage V — temperature increase from 125 ± 5 ° С to 340 ± 5 ° С in step mode with a step of 20 ÷ 25 ° С and holding at each stage for 15-20 minutes in a gas mixture of 20 vol.% HF + 80 vol. % N ₂ at a pressure of 0.1 ± 0.02 MPa.

Stage VI - an increase in the concentration of hydrogen fluoride in the gas mixture of HF-N ₂ from 20 to 100 vol.% HF in step mode with a step of 20 vol.% HF and exposure at each stage for 15-20 minutes at a temperature of 350 ± 5 ° C and pressure 0.1 ± 0.02 MPa.

Stage VII - an increase in temperature to 375 ± 5 ° C and, in stepwise mode, an increase in pressure HF from 0.1 to 0.4 ± 0.02 MPa in increments of 0.1 MPa with holding at each stage for 15-20 minutes.

The fluorinated catalyst has a specific surface area of 60 m ² / g (table 2). The atomic ratio of fluorine and oxygen to chromium calculated from the XPS data on the sample surface is F / Cr = 1.3, O / Cr = 1.5. This indicates the presence on the surface of the sample of oxyfluoride with the general formula CrO _1.5 F ₁₃

The catalyst was tested in the fluorination reaction of tetrachlorethylene at a molar ratio of HF / tetrachlorethylene of 11/1, pressure Р = 0.4 MPa, Т = 280-370 ° С, contact time 0.58-2.51 s. The properties of the catalyst and the results of the activity test are shown in table 2. After fluorinating activation, the specific surface area is 60 m ² / g. The atomic ratio O / Cr = 1.5 / 1, F / Cr = 1.3 / 1. The activity of the catalyst, expressed as the rate constant of the consumption of tetrachlorethylene of the first order, at a temperature of 320 ° C is 1.6 s ^-1 . The selectivity by the sum (R-125 + intermediate products) under the conditions of the activity test is 96.9-100 mol.%. R-115 formation was not detected even at 100% tetrachlorethylene conversion.

Example 2

Similar to example 1, characterized in that the catalyst includes chromium (III) compounds, the amount of which in terms of Cr ₂ O ₃ is 91 wt.%, And aluminum (III) compounds, the amount of which in terms of Al ₂ O ₃ is 8 wt. wt.%, as additional compounds contains, wt.%: 0.3 Fe ₂ O ₃ , 0.2 MgO, 0.2 ZnO, 0.2 Co ₂ O ₃ , 0.1 NiO.

After fluorinating activation, the specific surface area is 62 m ² / g. The atomic ratio O / Cr = 0.7 / l, F / Cr = 2.0 / 1. The activity of the catalyst at 320 ° C, expressed as a rate constant for the consumption of first order tetrachlorethylene, is 1.5 s ¹ .

Example 3

Similar to example 1, characterized in that the catalyst includes chromium (III) compounds, the amount of which in terms of Cr ₂ O ₃ is 97 wt.%, And aluminum (III) compounds, the amount of which in terms of Al ₂ O ₃ is 2.8 wt. %, as an additional compound contains Fe ₂ O ₃ 0.2 wt%.

After fluorinating activation, the specific surface area is 62 m ² / g. The atomic ratio O / Cr = 0.8 / 1, F / Cr = 2.8 / 1. The constant of the reaction rate of fluorination of perchlorethylene at 320 ° C is 1.5 s ^-1 .

Example 4

Similar to example 1, characterized in that the catalyst comprises chromium (III) compounds, the amount of which in terms of Cr ₂ O ₃ is 87 wt.%, And aluminum (III) compounds, the amount of which in terms of Al ₂ O ₃ is 13 wt. .%.

The activation stage is carried out analogously to example 1.

After fluorinating activation, the specific surface area is 64 m ² / g. The atomic ratio O / Cr = 1.0 / 1.0, F / Cr = 1.7 / 1. The constant of the reaction rate of fluorination of perchlorethylene at 320 ° C is 1.6 s ^-1 .

Example 5 (comparative)

Similar to example 1, it differs in that stage II is excluded from the set of successive activation stages — calcination in a stream of nitrogen at 470 ° C. After drying at 150 ° C in air, the sample is calcined in a stream of air at 330 ° C, then stage IV-VII of activation is carried out, similarly to example 1. After the specified calcination conditions in air, a significant amount of residual water is retained in the sample (~ 9 wt%) , which worsens operating conditions due to the corrosion activity of wet mixtures of HF + N ₂ . In addition, incomplete dehydration causes a relatively low specific surface area after calcination in air S _beats = 150-160 m ² / g, as well as a lower surface after the stages of fluorinating activation (S _beats = 40 m ² / g) and reduced catalytic activity at 320 ° C (K = 1.2 s ^-1 ) due to the possible blocking of active centers by water molecules.

Example 6 (comparative)

Similar to example 1, characterized in that the calcination in a stream of air is carried out at a higher temperature (450 ° C). This leads to a more complete dehydration of hydroxide phases (residual water content of 0.02 wt.%), But highly exothermic crystallization occurs with the formation of coarse α-Cr ₂ O ₃ (S _beats ~ 50 m ² / g). Fluorination is difficult for such a product, and after the stages of fluorinating activation the ratio is F / Cr = 1.0, and O / Cr = 1.7. Fluorinated catalysts exhibit a low specific surface area (25 m ² / g) and low catalytic activity at 320 ° C (K = 0.8 s ^-1 ).

Example 7. (comparative)

Similar to example 1, it differs in that stage III calcination in an air stream at 290-340 ° C is excluded from the set of successive activation stages. After calcining in nitrogen at 470 ° С, the sample has a surface of 250 m ² / g, a residual water content of 2.5 wt%, and an O / Cr ratio of 1.5, which indicates the formation of a stoichiometric Cr ₂ O ₃ oxide. Then it is subjected to the stages of fluorinating activation (IV-VII) as in Example 1. After stage VII, the sample has S _beats = 55 m ² / g, ratio O: Cr = 1.5, F: Cr = 1.1, activity K = 1.1 s ^-1 .

The lower activity compared to the sample of example 1 can be explained by the fact that in the absence of a low-temperature calcination step in an oxidizing medium, easily movable non-stoichiometric oxygen is formed, which upon fluorination activation gives particles of labile F ^- participating in Cl-F exchange during catalytic fluorination of chlorine-containing hydrocarbons .

Claims (8)

1. The activation method of the catalyst for producing fluorine-containing hydrocarbons by gas-phase hydrofluorination of halogenated hydrocarbons containing chromium (III) compounds, 98-85 wt. %, compounds of aluminum (III), 2-15 wt. %, metal compounds selected from the group comprising either iron, or nickel, or cobalt, or zinc, or magnesium, or any mixture thereof in an amount of 0.1-1.5 wt. % (in terms of oxides), characterized in that the activation process is carried out in seven stages, which include: drying the catalyst in an air stream; calcining the catalyst in an inert gas stream; calcining the catalyst in an air stream; calcining the catalyst in a gas mixture of hydrogen fluoride and nitrogen; stepwise increase in temperature; stepwise increase in the concentration of hydrogen fluoride in the HF-N ₂ gas mixture; increase in temperature to 370-380 ° C and stepwise increase in pressure HF. 2. The method according to p. 1, characterized in that the drying of the catalyst granules is carried out in a stream of air at a temperature of 70-200 ° C, preferably 110-150 ° C, and atmospheric pressure. 3. The method according to p. 1, characterized in that the calcination of the catalyst in a stream of inert gas, such as nitrogen, argon, helium, is carried out at a temperature of 450-500 ° C, preferably 470-480 ° C, and atmospheric pressure, the water content in the product is 2.5-3.5 wt. %, the specific surface area of the product is not less than 200 m ² / g 4. The method according to p. 1, characterized in that the calcination of the catalyst in a stream of air is carried out at a temperature of 290-340 ° C, preferably 300-330 ° C, and atmospheric pressure, the specific surface area of the product is at least 150 m ² / g, the atomic O / Cr ratio on the surface is 1.8–2.0. 5. The method according to p. 1, characterized in that the calcination of the catalyst is carried out in a gas mixture of 15-25 vol. % hydrogen fluoride and 85-75 vol. % nitrogen, preferably 20 vol. % HF, 80 vol. % N ₂ , at a temperature of 120-130 ° C and a pressure of 0.1 ± 0.02 MPa. 6. The method according to p. 1, characterized in that they carry out a stepwise increase in temperature from 120-130 ° C to 330-350 ° C, preferably up to 340-350 ° C. with a step of 20 ÷ 25 ° C and exposure at each stage for 15-20 minutes in a gas mixture of 20 vol. % HF, 80 vol. % N ₂ at a pressure of 0.1 ± 0.02 MPa. 7. The method according to p. 1, characterized in that they carry out a stepwise increase in the concentration of hydrogen fluoride in the HF-N ₂ gas mixture from 20 to 100 vol. % HF in increments of 20 vol. % HF and exposure at each stage for 15-20 minutes at a temperature of 340-360 ° C, preferably 340-350 ° C, and a pressure of 0.1 ± 0.02 MPa. 8. The method according to p. 1, characterized in that they carry out an increase in temperature to 370-380 ° C and a stepwise increase in pressure HF from 0.1 to 0.4 MPa in increments of 0.1 MPa with exposure at each stage for 15-20 minutes, while the specific surface area of the catalyst is at least 60 m ² / g, the atomic ratio of oxygen to chromium on the surface of the catalyst is O / Cr = 0.4-1.5, the atomic ratio of fluorine to chromium F / Cr = 1.3-2.8.

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