RU2243961C1 - Method for preparing 1,1,1,2-tetrafluoroethane - Google Patents

Abstract

FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention relates to a method for preparing fluoro-organic compounds. Method involves the gas-phase catalytic hydrofluorination of trifluoroethylene at increased temperature in the presence of the chrome-magnesium-fluoride catalyst comprising 8-24 wt.-% of trivalent chrome fluoride uniformly distributed in magnesium fluoride with the dispersity index from 0.125 to 0.315 mm. The process is carried out at temperature 140-190C and time contact for 4.5 s. Method provides the high yield of 1,1,1,2-tetrafluoroethane with selectivity index up to 99.9%.

EFFECT: improved preparing method.

2 tbl, 7 ex

Description

The invention relates to the field of chemical technology of fluorine compounds, and in particular to a method for producing 1,1,1,2-tetrafluoroethane.

1,1,1,2-tetrafluoroethane (Freon 134a), which has zero ozone depletion potential (ODP = 0), is one of the substitutes for the main ozone-hazardous coolant difluorodichloromethane in air conditioners and refrigeration units as the closest in physicochemical and thermodynamic properties, and also finds application as a propellant and blowing agent for the production of foams. In addition, HFC 134a is widely used in various refrigerant compositions.

One of the main methods for producing 1,1,1,2-tetrafluoroethane is gas phase catalytic hydrofluorination of halogen-containing olefins.

Known industrial two-stage "Method for producing 1,1,1,2-tetrafluoroethane" (application EP No. 449614, C 07 C 19/08, publ. 02.10.1991), including the interaction of trichlorethylene and hydrogen fluoride in the first reaction zone and the interaction formed 1,1,1-trifluorochloroethane with hydrogen fluoride in the second reaction zone. However, this process is accompanied by the receipt of significant quantities of hydrochloric acid, which requires further processing or sale, and is also quite difficult for industrial implementation because of the need to organize large recirculation flows and the use of large volume apparatuses due to the low yield at the fluorination stage 1,1,1- trifluorochloroethane, which is determined by the thermodynamics of the process.

The known "Method for producing high-purity partially fluorinated ethanes" corresponding to the general formula CF ₃ CHXY, where X-H or F, a Y - H, F, Cl, Br or I (German application No. 3009760, C 07 C 19/08, publ. 24.09.1981), which includes the interaction of the corresponding olefin of the formula CF ₂ = CXY with hydrogen fluoride at a temperature of from 20 to 200 ° C in the presence of chromium oxyfluoride treated with hydrogen fluoride as a catalyst. When using HF and C ₂ HF ₃ as starting reagents at a molar ratio of 1.45: 1 and a temperature of 124-143 ° C, the yield of 1,1,1,2-tetrafluoroethane is 97.6%. However, 1,1,1,2-tetrafluoroethane was obtained in the indicated yield after passing 2.87 mol of C ₂ HF ₃ for 3 hours, i.e. with a high average contact time (~ 28 sec). In addition, the use of chromium oxyfluoride is undesirable, as in the process of its activation by hydrogen fluoride, water is released, which leads to rapid corrosion of expensive equipment.

The closest in technical essence is the application of the UK No. 20044539, C 07 C 17/00, publ. 04/04/1979 "Obtaining 1,1,1,2-tetrafluoroethane in the gas phase", which includes the interaction of trifluoroethylene with hydrogen fluoride in the gas phase at an elevated temperature in the presence of a hydrofluorination catalyst. The synthesis of 1,1,1,2-tetrafluoroethane is carried out at a molar ratio of HF: C ₂ HF ₃ = (1-2): 1, a temperature of 200-500 ° C and a contact time of 1-15 seconds, the preferred catalyst is chromium oxide. The maximum yield of 1,1,1,2-tetrafluoroethane given in this application is 97.8% with a molar ratio of the starting reagents of 1.43: 1, a temperature of 350 ° C and a contact time of 14 seconds. However, the activation of chromium oxide as a catalyst, as well as chromium oxyfluoride, proceeds with the formation of a large amount of water, and the high temperature of the process reduces the duration of the catalyst and contributes to an increase in the rate of side reactions leading to a decrease in the selectivity of the process.

Therefore, to organize the industrial production of Freon 134a with a high yield of the target product at low operating temperatures, which allows to increase the life of the catalyst with high selectivity of the process, and a short contact time, which contributes to an increase in reactor productivity, it is necessary to use a more active catalyst.

Known chrome-magnesium fluoride catalyst, which is used in various processes for producing fluorinated compounds by gas-phase hydrofluorination (RF patent No. 2141467 C1, C 07 C 17/20, publ. 11/20/1999, "Method for producing pentafluoroethane"; RF patent No. 2134680 C 1, C 07 From 17/087, published on 08.20.1999, "Method for the production of 2-hydroheptafluoropropane or a mixture of 2-hydroheptafluoropropane with octafluoropropane").

However, a study of its activity in the process of hydrofluorination of trifluoroethylene and an approximate calculation of the thermal regime showed that the high catalytic ability of the chromium magnesium fluoride catalyst in this process leads to a high reaction rate proceeding with a high heat release (~ 160 kJ / mol), and the catalyst is heated to temperatures in which side reactions begin to occur that reduce the yield of 1,1,1,2-tetrafluoroethane and the selectivity of the process while reducing the catalyst life. Overheating of the reactor can be avoided by using a chromium magnesium fluoride catalyst with a dispersion of 0.125 to 0.315 mm, the fractional composition of which was chosen in such a way as to reduce the influence of factors leading to non-ideal fluidization.

The objective of the present invention is to improve the method of producing 1,1,1,2-tetrafluoroethane by gas-phase catalytic hydrofluorination of trifluoroethylene, providing a high yield of the target product and high selectivity of the process.

The essence of the present invention lies in the fact that 1,1,1,2-tetrafluoroethane is produced by gas-phase hydrofluorination of trifluoroethylene using a chromium magnesium fluoride catalyst containing 8-24% by weight. trivalent chromium fluoride uniformly distributed in magnesium fluoride, with a dispersion of from 0.125 to 0.315 mm, and the process is conducted at a temperature of 140-190 ° C and a contact time of at least 4.5 seconds.

The method of obtaining 1,1,1,2-tetrafluoroethane is as follows.

Example 1

The hydrofluorination experiment was carried out in a nickel fluidized bed reactor of chromium magnesium fluoride catalyst.

The volume of the reactor was 1 liter, the inner diameter was 0.036 m. The reactor was equipped with electric heating, a pocket for placing a thermocouple, which allows temperature measurements along the entire height of the reaction zone, and a gas distribution device with a specially made packing of nickel wire, which provides a high degree of uniformity of the fluidized bed. Chromium magnesium fluoride catalyst, obtained by RF patent No. 20055539 (B 01 J 37/04, publ. 15.01.1994) and crushed in such a way that the composition of the particles was from 0.125 to 0.315 mm, was loaded into the reactor.

Dosing of hydrogen fluoride and trifluoroethylene was carried out directly through nickel capillaries into an electric coil heater installed in front of the reactor. In the evaporator, the mixture of the starting components was heated to the synthesis temperature and fed to the reactor. From the reactor, the reaction gas was passed through containers filled with water, potassium alkali solution, a desiccant with NaA zeolite and condensed in a trap cooled with dry ice, or collected in a gas meter.

The analysis of the organic part of the synthesis products was carried out by the gas chromatographic method, as well as by fractionation, followed by the study of fractions by IR and chromatography-mass spectrometry.

At a molar ratio of NG: C ₂ HF ₃ = 1.3: 1, a temperature of 140 ° C and a contact time of 11.1 sec, the yield of 1,1,1,2-tetrafluoroethane was 97.9% with a selectivity of 99.9%.

Examples 2-5.

The experiments were carried out on the setup described in example 1.

The experimental results are summarized in table 1.

Table 1 No. Fractional composition of the catalyst,
mm Temperature ° C Contact time, sec The molar ratio of HF: C ₂ HF ₃ The output of Freon 134a,% Freon 134a selectivity,% 1 0.125-0.315 140 11.1 1.3: 1 97.9 99.9 2 0.125-0.315 160 4,5 1.3: 1 96.7 99.9 3 0.125-0.315 160 7.8 1.3: 1 98.3 99.9 4 0.125-0.315 160 10.6 1.3: 1 99.3 99.9 5 0.125-0.315 190 8.5 1.3: 1 99.9 99.9

To compare the process of hydrofluorination of trifluoroethylene on a chromium magnesium fluoride catalyst used in industry with a chromium magnesium fluoride catalyst with the dispersion indicated above, the experiments described in Examples 6 and 7 were carried out under conditions similar to those shown in table 1.

Examples 6.7.

The experiments were carried out on the setup described in example 1 in a nickel reactor with a fixed catalyst bed of 0.25 L. Chromium magnesium fluoride catalyst was loaded into the reactor in the form of granules with a diameter of 5-6 mm and a height of 6-7 mm.

The experimental results are shown in table 2.

table 2 No. Fractional composition of the catalyst, mm The initial temperature in the reactor, ° C The average temperature in the reactor, ° C Contact time, sec The output of Freon 134a,% Freon 134a selectivity,% 6 (5-6) × (6-7) 150 320 9.3 98.2 98.3 7 (5-6) × (6-7) 160 335 9.2 98.0 98.1

From the results of experiments 6 and 7, it is seen that when using a chromium magnesium fluoride catalyst with the indicated particle size, it is not possible to keep the temperature in a low range, which leads to an increase in the formation of by-products.

Thus, the dispersion of the catalyst is an important factor improving the characteristics of the process, and a high yield of Freon 134a with high selectivity (up to 99.9%) can be achieved at low temperatures and contact times.

The proposed method for producing 1,1,1,2-tetrafluoroethane provides a high yield of the target product in the process of gas-phase catalytic hydrofluorination of trifluoroethylene in the presence of chromium magnesium fluoride catalyst with a selectivity of up to 99.9%.

Claims (1)

A method of producing 1,1,1,2-tetrafluoroethane by gas-phase catalytic hydrofluorination of trifluoroethylene at elevated temperature and in the presence of a catalyst, characterized in that the catalyst is a chromium magnesium fluoride catalyst containing 8-24 wt.% Trivalent chromium fluoride uniformly distributed in fluoride magnesium, with a dispersion from 0.125 to 0.315 mm and the process is conducted at a temperature of 140-190 ° C and a contact time of at least 4.5 s.