RU2135451C1 - Method of preparing perfluoroalkanes - Google Patents

Abstract

FIELD: technology of preparing perfluoroalkanes, more particularly hexafluoroethane, octafluoropropane, decafluorobutane used as dielectrics, coolants and compositions in film- forming and other compositions. SUBSTANCE: perfluoroalkanes are prepared by fluorination of C₂-C₄ perfluoroalkanes in homogeneous phase in low molecular perfluorinated solvent at concentration of 1-5% of compound being fluorinated. Process temperature varies from minus 35 to minus 15 C. Yield of desired products is 99-99.9%. EFFECT: simplified process, and high purity and yield of the desired product. 2 cl, 3 ex, 2 tbl

Description

 The invention relates to a technology for producing perfluoroalkanes, in particular hexafluoroethane, octafluoropropane, decafluorobutane, used as dielectrics, refrigerants, components in foaming compositions and laser working media, a working fluid in plasma-chemical etching of semiconductor materials.

 Of the methods for producing perfluoroalkanes (PFA), the following are known: pyrolysis of organofluorine feedstocks, gas-phase fluorination of hydrocarbons and their halogen-substituted ones. The main disadvantage of these methods is the large number of by-products requiring expensive purification or destruction (US patent 3222406, 1965, US patent 4377715, 1983).

 With virtually no impurities, PFAs are prepared either by fluorination with elemental fluorine or cobalt trifluoride (Japanese Patent Applications 90-131438 and 85-81134, auth. St. USSR 1630241, 1984). To control the heat release, the processes are carried out in a diluent medium - tetrafluorodichloroethane (Japanese application laid out 90-131438) or in two stages with dilution of gesafluoropropylene with octafluoropropane at the start-up stage (ed. St. USSR 1630241).

The prototype adopted a method of producing one of perfluoroalkanes - hexafluoroethane, which consists in fluorinating tetrafluoroethylene with elemental fluorine in a diluent medium - tetrafluorodichloroethane taken in an amount of 10 - 100 mol per 1 mol of tetrafluoroethylene, the ratio of fluorine to tetrafluoroethylene 1.2 / 1, the process temperature - 80, 2 ^o C, the yield of hexafluoroethane - 87.8% (laid. Application of Japan 90-131438).

The disadvantages of this method include:
1. The method was developed to produce one perfluoroalkane - hexafluoroethane and was carried out in an ozone-active diluent.

 2. The yield of the target product is not high enough.

The problem solved by this invention is to develop a universal method of fluorination of perfluoroalkenes with a carbon chain C ₂ -C ₄ that optimally combines the thermal and material balances of the process and is suitable for industrial implementation in terms of productivity, simplicity of hardware design, as well as the purity and yield of target perfluoroalkanes.

The technical essence of the invention consists in the following: the process is conducted in a homogeneous phase in the environment of perfluorocarbon, which is a solvent for both fluorine and fluorinated perfluoroalkene, which together with the thermophysical properties of perfluorocarbons provides intense heat and mass transfer, which prevents the destruction of the carbon-carbon bond, while the concentration fluorinated compounds should not exceed 5 wt. %; process temperature - minus 35 - minus 15 ^o C; To prevent the transition of carbon-containing components into the gas phase, the process pressure is maintained not lower than the saturated vapor pressure of the solvent at the process temperature. Subject to the specified conditions, the yield is 99-99.9%.

Deviations from the technological regime lead to the following consequences:
when the temperature rises above minus 10 ^o C, as well as perfluoroalkene concentrations above 5%, the process becomes unstable, often accompanied by small pop explosions, and sometimes an explosion of the entire system; at temperatures above -15 ^o C decreases the yield of the target product;
at temperatures below minus 35 ^o C and perfluoroalkene concentrations below 1%, the process speed slows down, which leads to a decrease in the productivity of the process.

 Of the perfluorocarbon solvents used, the desired products are preferred, which greatly simplifies the process by eliminating the separation step.

 Example 1

In a reactor made of steel 12X18H10T with a diameter of 45 mm and a height of 250 mm, equipped with a jacket, stirrer, siphons for supplying fluorine and fluorinated perfluoroalkene, shutoff valves and a manometer, 200 ml of perfluorinated solvent are loaded and the reactor is cooled to a temperature of minus 30 ^o C, after which the initial perfluoroalkene, and then fluorine with a slight excess from stoichiometry (0.1 - 3%). After completion of the reaction, the reaction mass is neutralized by passing through a filter with CPI (a chemical lime scavenger) and analyzed by GLC. The results are presented in table. 1.

From the data table. Figure 1 shows that with an increase in the perfluoroalkene concentration of more than 5%, the fluorination process becomes unstable and is accompanied by popping explosions. Destructive fluorination products appear in the reaction mass — in op. 4 and 5 - CF ₄ , in op. 9 and 10 - CF ₄ C ₂ F ₆ , soot was detected on the inner walls of the reactor and siphons.

 Example 2

Fluorine and perfluoroalkene are simultaneously fed into the reactor described in Example 1 and filled with a solvent at a rate of 40.5 - 42 ml / min and 40 ml / min, respectively, and the reaction products are transferred to a cooled to a temperature of minus 20 - minus 30 ^o C collection, then to the filter with HPI. The products after neutralization are analyzed by GLC. If a solvent other than the target product is used, the products are subjected to rectification. Technological parameters and the results are shown in table. 2.

 From the table. Figure 2 shows that when the process is carried out within the indicated technological limits, a high yield of the target products is achieved, and the process itself proceeds calmly, without explosions.

 Example 3

A reactor made of steel 12X18H10T with a diameter of 0.4 m and a height of 1.9 m, equipped with a cooling jacket and a coil, two bubblers and an overflow fitting in the upper part, is loaded with cooling to -30 ^o C 120 kg C ₃ F ₈ . Fluorine is supplied through bubblers at a rate of 0.3-1.5 m ³ / h with an excess of 0.5% and hexafluoropropene at a rate of 0.3-0.5 m ³ / h. The reaction products through the overflow fitting enter the collector, cooled to minus 30-20 ^o C, then to the cartridge with CPI. The yield of the target product is 99.5%. Productivity is up to 15 kg / h.

 As can be seen from the given experimental material, the proposed organization of the technological process allows us to solve the problems of heat transfer and to obtain a number of perfluoroalkanes using the same technology with a high yield and productivity acceptable for industrial production. In addition, in this process, a slight excess of fluorine is required - 0.1-3% (in the prototype - 20%), which improves the technical and economic indicators of the process.

Sources of information
1. Pat. US 3222406, 260-653, 1965.

 2. Pat. US 4377715, 570-123, 1983.

 3. Lay out. Japan, 90-131438, C 07 C 19/08, 1990.

 4. Layout. Japan, 85-81134, C 07 C 19/08, 1985.

 5. Auto USSR 1630241, C 07 C 19/08, prior. 1984.

Claims (2)

1. The method of producing perfluorinated alkanes by fluorination of perfluoroalkenes with elemental fluorine in a fluorine-containing compound, characterized in that the process is conducted in a medium of low molecular weight perfluorinated solvent of the reaction components at a temperature of minus 15 - minus 35 ^o C and a concentration of the starting perfluoroalkene of 1-5 wt.%. 2. The method according to claim 1, characterized in that perfluoroalkenes with a carbon chain C ₂ - C ₄ are taken as the starting perfluoroalkene.

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