SU565909A1 - Method of obtaining tetrafluorethylene - Google Patents

Description

(54) METHOD FOR OBTAINING TETRAFTORETHYLENE

one

This invention relates to a process for the preparation of tetrifuoroethylene, which is widely used for the preparation of tetrafluoroethyshene.

A method is known for producing tetrafgorethylene by pyrolysis of monochlorodifluoromethane, according to which pyrolysis is carried out by contacting mo} ylchlorodifluoromethane with one or more molten lithium, sodium and potassium metal carbonates or with a molten mixture of one or more of the above carbonates and one or more chlorides of the aforementioned metals at 500 8OO ° s Ij Without diluting the starting monochlorodifluoromethane with gases that are inert with respect to this system, the conversion of the latter 74% yield of tetrafluoroethylene using this method is 59%

Another known method for producing tetrafluoroethylene by pyrolysis of monochlorodifluoromethane is characterized by the fact that pyrolysis is carried out by contacting mon chlorofluoromethane with a molten system containing the metal oxide and the chloride of the said metal and, at least,

one chloride of alkali metal G2. It is preferred to use a molten system in which sodium chloride and calcium chloride are present in a weight ratio equivalent to their eutectic mixture, and the proportion of calcium oxide is 515 mol. %

In this capable molten system temperature of 600-800 ° C, the yield of tetrafluoroethene is 75% with a monochlorodifluoromethane conversion of 64%.

However, the reactivity of the molten system with respect to hydrogen chloride and hydrogen fluoride released by pyrolysis changes the composition of the melt, enriching it with salts of chlorides and metal fluorides, which leads to unstable operation of the system and the need for its frequent replacement. In addition, this method gives a small yield of the target product.

. In order to improve the technological process and increase its productivity, it is suggested, when preparing tetrafluoroethylene by pyrolysis of monochlorodiphthomethane at 60 ° -800 ° C, to use a mixture of lithium fluoride and potassium eutectic composition as a molten substrate.

Example, In a steel reactor,.

a vertical cylinder with a vertical diameter of 22 mm, a height of 25O mm is loaded with 7O g of a mixture of lithium and potassium fluorides of a eutectic composition (5O, 5 wt.% Lif and 49.5 wt.% RC. The contents of the reactor are heated to 750 C and the initial monochlorine the difluoromethane is bubbled into the reactor at a rate of 28 l / h. The depth of the bubbler immersion into the lithium and potassium fluoride riser is 6O mm.

The gaseous pyrolysis products leaving the reactor are washed with water, then with a 10% sodium carbonate solution. The pyrolysis products that have been washed to neutrality are collected in a gasometer and analyzed by chromatography. The composition of the neutral products of pyrolysis, mol. %: tetrafluoroethane-49,571, trifluoromethane 6, 154; hexafluoropropylene - 1,973; difto methane - O, 017; trifluorochloroetchgen -1 DOH difluorodichloromethane — 0.224; monochlorodifluoromethane - 35,299, other impurities 5, 191.

The conversion of the starting monochlorodifluoromethane was 79%, the yield of tetrafluoroethylene was 74.5%.

Example 2. Under the same conditions at a rate of 4O l / h monochlorodifluoromethane given for pyrolysis, the conversion was 63.7% with a tetrafluoroethylene yield of 85.4%. The composition of neutral pyrolysis gases, mol. %: tetrafluoroethylene - 37.052; trifluorometak - 4.712; hexafluoropropylene, 4; trifluorochloroethene — 0.48; dichlorodifluoromethane - 0, O59; monochlorodifluoromethane - 50,106; other impurities - 1,937.

The proposed method makes it possible to improve the technology for producing tetrafluoroethylene, namely, to exclude the replacement of the melt during the pyrolysis process; provide

the stability of the composition of the resulting pyrolysis product, due to the stability of the composition of the molten mixture; increase vco tetrafluoroethylene by about 10%,

Ingenuity formula

The method of producing tetrafluoroethiene by pyrolysis of monochpordifluoromethane at 6006OO C in a molten coolant based on alkali metal halides, characterized in that, in order to increase the productivity of the process, a mixture of lithium and potassium fluorides of eutectic composition is used as the molten coolant.

Sources of information taken into account in the examination:

1.Patent UK No. 971995, cl. C 2 C, publ. 1964.

2.Patent UK No. 983222, No. Cl, C 2 C, publ. 1965 (prototype).