DE1228601B - Process for the production of tetrafluoroethylene from chlorodifluoromethane - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

BtSUOTHiK

OF THE GERMAN PATENT OFFICE

Int. CI .:

C07c

German KI .: 12 ο -19/02

Number: 1228 601

File number: D 44739IV b / 12 ο

Filing date: June 22, 1964

Opening day: November 17, 1966

As is well known, tetrafluoroethylene is the starting product for the manufacture of heat and chemical resistant products Polymers.

In known processes for the production of tetrafluoroethylene, C ₂ F ₄ , from chlorodifluoromethane in a purely pyrolytic way (see JD Park et al., Ind. Engng. Chem., 39 [1947], p. 354), good C ₂ F ₄ conditions are achieved of 90 to 94% achieved only with a relatively low chlorodifluoromethane conversion, which is around 25 to 30%, while an increase in conversion by increasing the reaction temperature or the length of time in the reaction _{zone leads to reduced C 2} F ₄ yields due to the increased formation of by-products with relative higher boiling points. At elevated temperatures, significant amounts of hydrogen fluoride and other aggressive gases are produced, so that noble metals such as platinum and / or gold have to be used to manufacture the reaction vessels.

The noticeable elimination of fluorinated water and more prominent secondary reactions also lead, in particular, to olefinic ones. By-products such as trifluoroethylene (bp -51 ° C), whose boiling points are _{not very different from that of C 2} F ₄ (bp -76 ° C). Since these cannot be completely separated from the C ₂ F ₄ , copolymers with lower heat resistance are formed during the polymerization.

When investigating the effectiveness of catalysts, FJ Norton (Refrigerating Engng., May 1957, pp. 33, 34 and 61 to 63) found that metal oxides such as CuO, Cu ₂ O and Fe ₂ O ₃ increase the rate of the reaction, but the Reduce the C ₂ F ₄ yield, with large amounts of by-products such as CO, CO ₂ , HF and CF ₄ being formed. Downing et al. (US Pat. No. 2551573) found that heavy metal or alkaline earth metal halides increase the elimination of fluorine and thus influence the reaction in an undesirable manner.

From the Swiss patent specification 350 643 a process is known in which mixtures or alloys of silicon or ferrosilicon are used as a catalyst or HCl acceptor. and copper can be used, the copper itself not acting as an HCl acceptor, but only stimulating the ferrosilicon used, which would react even without the addition of copper. In this process, temperatures above 250 ^° C. and reaction times of the order of magnitude of 1 to 10 minutes are used, and noticeable amounts of carbon-containing residues and products of mixed chlorine and fluorine elimination are formed. The space-time yields that can then be achieved are relatively unsatisfactory.

Process for the production of
Tetrafluoroethylene from chlorodifluoromethane

Applicant:

Daikin Kogyo Co., Ltd., Osaka (Japan)

Representative:

Dipl.-Ing. R. Beetz and Dipl.-Ing. K. Lamprecht,

Patent Attorneys, Munich 22, Steinsdorfstr. 10

Named as inventor:
Hiroyuki Wada, Osaka (Japan)

Claimed priority:

Japan June 25, 1963 (32 777)

Processes are also specified in which copper, iron, nickel, Manganese and molybdenum are used, their effectiveness, however, rapidly through a coating should decrease with solid reaction products.

The inventive method for the preparation of tetrafluoroethylene from chlorodifluoromethane by catalytic elimination of hydrogen chloride by thermal means in the presence of copper and Condensation of the products obtained is characterized in that the elimination of hydrogen chloride is carried out with a residence time of 0.01 and 10 seconds and temperatures of 400 to 1100 ° C in the presence of copper (I) chloride as a catalyst.

This process according to the invention can be carried out on an industrial scale. In the Carrying out the reaction in a tubular reaction vessel can be used in the form of copper Use turnings, wire netting or fabrics or also in ribbon or grain form, with granules with a diameter of 5 to 10 mm are preferably used. The copper (I) chloride can be used in Used in the form of powder packed together with copper wire mesh or cloth and / or copper grains or as a coating (in molten form) on the surface of filler materials inside the reaction tube. However, good results can be achieved in a short period of time Initiation of the reaction can be achieved with copper.

609 727/433

According to the invention, the following reaction conditions are provided:

The reaction temperature is between 400 and 1100 ° C., preferably between 700 and 900 ° C. At temperatures below this range, the reaction times required for the decomposition reaction are hardly economically viable for carrying out on an industrial scale, and above that, large amounts of by-products are formed, both of which are undesirable. The residence time of CHClF ₂ in the reaction zone is 0.01 to 10 seconds, preferably 0.1 to 0.5 seconds. With shorter residence times, the conversion is too low to be economical, and with longer residence times, large amounts of by-products are formed.

The yield increases with decreasing pressure; however, an absolute pressure of Ve up to 10 kg / cm ^{2 is} used, especially with regard to the equipment. Furthermore, if these conditions are observed, the CHClF _{2 is} preheated to a temperature of 350 to 600 ° C., as a result of which the concentration distribution in the tubular reaction vessel becomes more uniform. Gases such as nitrogen, carbon dioxide or water vapor can also be added.

As the reaction vessel, a tube type or fluidized bed type apparatus can be used does not need to be made of precious metal, but of some kind that is resistant to high temperatures Material. For example, copper can be used alone, or sheet copper can be used as the inner lining in one made from a nickel alloy commercially available under the name "Inconel" or apply nickel to the existing reaction vessel.

If a tube-type reaction vessel is used, the use of copper in the form of Chips, wire mesh or grains, as described above, due to its catalytic effectiveness and good thermal conductivity for favorable results.

The present invention can achieve the following advantages:

1. The percentage of conversion can be increased without reducing the yield of C ₀ F ₄ ; the conversion of CHClF ₁ is 65 to 70%, and the yield of C ₂ F ₄ is 95%.

The conversion of CHClF ₂ is even greater at the same temperatures and reaction times as in the conventional processes.

2. Despite the high conversion, only a very small amount of HF is observed; the education of HF is below 2%.

3. By-products, such as CHF-CF ₂ , which impair the stability of the polymer formed later, are hardly or not at all formed.

4. A reduction in the yield is not observed, even if a reaction vessel is used large diameter used for thermal decomposition. That is why it is a large-scale production easily and economically feasible.

5. The repair and maintenance of the reaction tube is much easier.

F i g. 1 shows the dependence of the conversion of CHClF ₂ on the reaction temperature when using copper grains as a catalyst according to Example 1 and

F i g. 2 the dependence of the yield of C ₂ F ₄ on the conversion of CHClF ₂ in the presence of ίο copper grains as a catalyst according to Example 1 and the effect of the presence of the catalyst.

example 1

HOg (12 m ³ ) metallic copper in grain form with a weight of 0.2 to 2.0 g per grain were placed in a copper tube with an inner diameter of 12 mm (the inside of a tube made of a nickel alloy available with the trade name "Inconel" is applied tightly) and the tube is heated to a desired temperature with an electric heating furnace. The useful length of the tube to be heated was 20 cm.

CHClF ₂ was introduced into the tube from a tank via an adjustable needle valve and a flow meter and thermally decomposed. The gas flowing out of the reaction tube was passed through a gas scrubber working with water and a drying tower with calcium chloride and then condensed in two receivers cooled with dry ice or liquid air, the non-condensable gases being collected in a gas collecting tube. The total acid, the chlorine and fluorine ions and the amount of the aqueous solution thus formed, the condensed liquid in the deep-frozen templates and the non-condensable gases were analyzed.

Example 2. ■

Experiments were carried out in the same way as in Example 1, but with copper (I) chloride (instead of copper) was brought into the pipe in powder form together with copper mesh.

At a reaction temperature of 800 ° C. and a residence time of 0.2 seconds, there was a conversion of 43%, a tetrafluoroethylene yield of 98% and 0.9% HF formation achieved.

Claims (3)

Patent claims: 1. Process for the production of tetrafluoroethylene from chlorofluoromethane by catalytic Elimination of hydrogen chloride by thermal means in the presence of copper and Condensation of the products obtained, characterized in that the Elimination of hydrogen chloride with a residence time of 0.01 to 10 seconds and temperatures carries out from 400 to 1100 ° C in the presence of copper (I) chloride as a catalyst. 2. The method according to claim 1, characterized in that the chloride fluoromethane heated to a temperature in the range of 700 to 900 ° C. 3. The method according to claim 1 or 2, characterized in that the reaction is carried out at a Carries out a residence time of 0.1 to 0.5 seconds. 1 sheet of drawings