DE1032239B - Process for the production of fluorocarbons - Google Patents

Description

GERMAN

Compounds that contain only carbon and fluorine, called fluorocarbons, have on many Areas of applied chemistry found considerable application. For example, the Fluorocarbons have been tried and tested as dielectrics, plastics, surfactants and the like. In particular, has polymeric tetrafluoroethylene in technology already enforced to a considerable extent. It has been found that fluorocarbons are economical Way can be produced by carbon and a fluoride of an element of main group V of the periodic table or sulfur at a temperature of at least 900 ° C in reaction brings.

For this purpose, the inorganic fluoride can be used in a vaporous state, if appropriate with an inert gas, ζ. B. nitrogen, pass over carbon, which is heated to at least 900 ° C. the The reaction temperature can be as high as can only be achieved in practice using the known methods can be. For example, the inorganic fluoride can arc with the carbon electrodes be brought into reaction, which is operated with either direct or alternating current, when the reaction temperature is estimated to be in the range of 2500 to 3500 and 4000 ° C. In fact, these high temperatures are preferably used because they lead to high yields of the lead extraordinarily valuable tetrafluoroethylene. The reaction can, however, also be carried out with simpler ones Means are obtained by z. B. the vaporized inorganic fluoride by a carbon containing pipe conducts, which suitably to 900 to 2000, preferably to at least 1000 ° C is heated. Another method is that the carbon arc in the liquid or immersed molten inorganic fluoride. One can also use the liquid or molten inorganic Drip fluoride onto finely divided carbon, which is brought to reaction temperature in a suitable reaction vessel is heated. A mixture of carbon and inorganic fluoride can be even simpler be heated in an open or closed vessel.

Any form of carbon, whether amorphous or crystalline, is suitable for the purposes of the invention. So you can get coal, graphite, diamond, charcoal, the different types of soot, such as lamp black, acetylene black and animal charcoal. At low temperatures, e.g. B. at 900 to 1500 ° C, the best Results obtained using activated carbon, which is commercially available in many varieties. in the In general, activated carbon is a very finely divided porous carbon, the entire surface of which is min-

Method of manufacture
of fluorocarbons

Applicant:

EI du Pont de Nemours and Company,
Wilmington, Del. (V. St. A.)

Representative: Dx.-Ing. W. Abitz, patent attorney,
Munich 27, Gaußstr. 6th

Claimed priority:
V. St. v. America July 16, 1553 and February 10, 1964

Mark Wendell Farlow, Wilmington, Del.,
and Earl Leonard Muetterties, Hockessin, Del.

(V. St. A.),
have been named as inventors

is at least 20m ² / g (Hassler, "Active Carbon", Chemical Publishing Co., 1951, p. 127). When using the coal arc, the activity or the state of division of the coal has no influence, but the carbon must of course have sufficient conductivity. It does not need to be absolutely pure, but for most activated carbons it can contain the normal ash content of, for example, 0.5 to 4 percent by weight.

The inorganic fluorides suitable for the purposes of the invention can according to the information of Literature are produced, and some of them are even commercially available. The fluorides of this Elements can be used in every possible valency state, but in general it is advisable to in the case of the elements of main group V of the periodic table, the fluorides of the elements are in their lowest Valence level to be used because such fluorides, ζ. B. arsenic (III) fluoride, in many cases can be obtained without having to work with free fluorine. They are therefore considerably lighter accessible than the higher fluorides of this group.

Both respondents, d. H. the carbon and the inorganic fluoride, are said to be advantageous practical be anhydrous, although the presence of some water is possible. It is often convenient to use the Dehydrate carbon before starting the reaction,

809 557/466

because they contain considerable amounts of water, especially in the active state, even at high temperatures can.

Even if the ratio of the two reactants from the standpoint of the reaction does not need to be adhered to within narrow limits, it is advisable for economic reasons to to use the carbon in excess to make the more expensive inorganic fluoride as complete as possible Apparatus with the exception of cylinder 1 is now evacuated to remove air, template? cooled with liquid nitrogen, valve 5 closed, argon or another inert gas through 5 valve 3 let in until the desired working pressure is reached and the pressure control device 8 like this adjusted to maintain the desired pressure. The arc 9 is now put into operation and the fluoride used with the

To remove condensable gases, whereupon the "cylinder" is closed and the product is at room temperature lets warm.

Fig. 2 shows a carbon arc that can be used according to the invention. The Copper tubes 25 and 26. The power supply cable 27 for the cathode is clamped to tube 25 and on the end of the tube 25 is the carbon electrode

To take advantage of. It is therefore advisable to use the two necessary speed (flow meter 10) reactants in such quantities that are passed through the sheet. The product condenses at least 0.25, preferably 1 to 5 grams of non-condensable gas present, with the exception of a small amount of atoms of carbon per gram atom of fluorine, which are by control. You can use up to 20 gram atoms of carbon device 8 and pump 11 flowing into the gas container 12, per gram atom of fluorine or even more 15 in the original ?. In operation, the pressure in front of the sheet is the. Of course, the inorganic fluoride in (pressure gauge 13) can be noticeably higher than after the arc. Arc reduces the cross-section of the flowing gas. The reaction product normally consists of gert. If you want to interrupt the reaction, a mixture of fluorocarbons, the most important of which is that the arc is switched off, taps 2 and 6, the most representative carbon tetrafluoride or tetra- are closed, tap 5 is opened, cylinders of fluorine or mixtures of both with generally 15 cooled with liquid nitrogen, template 7 allows smaller amounts of hexafluoroethane and octafluorane to warm to room temperature and the volatile propane and sometimes even smaller amounts of product is distilled into cylinder 15. Other saturated and unsaturated fluorocarbons can optionally be used to waste the cylinder 15. The crude reaction product contains pumped out to remove traces of argon or other inorganic fluoride, which in general has not been reacted, which is in the circuit
can be reused, as well as the free element whose fluoride has been applied, or Ver 3 °
ties of the same. The fluorocarbons can
be isolated, for example, by passing the gaseous reaction mixture through condensation devices and the condensate in suitable
Fractional distillation columns. If necessary, 35 28 can be attached. This expediently consists of a mixture of all parts of the length by passing the gaseous reaction graphite cylinder of 7.9 mm diameter and 7.62 cm mixture over cooled baffles, which is held back lengthways to the gas passage through the reaction product, which is bored in this (2, 54 mm diameter). The electrode 28 temperature are fixed, or you can conduct the reaction is on the copper tube 25 conductive and gas-tight mixed through liquid washing solutions, set around the 4 °, for which purpose copper foils are wrapped around the unchanged gray-inorganic fluoride and the phite cylinder, so that to wash out the element of the mixing gases of the inorganic fluoride formed in the course of the reaction by the turned fluoride. Usually the longitudinal bore of the electrode must flow. If it is advisable to discuss the reaction products quickly, the electrode 29 on the copper tube 26 is to be cooled in order to set up secondary reactions or polymerizations 45 and also to provide a through-hole at both high temperatures used - 2.54 mm in diameter. The power supply to the. This applies in particular when, as in the case 30 for the anode, very high temperatures are used, correspondingly to the carbon arc applied to the pipe 26.

will. In such cases, in particular when this also serves as a cladding vessel for the electrodes

Tetrafluoroethylene - as the main component of the reaction - 5 ° a water jacket provided glass vessel 31, which

The product to be obtained is very quick thanks to the flexible rubber connections 32 and

Quenching the reaction mixture is recommended- 33 is held in place and in this way

value. encloses the electrodes in a gas-tight manner. On the copper

The reaction can tubes 25 and 26 are also water jackets 34 at any pressure be performed. Usually you turn 55 and 35 on top. The bow is operating at atmospheric pressure at; but you can also at heights by manually adjusting the electrodes 28 and 29 work at lower pressures. brings in contact. You touch one of the two . In a preferred mode of operation, the flexible rubber joints 32 and 33 are routed and observed Fluoride in a gaseous state through a charcoal on it, a touch of the uninsulated parts of the turned through. This procedure is avoided by the 60 apparatus. On it is the electrode drawing explained. It shows distance adjusted by hand. Is attached to the electrodes

Fig. 1 shows the process in the flow diagram, applied in the usual way, a DC voltage.

Fig. 2 is a semi-schematic section of an invention. Fig. 3 shows another carbon arc, which is

appropriately usable carbon arc and also for the method according to the invention

Fig. 3 is a semi-schematic section of another 65 has proven excellent. This arc corresponds

ren, also suitable coal arc. the arrangement shown in Fig. 2 with the exception of the

According to Fig. 1, copper pipes are used for the gas lines, which are used to hold the carbon electrodes ..; -

pipes with an outer diameter of 7.9 mm were used. That serve, as well as the electrodes themselves. In the case of the one shown in Fig. 3: '

Inorganic fluoride is contained in cylinder 1. The bend shown is the end of the copper pipe 40, 'Is;

Cocks 2 and 3 are closed, 5 and 6 are open. The 70 that carries the carbon electrode 41, with perforations

42 provided. The electrode 41, which is expediently made of graphite, consists of a solid cylinder about 3.175 mm in diameter. The copper pipe 43 corresponds to the copper pipe 26 of Fig. 2, but carries the graphite electrode 44, which consists of a hollow cylinder with an outer diameter of 7.9 mm and 4.7 mm inside diameter. The opening in electrode 44 is arranged to be its diameter corresponds to that of electrode 41.

In the arrangement shown in FIG. 3, the fluoride used flows out of the perforations 42 of the Copper tube 40 into the electrode space, washes around the electrode 41 and then flows into the cavity electrode 44, whereby it flows through the arc formed by the electrodes. The reaction product flows through the electrode 44 and the copper pipe 43 to the outside.

This arc can be operated so that the electrode 41 a short distance into the through hole of electrode 44 protrudes, or the diameter of electrode 41 may be equal to or greater than that Outer diameter of the electrode 44 and be separated from the latter by a narrow gap. It is also possible to make electrode 41 the anode and electrode 44 the cathode. The ones given above Rating figures serve only to explain the invention and can be used accordingly be changed.

The invention is further illustrated by the following examples. In them parts mean parts by weight, unless otherwise stated.

example 1

A tubular nickel reaction vessel is charged with 40 parts of carbon black and four hours in one heated to 1000 ° C in a slow stream of dry nitrogen. On the outlet side are with liquid nitrogen chilled glass templates arranged. At 1075 to 1150 ° C there is a slow flow of phosphorus (III) fluoride passed through the plant, with the gaseous products in the nitrogen-cooled templates condense. In the course of 45 minutes, 4 parts of phosphorus (III) fluoride are passed through, with 3.5 parts of condensate are obtained. By ultrared spectroscopy it is found that still in the condensate some unreacted phosphorus (HI) fluoride, carbon tetrafluoride, and some carbon dioxide are included. The latter is apparently due to the reaction of the charcoal with traces of Oxygen is formed, which are contained in the phosphorus (HI) fluoride.

Example 2

A slow stream of vaporized arsenic (IH) fluoride is passed through an excess of carbon black, which in the reaction vessel of Example 1 on 1019 to 1186 ° C. Over the course of 3 hours 18 parts of arsenic (HI) fluoride have flowed through the system. This produces 3 parts of the gaseous reaction product recovered, which condenses in the refrigerated originals. The ultrared analysis shows that this product in addition to unreacted arsenic (III) fluoride and carbon tetrafluoride as well contains some carbon dioxide and hydrogen fluoride. The latter is created by hydrolysis of the Arsenic (III) fluorides due to traces of moisture.

Example 3

Gaseous arsenic (III) fluoride is displaced through the carbon arc shown in FIG of 32 g / hour. The pressure in front of the bow is 18 to 35 mm Hg abs. and after the arch 7 mm. 15 to 20% of the added arsenic (III) fluoride is converted into fluorocarbons in a single pass converted. The fluorocarbons are in a molar ratio of 80 to 90% tetrafluoroethylene, 5% carbon tetrafluoride and 0.5% hexafluoroethane were obtained.

Example 4

A carbon arc is made under liquid arsenic (HI) fluoride operated with 14 to 15 volts and 12 to 15 amps. The reaction is at atmospheric pressure carried out. The liquid arsenic (III) fluoride comes to a vigorous boil, and the return flow of the The ice-water-cooled cooling device is returned to the reaction vessel. The ones from the cooler contain escaping non-condensed gases except for a small amount of unchanged Arsenic (III) fluoride, tetrafluoroethylene and carbon tetrafluoride in a molar ratio of 7: 1.

Example-5

Nitrogen (III) fluoride, which according to the ultrared analysis contains about 6 percent by weight carbon tetrafluoride, is passed at a rate of 61.8 g / hour through the electric arc operated with graphite electrodes shown in FIG. The arc operates at 26 volts and 18 amps under a pressure of 12 to 34 mm Hg. The reaction time is 10 minutes. During this time, 10.3 g of the fluoride used (9.7 g NF ₃ ) have flowed through the .Bogen. The condensable gas obtained, which consists of unreacted nitrogen (III) fluoride and fluorocarbons, weighs 8.8 g. According to an ultra-red analysis, it contains "30 percent by volume carbon tetrafluoride, 15 percent by volume tetrafluoroethylene and 5% hexafluoroethane % Tetrafluoroethylene and 8.7% hexafluoroethane, which corresponds to a molar ratio of 56:33:11, and that the conversion of nitrogen (Hl) fluoride into fluorocarbons has taken place to 51.5%.

Example 6

Phosphorus fluoride is generated by the electric arc shown in FIG. 3 at a speed of 54.4 g / hour. The bow is under a pressure of 6 to 35 mm Hg with 24 volts and Operated from 18 to 20 amps. The weight of the phosphorus (V) fluoride flowing through the arch is with a reaction time of 30 minutes 27.2 g. 27.2 g of reaction product are obtained, which Except for unchanged phosphorus (V) fluoride, 5 percent by volume each of carbon tetrafluoride and tetrafluoroethylene contains, which corresponds to a 22.2% conversion of the phosphorus (V) fluoride into fluorocarbons.

Example 7

A graphite tube filled with carbon black is placed in a reaction vessel made of nickel and passed through it Vessel heated to 1000 ° C for 10 hours, dry nitrogen to thoroughly dehydrate the carbon and remove the air present. On the outlet side of the reaction vessel, liquid

Nitrogen-cooled glass templates arranged. Passing 3 * / ₂ hours showed a slow stream of sulfur (VI) fluoride through the system, keeping the reaction temperature at 950 to 1000 ° C. The gaseous products condense in the cooled receiver. 13 parts of a mixture of fluorocarbons are obtained from 18 parts of sulfur (VI) fluoride. The ultra-red analysis shows that this mixture consists mainly of carbon tetrafluoride and hexafluoroethane in a molar ratio of about 30: 1.

Example 8

Gaseous sulfur (VI) fluoride is displaced through the carbon arc shown in FIG. 2 at a velocity of 47.5 g / hour and an inlet pressure of 28 to 30 mm Hg abs. and an outlet pressure guided by 6 mm. The arc is operated with 25 volts and 18 amps. The product of one single passage contains 50 parts by volume of unchanged sulfur (VI) fluoride, 10 parts of tetrafluoroethylene, 25 parts of carbon tetrafluoride, 5 parts of hexafluoroethane, less than 0.5 part of hexafluoropropylene and 5 to 10 parts of silicon (VI) fluoride, which resulted from attack on the glass parts of the apparatus is.

Suitable special fluorides of main group V of the periodic table are in addition to those in the examples named fluorides nor the arsenic (V) fluoride, antimony (III) - and - (V) -fluoride, bismuth (III) - and - (V) -fluoride. Of these fluorides, arsenic (III) fluoride is particularly preferably used; this is particular can be used for a cheap cycle for the production of tetrafluoroethylene, since it is made of Calcium fluoride, arsenic (III) oxide and sulfuric acid is produced and arsenic (III) oxide by oxidation of the arsenic formed by the reaction of arsenic (III) fluoride and carbon can be easily regenerated can.

Because of the reaction conditions already given, the use of a carbon arc is preferred Process as it has higher degrees of conversion and greater yields of tetrafluoroethylene than that other methods. Therefore, a particularly expedient embodiment of the invention consists in that one arsenic (III) fluoride or sulfur (VI) fluoride brings it into contact with a carbon arc and isolates the resulting fluorocarbons.

Claims (7)

Patent claims: 1. Process for the production of fluorocarbons, characterized in that carbon and a fluoride of an element of main group V of the periodic table or sulfur at a temperature of at least 900 ° C in reaction. 2. The method according to claim 1, characterized in that the reaction in one Carries out carbon arc and conducts the fluoride in a gaseous state through the arc. 3. The method according to claim 1, characterized in that the fluoride is passed in the gaseous state through a pipe which contains carbon and is heated to 900 to 2000 ° C. 4. The method according to claim 1 to 3, characterized in that the reaction is at least 2500 ° C and the reaction products quenched very quickly. 5. The method according to claim 1 to 4, characterized in that there is arsenic (III) fluoride as the fluoride used. 6. The method according to claim 1 to 4, characterized in that the fluoride used is sulfur (VI) fluoride used. 7. The method according to claim 1 to 4, characterized in that the fluoride is phosphorus (V) fluoride used. 1 sheet of drawings © 809 557/466 6.58