DE1229515B - Process for the production of hexafluoropropene - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

int. α .:

C07c

German class: 12 ο -19/02

Number: 1229 515

File number: P 36796IV b / 12 ο

Filing date: May 14, 1965

Opening day:! December 1966

It has been made up to now been by a pyrolysis reaction of hexafluoropropene octafluoropropane at temperatures from 1000 to 1150 ⁰ C in contact with a heated platinum wire to obtain in the main hexafluoroethane low Mtengen hexafluoropropene. According to another method is used to small amounts of hexafluoropropene by the pyrolysis of tetrafluoroethylene at 600 to 700 ⁰ C forth. Hexafluoropropene has also been obtained as a by-product in the synthesis of tetrafluoroethylene from chlorofluoromethane. ·

The present invention is a process for the preparation of hexafluoropropene to the object, which is characterized in that 2-chloro-1,1,1,3,3,3-hexafluoropropane at temperatures of about 650 to about 850 ⁰ C and a residence time thermally cleaves from about 3 to about 120 seconds. The preferred temperature range is maintained from about 725 to about 775 ^° C. by means of an electrical heater.

The pyrolysis is carried out in a long pipe, which is built from or with a metal is lined, which is inert to the acidic reaction products. Suitable metals for one Such a reactor are silver, a high-temperature corrosion-resistant alloy of nickel and chromium and iron or an alloy of nickel, molybdenum and iron. A tube made of the alloy of nickel, Chromium and iron lined with platinum make a reactor with a longer life than that Alloy alone. The dimensions of the pipe depend on the type and scale of the operation Related to maintaining the required temperature in the pipe, at a rate of the gas supplied through the pipe, which the required contact time with the heated Zone allowed.

The 2-chloro-l, l, l, 3,3,3-hexafluoropropane (boiling point about 15 ° C) can be fed directly into the reactor as an undiluted gas, or it can be mixed with an inert gas such as nitrogen or helium, mix. The use of the reactant for pyrolysis in neat form is preferred. Usually, the gaseous chlorhexafluoropropane is fed to the reactor at about atmospheric pressure and at room temperature. Higher pressures and subatmospheric pressures may be used, and the gas can be preheated up to 600 ⁰ C. The feed rate of the 2-chloro-1,1,1,3,3,3-hexafluoropropane is adjusted in accordance with the dimensions of the reactor in order to have a residence time in the heated zone of about 3 to. Process for the production of hexafluoropropene

Applicant:

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

Representative:

Dr.-Ing. W. Abitz and Dr. D. Morf,
Patent Attorneys, Munich 27, Pienzenauer Str. 28

Named as inventor:

Donald George Hummel, Wilmington, Del .;

Frederic Wurl Swamer,

West Chester, Pa. (V. St. A.)

Claimed priority:

V. St. v. America May 15, 1964 (367 894)

about 120 seconds to achieve. A residence time of about 20 to about 30 seconds is preferred. at longer Verwsilzeiten there is the possibility that the hexafluoropropene formed is converted and lost, while less dehydrochlorinated by chlorhexafluoropropane with shorter residence times will.

When calculating the residence time, the volume of gas that is produced per minute at room temperature is used is fed to the reactor, the volume portion of the hexafluoropropene product in that washed with alkali The material flowing out of the reactor and the volume of the heated reactor zone are taken into account. Analysis of the reactor off-gas, which has been washed to remove the hydrogen chloride, reveals directly the extent of the conversion of the 2-chloro-1,1,1,3,3,3-hexafluoropropane in hexafluoropropene, there

509 729-20

the pyrolysis reaction essentially through the following Equation is reproduced:

CF ₃ CHClCF ₃

CF ₃ CF = CF ₂ + HCl (1)

Example 2 Table 1

Effect of temperature on formation
of hexafluoropropene by pyrolysis of 2-chloro-1,1,1,3,3,3-hexafluoropropane

The process according to the invention can also be carried out continuously.

The 2-chloro-1,1,1,3,3,3-hexafluoropropane starting material is produced in a manner not claimed here by reacting carbon tetrachloride with trichlorethylene or by reacting chloroform with tetrachlorethylene to form hexachloropropene if hydrogen chloride is released. The hexachloropropene is then in contact with an activated catalyst of anhydrous chromium oxide reacted with hydrogen fluoride to form 2-chloro-1,1,1,3,3,3-hexafluoropropane according to a method described for the preparation of chlorofluoroalkanes to surrender.

The hexafluoropropene produced by this process shows a high degree of chemical reactivity and is used as a chemical intermediate, e.g. B. in the representation of various halogenated propane. It is useful as a monomer for making fluorine-containing polymers and Mischpölymerer: The following exemplary embodiments serve for further explanation.

For example

A tube lined with platinum and made of a nickel-chromium-iron alloy with an inner diameter of 6.3 mm, which is heated to 706 to 713 ° C. over a length of 254 mm by means of an electric furnace, is introduced Mixture of 2-chloro-l, l, l, 3,3,3-hexafluoropropane and nitrogen. The feed rate is such that 22 ecm of the chlorohexafluoropropane and 10 ecm of nitrogen, measured at room temperature and atmospheric pressure, are fed into the reactor per minute. On the basis of a 30% conversion to n ^e hexafluoropropene, which was determined by analysis of the end products, the contact time is about 13 seconds. Velocity focusing mass spectrometry characterizes the reaction product as consisting essentially of hexafluoropropene.

Reaction temperature
CQ

680
725
750
773
800

Conversion to volume percent

(° / o hexafluoropropene
in the washed reactor exhaust gas)

13th
24
37
37
18th

Under the process conditions listed above the optimal temperature range for the formation of hexafluoropropene is about 750 to about 775 ° C.

Example 3

Following the procedure of Example 1, 2-chloro-l, l, l, 3,3,3-hexafluoropropane is introduced with variation of the velocities in the same pyrolysis tube heated to 735 ° C. The reactor exhaust gas is washed, dried and analyzed as in Example 2 for hexafluoropropene; the results are in Table 2 compiled.

Table 2

Effect of the feeding speed
on the formation of hexafluoropropene

Feeder
speed Dwell time Hexafluoropropene
content of the laundry
NEN reactor exhaust (ccm / min.) (Seconds) (Volume percentage) 6th 67 34 14th 28 45 21.5 20th 26th 31 13th 27 ' 43 10 20th 57 8th 18th

50

2-chloro-l, l, l, 3,3,3-hexafluoropropane is passed through the reactor used in Example 1 at a rate of 14 cc / min., While the temperature is varied from 400 to 800.degree. The effluent gas is washed with 10 ° / ₀ aqueous potassium hydroxide solution, then dried and analyzed by passing through anhydrous calcium sulfate by gas chromatography on its Hexafluorpropengehalt. No reaction takes place between 400 and 640 ° C. The residence time varies between 34 and 28 seconds based on a conversion varying between 0 and 40%. Above 640 ° C., hexafluoropropene forms to the extent that Table 1 shows. As shown above, the optimal feed rate, expressed as dwell time, is therefore about 30 seconds. At low feed rates and correspondingly high residence times, some of the hexafluoropropene formed is pyrolyzed to give other fluorine-containing compounds.

Claims (3)

Patent claims: 1. A process for the preparation of hexafluoropropene, characterized in that 2-chloro-l, l, l, 3,3,3-hexafluoropropane at temperatures of about 650 to about 85O ⁰ C and a residence time of about 3 to about 120 seconds thermally splits. 2. The method according to claim 1, characterized in that the thermal cleavage at about 725 to about 775 ° C. 3. The method according to claim 1 and 2, characterized in that the thermal cleavage at a residence time of about 20 to about 30 seconds. 609 7297420 1i: 66 © Bundesdruckerei Berlin