DE2145975A1 - PROCESS FOR THE CONTINUOUS PRODUCTION OF VINYLIDEN FLUORIDE - Google Patents

Description

Kali-Chemie Hanover, September 14, 1971

Stock company Z 3-PA. Dr. Ha / Hp

Patent registration

Process for the continuous production of

Vinyli denfluo r i d

Vinylidene fluoride is of considerable importance as a monomer for the production of thermoplastic homopolymers and of Elastomers by copolymerization with perfluoroolefins.

As starting material for the manufacture of vinylidene fluoride, the readily available 1, 1 serve -Difluoräthan. In this case, 1-difluoroethane is chlorinated in a first reaction stage to 1, 1, 1-Chlordifluoräthan 1, which is dehydrochlorinated in a second reaction stage to vinylidene fluoride according to the following equations:

(1) CH ₀ -CHF ₀ + Cl ₀ > CH ₀ -CClF ₀ + HCl

O & et O et

(2) CH ₀ -CClF ₀ > CH ₀ = CF ₀ + HCl

3 -—— 2 2

The conversion of 1, 1-difluoroethane in 1, 1, 1-chloro difluoroethane can done in different ways. You can for example by the method of US Pat. No. 2,499,629 by photochemical

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Chlorination can be carried out at temperatures between room temperature and 300 ° C or by the method of the US patent 2,899,472 by thermal chlorination at temperatures between about 375 and 475 ° C.

The dehydrochlorination of 1,1,1-chlorodifluoroethane to vinylidene fluoride can also be carried out in various ways, for example by pyrolysis according to US Pat. No. 2,551,573 at temperatures between 600 and 1000 C. According to the proposal of US Pat. No. 2,628,989, the dehydrochlorination small amounts of CCl used as a catalyst and the reaction Temperatures between 500 to 610 C carried out. According to DP 1 253 702, it is suggested that 0.5 to 4 percent by weight of chlorine should be added to use to accelerate the reaction and to work at reaction temperatures between 450 and 800 C.

The reaction product from the chlorination process according to equation (1) contains, in addition to the desired 1,1, 1-chlorine, difluoroethane and hydrogen chloride, even more highly chlorinated by-products and / or Starting products depending on the reaction conditions. The separation of the 1, 1, 1-chlorodifluoroethane from this reaction mixture before the Dehydrochlorination reaction requires a considerable amount of equipment and energy. That is why it has already been suggested that Chlorination of 1,1-difluoroethane with the subsequent dehydrochlorination of 1,1, 1 -Chlordifluoräthans to combine to vinylidene fluoride. According to U.S. Patent 2,722,558, the thermal Chlorination and the subsequent dehydrochlorination carried out in the same reactor by adding the mixture of 1, 1-difluoroethane and chlorine after passing through a preheating zone

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to about 610 C heated reaction zone is passed. According to Japanese notice 16 2 82/67, this is done at the photo chlorination of 1,1-difluoroethane obtained reaction mixture with excess chlorine subjected to pyrolysis.

These previously known combination processes have, however, compared to the two-stage process with isolation of the 1, 1, 1-chlorodifluoroethane major disadvantages due to intermediate cleaning. The yield of vinylidene fluoride, based on the 1,1-difluoroethane used, is much lower, as there are increased levels of side reactions caused by the pyrolysis reaction Presence of chlorine and higher chlorinated difluoroethane comes. During the pyrolysis reaction there is considerable formation of coal and tarry products from the decomposition of more highly chlorinated ones Difluoroethane, which can lead to a rapid clogging of the pyrolysis reactor. The presence of highly corrosive Components in the chlorinated gas mixture requires a larger apparatus in the pyrolysis reaction - especially under pressure Expenditure.

A process for continuous production has now been found of vinylidene fluoride, where in separate process steps 1, 1, 1-chlorodifluoroethane wins by chlorination of 1,1-difluoroethane and vinylidene fluoride by pyrolysis of 1,1-chlorodifluoroethane, which avoids the difficulties encountered with the previously known methods. The procedure is characterized by that the two process steps are carried out in parallel, the reaction products obtained are combined in a separation plant

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Removal of the hydrogen halides formed and any excess chlorine from the halocarbon and hydrogen mixture Vinylidene fluoride and 1, 1-difluoroethane and 1, 1, 1-chlorodifluoroethane isolated and the latter two compounds fed to the corresponding reaction reactors.

This procedure makes it possible for the second reaction stage Using a 1,1,1-chloro difluoroethane freed from all by-products, without the expense of a separate intermediate distillation of the reaction product of the first process stage is required. Both for chlorination and for pyrolysis the known methods can be used.

In a preferred embodiment, the chlorination reaction carried out as completely as possible. The reason for this is that the pyrolysis produces a small amount of by-products, which can only be separated from the 1,1-difluoroethane with difficulty, but which, if the Process can enrich in the chlorination stage. The continuous The method is preferably carried out as follows:

In several well-cooled reactors connected in series, 1,1-difluoroethane is continuously reacted with chlorine under UV irradiation at temperatures between 20 and 70 ° C. for a residence time between 10 and 120 seconds to give 1,1-chlorodifluoroethane. Under these reaction conditions it is possible, an approximately 100 percent conversion of starting material and 97 to 98 percent yield of 1, 1 to obtain 1-chloro difluoroethane. In one

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separate reaction tube is simultaneously 1, 1, 1-chlorine difluoroethane continuously, starting from a starting supply, at a temperature between 500 and 700 C at slightly increased pressure pyrolyzed to vinylidene fluoride. By suitable adjustment of the reaction temperature, pressure and residence time, one can, for example achieve an 80 percent conversion of the starting material to vinylidene fluoride without any significant formation of By-products occurs. The reaction products from both reaction stages are then combined and placed in a separator from hydrogen chloride and freed from excess chlorine by a single or multi-stage wash with water and sodium hydroxide solution. Possibly existing Hydrogen fluoride is also removed in the process. The remaining halogenated hydrocarbon mixture is dried and compressed and separated in several pressure distillation columns connected in series. In this way, both vinylidene fluoride and 1,1,1-chlorodifluoroethane of those formed in the respective reaction By-products are separated. The amount of 1, 1, l-chlorodifluoroethane obtained is made up of that in the first Reaction stage formed and the unreacted product in the second stage together. The one removed from the separation plant 1, 1, 1-chlorodifluoroethane is introduced into the pyrolysis reactor. on In this way, a mixture of the reaction products of both reactors can be continuously fed to the separation plant. With suitable Conducting the two reactions, it is possible to take a constant stream of vinylidene fluoride from the separation system. One can Yield of vinylidene fluoride can be achieved, which is 96 mol%, based to the amount used is 1, 1-Difluoroäthan.

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The continuous process according to the invention thus has all the advantages that were previously only available when carried out separately of the individual reaction stages with the interposition of a separation system for the reaction mixture resulting from the chlorination reaction achieved with pure recovery of 1,1,1-chlorodifluoroethane could become. This results in considerable energy and equipment savings.

Compared to the combined process, it is particularly noticeable that that better yields are achieved in the pyrolysis reaction because of the lower tendency to form by-products and that in particular the formation of such compounds is greatly reduced, which easily decompose with carbon deposition in the reaction tube and can give rise to clogging of the same. This results in a method according to the invention that is maintenance-free over a long period of time Process flow. In particular when practically complete chlorination is carried out in the first reaction stage to a product which can be broken down into its constituent parts in the separation stage in a relatively simple manner.

example

In a continuously operated system, a mixture of 10.0 moles of 1,1-difluoroethane / h and 10.4 moles of chlorine / h was passed through several photochlorination reactors connected in series, consisting of water-cooled hollow glass cylinders with an axially arranged fluorescent lamp with a power consumption of 125 VV and about 30 W. Radiation ini fU-rieh from HOO to 500 do with a maximum at:! 70 mn,

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conducted with a residence time in the irradiation field of over 60 seconds. The reaction temperature was kept below 35 C. A mixture of 49.0 mol% of organic constituents, 50.1 mol% of hydrogen chloride and 0.9 mol% of chlorine was obtained. The organic constituents had the following composition in mol% determined by gas chromatography: 97.8 CH “-CC1F _O , _{0.3 CH 0} Cl-CHF ₀ , 1.0 CH ₀ Cl-CClF ₀ ,

ό Δ Δ Δ Δ Δ

0.3 CHCl ₂ -CHF ₂ , 0.4 CHCl ₂ -CClFg, < _{0.1 CCl 3} -CClF ₂ , 0.1 CH ₃ -CHF

At the same time were from a 100 moles of 1, 1, 1-chlorodifluoroethane containing Storage vessel 11, 9 mol 1, 1, 1-chlorodifluoroethane / h removed and passed through a previously used, electrically heated nickel tube. The CH-CClF pyrolyzed in the reaction zone, which had an average temperature of 560 C

ο Δ

at about 1.2 atm in 36 seconds. Residence time to a mixture of 54.9 mol% organic constituents, 44.9 mol% hydrogen chloride and 0.2 mol% hydrogen fluoride. The composition of the organic components in mol% was 81.4 CH ₀ -CF ₀ , 0.1 CH ₀ = CClF, 18.4 CH ₀ -CClF ₀ and

Δ Δ Δ ο Δ

0, 1 not specific products. After 100 operating hours there was carbon formation of 40 g / kmol vinylidene fluoride formed in the reactor and the subsequent dust collector.

The reaction gas mixtures from the photochlorination and from the Pyrolysis were combined, washed with water and sodium hydroxide solution to remove hydrogen chloride, hydrogen fluoride and chlorine, dried on active alumina and put into the first of four consecutive FüUkörperdruckkolonnen pressed. The first column operated at a pressure of 25 at and a head temperature of -10 C as a stripper. The existing Inert gases were withdrawn overhead. The bottom product was in

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the second column passed, from which at 23 atm and a head temperature of 0 C 9, 6 mol vinylidene fluoride / h distilled off. The bottom product was transferred to the third column operating as a stripper. _{The chlorofluoroethylene and any CEL-CHF 0} , CEL-CF-CHCl = CF ₀ or CHClF _{0 were} distilled off at a pressure of 14 at and a head temperature of 20 C. The bottom of the third column was transferred to the fourth column. At 3.5 atm and a top temperature of 25 ° C., 11.9 mol of 1,1,1-chloro difluoroethane / h distilled off. These were introduced into the pyrolysis reactor via the storage vessel. Difluoroethane, was 96 mole percent.

In a comparative experiment, the unpurified reaction product coming from the photochlorination was directly subjected to pyrolysis subjected to a nickel tube reactor under conditions which also lead to formation at a pyrolysis temperature of 540 ° C of about 80 mol% of vinylidene fluoride. The yield of vinylidene fluoride was only 91 mol%, based on the amount used 1, 1-difluoroethane. In addition, after 100 hours of operation in the pyrolysis reactor and in the subsequent dust separator 170 g coal / kmol formed vinylidene fluoride is accumulated.

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Claims (3)

2U5975 3 claims 1. Process for the continuous production of vinylidene fluoride, where in separate process steps 1,1, 1-chlorodifluoroethane by chlorination of the 1, 1-difluoroethane and vinylidene fluoride Pyrolysis of 1, 1, 1 -chlorodifluoroethane wins, characterized in, that the two process steps are carried out in parallel, the resulting reaction products are combined in a separation plant after removing the hydrogen halides formed and, if appropriate, the excess chlorine from the halohydrocarbon mixture Vinylidene fluoride and 1, 1-difluoroethane and 1, 1, 1-chlorodifluoroethane isolated and the latter two compounds feeds the corresponding conversion reactors. 2. The method according to claim 1, characterized in that the both process stages are carried out in parallel, practically complete chlorination of the 1,1-difluoroethane to 1,1-chlorodifluoroethane undertakes, the reaction products obtained from both process stages combined, in a separation plant after removal the halogen formed hydrogen substances and optionally the excess Chlorine from the halogenated hydrocarbon mixture vinylidene fluoride and 1, 1, 1-chlorine difluoroethane isolated and the latter Compound of pyrolysis supplies. 3. The method according to claims 1 and 2, characterized in that that the Auftrenriung the Ilalogenkohlenwasserstoffgemisches makes by pressure distillation. 'J UiJlH "' '1 -