DE1568910A1 - Process for the purification of bromofluorocarbons and bromochlorofluorocarbons - Google Patents

Description

Kali-Chemie 'Hanover, February 14, 1966

Aktiengesellschaft Dr. Ha / H

Patent application

Process for the pure recovery of bromofluorocarbons and bromochlorofluorocarbons

The present application has a process for the purification of bromofluorohydrocarbons and bromochlorofluorohydrocarbons from Bromine and hydrogen bromide-containing gaseous reaction mixtures with simultaneous recovery of the bromine to the Object.

In the thermal bromination of multiply halogenated hydrocarbons with at least one hydrogen and a fluorine atom such as trifluoromethane, difluoromethane or chlorodifluoromethane, is used in addition to the corresponding Bromine compound also formed hydrogen bromide. This is how the bromination of chlorodifluoromethane to bromochlorodifluoromethane takes place for example according to the equation:

(T) CHClF ₂ + Br ₂ . CBrClF ₂ + HBr.

In order to achieve the highest possible yields of brominated compounds obtained, is often worked with a considerable excess of bromine. The gas mixture leaving the bromination reactor in this case contains the desired bromochlorodifluoromethane and the equivalent amount of hydrogen bromide excess bromine, unreacted chlorodifluoromethane and

009829/1680

as by-products dibroindifluoromethane, dichlorodifluoromethane and hydrogen chloride and other compounds in very small amounts.

The brominated halogenated hydrocarbons can be known Way, for example by fractional distillation, can be separated from the other halogenated hydrocarbons. Before however, the bromine and the hydrogen halides must be removed from the reaction mixture. To the economy To ensure the bromination process, it is necessary that this be done in the simplest possible manner. Above all, must but also the hydrogen bromide can be converted back into bromine so that it can be used again in the process.

The previously known processes for working up the reaction mixture obtained in the bromination have proven to be too proved elaborate. According to the usual method, a reaction mixture is initially produced by cooling the gaseous reaction mixture Part of the bromine is condensed and returned to the process. To remove the remaining bromine as well as the bromine and hydrogen chloride the reaction mixture is then washed with water and / or sodium hydroxide solution. The obtained in this way Hydrobromic acid or sodium bromide solution is with hydrogen chloride and small amounts of hydrogen fluoride and is used to recover the bromine, for example after so-called Kubierschky process worked up by treatment with chlorine. Such a work-up requires one of the actual production plant separate complete Kubierschk ^ y plant. The bromine produced here is moist and must be dried before being returned.

It has now been found that a significant simplification in the process for the purification of the bromofluorine and bromofluorofluorine · hydrocarbons from the bromine and bromine-containing

009829/1610

gaseous reaction mixtures with simultaneous recovery of the bromine can be achieved if the the bromination reactor leaving gas mixture is cooled to a temperature between 0 and 300 ° 0 »in particular 20 and 120 ° C, then mixed the mixture with the equivalent amount of ohlor for the hydrogen bromide present and in one Reaction tube is reacted, then part of the bromine is condensed out of the resulting mixture by cooling it and the remaining gas phase is washed, dried and fractionated. According to the present procedure, thus the separation and oxidation of hydrogen bromide carried out in one reaction stage. The resulting bromine can together with that not reacted during the bromination Bromine can be returned immediately to the bromination process, since the bromine recovery is carried out in an anhydrous medium.

After the condensed bromine has been separated off, they can be present in the gas mixture Remaining bromine residues with a solvent that is selective for bromine, for example dibromethane or bromobenzene, be separated from the gas mixture. This procedure has the advantage that the bromine residues are not mixed with an aqueous one Phase come into contact and can thus be returned to the bromination process without prior drying. the end This is because bromine can be expelled from these solvents by heating. Then the mixture is used for removal of hydrogen chloride and traces of other hydrogen halides still present with water and / or alkali lye treated.

But it is also possible after the separation of the condensed Bromine the bromine residues remaining in the gas mixture immediately by washing with water and / or alkali together with the hydrogen chloride in the gas mixture and the in Separate traces of present bromine and hydrogen fluoride from the gas mixture. The bromine can then optionally from the

009829/1680

- A -

acidified solution expelled with steam or with the help of extracted and recovered from an organic solvent.

The after separation of the bromine and the hydrogen halides remaining residual gases are then removed in the usual way, e.g. by fractionation. Surprisingly, it has been found that the composition of the bromination reactor leaving mixture of halogenated hydrocarbons due to the thermal treatment with chlorine in none Weiee is changed. There are therefore no losses in yield in the case of the brominated end products and the not yet converted hydrogen-containing starting products can again be fed back into the process. The process is therefore profitable in this respect as well.

example 1

During the bromination of ohlordifluoromethane I am a gas mixture with the average composition which is continuously produced and in an amount of 120 liters / h (under normal conditions)!
35.8 vol .-? 6 HBr
3.4 Vol. -I »HOl
35.3 vol .-? G Cf ₂ OlBr
5.2 vol .- # OF ₂ Br ₂
1.9 vol. -I * OP _{2 OlH}
18.0 vol. # Br ₂

was cooled to about 100 ° C. and continuously mixed with chlorine gas in such a way that for every 100 liters (under normal conditions) of the gas mixture 18 liters (under normal conditions) of chlorine are added. The resulting gas mixture was then durc. passed a tube filled with glass balls and then cooled to 0 ° 0 in a cooler. Then _r was the Gn, washed with dibromoethane and through two with. . · Water added .. Orphan bottles passed. After two hours

309829 / 168J

BATH ORIGINAL

During the course of the experiment, 180 g of bromine had separated out in the cooler and the dibromoethane had absorbed 130 g of bromine. In the Wash bottles could only be found in traces of bromine or hydrogen bromide.

The remaining gas mixture had a volume of 101 liters and the composition t

86.2 vol. #

8.1 vol .- $

4.5 vol .-? I OF ₂ OlH

1.2 Yol .- # Other gases

Example 2

One by bromination of rifluoromethane continuously and in an amount of 250 liters / h (under normal conditions) resulting gas mixture with the average composition »

39.0 V0I.-5S HBr

38.7 vol Si CF ₃ Br
2.5 vol .-? S CF ₃ H

19.7 Vol, - # Br,

'2

was cooled to about 100 ° C and continuously with Chlorine gas mixed in such a way that every 100 liters (under normal conditions) of the mixture 19.5 liters of chlorine (under normal conditions) were added. The resulting gas mixture was further treated as described in Example 1 An experiment lasting two hours had contained 430 g of bromine in the cooler deposited and the dibromoethane had taken up 268 g of bromine. Only traces of bromine and Hydrogen bromide can be detected ^ The remaining gas mixture had a volume of 199 liters and the composition i

93.5 % CF ₃ Br
6.0 H ₁ CF ₃ H

. 009829/1680

Claims (3)

Claims 1.) A method for recovering the bromofluorocarbons va & bromochlorofluorocarbons from the gaseous reaction mixtures containing bromine and hydrogen bromide with simultaneous recovery of the bromine *, characterized in that the gas mixture leaving the bromination reactor is at a temperature between 0 and 300 ° 0, in particular 20 and 120 ° 0 ', then mixed with the equivalent amount of Ohlpr for the hydrogen bromide present and reacted in a reaction tube, then part of the bromine is condensed out of the resulting mixture by cooling and the remaining gas phase is washed, dried and fractionated 2.) The method according to claim 1, characterized in that the reaction gases after separation of a rope from the bromine be washed by condensation with an organic solvent that is selective for bromine and the bro » is 'recovered from the solvent by heating' 3.) The method according to claim 1, characterized in) 4LaS the reaction gases, after separating off part of the bromine, are washed by condensation with water and / or alkali and the bromine is recovered from the washing liquid 009829/1680