DE1155104B - Process and device for the production of trifluorobromomethane - Google Patents

Description

It is known to split trifluorobromomethane into two of one another to produce separate reaction stages according to the following reaction equations:

CHCl ₃ + 3HF
CHF ₃ + Br ₂

CHF ₃ + 3 HCl (1)
CBrF ₃ + HBr (2)

Here the fluorination of chloroform is discontinuous under pressure with hydrofluoric acid and antimony pentafluoride carried out (J. Soc. former Ind., 66 [1947], p. 429). According to a different procedure a gaseous mixture of hydrogen fluoride and chloroform is passed through a with aluminum fluoride filled tube at about 350 ° C (U.S. Pat. No. 2,748,177). However, attempts by the inventor have shown that the reaction mixture obtained in this way does not consist of pure trifluoroniethane, but that it also contains up to 20% difluoromonochloromethane in addition to other impurities contains.

The bromination of trifluoromethane takes place according to older methods (J. Amer. Former Soc, 68 [1945], P. 968-969) by thermal bromination with HiKe of elemental bromine at temperatures between 500 and 600 ° C. In this case, trifluoromethane is first passed through an electric heater to 40 to 50 ° C heated vessel containing bromine. The gas mixture of trifluoromethane and an unknown excess bromine is then brominated on bromine in a Pyrex glass tube, yields of about 80 to 90%, based on on trifluoromethane. However, the Pyrex tube is completely unsuitable for continuous operation, as the necessary very high bromination temperatures already decomposition of the trifluoromethane with formation of hydrogen fluoride occurs, whereby the reaction tube is destroyed after a short time. Furthermore is a Controlled dosing of the bromine is not possible with this method.

Carrying out the two reaction steps in a separate arrangement one after the other is extremely cumbersome. For a technical description of trifluorobromomethane, it is therefore desirable to use both Reaction stages in immediate succession, continuously without isolation and purification of intermediates respectively.

For this it is especially necessary to direct the fluorination of chloroform so that one as possible extensive substitution of the chlorine atoms in the chloroform molecules by fluorine occurs. not completely fluorinated substances, such as monofluorodichloromethane and difluoromonochloromethane, are therefore undesirable because in the directly subsequent office procedure and apparatus for producing trifluorobromomethane

Applicant:

Farbwerke Hoechst Aktiengesellschaft

formerly Master Lucius & Brüning,

Frankfurt / M.

Dr. Otto Scherer, Bad Soden (Taunus),

Dr. Heinrich Kühn, Frankfurt / M.-Schwanheim,

Dr. Gerhard Hörlein, Frankfurt / M.,

and Dipl.-Ing. Karl Heinz Grafen,

Frankfurt / M.-Höchst,
have been named as inventors

brominated by-products which are difficult to separate and whose bromine content is lost is.

It has now been found that trifluorobromomethane can be obtained from chloroform by fluorination of the Chlorofonns and bromination of the trifluoromethane formed with elemental bromine can be produced by the fluorination of the choroform in the presence of aluminum fluoride as a fluorination catalyst above 350 ° C and the bromination of the resulting trifluoromethane after a water and Alkali washing as well as a subsequent drying without isolation and cleaning of intermediate products carried out continuously in one operation at reaction temperatures between 650 and 800 ° C, wherein the fluorination of chloroform with at least 3.5 times the molar amount of gaseous Hydrogen fluoride, based on 1 mole of chloroform, and the bromination of trifluoromethane carries out with controlled dosing of the bromine with the help of a dosing pump in a reaction zone, their inner walls made of sintered oxides of aluminum, zirconium or magnesium, preferably made of Aluminum oxide.

In the fluorination of chloroform, the excess of hydrogen fluoride is expediently up to 50 mol percent, the amount theoretically necessary according to the stoichiometric conversion equation.

309 690/285

3 4

It is preferable to use 3.5 to 4.5 moles of fluorine. Only with the aid of the precisely controlled

hydrogen, based on 1 mole of chloroform. The tenth dosage of the bromine could make for a large one Fluorination expediently takes place between about 420 variation range of the molar ratio of bromine to tri and 500 ° C. fluoromethane the most favorable conditions of equal

In the thermal bromination of trifluoro 5 weight reaction

methane lie next to each other at the same time elementary _ruc , r ,,. _ ^ _ / -ra ^ r? _l xro, -

and atomic bromine, hydrogen bromide and fluorine- ^ό * ^ό

hydrogen before. Determined in such an aggressive atmosphere as a function of the temperature. Sphere and at the high bromination temperatures as a result of a large number of series is Therefore the use of reaction vessels from io investigations has been found to be useful in this metallic or from carbonaceous or silica reaction a conversion of about 80% and an Austischem Material, for example the use of about 90% trifluorobromomethane, be quartz tubes, for continuous operation from the outset drawn on the amount of converted output excluded. The reaction can also take place among these products, if an excess of bromine is obtained extreme conditions are continuously carried out, 15 to 50 mol percent of the theoretically calculated amount, if the bromination of trifluoromethane is used based on the trifluoromethane used carries out a reaction zone, the inner walls of which and the bromination at a temperature of 650 the said sintered metal oxides, in particular up to 800 ° C, preferably 700 to 750 ° C, and one made of sintered aluminum oxide. Even the residence time of the reactants in the reaction Longer continuous operation is carried out from an ao zone of around 2 to 5 seconds. That such material existing reaction tubes to their excess bromine is together with the at the Inner walls are not attacked and remain absolutely reaction hydrogen bromide, which is gas-tight. One of the reasons for this is that it is regenerated to bromine in a known manner, surprising when it is known that aluminum is used again for bromination, oxide in a temperature range above 100 ° C 25 With the continuous Fluoriein described a decidedly exothermic reaction with propagation and bromination apparatus is in the Can convert hydrogen fluoride to aluminum fluoride. In a simple manner in continuous operation Trifluor-

The generally only available in a limited length bromomethane from chloroform in a total yield sintered aluminum oxide pipes standing upright by more than 80%, based on the amount of the binds it is advantageous to prepare it by means of metal couplings with added chloroform, each other, made of special steels or their Legje- To carry out the reaction one can

wrestle, but preferably made of nickel, advantageously the one shown in the drawing these couplings make use of the interruption points in the apparatus arrangement. There are radiators that allow the pipe to reach the required level.

Such high bromination temperatures brought hydrogen in gaseous form through an orifice plate will. By such any variation possible low pressure and a temperature of rand The length of the pipe is also at this aggressive 60 ° C at 1 in the heated by heating element 15 and difficult to handle reaction able to pass the nickel reaction tube 2, for example a dwell times required for any throughputs clear width of 80 mm and a heated length of to enable. 40 2000 mm and aluminum fluoride as a fluorination

For the purpose of adding bromine, catalysts have generally been used up to now. At the same time it becomes chloroform Dosing pumps used whose valves are fed out via a dosing pump at 3. At a spring-loaded metal balls, for example from the internal furnace temperature of a maximum of 400 to 500 ° C Manufactured from alloys containing nickel and molybdenum, trifluoromethane and hydrogen chloride are produced. the end were, passed. Such valves, which consist of a gas-ceramic head leaving the tube at the lower end with a ground stopper and balls mixture, the hydrogen chloride and the not made of mono alloy and a hydrogen fluoride reacted with plastic dispersant in the water wash 4 sion-coated steel spring are suitable for and alkali wash 5 removed. That about calcium that present process, as far as only a con-chloride at 6 dried trifluoromethane is over Continuous operation of several days in 5o a rotameter7 passed into the bromine evaporator 8. Comes into consideration. The bromine required for the bromination dissolves in the event of increased permanent load the plastic coating from the steel spring, so that the metering pump 9 provided with ceramic head in from this, a progressive corrosion through the bromine evaporator 8 is metered in. As the valves the bromine enters and a perfect metering of this pump made of glass spheres with a lower speciating force will. 55 fish weight as bromine are - against - It has now also been found that you can use suction and pressure for the valves that are otherwise usual the present process exchanged very essential bromine side. The mixture of bromine and tridosierang It is advantageous to use a metering pump, fluoromethane is supplied via the steam-heated riser pipe which has a ceramic head with a ground plunger 10, for example a clear width of 18 mm and owns and has a heated length of 2000 mm in place of the spring-loaded 60, in the out Metal balls Glass balls without a spring guide led to existing reaction tube 11 made of aluminum oxide, be turned. Since glass is specifically lighter than where the bromination at a temperature of 700 to Bromine, the suction and pressure side of the pump is 750 ° C (measured on the outer wall), exchanges, so that now the hydrostatic buoyancy as The bromination tube 11 consists of two aluminum closing pressure acts for the valves. The pump work- 65 umoxydrohren between the electrically heated tet in this embodiment according to the invention via ovens 12 at 13 by nickel glands together longer Periods are very reliably coupled with a maxi. The bromination marks emerging at 14 Error width of only about 5%. product is then mixed with water, then with

washed over a mixture of sodium hydroxide solution and sodium bisulfite, stored in a gasometer Calcium chloride dried, compressed and distilled.

example

780 g / h of hydrogen fluoride and 1020 g / h of chloroform (molar ratio 4.5: 1) are fed to the fluorination furnace containing aluminum fluoride. In the furnace there is a temperature gradient from top to bottom with an interval of 500 to 420 ° C. 540 are obtained g / h Trifiuormethan, corresponding to a yield of 90 ⁰ Zo based on starting chloroform equivalent.

The trifluoromethane, dried over calcium chloride, is used together with 1880 g / h of bromine (molar ratio 1: 1.5) sent through the bromination furnace and thermally brominated at an outer wall temperature of 750 ° C. Through the following Water and sodium hydroxide bisulfite wash removes the excess bromine and hydrogen bromide. 830 g / h of trifluorobromomethane are obtained. This corresponds to a conversion of 80% and a yield of 90%, based on converted trifluoromethane. After drying, compression and pressure distillation the trifluorobromomethane is obtained with a purity of 95 to 97% of theory.

Claims (5)

PATENT CLAIMS: 1. A process for the preparation of trifluorobromomethane from chloroform by fluorination of the chloroform and bromination of the trifluoromethane formed with elemental bromine, characterized in that the fluorination of the chloroform in the presence of aluminum fluoride as a fluorination catalyst above 350 ° C and the bromination of the resulting trifluoromethane after a water - and alkali washing and subsequent drying without isolation and purification of intermediate products at reaction temperatures between 650 and 800 ° C in a continuous operation, fluorination of the chloroform with at least 3.5 times the molar amount of gaseous hydrogen fluoride, based on 1 mole of chloroform and carries out the bromination of the trifluoromethane with controlled metering of the bromine with the aid of a metering pump in a reaction zone, the inner walls of which consist of sintered oxides of aluminum, zirconium or magnesium, preferably of aluminum oxide. 2. The method according to claim 1, characterized in that the fluorination of the Chloroform up to 4.5 moles of hydrogen fluoride, based on 1 mole of the chloroform used, used. 3. Process according to Claims 1 and 2, characterized in that the bromination is carried out of the trifluoromethane metered the bromine by adding the bromine via a metering pump, whose valves, made of glass, float through the without spring guide on the bromine hydrostatic buoyancy are closed. 4. Process according to Claims 1 to 3, characterized in that the bromination of the Trifluoromethane with a bromine excess of up to 50 mol percent of the theoretically calculated amount performs. 5. Device for performing the method according to claims 1 to 4, thereby core draws that a tube is used for the bromination of the trifluoromethane, which from Sintered aluminum oxide is made and which consists of pieces that are joined by metal couplings are connected to each other. 1 sheet of drawings © 309 690/285 9.