Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Patent
1998-06-10
2000-09-12
Siegel, Alan
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
570164, C07C 1708
Patent
active
061180335
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the continuous preparation of 1,1,1,2,3,3,3-heptafluoropropane (referred to hereinbelow as heptafluoropropane) by conversion of hexafluoropropene with HF in the presence of a liquid hydrofluoride of an organonitrogen base corresponding to the general formula [B.times.nHF], where n represents an integer or a fraction.ltoreq.4 and B represents an organonitrocen base.
Document EP-A-0,634,383 describes a general process for the addition of hydrogen fluoride to haloalkenes corresponding to the general formula R.sup.1 CF.dbd.CR.sup.2 R.sup.3 with such a hydrofluoride [B.times.NHF], preferably [(CH.sub.3).sub.3 N.times.2.8 HF] or [(C.sub.2 H.sub.5).sub.3 N.times.2.8 HF], as catalyst. The tests with hexafluoropropene are described on a laboratory scale, both in terms of batchwise production and continuous production. However, complete conversion is not obtainer in the case of the two embodiment variants. On account of its high price, the residual hexafluoropropene contained in the final heptafluoropropane product must be recovered by an expensive distillation.
The objective was to develop a continuous process or the preparation of heptafluoropropane with complete conversion of the hexafluoropropene.
In the abovementioned document EP-A-0,634,383, Examples 4 and 5 use a bubble column (container for the reaction with liquid hydrogen fluoride catalyst which is fully charged with gas bubbles of the reactants and of the product) for the continuous conversion of hexafluoropropene with HF. The degree of conversion of hexafluoropropene amounts to 98.4 and 99% respectively. Although these values appear to be relatively high, they are not, however, high enough to make the abovementioned distillation treatment redundant.
It has now been found that the degree of conversion of hexafluoropropene can be increased to at least 99.99% by passing the reaction mixture through two zones arranged in series, a higher pressure prevailing in the first zone by comparison with that in the second zone. On account of the virtually quantitative conversion, removal of the unconverted starting material by distillation is not necessary. In addition, the process in accordance with the present invention can be carried out on a large scale without any problems, which is not as easy to do in the case of a bubble column.
The subject of the present invention is a process for the continuous preparation of heptafluoropropane by conversion of hexafluoropropene with HF in the presence of at least one liquid hydrofluoride of an organonitrogen base corresponding to formula (I) a fraction.ltoreq.4, characterized in that HF and hexafluoropropene are converted, in a cyclic process, in the presence of a liquid hydrofluoride corresponding to formula (I), in a first zone under a pressure p.sub.1 =1.3 to 10 bar, in that the liquid reaction mixture is then transferred to a second zone and that it comes under a pressure p.sub.2 <p.sub.1 therein, in which p.sub.1 -p.sub.2 .gtoreq.0.3 bar and p.sub.2 .gtoreq.1 bar, in that the resulting heptafluoropropane is evaporated and isolated from the liquid reaction mixture, and in that the remaining liquid reaction mixture is then transferred, after addition of hexafluoropropene and HF, back into the first zone.
The reaction temperature in the first zone is preferably 40 to 100.degree. C., in particular 50 to 80.degree. C. Suitable hydrofluorides, that are liquid at these temperatures, corresponding to formula (I) are, for example, [(CH.sub.3).sub.3 N.times.2.8 HF], [(C.sub.2 H.sub.5).sub.3 N.times.2.8 HF] and [(C.sub.4 H.sub.9).sub.3 N.times.2.6 HF], as well as ##STR1##
One of the three hydrofluorides mentioned previously is preferably used. However, any of the other hydrofluorides corresponding to formula (I), mentioned in document EP-A-0,634,383, that are liquid at the reaction temperatures chosen, are also suitable. The preparation of the hydrofluorides is also described in document EP-A-0,634,383, to which reference is made explicitly herein. Besides hexafluoropropene, the haloalken
Hopp Peter
Kaufmann Wolf-Dietmar
Siegel Alan
Solvay ( Societe Anonyme)
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