Verfahren zur Herstellung von Polyfluorolefinen

A perfluorolefine is obtained by passing through a hot zone maintained at a temperature of 400 DEG C. to 650 DEG C. an aliphatic perfluoromono- or di-carboxylic acid or an aliphatic omega hydroperfluorocarboxylic acid, said acid containing at least 3 carbon atoms in the molecule, in vaporized form, in the presence of an excess by volume of an inert gaseous diluent and recovering the perfluorinated olefin. The perfluorocarboxylic acid is preferably one having the general formula F-CnF2nCOOH, n being an integer from 2 to 11 the resultant perfluoroolefin being of the formula F-Cn-2F2(n-2) CF=CF2. Specified gaseous diluents are nitrogen and carbon dioxide. In a preferred method of operation, a substantially anhydrous mixture of the acid and diluent is passed through a tube heated to the reaction temperature, preferably at hot zone contact times not exceeding five seconds, the reaction products are condensed in a cold trap and the perfluoroolefin separated by distillation. The tube may be made of stainless steel or steel lined with silver, platinum or other corrosion resistant metal and may, if desired, be filled with a refractory oxide. Atmospheric pressure or a higher or lower pressure may be used, but the pressure should not exceed the critical pressure of the acid at reaction temperature. Examples are given for the production of tetrafluoroethylene from perfluoropropionic acid, perfluoropropylene from perfluorobutyric acid, and perfluoroheptene-1 from perfluorooctanoic acid. Other perfluoroacids specified are perfluoro-isobutyric, -pentanoic, -heptanoic and -decanoic acids, perfluorosebacic acid which yields perfluorooctadiene 1,7,4-hydrohexafluorobutanoic acid which yields 3-hydropentafluoro propene-1 and 7-hydrododecafluoroheptanoic acid which yields 6-hydroundecafluorohexene-1. The products can be used to form perfluorinated polymers.