Perfluorocyclobutane (C-318, b.p. -6.degree. C.) is a valuable material which can be used as a propellant, etch gas and fire extinguishant. This compound is typically made by cyclodimerization of tetrafluoroethene (TFE) or is recovered as a by-product from the manufacture of TFE. As a result C-318 may be contaminated with unsaturates such as E- and Z-perfluoro-2-butene (i.e., CF.sub.3 CF.dbd.CFCF.sub.3 or FC-1318my) and perfluoroisobutene (i.e., (CF.sub.3).sub.2 C.dbd.CF.sub.2 or PFIB or FC-1318mmt). These compounds, especially the latter, are highly toxic and must be removed prior to commercial use. FC-1318's are difficult to separate from C-318 by distillation as the boiling points are similar.
U.S. Pat. No. 5,001,287 discloses a process for treating an impure mixture consisting essentially of at least one olefinic impurity and at least one saturated halocarbon by contacting the mixture with a source of hydrogen in the presence of a hydrogenation catalyst. The saturated halocarbon includes perfluorocyclobutane and the catalyst includes Group VIII metals and rhenium. The olefinic impurity is converted to a hydrogenated form. For example, CF.sub.3 CH.sub.2 F containing CF.sub.2 .dbd.CHCl impurity may be treated to produce CF.sub.3 CH.sub.2 F containing CHF.sub.2 CH.sub.2 Cl.
There is a need for alternative methods of purification. In particular, in the case of purifying certain perfluorocycloalkanes, there is a need for a process for obtaining products of reaction of the olefinic impurity which are not simply products of adding hydrogen at the point of unsaturation.