A continuous, vapor phase method for purifying a crude mixture of 1,1,1,3,3,3-hexafluoropropane and one or more unsaturated fluorocarbon compounds, the process comprising: a) providing a photochlorinator vessel comprising: 1) a UV lamp unit comprising a UV lamp located in a transparent inner well, the transparent inner well being located within a transparent outer well, the outer well being provided with material for cooling walls of the inner and outer wells; the inner well and the outer well defining separate chambers isolated from each other; and 2) a reaction vessel into which the UV lamp unit has been inserted; b) introducing into the reaction vessel a gaseous mixture of Cl2 and a distillation inseparable mixture of 1,1,1,3,3,3-hexafluoropropane and one or more unsaturated fluorocarbon compounds; c) reacting, in the gaseous state and in the presence of UV light from the photochlorinator, the mixture with Cl2 with the distillation inseparable mixture of 1,1,1,3,3,3-hexafluoropropane and one or more unsaturated compounds to saturate unsaturated fluorocarbons into a reacted mixture, and d) separating a purified 1,1,1,3,3,3-hexafluoropropane product containing less than 1000 ppm, most preferably less than 100 ppm unsaturated fluorocarbons.