A photochemical reaction apparatus including a reactor and a light source situated so that light from the light source is directed through a portion of the reactor wall is disclosed. The apparatus is characterized by the portion of the reaction wall comprising a copolymer of a perfluoro (alkyl vinyl ether). The perfluoro (alkyl vinyl ether) is selected from the group consisting of CF30CF═CF2, C2F5OCF═CF2, C3F7OCF═F2, and mixture thereof. Also disclosed is a photochemical reaction process wherein light from a light source is directed through said reactor wall to interact with reactants in said reactor. A process for increasing the fluorine content of at least one compound selected from hydrocarbons and halohydrocarbons, comprising: (a) photochlorinating said at least one compound; and (b) reacting the halogenated hydrocarbon produced in (a) with HF. A process for producing an olefinic compound, comprising: (a) photochlorinating at least one compound selected from hydrocarbons and halohydrocarbons containing at least two carbon atoms and at least two hydrogen atoms to produce a halogenated hydrocarbon containing a hydrogen substituent and a chlorine substituent on adjacent carbon atoms; and (b) subjecting the halogenated hydrocarbon produced in (a) to dehydrohalogenation.