Kinetics of the Gas-Phase Oxidation of Hexafluoropropylene In a Laminar Flow Reactor

The gas-phase oxidation of hexafluoropropylene (HFP) with molecular oxygen has been studied experimentally in an isothermal, laminar flow reactor at a pressure of 4.5 bar and over the temperature range of 453 to 503 K. Feed mixtures comprising 20 to 67% HFP in oxygen were used at total flow-rates of between 150 and 550 cm³ min^-1. Online GC/FID analysis was used for reactant and stable product quantification. The most significant products detected were hexafluoropropylene oxide (HFPO), trifluoroacetyl fluoride (CF₃COF) and carbonyl fluoride (COF₂). Minor products included tetrafluoroethylene (C₂F₄), hexafluorocyclopropane (c-C₃F₆) and carbon dioxide. A kinetic reaction scheme involving 11 species and 7 reactions was developed and used to model the oxidation of HFP. The initial steps in this scheme encompassed the addition of oxygen to the double bond of the fluoro-olefin and decomposition of the resultant dioxetane intermediate to form HFPO and the haloacetyl fluorides. Subsequent steps included the thermal decomposition of HFPO to yield CF₃COF, C₂F₄ and c-C₃F₆, elimination of C₂F₄ through oxidation and decomposition of CF₃COF via C-C bond scission to give COF• and CF₃• radicals, which undergo recombination and oxidation reactions. Rate parameters for the oxidation reactions were determined through a least-squares minimization procedure coupled with two-dimensional numerical integration of the governing equations utilizing the method of lines.