Initiation and Carbene Induced Radical Chain Reactions in CH2F2 Pyrolysis.

High temperature dissociations of organic molecules typically involve a competition between radical and molecular processes. In this work, we use a modeling, experiment, theory (MET) framework to characterize the high temperature thermal dissociation of CH2F2, a flammable hydrofluorocarbon (HFC) that finds widespread use as a refrigerant. Initiation in CH2F2 proceeds via a molecular elimination channel; CH2F2→CHF+HF. Here we show that the subsequent self-reactions of the singlet carbene, CHF, are fast multichannel processes and a facile source of radicals that initiate rapid chain propagation reactions. These have a marked influence on the decomposition kinetics of CH2F2. The inclusion of these reactions brings the simulations into better agreement with the present and literature experiments. Additionally, flame simulations indicate that inclusion of the CHF+CHF multichannel reaction leads to a noticeable enhancement in predictions of laminar flame speeds, a key parameter that is used to determine the flammability of a refrigerant.

A Literature Survey of the Chemistry of Flame Inhibition.

Evidence is beginning to accumulate indicating that catalytic recombination of oxygen atoms may be the mechanism of extinction of flames by halogenated extinguishing agents. The literature of flame inhibition and of oxygen atom chemistry has been examined to ascertain whether the available data would support such a mechanism. Considerable sustentative evidence was found. Kinetic rate-constant data are not available covering all reactions of interest, but those that are reported indicate that catalytic recombination of oxygen atoms can probably compete successfully with normal flame processes which require them.