High-temperature thermal decomposition of triphenyl phosphate vapor in an inert medium: Flow reactor pyrolysis, quantum chemical calculations, and kinetic modeling

Improving the fire resistance of polymeric materials is an important research problem, which is solved using various flame retardants. Organophosphorus compounds are among the most effective and en-vironmentally friendly flame retardants. This paper reports an experimental, theoretical, and kinetic modeling study of the conversion of triphenyl phosphate (TPP) during thermal decomposition in an inert medium, i.e., under conditions typical of the flame zone near the polymer surface. Pyrolysis of TPP vapor was examined in a thermal reactor under argon flow at a pressure of 1 atm. The temperature dependence of the composition of TPP pyrolysis products leaving the thermal reactor was investigated by molecular beam mass spectrometry in the temperature range of 50 0-130 0 K. The geometry of all structures on the potential energy surfaces of TPP and primary and secondary decomposition products of TPP was optimized using density functional theory (DFT) (omega B97XD) with the 6-31G(d) basis set. The kinetic rate constants of the thermal decomposition reactions of TPP were calculated using the Rice-Ramsperger-Kassel-Marcus theory with the master kinetic equation (RRKM-ME) implemented in the MESS code, and thermochemical parameters were obtained for TPP and primary and secondary decomposition products of TPP in the temperature range of 20 0-60 0 0 K. A detailed chemical kinetic mechanism for TPP pyrolysis was developed by combining the primary TPP decomposition reaction path-ways with the rate parameters derived from the theoretical calculations and submechanisms available in the literature for the conversion of the phenyl and phenoxy radicals and phosphorus containing products. The proposed kinetic mechanism quantitatively reproduces the measured temperature-resolved TPP mole fraction profile at the reactor outlet. The mechanism also provides a good fit to the experimentally observed trends in the conversion of major phosphorus-containing intermediates detected in this work. (c) 2023 The Combustion Institute. Published by Elsevier Inc. All rights reserved.