Flash pyrolysis of polyethyleneglycol .2. Kinetics determined by T-jump/FTIR spectroscopy

The rate of formation of all quantified products from flash-pyrolysis of polyethyleneglycol having Mw = 2090 (PEG-2090) was determined using T-jump/FTIR spectroscopy. In the 370-550 degrees C range and at 2 atm Ar, a discontinuity in the Arrhenius plot occurs at 460-470 degrees C. Below this temperature, E(a) = 7 +/- 8 kcal/mol and In(A/s) = 1 +/- 6. Above this temperature, E(a) = 22 +/- 4 kcal/mol and ln(A/s) = 12 +/- 3. The explanation for this discontinuity lies in the fact that pyrolysis of PEG-2090 forms both volatile products and a higher Mw residue below the transition temperature. Above the transition temperature, pyrolysis products from both the PEG-2090 and the residue are formed. In addition to global kinetics, the kinetics of formation of the individual products were analyzed separately. For both the global process kinetics and the kinetics for formation of individual species (except for 2-methoxy-1,3-dioxolane below 460 degrees C), the rate of desorption/evaporation controls the rate of release of species to the gas phase. At 11 atm, the global Arrhenius parameters for the formation of the products are E(a) = 52 +/- 0.3 kcal/mol and In(A/s) = 32 +/- 0.2 over the 400-550 degrees C range, with no discontinuity. Thus, condensed-phase reactions dominate in controlling the product evolution rate at 11 atm. (C) 1997 by The Combustion Institute.