Joshua S. Heyne

Uncertainty analysis in the use of chemical thermometry: a case study with cyclohexene.

A general method to evaluate the absolute uncertainties in temperatures derived using chemical thermometry is developed and applied to the retro Diels-Alder reaction of cyclohexene. Experiments from previous studies of this reaction are reanalyzed to establish the minimum absolute uncertainty limit. Chemical thermometry results are compared with thermocouple measurements in experiments performed in a flow reactor at 6.1 atm pressure and at temperatures from 957 to 978 K . Using conservative uncertainty estimates, our analysis yields absolute (1σ) uncertainties of temperature through chemical thermometry using this reaction greater than ±20 at 1000 K. Neither more refined experimental techniques nor computational theory is likely to refine rate correlation parameters sufficiently to reach the absolute temperature uncertainties often reported in the literature for chemical thermometry using the retro Diels-Alder reaction of cyclohexene. Published chemical thermometry uncertainty estimates typically have not quantitatively considered the absolute uncertainties of the original data from which the reference rate correlations were based.

Decomposition studies of isopropanol in a variable pressure flow reactor

Abstract Alternatives to traditional petroleum derived transportation fuels, particularly alcohols, have been investigated increasingly over the last 5 years. Isopropanol has received little attention despite bridging the gap between smaller alcohols (methanol and ethanol) and the next generation alcohols (butyl alcohols) to be used in transportation fuels. Previous studies have shown that decomposition reactions that dehydrate are important in the high-temperature oxidation of alcohols. Here we report new data on the dehydration reaction for isopropanol (iC3H7OH → C3H6 + H2O) in a Variable Pressure Flow Reactor at 12.5 atm pressure and temperatures from 976–1000 K. Pyrolysis experiments are performed in the presence of a radical trapper (1,3,5 trimethyl benzene or toluene) to inhibit secondary reactions of radicals with the fuel and product species. The recommended rate constant for the dehydration reaction is determined using an indirect method along with Latin Hypercube sampling to estimate uncertainties. Comparison of the rate constant data to previous works show that the reaction is considerably more rapid than the high level theoretical predictions of Bui et al. (Bui et al., J. Chem. Phys., 2002). The dehydration reaction rate for isopropanol is well described by k = 8.52 × 106T2.12 exp (− 30, 667/T) with an estimated uncertainty of σ  ln  A2 = 0.0195. The C–C bond fission reaction is also investigated, but the insensitivity of the decomposition data to this reaction results in an uncertainty in the determined rate constants to approximately 2 orders of magnitude. Theoretical estimates lie within these experimental uncertainties.