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 (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.

Kinetics of isopropanol decomposition and reaction with H atoms from shock tube experiments and rate constant optimization using the method of uncertainty minimization using polynomial chaos expansions (MUM‐PCE)

“…When extrapolated, our results are about a factor of 25 smaller than those of Trenwith, which supports his conclusion that his rate constants pertain to a radical chain rather than molecular process. Our agreement with Thomas, who attempted to inhibit chain processes with added nitric oxide, is much better, with our extrapolated rate constant about 25% smaller than his at 800 K. The 2015 experiments of Heyne et al 31 at 976-999 K and 12.5 atm (1266 kPa) partially overlap our temperature range and give rate constants about a factor of 3 larger than ours. Extrapolated to 800 K, they are a factor of 2.3 larger than those of Thomas.…”

“…Our experimental data for isopropanol dehydration (propene formation, black squares) compared to the prior 32 and posterior models and to available experimental work, 31,99 theoretical work, 30,100 and recent isopropanol kinetics models 6,16 [Color figure can be viewed at wileyonlinelibrary.com]…”

“…21,[23][24][25][26][27][28][29] Combustion chemistry is often initiated by decomposition reactions, and previous studies suggest that alcohols decompose mainly through molecular dehydration or through C−C bond scissions ubiquitous to hydrocarbon chemistry. 6,[30][31][32][33] Fission of the C−O bond has too large a barrier to play a significant role. 30 Scheme 1 shows the main unimolecular reactions of isopropanol: dehydration (R1498) produces propene (C 3 H 6 ) and water; C−C bond fission (R1499) produces a methyl radical (CH 3 ) and a CH 3 CHOH radical, whichaccording to calculations by Dames 34 -will decompose to either acetaldehyde (CH 3 CHO) or formaldehyde (CH 2 O).…”

“…Work to understand the mechanism of isopropanol combustion is in progress 21,23–29 . Combustion chemistry is often initiated by decomposition reactions, and previous studies suggest that alcohols decompose mainly through molecular dehydration or through C−C bond scissions ubiquitous to hydrocarbon chemistry 6,30–33 . Fission of the C−O bond has too large a barrier to play a significant role 30 .…”

Isopropanol dehydration reaction rate kinetics measurement using H2O time histories

“…Trenwith 45 studied the reaction in a batch reactor at low pressures between 0.0133 and 0.13 atm at temperatures between 745 and 801 K. The resulting Arrhenius expression has a reported uncertainty of nearly 172%. More recently, Heyne et al 46 studied the reaction in a variable-pressure flow reactor at 12.5 atm over a very limited range of temperatures: 976, 978, and 999 K.…”