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)

Abstract

We have used the single-pulse shock tube technique with postshock GC/MS product analysis to investigate the mechanism and kinetics of the unimolecular decomposition of isopropanol, a potential biofuel, and of its reaction with H atoms at 918-1212 K and 183-484 kPa. Experiments employed dilute mixtures in argon of isopropanol, a radical scavenger, and, for H-atom studies, two different thermal precursors of H. Without an added H source, isopropanol decomposes in our studies predominantly by molecular dehydration. Added H atoms significantly augment decomposition, mainly by abstraction of the tertiary and primary hydrogens, reactions that, respectively, lead to acetone and propene as stable organic products. Traces of acetaldehyde were observed in some experiments above ≈ 1100 K and establish branching limits for minor decomposition pathways. To quantitatively account for secondary chemistry and optimize rate constants of interest, we employed the method of uncertainty minimization using polynomial chaos expansions (MUM-PCE) to carry out a unified analysis of all datasets using a chemical model-based originally on JetSurF 2.0. We find: k(isopropanol → propene + H 2 O) = 10 (13.87 ± 0.69) exp(−(33 099 ± 979) K/ T) s −1 at 979-1212 K and 286-484 kPa, with a factor of two uncertainty (2σ), including systematic errors. For H atom reactions, optimization yields: k(H + isopropanol → H 2 + p-C 3 H 6 OH) = 10 (6.25 ± 0.42) T 2.54 exp(−(3993 ± 1028) K /T) cm 3 mol −1 s −1 and k(H + isopropanol → H 2 + t-C 3 H 6 OH) = 10 (5.83 ± 0.37) T 2.40 exp(−(1507 ± 957) K /T) cm 3 mol −1 s −1 at 918-1142 K and 183-323 kPa. We compare our measured rate constants with estimates used in current combustion models and discuss how hydrocarbon functionalization with an OH group affects H abstraction rates.