Theoretical study of H-abstraction reactions of di-n-propyl ether oxidation by H, CH3, HO2 and OH radicals

The H-abstraction reactions from di-n-propyl ether (DPE) by radicals are significant in the DPE oxidation process. However, corresponding rate constants only rely on either analogy from alcohols or estimation from alkanes due to the lack of experimental and theoretical studies. In current work, thermochemistry and kinetics of DPE oxidation by the H, CH3, HO2 and OH radicals have been studied using the composite methods (CBS-QB3 and G4). Four H-abstraction reaction systems have been discussed, all of them occur through energy barriers of -5.4-20.5 kcal/mol. The energy barriers increase in the order & alpha; < & beta; < & gamma; at CBS-QB3 and G4 levels. The hydrogen-bond reactant complexes, RC & beta;HO2, RC & alpha;OH, RC & beta;OH and RC & gamma;OH, are identified in the entrance channel for the H-abstraction by HO2 and OH radicals. The rate constants for target reactions are calculated with the transition state theory and canonical variational transition state theory over a broad temperature range of 400-1400 K. Rate constants and branching ratios show that the H-abstraction reaction from C & alpha; is the dominant reaction over the investigated temperature range. The total rate constants of the DPE + OH system have been fitted as follows: k = 1105 x T 3.185 exp(1720/T) (cm3 mol-1 s- 1). The G4 data well reproduce the available experimental rate constant for DPE + OH system. The rate constants of H-abstraction reactions in the kinetic model of Serinyel et al. [Fuel 263 (2020) 116554] are modified based on the current calculated results to obtain a revised model. A validation for the revised model against the jet-stirred reactor (JSR) measurements from the literature are also provided, and the modified mechanism shows good performances to predict the JSR data. Reaction pathway and sensitivity analyses are performed to identify the fuel consumption paths and key re-actions in oxidation process of DPE.