A Systematic Theoretical Kinetics Analysis for the Waddington Mechanism in the Low-Temperature Oxidation of Butene and Butanol Isomers

Abstract

The Waddington mechanism, or the Waddington-type reaction pathway, is crucial for low-temperature oxidation of both alkenes and alcohols. In this study, the Waddington mechanism in the oxidation chemistry of butene and butanol isomers was systematically investigated. Fundamental quantum chemical calculations were conducted for the rate constants and thermodynamic properties of the reactions and species in this mechanism. Calculations were performed using two different ab initio solvers: Gaussian 09 and Orca 4.0.0, and two different kinetic solvers: PAPR and MultiWell, comprehensively. Temperature- and pressure-dependent rate constants were performed based on the transition state theory, associated with the Rice Ramsperger Kassel Marcus and master equation theories. Temperature-dependent thermochemistry (enthalpies of formation, entropy, and heat capacity) of all major species was also conducted, based on the statistical thermodynamics. Of the two types of reaction, dissociation reactions were significantly faster than isomerization reactions, while the rate constants of both reactions converged toward higher temperatures. In comparison, between two ab initio solvers, the barrier height difference among all isomerization and dissociation reactions was about 2 and 0.5 kcal/mol, respectively, resulting in less than 50%, and a factor of 2–10 differences for the predicted rate coefficients of the two reaction types, respectively. Comparing the two kinetic solvers, the rate constants of the isomerization reactions showed less than a 32% difference, while the rate of one dissociation reaction (P1 ↔ WDT12) exhibited 1–2 orders of magnitude discrepancy. Compared with results from the literature, both reaction rate coefficients (R4 and R5 reaction systems) and species’ thermochemistry (all closed shell molecules and open shell radicals R4 and R5) showed good agreement with the corresponding values obtained from the literature. All calculated results can be directly used for the chemical kinetic model development of butene and butanol isomer oxidation.

Pressure-dependent kinetics of peroxy radicals formed in isobutanol combustion

“…A recent study by Li et al looked at bAlkoxyIsom and b-bscissionFromAlkoxy using two methods, CCSD(T) and DLPNO-CCSD(T), with basis set extrapolation. 42 Relative to the current work, DLPNO-CCSD(T) resulted in a larger difference in barrier heights than CCSD(T) did (see Table 1). For these two reactions larger barrier hight differences exist between the present work and that of Li et al than between this work and that of Sun et al 18 or Lizardo-Huerta et al 19 The high-pressure-limit rates in this network can be compared to those presented in Sun et al, Lizardo-Huerta et al and Li et al 18,19,42 Nine out of the ten rates in Lizardo-Huerta et al come within one order of magnitude with the rates of corresponding reactions in this work over the temperature range 500-1000 K, indicating good agreement.…”

“…There have been more previous quantum calculations of the bRO 2 surface than of the other two isomers' surfaces because bR can also form from OH addition to isobutene. 18,19,42 This section compares this work's results with those of two other quantum studies. They include all the reactions in this work except for bH2OForm, 16 which has not been published for the b-isobutanol surface before.…”

“…The rate coefficients by Sun et al over the same temperature range differed from this work by an average factor of 23. Adjusting the activation energy of the Sun et al rates based on the differences in energies shown in Table 1 reduced this difference in rates to an average factor of 15, indicating that energy differences do not entirely account for the difference in rates; this indicates Lizardo-Huerta et al 19 Li et al DLPNO 42 Li et al that differences in calculated partition functions are also contributing. In the work of Li et al, only the bAlkoxyIsom using the DLPNO-CCSD(T) method, differed by more than a factor of 10 over the same temperature range, due in part to the 16 kJ mol À1 barrier height difference.…”

On the similarities and differences between the products of oxidation of hydrocarbons under simulated atmospheric conditions and cool flames

“…These chemical compounds are mainly in the (d) area. In ozonolysis/photooxidation studies, initial oxidation phase, by ozone and/or the radical OH q have been widely described (Walser et al, 2008;Kundu et al, 2012;Nørgaard et al, 2013;Librando and Tringali, 2005). Although the experimental conditions and the associated reaction mechanisms are different, it is observed, similarly to Fang et al (2017), many common products of these different oxidation modes.…”

On the similarities and differences between the products of oxidation of hydrocarbons under simulated atmospheric conditions and cool-flames

“…Considering the presence of the radicals OH˙, we also searched for chemical compounds resulting from the Waddington mechanism (Li et al, 2020). This mechanism, through which oxidation of alkenes can occur, has two reaction pathways in the case of limonene.…”