An Ab Initio RRKM-Based Master Equation Study for Kinetics of OH-Initiated Oxidation of 2-Methyltetrahydrofuran and Its Implications in Kinetic Modeling

Abstract

Cyclic ethers (CEs) can be promising future biofuel candidates. Most CEs possess physico-chemical and combustion indicators comparable to conventional fuels, making them suitable for internal combustion engines. This work computationally investigates the kinetic behaviors of hydrogen abstraction from 2-methyl tetrahydrofuran (2MTHF), one of the promising CEs, by hydroxyl radicals under combustion and atmospheric relevant conditions. The various reaction pathways were explored using the CCSD(T)/cc-pVTZ//M06-2X/aug-cc-pVTZ level of theory. The Rice–Ramsperger–Kassel–Marcus-based master equation (RRKM-ME) rate model, including treatments for hindered internal rotation and tunneling, was employed to describe time-dependent species profiles and pressure and temperature-dependent rate coefficients. Our kinetic model revealed that the H-abstraction proceeds via an addition-elimination mechanism forming reaction complexes at both the entrance and exit channels. Eight different reaction channels yielding five radical products were located. The reaction exhibited complex kinetics yielding a U-shaped Arrhenius behavior. An unusual occurrence of negative temperature dependence was observed at low temperatures, owing to the negative barrier height for the hydrogen abstraction reaction from the C-H bond at the vicinity of the O-atom. A shift in the reaction mechanism was observed with the dominance of the abstraction at Cα-H of 2MTHF ring (causing negative-T dependence) and at CH3 (positive-T dependence) at low and high temperatures, respectively. Interestingly, the pressure effect was observed at low temperatures, revealing the kinetic significance of the pre-reaction complex. Under atmospheric pressure, our theoretical rate coefficients showed excellent agreement with the available literature data. Our model nicely captured the negative temperature-dependent behaviors at low temperatures. Our predicted global rate coefficients can be expressed as k (T, 760 Torr) = 3.55 × 101 × T−4.72 × exp [−340.0 K/T] + 8.21 × 10−23 × T3.49 × exp [918.8 K/T] (cm3/molecule/s). Our work provides a detailed kinetic picture of the OH-initiated oxidation kinetics of 2MTHF. Hence, this information is useful for building a kinetic me chanism for methylated cyclic ethers.

Probing the Thermochemistry Properties and Rate Kinetics of Trimethyl Phosphate (TMP): An H-Atom Abstraction (HAA) Reactions Perspective

“…Single point energies (SPE) are calculated by using coupled-cluster theory CCSD/cc-pVXZ (where X = D and T) and Møller–Plesset perturbation theory MP2/cc-pVXZ (where X = D, T, and Q), The resulting SPEs were extrapolated to the complete basis set (CBS) limit using eq The Master Equation System Solver (MESS) package via the eigenvalue method was used to evaluate temperature- and pressure-dependent rate coefficients for fine-tuning rates or reactions. The MESS package was used to solve the one-dimensional (1-D) master equation and to compute temperature-dependent phenomenological rate constants in the zero and high-pressure limits within the Rice–Rampsberger–Kassel–Marcus (RRKM) Master Equation theory . The rigid-rotor harmonic oscillator (RRHO) model was used to compute densities of states and partition functions of local minima and number of transition states.…”

“…Single point energies (SPE) are calculated by using coupled-cluster theory CCSD/cc-pVXZ (where X = D and T) and Møller–Plesset perturbation theory MP2/cc-pVXZ (where X = D, T, and Q), The resulting SPEs were extrapolated to the complete basis set (CBS) limit using eq E CCSD / cc ‐ pVTZ + false( E CCSD / cc ‐ pVTZ − E CCSD / cc ‐ pVDZ false) * 3 4 / ( 4 4 − 3 4 ) + E MP 2 / cc − pVQZ + false( E MP 2 / cc − pVQZ − E MP 2 / cc ‐ pVTZ false) * 4 4 / ( 5 4 − 4 4 ) − E MP 2 / cc ‐ pVTZ + false( E MP 2 / cc ‐ pVTZ − E normalQ / cc ‐ pVDZ false) * 3 4 / ( 4 4 − 3 4 ) The Master Equation System Solver (MESS) package via the eigenvalue method was used to evaluate temperature- and pressure-dependent rate coefficients for fine-tuning rates or reactions. The MESS package was used to solve the one-dimensional (1-D) master equation and to compute temperature-dependent phenomenological rate constants in the zero and high-pressure limits within the Rice–Rampsberger–Kassel–Marcus (RRKM) Master Equation theory . The rigid-rotor harmo...…”

“…The MESS package was used to solve the one-dimensional (1-D) master equation and to compute temperature-dependent phenomenological rate constants in the zero and high-pressure limits within the Rice–Rampsberger–Kassel–Marcus (RRKM) Master Equation theory. 63 The rigid-rotor harmonic oscillator (RRHO) model was used to compute densities of states and partition functions of local minima and number of transition states.…”