High-Temperature Rate Constant Determination for the Reaction of OH with iso-Butanol

Abstract

This work presents the first direct experimental study of the rate constant for the reaction of OH with iso-butanol (2-methyl-1-propanol) at temperatures from 907 to 1147 K at near-atmospheric pressures. OH time-histories were measured behind reflected shock waves using a narrow-linewidth laser absorption method during reactions of dilute mixtures of tert-butylhydroperoxide (as a fast source of OH) with iso-butanol in excess. The title reaction's overall rate constant (OH + iso-butanol →(k(overall)) all products) minus the rate constant for the β-radical-producing channel (OH + iso-butanol →(k(β)) 1-hydroxy-2-methyl-prop-2-yl radical + H(2)O) was determined from the pseudo-first-order rate of OH decay. A two-parameter Arrhenius fit of the experimentally determined rate constant in the current temperature range yields the expression (k(overall) - k(β)) = 1.84 × 10(-10) exp(-2350/T[K]) cm(3) molecule(-1) s(-1). A recommendation for the overall rate constant, including k(β), is made, and comparisons of the results to rate constant recommendations from the literature are discussed.

Intermediate species measurement during iso-butanol auto-ignition

“…Results (Fig. 14) show that the overall rate constants of Zheng et al [30] are consistent with Pang et al [31], which are higher than that of the Sarathy mechanism by a factor of 1.3 at the temperature range of 700-1100 K. Figure 15 shows that the branching fractions for four H-atom abstraction branches by the OH radical from the α, β, γ carbon sites and from the OH group of iso-butanol. The legends indicate the site of the H-atom abstraction and the corresponding radicals produced.…”

“…The rate coefficients for the reactions of iso-butanol with OH have been the subject of recent experimental and theoretical studies [30,31]. Pang et al [31] measured the rate constant of the non-β channels in the temperature range of 907-1147 K at near atmospheric pressures using a shock tube, leading to the expression (k overall − k β ) = 1.84×10 −10 exp (−2350/T [K]) [cm 3 mol −1 s −1 ].…”

“…Pang et al [31] measured the rate constant of the non-β channels in the temperature range of 907-1147 K at near atmospheric pressures using a shock tube, leading to the expression (k overall − k β ) = 1.84×10 −10 exp (−2350/T [K]) [cm 3 mol −1 s −1 ]. The shock tube data are in good agreement with the recent theoretical calculations of Zheng et al [30], who used multi-path variational transition-state theory with small curvature tunneling (MP-CVT/SCT) and taking vibration anharmonicity into account, to determine the overall rate constants for iso-butanol + OH-abstractions.…”

“…Solid lines: Sarathy mechanism[17], dashed lines: Zheng et al[30], red square symbols: Pang et al[31]. the dashed lines are those recommended by Zheng et al[30] based on the MP-CVT/SCT(P = 4) calculation.…”

“…the dashed lines are those recommended by Zheng et al[30] based on the MP-CVT/SCT(P = 4) calculation. The recommended branching fractions for the β carbon site from Pang et al[31] at the temperature range of 900-1150 K (square symbols) are also plotted for comparison. It is clear that the branching fractions of α-channel (producing i-C 4 H 8 OH-1) and β-channel (producing i-C 4 H 8 OH-2) recommended…”