A theoretical study of 1-propanol H-abstractions and successive reactivity

A mechanistic understanding of alcohol pyrolysis and oxidation is critical to their effective integration into the fuel industry. 1-propanol (1-C3H7OH) is a promising biofuel and, moreover, its mechanism is a foundation for that of larger alcohols. As part of a combined modeling-experimental-theoretical investigation into 1-C3H7OH, we explore the H abstractions from 1-C3H7OH with ab initio transition state theory-based master equation (AI-TST-ME) evaluations for the two abstractors, OH and H, that are influential during 1-C3H7OH combustion. We report branching fractions between the resulting C3H7O radicals (i.e., at 1500 K, for the OH abstractor: 0.40, 0.27, 0.24, and 0.09 to alpha-, beta-, gamma-, and omicron-C3H7O; for the H abstractor: 0.80, 0.14, 0.06, and 0.00). The sensitivity to level of theory as well as the influence of multidimensional torsional effects are evaluated for the abstractions by OH. Notably, the correction for torsional coupling for the alpha-C3H7O is about half of that as for the beta-C3H7O - fully neglecting the multidimensional effect, then, would lead to significantly different branching fractions. The subsequent dissociation of the C3H7O radicals to nine products, including CH3, OH, ethene, ethyl radical, and H is also reported with AI-TST-ME computations. We find, however, that at relevant temperatures and pressures, very little 1-C3H7OH + OH collisionally stabilizes to thermalized C3H7O radicals (i.e., 7 % at 1 atm and 1500 K). Instead, the abundant, rovibrationally excited populations of C3H7O radicals promptly dissociate to the products. In the first exploration of the influence of non-thermal effects on the branching fractions to dissociation products, we find that H production enhances significantly (i.e., more than a factor of 2) at the cost of OH production.