Understanding the reactivity of unsaturated alcohols: Experimental and kinetic modeling study of the pyrolysis and oxidation of 3-methyl-2-butenol and 3-methyl-3-butenol

The reactivity of unsaturated alcohols with a C=C double bond in the β- and γ-positions to the hydroxyl group is not well established. The pyrolysis and oxidation of two such unsaturated alcohols have been studied, i.e. 3-methyl-2-butenol (prenol) and 3-methyl-3-butenol (isoprenol). Experiments at three equivalence ratios, i.e. φ = 0.5, φ = 1.0 and φ = ∞ (pyrolysis), were performed using an isothermal jet-stirred quartz reactor at temperatures ranging from 500 to 1100 K, a pressure of 0.107 MPa and a residence time of 2 s. The reactant and product concentrations were quantified using gas chromatography. A kinetic model has been developed using the automatic network generation tool “Genesys”. Several important rate coefficients are obtained from new quantum chemical calculations. Overall, there is a good agreement between model calculated mole fraction profiles and experimental data. Reaction path analysis reveals that isoprenol consumption is dominated by a unimolecular reaction to formaldehyde and isobutene. At the applied operating conditions, the equivalence ratio has no effect on the isoprenol conversion profile. Pyrolysis and oxidation of prenol is dominated by radical chemistry, with hydrogen abstractions from prenol forming resonantly stabilized radicals as dominating conversion path. Oxidation and decomposition of the resulting radicals are predicted to form 3-methyl-2-butenal and 2-methyl-1,3-butadiene, which have been detected as important products in the reactor effluent.