(375c) Gas-Phase Catalysis for Pyrolyzing Acetic Acid

We compare our quantum-chemically predicted rate constants with new experimental measurements for pyrolysis of acetic acid to ketene. Previously, Padmanabhan et al. (1968) measured first-order kinetics with respect to acetic acid concentration, reporting different rate constants for overall conversion and ketene formation rate. Grottoli et al. (1991) combined experiments with reactor modeling, fitting the data to rate expressions for ketene formation, decarboxylation, and ketene decomposition.

In the present work, we measure conversion of acetic acid in a tubular flow reactor using the homogeneous catalyst triethyl phosphate that was studied by Padmanabhan et al. and by Grottoli et al. Exhaust gases are analyzed by molecular-beam mass spectrometry, allowing us to infer overall rate coefficients using plug-flow and CSTR models. We also compute gas-phase thermochemistry of species and transition states and kinetics for thermal and and phosphoric-acid-catalyzed conversion of acetic acid to ketene and water. Structures, vibrational frequencies, and energies are computed by quantum chemistry with Gaussian 09. Rate coefficients are computed with the NIST ChemRate code using the Gaussian output files. The results agree well, supporting our new process-chemistry model.