Supercritical Water Treatment of Alkyl Aromatics: Observations Beyond Model Predictions

Heavy oils are much less valuable than cleaner burning lighter fuels. Thermal cracking (pyrolysis) is a conventional way to convert heavy oils into lighter fuels, with the downside of producing a considerable amount of coke. Here, we study the cracking of heavy oil and model alkyl aromatics in supercritical water experimentally and with computer-generated kinetic models based on quantum chemistry calculations. Hexylbenzene was used as a model compound, and the computer-generated detailed model accurately predicts many of the experimental observations. Here we focus on several mysteries and discrepancies between the model and the experiments, including: (1) mis-predicted yields of alkanes vs. alkenes and styrene vs. ethyl benzene, (2) the formation of a dark colored product as well as multi-ring aromatics not predicted by the kinetic model, as well as (3) the unexpectedly slow conversion the alkyl aromatics in a heavy oil distillate relative to a pure alkyl aromatic model compound.