(130f) Thermochemistry of Coking in Hydroprocessing Units: Modeling Competitive Naphthalene Saturation and Condensation Reactions

The condensation of polyaromatic hydrocarbons (PAH) often is cited as a mechanism for coke formation in fixed-bed hydroprocessing units. In such units, hydrogen saturates PAH, which inhibits their condensation. There is a competition between PAH saturation and PAH condensation reactions. The competition between the saturation and condensation of naphthalene was simulated at start-of-run (SOR) through end-of-run (EOR) conditions by calculating equilibrium concentrations for a simple system comprised of hydrogen, naphthalene, tetralin, decalin, o-xylene and chrysene. Chrysene is representative of a ?coke precursor?. The calculations show that, as expected, chrysene formation is favored by high temperatures and low H2 pressures. But they also show that small amounts of chrysene are present at moderate pressures and temperatures. The calculations show the change in the relative extents of saturation and condensation reactions as process conditions change from SOR to EOR and the influence of aromatics saturation equilibrium on these reactions.