Hydrogenation kinetics of typical polycyclic aromatic hydrocarbons in direct coal liquefaction solvent

As a crucial component in the solvent for direct coal liquefaction, the partially hydrogenated products of polycyclic aromatic hydrocarbons exhibit excellent hydrogen-donating performance. This study investigates the distribution of hydrogenation reaction products from naphthalene and phenanthrene in the presence of a NiMo/γ-Al₂O₃ catalyst under varying reaction conditions The kinetic models of the naphthalene and phenanthrene hydrogenation reactions were developed based on the Langmuir-Hinshelwood-Hougen-Watson theory of competitive adsorption. In which, the regression analyses were performed using Arrhenius and van’t Hoff reparameterisation methods. The model parameters include the prefactor, activation energy, and the entropy and enthalpy of adsorption. Adsorption entropy and enthalpy are used to describe the adsorption behavior of substances adsorbing onto the catalyst surface. The parameters are both statistically and thermodynamically consistent, providing an accurate description of the hydrogenation reactions occurring simultaneously with naphthalene and phenanthrene. It was found that the entropy change and enthalpy change of the adsorption of reactants on the catalyst were correlated with the number of aromatic rings. The hydrogenation of naphthalene and phenanthrene follows the principle of ring-by-ring. The reactivity of end-ring hydrogenation of phenanthrene is greater than that of intermediate ring. The hydrogenation of phenanthrene can easily generate tetrahydro-phenanthrene, which can be further hydrogenated to generate asymmetry-octahydrohexaphenanthrene. Competitive adsorption of reactants in the active sites of the catalyst during mixed co-hydrogenation of naphthalene and phenanthrene will change the entropy of reactants adsorbed on the catalyst and thus affect the rate of hydrogenation reaction. This, in turn, leads to an increase in the yield of partially hydrogenated products.