Kinetic modelling of the catalytic hydrogenation of CO2-expanded α-methylstyrene

Kinetic modelling of the catalytic hydrogenation of CO2-expanded α-methylstyrene is reported. Langmuir–Hinshelwood rate equations are evaluated for the correlation of kinetic rate data obtained in an earlier study in which the reaction was carried out at 323 K and 7–13 MPa using a Pd/C catalyst. The Peng-Robinson equation of state is used for the estimation of concentration terms that appear in the rate equations. Overall, the phase equilibria and kinetic modelling provide evidence that the rate-enhancing effect of CO2 is influenced by two competing factors: solvent strength and reactant concentration. The presence of CO2 modifies the solvent strength of the liquid phase, leading to more favourable adsorption equilibrium constants for the surface reaction. However, CO2 also acts as a diluent, an effect that leads to reduced reaction rates. The optimum level of CO2 for rate enhancement depends on the operating pressure.