Revisiting the reaction kinetics of selective hydrogenation of phenylacetylene over an egg-shell catalyst in excess styrene

Abstract

Selective hydrogenation of phenylacetylene is an important reaction for the removal of a small amount of phenylacetylene from styrene monomer. In this work, the kinetics of phenylacetylene hydrogenation over an egg-shell Pd/Al2O3 catalyst in the presence of excess styrene was investigated by using a laboratory-scale fixed-bed reactor. The liquid-phase residence time distribution (RTD) in the reactor under different operating conditions was measured by tracer pulse method, and the Peclet number was determined based on the experimental data and the RTD model. The kinetic experiments showed that an increase in temperature and pressure or a decrease in the liquid hourly space velocity gave rise to increased conversion of phenylacetylene and decreased concentration of styrene. A rigorous mathematical model combining reaction kinetics, external mass transfer, intraparticle diffusion as well as axial dispersion of the liquid phase was developed to describe the selective hydrogenation of phenylacetylene in the reactor, and the kinetic and adsorption parameters involved in the kinetic model were estimated by minimization of the sum of squares of relative residuals between observed and model-derived concentrations of different components. The kinetic model can describe the phenylacetylene hydrogenation over the Pd/Al2O3 catalyst very well, and the activation energies for the hydrogenation reactions of phenylacetylene to styrene, styrene to ethylbenzene and phenylacetylene to ethylbenzene were 48.6, 52.2 and 57.9kJ/mol, respectively.