BEHAVIOR OF AN ADIABATIC PACKED-BED REACTOR .2. MODELING

The steady state and dynamic behaviour of an adiabatic packed bed reac tor for the selective hydrogenation of mixtures of ethyne and ethene i s studied. A heterogeneous model with axial dispersion of heat is solv ed numerically by means of a fully implicit discretisation scheme. Fro m an analysis of the inlet and outlet boundary conditions, it follows that in order to avoid an influence of the type of boundary condition on the reactor behaviour, sufficiently long inert zones before and aft er the active bed should be present. Using preliminary kinetic express ions adapted from Men'shchikov et al. (1975), the model calculations s how a reasonable agreement with the experiments performed in a laborat ory scale reactor and demonstrate the importance influence of small am ounts of carbon monoxide both on the steady state as well as on the tr ansient behaviour of the reactor. However, using the rate expressions derived from our own kinetic experiments in a Berty reactor, the behav iour under runaway conditions and the transition from non-runaway to r unaway conditions can not be described well. Several factors that cont ribute to this discrepancy are discussed. This work shows that, in par ticular for a complex reaction system such as the selective hydrogenat ion of ethyne in ethene, the limited accuracy of the kinetic model and kinetic parameters dominates the precision attainable with packed bed reactor models.