Dynamic models were developed for three phase slurry and trickle bed reactors operating in non-isothermal conditions. The model equations for the gas, liquid and catalyst phases consisted of parabolic partial differential equations (PDE) and ordinary differential equations (ODE), which were converted to ODEs using finite difference approximations for the spatial derivatives. The ODEs were solved by a stiff ODE solver (LSODE) using the backward difference method. The numerical strategy proved to be reliable. The reactor simulation programs were included in a flowsheet simulator. The use of the programs was illustrated with two case studies : oxidation of SO2 and hydrogenation of toluene. The example simulations showed that the dynamic approach provides a meaningful path to the steady state of the reactor and gives valuable information of the reaction dynamics.