A new reactor concept to replace slurry bed catalysts with monolithic catalysts is described. Different configurations are presented, all requiring minimal hardware modifications for revamp. One key feature of the new concept is that no troublesome filtration step is required, while maintaining the benefits of high catalyst effectiveness and selectivity. Furthermore, higher catalyst loads per reactor volume can be achieved with the monolith. Cold flow experiments are used to demonstrate the feasibility of the concept and to determine some empirical parameters for a simple hydrodynamic model. Characteristic performance data for the monolith reactor, such as mass transfer, heat transfer, and reactive performance, as well as their dependence on the type of monolith used are discussed on the basis of model calculations. (C) 2003 Elsevier Science B.V. All rights reserved.