Monolith catalyst supports are attractive as fixed bed reactors that, at the scale of the catalyst dimension, exhibit the mass transfer characteristics of slurry reactors. This paper presents a reactor design study for the single-pass conversion of dinitrotoluene in a loop configuration with an external heat exchanger. The advantage of such a loop system is the elimination of a solvent, which in turn allows more reaction heat to be recovered. The advantages of using a monolith are the low pressure drop at high recycle ratio, while maintaining good mass transfer characteristics. The modelling includes internal diffusion limitation, external mass transfer characteristics, heat effects, maldistribution and flow stability. The optimal design is found at the lowest hydrodynamic stable flow rates, where the mass transfer is fastest and the residence time in the column maximal. (c) 2005 Elsevier B.V. All rights reserved.