An interesting technology to carry out slow reactions with small catalyst particles is the use of static packing elements, where the solid catalyst particles are placed inside a metal network in a bubble column. The static element acts as a static mixer and ensures a low pressure drop in spite of small particle sizes. The present work concerns the mathematical modelling of bubble columns with static packing elements. Exothermic simultaneous homogeneous and heterogeneous oxidation of ferrous sulfate was chosen as a three-phase model system. (C) 2003 Elsevier Science B.V. All rights reserved.