The hydrodynamics in a pervaporation membrane reactor for resin production has been investigated. In this type of reactors it is important to reduce concentration and temperature polarization to obtain high water fluxes during operation. The influence of secondary flow on polarization, as induced by small density differences, is studied using Computational Fluid Dynamics in a model system. This model is operated in three parallel flow situations: horizontal, vertical opposed and vertical adding flow. Density-induced convection is found to be most effective in the horizontal situation increasing water fluxes up to 50%. Water fluxes were also determined experimentally using the horizontal setup. Influence of density-induced convection was observed experimentally.