Despite their industrial importance, only few experimental studies on distillation of aqueous, methanolic formaldehyde solutions are described in the literature. In the present work, for the first time, results from pilot-scale distillation of mixtures of formaldehyde, water, and methanol are presented. The experiments were carried out in a 250 turn diameter distillation column equipped with 2 m Sulzer BX wire gauze packing. Two variants of that packing were studied: the commercially available type and a modified type with increased specific surface. The column was operated at 1 bar at total reflux. Both the overall feed composition and the fluid dynamic loads were varied systematically in the experiments. Samples were taken above and below the packing bed as well as at one intermediate position. For analysis, the sodium-sulfite method (formaldehyde), gas chromatography (methanol), and Karl-Fischer titration (water) were used. A total of 19 experiments were carried out. The studied formaldehyde distillations are complex reactive processes due to a series of reactions taking place in both phases. The experimental data were successfully modelled with a stage based physico-chemical model for thermal separations of formaldehyde containing mixtures, which was recently developed. (c) 2004 Elsevier B.V All rights reserved.