Measurements of the vapor-liquid equilibrium in the system formaldehyde + water + butynediol were performed at 393 K and 413 K for overall formaldehyde mass fractions between 0.1 g g(-1) and 0.2 g g(-1) and overall butynediol mass fractions between 0.05 g g(-1) and 0.35 g g(-)1. The studied system is a complex reactive multicomponent mixture as formaldehyde reacts both with formaldehyde and butynediol. A predictive physico-chemical model of the vapor-liquid equilibrium from the literature [1] is validated by the experiments of the present work. Residue curves are calculated to illustrate the distillation behavior of the studied system. (C) 2019 Elsevier B.V. All rights reserved.