Heat of Dilution in Aqueous and Methanolic Formaldehyde Solutions

As part of an ongoing project dealing with thermodynamic properties of formaldehyde containing fluid mixtures, heats of dilution of formaldehyde, water, methanol and trioxane containing mixtures have been measured in a heat flow calorimeter at temperatures between 298 and 363 K. New mixing cells, allowing pressurization and avoiding vapor‐space, were used to take over 300 data points covering binary, ternary and quarternary mixtures. The observed heats of dilution are generally small (less than 250 J/mol). They are correlated using a physico‐chemical model. Physical effects are considered by the UNIFAC‐group contribution method, reaction enthalpies are used for the description of the chemical contributions. The model allows a good representation of most of the binary data, extrapolations to multicomponent systems using binary data alone are, however, only qualitatively correct.