ENTHALPY CHANGE ON VAPORIZATION OF AQUEOUS AND METHANOLIC FORMALDEHYDE SOLUTIONS

A physicochemical model for vapor-liquid equilibrium in multicomponent formaldehyde-containing mixtures (Maurer, 1986; Hasse et al., 1990; Hasse and Maurer, 1991a) is extended to describe enthalpy changes upon vaporization. Predicted enthalpy changes are compared with new experimental results. The measurements were carried out with a thin-film evaporator flow-calorimeter (Liu and Maurer, 1991). More than 80 experimental data points for mixtures of formaldehyde + water and formaldehyde + methanol + (small amounts of water) are reported. The data cover the temperature range from 323 to 363 K (formaldehyde + water) and 312 to 347 K (formaldehyde + methanol) at liquid phase formaldehyde mole fractions up to about 0.3 (formaldehyde + water) and 0.6 (formaldehyde + methanol). Comparisons between predicted and experimental results for the enthalpy change reveal deviations of only a few percent. Further improvements are achieved by fitting some model parameters, which originally were estimated from noncalorimetric data.