THE SYSTEM FORMALDEHYDE WATER-METHANOL - THERMODYNAMICS OF SOLVATED AND ASSOCIATED SOLUTIONS

The vapor-liquid equilibria in the binary mixtures water-formaldehyde and methanol-formaldehyde are satisfactorily correlated by superimposing a physical model onto the chemical theory for describing the liquid phase. In a previous work, a thermodynamic model was built up which requires three adjustable parameters to describe the behavior of the liquid phase at isothermal conditions. The description of the isothermal vapor-liquid equilibrium requires an additional adjustable parameter: Henry's constant of formaldehyde in the active solvent. In this work, using the parameters obtained by fitting the experimental data of two selected sets of data, the prediction of the model is compared with all the existing literature data for the binary systems water-formaldehyde and methanol-formaldehyde. Moreover, we present an extension of the model for predicting vapor-liquid equilibria of the ternary system water-methanol-formaldehyde. From binary data alone the model is capable of accurately predicting vapor-liquid equilibria in a ternary mixture.