A PHYSICAL THEORY SUPERIMPOSED ONTO THE CHEMICAL THEORY FOR DESCRIBING VAPOR-LIQUID-EQUILIBRIA OF BINARY-SYSTEMS OF FORMALDEHYDE IN ACTIVE SOLVENTS

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 previous works, the liquid phase for the binary systems water-formaldehyde and methanol-formaldehyde was described in terms of chemical theory only, while both physical and chemical forces were taken into account in describing the vapor phase. In this work, we take into account the physical forces acting upon the molecules of the true species, which are present in the liquid phase, without modifying the description of the vapor phase. For the liquid phase, we use the UNIQUAC equation to express the effect of physical forces by using only one adjustable physical parameter independent of temperature for each binary system.