Effect of small amounts of methanol on the vapour-liquid equilibrium for the water-formaldehyde system

Abstract

The total vapour pressures of three mixtures of the water-methanol-formaldehyde system have been measured over the range of temperatures 55-95°C. The formaldehyde composition was in the range 34-44 wt.%, while that of methanol was <1 wt.%. These measurements were carried out with the aim of demonstrating that, for studying the vapour-liquid equilibrium for the water-formaldehyde system, it is necessary to eliminate methanol to a greater extent than is usual. The experimental results compare favourably with those calculated by a predictive thermodynamic model which explains nonideality in the liquid phase in terms of chemical forces for the binary systems water-formaldehyde and methanol-formaldehyde and in terms of physical forces (Wilson equation) for the binary system water-methanol. The proposed model was also utilized in bubble-point calculations for the binary system methanol-formaldehyde and for the ternary system over a large range of compositions. The results were compared with literature data. © 1985.