DEVELOPMENT OF A NEW ADVANCED PROCESS FOR MANUFACTURING POLYACETAL RESINS .2. VAPOR-LIQUID-EQUILIBRIUM OF FORMALDEHYDE WATER-SYSTEM

To develop a new technology for the purification of formaldehyde from formalin by a distillation method, the vapor-liquid equilibrium of for maldehyde-water binary systems was investigated. Based on the studies of Thompson et al. and Iliceto et al., the vapor-liquid equilibrium of formaldehyde and water are calculated and these calculations are in g ood agreement with the reported data. It was found that the vapor pres sure of formaldehyde is determined by the free formaldehyde concentrat ion (mol/L), whereas the vapor pressure of water is determined by the molar ratio of free water. The vapor liquid equilibrium of formaldehyd e-water in the presence of a diluent was also investigated. It was sho wn by calculation that in some cases, when the concentration of the di luent is high, the volatility of formaldehyde is always higher than th at of water and these calculations are in good agreement with experime ntal data. Based on this principle, the purification of formaldehyde b y an extraction distillation method was established. (C) 1993 John Wil ey & Sons, Inc.