Interpretation and prediction of the vapor-liquid equilibrium of formaldehyde-water-methanol ternary system by the conductor-like screening model for real solvents

- COSMO-RS predicted the thermodynamic behavior of formaldehyde-water-methanol system.
- Vapor pressures of MG and HF were calculated using quantum chemistry method.
- Average relative deviation of species distribution no greater than 10% for HF1-3 and MG1-3 were predicted.
- The maximum value of partition coefficient for formaldehyde was discussed.

In this study, a thermodynamic model was combined with the conductor-like screening model for real solvents (COSMO-RS), coupled with chemical reaction equilibrium and mass balance, for describing the phase behavior and complex chemical equilibrium in the ternary system of formaldehyde-water-methanol at temperatures between 323 and 383 K. To the best of our knowledge, this is the first time accurate and reasonable predictions were made for the species distribution and vapor-liquid equilibrium (VLE). Meanwhile, the σ-profiles and σ-potential were employed to interpret the molecular interaction in the system. Compared to the extrapolation method, COSMOtherm implementation was preferred here for the prediction of the vapor pressures of methylene glycol (MG) and hemiformal (HF). Furthermore, the maximum partition coefficient for formaldehyde in the dilute formaldehyde-water-methanol mixture at low temperature was discussed.