Experimental results for the vapor–liquid equilibria of (formaldehyde + 1,3,5-trioxane + methanol + salt + water) systems and comparison with predictions

The salt effect on the vapor–liquid phase equilibrium (VLE) of solvent mixtures is of significant interest in the industrial production of 1,3,5-trioxane. Experimental data for the VLE of quinary systems (formaldehyde + 1,3,5-trioxane + methanol + salt + water) and their ternary subsystems (formaldehyde + salt + water), (1,3,5-trioxane + salt + water), and (methanol + salt + water) were systematic measured under atmospheric pressure. The salts considered included KBr, NaNO3, and CaCl2. The extended UNIFAC model was used to describe the VLE of the salt-containing reactive mixtures. The model parameters were determined from the experimental VLE data of ternary systems or obtained from the literature, and then were used to predict the VLE of systems (1,3,5-trioxane + KBr + water), (methanol + KBr + water), (formaldehyde + KBr + water), and (formaldehyde + 1,3,5-trioxane + methanol + salt + water) with salt = KBr, NaNO3, and CaCl2. The predicted results showed good agreements with the measured results. Furthermore, the model was used to uncover the salt effect on the VLE of these multi-solvent reactive systems.