Vapor–liquid and chemical equilibria model for formaldehyde + 1,3,5-trioxane + methanol + salt + water system

The salt effect on vapor–liquid phase equilibrium (VLE) has potential applications in industrial production of 1,3,5-trioxane. Optimizing reactive distillation process and developing new catalysts for industrial production of 1,3,5-trioxane require a reliable model for VLE of the reaction mixtures. Here an extended UNIFAC model combined a Debye–Hückel type is developed to describe the vapor–liquid and chemical equilibria of the multi-solvent salt-containing reactive mixtures associated with the 1,3,5-trioxane synthesis. New experimental data for the VLE of the quinary systems (formaldehyde + 1,3,5-trioxane + methanol + salt + water) and their ternary subsystems (1,3,5-trioxane + salt + water), (methanol + salt + water), and (formaldehyde + salt + water) are systematically measured at atmospheric pressure. The salts considered include LiCl, NaCl, KCl, NaBr, MgSO 4 , MgCl 2 , and Na 2 SO 4 . The model parameters, which are either obtained from the literature or determined from the VLE data of the above-mentioned ternary systems , are used to provide predictions for the quinary systems (formaldehyde + 1,3,5-trioxane + methanol + salt + water). The agreements between measured and predicted results are accurate. Furthermore, the model is used to uncover the effects of the salts considered on the VLE of these chemical reactive systems. The results show that MgSO 4 is a potential additive that can be used to improve the vapor–liquid phase separation during the reactive distillation process of 1,3,5-trioxane production.