Isobaric Vapor-Liquid Equilibria and Extractive Distillation Process Design for Separating Methanol and Methylal

Methanol and methylal form a minimum boiling point azeotrope and cannot be separated by conventional distillation. In this paper, the azeotrope was separated by extractive distillation with cyclohexanol as the entrainer. First, the vapor-liquid equilibrium data of methanol + cyclohexanol and methylal + cyclohexanol were measured at 101.3 kPa, and the thermodynamic consistency of the experimental data was tested by the van Ness and pure component consistency test methods. The experimental results were correlated by activity coefficient models, which are nonrandom two-liquid (NRTL), universal quasichemical (UNIQUAC), and Wilson. Then, the feasibility of separating the azeotrope with cyclohexanol as the entrainer and the separation sequence were studied by thermodynamic topological analysis of phase diagrams and residual curve map. Finally, the appropriate operating conditions were obtained by sensitivity analysis, and the extractive distillation simulation was carried out. The results show that cyclohexanol can be used to separate methanol and methylal by extractive distillation.