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

Abstract

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.

Isobaric Vapor–Liquid Equilibrium Measurements of Binary Systems of Dimethyl Carbonate with Dimethyl Sulfoxide, Anisole, and Diethyl Oxalate at 101.3 kPa

“…In the synthesis process of DMC, methanol is used excessively as a raw material. , Under atmospheric pressure, the mixture of DMC and methanol is difficult to be separated by conventional separation methods for the formation of the homogeneous azeotrope. , Therefore, some special separation techniques need to be considered, including cryogenic crystallization, pressure swing distillation, − extractive distillation, ,− azeotropic distillation, , membrane separation, and so forth. It has been proved that the extractive distillation is an effective method, but the selection of the entrainer is the crucial step. − …”

Strategy for the Separation of the Mixture of Dimethyl Carbonate, Formaldehyde, and Water

“…The azeotrope mixture 5,10 of DMC and water obtained from the extraction needs to be further separated via extractive distillation. 11,12 Based on our experiments, it was verified that water was a great choice as the extractant for the extraction of formaldehyde from the by-product DMC. The separation process not only achieved the purpose of separating formaldehyde but also avoided the addition of new components.…”

Isobaric Vapor–Liquid Equilibrium of Ethyl Acetate + 1-Hexanol, Methanol + 1-Hexanol, and n-Heptane + Cyclohexanol Binary System at 101.3 kPa

“…Organic solvents have been used as extractants in industry, while some extractants such as ethylene glycol, glycerol, 1-hexanol, cyclohexanol, and dimethyl sulfoxide are commonly used in industry. , Wang et al used cyclohexanol as the extractant to separate the lowest boiling point azeotrope of methanol and methylal, measured the vapor–liquid equilibrium (VLE) data, and successfully used cyclohexanol to separate a methanol and methylal azeotrope system using simulation software. In order to separate the azeotropic system of water and dimethyl ether, Lin et al used extractants such as n -heptanol, isopropyl ether, 4-methyl-2-pentanol, and 1-hexanol.…”