Thermodynamic and economic comparison of extractive distillation sequences for separating methanol/dimethyl carbonate/water azeotropic mixtures

Abstract

The separation of dimethyl carbonate (DMC)/methanol/water azeotropic mixtures has been a hot topic in the study of DMC synthesis process. In this work, the efficient organic solvent methyl salicylate, ionic liquids (ILs) 1‐butyl‐3‐methylimidazolium chloride ([BMIM][Cl]), or 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTf2]) was employed to break azeotropic mixtures. Interaction mechanisms between DMC/methanol/water and entrainers were revealed by sigma-profile. Energy and economic comparison of two alternative separation sequences including pre-separation integration with extractive-heterogeneous distillation and direct extractive distillation processes were investigated. The average relative deviations (ARD) were used to check the reliability of the NRTL model. The effect of high viscosity fluid on the mass transfer was analyzed from the perspective of the overall efficiency of column. For [BMIM][Cl], the separation mechanism is the formation of H-bond between [BMIM][Cl] and methanol/water. Direct extractive distillation process is superior to pre-separation integration with extractive-heterogeneous distillation process in terms of steam consumption, capital cost, mass transfer efficiency and total annual cost (TAC), and [BMIM][Cl]-based direct extractive distillation process is the best. This work provides a green and efficient separation route for replacing organic solvent-based process.