Extractive distillation of methylal/methanol mixture using the mixture of dimethylformamide (DMF) and ionic liquid as entrainers

• Published in: Fuel (Guildford) 2018-03, Vol.216, p.503-512
• Main Authors: Dong, Yichun, Dai, Chengna, Lei, Zhigang
• Format: Article
• Language: English
• Subjects: Air pollution; Computer simulation; Diesel fuels; Dimethylformamide; Distillation; Emissions; Entrainment; Extractive distillation; Flux density; Interaction parameters; Ionic liquid (IL); Ionic liquids; Liquid-vapor equilibrium; Methanol; Methylal; Natural gas; Particulate emissions; Pollutants; Separation; Synthetic fuels; Thermodynamics; UNIFAC-Lei model; Volatility
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2017.12.043

[Display omitted] •Methylal (DMM) is used as an important synthetic fuel blended with diesel oil.•The mixed entrainers were proposed for the separation of methylal and methanol.•The separation mechanism was clarified at the molecular scale.•The UNIFAC-Lei model for ILs was extended to the methylal-methanol-DMF-IL system.•The overall heat duty of reboilers decreases by 9.25% when using the mixed entrainers. Methylal is used as an important synthetic fuel blended with diesel oil to reduce the particulate emissions of toxic gas pollutants without affecting the energy density. The mixed entrainers (dimethylformamide (DMF) + ionic liquid (IL)) are proposed to replace conventional DMF for the separation of methylal and methanol by extractive distillation. [EMIM]+[Ac]− might be the most promising entrainer screened by COSMO-RS model considering relative volatility and solvent capacity together. Vapor–liquid equilibrium (VLE) experiments demonstrated that the relative volatility of methylal to methanol is obviously improved after the addition of [EMIM]+[Ac]− into DMF. Moreover, the UNIFAC-Lei model was extended to the methylal-methanol-DMF-IL system, and the corresponding interaction parameters were obtained and input into the equilibrium (EQ) stage model established in this work. Based on the thermodynamic study, process simulation was developed. It was found that the overall heat duty of reboilers decreased 9.25% using the proposed mixed entrainers when compared to pure DMF. In addition, the COSMO-RS model and DFT calculation provide some theoretical insights into the separation mechanism.