tThe relatively high viscosities of ionic liquids could reduce the mass transfer efficiency of the extractivedistillation process. The rate-based model was adopted to analyze this phenomenon since it predicted theperformance of an extractive distillation pilot plant using ionic liquids as solvent. For the water¿ethanolseparation, three ionic liquids: 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazoliumacetate and 1-ethyl-3-methylimidazolium dicyanamide and the organic solvent ethylene glycol wereused for the analysis. Simulations were conducted for sieve trays and Mellapak®250Y. The results indi-cate that relatively high viscosities affect the mass transfer efficiency. However, the improvements inrelative volatilities obtained from the ionic liquids help to overcome this effect. However, with high sol-vent viscosities (>65 mPa s at T = 353.15 K) it was not possible to overcome the reductions. Additionally, athigher distillate rates high relative volatilities yielded negative effects on mass transfer efficiency becauseof a decrease in vapor velocity.@en

Separation of the close-boiling mixture: toluene ¿ methylcyclohexane (MCH) has been carried out by extractive distillation (ED) using the ionic liquid [HMIM][TCB]. High solvent-to-feed ratios are needed to maintain one liquid phase and increased liquid phase viscosities are expected compared to the reference solvent NMP. Experiments in an extractive distillation pilot plant were carried out at a solvent-to-feed mass ratio of 5 to evaluate the effect of solvent selectivity and viscosity on the separation performance and mass transfer efficiency. The results confirm that at the used operating conditions one liquid phase was maintained and that with [HMIM][TCB] a MCH purity >99.7% could be achieved. The liquid phase viscosities in the ED column when using [HMIM][TCB] appeared four times higher than with NMP. As a result the mass transfer efficiency decreased, which was reflected in a doubling of the HETP (height equivalent to a theoretical plate) compared to NMP@en