(330f) Optimization of An Extractive Distillation With Mixed Solvents As Entrainer

Anhydrous ethanol is widely used in the biofuels industry, since it has demonstrated to be environmental friendly and to have excellent properties for clean-burning. In mixtures of ethanol and gasoline, alcohol must have purity higher than 99.5% in order to avoid phase separation. Among the most popular processes used in ethanol dehydration, extractive distillation has demonstrated to be an adequate alternative due to the low energy consumption compared with other techniques and its economic feasibility. In this work, an extractive distillation process was simulated with the Aspen Plus software platform, using the RadFrac module for distillation columns. A mixture of ethylene glycol and glycerol is proposed as entrainer. This enhanced entrainer combines the low viscosity and the ability of the ethylene glycol to break the binary azeotrope with the low prices of glycerol. Phase equilibrium of this quaternary system was calculated with the NRTL model, which correlates well these strongly polar mixtures. The nominal case consists in the dehydration column, the recovery column and the solvent recycle loop. In order to establish the most adequate operating conditions, it was studied for each column the effect of the molar reflux ratio, the feed stage and the feed condition in the ethanol and solvent compositions. For the dehydration column, it was also investigated the effects of the ethylene glycol-glycerol mixture composition, the separating agent feed stages, the separating agent split stream, and the azeotropic feed temperature on the separation. Subsequently, the thermal and hydraulic analysis of both columns was established, so that the system operates energetically efficient. Finally, the economic optimization of the system was achieved, using the maximization of the profit as objective function. In this case, the solvent to feed ratio, the reflux ratio and the number of stages in the extractive column were the optimization variables, while the design parameters of the recovery column were fixed.