Pilot plant validation of a rate-based extractive distillation model for water–ethanol separation with the ionic liquid [emim][DCA] as solvent

Abstract

The separation of water–ethanol mixtures is an important research topic due to the use of ethanol as a replacement of fossil fuels. Extractive distillation with ionic liquids has been proposed as a promising and attractive technology to separate this mixture. However, ionic liquids show high viscositites and this could markedly decrease the mass transfer efficiency of the column. A rate based-model is able to predict and evaluate mass transfer efficiencies while only knowing the physical and transport properties of the system in question. With the objective of validating a developed rate-based model for the separation of water–ethanol mixtures by using 1-ethyl-3-methylimidazolium dicyanamide and ethylene glycol as solvents and investigating the effect of the solvent physical properties on mass transfer efficiency, an extractive distillation pilot-plant equipped with Mellapak® 750Y was constructed and operated in continuous mode. It was found that the rate-based model predicts the performance of this pilot plan very well for all the studied conditions within a 10% relative error. Slightly more optimistic water contents of the distillate stream were predicted and experimentally the ionic liquid produced lower water contents than ethylene glycol. The use of this ionic liquid provides higher mass transfer efficiencies for all the studied solvent-to-feed ratios. Finally, increasing the solvent-to-feed ratio enhances the mass transfer efficiencies for both solvents and effects of liquid viscosity decreasing the mass transfer efficiency are observed in the rectifying section of the extractive distillation column.