Abstract
Extractive distillation is one of the most common processes used to separate components of azeotropic mixtures. Its most distinct constrains are the tremendous energy costs required to achieve a fluid phase system. In the given process, solvent interacting with the components of the original mixture and changing their relative volatility is used. Extractive distillation with conventional solvents provides products of poor quality and the solvents occur at the top of the column. Therefore, additional separation steps are required to separate the solvent from both the distillate and the bottom products. The use of ionic liquids (ILs) as the extractive solvents provides a cost-effective solution. Due to the negligibly low vapor pressure of ILs, the distillate obtained by extractive distillation does not contain solvent and IL can be separated from the bottom product relatively easily in a secondary regeneration column. Thus, appreciable investment an also operational costs reduction can be achieved by simple substitution of common extractive solvents with ILs. The present study focuses on the separation of the azeotropic system ethanol – water using extractive distillation. As the extractive solvents, two ionic liquids were compared: 1-butyl-3-methylimidazolium methylsulfate and 1-ethyl-3-methylimidazolium ethylsulfate. The separation was carried out in two distillation columns, extraction and recovery ones. Purity of the final products (ethanol and recovered IL) was prescribed. For the extraction and regeneration columns, various parameters were optimized, such as the reflux ratio, number of theoretical stages, quality of feed, position of the feed stage, solvent consumption, etc. Qualitative comparison of the operational costs for ethanol – water mixture separation using the two extraction solvents is discussed.
