(391g) Conceptual Design of Distillation Colums for Ethanol Dehydration By Using Ionic Liquids

In the early 80’s and 90’s several authors studied the use of inorganic salts as entrainers for the ethanol dehydration. However, despite the benefits provided by salt-containing distillation, the design and implementation of this process faces some important drawbacks because of the limited solubility of such solid entrainers (Llano-Restrepo and Aguilar-Arias, 2003). In the last decade, Ionic Liquids (ILs) have been considered for several applications in chemical processes, performing roles as reaction media, solvents and separation agents (Shen et al 2011; Pereiro et al, 2012). Particularly, the utilization of ILs for the ethanol-water separation is gaining wider interest, since ILs integrate the advantages of a liquid entrainer and the benefits of a solid salt, as they promote an evident salting out effect over the vapor-liquid equilibrium properties. To determine the feasibility of this new technology, some modeling approaches have been recently proposed (Chavez-Islas et al, 2010; Meindersma et al, 2012).

The aim of this work is to present a methodology for the conceptual design of a distillation system for ethanol dehydration using an IL as entrainer. The proposed method is based on tray by tray calculations from the outside to the inside of the column, similar to the Boundary Value Method (BVM) proposed by Van Dongen and Doherty (1985) for ternary mixtures. In the BVM the feed stage is found where the liquid composition of both profiles intersect each other. However, although the system here under consideration is a ternary mixture, the IL is non volatile, such that its concentration remains essentially constant along each section, although it changes in the feed stage; as a result, the rectifying and striping profiles never intersect. In this work, the feed stage was located by using the minimum distance concept proposed by Gutiérrez and Jiménez (2007), which completed a successful design method for these types of systems. The effects of different feed composition and IL concentrations on the separation task were analyzed. In all cases, feasible designs were obtained. The behavior of the composition profiles is an interesting point worth of special discussion.

References

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