Conceptual Design and Assessment of Extractive Distillation Processes Using Deep Eutectic Solvents

Abstract

Extractive distillation with organic solvents as entrainers is one of the most commonly used separation techniques for azeotropic mixtures in the chemical industry. To reduce the large energy requirements, and the secondary pollution problems, both of which are associated with the use of organic solvents, the search for alternative entrainers has received much attention. Recently, deep eutectic solvents that are known as green and non-volatile components have been considered as entrainers for extractive distillation processes. However, research focuses mainly on vapour-liquid equilibrium measurements, and an economic comparison with the conventional organic solvents has not been done yet. This work investigates extractive distillation with deep eutectic solvents where a conceptual process design is carried out for the separation of ethanol and water, as well as isopropanol and water with the aid of Aspen Plus as process simulator. In order to fulfil the research aim of exploring whether deep eutectic solvents reduce both cost and overall energy consumption, first, a database for the investigated deep eutectic solvents is created. Based on the effect of the deep eutectic solvents on the vapour-liquid equilibrium, choline chloride:urea (1:2) and choline chloride:triethylene glycol (1:3) are chosen for the ethanol system and isopropanol system, respectively. Subsequently, different entrainer recycle alternatives are investigated, and a sensitivity analysis of the design variables is performed. For both systems, it is found that a series of two evaporators are the most economical entrainer regeneration option. Last, a consistent comparison of the final processes with the process using the conventional organic solvents and ionic liquids is carried out. The results show that the considered deep eutectic solvents are not only beneficial in terms characteristics such as biodegradability, toxicity and selectivity, but also regarding specific energy requirements and the total annual costs. The process using conventional organic solvents is improved by at least 20.1% from an energetical perspective and by a minimum of 16.6% from an economic perspective for both systems. The replacement of ionic liquids by deep eutectic solvents also results in an energy reduction of a minimum of 6%. The additional use of heat integration further improves the final processes by 8 to 10% with respect to specific energy requirements in steam and therefore reduces the carbon footprint. Finally, it is concluded that the extractive distillation using deep eutectic solvents outperforms the process using conventional organic solvents and ionic liquids in both separations; ethanol and water, and isopropanol and water.