(620s) Effect of Salt Addition On Extractive Distillation Process

In the last decade, anhydrous ethanol production has been acquiring an increasing industrial importance due to its growing demand as a renewable fuel. Most bioethanol industrial production is based on the fermentation process, from which a maximal yield is about 15% (v/v), a reason why the product purification is an important stage for the process. The ethanol-water separation is the energetic bottleneck for bioethanol production because of the presence of the azeotrope, which makes it necessary the use of alternative techniques to common distillation to achieve the required purity. Extractive distillation using liquid entrainers for the separation of homogeneous azeotropic mixtures is a widely accepted technique in the industrial environment; however, in most cases its implementation requires a high demand on solvent feed flow. On the other hand, from several experimental researches it is known that salt addition can modify activity coefficients, even breaking the azeotropic points, but their industrial implementation has been rejected because of problems associate to the potential salt precipitation. In this work we explore the implementation of a hybrid extractive process combining a liquid entrainer (ethylene glycol) and a salt, in this case CaCl₂. The analysis was conducted using the Aspen Plus process simulator. In order to identify the convenience of using an ethanol pre-concentrator column in this process, different feed compositions for the ionic-extractive distillation were analyzed. According to the obtained results, in most cases there is not an important reduction on energy consumption (3 to 5%), but the combination of both entrainers allows reducing significantly the use of liquid solvent, even more than 50% in comparison with the conventional process. As in conventional extractive distillation, in this hybrid process the minimum solvent and energy requirements are reached when the mixture is fed close to the azeotropic composition.