Exergy Minimization in Ethanol Dehydration using Hybrid DistillationMembrane Systems

Abstract

As a renewable energy source, bioethanol is widely used for blending in gasoline in an attempt to partly alleviate the energy crisis and reduce the greenhouse gas emissions. To produce fuel grade ethanol, the dehydration process of bioethanol is a critical step for the economic viability of the whole process. With a single distillation column it is not possible to overcome the azeotropic point of the ethanol/water mixture. In addition, the distillation process is a very energy intensive and costly process. In this thesis, two major topics concerning the dehydration process of bioethanol are discussed. First, the multiple objective optimization of the fuel grade bioethanol dehydration is performed along with a parametric analysis of A-type zeolite membrane pervaporation. Three cases were investigated using the ranked Pareto domain that was obtained in each case. The optimal results were identified as attractive compromised solutions considering the four objectives: the total number of stages, the total area, the energy consumed, and the exergy loss. The temperature drop per stage was found to be the dominating factor. The second theme is the exergy loss minimization of the pervaporation/distillation hybrid system at the tangent pinch on the vapor-liquid equilibrium curve. Results show that both the exergy loss and the reflux ratio of the hybrid system are reduced compared to a single distillation column. In addition, the exergy loss of the hybrid system is correlated with the variation of the reflux ratio.