Optimization of a Wastewater System Containing the Ternary Homogeneous Azeotropic System Ethyl Acetate−Ethanol−Water

A wastewater stream containing minor amounts of ethyl acetate and ethanol could produce clean water with a low solvent composition by the use of direct steam injection or by the use of a distillation column. A problem that arises in this system is the approach to a homogeneous azeotrope in the distillate as the number of ideal stages is increased. Higher compositions of ethanol can be produced at low distillate flow rates by limiting the number of ideal stages. The prediction of the azeotrope in this system requires new UNIFAC vapor−liquid equilibrium interaction parameters, which have been determined. Simulation of a distillation column at total reflux then predicts a maximum in the ethanol composition which could be recovered and recycled in the plant. The value of this recycled ethanol can exceed the steam operating costs for the wastewater plant. A cost optimization shows that there is a cost-feasible region that satisfies the composition constraints when the reflux ratio is between 10 and 30, with lo...