Multiplicities in ethanol dehydration by extractive distillation processes with ethyleneglycol

This work presents three process examples, for ethanol dehydration by extractive distillation with ethyleneglycol, where the possibility of multiplicities depends on the specifications. The processes used are the following: classical sequence with two columns, thermally coupled sequence with prefractionator and thermally coupled sequence with a side rectifier. In each sequence analyzed was possible to calculate input multiplicities when the global products purities for ethanol and water are specified variables. The work focuses on the search of a specifications set where the solution of the model equations is unique. It was found that if the degrees of freedom are used to completely specify the separation in the extractive distillation column then there are not input multiplicities. There are no previous reports related with multiplicities for the system ethanol-water-ethyleneglycol. This work enriches the knowledge of this system and contributes with a new concept to calculate the minimum energy consumption without multiplicities. Results are also applicable to extractive distillation processes with dividing wall columns (DWC) because the analyzed thermally coupled sequences are used to represent processes with DWC. Calculations were carried out in the Aspen Plus V10 (R) simulator using RADFRAC modules with the equilibrium stage model to represent distillation units.