Near-critical separation of aqueous azeotropic mixtures: process synthesis and optimization

The near critical extraction of alcohols from aqueous solutions is addressed, combining reliable thermodynamic models with robust simulation and optimization methods. Based on the process key phase equilibrium properties, a methodology for process optimization is proposed and illustrated for the extraction of ethanol using near-critical propane as solvent. Several process schemes are evaluated. (i) conventional heating, (ii) vapor recompression, and (iii) feed preconcentration. The optimal schemes and conditions for this separation problem are obtained. The process constraints are determined and removed through structural modifications of the process. The effect of the process constraints on economics and operating conditions is analyzed. The methodology results in a general process flowsheet for the near-critical separation of aqueous azeotropic mixtures. (C) 1998 Elsevier Science B.V.