A NEW PRESSURE-SWING-DISTILLATION PROCESS FOR SEPARATING HOMOGENEOUS AZEOTROPIC MIXTURES

Mixtures in which the desired products lie in different distillation regions can be separated by a new pressure-swing process when one end of the distillation boundary is a pressure-sensitive azeotrope. Thus pressure-insensitive binary azeotropes can be separated using novel entrainers that form pressure-sensitive distillation boundaries. Because the columns already operate at different pressures, such sequences are readily thermally integrated. The separations of ethanol from water and acetone from methanol are used to demonstrate the new pressure-swing technique. These examples exhibit some interesting behavior such as (1) a region of multiplicity in the number of trays required to achieve the same separation at fixed reflux ratio, (2) a maximum reflux above which no feasible column exists, (3) a separation where the unexpected component is the distillate due to a reversal of the relative volatility as the pressure changes, and (4) a nonazeotropic separation that becomes easier as the pressure is increased.