A Break-Even Analysis of Distillation-Membrane Hybrids

The use of distillation - membrane hybrids is examined for the separation of two component mixtures exhibiting a tangent pinch, azeotrope, or low relative volatility. The merits of various process alternatives are discussed. A procedure for screening calculations is presented that allows the determination of the break-even cost for a membrane, above which the hybrid would be too costly to be competitive. This approach is applicable to the screening of all the types of membranes and can be used to target the desirable membrane properties. Screening calculations are performed for water-acetic acid, ethanol - water, and propylene - propane systems to demonstrate the inherent trade-offs of the hybrids and the effect of phase behavior on the performance.