Separation factors in permeation stages

A comparison is made of separation factors commonly used to characterize separations in single-entry barrier-permeation stages. These include the overall, heads, tails and Sandell's separation factors together with Rony's extent of separation. Equations are developed which show how the various separation indexes are related to stage cut, recovery and loss terms, and to each other. Calculations were made to compare the various separation indexes to determine which are suitable to characterize the “goodness” of separation in ideal countercurrent, cross-flow, cocurrent, and perfect mixed permeation stages. When compared at the same stage cut all of the separation indexes can be used as a qualitative measure of separation. However, only Rony's extent of separation appears to be generally applicable when comparing separations that are based on different stage cuts, or product stream rates. In all cases the extent of separation index gives a qualitative, and presumably a quantitative, measure of the goodness of separation.