OPTIMAL THERMODYNAMIC FEED CONDITIONS FOR DISTILLATION OF IDEAL BINARY-MIXTURES

Optimal thermodynamic feed conditions for distillation of ideal binary mixtures are identified through thermodynamic efficiency analysis of distillation columns. Due to simplifying assumptions, temperatures do not appear explicitly in the final thermodynamic efficiency equations. These equations are found to be functions of only feed composition, t he thermodynamic state of the feed and the relative volatility of the more volatile component A with respect to component B! When a single o ne-phase feed AB, is used the preferred state of the feed is all liqui d when the amount of heavy component B is greater than 50% and is all vapor when the amount of volatile component A is greater than 50%. For a single two-phase feed a simple heuristic is presented to adjust the liquid fraction of a given feed to maximize the thermodynamic efficie ncy of the distillation column. For most binary mixtures, two feeds wi th the same composition, but one saturated vapor and the other saturat ed liquid can improve a distillation column's efficiency substantially . The maximum benefit is obtained for a 50-50 mixture. This two-feed c ase is less efficient than the single two-phase feed case when the rel ative volatilities exceed certain calculable values.