There is a substantial heat of mixing, the calculations become much more tedious.įor binary mixtures of this kind a graphical model has been developed by RUHEMANN, PONCHON, and SAVARIT, based on the use of an enthalpy-composition chart. x and y.Įnthalpy will be required in future problems utilizing energy balances.įor a non-ideal system, where the molar latent heat is no longer constant and where Presents the temperature equilibrium relationship for enthalpy vs.
Thus, the liquid fed from one stage to another stage can be assumed to be a saturated liquid and the vapor feed to another stage can be assumed to be a saturated vapor.Įnthalpy vs. We will use this assumption when we do our multi-stage solutions the vapor and liquid streams exiting a stage will be assumed to be at saturated conditions. When a two-phase mixture separates at vapor-liquid equilibrium conditions, the vapor phase will be at saturated vapor conditions and the liquid phase will be at saturated liquid conditions. Of the liquid-phase and vapor-phase quantities,įrom inspection, other useful relationships can beĪt vapor-liquid equilibrium, the temperatures of the vapor and liquid are equal. Phase diagram indicates that the distance between points AĪnd C and points A and B are equivalent to the magnitudes Where L/V is the ratio of liquid to vapor.Ĭomparing the numerator and denominator with the two. Then the mass balances before and after separation are L = the moles of liquid of composition xB zF is not equal to either x or y, but x and y be determined from the T vs. If zF is in the two-phase region, the system will separate into a liquid and vapor of new mole fractions x and y, respectively. If zF is a saturated vapor, zF is essentially yF with a single liquid drop formed of new mole fraction x. If zF is a saturated liquid, zF is essentially xF with a single vapor bubble formed of new mole fraction y. If zF is a superheated vapor, zF is yF and there is no x. If zF is a subcooled liquid, then zF is simply xF and there is no y. The feed phase is dependent upon the temperature, pressure, and the composition (mole fraction).Īssuming that the equilibrium stage is at the same temperature and pressure of the feed: Mixture, a saturated vapor, or a superheated vapor. Note that a feed mole-fraction, zF,can be a subcooled liquid, a saturated liquid, a two-phase 圎tOH is the mole fraction of ethanol in the liquid stream. yEtOH is the mole fraction of ethanol in the vapor stream. zEtOH is the mole fraction of ethanol in the feed. L is the total moles in the liquid stream exiting the stage. V is the total moles in the vapor stream exiting the stage. Single Equilibrium Stage Ethanol-Water, P = 1 atmį is the total moles of ethanol and water fed to the stage. Distillation Equilibrium (Review) Flash Distillation Multistage Distillation