化工原理chapter10.1课件.pptVIP

Chapter 10  Distillation;Principle;Basic definitions;Classification;Vapor-liquid phase equilibrium for two components; Since the total pressure of the gas is the sum of partial pressure of all components It can be transformed into as follows ;Another form—dew point equation ; From the Phase Law , for a 2-component and 2-phase system, the freedom is 2, i. e., there are two independent variables. ;A distillation column is used for separating benzene toluene. There is a part condenser and a total condenser on its top, and the operation pressure is 101.3 kPa. It is measured that the molar fraction of benzene in the distilled liquid at the outlet of total condenser is 0.923. Let the gas/liquid at the outlet of the part condenser keep equilibrium. Try to find the composition here and the temperature.;steps to solve;Gas-liquid phase diagram;P-x figure for benzene-toluene system;x;y-x figure for benzene-toluene system;Figure 10-3 ethanol-water system;Expressions used in distillation;definition of volatility: the ratio of equilibrium vapor pressure and molar fraction in liquid. For a two-component system, we have The ratio of two volatilities is called relative volatility, given by ;For two-phase system, yB= 1 - yA and xB= 1 - xA，substitute in Eq. (10.2.16) and omit the subscript A, we have This Eq. is also called phase equilibrium Eq., which uses the relative volatility to show the equilibrium relationship. ;Equilibrium and simple distillations;Mass balance of flash evaporation ; Let the fraction of liquid product to feed, q，then W/F = q and D/F=（1-q），substitute those in Eq. (10.3-3) and reorganize it to give