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I’m currently working on my graduation project and have a question I can’t figure out; I hope everyone can offer some guidance. I’m designing distillation columns for benzene (a) and toluene (b). The design parameters specify an operating pressure at the top of the column of 5 kPa (gauge pressure), with a molar fraction of x(d) at the top equal to 0.9745. When determining the operating conditions at the top of the column, the manual suggests using the formula p = p(a)×x(a) + p(b)×x(b), along with Antoine’s equation for saturated vapor pressures, to determine the operating temperature at the top. Since we already know the molar fraction of the vapor leaving the top of the column, we could use the gas-liquid equilibrium data to find the corresponding equilibrium temperature. So why is it still necessary to use iterative calculations? :Furthermore, the operating pressure is specified. If an temperature is determined through trial and error, and this temperature meets the required operating pressure at the top of the tower, but if the corresponding values of x(a) and x(d) at this equilibrium temperature are not equal, then the top of the tower is in a state of imbalance. Once equilibrium is reached, won’t x(d) no longer be 0.9745? ? ? What is even more confusing is that the reflux ratio and theoretical number of theoretical plates were previously calculated using the gas-liquid equilibrium data t-x,y at a certain pressure; yet the pressure at each tray in a distillation column is different. How can the gas-liquid equilibrium data at one specific pressure be used to calculate the parameters for the entire distillation column? ? ? ? ? I’m completely confused now; I hope an expert can give me some guidance! !