Distillation thermodynamic efficiency equation

The benzene-toluene system shows a maximum thermodynamic efficiency of about 80 per cent for a feed composition of 40 per cent benzene. The efficiency decreases for feeds both weaker and stronger, but in the range of feed compositions from 0.1 to 0.8 it is good. Equation (7-44) shows that the efficiency is zero both for xf approaching 0 and 1.0. In the case of the ethanol-water system, the heat requirement per mol of distillate is essentially independent of the feed composition over the range shown because the minimum reflux ratio condition corresponds to a tangency with the equilibrium curve at about 84 mol per cent alcohol. Thus the reflux ratio is the same over the whole concentration region considered. This reflux ratio corre-... 

Separation Efficiency of a Distillation Column. The minimum isothermal thermodynamic work required for separating 1 mol of a liquid binary mixture into its pure liquid constituents is given by the following equation ... 

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