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Multicomponent Batch Distillation
Multicomponent Batch Distillation
Consider a ternary mixture of chloroform, acetone, and methanol. This mixture is to be separated in a still pot, which initially contains user-set values of the masses in grams of all three components. You can set the operating pressure from 90 to 110 kPa, so that the ideal-gas approximation is appropriate. Here, a constant-heating policy of the still pot is applied. You can select the heater duty .
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This Demonstration plots the temperature of the liquid in the still versus time, as well as the composition of the vapor phase (dashed curves) and that of the liquid phase (solid curves). In the composition plot, the green, blue, and yellow curves represent the mole fractions of methanol, chloroform, and acetone, respectively.
For this transient problem, computations include both the mass and the energy balance equations (for details see [1]). In addition, vapor-liquid equilibrium data was obtained using the modified Raoult's law and the Wilson model for activity coefficients. Finally, the dependence of enthalpy on temperature was obtained from ASPEN-Hysys, while the change in enthalpy due to mixing was ignored.
As expected, higher total pressure values shift the temperature profiles toward higher values. If the heater duty is increased, the distillation is more rapid: at shorter times the still runs dry (i.e., when , where is the number of moles in the still and is the final batch distillation time).
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M()=0
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The first two snapshots show typical situations that occur if a series of batch distillation experiments with different initial composition in the still is performed. Indeed, either only methanol is left at the end (Snapshot 1) or the binary azeotrope between chloroform and acetone is left at the end (Snapshot 2). These results could also be deduced from a residue curve map computation for this ternary mixture at a specific total pressure .
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