How to Use the McCabe-Thiele Method for Fractional Distillation
How to Use the McCabe-Thiele Method for Fractional Distillation
This Demonstration shows how to use the McCabe–Thiele method to determine the number of equilibrium stages needed to separate a binary mixture (methanol and water) in a distillation column.
First, select "plot points" to show the location of the feed, distillate and bottoms compositions on the - diagram. The methanol feed mole fraction is =0.5, the desired methanol mole fraction in the distillate is =0.85, and the desired methanol mole fraction in the bottoms is =0.05. Next, select "draw operating lines" to set the feed quality with a slider and plot the operating lines for the feed, rectifying and stripping sections. The diagram on the right shows a representation of part of the distillation column and explains the equations used for the operating lines.
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Then, select "count stages" and use the slider to step off stages and draw lines for each stage; the diagram on the right highlights the corresponding location on the column. The partial reboiler is considered an equilibrium stage. The green horizontal lines on the - diagram result from a material balance between stages. The purple vertical lines correspond to vapor-liquid equilibrium (VLE) on each stage. Finally, select "optimal feed location" to determine where the feed should enter the column; the feed should enter above the stage where the rectifying and stripping sections meet. Mouse over the stage numbers on the - diagram to see which section the numbers correspond to.
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