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Acetone must be recovered from a waste process stream, which also contains chloroform , so that it can be reused in the chemical process. The chemical process requires however that before the recovered acetone can be reused in the process that it meets certain criteria. The distillation column to be used for this separation is already in place and has the equivalent to 12 theoretical trays (not including the reboiler) The waste stream is a mixture containing 60 mole % acetone and 40 mole % chloroform. The chemical process requires the top product to contain not less than 90 mole % acetone in order for it to meet specification required for reuse into the chemical process. It is also required that the bottom product contains 50 mole % acetone. As part of the setup of the existing distillation column there is a heat exchanger on the feed line into the column that allows the feed to enter at its bubble point and at a rate of 100 mol/hr.

So far I have tried to calculate the equilibrium curve which looks something like this:

I am unsure though if this curve can be used for the calculation

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What you've got there is a maximum boiling azeotrope mixture. It occurs when the negative deviations are very large, and the total pressure curve, in this case, passes through a minimum, giving rise to a maximum in the temperature (i.e. boiling point). Azeotropic mixtures cannot be easily separated by ordinary distillation methods. For example, in the case of ethanol-water, one cannot recover more than 89.4 mole% ethanol using ordinary distillation, as the mixture becomes azeotropic at this point. Other separation techniques (such as azeotropic distillation) must be used. Often the equipment and set-up used are unique for each mixture.

I would suggest not using the McCabe-Thiele method at all it would yield poor results. Your best bet would be using Ponchon-Saviart or Lewis-Sorell method, they are bit tedious but will definitely yield better results.

Practically though, one would not use a distillation directly, a precursor step would be to use extractive distillation followed by rectification. Such a problem usually demands a binodal graph.

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Seems like you have an azeotropic mixture over there means you can't separate it to get a bottom product < 40 % acetone with a straightforward distillation. However, since you don't, ie the feed, top and bottoms compositions as well as feed conditions (saturated liquid) all put you to the right of this point (of x=y on the equilibrium line) you should be able to use McCabe Thiele method for this problem.

You can do a) find Rmin that would yield you your top product composition. Then with this Rmin you can calculate what the bottoms composition would be with 12 stages.

b) If you can't meet the bottoms composition with Rmin from a) (and I think you won't) then start increasing R till you get the bottoms composition you want with 12 stages.

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You cannot use Mc cabe Thiele because at Rmin it requires infinite number of steps. Constantly changing R to see what sticks sounds like a huge amount of work. Maybe go with Lewis Sorel method, it's tedious but gives a stage wise calculation and since you know the number of trays already, it will give you more definite results.

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