A distillation column operates at steady state with a 10.0 kg/s continuous feed

Question

A distillation column operates at steady state with a 10.0 kg/s continuous feed consisting

of 55.0 wt% ethanol, 5.0 wt% of a dissolved solute, and 40.0 wt% water. The overhead

and bottoms product streams emerge from the column with equal mass flow rates. The

top stream contains 90.0 wt% ethanol and no solute.

A) Carefully and completely draw and label the flowchart for this process.

B) Show the degree of freedom analysis for the distillation column.

C) Calculate the mass fraction of solute in the bottoms product. Also calculate the

fraction of ethanol in the feed that leaves in the bottoms product.

Explanation / Answer

The problem also states that the top and bottom flow rates are equal in mass so they both must be 5 kg/sec. The top stream is 90 wt% ethanol so the ethanol is 4.5 kg/s There's no solute so the balance must be water or 0.5 kg/sec

By mass balance with the feed and overhead, work out the composition of the bottom stream. Once you know that, the three questions in B.3 are trivial.

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