A liquid mixture containing 30.0 mol% benzene (B), 25.0% toluene (T), and the rest xylene (X) feeds a distillation column. The bottom product contains 98.0 mol% X and no B, and 96.0% of the X in the feed is recovered in this stream. The top product feeds a second column. The top product of the second column contains 97.0% of the B in the feed to this column. The composition of this stream is 94.0 mol% B and the rest T. (a) Draw and label a flow diagram for this process and perform a degree of freedom analysis to prove that, for an assumed basis of calculation, the molar flow rates and compositions of all process streams can be calculated with the given information. Write the equations you would solve in order to calculate the unknown process variables. In each equation (or set of simultaneous equations), indicate the variables you would solve for. Do not perform any calculations yet. (b) Calculate (i) the percentage of benzene in the process feed (i.e., the feed to the first column) that exits in the top product of the second column and (ii) the percentage of toluene in the process feed that exits in the bottom product of the second column. Answer: (i) 97%; (ii) 89%.
A liquid mixture containing 30.0 mol% benzene (B), 25.0% toluene (T), and the rest xylene (X) feeds a distillation column. The bottom product contains 98.0 mol% X and no B, and 96.0% of the X in the feed is recovered in this stream. The top product feeds a second column. The top product of the second column contains 97.0% of the B in the feed to this column. The composition of this stream is 94.0 mol% B and the rest T.
(a) Draw and label a flow diagram for this process and perform a degree of freedom analysis to prove that, for an assumed basis of calculation, the molar flow rates and compositions of all process streams can be calculated with the given information. Write the equations you would solve in order to calculate the unknown process variables. In each equation (or set of simultaneous equations), indicate the variables you would solve for. Do not perform any calculations yet.
(b) Calculate (i) the percentage of benzene in the process feed (i.e., the feed to the first column) that exits in the top product of the second column and (ii) the percentage of toluene in the process feed that exits in the bottom product of the second column. Answer: (i) 97%; (ii) 89%.
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