Question

One thousand kilograms per hour of a mixture of benzene (B) and Toluene (T) containing 60% benzene by mass is separated by distillation into two fractions. The mass flowrate of the benzene (B) in the top stream is 500 kg (B) /h and that of toluene in the bottom stream is 485 kg (T) / h. The unit operates at steady state.

3.1.1. Draw a schematic diagram showing all the relevant streams in the distillation unit. (8)

3.1.2. Write the basis for calculation.

Answer 1

Overall balance

$1000=D+B.........(1)$

Applying benzene balance

$(1000)(0.5)=D \times D + B \times B = 450 + B \times B\\ B \times B =50$

This is the benzene flow rate at the bottom

Applying tolere balance

$(1000)(0.5)=D y D + B y B = DyD+475\\ DyD= 25$

This is the tolere flow rate at the top