Question $4$

a$.$ Explain the difference in the location of the operating line in relation to the

equilibrium line depending on whether there is stripping or absorption for dilute

systems $(2$ marks$).$

b$.$ A packed column with six equilibrium stages is used for stripping benzene from a

liquid stream using countercurrent air at $1$ atm and $25\mathrm{.}0C.$ The inlet liquid stream

contains $0\mathrm{.}5$mol$\%$ benzene, and the inlet air is free of benzene. The liquid flow

rate is $26\mathrm{.}8k\frac{g}{h},$ and the gas flow rate is $28\mathrm{.}3\frac{m^3}{h}.$ The density of air at $25\mathrm{.}0C$

and $1$atm is $1\mathrm{.}184k\frac{g}{m^3},$ the molar mass of air is $29\frac{g}{m}ol$ and that of the liquid

stream is $18\frac{g}{m}ol.$ The equilibrium relationship for benzene can be described by

the following relationship: $y=1\mathrm{.}24x.$ Calculate the concentration of the benzene

in the exit stream. $(8$ marks$).$

c$.$ Derive the operating equation for an absorption process where the inlet gas and

the outlet liquid are concentrated in the solute. The final equation must be a

function of the outlet gas and inlet solvent parameters. State all relevant

assumptions and describe all symbols you use. $(10$ marks$).$