Benzene is being stripped from a coal seam gas by using countercurrent gas

absorption with a wash oil in a packed column. The inlet gas contains $2\mathrm{.}0$vol$\%$

benzene and this must be reduced to $0\mathrm{.}4$vol$\%$ before the gas can be supplied to the

consumer. The wash oil enters the absorber containing $0\mathrm{.}5$mol$\%$ benzene. The

absorber has a diameter of $1\mathrm{.}7m$ and operates at a constant pressure of $150$kPa and

temperature of $40C.$ The coal seam gas enters the column at this temperature and

pressure and with a total flowrate of $0\mathrm{.}63\frac{m^3}{s}.$ You may assume dilute solutions and

that the gas phase behaves as an ideal gas.

The individual mass transfer coefficients have been determined as:

$k_{G}a=0\mathrm{.}16mo\frac{l}{m^3}.$skPa

$k_{L}a=0\mathrm{.}006s^{-1}$

Oil Density $=820k\frac{g}{m^3}$

Oil Molecular Weight $=196\frac{g}{m}ol$

Ideal Gas Constant, $R=8\mathrm{.}314\frac{J}{m}ol.K$

An equilibrium diagram of the benzene solubility in the wash oil is attached as Figure

a$)$ What is the minimum amount of oil required in $mo\frac{l}{s}?$

$(6$ marks$)$

b$)$ The actual oil flowrate is determined to be $35mo\frac{l}{s}.$ While operating at this

flowrate, you measure a bulk gas phase concentration as $1\mathrm{.}5$vol$\%$ benzene at one

point in the column. Determine the mol fraction of benzene the bulk liquid phase

at this point and the corresponding interfacial mol fractions of both the gas and

liquid phases.