ERT 313/4 – BIOSEPARATION ENGINEERING
ASSIGNMENT 1
Date of submission: 20 Jan 2011
QUESTION 1
It is desired to reduce carbon dioxide content in gaseous stream by contacting the gas
countercurrently with pure water in a packed tower. The total inlet gas flow to the tower
is 20 kg mol/h.ft2 which contains 20 mol % carbon dioxide. The inlet pure water flow is
90 kg mol H20/h.ft2. Of the carbon dioxide in the gaseous stream, 98% is to be absorbed
into pure water. The absorber will operate isothermally at 250C and 1 atm. Mass transfer
coefficients and equilibrium data are given below:
y* = 3.1x
at 250C
kx a = 60 mol/h.ft3.unit mol fraction
ky a = 15 mol/h.ft3.unit mol fraction
(i)
Calculate the mol fraction of carbon dioxide in the gas and liquid outlets.
(ii)
Find the number of transfer units NTU (N0y), height of transfer units
(Hoy), and tower height (ZT).
QUESTION 2
Rectification of a Heptane - Ethyl Benzene Mixture.
A saturated liquid feed of 250 mol/h at the boiling point containing 40 mol % heptane
and 60% ethyl benzene is to be fractionated at 101.32 kPa abs to give a distillate
containing 98 mol % heptane and a bottoms containing 1.0 mol % heptane. The reflux
ratio used is 2:1. Calculate the mol/h distillate, mol/h bottoms, theoretical number of
trays, and the feed plate location. Equilibrium data are given below at 101.32 kPa abs
pressure for the mole fraction n-heptane xH and yH:
QUESTION 3
Minimum Reflux Ratio and Total Reflux in Rectification
A liquid mixture of benzene - toluene is to be distilled in a fractionating tower at 101.3
kPa pressure. The feed of 100 kg mol/h is liquid, containing 45 mol % benzene and 55
mol % toluene, and enters at 327.6 K. A distillate containing 95 mol % benzene and 5
mol % toluene and a bottoms containing 10 mol % benzene and 90 mol % toluene are to
be obtained. The reflux ratio is 4:1. The average heat capacity of the feed is 159 kJ/kg
mol . K and the average latent heat 32099 kJ/kg mol). Equilibrium data for this system
are given in Table 11.1-1. Calculate:
a)
kg moles per hour distillate,
b)
kg moles per hour bottoms,
c)
minimum reflux ratio Rm
d)
Minimum number of theoretical plates at total reflux