Question

The vapor-liquid equilibrium data for heptane – ethylbenzene at 1 atm pressure is given below:

x	0	0.10	0.20	0.40	0.50	0.60	0.70	0.90	1
y	0	0.25	0.45	0.65	0.74	0.82	0.86	0.96	1

            A feed mixture containing 40 mol% heptane and 60 mol% ethylbenzene is to be fractionated at 1 atm pressure to produce a distillate containing 95 mol% heptane and a bottom product stream containing 96 mol% ethylbenzene.

Determine the minimum reflux ratio if the feed is a saturated liquid.

Determine the minimum reflux ratio if the feed is a saturated vapor.

Determine the minimum reflux ratio if the feed is an equilibrium mixture of liquid and vapor, with 20% vapor.

Determine the minimum number of theoretical plates using McCabe-Thiele graphical method.

Determine the minimum number of theoretical plates using Fenske equation.

For a saturated liquid feed and a reflux ratio that is 2.25 times the minimum, determine:

-The number of theoretical stages, using McCabe-Thiele graphical method.

-The optimum feed stage location.

-The actual number of stages if the average column efficiency is 58%.

-The top product and bottom product rates if the feed rate is 100 kmol/s.

-The condenser duty.

-The reboiler duty.

	Latent heat, kJ/kmol	Heat capacity, kJ/kmol-K
Heptane	35,000	220
Ethylbenzene	40,000	183

Feed temperature	30C
Condenser temperature	95C
Reboiler temperature	99C

                                                                          

Answer 1

Draw the equilibrium diagram from the given x and y values.

Feed is 40 mol% heptane and 60 mol% ethylbenzene.

Distillate from the distillation column consists of 95 mol% heptane and bottoms from the distillaiton column consists of 96 mol% ethylbenzene.

Therefore,

Here shows mole fraction of more volatile component. i.e heptane.

(a)  Determine the minimum reflux ratio if the feed is a saturated liquid.

If feed is saturated liquid,

Slope of feed line is infinity. i.e feed line vertical line from the feed location.

At minimum reflux ratio all rectifying section operating line, stipping section operating line, and feed line will intersect on equilibrium curve.

(b) Determine the minimum reflux ratio if the feed is a saturated vapor.

(c) Determine the minimum reflux ratio if the feed is an equilibrium mixture of liquid and vapor, with 20% vapor.

is the fraction of liquid in feed.

(d) Minimum number of plares required for given separaion at total reflux ratio. at this condition both rectifying section and stripping section operating lines will coinside with diagonal line.