Page 189 - Separation process principles 2

154 Chapter 4 Single Equilibrium Stages and Flash Calculations

VAPOR PRESSURE OF n-HEPTANE liquid is at 125°C and 687 kPa and contains 57 mol% A. The feed
is introduced to the column through an expansion valve so that it
Vapor pressure, tom: enters the column partially vaporized at 60°C. From the data below,
20 40 60 loo 200 400 760 determine the molar ratio of liquid to vapor in the partially vapor-
Temperature, "C: ized feed. Enthalpy and equilibrium data are as follows:
9S 22.3 30.6 41.8 58.7 78.0 98.4 124 Molar latent heat of A = 29,750 Who1 (constant)
(a) Plot an x-y equilibrium diagram for this system at 1 atm by Molar latent heat of Hz0 = 42,430 Wflunol (constant)
using Raoult's and Dalton's laws. Molar specific heat of A = 134 kJ/kmol-K (constant)
(b) Plot the T-x bubble-point curve at 1 atm. Molar specific heat of H20 = 75.3 kJ/kmol-K (constant)
(c) Plot a and K-values versus temperature. Enthalpy of high-pressure, hot feed before adiabatic expansion = 0
(d) Repeat part (a) using the arithmetic average value of a, calcu- Enthalpies of feed phases after expansion: hv = 27,200 Whol,
lated from the two extreme values. hL = -5,270 Who1
(e) Compare your x-y and T-x-y diagrams with the following
experimental data of Steinhauser and White [Ind. Eng. Chem., 41, VAPOR-LIQUID EQUILIBRIUM DATA FOR
2912 (1949)l. ACETONE-H20 AT 101.3 kPA
T, "C
VAPOR-LIQUID EQUILIBRIUM DATA FOR
n-HEPTANElTOLUENE AT 1 ATM 56.7 57.1 60.0 61.0 63.0 71.7 100
Mol% A
in liquid: 100 92.0 50.0 33.0 17.6 6.8 0
Mol% A
in vapor: 100 94.4 85.0 83.7 80.5 69.2 0

4.12 Using vapor pressure data from Exercises 4.6 and 4.8 and
the enthalpy data provided below:
(a) Construct an h-x-y diagram for the benzene-toluene system at
1 atm (101.3 kPa) based on the use of Raoult's and Dalton's laws.
Saturated Enthalpy, kJ/kg
4.10 Saturated-liquid feed, of F = 40 mom, containing 50 mol% Benzene Toluene
A and B is supplied continuously to the apparatus shown in T, "C h~ hv h~ hv
Figure 4.37. The condensate from the condenser is split so that half
of it is returned to the still pot.
(a) If heat is supplied at such a rate that W = 30 molh and a = 2,
as subsequently defined, what will be the composition of the over-
head and the bottoms product?
(b) Calculate the energy required for 50 mol% vaporization of a
(b) If the operation is changed so that no condensate is returned to 30 mol% liquid solution of benzene in toluene, initially at satura-
the still pot and W = 30 as before, what will be the composition of
tion temperature. If the vapor is then condensed, what is the heat
the products?
load on the condenser in kJkg of solution if the condensate is satu-
rated and if it is subcooled by 10°C?
Section 4.3
4.11 It is required to design a fractionation tower to operate at
4.13 Vapor-liquid equilibrium data at 101.3 kPa are given for
101.3 kPa to obtain a distillate consisting of 95 mol% acetone (A)
the chloroforn-methanol system on p. 13-11 of Perry's Chemical
and 5 mol% water, and a residue containing 1 mol% A. The feed
Engineers'Handbook, 6th ed. From these data, prepare plots like
Figures 4.6b and 4.6~. From the plots, determine the azeotropic
Vapor
composition and temperature at 101.3 kPa. Is the azeotrope of the
minimum- or maximum-boiling type?
4.14 Vapor-liquid equilibrium data at 101.3 kPa are given for
(jc Condenser the water-formic acid system on p. 13-14 of Perry's Chemical
;'PA> Engineers'Handbook, 6th ed. From these data, prepare plots like
.
...
~eed qf7:.;',?.;:::: and 4.7~. From the plots, determine the azeotropic
4.7b
.
...
Figures
.
:.
.-
,
..
,
Distillate
,
..-2
,_
F . : . ;;;;,.:.: Reflux D composition and temperature at 101.3 kPa. Is the azeotrope of the
:. ' .*., , -, : .;. , ;,. ,'. . .'.. R
minimum- or maximum-boiling type?
4.15 Vapor-liquid equilibrium data for mixtures of water and
Bottoms
W isopropanol at 1 atm (101.3 kPa, 760 torr) are given below.
Figure 4.37 Conditions for Exercise 4.10. (a) Prepare T-x-y and x-y diagrams.