Page 54 - Applied Process Design For Chemical And Petrochemical Plants Volume II

Distillation 43

Mixture densities of the binary mixtures require a For the example,
knowledge of volume fraction for each component. The
component molar volume is: p~,~i~= [(0.637) (0.5082)'/3 + (0.363) (0.8155)'/3]3
= 0.609 lb/hr-ft
Vi = Mi/pi
Liquid surface tension is calculated using the Sugden
For acetone and benzene, respectively: Parachor method [242]. Neglecting vapor density, surface
tension for the liquid mixture is:
VL,~ (58.08)/45.3
5 1.282 ft3/lb mole
= (78.11)/51.2
VL,~ where (5 is in dynes/cm, p is in gm/cm3 and the pardchor,
= 1.526 ft3/lb mole

For the liquid mixture:
Values of the parachor are given in the literature [240].
VL,mix = X~VL,I XZVL,~ Then the example gives:
+
= (0.637) (1.282) + (0.363) (1.526)
= 1.371 ft3/lb mole Mmix = (0.637) (58.08) + (0.363) (78.11)
= 65.35 lb/lb mole
Then the volume fraction of a component is calculated [PImix = (0.637) (162.1) + (0.363) (207.1)
assuming an ideal mixture. = 178.4
pmix = 47.6/62.32 = 0.7638 gm/cu cm
vi = Vi/Vmix omix = [(0.7638/65.35) (178.4)14
= 18.96 dynes/cm
For acetone and benzene, respectively:
Diffusivity of the liquid light key component is calculat-
VL,~ = 0.817/1.371 = 0.596 ed by the dilute solution equation of Wilke-Chang [243].
DLK = (3.24 x (I#M~~~)'" (T + 460)/pmix (VLK)'.'
UL,~ = 0.554/1.371 = 0.404
Wilke-Chang reported the recommended values for
The liquid density of the binary mixture is then: as follows: water, 2.6; benzene, heptane and ether, 1.0;
methanol, 1.9; ethanol, 1.5; unassociated solvents, 1.0.
PL,mix = VL,~ PL,I + VL,Z PL,Z The mixture parameter for the example problem is con-
= (0.596) (45.3) + (0.404) (51.2) sidered unity.
= 47.6 lb/ft3
Then,
The vapor density can be found in an analogous manner. DLK = (3.24 x (65.35)"' (166 + 460)/(0.609) (1.282)0.6
= 2.32 x ft2/hr
Pv,v,,x = UV,l Pv,l + vv,2 Pv,2
Dimensionless groups for the example problem are:
However, the example problem does not require a cal-
culation for vapor density. Instead, the superficial vapor ND, = ~L/PLUV (8-71)
mass velocity G can be substituted into Equation 8-73 = (5.417 x 105)/(0.609) (2.4092 x lo4)
because: = 37
Nsc = PL/ PLDLK (8-72)
G = Uvp~ = (0.609)/(47.6) (2.32 x
= 55
NRe hwG/ WL (FA) (8 - 73)
Liquid viscosity of the binary mixture, when not report- = (0.2082) (3.82 x 10")/(0.609) (0.063)
ed with the experimental efficiency results, is estimated = 2.07 104
using:
Murphree vapor plate efficiency is calculated two ways:

EM = 7.0 (ND )0.14 (NS~)~'.~~ (NRe)'.O8 (8-70A)
The pure component viscosities are given in the literature = 7.0 (37)5.14 (55)o.2" (2.07 x 104)0.08
[240, 2411 as a function of temperature. = 7.0 (1.66) (2.72) (2.26) = 71%