Simple Distillation Residue Curves for a Mixture of Pentane and Dichloromethane at 750 mmHg
Simple Distillation Residue Curves for a Mixture of Pentane and Dichloromethane at 750 mmHg
The vapor-liquid equilibrium behavior of the binary mixture composed of pentane and dichloromethane at 750 mmHg can be represented by the following empirical equation:
y=+bx(1-x)
ax
1+(a-1)x
a=4.2
b=-1.2
This mixture exhibits a minimum boiling azeotrope at approximately 52.08% pentane mole fraction.
The simple distillation residue curve is given by the following implicit relation:
ξ=ln(1-x)+ln
1
(a-1+b)
x
0
x(1-)
x
0
2
(a-1)
(a-1+b)(a-1+ab)
(1-x)(a-1+b[1+(a-1)])
x
0
(1-)(a-1+b[1+(a-1)x])
x
0
where is the warped time, is the pentane mole fraction in the still at , and is the initial pentane composition in the still. The warped time is related to clock time by , where is the vapor rate from the still in mole/s and is the liquid hold-up in the still in moles.
ξ
x(ξ)
ξ
x
0
ξ
t
dξ=dt
V
H
V
H
If the initial composition is =0.5208, the azeotropic composition, then .5208 ∀ ξ. Indeed, this mixture forms a positive azeotrope at 52.08% pentane mole fraction.
x
0
x(ξ)=0
If the initial composition in the still is rich in pentane (i.e., >0.5208), then the only component that is left in the still at large values of the warped time is pentane (i.e., as ).
x
0
x(ξ)->1
ξ→∞.
If the initial composition in the still is rich in dichloromethane (i.e. <0.5208), then the only component that is left in the still at large values of the warped time is dichloromethane (i.e., as ).
x
0
x(ξ)0
ξ→∞.