# 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→∞.