Add a Component to a Mixture with an Azeotrope

piston-cylinder

P-x-y diagram

add benzene

add ethanol

add moles

10

inject isothermally

Benzene and ethanol, in vapor-liquid equilibrium (VLE) inside a cylinder fitted with a piston, have an azeotrope (with the same vapor and liquid composition) at a mole fraction of 0.6. Either benzene (more volatile) or ethanol (less volatile) can be added to the system, which then returns to equilibrium. Because of the azeotrope, the behavior is different depending on how many moles are added. The piston-cylinder shows the relative amounts of liquid and vapor. Total moles in the liquid phase

L

n

and vapor phase

V

n

are displayed, as well as the mole fraction of benzene in the liquid phase

x

B

and the vapor phase

y

B

. The saturation pressure of benzene

sat

P

B

is higher than the saturation pressure of ethanol

sat

P

E

. The

P-x-y

diagram helps visualize the observed behavior. If conditions are changed, click reset before clicking "inject isothermally".