Distillation Cards

Chemical Engineering

Year 2, Semester 2

Lande Liu

University of Manchester

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  • Created by: Foteini
  • Created on: 28-05-12 21:31

How do we derive the equation for the intersection

The two operating lines intersect at xq, yq

  • ESOL LINE: Yq Vn = Xq Ln + D Xd
  • SSOL LINE: Yq Vm = Xq Lm - B Xb
  • Remember F Zf = D Xd + B Xb

        So VYq = -Lf Xq + Ff Zq

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What is the slope of the q line?

 q gradient = -(Lf)/(Vf)

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What are the q line limits and what do they repres

q line limits are from 0 to -infinity

0 represents the dew point

-infinity represents the boiling point

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What is q defined as?

q = (Enthalpy required to vaporise 1 mole feed) / (Enthalpy required to vaporise 1 mole of liquid at its boiling point)





q = (Enthalpy required to vaporise 1 mole feed) / (Molar Enthalpy of Vaporisation)


= (hv - hf) / (hv - hl) or    (hv - hf) / (hlv)

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What is the relative volatility equal to?

α = (Saturated vapour pressure of A) / (Saturated Vapour pressure of B)

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What is Raoult's Law?

Pa=Xa Poa

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What is Dalton's law?

Pa=Ya PT

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How can one find the degrees of vaporisation?

First do a mass balance multiplying compositions and flowrate. Feed equals vapour plus liquid of the more volatile component. Then try to find an equation V/F

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What does the Murphree Plate Efficiency represent?

It is when the vapour composition from one plate to the next is divided by the equilibrium change.

You can redraw the VLE line closer to the operating line. Allow for ηm.

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How to calculate the total amount of distillate co

They are asking you to calaculate Db which is S1-S2

which is equal (Xd - Xs1) / (Xd - Xs2)  

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When is the Ponchon-Savarit used?

It is used when  CONSTANT MOLAR OVERFLOW can not be assumed

1.Latent of Vaporisation change from stage to stage

2.Significant heat of mixing

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When they give you composition of bottom and top t

On the x=y, draw Xb

Then start from there and draw the number of stages

Stop when 0.95 is exceeded on the x=y line

These are the number of theoretical stages

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