Composition of Methanol-Water Batch Distillation

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Composition of Methanol-Water Batch Distillation
September 20, 2005

• Prepared by Jason Hixson
  Don Scott Michael Hickey

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Objective

• Determine the composition of liquid
  methanol-water binary system at equilibrium based
  on temperature in a distillation column.

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Vapor-Liquid Equilibrium Diagram
Antoine Equation
Vapor Pressure in mmHg of methanol and water.
T is the absolute temperature A, B, and C are
constants.
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Antoine Constants

• Are calculated using using the known temperatures
  and vapor pressures from Perrys Chemical
  Engineers Handbook.

Water
Methanol
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Antoine Constants

• Arbitrary values are then chosen for A, B, and C
  giving an incorrect vapor pressure.
• Excel solver is then used to find values of A, B
  and C for both methanol and water which gives the
  correct pressure.

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Van Laars Model
Gamma correction factors for non-ideal system.
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Gamma Correction Factor
A and B are constants
Ideal Gas Constant 1.987 cal/Kg-mol
Temperature (K)
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Using data from Perrys where P is 760 mmHg the
constants A and B can be calculated using solver
in Excel
Gives
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Raoults Law
Vapor
Liquid
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Set Up
(Pcalc-Pactual)

• Set arbitrary temperature

Use Solver to minimize DIF cell by changing T(C).
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VLE Diagram
Vapor
Liquid
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Composition Calculation Using WFIT Program
0.386520.39727B2-0.012737B220.00013528B23-(
0.00000048036)B24)1
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Reboiler Composition vs Time
0 Reflux
75 Reflux
2500 W
Initial xm 23
Initial Vm 16.86 L
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Tray 12 Composition vs Time
0 Reflux
75 Reflux
2500 W
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Tray 11 Composition vs Time
0 Reflux
75 Reflux
2500 W
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Tray 10 Composition vs Time
0 Reflux
75 Reflux
2500 W
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Tray 9 Composition vs Time
0 Reflux
75 Reflux
2500 W
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Tray 8 Composition vs Time
0 Reflux
75 Reflux
2500 W
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Tray 7 Composition vs Time
0 Reflux
75 Reflux
2500 W
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Tray 6 Composition vs Time
0 Reflux
75 Reflux
2500 W
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Tray 5 Composition vs Time
0 Reflux
75 Reflux
2500 W
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Tray 4 Composition vs Time
0 Reflux
75 Reflux
2500 W
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Tray 3 Composition vs Time
0 Reflux
75 Reflux
2500 W
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Tray 2 Composition vs Time
0 Reflux
75 Reflux
2500 W
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Tray 1 Composition vs Time
0 Reflux
75 Reflux
2500 W
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Reflux Composition vs Time
0 Reflux
75 Reflux
2500 W
Collected 1.69 L
Collected 6.38 L
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Conclusions

• At 0 reflux the amount of distillate collected
  was larger than 75 reflux.
• At 75 reflux the purity of methane was a much
  higher quality.
• If quality is more important then a high reflux
  percentage is needed.
• If quantity and timeliness is more important then
  a low reflux is needed.

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QUESTIONS?