Composition of Methanol-Water Batch Distillation

Prepared by: Jason Hixson Don Scott

Michael Hickey

September 20, 2005

Objective

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

Vapor-Liquid Equilibrium Diagram

Antoine Equation

*ln m

Bp A

C T

*,m wp Vapor Pressure in mmHg of methanol and water.

T is the absolute temperature

A, B, and C are constants.

*ln w

Bp A

C T

Antoine Constants

• Are calculated using using the known temperatures and vapor pressures from Perry’s Chemical Engineers Handbook.

p*(mmHg) T(C )1.00 -44.005.00 -25.30

10.00 -16.2020.00 -6.0040.00 5.0060.00 12.10

100.00 21.20200.00 34.80400.00 49.90760.00 64.70

p*(mmHg) T(C )1.00 -17.305.00 1.20

10.00 11.2020.00 22.1040.00 34.0060.00 41.50

100.00 51.60200.00 66.50400.00 83.00760.00 100.00

WaterMethanol

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.

*,ln m w

Bp A

C T

METHANOL A 18.5875B 3626.5500C -34.2900

WATER A 18.3036B 3816.44C -46.13

* ** * (1 )* *total m m m m w wP x p x p

Van Laar’s Model

Gamma correction factors for non-ideal system.

2

exp[(1 )

mm

m

AAx

RTBx

2

exp[(1 )

ww

w

AAx

RTBx

Gamma Correction Factor

Ideal Gas Constant = 1.987 cal/K*g-mol

Temperature (K)

A and B are constants

, *

*

*m

m actualm m

y P

x p , *

*

*w

w actualw w

y P

x p

Using data from Perry’s where P is 760 mmHg the constants A and B can be calculated using solver in Excel

T (C) xa ya100 0 096.4 0.02 0.13493.5 0.04 0.2391.2 0.06 0.30489.3 0.08 0.36587.7 0.1 0.41884.4 0.15 0.51781.7 0.2 0.57978 0.3 0.665

75.3 0.4 0.72973.1 0.5 0.77971.2 0.6 0.82569.3 0.7 0.8767.5 0.8 0.91566 0.9 0.95865 0.95 0.979

64.5 1 1

GivesVAN LAAR A= 585.6215111LIQ MODEL B= 375.733096

Raoult’s Law

** /a a a totaly x p P

Vapor Liquid

Set Up

Xa yA T(C) T(K) pA (mmHg) pB (mmHg) G A CALC G B CALC P DIF0.020 0.133 96.591 369.751 2384.780601 672.2824004 2.114262724 1.000486141 760 0.001905382

•Set arbitrary temperature = (Pcalc-Pactual)

Use Solver to minimize DIF cell by changing T(C).

METHANOL- WATER

65.000

70.000

75.000

80.000

85.000

90.000

95.000

0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000

xm, ym

Tem

per

atu

r (C

)

Liquid

Vapor

VLE Diagram

Composition Calculation Using WFIT Program

0.38652+0.39727*B2-0.012737*B2^2+0.00013528*B2^3-(0.00000048036)*B2^4)+1%

Reboiler Composition vs TimeTime Vs Composition

0

5

10

15

20

0 10 20 30 40 50 60 70 80 90

Time (minutes)xM

eth

ano

l (%

)

0% Reflux75% Reflux 2500 W

Time Vs Composition

0

5

10

15

20

0 10 20 30 40 50

Time (minutes)

xMet

hano

l (%

)

Initial xm: 23% Initial Vm: 16.86 L

Tray # 12 Composition vs Time

0% Reflux75% Reflux 2500 W

Time Vs Composition

0

510

15

20

2530

35

0 10 20 30 40 50 60 70 80 90

Time (minutes)

xMet

han

ol

(%)

Time Vs Composition

0102030405060708090

100

0 10 20 30 40 50

Time (minutes)

xM

eth

an

ol

(%)

Tray # 11 Composition vs Time

0% Reflux75% Reflux 2500 W

Time Vs Composition

0

5

10

15

20

25

0 10 20 30 40 50 60 70 80 90

Time (minutes)

xMet

han

ol

(%)

Time Vs Composition

0102030405060708090

100

0 10 20 30 40 50

Time (minutes)

xMet

han

ol

(%)

Tray # 10 Composition vs Time

0% Reflux75% Reflux 2500 W

Time Vs Composition

0

5

10

15

20

25

0 10 20 30 40 50 60 70 80 90

Time (minutes)

xMet

han

ol

(%)

Time Vs Composition

0102030405060708090

100

0 10 20 30 40 50

Time (minutes)

xMet

han

ol

(%)

Tray # 9 Composition vs Time

0% Reflux75% Reflux 2500 W

Time Vs Composition

0

5

10

15

20

25

0 10 20 30 40 50 60 70 80 90

Time (minutes)

xMet

han

ol

(%)

Time Vs Composition

0102030405060708090

100

0 10 20 30 40 50

Time (minutes)

xMet

han

ol

(%)

Tray # 8 Composition vs Time

0% Reflux75% Reflux 2500 W

Time Vs Composition

0

5

10

15

20

25

0 10 20 30 40 50 60 70 80 90

Time (minutes)

xMet

han

ol

(%)

Time Vs Composition

0102030405060708090

100

0 10 20 30 40 50

Time (minutes)

xMet

han

ol

(%)

Tray # 7 Composition vs Time

0% Reflux75% Reflux 2500 W

Time Vs Composition

0

5

10

15

20

25

0 10 20 30 40 50 60 70 80 90

Time (minutes)

xMet

han

ol

(%)

Time Vs Composition

0102030405060708090

100

0 10 20 30 40 50

Time (minutes)

xMet

han

ol

(%)

Tray # 6 Composition vs Time

0% Reflux75% Reflux 2500 W

Time Vs Composition

0

10

20

30

40

0 10 20 30 40 50 60 70 80 90

Time (minutes)

xMet

han

ol

(%)

Time Vs Composition

0102030405060708090

100

0 10 20 30 40 50

Time (minutes)

xMet

han

ol

(%)

Tray # 5 Composition vs Time

0% Reflux75% Reflux 2500 W

Time Vs Composition

05

10152025303540

0 10 20 30 40 50 60 70 80 90

Time (minutes)

xMet

han

ol

(%)

Time Vs Composition

0102030405060708090

100

0 10 20 30 40 50

Time (minutes)

xMet

han

ol

(%)

Tray # 4 Composition vs Time

0% Reflux75% Reflux 2500 W

Time Vs Composition

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90

Time (minutes)

xMet

han

ol

(%)

Time Vs Composition

0102030405060708090

100

0 10 20 30 40 50

Time (minutes)

xMet

han

ol

(%)

Tray # 3 Composition vs Time

0% Reflux75% Reflux 2500 W

Time Vs Composition

0

1020

30

40

5060

70

0 10 20 30 40 50 60 70 80 90

Time (minutes)

xMet

han

ol

(%)

Time Vs Composition

0102030405060708090

100

0 10 20 30 40 50

Time (minutes)

xMet

han

ol

(%)

Tray # 2 Composition vs Time

0% Reflux75% Reflux 2500 W

Time Vs Composition

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90

Time (minutes)

xMet

han

ol

(%)

Time Vs Composition

0102030405060708090

100

0 10 20 30 40 50

Time (minutes)

xMet

han

ol

(%)

Tray # 1 Composition vs Time

0% Reflux75% Reflux 2500 W

Time Vs Composition

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90

Time (minutes)

xMet

han

ol

(%)

Time Vs Composition

0102030405060708090

100

0 10 20 30 40 50

Time (minutes)

xMet

han

ol

(%)

Reflux Composition vs Time

0% Reflux75% Reflux 2500 W

Time Vs Composition

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90

Time (minutes)

xMet

han

ol

(%)

Time Vs Composition

0102030405060708090

100

0 10 20 30 40 50

Time (minutes)

xMet

han

ol

(%)

Collected 1.69 L Collected 6.38 L

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.

QUESTIONS?