A NonIsothermal Pervaporation

1
A Non-Isothermal Pervaporation

• Juan P. G. Villaluenga(1) , Wayne Yoshida(2)
• and Yoram Cohen(2)

(1) Complutense University of Madrid (2)
University of California, Los Angeles
http//www.polysep.ucla.edu
2
Pervaporation
Selective Layer
Support
3
Motivation Approach

• Develop a numerical finite-element model to
  simulate non-isothermal pervaporation.
• Full coupling of the momentum, energy and mass
  balance equations.
• Provide for future interface with a sub-model
  (2-D or 3-D) of detailed transport within the
  membrane itself.

4
Pervaporation in a 2-D Membrane Channel
H2h
L
5
Pervaporation Equations of Motion
6
Energy Equation
7
Pervaporation Boundary Conditions
Entrance
Exit
8
Boundary Conditions Membrane Surface
Mass Transfer
Heat Transfer
9
Membrane Resistance
10
Problem Domain Finite-Element Mesh
11
Water Concentration and Temperature Fields for
Ethanol-Water Dehydration
T C
y/H1
y/H0
Re135 Sc451 Pr15 Tp293 K To 298 K H/L0.01
Cwo10
12
Ethanol Dehydration
T Cwater
y/H0.5
To318 K, Tp293K
Re384 Sc209 Pr10 H/L0.02 Cwo5
y/H0
13
TCE/Water Pervaporation
T CTCE
y/H0.5
Sc418 Re 542 Tfeed 308 K Tp 293 K H/L0.02
y/H0
14
TCE/Water Pervaporation
CTCE T
y/H0.5
Sc418 Re 542 Tfeed 308 K Tp 293 K H/L0.02
y/H0
15
TCE/Water Pervaporation
CTCE T
y/H0.5
Sc98 Re 1118 Pr 2.4
Tfeed 348 K Tp 293 K
y/H0
16
Ethanol Dehydration
Re 226 Sc 147 H/L 0.01 Cwo 5
Tp318 K
Tp313 K
17
Ethanol Dehydration
Effect of Permeate Temperature
Re 226 Sc 147 H/L 0.01 Cwo 5
18
Ethanol Dehydration Effect of Permeate
Temperature on water concentration at membrane
surface
1
0.98
0.96
Feed Temperature 298 K
0.94
PermeateTemperature
0.92
Water Concentration (Cs/Co)
0.9
T
293 K
P
?Tm5 K
0.88
0.86
T
288 K
P
0.84
?Tm10 K
Cwo10 H/L0.01
0.82
0
0.2
0.4
0.6
0.8
1
Axial Position (x/L)
Dimensionless Axial Position (x/L)
19
Ethanol Dehydration Water Concentration at
Membrane Surface
1
0.95
Feed Temperature
0.9
o
Water Concentration (Cs/Co)
0.85
o
o
0.8
?Tm5 K
Cwo 10
0.75
0
0.2
0.4
0.6
0.8
1
Axial Position (x/L)
20
Ethanol Dehydration
Isothermal
Non-isothermal
21
TCE Pervaporation Effect of Feed Temperature
Sc745 Re 219
Sc418 Re 542
Temperature at Membrane Surface (Ts/To)
Sc162 Re 869
Sc98 Re 1118
Axial Position (x/L)
22
TCE-Water Pervaporation Membrane Surface
Concentration
TCE Concentration (Cs/Co)
Sc745 Re 219 Tfeed298 K
Sc418 Re 542 Tfeed308 K
Sc162 Re 869 Tfeed 333 K
Sc98 Re 1118 Tfeed348 K
Axial Position (x/L)
23
TCE/Water Pervaporation
(Tp 293 K)
Sc98 Re 1118
Sc162 Re 869
Sc745 Re 219
24
TCE/Water Pervaporation
n2/3 (Lévêque Solution)
25
Summary

• A evaporation finite-element transport model
  (PERFEM) was developed considering the coupled
  momentum, energy and mass transfer balance
  equations.
• PERFEM is capable of high resolution analysis of
  the concentration and temperature profiles in
  non-isothermal pervaporation.
• Case studies with TCE/Water and Ethanol/water
  systems show that pervaporation flux under
  non-isothermal conditions can be 10-50 lower
  than based on fully-developed isothermal
  estimates.
• .

26
Acknowledgements

• National Science Foundation
• United States Department of Energy
• Asahi Chemical Industry

27
Extra Slides
28
Pervaporation
29
Ethanol Dehydration
Tp 313 K
Tfeed 328 K
30
Local Mass Transfer Coefficient
Tp293 K, Tfeed 298 K
Cwo10
31
Ethanol Dehydration Local Mass Transfer
Coefficient
Tp 293 K, Tfeed 298 K
This slide may be replaced by the results
contained in k_coefficient.xls
Deviation w.r.t the Lévêquesolution 20-23
32
Ethanol Dehydration Local Mass Transfer
Coefficient
Re 226 Sc 147 H/L 0.01 Cwo 5
Tfeed328 KTp 313 K
Deviation w.r.t the non-isothermal solution
18-20
33
Outline

• Motivation and Approach
• Overview of Pervaporation
• Model Description
• Study Cases
• Conclusions

34
Dimensionless Groups
35
Mass Transfer Coefficient
36
Problem Domain Finite-Element Mesh
y/h1
6312 Elements 3317 Nodes
y/h0
x/L0
x/L1
37
Axial Velocity Profile
Re135 Sc451 Pr15 H/L0.01
To298 K
38
Velocity Field in a 2-D Membrane Channel
Re135 Sc451 Pr15 H/L0.01 T298 K
39
Membrane Resistance
Simulation variables Hi, ?
? 8.5 x10-5 m
40
TCE/Water Pervaporation
T CTCE
y/h0.5
Sc98 Re 1118 Pr 2.4
Tfeed 348 K Tp 293 K
y/h0
41
Water Concentration and Temperature Fields for
Ethanol-Water Dehydration
T C
Re135 Sc451 Pr15 Tp293 K H/L0.01 To 298 K
Cwo10
42
TCE/Water Pervaporation
T CTCE
y/h0.5
Sc98 Re 1118 Pr 2.4
Tfeed 348 K Tp 293 K
y/h0
43
Ethanol Dehydration
1.016
Re 135
1.014
Sc 451
y 0
Pr 15
1.012
Tfeed 298 K Tp 293 K H/L 0.01
y 0.01
1.01
y y/h distance above membrane surface
1.008
y 0.05
Ethanol Concentration (Cs/Co)
1.006
1.004
y 0.1
1.002
y 0.2
1
y 0.5
0.998
0
0.2
0.4
0.6
0.8
1
Axial Position (x/L)
44
Ethanol Dehydration Temperature-Dependent
Membrane Resistance
Dimensionless concentrations at the membrane
surface
1.05
Rm
constant
Rm
(T)
Etoh
1
water
Re 135 Sc 451 Pr 15
Surface Concentration (Cs/Co)
0.95
dimensionless concentration
Cwo10
0.9
0.85
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
dimensionless channel length
Axial Position (Dimensionless)
45
TCE/Water Pervaporation
Sc98 Re 1118
Sc162 Re 869
Sc745 Re 219
Tp 293 K
46
Ethanol Concentration and Temperature Fields
T CEtOH
Re135 Sc451 Pr15 H/L0.01 To 298 K Tp 293
K Cwo10
47
Ethanol Dehydration Water Concentration and
Temperature Fields
C T
Re135, Sc451, Pr15 H/L0.01 To 298 K Tp 293
K Cwo10
48
Ethanol Dehydration
y 0.5
1
y 0.2
0.98
y 0.1
0.96
0.94
y 0.05
Water Concentration (Cs/Co)
Re 135
0.92
Sc 451
Pr 15
y 0.01
0.9
H/L 0.01
Cwo10
y distance above membrane
y y/h
y 0
0.88
0.86
0
0.2
0.4
0.6
0.8
1
Axial Position (x/L)