Institut für
Verfahrenstechnik
CHARACTERIZATION OF MACROPOROUS
HYDROPHOBIC MEMBRANES USED IN
MEMBRANE DISTILLATION PROCESS
Mohammad Rezaei, Wolfgang M. Samhaber
Institute of Process Engineering
Johannes Kepler University Linz, Austria
Institut für
Verfahrenstechnik
Outline

Introduction (3W)

Background (story)

Theoretical

Experimental (How)

Results and discussions

Summery
Characterization of macroporous hydrophobic membranes used in membrane distillation process
24.03.2015
2
Institut für
Verfahrenstechnik
Introduction (3W)

What is characterization?
— Morphological and physical properties

Why characterization?
— MD Performance ↔ Membrane morphology
— Commercial MF membrane and manufacturer specification

Which characters?
— Mean Pore Size
— Pore Size Distribution
— Effective Porosity
— Penetration Pressure
Characterization of macroporous hydrophobic membranes used in membrane distillation process
24.03.2015
3
Institut für
Verfahrenstechnik
Background (story)
Permeate Conductivity at 30 mbar TP
5000
4000
3000
2000
1000
0
0,00
5,00
10,00
15,00
20,00
25,00
25
20
15
10
5
0
30,00
Time,t (h)
Feed Conductivity (µs/cm)
Permeate conductivity (µs/cm)
Permeate Conductivity at 300 mbar TP
Understanding the membrane characteristcs is a prerequisite.
Characterization of macroporous hydrophobic membranes used in membrane distillation process
24.03.2015
4
Institut für
Verfahrenstechnik
Theoretical - 1

Mean pore size and effective porosity by gas permeation test
—
—
.
.
—
Characterization of macroporous hydrophobic membranes used in membrane distillation process
= gas permeance (mol m-2 s-1 Pa-1)
= mean pressure (Pa)
= intercept of
vs.
plot
= slope of
vs.
plot
= the molecular weight of the gas (g mol-1)
= the gas constant (Pa m3 mol-1 K-1)
= absolute temperature (K)
= pore diameter (m)
µ = gas viscosity (Pa s)
= effective porosity (m-1)
24.03.2015
5
Institut für
Verfahrenstechnik
Theoretical - 2

Maximum pore size, the mean pore size and the pore size distribution
by liquid displacement method
∑
—
—
—
—
—
—
1
∑
1
/
.
= cumulative distribution of number of pores
number of the jth pores (with size dp(j))
= incremental flow rate ratio occurring in jth pores
Jw = gas permeation rate through wet membrane
Jd = gas permeation rate through dry membrane
K = normalization factor
μ = mean pore size (50% of cumulative number of pores)
= geometric standard deviation (ratio of 84.13% of
cumulative number of pores to that of 50%)
24.03.2015
6
Institut für
Verfahrenstechnik
Experimental - 1

Materials
— ACCUREL® PP V8/2HF and PP 150/330

Membrane characterization methods
1. Gas permeation test
—
,
∆ J = gas permeance (molm-2 Pa-1 s-1)
∆p = transmembrane pressure drop (Pa)
T = absolute temperature (K)
V = volume of gas permeated through the membrane (m3)
A = effective membrane area (m2)
t = permeation time (s)
R = universal gas constant (8.314 J mol-1 K-1)
101,325 = atmospheric pressure in Pa
7
Institut für
Verfahrenstechnik
Experimental - 2

Membrane characterization methods (cont.)
2. Liquid displacement method
Characterization of macroporous hydrophobic membranes used in membrane distillation process
3. Liquid entry pressure measurement
•
Type of Alcohol
•
Alcohol Concentration
•
Membrane Type
8
Institut für
Verfahrenstechnik
1,4
1
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0
Tubular
Capillary
Scaled Tubular
0
0,1
0,2
0,3
0,4
Probability density function,
df (dp)/d(dp), (µm–1)
Jwet/Jdry
Results and discussions - 1
0,5
d (µm)
Ratio of dried membrane gas permeance to wetted
membrane gas permeance versus pore radius
Characterization of macroporous hydrophobic membranes used in membrane distillation process
1,2
Tubular
Capillary
1
Scaled Tubular
0,8
0,6
0,4
0,2
0
0
0,1
0,2 d (µm) 0,3
0,4
0,5
Pore size distributions
24.03.2015
9
Institut für
Verfahrenstechnik
Results and discussions - 2
Pore diameter and effective porosity by gas permeation test
Liquid Entry Pressure (bar)
Membrane name
PP V8/2HF
PP 150/330
Material
Polypropylene
Polypropylene
3,5
3
2,5
2
1,5
1
0,5
0
Bubble point (bar)
1.07
1.1
Mean pore
diameter (µm)
0.136
0.195
Effective porosity
(m-1)
6572.12
6020.43
Methanol‐Tubular
Ethanol‐Tubular
2‐Propanol‐Tubular
The length of the alcohol hydrocarbon
chain
LEP
Wettability
2‐Propanol‐Capillary
The pore size
0
5
10
15
20
LEP
Wettability
25
Alcohol Concentration (wt%)
Liquid entry pressure as a function of alcohol concentration for different
alcohols in aqueous solutions and effect of membrane type on LEP. Solid
lines represent the fits of the experimental data
24.03.2015
10
Institut für
Verfahrenstechnik
Summery

Gas permeation test
— to measure the diameter of the large pores of the membrane

liquid displacement method
— to measure the diameter of the smaller pores of the membrane

Liquid entry pressure measurement
— to determine the minimum required pressure for wetting
Membrane morphology ↔ MD Performance
Characterization of macroporous hydrophobic membranes used in membrane distillation process
24.03.2015
11
Institut für
Verfahrenstechnik
The application of MD (to ensure MD efficiency and to avoid pore wetting) is
aided by knowing the membrane morphological parameters
Thank you for your attention!
The End!