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STUDY ON THE GAS PERFORMANCE OF CERAMIC MEMBRANE FROM
KAOLIN PREPARED BY PHASE INVERSION TECHNIQUE
SITI KHADIJAH HUBADILLAH
A thesis submitted in
fulfillment of the requirement for the award of the
Master of Engineering
Faculty of Mechanical Engineering
Universiti Tun Hussein Onn Malaysia
July, 2015
ABSTRACT
Membrane for gas application have been widely used. Apart from that, ceramic
membrane is gaining much attention towards separation technology due to its
characteristics of offering high mechanical strength, chemical resistivity and thermal
compatibility. However, production of ceramic membrane for gas separation in term
of cost and energy reduce still remains as challenge until now, therefore this work
addressed to the development of ceramic membrane from kaolin via simple phase
inversion technique. First, ceramic membrane suspension have been prepared by
stirring kaolin as raw material, N-methyl-2-pyrollidone (NMP) as solvent and
polyethersulfone (PESf) as binder. Phase inversion tchnique conducted by casted the
suspension on the glass plate with casting knife. In order to achieve the aims of this
study, the development of ceramic membrane from kaolin were conducted into two
objectives: (1) effect of particles sizes and, (2) effect of non-solvent coagulant bath.
The types of kaolin particle sizes devoted as Type A kaolin (0.4-0.6µm) and Type B
kaolin (10-15µm) whereas for different types of non-solvent were distilled water,
ethanol and mixture of 70% NMP and 30% distilled water. Overall analysis showed
that both effect of particle size and different caogulant generated different structure,
properties and characteristic of membrane at two different composition. Polymer phase
inversion is dominated at kaolin content of 24 to 34wt.% that caused the formation of
finger-like voids of the phase inversed structure with Type A kaolin and strong
caogulant of distilled water. An opposed condition was shown at highest kaolin content
of 39 wt.% for both parameter that can be correlated to the viscous fingering
mechanism in the formation of ceramic membrane structure. A slightly similar results
trends and pattern was demostrated with Type B kaolin and weakest coagulant
(mixture of 70% NMP and 30% distilled water). Overall performance showed that
membrane with Type A kaolin and immersed into ethanol as coagulant at kaolin
content of 39 wt.% showed the highest rejection (5.49 and 5.82 for CO2/N2 and O2/N2,
respectively).
ABSTRAK
Membran bagi aplikasi gas telah digunakan secara meluas. Selain itu, membran
seramik mendapat banyak perhatian terhadap teknologi pemisahan kerana ciri-cirinya
dalam menawarkan kekuatan mekanikal yang tinggi, rintangan kimia dan keserasian
terma. Walau bagaimanapun, pengeluaran membran seramik untuk pemisahan gas dari
segi kos dan tenaga masih kekal sebagai cabaran sehingga sekarang, oleh itu kerja-
kerja ini ditujukan kepada pembangunan membran seramik dari kaolin melalui teknik
fasa penyongsangan mudah. Pertama, membran seramik telah disediakan dengan
teknik kacau daripada kaolin sebagai bahan mentah, N-methyl-2-pyrollidone (NMP)
sebagai pelarut dan polyethersulfone (PESf) sebagai pengikat. Teknik fasa
penyongsangan dijalankan pada plat kaca dimana membrane dibentuk oleh pisau
pembentuk. Untuk mencapai matlamat kajian ini, pembangunan membran seramik dari
kaolin telah dijalankan kepada dua matlamat: (1) kesan zarah saiz dan, (2) kesan mandi
koagulan bukan pelarut. Jenis-jenis saiz kaolin dikhaskan sebagai Jenis A kaolin (0.4-
0.6μm) dan Jenis B kaolin (10-15μm) manakala bagi jenis bukan pelarut ialah air
suling, etanol dan campuran 70% NMP dan 30% air suling . Analisis keseluruhan
menunjukkan bahawa kedua-dua kesan saiz zarah dan koagulan berbeza menghasilkan
struktur berbeza, sifat-sifat dan ciri-ciri membran daripada dua komposisi yang
berbeza. Fasa polimer penyongsangan dikuasai pada kandungan kaolin daripada 24
hingga 34wt.% Yang menyebabkan pembentukan lompang jari daripada kaolin Jenis
A dan koagulan kuat air suling. Keadaan bertentangan ditunjukkan pada kandungan
kaolin tertinggi 39 wt.% Untuk kedua-dua parameter yang boleh dikaitkan dengan
mekanisma jari likat dalam pembentukan struktur membran seramik. Trend yang sama
telah dihasilkan oleh membran daripada kaolin Jenis B kaolin dan koagulan paling
lemah (campuran 70% NMP dan 30% air suling). Prestasi keseluruhan menunjukkan
bahawa membran dengan kaolin Jenis A dan etanol sebagai koagulan di kandungan
kaolin 39 wt.% menunjukkan gas penolakan yang paling tinggi (5.49 dan 5.82 untuk
CO2 / N2 dan O2 / N2).
vii
TABLE OF CONTENT
TITLE i
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENT vii
LIST OF TABLES xi
LIST OF FIGURES xii
LIST OF ABBREVIATIONS xvi
LIST OF SYMBOLS xvii
CHAPTER 1 INTRODUCTION 1
1.1 Background of study 1
1.2 Statement of Problems 5
1.3 Objective of Study 7
1.4 Scope of Study 7
1.5 Significant of Study 8
viii
CHAPTER 2 LITERATURE REVIEW 9
2.1 Introduction 9
2.2 Ceramic Membrane 9
2.3 Material Selection for Ceramic Membrane 11
2.4 Fabrication of Ceramic Membrane 15
2.4.1 Traditional Method 15
2.4.2 Phase Inversion Method 18
2.5 Characterization nd Properties of Ceramic
Membrane prepared via Phase Inversion Technique
21
2.6 Effect of Particle Size on Ceramic Membrane
Preparation
26
2.7 Effect of Different Types of Non-solvent
Coagulant Bath on the Ceramic Membrane
Preparation
28
2.8 Membrane Separation Processes 32
2.9 Membrane for Gas Separation Application 33
2.9.1 Application of Ceramic Membrane in Gas
Separation
34
2.10 Closure 35
CHAPTER 3 METHODOLOGY 37
3.1 Introduction 37
3.2 Material Selection 39
3.2.1 Kaolin 41
ix
3.2.2 N-Methyl-2-pyrrolidone (NMP) 44
3.2.3 Polyethersulfone (PESf) 44
3.2.4 Non-solvent Coagulant Bath 44
3.3 Preparation of Kaolin Ceramic Membrane 45
3.3.1 Preparation of dope suspension with
different kaolin particle size and
composition
45
3.3.2 Membrane Casting 47
3.3.3 Sintering of Kaolin Ceramic Membrane 48
3.4 Characterization 49
3.4.1 Kaolin Powder Characterization 49
3.4.2 Viscosity Test for Ceramic Suspension 50
3.4.3 Membrane Characterization 50
3.4.3.1 Field Emission Scanning Electron
Microscope (FESEM)
50
3.4.3.2 Atomic Force Microscopy (AFM) 51
3.4.3.3 Pore Size Distribution (PSD)
analysis
52
3.4.3.4 Mechanical Strength 54
3.4.3.5 Gas Permeation Test 55
CHAPTER 4 RESULTS AND DISCUSSIONS 57
4.1 Introduction 57
x
4.2 Characteristics of Kaolin Powder 58
4.2.1 Particle Size Distribution of Kaolin
Powder
58
4.2.2 Morphological Analysis on the Kaolin
Powder at Different Sizes
59
4.2.3 Functional Groups in Kaolin 60
4.3 Viscosity of Ceramic Suspension 61
4.4 Effect of Kaolin Particle Size and Composition
on Properties and Gas Separation Performance
of Kaolin Ceramic Membrane
62
4.4.1 Introduction 62
4.4.2 Morphological Properties of Membranes 62
4.4.3 Membrane Surface Roughness 67
4.4.4 Membrane Pore Size Distribution (PSD)
and porosity
69
4.4.5 Membrane Mechanical Strength 73
4.4.6 Gas Permeation Properties 74
4.5 Effect of Different Coagulant Bath on the
Properties and Gas Separation Performance of
Low Cost Ceramic Membrane
77
4.5.1 Introduction 77
4.5.2 Membrane Cross Sectional Images
prepared by Immersion into Different
Types of Non-Solvent Coagulant Bath
78
xi
4.5.2.1 Distilled Water 78
4.5.2.2 Ethanol 80
4.5.2.3 Mixture of 70% NMP nd 30%
Distilled Water
82
4.5.3 Membrane Surfaces Images prepared by
Immersion into Different Types of Non-
Solvent Coagulant Bath
84
4.5.4 Membrane Surface Roughness 90
4.5.5 Membrane Pore Size Distribution (PSD)
and porosity
92
4.5.6 Membrane Mechanical Strength 96
4.5.7 Gas Permeation Properties 97
4.5.7.1 Permeability 93
4.5.7.2 Selectivity 95
CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS 97
5.1 Conclusions 97
5.2 Recommendations 98
REFERENCES 99
APPENDIX A 117
APPENDIX B 119
APPENDIX C 122
APPENDIX D 125
xii
APPENDIX E 130
APPENDIX F 131
VITA 132
xiii
LIST OF TABLES
2.1 Various applications of membranes 11
2.2 Properties of high cost ceramic material 12
2.3 Several studies used kaolin as the raw material in membrane
fabrication
14
2.4 Comparison of ceramic materials in term of its price and
application
14
2.5 Various method in ceramic membrane fabrication 15
2.6 Ceramic membrane prepared via phase inversion 20
2.7 Pore size distribution for the Ni and NiO hollow fibres with
three structures
25
2.8 Characteristics of various membrane separation processes 32
2.9 Summary of available membrane processes 33
2.10 Summary for gas separation system available 34
3.1 List of chemical used in this study 39
3.2 The physical and chemical properties of chemicals used in
this study
40
3.3 Experiment of kaolin powders at different particle size of
previous study
43
3.4 Properties of different types of non-solvent coagulant bath 45
3.5 Summary of ceramic suspension composition for low cost
ceramic membrane for the effect of kaolin particle size
46
3.6 Membrane Casting Process 48
4.1 Membrane composition for study the effect of particle size 62
4.2 Kaolin content for study the effect of non-solvent coagulant
bath
77
xiv
LIST OF FIGURES
1.1 Ceramic membrane structure prepared using different
techniques
3
1.2 Ceramic membrane structure fabricated via phase
inversion
5
2.1 Schematic diagram of Membrane Structure; a(i)
symmetric membrane and b(i) asymmetric membrane;
SEM Micrographs of a(ii) symmetric membrane and
b(ii) asymmetric membrane
10
2.2 Schematic of membrane separation process 10
2.3 Image for high cost ceramic material; (a) aluminium
oxide, (b) Zirconium dioxide, (c) Titanium dioxide and
(d) Silica dioxode
13
2.4 Asymmetric membrane structure via combined tape
casting and phase inversion method
18
2.5 Ternary diagram represents the study of different types
of solvent
19
2.6 Alumina membrane finger-like structure resulting from
membrane fabrication via phase inversion system at
different air-gap
20
2.7 Reduced finger-like structure observed 22
2.8 Ceramic Membrane finger-like and sponge-like structure 23
2.9 Ceramic Membrane sandwich-like structure 23
2.10 Pore size distribution for membrane M2 by mercury
porosimetry
25
2.11 Macrovoids formation caused by the agglomeration of
smaller particle sizes
28
xv
2.12 Ternary diagram of PVDF/NMP/non-solvent system at
25oC
29
2.13 SEM images of PVDF hollow fibre membrane at
different coagulation bath: (a) 15:85 of ethanol:water
bath, (b) 30:70 of ethanol:water bath and, (c) 50:50 of
ethanol:water bath
30
2.14 SEM images of surface PVDF membranes prepared from
different concentration of ethanol at (a) 0%, (b) 25%, (c)
50% and, (d) 75%
31
3.1 Research Design 38
3.2 Kaolin used in this work: a) particle size less than 1µm
and b) particle size more than 10µm
41
3.3 Mechanism of particles agglomeration; repulsive force
(↔)
43
3.4 Polyethersulfone (PESf) 44
3.5 Flowchart of kaolin ceramic membrane 45
3.6 Experimental setting for ceramic suspension preparation 47
3.7 Sintering profile for kaolin ceramic membrane 49
3.8 (a) top view, (b) side view for membrane attachment on
studs
51
3.9 The capillary action of wetting and non-wetting liquid 54
3.10 Sample preparation for 3-point bending test 55
3.11 Gas permeation system 56
4.1 Particle size distribution of kaolin powders at different
types
58
4.2 FESEM images of kaolin particles at (a) less than 1 µm
and (b) more than 10 µm
59
4.3 FTIR comparison of kaolin at different particle size: (a)
Type A kaolin and (b) Type B kaolin
60
4.4 Viscosity versus kaolin content at different particle size 61
4.5 FESEM images of the cross section prepared at different
kaolin particle size and composition (x300)
63
4.6 Mechanism of agglomerated particle size hold by binder 65
xvi
4.7 Schematic diagram of kaolin particle movement in
ceramic suspension containing NMP and PESf;
(a)Type A (b) Type B
4.8 FESEM images of the surface prepared at different
kaolin particle size and composition
66
4.9 Membrane surface roughness and AFM 3D-images from
the effect of kaolin particle size at different kaolin
composition
68
4.10 Pore size distribution for membrane fabricated at
different kaolin particle size and kaolin content;
(a)14wt.%, (b)19wt.%, (c)24wt.%, (d)29wt.%,
(e)34wt.% and (f)39wt.%
70
4.11 Porosity of ceramic membrane from kaolin as a function
effect of particle sizes
72
4.12 Bending strength of the prepared ceramic membrane
from kaolin on the effect of particle size at different
kaolin composition
73
4.13 Effect of different types of non-solvent coagulant bath of
ceramic membrane prepared at different kaolin
composition onto gas permeance. (a) Carbon Dioxide,
(b) Oxygen and (c) Nitrogen
75
4.14 Effect of different types of non-solvent coagulant bath of
ceramic membrane prepared at different kaolin
composition onto gas selectivity. (a) CO2/N2 and (b)
O2/N2
76
4.15 FESEM images of the cross section prepared at different
kaolin content and immersed into distilled water; a) 24
wt.%; b) 29 wt.%; c) 34 wt.%; d) 39 wt.% kaolin content
78
4.16 Mechanism of solvent/non-solvent exchange 80
4.17 FESEM images of the (i) overall cross section (ii)
zoomed at 600x magnification prepared at different
kaolin content and immersed into ethanol; E1= 24
80
xvii
wt.%; E2 = 29 wt.%; E3 = 34 wt.%; E4 = 39 wt.% kaolin
content
4.18 FESEM images of the (i) overall cross section (ii)
zoomed at 600x magnification prepared at different
kaolin content and immersed into mixture of 70% NMP
and 30% distilled water; N1= 24 wt.%; N2 = 29 wt.%;
N3 = 34 wt.%; N4 = 39 wt.% kaolin content
83
4.19 FESEM images of membrane surface prepared at
different kaolin composition and immersed into different
coagulant; M=distilled water; E= ethanol; N=mixture of
70%NMP and 30% water
85
4.20 Membrane surface roughness on the effect of different
types of non-solvent coagulant bath
87
4.21 Pore size distribution for membrane fabricated at
different non-solvent coagulant bath and kaolin
composition; a)24 wt.%; b)29 wt.%; c)34 wt.%; and
d)39 wt.%
89
4.22 Porosity of the kaolin ceramic membrane as a function
effect of non-solvent coagulant bath
91
4.23 Bending strength for membrane fabricated at different
non-solvent coagulant bath and kaolin composition
92
4.24 Effect of different types of non-solvent coagulant bath of
ceramic membrane prepared at different kaolin
composition onto gas performance
93
4.25 Effect of different types of non-solvent coagulant bath of
ceramic membrane prepared at different kaolin
composition onto gas selectivity. (a) CO2/N2 and (b)
O2/N2
95
xviii
LIST OF ABBREVIATIONS
AFM - Atomic Force Microscopy
Al - Aluminum
Al2O3 - Alumina Oxide
BSCF - Ba0.5Sr0.5Co0.8Fe0.2O3-δ
CH4 - Methane
CO2 - Carbon Dioxide
FESEM - Field Emission Scanning Electron Microscopy
FTIR - Fourier Transform Infrared Spectroscopy
MF - Microfiltration
MIP - Mercury Intrusion Porosimetry
N2 - Nitrogen
NF - Nanofiltration
Ni - Nickel
NiO - Nickel (II) Oxide
NMP - N-methylpyrrolidone
O - Oxide
O2 - Oxygen
PESf - Polyethersulfone
PSA - Particle Size Analysis
PSD - Pore Size Distribution
PVDF - Polyvinylidenedifloride
RO - Reverse Osmosis
SEM - Scanning Electron Microscopy
Si - Silica
SiO2 - Silica (II) Oxide
SOFc - Solid Oxide Fuel Cell
ZrO2 - Zirconia Oxide
LIST OF SYMBOLS
σb - Mechanical Strength
Ra - Surface Roughness
F - Fracture Force
L - Membrane Span Length
w - Membrane Width
t - Membrane Thickness
P - Gas Permeability
Q - Flowrate
A - Membrane Area
∆𝑝 - Pressure Gradient
CHAPTER 1
INTRODUCTION
1.1 Background of Study
The impact of global warming caused by discharges of CO2 from various sources is a
major worry. According to the Environmental Protection Agency, the U.S. emitted
6,673 million metric tons of CO2 into the atmosphere in 2013 [1]. The escalating level
of atmospheric CO2 has caused widespread public concern [2]. One of the major
sources of CO2 emission is fossil fuel combustion. Today, coal-fired power plants alone
emit about 2 billion tons of CO2 per year [3]. Imagine for another 30 years, fossil fuels
will remain an important source of the world’s energy. For instance, high indoor levels
of CO2 could lead to severe health effects, even death. In fact, carbon dioxide level is
allowed to be at the 5% level or 600 ppm [4] in normal environment. The exceed value
will help increase a poisonous quality which harm to health. A recent data from
Intergovermental panel on climate change in 2014 reveal that the CO2 concentration
has reached 394ppm [5] in the atmosphere which is far beyond the upper safety limit
of 350ppm [6]. Hence, separation of CO2 removal is crucially required for most of
industry actions to avoid excessive CO2 gas pollution. Other than CO2, the separation
of oxygen from nitrogen in the air also is an important procedure that is widely used in
manufacturing. Oxygen is utilized to give advantages in various chemical processes
such as natural gas combustion, coal gasification, sewage treatment and welding.
Whilst, nitrogen used as a low-temperature coolant, an inert diluent and in the
production of ammonia.
There are various method used in gas separation technology such as cryogenic
distillation, pressure swing adsorption and liquid solvent absorption have been
proposed. However, the cost associated with the above mentioned processes are about
80% of the total cost of CO2 sequestration and thus are not fiscally viable. Membranes
2
offer a promising separation technology to execute process intensification strategies,
that is the cutback of production costs by minimizing equipment size, energy
consumption and waste production [7]. Apart from that, there are two types of
membrane: (1) polymeric membrane and (2) inorganic membrane. Polymeric
membranes are widely used among all types of membranes. This has, in accordance
of polymeric membranes offered a cheaper method, and yet the simple fabrication
process involved. However, it is well known challenges of low selectivity and
permeability in polymer membranes which have been addressed with some degree of
success with advanced engineering polymers [7]. Furthermore, the physical and
properties of polymer which cannot endure the application requiring high thermal,
chemical and strength has limit the application of polymer membrane for critical
applications. Because of this, researchers have taken attention towards inorganic
membranes that has the ability to sustain at high temperature and extreme condition.
In general, ceramic membrane can be subdivided into another three types: (1) ceramic
membrane, (2) metal membrane and, (3) carbon membrane. The latest development
has shown that ceramic membrane is gaining a place in gas separation compared to
other membranes as it is offer simple sieving mechanism through the pore size obtained
[8]. Since ceramic membranes offer significant advantages over polymeric membranes,
therefore, it has been widely used especially in oilywater separation [9], wastewater
separation [10] and water separation [11]. However, for the past few years the
application of ceramic membrane still dominated the application in many gas industries
which demanded high thermal and pressure.
There are sundry unique structure could be obtained in ceramic membrane
fabricated at different method as shown in Figure 1.1. In gas application, each type of
dense membrane structure could be applied according to felicitous gas application
based on their pore size and surface properties in order to have a high selectivity and a
low permeation rate. The ability of ceramic membranes could be produced or fabricated
towards desired structure such as dense or porous membranes has attracted intensive
study of ceramic membrane development and modification such as high temperature,
highly acidic or basic feed [12-14]. For instance, the past decade has witnessed major
changes in this area as dense ceramic membranes exhibiting high oxygen ionic and
electronic conductivity have become of greatest interest as it is economical, clear and
effective way of producing oxygen by separation from air or other oxygen containing
gas mixtures.
3
Slip casting
Tape casting
Pressing method
Phase Inversion
Figure 1.1 :Ceramic membrane structure prepared at different techniques
In fabricating ceramic membranes, there are many methodc can be used as tape
casting, slip casting, pressing method and extrusion. All of these methods have been
established and applied for years. Fabrication of ceramic membranes by these
4
techniques generally involves multiple steps. Generally, it can be subdivided into three
stages: (1) preparation of the ceramic powder paste or suspension, (2) shaping of the
ceramic powder into the desired geometry and, (3) heat treatment which including
calcination and sintering [15]. After completing these main steps, additional deposition
layer or coating layer needs to be formed to allow selective mechanism at the top layer,
Then, further heat treatment steps need to be conducted in orders to have a good
selectivity as well as to improve other membrane properties. The choice of method for
each step depends on the desired membrane configuration, quality, morphology,
mechanical, chemical stability and selectivity of the desired final membranes.
However, the fabrication method should also be economical and easy to replicate
without compromising the quality of final membrane [16].
Phase inversion is a simple technique of membrane fabrication which
commonly used in polymeric membranes. The first invention by Loeb and Sourirajan
in 1963 is one step technique that able to form asymmetric membrane structure offer a
high ability of high flux as well as rejection and selectivity [17]. Recent development
of ceramic membrane have shown the implementation of this technique is able to
improve gas separation property. As reported, membrane fabrication via phase
inversion has promoted a dense top layer with smallest pore size. However, ceramic
membrane fabricated via phase inversion so far appear to hold two types of structure:
finger-like and sponge-like structure. Figure 1.2 illustrates the structure of membrane
that could be obtained by phase inversion. The structure of macrovoids is sometimes
observed in ceramic membrane structure. In phase inversion technique, commonly the
description of structure always been explained by the concept of ternary diagram,
involving three main components: solvent, non-solvent and polymer. However, due to
ceramic membranes involve an additional component of ceramic powder, the
formation of ceramic membranes can be explained by the viscous fingering mechanism
as demonstrated by previous researcher [12, 18]. Viscous fingering is the responsible
mechanism that permits the establishment of dense porous structure with certain
selectivity. The capability of phase inversion in formation of ceramic membrane
lifetime and properties in single step technique has attracted many researchers in
developing ceramic membrane especially in gas application.
5
Figure 1.2: Ceramic Membrane Structure fabricated via phase inversion [15]
Ceramic membrane fabricated from phase inversion technique used materials
like Alumina, Zirconia and Titania which considered as very expensive materials.
Overall comparisons showed that polymeric membranes are still more inexpensive to
get compared to ceramic membranes. Even so, a technical and economical comparison
between different membrane processes must take into account both investment and
maintenance. Investment involves the price of equipment for pretreatment and post
treatment of fluids in addition to the monetary value of the membrane plant.
Maintenance includes replacement of membranes, electricity consumption, cleaning
products and labor prices. Consequently, a comparison of overall costs, including
membrane lifetime, cleaning procedures and pretreatment has put a ceramic membrane
is a preferable material in a number of applications. More than that, the technical
progress made in the manufacture of ceramic membranes with production costs getting
closer to those of many polymeric membranes explains why they are entering markets
much more extensive than those accessible of the first polymer membranes. In fact,
ceramic membrane developed from kaolin and clay has gained attention recently as it
employs to offer better properties and at the same time cut off the cost of materials.
1.2 Statement of Problems
Gas separation application seems to be an important research nowadays. This is due to
the problem of carbon dioxide emission that could affect severe health. In addition,
others gas separation such as oxygen and nitrogen that could be used in medication and
production of ammonia, respectively have attracting many researchers in this research.
Finger-like voids
Sponge-like
voids
Dense layer
macrovoids
6
Membrane for gas separation application have been used in past few years
according to the advantages have been promoted. There are two types of membrane
which are polymeric and inorganic membrane. However, polymeric membrane has
disadvantages which cannot endure high temperature, chemical resistivity and
mechanical strength, thus, not suitable for gas application. Due to this, ceramic
membrane, a part of inorganic membrane have gaining attention. The combination of
high chemical, thermal and mechanical resistance has made ceramic membranes an
attractive alternative to polymeric membranes.
In ceramic membrane fabrication process, two most important parameters that
always being investigated are materials and fabrication method. For materials, previous
study have focused towards refractory ceramic materials such as alumina, nickel and
zirconia. These materials are just not requiring high sintering temperature, but
expensive too. Due to this, kaolin have become attractive materials to be study in
ceramic membrane fabrication. Kaolin is not only cheap, but provides low plasticity
and high refractories properties to the membranes [19]. For fabrication methods,
pressing method is the one most method that have been used in ceramic membrane
fabrication and is well-known method for ceramic membrane. However, pressing
method could only produce symmetric membrane structure and need additional method
to produce separation layer. Furthermore, pressing method is the most expensive
method. Clearly, combining a suitable materials and fabrication method which can cut
the time and cost, and hence ceramic membrane price is desirable.
Phase inversion into ceramic membrane fabrication is a promising
technique to produce ceramic membrane in a single step at lower cost. It is fast and
cost effective technique which hence can promote unique structure (finger-like and
sponge-like structure). However, phase inversion in ceramic membrane requiring
complex system as many parameters can be involved during fabrication process. Thus
the investigation on ceramic membrane fabrication via phase inversion technique was
be conducted in this study by study the effect of kaolin particle size, kaolin content and
different types of non-solvent coagulant bath.
7
1.3 Objective of study
The main objective of the study is to develop new ceramic membrane from kaolin via
phase inversion technique by investigating the effect of kaolin particle size and non-
solvent coagulant bath. Hence, the objectives of the study can be separated into the
following:
1. To prepare ceramic membrane from kaolin at different types of particles size,
kaolin composition and non-solvent coagulant bath via phase inversion
technique.
2. To study the ceramic membrane from kaolin towards the morphology,
membrane roughness, mechanical strength and pore size distribution.
3. To determine the gas performance of ceramic membrane from kaolin towards
gas permeability and selectivity.
1.4 Scope of Study
1. Preparing the kaolin powder into two types of particle size of less than 1µm and
more than 10µm and characterize in term of particle size distribution,
morphology and FTIR.
2. Preparing ceramic suspension at the different kaolin particle size and
composition, which the kaolin content used are 14 wt.%, 19 wt.%, 24 wt.%, 29
wt.%, 34 wt.% and 39 wt.% with PES as a binder and NMP as solvent.
3. Analyzing the viscosity of the ceramic suspension at different kaolin particle
sizes and composition.
4. Fabricating the ceramic membrane via phase inversion technique and immersed
into distilled water for study the effect of kaolin particle size.
5. Selecting the ceramic membranes from the study of the effect of particle size
and fabricate via phase inversion technique by immersing into different types
of non-solvent coagulant bath: distilled water, ethanol, and a mixture of 70%
NMP and 30% distilled water.
6. Analyzing the membrane morphology for both of effects using Field Emission
Scanning Electron Microscopy (FESEM).
8
7. Analyzing the membrane roughness for both effects using Atomic Force
Microscopy (AFM).
8. Investigating the bending strength of the each kaolin ceramic membrane
prepared by using 3-point bending strength.
9. Analyzing the membrane pore size distribution from both effects by using
Mercury Intrusion Porosimetry (MIP).
10. Testing the kaolin ceramic membrane with regard both effects via gas
permeability and gas selectivity.
1.5 Significant of Study
The development of ceramic membrane have gained much attention nowadays
due to its characteristics that provide high mechanical strength, chemical resistivity and
temperature stability that able to sustain extreme condition. However, preparation of
ceramic membrane always associated to complex preparing routes i.e involve with
multifabrication steps or complex treatment and modification and high cost production
material (expensive ceramic material i.e. Alumina, Titania, Nickel, etc.) has limited
their applications. With regard to the above problem, the development of ceramic
membrane from low cost material i.e kaolin will provide an initial tip to trim back the
ceramic membrane production cost. The option of phase inversion technique which
offer better approach information of asymmetric membrane structure that not only can
reduce the multistep in membrane layering structure, but also give better strength,
structure that able to avoid membrane leaking or failure due to incompatibility issue of
interface multilayer structure. In this study, two parameters based on the result of
particle size and coagulant mediums were selected to be studied as its count as simple
parameters that able to be controlled easily and can raise significantly the membrane
performance.
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
This chapter reports the most pertinent work that is relevant to the preparation and
characterization of ceramic membrane via phase inversion technique. An introduction
to problem statement and membrane was presented in Chapter 1 and this provides an
outline to support the explanation and description in this chapter. A description of the
membrane materials and fabrication methods towards the membrane characterization
need to be included as it is the main objectives in this work. The membrane
characterization includes membrane microstructure, surface roughness, pore size
distribution, porosity and mechanical strength. Whilst, the gas permeation result from
others ceramic membrane is also be included. As based on the objectives of this work,
previous work on effect of particle size and non-solvent coagulant bath is discussed.
2.2 Ceramic Membrane
In membrane technology, ceramic membrane generally is known as a perm selective
barrier of interface between two phases [20]. This permselective barrier technology is
capable to control the permeation rate of a chemical species passing through the
membrane structure. In membrane technology, there are two types of membrane
structure have been introduced: symmetric and asymmetric structure, as described in
Figure 2.1. Ceramic membranes are usually composite with consisting of several layers
of one or more different ceramic materials. According to Li (2007), they generally have
a macroporous support, one or two mesoporous intermediate layers and a microporous
(dense) top layer that acting as separation layer [15]. Thus, the main objective of
membrane separation is to allow one component of a mixture to permeate the
10
membrane freely, while preventing permeation of other unwanted component [21].
Commonly, the particle which is bigger than the other particle in a solution will be
blocked and the smaller particle will pass through the membrane which called
permeates. The bigger particles which are blocked by the membrane are called
rejection. The most significant characteristic used to categorize membrane is maximum
permeate particle size. Figure 2.2 explains the mechanism in detail. In conclusion,
membrane could be also called as a ‘filter’. Anyway, due to its ability to diffuse,
synthesis, absorb and repel has made membrane widely used in separation application.
Figure 2.1 Schematic diagram of Membrane Structure; a(i) symmetric membrane and
b(i) asymmetric membrane ; SEM Micrographs of a(ii) symmetric membrane and
b(ii) asymmetric membrane [22]
Figure 2.2 Schematic of membrane separation process [23]
a (i) b (i)
a (ii) b (ii)
11
The interesting part of membrane technology is the fact that it is functioning
without the addition of chemicals, with a comparatively low energy utilization and easy
well-arranged process conductions. The operation principle used is quite simple. Due
to this, membrane technology have been widely used in various application. Table 2.1
lists various applications of ceramic membrane separation technology.
Table 2.1: Various Applications of Membranes [24-31]
Types of
Membrane
Application References
Ceramic Air separation Wu et al, 2015
Ceramic O2 and N2 permeation Ahmad et al, 2011
Ceramic Water treatment Lee et al, 2015
Ceramic Corn Syrup clarification Almandoz et al, 2010
Ceramic Oxidation Butane Gandhi and
Mok, 2014
Ceramic Solid Oxide Fuel Cells Othman, 2010
Carbon CO2/CH4 separation Yoshimune and Haraya,
2013
Carbon Gas Separation Mahurin et al, 2011
2.3 Material Selection for Ceramic Membrane
In membrane fabrication, the economic factors that determine the selection, design and
operation of the membrane system are: (1) the cost of materials; (2) power consumption
in operating and (3) ease of replaceability. Instead of design and energy consumption,
the selection of novel materials in cutting the cost of membrane production is gaining
attention by most researchers now. Basically, the ceramic materials are categorized into
two types: (1) High cost ceramic material and (2) Low cost ceramic material. The large
majority of ceramic membranes are fabricated from particles of ceramic oxides, such
as Al2O3, TiO2, ZrO2 and SiO2 which are in group of expensive ceramic materials [24].
Powder like clay, dolomite, apatite, fly ash, natural raw clay and kaolin which are
categorized into cheap ceramic materials and also have been quite oftenly used in
ceramic membrane fabrication in order to reduce the cost production.
Early research on the ceramic membrane fabrication is focused towards the
utilization of α-alumina which is an expensive precursor to fabricate the membrane
12
component [25]. Indeed, alumina have been applied widely in ceramic membrane
fabrication towards various separation technologies. Alumina membrane has received
considerable attention in membrane separation processes because of its thermal,
chemical and mechanical stability. The latest finding of alumina membrane has
revealed that it can endure high temperature up to 1580oC with an open porosity of
41.14% and a flexural strength of 61.9MPa [26]. However, alumina membrane is
thought to be at high price. It was reported that alumina membrane were costing around
$1200-2000/m2 which is more than half of the price of polymeric membranes [27].
ZrO2 and TiO2 are also gaining attention in ceramic membrane fabrication. This is
imputable to the ZrO2 and TiO2 were considered for mesoporous and microporous
membrane formation and produce higher chemical stability at high and low pH values
[28]. In fact, ZrO2 is the expensive among other type of ceramic material as can be seen
in the next section (Table 2.4). The price of ZrO2 is more than ten times of the alumina
price. Table 2.2 lists the properties of high cost ceramic materials and Figure 2.3
presents the image for high cost ceramic materials.
Table 2.2: Properties of high cost ceramic material [31-34]
Ceramic
Materials
Chemical
Formula
Molar
Mass
(g.mol-1)
Density
(g/cm3)
Melting
Point
(oC)
Boiling
Point
(oC)
Reference
Aluminium
oxide
Al2O3 101.96 3.95-4.1 2072 2977 https://en.wikipe
dia.org/?title=Al
uminium_oxide
Zirconium
dioxide
ZrO2 123.22 5.68 2715 4300 https://en.wikipe
dia.org/wiki/Zirc
onium_dioxide
Titanium
dioxide
TiO2 79.87 4.23
(rutile)
3.78
(anatase)
1843 2972 https://en.wikipe
dia.org/wiki/Tita
nium_dioxide
Silica
dioxide
SiO2 60.08 2.65 1600 2230 https://en.wikipe
dia.org/?title=Sil
icon_dioxide
13
(a)
(b)
(c)
(d)
Figure 2.3: Image for high cost ceramic material (a) aluminium oxide, (b) Zirconium
dioxide, (c) Titanium dioxide and (d) Silica dioxide
Recent research on the fabrication of ceramic membranes is focused towards
the utilization of cheapest raw materials such as apatite powder, fly ash, natural raw
clay, dolomite and kaolin. [19, 29-33]. Among of these ceramic precursors, kaolin
appears to be an important inexpensive raw material that is oftenly used for separation
application at a lesser monetary value [34]. Kaolin is one of the most widely used
industrial minerals and has an important role in numerous industrial applications such
as ceramics, paints, cosmetic, rubber, plastic and refractory industries [35]. In addition,
kaolin is one of the cheapest membrane raw materials and it is easily purchased in
Malaysia. Various researchers have reported the use of kaolin as a starting material
with other additives for membrane applications [36]. In addition, porous ceramics have
attracted increasing attention for its successful application such as supports for catalyst
and membrane and even kaolin is reported to be the best raw material for porous
ceramic structure [37]. Table 2.3 lists several studies used kaolin as the ceramic
material in membrane fabrication.
14
Table 2.3: Several studies used kaolin as the ceramic material in membrane
fabrication [9, 38-40]
Fabrication Method
Application Year
Pressing
Water Separation 2013
Dry compaction
Oil-water emulsion 2014
Pressing
Oil-bacteria separation 2011
Pressing (combined with
alumina powder)
Gas separation 2014
As discussed in the previous section, the limitation of using polymeric
membrane in separation technology has led to the exploration of ceramic membrane
that possessed good thermal and chemical properties. Because of the economic
competitiveness of existing separation technologies and this has taken the present
challenges of more expensive ceramic membranes. The power of low cost ceramic
material to produce ceramic membrane with desirable properties at low cost has
attracted many industries to put much effort on this material development. Table 2.4
lists the comparison of ceramic materials used in ceramic membrane fabrication in term
of its price and application. The price is given by BGOIL CHEM SDN BHD, Malaysia.
Table 2.4: Comparison of ceramic materials in term of its price and application
Categories Ceramic Powder Price (*MYR) a
/kg
Membrane Application
High Cost Al2O3 135.00 Water separation,
wastewater separation, gas
separation,
NiO2 2400.00 SOFc, Gas separation
ZrO2 1900.00 Water Separation,
SOFc, gas separation
TiO2 1208.00 Water Separation,
Wastewater separation, gas
separation
Low Cost Ball clay 7.00 Wastewater treatment
Kaolin(China clay) 65.00 Oily Wastewater treatment,
Water Separation
Raw Clay 4.80 Oily Water Separation
Dolomite 85.00 Usually combine with
others material like kaolin
15
2.4 Fabrication of Ceramic Membrane
Ceramic membrane is one type of inorganic membrane which have been used for a
long time in gas separation application [41]. Basically, preparation of ceramic
membrane involves three main steps which are (1) formation of suspension consist of
mixture ceramic particle and liquid medium; (2) packing of the particles in the
suspension into a membrane precursor with a certain shape; and (3) consolidation of
the membrane precursor at high temperatures [15]. Basically, there are two methods of
ceramic membrane fabrication;
1. Traditional/Conventional Method
2. Phase Inversion Method
2.4.1 Traditional Method
Ceramic Membrane fabricated through traditional method have been applied for
decades. Table 2.5 summarizes some traditional method that have been applied in
ceramic membrane fabrication and its application. Traditionally, in membrane
preparation, there are four methods:
1. Slip casting
2. Tape casting
3. Pressing Method
4. Extrusion
Table 2.5 Various Method in Ceramic Membrane Fabrication
Fabrication
Method
Application Advantage Reference
Slip casting Oxygen permeation Cost effective
method
Zhang et al.
(2015)
Slip casting Pure water permeability Higher PWF Fang et al. (2011)
Extrusion Alkaline wastewater Low cost of
starting materials,
low sintering
temperature and
good alkali
resistance
Dong et al. (2007)
16
Table 2.5 (Continued)
Extrusion Bacteria filtration Obtain desired pore
size (≤ 0.2µm)
Kroll et al. (2010)
Tape casting Solid Oxide Fuel Cells
(SOFc)
Grain size of around
200 nm
Meier et al. (2004)
Isostatic Pressing Microfiltration and
ultrafiltration
Obtain together top
layer and support
Colle et al. (2011)
Slip casting is one of the most commonly used methods. According to Choi et
al (2012), slip casting technique may provide additional advantages as it needs less
equipment and a lot cheaper than other techniques [42]. In addition, this technique able
to form various shapes from simple to complex shapes only using particle suspension
[43]. In slip casting method, the prepared suspension is poured into mould of the
desired shape. This is accompanied by the formation of the solid consolidated layer as
the drying takes place and water is taken away from the consolidated body. However,
this technique needs a long period of casting time as involves a slow drying process.
Furthermore, during the consolidation of drying stage, the wall thickness is hard to
control and is usually thick. As described by Li (2007), the thickness and value of
ceramic membrane made by slip casting was depended on the slurry condition and
casting time [15]. Besides proposing a difficulty in controlling, this mechanism also
creates a thickness of the film due to the large thickening rate of consolidation [44].
Tape casting is another well know technique in the fabrication of flat sheet
ceramic membranes. It is well-established technique for large scale fabrication of
ceramics suspension and multi-layered structures. Tape casting is particularly applied
for constructing large, thin and flat ceramic parts. This technique is also known as
traditional slip casting as it also uses a fluid suspension of ceramic particles as the
starting point for processing [45].
Pressing method is also commonly used in ceramic membrane in a disc shape.
In this method, the pressure applied to the ceramic membrane to force the particle into
a disc shape to form dense structure. A previous study has reported that this kind of
technique produces membrane less than 50 µm especially for SOFc application [46].
Nevertheless, the fabrication of ceramic membrane via pressing method demanded
high cost, which, therefore, produce symmetric membrane instead of asymmetric
membrane.
Extrusion is another type of method in fabrication of ceramic membrane.
Basically, extrusion is widely used for the mass-production of porcelains and
17
honeycombs, and also for the preparation of fiber reinforced ceramic composite [47].
Many attempts have been reported in the ceramic membrane fabrication by this
method. The comparison in the fabrication of porous ceramic membrane via extrusion
and pressing proved that extrusion produced excellent orientation of membrane pores.
According to Isobe et al., controlling the microstructure of porous ceramic membrane
is extremely important in order to produce ceramic membrane with high permeability
and mechanical strength [8]. However, this method only can be applied in the
fabrication of ceramic membrane in tubular shape. In addition, the ceramic suspension
also should show certain value within the control of plastic behaviour to get a
homogenous structure [15]. Recently, this method used in the preparation of
Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) feedstock with different thermoplastic binders
and also use to produce thin tubular [48]. Even this method offer a good membrane
structure especially for tubular, this method involves a complicated preparation process
in general, including difficulty in controlling the temperature to reach an ideal
temperature for a stable extrusion process.
In general, these traditional methods in ceramic membrane fabrication are
broadly used and known. Cheap fabrication such as slip and tape casting would cut the
cost, but, it is complex methods. In order to reduce fabrication cost, several effective
methods have been developed such as low temperature sintering with low melting-
points aids [49], adoption of simplified fabrication process (control casting, one-step
co-sintering), and use of cheap raw materials such as natural clay minerals like kaolin
[19], bauxite [50] and natural topaz [51].
Interestingly, this work will introduce the ceramic membrane fabricated via
phase inversion technique. Phase inversion is a technique that is commonly used in
fabrication of polymeric membranes. In spite of that, this technique has been applied
greatly in ceramic membrane fabrication for past years. Normally, in fabrication of
ceramic membrane via tape casting involved another step of coating the surface of
membrane. As been reported from previous study, dip coating [52] and sol-gel coating
[53] was conducted to develop the dense structure on the top of the membrane structure.
Up to date, the advancement fabrication of ceramic membranes via tape casting had
used the concept and condition of phase inversion system in order to produce
asymmetric membrane as shown in Figure 2.4 [54]. This is according to the phase
inversion technique that promotes simple method, thus produce asymmetric membrane
structure.
18
Figure 2.4: Asymmetric membrane structure via combined tape casting and phase
inversion method [54]
2.4.2 Phase Inversion Method
Historically, Loeb and Sourirajan (1963) invented the first asymmetric integrally
skinned cellulose acetate reverse osmosis membrane via phase inversion [17]. It is first
introduced in polymeric membrane fabrication. According to Lalia et al (2013), phase
inversion can be described as a demixing process whereby the transformation of the
initial homogeneous polymer solution from liquid phase into solid phase within a short
duration [55]. This process can be influenced or controlled by many factors, for
instance the concentration of the polymer and solvent, different type of non-solvent
coagulant bath and incorporation of additives [56]. In membrane fabrication via phase
inversion, the process was induced by immersion precipitation method. The membrane
is casted onto a suitable glass plate with desired thickness with casting knife and
immediately immersed into the non-solvent coagulant bath [57]. This precipitation
involves the exchange of solvent and non-solvent of coagulant that change the polymer
solution from thermodynamically stable to a metastable or unstable state [58]. After
that, the liquid-liquid demixing takes place in the solution which result in the formation
of membrane structure.
Conceptually, membrane fabrication via phase inversion involves three main
components which are non-solvent, solvent and polymer which is described by ternary
diagram. Figure 2.5 shows example of a basic ternary diagram that consist of solvent
such as Dimethylacetamide (DMAc) and N-Methyl-2-pyrrolidoe (NMP), non-solvent
(water) and polymer polyethersulfone (PESf) [59]. Straight line represents theoretical
19
binodal while dotted line represents spinodal line. Both line represent the demixing
process of polymeric membrane fabricated via phase inversion technique. However,
the application ternary diagram is limited in order to describe the phase inversion of
ceramic membrane due to additional of ceramic powder in a big volume that able to
reduce the effect of polymer phase inversion. The reduction of phase inversion can be
related to the mechanism viscous fingering that able to form finger-like voids structure
[12, 18]. Detail study that carried out by Wang et al (2012) had shown that finger-like
voids was induced by viscous fingering mechanism during phase inversion of
alumina/PES/NMP suspension [13]. Figure 2.6 shows the resulting alumina membrane
finger-like structure fabricated via phase inversion system. This unique structure has
made the ceramic membrane have been extensively used in many gas and SOFc
applications [18, 60].
Figure 2.5: Ternary diagram represents the study of different types of solvent [59]
Recently, there are many studies combining phase inversion in the ceramic
membrane preparation with conventional method. For example, preparation of tubular
SOFc by slip-phase inversion combined with a vacuum-assisted coating technique was
studied by Xiao et al (2014) [61]. Besides, He et al (2014) also produced to support
ceramic membrane for oxygen separation via combined phase inversion tape casting
[54]. Conversely, phase inversion technique has many advantages over other methods
as it able to form an assymetric layering structure which is suitable to be applied for
separation. Other than that, it only involves simple equipment, easy processing and
short duration time.
20
Figure 2.6: Alumina membrane finger-like structure resulting from membrane
fabrication via phase inversion system at different air-gap [12].
Table 2.6: Ceramic membrane prepared via phase inversion
Year Researcher Material Application
2013 Wu, Z Sr(NO3)2 Oxygen permeation
2003 Liu, S Al2O3 Gas permeability
2009 Wang, B YSZ-SiO2 N2 and H2 permeation
2008 Wei, C.C Yttria-stabilised
zirconia
Nitrogen permeance
2014 Li, T Cerium-gadolinium
oxide
Solid oxide fuel cells (SOFc)
21
2.5 Characterization and Properties of Ceramic Membrane prepared via
Phase Inversion Technique
Phase inversion technique has been applied in ceramic membrane fabrication for past
decades. By applying this technique, membrane structure could be controlled. In
addition, other characteristics such as pore size, porosity, surface roughness and
mechanical strength could also be affected by phase inversion. Therefore, this section
discussed the improvement of ceramic membrane characterization and properties via
phase inversion technique.
Membrane structure plays an important role in membrane characterization and
performance. Due to this, most investigations have been focused more on ceramic
membrane structure of the phase inversion technique. As mentioned earlier, ceramic
membrane fabricated via phase inversion commonly induced two types of structures:
finger-like and sponge-like structure. These structures have been reported by most
previous studies [12, 18, 62, 63]. According to Zhang (2009), these structures are
generated from instantaneous phase demixing [64]. Others researchers reported that
these structures could also be obtained by playing with the dope suspension viscosity
[12, 63]. For example, Othman (2010) reported that the increased of suspension
viscosity could be diminished membrane’s finger-like structure as shown in Figure 2.7.
This phenomenon due to the effect of viscosity can disturb the viscous fingering
mechanism during phase inversion. Details about viscous fingering mechanism have
been discussed in section 2.3.2 and also reported by other study [63]. However, the
improvement of recent studies of phase inversion promoted sandwich-like structure in
ceramic membrane. Figure 2.8 shows the sandwich-like structure with the combination
of sponge and finger-like structure in the ceramic membrane cross section, as reported
by Othman et al (2014) [65]. As discussed and revealed in that work, the structure
obtained was due to the short air gap used that promotes less viscous dope suspension,
that allow the instantaneous demixing to take place. Same observation has been
obtained by Wang et al (2009) [66]. Up to date, asymmetric membrane with pear-
shaped structure have been recognized as reported by Lee et al (2015) [67]. The
structure is as shown in Figure 2.9. Generally, the structure consists of common finger
and sponge-like structure, however, the shape and size of finger-like propagate from
the bottom part of the membrane and grow larger in size, thus, being called as pear-
shaped structure. This structure is due to the NMP was used as solvent and promoted
22
higher suspension viscosity, which was in contradiction with the study conducted by
Lee et al (2015). This is according to the different parameters applied by Lee et al
(2015), in which the effect of different solvents has been applied [67]. This concluded
that different parameters applied would promoted different membrane structure.
Figure 2.7: Reduced finger-like structure observed [63]
23
Figure 2.8: Ceramic membrane finger-like and sponge-like structure [67]
Figure 2.9: Ceramic membrane sandwich-like structure [68]
In most cases, ceramic membrane fabricated through phase inversion always
described and measured via it structures has been discussed before. Conversely, the
membrane surface roughness also plays an important role in membrane
characterizations and performances as it strongly influenced the membrane
performance as well. According to Zhong et al (2013), rough surface is more easily to
be fouled due to larger surface area [69]. The mechanism of fouling is always observed
in liquid separation such as water separation [70], oil-water separation [69] and
removal of heavy metal in wastewater [71]. As reported by Khulbe et al (1997) who
studied the relationship between the surface roughness and the gas permeability of
dense homogeneous membranes prepared from poly (phenylene oxide) [72]. From the
study, the permeability increased while the selectivity decreased with increased
membrane roughness. Furthermore, Tan and Matsuura (1999) also reported that
smoother membrane roughness could enhance the selectivity of the gas mixtures [73].
As far as concerned, there are no studies of membrane roughness towards ceramic
membrane via phase inversion technique for gas application. Thus, the roughness result
obtained from this work will be related to the result of polymeric membrane fabricated
from phase inversion system.
Sponge-like
Finger-like
Sponge-like
Finger-like
24
Membrane pore structure characterization such as pore size and porosity are
become one of crucial measurement in gas separation analysis [74]. This is imputable
to the performances of the membrane itself is related to the membrane pore size and
porosity. According to Li (2007), there are many methods can be employed in
measuring ceramic membrane pore size and porosity such as a bubble point method,
nitrogen separation and mercury intrusion porosimetry (MIP) [15]. In this study, the
literature is concentrated along the membrane pore size measured by MIP due to large
numbers of studies used this method [63, 68, 75]. Futhermore, MIP is based on the fact
that mercury is a strongly non-wetting liquid on most materials [15]. Therefore, when
mercury is forced into a dry membrane with the volume of mercury being determined
at each pressure, a cumulative volume of mercury can be determined. Interestingly,
using MIP, both pore size and pore size distribution can be determined and at the same
time porosity could be also measured.
As reported by Othman et al (2010), there are more than one pore size could be
obtained by ceramic membrane fabricated via phase inversion [63]. For example,
Figure 2.10 shows the pore size distribution corresponding to mercury porosimetry
measurements for ceramic membranes fabricated via phase inversion technique used
for application of gas deposition [65]. M1 represent before while M2 represent after
deposition. As discussed in that work, the results indicated that the membranes show
two pore sizes with the SEM analysis, which show that microchannel structure without
blocking the channel entrance and sponge-like pores. Whilst, Table 2.7 shows three
types of pores have been recognized due to the finger-like, sponge-like and pores
obtained via the reduction of Nickel (II) Oxide (NiO) to Nickel (Ni) structure [63]. The
membranes indicate same pore size for certain membrane, for example A-10 to A-20
for finger-like structure, but in different mercury intrusion. Up to date, the pore size
distribution analysis by mercury intrusion porosimetry indicated a single (mono)
distribution modal which form uniform membrane pore sizes [76]. In spite of all, the
membrane pore size have a relationship with membrane structure obtained from SEM
or FESEM as have been discussed before. Thus, in this study, the MIP would be
conducted in order to measure the FESEM images obtained.
158
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