Novel Copolymer Mixed Matrix Membranes for Gas Separation

Functionalized Novel Copolymer Mixed
Matrix Membranes for Gas Separation
2017-2019
Submitted By:
Muhammad Hashim Khan
M.Sc.-17-F-25
Supervised By:
Prof. Dr. Rafi Ullah Khan
Dr. Bilal Haider
Institute of Chemical Engineering & Technology
University of the Punjab, Lahore

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The DireCtO「,
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Laho「e.
Subject:- Simiia「itv Report
DearSir,
The 「eport ofMr. Muhammad Hashim Khan is as unde「:-
エurnitin Oriqinality Rep〔哩
Functionaiized Novei Copoiyme「 Mixed Matrix Memb「anes fo「 Gas Sepa「ation
by Muhammad HashIm Khan
From Ins航ute of Chemical Engi=ee而g & Techno-ogy
Degree’ M.Sc.

CERTIFICATE
This is to confirm that the research work titled “Functionalized Novel Copolymer
Mixed Matrix Membranes for Gas Separation” is the original work of Mr. Muhammad Hashim
Khan. The research was conducted under my supervision according to the set procedures and
I certify that the material included in free of plagiarism according to the rules and regulations
of the institute. I endorse its evaluation for the award of M.Sc. degree through the official
procedures of the University.
Prof. Dr. Rafi Ullah Khan
Thesis Supervisor
University of the Punjab, Lahore

DECLARATION
I Muhammad Hashim Khan S/O Muhammad Saleem Khan; hereby state that no part of
this thesis is plagiarized. If found contrary, I shall solely be responsible.
__________________________
Name of student with signatures
__________________________
Roll No. & Session
____________________________
Name of supervisor with signature

DEDICATION
To those, who taught me
The first word to speak
The first word to write
And who are the architect of my personality
MY PARENTS
& MY LOVING GRANDFATHER
Muhammad Anwar Khan Wardag

ACKNOWLEDGEMENTS
I feel great pleasure to express my deepest gratitude to my academic mentor and most
respected supervisor, Prof. Dr. Rafi Ullah Khan, Chairman Polymer Engineering Department,
for his inspired guidance, invaluable counseling, constructive criticism, active cooperation, and
for the timely provision of adequate facilities during the course of this research thesis.
Furthermore, I express my profound gratitude to my co-supervisor Dr. Bilal Haider for his
indispensable guidance and cooperation. I would also like to mention here Mr. Idrees and Mr.
Rizwan Dilshad for their invaluable mentorship, I am extremely grateful to them. Last but not
the least; I would like to acknowledge the cooperation, assistance and dedication of all the lab
attendants, workers and helpers. My heartiest gratitude to my parents, who made great devotion
to my studies and always kept praying for my success. I have had a remarkable learning during
this project and hope that this experience will benefit me in my future endeavors.

1
ABSTRACT
Mixed matrix membranes (MMMs) with shared benefits of both polymeric and
inorganic materials have been long studied to overcome the shortcomings of pure species
(polymeric and inorganic) membranes. It has been reported that the dense membranes offer
higher selectivity due to their packed polymeric symmetric structure. On the other hand,
asymmetric membranes with their porous structure offers higher permeability. The aim of this
work is to study the effect of membrane morphology as well as filler concentration on
membrane performance. In this context, flat sheet dense and asymmetric membranes (both pure
and mixed matrix) were synthesized using a novel copolymer Poly (vinyl chloride-co-vinyl
acetate) in dense as well as asymmetric morphology.
Membranes were synthesized with a polymer concentration of (22 %) by weight and
1,3 and 5 % filler w.r.t polymer was added to the casting mix. Vinyl-tri-ethoxy-silane (VTES)
functionalized sepiolite clay particles were used to counter the issue of polymer filler
incompatibility. These particles were incorporated in flat sheet asymmetric as well as dense
membranes. The fabricated MMMs were characterized by Infrared Spectroscopy (FTIR),
Electron Microscopy (SEM) and pure gas permeation testing as well as tensile strength testing
and thermogravimetric analysis (TGA) for the assessment of thermal properties.
Gas transport properties were studied by means of pure gas permeation tests utilizing
N2, CO2 and O2. The effect of pressure gradient, filler concentration, and membrane
morphology on varying transport behavior. Asymmetric membranes showed an increase in
permeability with increasing pressure and concentration of filler with subsequent decrease in
their ideal selectivity. Dense membrane on the other hand showed an increase in their ideal gas
selectivity with rising pressure and filler concertation but the increase observed was in their
ideal selectivity of CO2 vis a vis N2 and O2. Overall the dense membrane fared much better as
compared to the asymmetric membrane for gas separation application. Furthermore,
mechanical strength testing and TGA analysis of the membrane samples revealed an increase
in tensile strength of the composite material and their thermal stability.
Key Words: Functionalized, Novel Copolymer, PVCA, Highly Permeable, Gas
Separation Membrane

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TABLE OF CONTENTS
CHAPTER 1. INTRODUCTION ............................................................................7
1.1 Research Objective ............................................................................................9
1.2 Thesis Structure ...............................................................................................10
CHAPTER 2. LITERATURE REVIEW ..............................................................11
2.1 Historical Perspective on Gas Separation Membranes ....................................12
2.2 Comparison of Conventional Technologies with Membrane Technology......13
2.3 Membrane Classification .................................................................................14
2.3.1 Symmetric & Asymmetric Membranes .......................................................14
2.3.2 Ceramic, Metal, and Liquid Membranes .....................................................16
2.4 Mixed Matrix Membranes (Concept and Types).............................................17
2.4.1 Types of MMMs ..........................................................................................18
2.4.2 Major Factors Affecting the MMMs............................................................19
2.5 Choice of Polymer ...........................................................................................20
2.6 Filler Selection.................................................................................................22
2.6.1 Challenges in Filler Incorporation ...............................................................23
2.7 Membrane Transport Mechanism....................................................................24
2.7.1 Concept of Gas Permeation Through Non-Porous Dense Membranes .......26
2.7.2 Concept of Gas Permeation Through Porous Membranes...........................28
2.8 Methods of Membrane Fabrication..................................................................30
2.8.1 Phase Inversion ............................................................................................30
2.8.2 Coating.........................................................................................................31
2.8.3 Track Etching...............................................................................................31
CHAPTER 3. MATERIALS & METHODS ........................................................32
3.1 Materials ..........................................................................................................33
3.1.1 Polymer........................................................................................................34
3.1.2 Filler.............................................................................................................34
3.1.3 Solvent .........................................................................................................34
3.2 Filler Functionalization....................................................................................35
3.2.1 Sepiolite Modification .................................................................................35
3.3 Membrane Synthesis........................................................................................36

3
3.3.1 Preparation of 30 wt. % Polymer Mother Solution......................................37
3.3.2 Preparation of Dispersed Phase ...................................................................37
3.3.3 Making Casting Solutions of Varying Filler Concentration........................37
3.3.4 Asymmetric Membrane Preparation............................................................38
3.3.5 Dense Membrane Preparation......................................................................38
3.4 Membrane Characterization.............................................................................38
3.4.1 Mass Transport.............................................................................................40
3.4.2 Membrane Morphology ...............................................................................40
3.4.3 Thermal Properties.......................................................................................43
3.4.4 Mechanical Properties..................................................................................44
3.4.5 Fourier Transform Infrared Spectroscopy ...................................................45
3.4.6 Gas Separation Measurements.....................................................................45
CHAPTER 4. RESULTS & DISCUSSION ..........................................................48
4.1 FTIR Characterization .....................................................................................49
4.1.1 Functionalized Sepiolite Clay......................................................................49
4.2 Morphology / Electron Microscopy.................................................................50
4.2.1 Pure PVCA Asymmetric Membrane ...........................................................50
4.3 Gas Separation Ability of Synthesized Membrane..........................................51
4.4 Gas Permeation Data of Asymmetric Membranes...........................................51
4.4.1 Pure PVCA Asymmetric Membrane ...........................................................52
4.4.2 PVCA Asymmetric Membrane with 1% Modified Sepiolite ......................53
4.5 Gas Permeation Data of Dense Membranes ....................................................55
4.5.1 Pure PVCA Dense membrane......................................................................56
4.5.2 PVCA Dense membrane with 1 % Modified Sepiolite ...............................57
4.5.3 PVCA Dense membrane with 3 % Modified Sepiolite ...............................58
4.5.4 PVCA Dense Membrane with 5 % Modified Sepiolite...............................59
4.6 Filler Concentration Vs. Permeability .............................................................59
4.7 Mechanical Strength Testing ...........................................................................61
4.8 Thermal Stability .............................................................................................63
CHAPTER 5. CONCLUSIONS & RECOMMENDATIONS.............................65
5.1 Recommendations............................................................................................67

4
LIST of FIGURES
Figure 1.2-1 Working of a Membrane ........................................................................12
Figure 2.3-1 Membrane Classification........................................................................15
Figure 2.4-1 Cross Section of an Asymmetric MMM [21].........................................18
Figure 2.4-2 Asymmetric Membrane [3]....................................................................19
Figure 2.5-1 Mean Free Path.......................................................................................20
Figure 2.6-1 Membrane Defects Caused Due to Filler Addition................................24
Figure 2.7-1 Solution Diffusion Model.......................................................................26
Figure 2.7-2 Gas Permeation Through Different Membrane Types...........................29
Figure 3.1-1 PVCA Structure......................................................................................34
Figure 3.1-2 NMP Structure........................................................................................35
Figure 3.2-1 Sepiolite Modification (Possible Chemical Reaction) ...........................36
Figure 3.3-1 Polymer Solutions with Varying Concentration of Filler ......................37
Figure 3.4-1 Membrane Synthesis Graphical Procedure ............................................39
Figure 3.4-2 Permeability Apparatus PFD..................................................................41
Figure 3.4-3 Cracking Membrane Sample in Liquid N2.............................................42
Figure 3.4-4 Tensile Testing Machine ........................................................................45
Figure 3.4-5 Permeability Module..............................................................................47
Figure 4.1-1 Sepiolite FTIR........................................................................................50
Figure 4.2-1 Cross Section of Pure PVCA Asymmetric Membrane Using SEM.......51
Figure 4.4-1 Gas Permeation of Pure PVCA Asymmetric Membrane.......................52
Figure 4.4-2 Gas Permeation of PVCA Asymmetric Membrane with 1% MS..........53
Figure 4.4-3 Gas Permeation of PVCA Asymmetric Membrane with 3% MS ..........54
Figure 4.4-4 Gas Permeation of PVCA Asymmetric Membrane with 5% MS ..........55
Figure 4.5-1 Gas Permeation of Pure Dense PVCA Membrane.................................56
Figure 4.5-2 Gas Permeation of Dense PVCA MMM with 1% MS ..........................57
Figure 4.6-1 Effect of Filler Loading on Permeability of Membranes:......................60
Figure 4.7-1 Mechanical Properties of Membranes:...................................................62
Figure 4.8-1 TGA Thermogram of Select Membranes...............................................63

5
LIST of TABLES
Table 1.1-1 Membrane Applications [5].......................................................................9
Table 2.2-1 Comparison Between Conventional & Membrane Technologies ...........13
Table 2.3-1 Examples of Inorganic Membranes by Classification .............................16
Table 2.5-1 Examples of Rubbery & Glassy Polymers [3].........................................21
Table 2.5-2 Choice of Polymer ...................................................................................22
Table 2.7-1 Knudsen Selectivity.................................................................................29
Table 3.4-1 Polymers and their Glass Transition Temperature ..................................43
Table 4.4-1 Ideal selectivity of Pure Asymmetric PVCA Membranes.......................53
Table 4.4-2 Ideal selectivity of Asymmetric PVCA MMM with 1% MS ..................53
Table 4.5-1 Ideal selectivity of Pure Dense PVCA Membranes.................................56
Table 4.5-2 Ideal selectivity of Dense PVCA MMM with 1% MS............................57

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NOMENCLATURE
List of Greek Letters
ε Porosity
α Selectivity
λ Mean Free Path
µ Activity Coefficient
Abbreviations
MMM Mixed Matrix Membrane
PSA Pressure Swing Adsorption
PVCA Poly (vinyl chloride-co-vinyl acetate)
PDMS Polydimethylsiloxane
NMP N-Methyl-2-pyrrolidone
GPU Gas Permeation Units
VTES Vinyltriethoxysilane
FTIR Fourier Transform Infrared Spectroscopy
SEM Scanning Electron Microscopy
DSC Dynamic Scanning Calorimetry
DTA Dynamic Thermal Analysis
TGA Thermogravimetric Analysis
MS Modified Sepiolite
EAB Elongation at Break
STP Standard Temperature and Pressure
AFM Atomic Force Microscopy
SEM Scanning Electron Microscopy
TEM Transmission Electron Microscopy

8
Conventional gas separation technologies including physical absorption, reactive
absorption, pressure swing adsorption and solid bed absorption are energy intensive and bulky
processes. They also suffer from high capital and operational costs. Membrane technology
provides an alternative with advantages such as energy conservation, cost competitiveness,
versatility and modularity of process. Land signature for membrane processes is also
significantly low for membrane units as compared to conventional plants. Comparing
conventional amine absorption to membrane separation it has been observed that we save about
77% of energy consumed per ton of CO2 taken out from natural gas [1]. Due to these advantages
gas separation has acquired an important place in the chemical processing industry. A
membrane is essentially a thin semi permeable structure which separate gaseous/liquid
mixtures. Current commercial gas separation devices exclusively employ dense (symmetric)
polymeric membranes which are based on the solution-diffusion mechanism.
A few gas separation application utilizing membranes include [2]; nitrogen and/or
oxygen separation from air, recovery of hydrogen in oil refinery processes, separation of
methane from the other components of biogas, carbon di oxide removal from natural gas and
removal of H2S from natural gas. It is worth mentioning here that membrane processes form a
suite of very mature industrial technologies. Some industrial applications along with the
installed units are listed in Table 2.1-1.
As stated earlier, membranes provide an interface through which only selective
components can pass while the rest are thwarted. This is what is called as the gas permeation
technique according to which non-porous membrane having a selective permeability to gas
fraction the gaseous mixture according to the dissolution-solution-diffusion mechanism [3].
Most of the membranes used commercially worldwide are manufactured from polymers hence
the designation polymeric membranes. The advantages using polymer membranes include
good processability, inexpensive production and low operating cost and modular design [4]. It
is due to their ease of manufacture and economical nature as compared to other solutions along
with the ability of modification for more custom solutions. However, their performance is
limited given the two parameters that are used to judge them i.e. their permeability and
selectivity. It was observed by Robeson that in polymeric membranes an increase in
permeability meant a decrease in corresponding selectivity i.e. with an increased flux the ability

9
of the membrane to separate went down. One way to mitigate this effect is to consider
combinations of polymers with materials such as zeolites with excellent gas sieving properties.
Table 1.1-1 Membrane Applications [5]
Separation Process
Traditional
Technology
Membrane
Material
Status of
Membrane
Technology
H2/N2
Ammonia
Purge Gas
Pressure Swing
Adsorption (PSA)
Polysulfone
Plant Installed
(Prism by
Permea)
H2/CO
Adjustment
of H2/CO
ratio in
syngas plant
PSA
Polysulfone Lab Scale
Silicone Rubber Lab Scale
Polyimide
Plant Installed
by (Separex)
H2/Light
Hydrocarbons
Ethylene
Cracker old
Trains
Air
Separation
Cryogenic
Distillation
Silicone Rubber
Plant installed
(Sinopec
Zhen Hai
China)
Polyimide
Prism by
Permea
Du Pont
N2/CH4
Nitrogen
Removal
Cryogenic
Distillation
Silicon Rubber
Pilot Plant
PMP
Parel
PEBAX
H2O/CH4 Dehydration
Glycol
Absorption
Cellulose Acetate
Plant InstalledPolyimide
Polyaramid
1.1 Research Objective
The aim of this research is to investigate the gas permeation properties of novel co
polymer called Poly (vinyl chloride-co-vinyl acetate). Extensive literature suggests gaps in the
studies of gas permeation properties of this polymer. Thus, this study will contribute towards
our knowledge on membrane synthesis materials as well as contribute towards a more safe,
economical and environmentally friendly means of gas separation. Thin polymeric films are
prepared using conventional methodologies using polymers and fillers. Concentration of the
filler in the said films is varied, however the polymer concentration remains the same since it
has been argued that polymer solutions behave best at certain concentrations. Membrane
performance is investigated in terms of its morphology, mechanical strength and its gas
permeation ability at varying pressures (10-40 psi) and filler concentrations.

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1.2 Thesis Structure
This research thesis has the following structure: Chapter 1 is tilted “Introduction” and
deals with the background and significance of the research problem as well as the overall aims
of the research work. “State of the Art” is discussed in Chapter 2 which provides a historical
perspective on membrane technology, gives a brief comparison of conventional and membrane
separation, discusses basic fundamental principles of membrane technology, its transport
mechanisms and important characteristics of materials used for membrane synthesis along with
procedures of membrane synthesis. Chapter 3 is aptly titled “Materials and Methods” as it sheds
light on the physical resources and the procedures through which the materials are formed into
membranes as well as discusses some significant characterization techniques including those
utilized during this research work. The results obtained as a result of experimentation are
detailed in Chapter 4 “Results and Discussion”, which is divided into sections relevant to the
types of membrane characterized i.e. asymmetric membrane (porous membranes) and dense
membranes (non-porous membranes). These include pure polymer asymmetric and dense
membrane as well as mixed matrices with added fillers. In respective sections the effect of
pressure and filler concentration on calculated permeabilities are discussed along with the
outcomes of the thermo-physical characterizations. This is done in order to establish correlation
between synthesized morphology and its performance. Conclusively, Chapter 5
“Conclusions/Recommendation” provides conclusion and outcomes from the project along
with further research directions regarding improvement.

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Chapter 2. LITERATURE REVIEW

12
In this chapter are present brief information on the origins of membrane technology and
its comparison with conventional technologies used for the removal of unwanted gases from
product streams. Peer reviewed journals, books, patents, standard and various other sources
have been consulted on updated literature relative to the permeation of gases through polymeric
membranes, how we can increment the permeation through the polymeric membranes via
addition of functionalized fillers. This chapter also sheds light on manufacture of mainly
polymeric membranes and how they may be characterized for desired characteristics.
2.1 Historical Perspective on Gas Separation Membranes
Interest in membrane technology was shown long before its commercial applications
appeared whether it be water purification or gas separation. During the eighteenth century it
was a Frenchman named Nollet who discovered that a pig’s bladder had the ability to
referentially pass alcohols as compared to water [6]. This is regarded as one of the first known
studies on membrane separations which lead to the discovery of osmosis phenomena. Notably,
GasB
Membrane Can Be
Porous or Dense
Figure 1.2-1 Working of a Membrane

13
it was Thomas Graham who studied the application of semi permeable barriers regarding gas
separation by researching the permeation rates of various gases through these barriers which
we now know as membranes [7]. It the 80s polyimide membranes were used for the elimination
of carbon di oxide and hydrogen di sulfide from gas streams at an industrial scale. In the 80s a
gas separation membrane, composite in nature, was synthesized by the process of coating a
thin semi permeable film onto an anisotropic membrane. Membrane gas separation technology
continues to expand with a greater emphasis on economic viability and CO2 signature reduction
of gas separation processes.
2.2 Comparison of Conventional Technologies with Membrane Technology
Energy costs during separations constitute roughly constitute half of the total cost
incurred by a chemical related industry (pharmaceuticals, petroleum, paints/inks/specialty
chemicals etc.) [8]. Process intensification of these units could significantly bring down the
cost of products such as precursors ethylene, propylene, and benzene or even finished products
such as aspirin, paracetamol. This makes the process cost efficient and profitable as a result
whilst enhancing efficiency and eventually benefiting the environment. In this regard
membranes technology provides us with an alternative that is simpler, greener, versatile and in
some cases even cheaper. Considering CO2 as our primary gas there are several ways, we can
remove it from gas stream [9]. Some of the conventional processes include those utilizing
chemical and physical solvents as well as solid adsorbents. Table 2.2-1 gives the comparison
between the above-mentioned technologies with membrane separation.
Table 2.2-1 Comparison Between Conventional & Membrane Technologies
Characteristic Membrane Absorption Distillation
Energy Requirements
[10, 11]
Low High Very High
Cost [11] Moderate Moderate High
Efficiency [11] Moderate Moderate Low
Waste [11] Low High High
Complexity [11] Very Low Moderate High
It is noteworthy that in some cases we can even combine the conventional processes
with membrane ones to conceive hybrids that give us the best of both worlds.

14
2.3 Membrane Classification
Membranes provide a thin interface for the discrete permeation of chemical species
across it. Process of membrane gas separation is highly dependent on the interaction of the
gaseous phase with the membrane materials. Ability of passage of gas molecules through the
membrane is referred to its permeability, in other terms it is also the productivity of the
membrane as greater permeability means greater amount of flux through the membrane.
However, this increase in flux is not very useful unless the gas molecules are being separated
which leads us to another very important parameters called as selectivity which is the measure
of separation ability of the membrane. They can be classified into multiple types; they could
be made of inorganic materials or organic polymers and similarly the thin interface could be
chemically and physically homogenous or it could be of heterogenous nature. Some of the
types include.
1. Symmetric Membranes
2. Asymmetric Membranes
3. Ceramic, Metal & Liquid Membranes
4. Mixed Matrix Membranes
In this project we will be dealing exclusively with symmetric dense membranes and
asymmetric porous membranes and their mixed matrix counterparts. Classification of
membranes based on pore size can be done as; microfiltration (0.1-2µm), ultrafiltration (0.005-
0.1µm), nanofiltration (0.0005-0.005µm) and reverse osmosis membranes (< 0.5nm).
2.3.1 Symmetric & Asymmetric Membranes
Within the symmetric membrane classification there are several distinctly different
structures that may be either nonporous or porous i.e. homogenous membranes or microporous
membranes respectively. Homogenous or dense membranes are usually used in the labs to
study the intrinsic property of the membranes. These types of membranes have low
permeability i.e. passage of gas species is lower but the selectivity or purity of the permeate
gas is higher in comparison.

15
Since the gas passage is not encouraged in the dense membranes the permeation of the
species depends greatly on the solubility aspect of the membrane material and affinity of the
feed gas towards the respective material. These can be prepared by two methods [3]. Namely
melt extrusion and solution casting.
We have been preparing dense membranes in the lab via the solution casting methods
which involves the preparation of the dope solution which consists of the polymer and a
suitable solvent. Membranes are cast from this dope solution and the process is called as
casting. Afterwards the solvent is evaporated from the dope leaving behind the polymer
membrane structure thereby completing the solution casting process. On the other hand, melt
extrusion simply involves heating the polymer to form a suitable membrane structure.
Asymmetric membranes are a formed of very thin layers supported on a highly porous
support material. Support material provides the mechanical strength to the membrane, it also
eliminates a lot of resistance to the feed gas allowing increased gas transport through the
polymer matrix. These are prepared mainly through the phase inversion method.
In general, asymmetric membranes can be classified into the following four structures
[3]:
1. An Integrally Asymmetric Membrane with a Porous Skin Layer
Gas
Separation
Membranes
Metallic
Carbon
Molecular
Sieves
Metal
Organic
Framework
Zeolites...
Glassy
Polymers
Rubbery
Polymers
Inorganic
Organic
Polymer
Mixed Matrix /
Composite Membranes
Figure 2.3-1 Membrane Classification

16
2. An Integrally Asymmetric Membrane with a Dense Skin Layer
3. Composite Membrane with a Thin Porous Film
4. Composite Membrane with a Thin Dense Film
Membranes mentioned in point 1 and 2 are made of a single material, while those
mentioned in point 3 and 4 are made of at least two different materials. These composites are
made of a thin layer atop a porous support. Purpose of the support is to provide mechanical
support to the structure while the separation mainly depends on the thin layer of a polymeric
or inorganic membrane. The thin layer is what defines the performance characteristics of the
composite membranes.
2.3.2 Ceramic, Metal, and Liquid Membranes
Even though most commercial membranes used are polymer based, inorganic
membranes are increasingly being studied [7]. One of the reasons that warrants their study in
the field of gas separation is their improved thermal and chemical stability. This is due to the
average maximum operating conditions of polymeric membranes, which is about 100 °C. On
the other hand, the temperatures faced in many industrial processes tend to be significantly
higher [3]. Recently however, interest has increased in membranes formed from less than
conventional materials. Inorganic membranes can mainly be divided into two types; either
dense or porous. Example of these two types can be found in Table 2.3-1. A special type of
porous structure made from ceramics are being employed for ultrafiltration as well as
microfiltration applications. These membranes provide superior thermal and mechanical
stability as well as solvent resistance for demanding applications. These ceramics are usually
permselective composites made from multiple layers of several types of ceramic materials. Gas
separation in such membranes takes place based on molecular mass, its size/shape or a potential
in the membrane’s materials for respective gas molecules. Dense metal membranes made of
palladium metal, have been evaluated for hydrogen separation from gaseous mixtures, while
supported liquid films are being researched for carrier facilitated transport processes.
Table 2.3-1 Examples of Inorganic Membranes by Classification
Dense Inorganic Membranes Porous Inorganic Membranes
Palladium Alloys Alumina
Silica
Titanium
Glass
Porous Metals Such as Stainless Steel

17
Dense membranes have considerably high selectivity but rather limited permeability.
They are also very specific in their separation performance i.e. palladium membranes are
hydrogen specific. On the other hand, metal oxides are more prone to separate oxygen as
compared to other gases. One of the significant cons of inorganic membranes is their higher
cost as compared to polymeric membranes. This is due to the use of precious metals and
otherwise severe synthesis and operation procedures.
2.4 Mixed Matrix Membranes (Concept and Types)
Robeson [12] in early 90s presented the idea that pure polymer membranes had reached
a so-called upper limit regarding the mass transport efficiency. However according to his
findings certain inorganic materials have mass transport properties far exceeding those of pure
polymer membranes. Due to the complex and costly manufacture of inorganic membranes it
was thus deemed reasonable that if inorganic materials were to be incorporated in the polymer
mix the resultant would be the best of both worlds.
It is therefore that we have decided to explore the change in mass transport properties
incurred when certain inorganic fillers are incorporated into dense polymer mix. These
membranes are commonly referred to as the mixed matrix membranes since the inorganic
particles are sewn within the polymer matrix.
Addition of filler to the polymeric material can have three different outcomes. It can
either be that the particles may perform as sort of molecular sieves eventually varying
permeability of the membrane. Or they can cause disruption in the polymer matrix which may
result in an increase in interfacial voids decreasing the ability of the membrane to separate gas
molecules. Lastly, they may also act as a non-permeable barrier reducing permeability. The
main motivation behind the concept of mixed matrix membranes is that they allow the
membrane to overcome the individual shortcoming of inorganics and polymers and yield
separation of gaseous mixtures well above the famous Robeson’s upper bound.
Typically, synthesis is brought about by dispersing particles in a solvent via mechanical
mixing. This mix is afterwards sonicated, and the polymer is added to form a uniform
dispersion, which is also referred to as a casting solution. This solution is casted on a flat
surface either in a petri dish or on a glass plate using a doctor blade system, the solvent is left
to evaporate. This procedure gives us a dense membrane.

18
Another type of MMM is the asymmetric MMM which consists of a filler embedded in
a porous polymeric thin film which serves as the membrane. It has been observed that it is the
skin layer that performs the separation while porous structure is there as the mechanical
support. It is generally known that compared to dense membranes, asymmetric membranes
offer a higher permeability and higher filler loading in the top layer. Figure 2.4-1 gives a cross
section of an asymmetric MMM with filler particles in the top layer visible clearly.
2.4.1 Types of MMMs
There are principally three types of mixed matrix membrane reported in literature.
1. Solid Polymer
2. Liquid Polymer
3. Solid Liquid-polymer
Figure 2.4-1 Cross Section of an Asymmetric MMM [21]

19
It is noteworthy to mention here that the filler can be in either solid or liquid form or
both liquid and solid. In this research work we have specifically targeted the synthesis and
characterization of solid polymer mixed matrix membranes.
2.4.2 Major Factors Affecting the MMMs
For MMMs it is necessary the polymer chains be attached directly to the filler particle
embedded in the polymer matrix. Pores of the filler ought not to be blocked by polymer chains.
Neither should there be chain rigidification around the filler particles. All of these can seriously
hamper the separation capability of the synthesized membranes by creating no selective voids
or by blockage of filler particles hence their non-utility. Some of the factors that need to be
kept in mind in order to prevent the above phenomena are as such:
1. Filler /Polymer Compatibility
2. Selection of Solvent
3. Preparation Procedure of the MMM and Post Treatment
4. Shrinkage of Polymer Matrix etc.
The next chapter discusses in detail the above given factors and effort is made in order
to select the best materials and methods for the synthesis of membranes.
Non Porous Dense
Membrane
Loeb Sourirajan
Anisotropic Membrane
Thin Film Composite
Anisotropic Membrane
Asymmetric Membrane
Figure 2.4-2 Asymmetric Membrane [3]

20
2.5 Choice of Polymer
Membranes manufactured out of polymeric materials are usually economically viable
as compared to inorganic membranes which cost more in terms of raw materials and
processing. Polymeric membranes provide an entangled matrix of polymer chains through
which some components of our gaseous feed can pass while others are retained hence the term
semi permeable is frequently used. Choosing the right polymer is one of the most important
decisions in membrane synthesis. Polymeric membranes are characterized by their
permeability and selectivity. Each polymer comes with their own set of properties and
characteristics. It is these characteristics that eventually decide the membrane performance. An
ideal membrane has the following properties.
1. It is Defect-free Throughout
2. It Has High Chemical Resistance
3. It Has High Thermal Stability
4. Mechanically Strong
5. High Selectivity & Permeability
For gas separation purposes nonporous membranes are usually preferred and in case
porous membranes are used it must be made sure that the pore diameter is less as compared to
the mean free path of the gas molecules. Mean free path is the average displacement a molecule
covers before it strikes with another molecule in its path. Mean free path of a molecule is related
to its size; larger the molecule’s size the smaller is its mean free path.
Figure 2.5-1 Mean Free Path

21
Other than that, we must keep in mind the availability and cost of the said polymer.
Membrane materials can be classified based on their organic or inorganic nature. Inorganics
include metals, metal oxides, glass silicate and zeolite type materials. Recently however there
has been a push towards a new type of material called as metal organic frameworks which is
mostly being utilized as a filler in mixed matrix membranes for gas separation. Mixed matrix
membranes are however polymeric membranes and materials for this type can again be
characterized as glassy or rubbery polymers both of which have their own distinct properties.
For example, glassy polymers have good separation characteristics such as high selectivity. On
the other hand, rubbery polymers give high permeability but lower selectivity [13]. For the
purposes of this thesis it is also very important that the polymer is novel and has not been
extensively researched before. Examples of some glassy and rubbery polymers are provided
in Table 2.5-1.
Eventually we must decide on a polymer which offers high permeability as well as high
selectivity. The reason being that a highly permeable membrane is required to treat given
amounts of gas while high selectivity ensures that optimal separation is taking place resulting
in higher purity of product gas.
Table 2.5-1 Examples of Rubbery & Glassy Polymers [3]
Rubbery Polymer Glassy Polymer
PDMS Poly Sulfone
Polyisoprene Cellulose Acetate
Polyimides
Poly Ether Sulfone
Polyvinyl Acetate
Polyvinyl Chloride
Table 2.5-2 states the criteria behind the choice of the polymer.
1. Availability
2. Thermal Stability
3. Chemical Stability
4. Mechanical Strength
5. Novelty

22
Table 2.5-2 Choice of Polymer
Polymer Availability
Thermal
Stability
Chemical
Stability
Mechanical
Strength
Novelty
PS Available High High High Low
PES Available High High High Low
PVCA Available Moderate Moderate Moderate High
Based on above table, it was decided to use the polyvinyl chloroacetate on accounts of
its high novelty. Since the literature on the polymer is very limited hence during the
experimentation some qualitative observations were made which have been filled into the table.
2.6 Filler Selection
It was Robeson who predicted the performance limits of polymeric materials and
established an upper bound for their gas permeation characteristics. It was then observed that
the inorganic materials possessed properties beyond the said upper bound. This incentivized
the idea that combining the two could lead to improvement of present membranes. It has been
since discovered that we can alter the gas permeation properties of a polymeric matrix by
embedding inorganic materials such as zeolites, clays, activated carbon etc. This can be brought
about in several ways. However, in order to reap the maximum benefits, it is important that
filler particles are uniformly dispersed in the matrix. Uneven dispersion of the filler particles
in the mixed matrix gives rise to defects since it tends to provide a non-selective path for the
gas thus undermining the separation capability of the membrane. Dispersed particles can also
change the gas transport by altering the chain packing of the polymeric matrix especially near
the polymer filler interface. Particularly the interface between the inorganic filler and polymer
matrix is of significance as it can provide alternate pathway to one of the gases over the others.
This is the reason we are functionalizing our filler in order to make sure that appropriate
bonding is formed at the filler/polymer interface so that there are no voids that may cause a
decrease in membrane selectivity. Ideally, we expect that the addition of the filler will boost
both the permeability as well as the selective trait of the membrane. One can view these
particles as being nodules suspended in a matrix of polymer molecules which is accurate and
hence the name. However, as stated earlier in this section it must be kept in mind that this often
induces defects into the membrane which drastically decreases the selectivity. Some important
defects include [14];the poor compatibility between the inorganic filler and the organic

23
polymer which may cause interfacial non-selective defects. In addition, the agglomeration of
the particles within the matrix may also reduce the selective characteristic of the membranes.
Interfacial defects caused due to the incompatibility between the polymer and the inorganic
filler may also cause deterioration of the membrane’s mechanical structure. Similarly,
occurrence of agglomeration of particles during membrane formation can also cause significant
voids which are detrimental to the mechanical strength of the membrane. Thus, we can say that
fillers have a great role to play during the function of the mixed matrix membranes. It has been
observed, however, that a higher loading of the filler can make the membrane worse [14].
In the light of above grounds, to reduce the adverse effects caused due to incorporation
of the inorganic phase, the uniform dispersion and inter compatibility between the inorganic
particles and polymeric matrix in the mixed matrix is one of the most significant issues. In
order to do this, surface chemistry of the particles may need to be modified using available
treatment methods [11]. In this research work we have modified the surface chemistry of our
filler in order to mitigate the issued established in this section.
Literature review suggests that there are inherently two types of fillers, inorganic and
those with partial organic properties. This new breed of fillers is called as the metal organic
framework. They have high surface area and are highly customizable from a synthesis point of
view. However, the inorganic fillers can also be made to possess organic properties by
modifying their surface using long alkyl chains which will help them bind better with the
polymer and prevent the void age caused due to the defects that arise out of polymer-filler
incompatibility [14]. One such way of functionalizing inorganic particles albeit for catalysis
purposes is mentioned in [15]. Vinyl tri ethoxy silane (VTES) was used to graft amino and
alkyl groups onto the surface of sepiolite while acetyl trimethyl ammonium bromide
(CTMABr) was used as what is called the structure directing agent or SDA in the synthesis.
Complete synthesis procedure is mentioned in further Section 3.2.1 of the thesis.
2.6.1 Challenges in Filler Incorporation
Whilst incorporating inorganic fillers into organic polymers we must keep in mind a
few points which may cause problems down the road. Often poor membrane mobility results
in a poor interaction between the polymer and the filler [16, 14]. This can cause undesirable
channels in the finished product negatively affecting our mass transport (i.e. selectivity). In
simpler words the membrane loses its ability to separate the gases from one another even if it
is treating a larger flux due to the created voids. It is therefore that a “bridging agent” is

24
recommended as a mediation source between the polymer matrix and the filler. This can help
minimize the creation of voids which leads the product having not only good permeability
values but also greater selectivity. This agent can be added to the filler particles by modifying
the filler surface with appropriate functional groups having grater affinity with organic
compounds. Examples include phenyl acetyl groups, decanoyl acetyl groups, and succinic acid
groups.
Another relevant problem is the partial blockage of filler pores by polymer chains. This
decreases the utility of the incorporated particles. These phenomena are shown in the Figure
2.6-1. The figure lists some types of defects that may arise in the polymeric matrix as a result
of filler inclusion.
2.7 Membrane Transport Mechanism
Permeation of gases through membranes (thin semi permeable barriers) is usually
driven by pressure difference and a concentration gradient across the membrane. When the
pressure difference is applied a potential is set up for gas molecules to transport from regions
of one concentration (high in the case of diffusivity dependent membrane processes) to regions
of another. However, there is another important factor that is at play here and that is the factor
Polymer Polymer
Polymer Polymer
Filler Filler
Filler Filler
Rigidified Polymer
Volume
Reduced Permebaility
Region within Filler
Ideal Mophology Interfacial Void
Case-1 Case-2
Case-3 Case-4
Figure 2.6-1 Membrane Defects Caused Due to Filler Addition

25
of solubility. This is because different gases have different affinities towards polymers which
make up the membranes. It is generally accepted that gas permeation across dense membranes
takes place in the three steps: absorption of permeating gas into the polymeric matrix, diffusion
through the matrix and eventual removal of the permeating species from the polymer surface
via desorption. On the other hand, porous asymmetric membranes permeate gases mainly on
the principle of pressure driven convective flow.
It can be deduced from the above points that gas transport through the membranes is
affected by a multitude of factors some of which include solubility and diffusivity of the small
molecules in the polymer. Also, factors such as chain packing and side group complexity,
polarity, crystallinity, orientation, fillers, moisture and plasticization play an important role.
Classification of membrane separation processes can be done according to their separation
modes. For example, molecular sieving occurs when the pores size is extremely small i.e. (3.0-
5.2 Å), because at this pore size only the gas molecules of a certain kinetic diameter can pass
through the membrane. Another important mode of separation is solution diffusion which is
discussed in the section explaining transport through dense membranes. Apart from these two,
gas separation can also take place via difference of charges in gas molecules, by carrier
facilitated transport and by time-controlled diffusion.
Different mechanisms may be involved in transport of gases across membranes
depending on their physical structures such as their porosity, non-porosity or their asymmetric
nature. In this regard the physical classification of the polymer that is used to synthesize the
membrane also plays a great role. Selectivity and permeability of the membrane play a key role
in determining the efficiency of the gas separation process. Based on these two a membrane
can be classified as either porous or non-porous membrane. In order to understand
permeability, let us first discuss permeance. It is the capability of a material to allow gases or
liquids to pass through it. This parameter is what we use to gauge the productivity of a
membrane. For a given pressure difference it is the amount of the permeate that passes through
a certain membrane area in a specific time. Its units are GPU.
1 𝐺𝑃𝑈 = 10−06
𝑐𝑚3 (𝑆𝑇𝑃) 𝑐𝑚−2
𝑠−1
𝑐𝑚 𝐻𝑔−1
When Permeance of the membrane is multiplied by its thickness it equals its
permeability. Such measurements are frequently made on thick (20-100 micrometers) films but
for practical applications a very thin active layer (<1 micrometers) is desired in order to
increase the permeance. It is measured in Barrer.

26
1 𝐵𝑎𝑟𝑟𝑒𝑟 = 10−10
𝑐𝑚3 (𝑆𝑇𝑃) 𝑐𝑚 𝑐𝑚−2
𝑐𝑚 𝐻𝑔−1
2.7.1 Concept of Gas Permeation Through Non-Porous Dense Membranes
Porous membranes although applicable in the gas separation domain are not much
preferred due to the lack of their selectivity i.e. their separation efficiency. Therefore, we must
look at non-porous membranes or dense membranes as they are called. In such membrane’s
solution diffusion is believed to be responsible for the transport of gases through the membrane.
It is essentially a three-step process: in the first step the permeating gas is absorbed into the
pure polymeric or mixed matrix of the dense membrane. In the second step the permeating
species diffuses through the polymer through the thermal expansion and contraction of polymer
chains and in the final third step the permeating species is desorbed from the matrix. The
driving for which could be the temperature, concentration or pressure difference is referred to,
in the domain of thermodynamics as the chemical potential. Take for example a permeant I it’s
flux through the membrane can be shown by the given equation.
𝐽𝑖 = 𝑐𝑖 𝑉𝑖 = 𝑐𝑖 𝑈𝑖
𝑑µ𝑖
𝑑𝑥
2.1
In above Equation 2.1 𝐽𝑖 (g cm-2
s-2
) stands for the flux while 𝑐𝑖 (mol dm-3
) denotes the
concentration of the component. Furthermore 𝑉𝑖 (m s-1
) is the velocity component of the
placeholder component.
𝑑µ 𝑖
𝑑𝑥
is the chemical potential gradient. 𝑈𝑖 is the constant of
Region of High H2 Pressure
Impurity Molecule (CO2, CO)
Hydrogen Gas Mixture Containing Impurity
Region of Low H2 Pressure
Ultra High Pure Hydrogen Gas
2-Dissociation
4-Diffusion
5-Recombination
Membrane
Figure 2.7-1 Solution Diffusion Model

27
proportionality which links the chemical potential gradient and the velocity. Chemical potential
can be given by the Equation 2.2.
𝑑µ𝑖 = 𝑅𝑇𝑑(𝑙𝑛((γ𝑖 𝑛𝑖)) + 𝑣𝑖 𝑑𝑝 2.2
In the above equation 𝑅 is the ideal gas constant and 𝑇 is temperature. Similarly, γ𝑖 is
the activity coefficient of the arbitrary component, 𝑣𝑖 is the partial molar volume of the
assumed component while 𝑝 stands for pressure. Whilst applying the solution diffusion model
it is implied that the pressure does not change within the membrane. The chemical potential is
directly linked to the concentration gradient of a specific gas. Combining the above two
equations we get the following equation.
𝐽𝑖 = (
−𝑅𝑇𝑐𝑖 𝑈𝑖
γ𝑖 𝑛𝑖
)(
𝑑(γ𝑖 𝑛𝑖)
𝑑𝑥
) 2.3
Putting 𝑐𝑖 = M𝑖ρ𝑛𝑖 where M is the molecular weight and ρ is the molar density of the
component then eq. 2.4 becomes.
𝐽𝑖 = (
−𝑅𝑇𝑈𝑖
γ𝑖
) (
𝑑(γ𝑖 𝑐𝑖)
𝑑𝑥
) 2.4
Fick’s Law is similar
𝐽𝑖 = −𝐷𝑖 (
𝑑(𝑐𝑖)
𝑑𝑥
) 2.5
𝐽𝑖 = (
𝐷𝑖(𝑐𝑖𝑜 − 𝑐𝑖𝑙)
𝑙
) 2.6
Where 𝑐𝑖𝑜 and 𝑐𝑖𝑜 are the concentration of components 𝑖 at membrane interface and at
length l. It can be inferred from the above three steps that the permeation of the module is
controlled by two major factors i.e. diffusivity coefficient and selectivity coefficient. Coming
back to permeability, in simpler words it is the productivity of the membrane and can be
mathematically stipulated as:
𝑃𝑒𝑟𝑚𝑒𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑜𝑓 𝐺𝑎𝑠 𝐴 (𝑃𝐴) = 𝐷𝑖𝑓𝑓𝑢𝑠𝑖𝑣𝑖𝑡𝑦 𝐶𝑜𝑒𝑓𝑓. (𝐷 𝐴) × 𝑆𝑜𝑙𝑢𝑏𝑖𝑙𝑖𝑡𝑦 𝐶𝑜𝑒𝑓𝑓. (𝑆𝐴)
𝑃𝐴 = 𝐷𝐴 × 𝑆𝐴 2.7

28
Practically speaking however permeability can also be specified also be expressed as
the flux normalized by film thickness (𝑙) and the transmembrane pressure (𝛥𝑝 𝐴) expressed
mathematically as:
𝑃𝐴 =
𝐹𝑙𝑢𝑥 𝐴 × 𝑙
𝛥𝑝 𝐴
2.8
Above mentioned permeability can help calculate us the ideal selectivity of the
membrane. We simply calculate permeability of two pure components passing through the
membrane and divide them. Hence for a mixture of two gases A and B we can specify the ideal
selectivity:
𝛼 𝐴
𝐵
=
𝑃𝐴
𝑃𝐵
2.9
It goes without saying that the dense membranes possess high selectivity value but
their throughput i.e. permeability is rather low. In their defense however, dense membranes can
separate gases of similar molecular/atomic dimensions based on their solubilities in the
polymer matrix. Considering that the dense membranes are mainly synthesized from polymers
it has been found that contrary to the porous membranes their (dense membrane) structure
consists of disconnected passages in the polymer chain matrix. These pathways are randomly
created and destroyed due to the thermally induced motion of the polymer chains. Movement
of the permeant through these passageways dictates the transport of the membrane. This means
that the said process is highly dependent on the pressure differential and the external operating
conditions.
2.7.2 Concept of Gas Permeation Through Porous Membranes
In case of a porous membranes structure of the membrane tends to be a highly voided
with interconnected channels which are randomly spread across the polymer matrix. It has been
observed that the feed separation depends highly on the chemical and physical properties of
the membrane including molecular size of the polymer along with distribution and size of the
pores inside the membrane. This makes the porous membrane very similar in working to a
conventional filter. Porous membranes can be further subdivided into microporous, micropores
and mesoporous membranes depending on their pore size. However, to the detriment of this
simplicity porous membranes suffer from low selectivity values but high permeability can be
expected. Before applying a porous membrane to gas separation, one must make sure that the
mean free path of the gas molecule must be large than the average pore diameter. Velocity of

29
the gas molecules plays a great role in determining the gas flux through the membrane with a
direct correlation between the two while the correlation is inverse in the case of molecular mass
(Knudsen Diffusion).
Table 2.7-1 Knudsen Selectivity
Gas Pair Knudsen Selectivity
CO2/N2 0.80
O2/CO2 1.17
𝑃𝑜𝑟𝑜𝑢𝑠 𝑀𝑒𝑚𝑏𝑟𝑎𝑛𝑒𝑠 𝐹𝑙𝑢𝑥 = 4 × 𝑁𝑜𝑛 𝑃𝑜𝑟𝑜𝑢𝑠 𝑀𝑒𝑚𝑏𝑟𝑎𝑛𝑒𝑠 𝐹𝑙𝑢𝑥 2.10
In porous membrane gases move through a convective driven by pressure gradient
across the membrane.
𝐽𝑖 = 𝑐𝑖 𝑈𝑖 𝑣𝑖
𝑑𝑝
𝑑𝑥
2.11
The Equation 2.11 if integrated across the membrane length and substituting 𝑐𝑖 𝑈𝑖 𝑣𝑖
with 𝑘 gives the following form.
𝐽𝑖 =
𝑘(𝑝 𝑜 − 𝑝𝑙)
𝑙
2.12
Permeate
Feed
Size Exclusion
Knudsen Diffusion Molecular Sieving Solution Diffusion
Solubility Difference
P
Figure 2.7-2 Gas Permeation Through Different Membrane Types

30
2.8 Methods of Membrane Fabrication
Method of preparation is another critical step of membrane synthesis right at par with
the material selection which governs the final characteristics of the membrane. Slightest of
change such as temperature or residence time can cause major changes in membrane mass
transport characteristics. The two types of membrane geometries that can be manufactured
using membrane fabrication methods available today are as such.
1. Flat sheet: as the name suggest this geometry consist of flat sheets / discs of
membranes suitable for use in plate and frame / spirally wound modules.
2. Cylindrical: utilized in tubular and capillary, or hollow fiber modules.
Both polymers and inorganics are widely used in the synthesis of membranes. It is
known that the chemical and heat resistance of inorganic membranes is higher as compared to
the polymeric ones. However, their widespread use is inhibited owing to their expensive cost.
Now coming to methods of membrane fabrication we have the following techniques which we
can employ to manufacture synthetic membranes.
1. Phase Inversion
2. Coating
3. Track Etching
2.8.1 Phase Inversion
This is one of the initial techniques that was used to manufacture membranes. In the
60s the very first cellulose acetate anisotropic (asymmetric) membrane was invented by Loeb
et. al [17]. Although several techniques were discovered after phase inversion such as solution
casting, interfacial polymerization and plasma polymerization all of which are being practiced
to date; yet phase inversion remains the most popular and important membrane preparation
technique. It is essentially the conversion of liquid polymer solution into a solid under specified
conditions. It is initiated by the transitioning of the solvent from one to another via liquid-liquid
de-mixing. During this process the liquid phase high in polymer concentration (polymer casting
solution) solidifies forming an asymmetric solid polymer matrix. Its significance lies its
prevalent use in the manufacture of industrially available polymer membranes. One of the
important phase inversion techniques and the one used during this project is the immersion
precipitation.

31
2.8.1.1 Immersion Precipitation
In general, commercially manufactured membranes are prepared via immersion
precipitation. The casting solution is spread onto a support which is dipped in a coagulation or
de mixing bath. The whole process in summary involves the following steps; formation of
polymer solution in an appropriate solvent, casting of the solution onto a suitable support via a
casting knife/blade and placing the support carefully in the immersion (coagulation) bath. The
de mixing stage involves the solidification of the polymeric casting solution into a matrix.
Membranes formed by immersion precipitation are asymmetric in structure. They have
a porous sublayer but a dense top. There are multiple factors which control the formation of
both these layers such as solution composition, temperature of the coagulation bath and the
additives in the polymer casting solution. This method has been heavily employed not only in
the lab but also in the industry.
2.8.2 Coating
Coating procedures are vital regarding symmetric (dense) polymer membranes as well
as inorganic composite membrane preparation. Using these methods, we can keep the
membrane thickness within a limit while enhancing the mechanical integrity of the membrane.
Some methods to coat the membranes include dip coating, plasma polymerization, interfacial
polymerization and in situ polymerization. In order to synthesize composite membranes using
coating methods we may use dip coating in a dilute polymer solution of the porous support and
subsequent solvent evaporation. In this regard dip coating is a rather convenient method for
preparation of supported ceramic membranes with micro to macroporous pores. An improved
dip coating technique has been developed which offers the advantages such as reduced increase
in membrane thickness, sustenance of membrane permeation properties over traditional
coating-sintering procedures.
2.8.3 Track Etching
Using this method, a polymeric film is subjected to a source of radiation comprising of
highly potent energy particles. The sites exposed to shower of the particles decompose and are
chemically modified amid this procedure [3]. Afterwards an etching process is applied using a
basic solution or a hydrogen peroxide bath (this may vary from material to material) this etches
the polymer along the irradiated path.

32
Chapter 3. MATERIALS & METHODS

33
This chapter lists the materials that were utilized to synthesize the membranes. Practical
steps that were taken in the laboratory during the execution of the project are also listed along
with figures and tables where necessary. Analyses used for membrane characterization are
discussed at the end of the chapter not all of which have been employed during this research
work.
The experimental work can be divided into the following steps
1. Selection of Suitable Filler and Its Functionalization
2. Selection of Suitable Polymer
3. Membrane Synthesis
4. Characterization of Synthesized Membranes
During the literature survey it was found that in order to achieve good gas separation
performance using polymer membranes it is necessary that we introduce inorganic fillers which
have separation properties lying beyond the Robeson limit [14, 2]. The task however is not
simply adding a suitable filler to the polymer solution and expect it to work as doing that has
found to cause defects in the polymer matrix such as poor interfacial interaction and particle
agglomeration.
It was therefore decided to modify the filler first in order to increase its compatibility
with the polymer solution.
3.1 Materials
Material selection and method of preparation are of the most important parts in
fabricating a membrane as they play an imperative role in defining the properties of final
product. Some of these properties include membrane mass transport, membrane morphology
and it thermal and chemical stability. Therefore, it is highly important that materials be chosen
with the product in mind. Regarding polymer, for this research we have chosen Poly (vinyl
chloride-co-vinyl acetate) which is a novel co polymer. Its properties regarding gas separation
have not been studied extensively hence making it a prime candidate for our studies. Regarding
our dispersed phase (inorganic phase filler) for the synthesis of mixed matrices we chose
sepiolite. Brief detail on our materials is provided in the ensuing sections.

34
3.1.1 Polymer
Poly (vinyl chloride-co-vinyl acetate) is a co-polymer with alternating units of poly
vinyl alcohol and polyvinyl chloride. It’s relatively low cost with excellent film-forming
characteristics, high mechanical as well as chemical resistance which can prove to be an
advantage in gas separation applications [18]. Detailed information on PVCA can be found in
Appendix-A1. PVCA was purchased from Sigma Aldrich UK and used without any further
purification.
3.1.2 Filler
Sepiolite is a naturally occurring clay mineral of sedimentary origin and a part of the
phyllosilicate mineral genus. It has already reportedly been employed for the synthesis of
mixed matrices using different polymers [19]. It has a large specific surface area and is a non-
swelling, lightweight and porous in nature. It is essentially a hydrous magnesium silicate
having micro fibrous morphology. Structurally it consists of an octahedral sheet of magnesia
sandwiched between two tetrahedral silica sheets. Presence of silanol (Si-OH) groups on
saprolite’s surface make it possible for the functionalization/modification to take place. It has
a high surface area and porosity.
3.1.3 Solvent
Solvent plays a critical role in the determination of separation performance and
membrane morphology. In case of MMMs solvents with high boiling, point and viscosity may
provide superior membrane performance [20]. Some important solvent properties include its
density, viscosity and boiling point. N-Methyl-2-pyrrolidone or NMP for short was chosen as
Figure 3.1-1 PVCA Structure

35
the solvent for this research. 99.9% purity NMP was purchased from Merck and used without
any added purification. NMP is a high boiling (202 °C) solvent commonly used for dissolving
substances such as polymers. It is colorless and has a molecular weight of 99.13 g. mol-1
.
3.2 Filler Functionalization
Details regarding filler selection and functionalization are provided in Section 2.6. We
adopted the procedure researched in [15, 21, 19] to functionalize our filler. This was primarily
done in order to increase its compatibility with the organic polymer. Using this method
described in the referenced articles, we functionalized sepiolite by a co-condensation method
using Vinyl-tri-ethoxy-silane or VTES for short.
3.2.1 Sepiolite Modification
Sepiolite was treated prior to its modification. The experimental procedure consists of the
following major steps:
Sepiolite Purification:
1. Pour 1000 ml of water in a round bottom flask and disperse 10 grams of raw sepiolite
in it.
2. The dispersion was stirred for a period of 72 hours using a magnetic stirrer.
3. Afterwards the dispersion was filtered by a Whatman filter paper. This was done in
order to remove any dust or similar impurities present in sepiolite.
Figure 3.1-2 NMP Structure

36
4. Dry the product using an air dryer and then put it in the oven at 95 °C for a day. Dried
sepiolite was grounded in pestle and mortar to make amorphous sepiolite for further
processing [22].
Sepiolite Modification:
1. Functionalization of sepiolite was carried out by treating purified clay with VTES using
method given in [23].
2. Initially 333.3 ml of isopropanol solvent was used to disperse the purified sepiolite in
a round bottom flask.
3. 15 minutes of stirring was applied to the suspension at an ambient temperature. Then 5
ml of 4 M HCl solution was added into it which was followed up by 28.28 ml drop wise
addition of VTES.
4. The reaction mixture was then gently refluxed for 4 hours with constant stirring at 60
°C. Resultant modified sepiolite (MS) was recovered by filtration and was vacuumed
for 8 hours. [19].
3.3 Membrane Synthesis
Following section details the preparation of asymmetric and dense membranes studied
during this project. Thorough safety guidelines were followed during the experimentation to
ensure minimum health risk. Apparatus Required: Weighing balance, beakers, graduated
cylinder or volumetric flask, thermocouple, spatula, safety gloves and glasses, casting knife,
casting board (glass board), vacuum oven, magnetic stirrer, sample bottles (100 ml and 10 ml),
spatula.
Figure 3.2-1 Sepiolite Modification (Possible Chemical Reaction)

37
3.3.1 Preparation of 30 wt. % Polymer Mother Solution
1. Weight 4.45 grams of PVCA on a balance. Now take a 100 ml sample bottle and pour
10 grams of NMP in this sample bottle.
2. Place the bottle on a magnetic stirrer and allow to stir for 3 hours straight. Leave the
solution overnight until it is homogenized properly.
3. Now sonicate for half an hour for homogenization before casting the membrane. Keep
an eye on temperature though (It should preferably not exceed 55 °C).
3.3.2 Preparation of Dispersed Phase
1. Take a small vial 10 ml in volume. Pour 2 grams of NMP in the bottle along with the
modified filler according to the % concentration with respect to the dry polymer weight.
2. Sonicate the mixture for 5 hours straight.
3.3.3 Making Casting Solutions of Varying Filler Concentration
1. Pour 5 grams of the polymer mother solution into the vial containing the sonicated
dispersed phase. This reduces the weight percent from 30 % to 22 %. This is our casting
solution which we shall use to cast the membranes of varying filler concentration i.e.
1, 3 and 5 %.
Figure 3.3-1 Polymer Solutions with Varying
Concentration of Filler

38
3.3.4 Asymmetric Membrane Preparation
1. Cast the casting solution on glass plate using a doctor blade. Pour some casting solution
on the glass plate in a horizontal line and spread it using the blade at a thickness of 120
µm. Make sure to pour some acetone on the blade and clean it before the operation.
Pour some acetone below the glass plate too so that it sticks and does not move.
2. After making the cast wait for 1 minutes and put the glass plate it in the inversion vessel
which contains distilled water. Please note that the glass plate must be lowered in the
vessel in a very gentle/careful manner. Make sure that solution spread meets the
antisolvent at the same time. Let it remain in the distilled water for 1 night.
3. Now place the membrane in methanol. This is done so that the methanol can seep into
the membrane and mix with water so that when we place the membrane in the vacuum
oven methanol takes the excess water along with it.
4. Now place the membrane in vacuum oven under 10 mm Hg vacuum at 65 °C overnight.
Note: Keep replacing the distilled water in our inversion vessel however we will not
replace methanol often.
3.3.5 Dense Membrane Preparation
1. Cast the casting solution on glass plate using a doctor blade. Pour some casting solution
on the glass plate in a horizontal line and spread it using the blade at a thickness of 120
µm. Make sure to pour some acetone on the blade and clean it before the operation.
Pour some acetone below the glass plate too so that it sticks and does not move.
2. Now place the membrane in vacuum oven under 10 mm Hg vacuum at 65 °C for 1 hour.
3.4 Membrane Characterization
Characterization is performed in order to assess the characteristics of a material; this
helps in the justification of material’s behavior as well as assessment of a its potential
applications. Membrane users (researchers, academics and commercial) need information of
membrane characteristics in order to choose the right membrane against their potential purpose.
Therefore, characterization is important in order to relate membrane’s structural properties
such as pore size and pore size distribution to membrane separation properties as well as
gauging it thermal and mechanical perseverance [24]. Some of the important characteristics
of membranes include.

39
1. Mass Transport of Membrane
2. Membrane Morphology
3. Physical Properties Such as Mechanical and Thermal Stability
Furthermore, characterization allows us in maintaining quality and control in industrial
settings as well as improving previous benchmark characteristics further via research and
development. For example, we can improve the casting technique or conditions thereby
increasing mass transport through the membrane. Ideally a characterization technique is
nondestructive, provides accurate results in a short period of time and is repeatable. Well
established protocols have been established in order to characterize membranes for gas
separation which are discussed in this section.
1
Polymer Solvent
2
Filler Solvent
Casting
Solution
Polymer
Solution
Filler
Suspension
Glass Plate
Cast
Knife
Move
Polymer
Solution
Coagulation Bath
24Hours
Asymmetric
Membrane
Characterization
60°Cfor2Hours
Dense Membrane
Route
Gas Permeation Testing + SEM
+ TGA + UTM
Asymmetric Membrane
Route
Figure 3.4-1 Membrane Synthesis Graphical Procedure

40
3.4.1 Mass Transport
Permeability is the ability of the separation interface (membrane) to allow gases such
as O2, N2, CO2 etc. through in a specific time period. Assessing the mass transport of a
membrane material and relating it to the polymer used to synthesize the membrane is crucial
in designing the future appropriate materials for required permeabilities. It is not uncommon
for the rate of gas transport through polymer interfaces (membranes) to differ by several orders
of magnitude. Characterization of gas transport properties of membrane comprises working out
the following gas transport attributes.
1. Permeability
2. Diffusion
3. Solubility Coefficient
Several techniques exist in order to calculate the gas transport of membrane material.
Two of these techniques i.e. variable volume and variable pressure technique have become the
standard [25]. In the variable pressure method, a constant gas pressure is applied to one side of
the membrane in a vacuumed permeability cell and increase in pressure vis a vis time is
evaluated for gas permeation calculation. While in the variable volume method a constant
pressure is applied to one side of the membrane whilst the opposite side is at room pressure.
The volumetric flow rate of the gas is then conveniently measured by timing the upward
movement of a liquid column in a capillary. This liquid can be an alcohol or a ketone.
The permeability apparatus we have available in the polymer engineering department
is called as the (CSI-135) permeability apparatus. It is based on the variable volume working
principle. In this type of apparatus, the membrane is exposed to the atmosphere unlike variable
pressure type where the permeate flow is measured via volumetric flow meter. Complete
working of the apparatus employing the variable volume method is provided in Section 3.4.6
of this thesis.
3.4.2 Membrane Morphology
There are many techniques developed for characterizing the membrane morphology
however we shall only go through the techniques that are readily available. There are several
methods that can be used to assess the morphology of the membrane, these include but are not
limited to the bubble point method, mercury intrusion porometry, gas adsorption-desorption,
thermo porometry, liquid displacement etc. [24]. However, our focus shall be the microscopic
methods since method are suitable for both porous as well as non-porous (dense) membrane.

41
Assessment of morphology of a membrane is extremely crucial since separation property of
membranes especially asymmetric membrane and thin film composite membrane is essentially
highly dependent on surface phenomena.
As stated earlier a great deal of membrane transport happens on the surface of the
membrane making the study of morphology of membrane highly crucial. Primarily three main
microscopic methods can be utilized to research membrane surface or cross-sectional
morphology, these include; AFM, SEM and TEM.
Atomic force microscopy was invented by Gerd Binnig. Through this technique we can
observe surfaces down to atomic level even under ambient conditions. A sharp tip on a
cantilever’s end scans the surface of the specimen. When placed close to the surface of a sample
the cantilever faces deflection owing to the forces between the tip and the sample surface. A
laser spot is used to measure the said deflection. The forces causing the deflection of the
cantilever are measured in the three axes and the piezoelectric decoder creates graphical
representation of the surface.
6mm Tubing
Primary Gas
Regulator
Membrane Module
Gas
Cylinder
Secondary Gas
Regulator
Volumetric Flow
Measuring Device
Flexible
Connection
P1 P2
P3
DAQ
Figure 3.4-2 Permeability Apparatus PFD

42
Electron Microscopy can be further divided into two main techniques; Scanning
Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Amongst these
two the scanning electron microscopy is comparatively convenient, cheaper and readily
available method for analysis of surface and cross-sectional morphology of porous as well as
dense membranes. It also offers basic analysis of species existing in the membrane sample. An
average scanning electron microscope has the resolution limit in the 10 nm range. More
sophisticated microscopes may possess a resolution limit of 5 nm.
In a SEM, a narrow emission of high energy electrons (ranging from 1-25 kV) is
bombarded on the membrane sample. These are called as the primary electrons and they are
high in energy while on the other hand the electrons reflected are called as the secondary
electrons. Keep in mind that when a membrane sample is placed in the way of high energy or
primary electrons it could burn or deteriorate which depends on the voltage and materials
employed for membrane synthesis. In order to avoid this, samples are coated with a thin layer
of gold to avoid charge build-up on the membrane surface. Using this technique not only can
we can study the cross section but also the surface morphology of the top and bottom of the
membrane specimen. We can also determine important characteristics such as pore size, pore
size distribution and surface porosity to be obtained.
Figure 3.4-3 Cracking Membrane Sample in Liquid N2

43
3.4.3 Thermal Properties
It is often that we employ membranes at higher temperature especially in the case of
gas separations or when membranes are used as catalysts as well as separation interfaces in
membrane reactors. This leads to an irreversible decomposition or degradation of the polymer
matrix. Chemically this means the cleavage of covalent bonds present in the polymer chains or
side chains. A measure of extent of such change in the amorphous polymers is the glass
transition temperature (Tg) while for the crystalline polymer it is the melting point (Tm). It is
therefore pertinent that we assess the thermal stability of our membranes [24].
Table 3.4-1 Polymers and their Glass Transition Temperature
Polymer Glass Transition Temp. (°C) [26, 27, 28]
Polyvinyl Acetate (PVAc) 35
PDMS -123
Polyimide (PI) 300
Polyvinyl Chloride (PVC) 80
Poly (vinyl chloride-co-vinyl acetate) 58-75 [28]
Sone of the techniques that can be used to ascertain the change on the sample with
temperature change are differential scanning calorimetry or DSC, differential thermal analysis
DTA and thermogravimetric analysis or TGA for short.
DSC and DTA are similar techniques used to assess the heat uptake or release as well
as temperature difference between a sample in comparison with a reference specimen going
through heating and/or cooling cycles. This is done in order to determine the transitions and
chemical changes in the polymeric specimen. Similar temperatures are maintained for both the
sample and the reference throughout the procedure. The difference between the quantity of
heat energy needed to increment the temperature of sample being assessed as well as the
reference is calculated as a function of their temperature.
In short using DSC we can measure how physical properties of a sample may change
along with temperature against time. It measures the quantity of heat discharged or absorbed
by the sample based on the difference in temperature between the sample and the reference.
Curves obtained from DSC analysis are particularly useful when monitoring phase transitions
in polymers such as the glass transition temperature as well as the degree of crystallinity of the
polymer.

44
Thermogravimetric Analysis can be utilized to assess the thermal stability of the
membrane. In this method we measure the weight loss of the membrane sample w.r.t
temperature. For the thermogravimetric analysis membrane samples are first freeze-dried and
crumpled into bits using liquid N2. This is then followed by taking approximately 5.0 milli
grams of sample and heating it from 40 to 800 °C at 10 °C per minute under nitrogen or helium
induced inert conditions.
3.4.4 Mechanical Properties
One of the important indicators of the mechanical strength of a material is its tensile
strength. It is one of the most widely used properties of a material regarding structural
applications. It deals with the physical effects (deformation) on the material upon an applied
force also called as stress. In the case of membranes, it is important to assess their mechanical
properties since they tend to become brittle over time thus causing loss of structural integrity.
This is especially true for self-supporting membranes such as hollow fibers and capillary
membranes. Formally defined the force per unit area required to break material is called as its
ultimate tensile strength.
𝑠𝑡𝑟𝑒𝑠𝑠(𝜎) =
𝐹𝑜𝑟𝑐𝑒
𝐴𝑟𝑒𝑎
=
𝐹
𝐴
3.1
𝑠𝑡𝑟𝑎𝑖𝑛(𝜀) =
𝐶ℎ𝑎𝑛𝑔𝑒 𝐼𝑛 𝐿𝑒𝑛𝑔𝑡ℎ
𝑂𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝐿𝑒𝑛𝑔𝑡ℎ
=
𝛿
𝐿
3.2
However, before calculating the tensile strength of membranes one must work out the
stresses & strains the membrane might have to face in its application i.e. gas separation. After
appropriate assessment and sample preparation the membrane is exposed to stress testing. The
material is pulled upon from both top and bottom, it elongates under the strain applied and after
a certain point it breaks. The apparatus is shown in the Figure 3.4-4, reaction of the membrane
sample to the applied stress in the form of strain is shown by a curve. Standard test method and
the equipment for stress testing of plastics is specified is specified in ASTM D 638-77. The
point at which the membrane sample breaks or snaps due to the resultant stress and the
elongation that occurs is the actual point of interest of the study. Elongation at break or EAB
for short is the capacity of the specimen to stretch before breaking. It is an indicator of
membrane plasticity or extensibility which is generally required for preservation of structural
integrity [29]. A standard used commonly for the tensile strength testing of polymer films is
the ASTM D 882.

45
Apart from the above-mentioned analytical techniques another analysis method used
rather frequently during this project is the FTIR. The details for which are presented below.
3.4.5 Fourier Transform Infrared Spectroscopy
FTIR can provide insight into the composition and configuration of functional groups
within the sample chemical structure, this stands true not only for the organic polymer but also
the inorganic part. It works on the principle that specific wavelengths of infrared radiation
excite a specific group of atoms within the atomic structure of a material. This can be used not
only to determine the composition as stated earlier it can also help determine impurities in the
membrane materials which could either be solvent or apart from that. It is easier as compared
to other analytical techniques and consumes less time. Infrared measurements were performed
on the IR Prestige-21, Shimadzu, Japan. Background corrections were performed first and then
specimen measurements were taken in the infrared region (4000-400 cm-1
).
3.4.6 Gas Separation Measurements
Before we start with permeability calculation steps let us first discuss permeance and
permeability concepts. During the project we designed a module to work with smaller diameter
membranes. Rest of the apparatus remained the same. Using the new module, we checked the
permeability of the following gases through our membranes CO2, N2 and O2 at pressures
ranging from 10 psi to 40 psi at ambient temperatures. Procedure to conduct the experiments
is provided in the “Experimentation” chapter of the thesis. Here permeability and selectivity of
Base
Ductile and Tough
Stress(MPa)
Strain (%)
Hard and Tough
Hard and Brittle
σγ
εγ
Elongation at Break
Test Speciman
Adjustable
Lower Cross
Head
Wedge Grips
Adjustable
Upper Cross
Head
Screw Column
Control Panel
Figure 3.4-4 Tensile Testing Machine

46
the synthesized membranes is given. ASTM standard D 1434 deals with the calculation of gas
permeability characteristics of thin polymer films [30].
1. Membrane of area 14.64 cm2
is cut from the casted films. It is then placed on
perforated stainless-steel ring(s) and filter paper(s). Support and mount the
membrane along with the supports in a permeability module that looks like a flange
and seal it with rubber O-rings.
2. Now open the main cylinder supply using a key and check the primary pressure gauge
of the cylinder. A gas pressure is maintained and valves supplying gas to the
permeability module were opened. Initially the vent was opened for half a minute so
that any residue gas could escape. It is to be noted that gas mixtures were not used
during these experiments.
3. After the vent was closed, we can observe the pressure rise from the gauge built inside
the permeability apparatus.
4. Module was checked for any major leaks before proceeding.
5. Attach the permeability module to a glass capillary filled with fluid or connect it to a
bubble flow meter depending. Both (capillary and the bubble flow meter) are used to
measure the volumetric flow rate of the feed gas. Now depending on the permeability
of the gas and on the type of membrane (asymmetric or dense) one can either use the
glass capillary with fluid inside or bubble flow meters for measuring volumetric flow
rate.
6. Once the volumetric flow rate is known we can start plugging the values in the
permeability formula to get our permeability.
𝑄 = 𝑉𝑜𝑙𝑢𝑚𝑒𝑟𝑡𝑟𝑖𝑐 𝐹𝑙𝑜𝑤 𝑅𝑎𝑡𝑒 (
𝑐𝑚3
𝑠𝑒𝑐
) 3.3
Where,
𝐴 = 𝑀𝑒𝑚𝑏𝑟𝑎𝑛𝑒 𝐴𝑟𝑒𝑎 (𝑐𝑚2
)
𝑃 = 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑡𝑖𝑎𝑙 (𝑐𝑚𝐻𝑔)
𝑙 = 𝑀𝑒𝑚𝑏𝑟𝑎𝑛𝑒 𝑇ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠 (𝑐𝑚)
𝑝 = 𝑃𝑒𝑟𝑚𝑒𝑎𝑏𝑖𝑙𝑖𝑡𝑦

47
Equation 3.4 can be used to find permeability of the gas separation membrane while
Equation 3.5 can be used to find the ideal selectivity.
𝑝 =
𝑄
𝑃 ∗ 𝐴
∗ 𝑙 3.4
𝛼 𝐴
𝐵
=
𝑃𝐴
𝑃𝐵
3.5
To Bubble Flow Meter / Glass CapillaryO-Ring
Vent
Valve (Usually Closed During Operation)
Holes For Screws
Membrane
Feed Gas Inlet
4.318 cm
Figure 3.4-5 Permeability Module

48
Chapter 4. RESULTS & DISCUSSION

49
This chapter encloses findings of morphological, thermal and mechanical
characterization of polymer films (both pure and mixed matrix) synthesized during the research
project. These thin films are used as gas separation membranes. Regarding the inorganic
component only surface modification of the filler via FTIR is discussed in order to determine
the extent of silane assisted modification. Most importantly the gas permeation data obtained
during the permeation testing are provided and useful inferences are made. These include the
gas permeation testing of the pure and MMMs (effect of pressure and filler loading on gas
permeability is discussed). This is because for gas separation applications parameters other
than permeability and selectivity also play an important role. Reason behind this is the presence
of high pressure and temperature conditions observed in gaseous separations in the industry.
Therefore, materials from which membrane are synthesized ought to be mechanically and
thermally sound, resilient to plasticization and membrane fouling to warrant continued
performance over longer time periods. Conclusions and future recommendations based on
these results are specified in the next chapter
4.1 FTIR Characterization
FTIR is a technique which provides us information about the presence of specific
functional groups in a specimen’s chemical structure. In the context of membrane analysis, we
can also utilize FTIR to gain information about the presence of solvent impurity as well as any
side products formed during membrane fabrication. It utilizes infrared radiation which causes
motion in the sample’s functional groups when a specific wavelength radiation is absorbed by
the sample. Infrared studies were performed in order to assess the functionalization of the filler.
FTIR of sepiolite is provided in the following sections. The FTIR gives clear indication
regarding presence of alkyl groups on the sepiolite.
4.1.1 Functionalized Sepiolite Clay
FTIR spectra of sepiolite and its modified form are shown in Figure 4.1-2. Results show
the O-H distinctive bands in the region of (3700-3300 cm-1
) and (800– 650 cm-1
). These
potentially point towards moisture. The stretching vibration of Si-O appeared at 1210, 1008,
976 cm-1
while its bending vibration at 460 cm-1
. The Si-O-Mg band is observed at 440 cm-1
.
Modified sepiolite spectrum also exhibited new bands linked to C-H group at 2970, 2930, and

50
1391 cm-1
verifying the grafting of silane groups onto sepiolite thus making it modified
sepiolite or MS.
4.2 Morphology / Electron Microscopy
Electron microscopy was performed in order to analyze the morphology of the
synthesized membranes. Cross sections of the membranes were observed after cryogenic
fracture and gold plating of the respective specimen. Samples were placed the under the
microscope and observed at various resolutions. Owing to their greater utility morphology
studies of only asymmetric membranes were performed. Cross sectional morphologies of the
microporous membrane were studied by FE-SEM (Inspect S50 Thermoscientific, USA).
4.2.1 Pure PVCA Asymmetric Membrane
Figure 4.2-1 at 5000x indicates a highly porous structure with interconnected voids.
Finger like pores start from the surface of the membrane giving rise to the asymmetric structure
of the membrane. This Indicates the potential for higher permeability while the membrane
grows dense in the opposite direction. This means this membrane has the potential to provide
very high permeability values along with some decent selectivity. Membrane has an anisotropic
or asymmetric structure and can be classified as such. According to [3] Knudsen separation can
be achieved with membranes having pore sizes smaller than 50 nm. From Figure 4.2-1 it is
5001000150020002500300035004000
60
70
80
90
100
110
120
Wavenumber (cm-1)
Transmittance(%)
Modified Sepiolite
Sepiolite
-OH
C-H
Si-O
Si-O-Mg
Figure 4.1-1 Sepiolite FTIR

51
evident that the pore size is smaller than 50 nm, so it is safe to say that the transport mechanism
is Knudsen diffusion which also correlates with the separation factor provided in the reference
as our selectivity is slightly below it. Hence, we can say that an asymmetric membrane made
from PVCA will work on the principle of Knudsen diffusion.
4.3 Gas Separation Ability of Synthesized Membrane
Gas separation ability of the membrane was determined using state of the art
permeability testing apparatus called as “CSI 135”. Permeation testing of pure gases CO2, O2
and N2 was performed using the afore mentioned apparatus. Owing to the safety concerns, high
pressures were not explored rather the experiments were limited to 2.72 bar max. Experiments
were performed with pressure was varied from 10 psi to 40 psi (with 10 psi intervals) at a room
temperature of 25 °C. Permeability and ideal selectivity values are calculated using Equation
3.2 and Equation 3.3 respectively. The data is presented in the form of a bar chart with each
bar signifying the permeability of a single pure gas. Selectivity data is presented in simple
tabular form with numerical values. However, one can also assess the selectivity of the
membrane by eyeing the difference in the height of the bars.
4.4 Gas Permeation Data of Asymmetric Membranes
Asymmetric membranes were synthesized in the thickness range of 50-60 µm.
Synthesis procedure is discussed in the Section 3.34. According to the SEM micrograph in the
Figure 4.2-1 Cross Section of Pure PVCA Asymmetric Membrane Using SEM

52
previous sections it can be concluded that the synthesized membrane can be classified as a
microporous membrane [3]. The following section details not only the gas permeation data but
also discuss in detail the effect of change in operating pressure on the permeability of the
membranes. It is to be noted here that due to the high permeabilities obtained with the
asymmetric membranes as well as safety concerns the measurements were made at relatively
low pressures.
4.4.1 Pure PVCA Asymmetric Membrane
Figure 4.4-1 shows the effect on permeability of pure gases cause by an increase in
pressure. It is observed that there is a slight increase in permeability of the gases by an increase
in the pressure. Selectivity of the pure asymmetric PVCA membranes is provided in Table 4.4-
1 below. With increasing pressure, the selectivity decreases indicating that process is driven by
the pressure gradient. As the gradient increases so does the permeability of the gases through
the membrane. Porous structure of the membrane is detailed in Section 4.2. The order of
permeance is as follows PCO2>PO2>PN2. A slight increase in permeability of the membrane is
observed as a result of pressure increase hinting that the gas flow takes place via viscous flow
and Knudsen diffusion.
10 15 20 25 30 35 40
40
60
80
100
120
140
160
180
200
Pure Assymetric Membrane
Pemeability(Barrer)
Pressure (PSI)
CO2
N2
O2
Figure 4.4-1 Gas Permeation of Pure PVCA Asymmetric Membrane

53
Table 4.4-1 Ideal selectivity of Pure Asymmetric PVCA Membranes
Pressure (psi) CO2/N2 CO2/O2
10 3.06 2.36
20 2.84 2.36
30 2.58 2.33
40 2.52 2.07
4.4.2 PVCA Asymmetric Membrane with 1% Modified Sepiolite
Figure 4.4-2 shows the correlation between pressure and permeability for PVCA
asymmetric membrane with 1 % MS It can be observed that the increase in permeability is
much greater as compared to the pure asymmetric membrane. Selectivity of the asymmetric
PVCA membrane with 1 % sepiolite is provided in Table 4.4-2 below. An increase in
selectivity is observed which could mean the proper interfacial compatibility between the
polymer and the filler. The order of the permeability remains the same i.e. PCO2>PO2>PN2.
Table 4.4-2 Ideal selectivity of Asymmetric PVCA MMM with 1% MS
10 1.38 1.24
20 1.44 1.31
10 15 20 25 30 35 40
440
480
520
560
600
640
680
720
760
Assymetric Membrane w/ 1% Sepiolite
Permeability(Barrer)
Pressure (PSI)
CO2
N2
O2
Figure 4.4-2 Gas Permeation of PVCA Asymmetric Membrane with 1% MS

54
30 1.48 1.32
40 1.53 1.37
Ideal selectivity of CO2 w.r.t other gases through the asymmetric PVCA membrane
with 3 % sepiolite is provided in the Table 4.4-3 below. Decreasing selectivity points towards
an incompatibility of the polymer matrix with the particulate. However, the order of the
permeability remains pretty much the same i.e. PCO2>PO2>PN2. The decrease in selectivity could
be due to the needle like spatial configuration of the sepiolite particles responsible for
disrupting the matrix.
10 1.38 1.13
20 1.23 1.14
30 1.16 1.12
40 1.06 1.03
10 15 20 25 30 35 40
900
1000
1100
1200
1300
1400
1500
1600
Assymetric Membrane w/ 3% SepiolitePermeability(Barrer)
Pressure (PSI)
CO2
N2
O2

55
Selectivity of the PVCA membranes with 5 % modified sepiolite is provided in the
Table 4.4-4 below. The order of permeability was changed as compared to the previous cases.
Another noteworthy observation is that except for pure and 1% MS asymmetric membranes
rest of the asymmetric membranes show less ideal selectivity is the face of a pressure increase.
10 1.10 1.13
20 1.10 1.15
30 1.04 1.04
40 1.03 1.02
4.5 Gas Permeation Data of Dense Membranes
Dense PVCA membranes were synthesized in the thickness range of 25-35 µm.
Synthesis procedure for the dense membranes is discussed in the Section 3.35 of this research
thesis. Permeability of the dense PVCA membranes for pure gases (CO2, N2 and O2) is provided
below for both pure and mixed matrix specimen at respective pressures ranging from 10 to 40
10 15 20 25 30 35 40
1600
1650
1700
1750
1800
1850
1900
1950
2000
Assymetric Membrane w/ 5% Sepiolite
Pressure (PSI)
CO2
N2
O2

56
psi. Meanwhile the effect of pressure on permeability is also studied. Units of the permeability
coefficient are in Barrer.
4.5.1 Pure PVCA Dense membrane
Figure 4.5-1 shows the downward trend of CO2 permeability with increasing pressure
as with the other gases. CO2 follows a dual-mode of sorption at higher pressures in glassy
polymers which leads to such behavior. This data when compared to the selectivity values of
pure PVAc membrane (8 bar, 30 °C) provided in [31] shows that in the case of dense membrane
the selectivity increases with the pressure. The order of permeability is PCO2>PO2>PN2.
Table 4.5-1 Ideal selectivity of Pure Dense PVCA Membranes
10 1.18 1.03
20 1.12 1.14
30 1.15 1.19
40 1.19 1.23
10 15 20 25 30 35 40
35
40
45
50
55
60
65
70
75
80
Pure Dense Membrane
Pressure (PSI)
CO2
O2
N2
Figure 4.5-1 Gas Permeation of Pure Dense PVCA Membrane

57
4.5.2 PVCA Dense membrane with 1 % Modified Sepiolite
It can be seen in Table 4.5-2 that the selectivity increases with pressure. Order of
permeability is PCO2>PO2>PN2. The relatively low permeability and the higher glass transition
temperatures of the membrane materials (see Appendix-A1) confirm the rigid structure of the
polymer.
Table 4.5-2 Ideal selectivity of Dense PVCA MMM with 1% MS
10 1.44 1.79
20 1.51 1.94
30 1.39 1.93
40 1.50 1.95
10 15 20 25 30 35 40
10
20
30
40
50
60
70
80
Dense Membrane w/ 1% Modified Sepiolite
Pressure (PSI)
CO2
O2
N2
Figure 4.5-2 Gas Permeation of Dense PVCA MMM with 1% MS

58
4.5.3 PVCA Dense membrane with 3 % Modified Sepiolite
Looking at Table 4.5-3 as the loading of MS increases, membrane permeability declines
for all three gases N2, O2, and CO2 with a corresponding rise in the selectivity. The order of
permeability is PCO2>PO2>PN2.
Table 4.5-3 Ideal selectivity of Dense PVCA MMM with 3% MS
10 2.72 3.92
20 2.70 3.93
30 2.78 3.98
40 2.82 4.36
10 15 20 25 30 35 40
20
40
60
80
Dense Membrane w/ 3% Modified Sepiolite
Pressure (PSI)
CO2
O2
N2
Figure 4.5-3 Gas Permeation of Dense PVCA MMM with 3% MS

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