i

DEVELOPMENT OF POLYSULFONE-

POLYDIMETHYLSILOXANE (PSf-PDMS) THIN FILM

COMPOSITE (TFC) MEMBRANE FOR CO2/ N2 GAS SEPARATION

NUR ATIKAH BINTI CHE EMBEE

A thesis submitted to the Faculty of Chemical and Natural Resources Engineering in

partial fulfillment of the requirement for the Degree of Bachelor of Engineering in

Chemical Engineering (Gas Technology)

Faculty of Chemical and Natural Resources Engineering

Universiti Malaysia Pahang

FEBRUARY 2013

vi

DEVELOPMENT OF POLYSULFONE-POLYDIMETHYLSILOXANE

(PSf-PDMS) THIN FILM COMPOSITE (TFC) MEMBRANE FOR

CO2/ N2 GAS SEPARATION

ABSTRACT

The capture and storage of carbon dioxide has been identified as one potential

solution to greenhouse gas driven climate change. Efficient separation technologies

are required for removal of carbon dioxide from flue gas streams to allow this

solution to be widely implemented. This study is mainly focusing on the effect of

different concentration of PDMS in dip-coating solution on the membrane’s

performance. The asymmetric thin flat sheet membrane was prepared by dry/ wet

phase inversion process consisting 20 wt% of polysulfone (PSf) as the support layer

polymer and 80 wt% of N-methyl-2-pyrrolidone (NMP) as the solvent. PDMS was

coated on the support PSf membrane with the composition of 10, 15 and 20 wt% of

PSf in n-hexane respectively. The characterization of morphology of TFC membrane

will be conducted by using Scanning Electron Microscopy (SEM) and Fourier

Transform Infrared Radiation (FTIR). The membrane’s performance and the

selectivity of CO2/N2 separation will be determined by conducting gas permeation

test. The result obtained, show that membrane with highest concentration of PDMS

in dip-coating solution give a highest performance in selectivity and unfortunately it

contribute to lower permeability. It is vice versa from the membrane without PDMS

in the top layer which gives highest value of permeability but lowest in selectivity.

From the characterization and permeation test of the membrane, hereby the

membrane with highest percentage of PDMS should be selected for the future

development of membrane due to its highest value of selectivity which contributes to

highest efficiency in separating the gas.

vii

PENGHASILAN POLISULFON-POLIDIMETILSILOKSAN

(PSf-PDMS) KOMPOSIT FILEM NIPIS (TFC) MEMBRAN UNTUK

PENGASINGAN GAS CO2/ N2

ABSTRAK

Penangkapan dan penyimpanan karbon dioksida telah dikenal pasti berpotensi

untuk penyelesaian gas rumah hijau yang didorong oleh perubahan iklim. Teknologi

pemisahan yang cekap diperlukan untuk penyingkiran karbon dioksida daripada

serombong aliran gas untuk membolehkan penyelesaian ini dapat dilaksanakan

secara meluas. Kajian ini memberi tumpuan kepada kesan kepelbagaian kepekatan

PDMS dalam larutan lapisan atas pada prestasi membran. Simetri nipis lembaran rata

membran telah disediakan melalui proses fasa balikan kering/ basah yang terdiri

20 wt% polysulfon (PSf) sebagai polimer lapisan sokongan dan 80 wt% N-methyl-2-

pyrrolidone (NMP) sebagai pelarut. PDMS telah disalut pada setiap membran

sokongan dengan komposisi 10, 15 dan 20 % dalam n-heksana. Pencirian morfologi

membran TFC akan dijalankan dengan menggunakan Imbasan Electron Microscopy

(SEM) dan Sinaran Inframerah Transformasi Fourier (FTIR). Prestasi membran iaitu

kepilihan pemisahan gas CO2/N2 akan ditentukan dengan menjalankan ujian

penyerapan gas. Berdasarkan keputusan yang diperolehi, ia menunjukkan bahawa

membran dengan kepekatan tertinggi PDMS dalam larutan lapisan atas memberikan

prestasi tertinggi dalam selektiviti dan malangnya ia menyumbang kepada

kebolehtelapan yang rendah. Ia adalah sebaliknya dari membran tanpa PDMS di

lapisan atas yang memberikan nilai tertinggi kebolehtelapan tetapi terendah pada

nilai selektiviti. Dari ujian pencirian dan penyerapan membran, dengan ini membran

dengan peratusan tertinggi PDMS perlu dipilih untuk penyediaan membran pada

masa hadapan kerana nilai tertinggi selektiviti yang menyumbang kepada kecekapan

tertinggi dalam mengasingkan gas.

viii

TABLE OF CONTENT

SUPERVISOR’S DECLARATION ii

STUDENT’S DECLARATION iii

DEDICATION iv

ACKNOWLEDGEMENT v

ABSTRACT vi

ABSTRAK vii

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF EQUATION xiv

LIST OF ABBREVIATIONS xv

LIST OF SYMBOLS xvi

CHAPTER 1 INTRODUCTION

1.1 Background 1

1.2 Problem Statement 3

1.3 Research Objectives 4

1.4 Scope of Research Proposed 5

1.5 Rationale and Significance 5

CHAPTER 2 LITERATURE REVIEW

2.1 Background Study of the Membranes 7

2.1.1 Definition of Membranes 9

2.1.2 Fundamental of Membrane Gas Separation 9

2.1.3 Classification of Membrane Process 10

2.1.4 Classification of Membrane 11

2.2 Materials for Polymeric Membranes 14

2.2.1 Polymer Selection Criteria 15

2.2.2 Type of Polymeric Material 15

2.2.2.1 Polysulfone (PSf) 15

2.2.2.2 General Properties of PSf 16

2.2.2.3 Polydimethylsiloxane (PDMS) 18

2.2.2.4 General Properties of PDMS 19

ix

2.3 Manufacturing Process 19

2.3.1 Dry Process 20

2.3.2 Wet Process 20

2.3.3 Dry/ Wet Process 21

2.4 Membrane Separation Technology 22

2.4.1 Types of Membranes 22

2.4.1.1 Porous Membranes 23

2.4.1.2 Non-Porous Membranes 24

2.4.2 Application of Membranes 26

2.4.2.1 Gas Separation 26

2.4.2.2 Carbon Capture 29

2.4.3 Advantages and Disadvantages of the Membranes 30

2.5 Membrane Processes and Separation Mechanisms 33

CHAPTER 3 METHODOLOGY

3.1 Research Design 35

3.2 Material Selection 37

3.2.1 Polymer Selection 37

3.2.1.1 Polysulfone (PSf) 37

3.2.2 Solvent Selection 38

3.2.2.1 N-Methyl-2-Pyrrolidone (NMP) 38

3.2.3 Coagulation Medium 38

3.2.3.1 Water (H2O) 38

3.2.4 Coating Solution 39

3.2.4.1 Polydimethylsiloxane (PDMS) 39

3.2.4.2 n-Hexane 39

3.3 Dope Solution Preparation 39

3.4 Asymmetric Flat Sheet Membrane Film Formation 42

3.5 Composite Membrane Preparation 42

3.6 Gas Permeation Test 43

3.7 Membrane Characterization 46

3.7.1 Scanning Electron Microscopy (SEM) 46

3.7.2 Fourier Transform Infrared Radiation (FTIR) 47

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CHAPTER 4 RESULTS & DISCUSSIONS

4.1 Membranes Characterization 48

4.1.1 Effect of Dip-Coating Percentage on the 48

Membrane Morphology

4.1.2 Effect of Concentration of Top Layer on the 53

FTIR Analysis of Membrane

4.1.2.1 FTIR Theory 53

4.1.2.2 FTIR Characterization 54

4.2 Gas Permeation Test 58

4.2.1 Effect of Concentration of Selective Top Layer 58

on the Membrane Performance for Gas Separation

CHAPTER 5 CONCLUSIONS & RECOMMENDATIONS

5.1 Conclusions 65

5.2 Recommendations 66

REFERENCES 68

APPENDICES 74

xi

LIST OF TABLES

PAGE

Table 2.1 Size of Material Retained, Driving Force and Type of

Membrane for Various Membrane Separation Processes

13

Table 2.2 Driving Force and Their Related Membrane Separation

Processes

28

Table 2.3 Advantages and Disadvantages of Using Membrane in Gas

Separation

31

Table 2.4 Classification of Membranes and Membrane Processes for

Separations via Passive Transport

34

Table 4.1 Gas Permeance and Selectivity for PDMS Based Polysulfone

Membranes

59

xii

LIST OF FIGURES

Figure 2.1 A Schematic Representation of a Simple Membrane Process 8

Figure 2.2 Dead-end and Cross-flow Filtration Process 11

Figure 2.3 Pore Diameter Based on Different Type of Membrane

Process

12

Figure 2.4 Molecular Structure of PSf 17

Figure 2.5 Molecular Structure of PDMS 19

Figure 2.6 Schematic Diagram of Dry, Wet and Dry/ Wet Process 22

Figure 2.7 Membrane Classifications 25

Figure 2.8 Basic Principle of Membrane Separation 26

Figure 2.9 Relevant Parameters of a Single-Stage Membrane Process. 28

Figure 3.1 Research Design Flow Chart 36

Figure 3.2 Dope Solution Preparation Set Up 41

Figure 3.3 Gas Permeation Test Apparatus 44

Figure 3.4 A Cross-Sectional View of Assembled Permeation cell and

Gas Flow Direction

44

Figure 4.1 SEM images of PSf pure membrane and PDMS/ PSf

composite membrane

51

Figure 4.2 Schematic of FTIR during Operation 54

Figure 4.3 FTIR Absorbance Peak for 0% PDMS of PDMS–PSf

Membrane

56

Figure 4.4 FTIR Absorbance Peak for 10% PDMS of PDMS-PSf

Membrane

56

Figure 4.5 FTIR Absorbance Peak for 15% PDMS of PDMS–PSf

Membrane

57

Figure 4.6 FTIR Absorbance Peak for 20% PDMS of PDMS–PSf

Membrane

57

Figure 4.7 Graph of CO2/ N2 Selectivity against Feed Pressure 63

Figure 4.8 Graph of CO2 Permeability against Feed Pressure 63

Figure 4.9 Graph of N2 Permeability against Feed Pressure 64

Figure A.1 Dope Solution Preparation 74

Figure A.2 Membrane Casting Process 74

Figure A.3 Dip-Coating Process 75

xiii

Figure A.4 Scanning Electron Microscopy (SEM) 75

Figure A.5 Fourier Transform Infrared Radiation (FTIR) 76

Figure A.6 Gas Permeation Test 76

xiv

LIST OF EQUATION

PAGE

Equation 3.1 Permeation rate 45

Equation 3.2 Permeance 45

Equation 3.3 Conversion to GPU 45

Equation 3.4 Selectivity 46

xv

LIST OF ABBREVIATIONS

CH4 - Methane gas

CO2 - Carbon dioxide

FTIR - Fourier Transform Infrared Radiation

H2O -Water

HMWC - High Molecular Weight Component

LMWC - Low Molecular Weight Component

MF - Microfiltration

N2 - Nitrogen

NF - Nanofiltration

NMP - N-Methyl-2-Pyrrolidone

PDMS - Polydimethylsiloxane

PSf - Polysulfone

RO - Reverse Osmosis

SEM - Scanning Electron Microscopy

TFC - Thin Film Composite

UF -Ultrafiltration

xvi

LIST OF SYMBOLS

°C - Degree Celcius

min - minute

% - Percentage

ppm - Part per million

mm - milimeter

1

CHAPTER 1

INTRODUCTION

This chapter will give the ideas about the significant of the research formulation.

The first chapter will cover up the subtopic of background of study or information,

problem statement, research objectives, scope of proposed research, expected outcomes

and significant of the proposed research.

1.1 Background

Enhancements of the greenhouse effect in the worldwide have contributed to the

study that can recover this problem. The most abundant greenhouse gas CO2 has risen

from preindustrial levels of 280 parts per million (ppm) to present levels of over 365

ppm (Dantas et al, 2011). Carbon dioxide, CO2 arise from different emission sources,

particularly flue gas from power stations, steel works and chemical industries.

According to the study done by Mitsubishi Heavy Industries, Ltd., 98% of CO2

emissions are derived from fossil fuel combustion, exhausted to atmosphere by flue gas

2

stacks from furnace boilers, gas turbines and engine emission. The content of the flue

gases that released at atmospheric pressure usually containing Oxygen, Carbon Dioxide,

Nitrogen, NOx, SOx and dust particulate impurities. Referring to Halmann research, the

actual warming of the earth due to the atmospheric blanket is strongly influenced by

small amounts of gases in the earth’s atmosphere, particularly CO2 and water vapors.

These gases trap the heat due to their molecular structures, which absorb mainly

reflected solar radiation from the earth’s surface. H2O vapor absorbs solar radiation in

the range 4 to 7 microns while CO2 absorbs radiation in the range of 13 to 19 microns.

Because of their behavior, hence they are called greenhouse gases.

A large number of polymeric membranes have been developed for a variety of

industrial applications. Each application imposes specific requirement on the membrane

material and pore structure.

The separation process in the membrane involves three phases, which is two

gases (vapor) phases, two liquid phases and a vapor and liquid phases. In the membrane

process, the feed mixture can be separated into two types. Firstly, retentate which means

the part of the feed that does not pass through the membrane. Secondly, permeate which

means the part of the feed that passes through the membrane.

3

1.2 Problem Statement

Anthropogenic climate change is rapidly becoming one of the major issues in

environmental science. Global temperatures are projected to raise between 1.4 and 5.8

oC by 2100 in the absence of climate change policies (Houghton, 2001). This increase in

global temperature is likely to cause a number of negative effects; including rising sea

level, changes in ecosystem, loss of biodiversity and reduction in crop yields (McCarthy

et al., 2001). One of the major factor contribute to the global warming is an emission of

flue gas from power plant. The main components of the flue gas are CO2, N2, O2 and

H2O, air pollutant such as SOx, NOx, particulates, as well as other contaminants. CO2 is

an undesirable gas that contributes to the corrosion and other operational problems. The

treatment of flue gas to enable the capture and storage of relatively pure CO2 involves

identifying the impurities in the flue gas that may affect the transport and storage of

CO2.

Membrane technology is considered as a feasible option, but the membranes

currently available for industrial gas separations have not been applied for commercial

flue gas applications. To be economically viable, the membrane should exhibit a high

permeability and a high selectivity for the components to be separated. Normally,

conventional membranes are good only for bulk separations, and they are often

combined with other gas separation techniques when the acid gases are present at low

concentrations (Francisco et al., 2007).

4

It may be mentioned that facilitated transport for CO2 separation has been

studied using immobilized liquid membranes where the carrier solution is confined in

the pores of a membrane matrix. However, this matrix membrane suffers from problems

associated with solvent loss and washout. Moreover, other technologies in gas separation

systems such as chromatography or distillation in which required high energy

requirement.

1.3 Research Objectives

The main objective of this research is to develop PSf-PDMS-TFC membrane for

CO2/N2 gas separation. The developed membrane should have considerably high CO2

permeability in conjunction with high CO2/N2 selectivity, can withstand high trans-

membrane pressure differentials and have long term stability.

Specific objectives are:

i. To synthesis thin film composite membrane by using PSf and PDMS.

ii. To test the membrane performance in CO2/N2 gas separation.

iii. To characterize TFC membrane by using Scanning Electron Microscopy (SEM)

and Fourier Transform Infrared Spectroscopy (FTIR).

5

1.4 Scope of Research Proposed

The main scopes of research are:

i. Conduct dry/ wet phase inversion process in developing membrane.

ii. Conduct permeation test to examine the performance of membrane by study the

effect of different percentage of PDMS used in dip-coating solution.

iii. Characterization of the membrane is conducted by using Scanning Electron

Microscopy (SEM) and Fourier Transform Infrared Radiation (FTIR) with help

of the physical and chemical properties of membrane.

1.5 Rationale and Significance

The rationale and significance implement membrane as a medium in gas

separation are it capable to increase process performance, save energy, reduce costs and

minimize the environment impact. Membrane operations are in principle the most

attractive candidates to satisfy the process intensification concepts and requirements.

Their intrinsic characteristic of efficiency and operational simplicity, high

selectivity and permeability for the transport of specific components, compatibility

between different membrane operations in integrated systems, low energetic

requirement, good stability under operating conditions and environment compatibility,

6

easy control and scale up, and large operational flexibility represent the membrane is the

most rational and significance in industrial productions (Drioli and Romano, 2001).

7

CHAPTER 2

LITERATURE REVIEW

2.1 Background Study of the Membranes

Membranes offer the greatest potential in the gas separation process. Membrane

applications in the gas separation are available for bulk removal of carbon dioxide, CO2,

removal and separation of nitrogen, N2 from natural gas and separation of natural gas

liquid from methane, CH4. The separation of gas by thin barrier termed as membranes is

a dynamic and rapidly growing field, and it has been proven to be technically and

economically superior to other emerging technology.

Figure 2.1 illustrate simplified and generalized schematic diagram of the

membrane in separation process.

8

Figure 2.1 A Schematic Representation of a Simple Membrane Process (Farid, 2010).

The barrier which is called as a membrane is a medium to separate two bulks of

phases. The membrane controls the passage of different chemical substances through it

which depend upon the nature of the chemical substances and the membrane (Scott,

1995).

Membrane technology has been widely used in the industry for many years for

separating liquids and liquid-solid mixtures before it being applied to gas separation. In

order to obtain more profitable method in gas separation process, membrane systems

was then gradually introduced for gas separating systems (Dhingra, 1997). Concomitant

with developments in the field of synthetic polymeric materials, this new technology is

successfully addressed.

As stated by Abedini & Nezhadmoghadam in their research, the progress in

membrane science and technology was accelerated during the 1980s by the development

and refinement of synthetic polymeric membranes. During 1980s, membrane gas

9

separation emerged on a large scale as a commercial process. During this period,

significant progress was made in virtually every aspect of membrane technology,

including improvements in membrane formation process, chemical and physical

structures, configuration and applications.

2.1.1 Definition of Membranes

As mentioned by Mulder (1996), membrane can be defined as a selective barrier

between two phases, the “selective” being inherent to a membrane process. In addition

membrane is an inter-phase between the two bulk phases. It is either a homogenous

phase or a heterogeneous collection of phases (Sakai, 1994).

In the concept of the membrane science, a synthetic membrane behaves as a thin

barrier between two phases through which differential transport can occur. Driving

forces that facilitate this transport are pressure, concentration, and electrical potential

across the medium (Koros, Ma, Shimidzy, 1996). The transportation process is a non-

equilibrium process and the difference in transport rates through the membrane will

make the chemical species is separated.

2.1.2 Fundamental of Membrane Gas Separation

In the process of selecting the proper polymer for the preparation a membrane in

which capable of removing organic solvents efficiently from air, a brief discussion of the

basics of the mass transport through membranes is very helpful.

10

The permeation of a gaseous component through a homogenous membrane can

to a first approximation be described by the solution diffusion membrane model and is

determined mainly by three parameters: (1) The permeability, (2) the concentration of

the components in the membrane phase and (3) the driving force or driving force acting

on this component (Strathman, Bell and Kimmerle, 1986).

2.1.3 Classification of Membrane Process

In filtration process by using membrane, there are two main classifications that

been highlighted which are Dead-end and Cross-flow filtration. In Dead-end (or in line

filtration), with under pressure condition, the entire fluid flow is forced through the

membrane and any solid or colloidal particles accumulate on the membrane surface or in

its interior to form a cake. The membrane pores can be blocked by accumulation of

solids on the surface. The pressure should be implemented on the membrane in order to

maintain the required flow increase until a washing cycle is performed or the membrane

must be replaced. Membrane fouling due to accumulation of suspended or dissolved

substances on external surface within the pore structure can result severe reduction in

permeability (Mhurchu and Foley, 2006).

Meanwhile in cross-flow system, the fluid on the downstream side of the

membrane moves away from the membrane. this flow is circulated across the membrane

surface producing two streams, a clean permeate stream and concentrated retentate

stream. A shear force created on the surface of the membrane due to feed flow is

circulated over the membrane will reduces blocking of membrane pores on the surface

11

of material (Kim et al., 2006). This flow type reduces membrane fouling, however,

concentration polarization, where the retained species become concentrated at the

membrane surface can occur with a solvent-particles system (Farid, 2010). Figure 3.2

shows Dead-end and cross-flow filtration process.

Figure 2.2 Dead-end and Cross-flow Filtration Process (Farid, 2010)

2.1.4 Classification of Membrane

There are four main membrane processes. They can be classified as Reverse

Osmosis (RO), Nanofiltration (NF), Ultrafiltration (UF) and Microfiltration (MF). These

four types of membranes are differentiating based on the type of membrane used,

thickness of the thin film, pore size, type of rejection materials, and operating pressure

(Wagner, 2001).

12

Figure 2.3 Pore Diameter Based on Different Type of Membrane Process (Hu, 2001)

Reverse Osmosis (RO) is the tightest possible membrane process in liquid/liquid

separation. Water is in principle the only material passing through the membrane;

essentially all dissolved and suspended material is rejected. In RO process, a membrane

which impedes the passage of a low molecular weight solute is placed between a solute-

solvent solution and a pure solvent. The solvent is diffuses into the solution by osmosis.

In RO, a reverse pressure difference is imposed which causes the flow of solvent to

reverse, as in the desalination of seawater (Wagner, 2001, Geankoplis, 2003).

Nanofiltration (NF) rejects only ion with more than one negative charge, such as

sulfate or phosphate, while passing single charged ion. NF also rejects uncharged,

dissolved materials and positively charged ions according to the size and shape of the

molecule in question. Rejection of sodium chloride with NF varies from 0-50 percent

depending on the feed concentration (Wagner, 2001).