DEVELOPMENT AND CHARACTERIZATION BETWEEN

POLYETHERSULFONE/POLYSULFONE (PES/PSF) MICIBLE BLEND WITH

PRIMARY POLYMER (PES AND PSF) MEBRANE FOR O2/N2 SEPARATION

SUFINAH BT YUSSOF

A thesis submitted in fulfillment

of the requirements for the award of the Degree of

Bachelor of Chemical Engineering (Gas Technology)

Faculty of Chemical & Natural Resources Engineering

Universiti Malaysia Pahang

DECEMBER 2010

v

ABSTRACT

Membrane technology becomes more interesting in industrial level for gas

separation and purification. Main problem in membrane technology industries is hard

to find membrane that high performance both in selectivity and permeability.

Membrane that provide high permeability offered low selectivity and vice versa.

Therefore, blend polymer is introduced to overcome this problem. Means that,

beneficial properties of polymers are combining in one single material. In this study,

four difference compositions of dope solutions have prepared which are 25%

polyethersulfone (PES), 25% polysulfone (PSF), 20% polyethersulfone 5%

polysulfone (PES/PSF) and 5% polyethersulfone 20% polysulfone (PES/PSF) in

order to prepared the asymmetric membrane. The membrane was fabricated by using

dry/wet phase inversion technique. Two type of membrane were produced from each

of the sample membrane which are coated and uncoated membrane. The coating

membrane was coated by coating agent, polydimethylsiloxane (PDMS). The

performance of the membrane was evaluated by gas permeation unit with pure

oxygen (O2) and nitrogen (N2) as a test gaseous. From the result, PES/PSF blend

polymers show the best result compared the others, where the permeability value for

O2 is about 19.93 GPU and N2 is 14.95 GPU whereas the selectivity of O2/N2 is 1.33.

The lowest selectivity can be achieved by using primary polymer dope solution of

PES and the selectivity for O2/N2 is 1.12 where the permeability of O2 is 91.84 GPU

and N2 is 82.07 GPU. At 25% total polymer show not many difference to the

selectivity. This is because only small amount of second polymer was added in order

to blend the polymer. Then, the membrane morphology was characterized by

Scanning Electron Microscopy (SEM) for identified the surface structure and cross

section of the membrane. Cross section for blend polymer show the pore is smallest

than primary polymer while surface structure for coated membrane is smooth as

compared to uncoated membrane. From this study, by blending two type of polymer

increase the performance of the membrane.

vi

ABSTRAK

Teknologi membran menjadi sangat terkenal di peringkat industri dalam

proses pemisahan dan penulinan gas. Masalah utama dalam teknologi membran ialah

sukar untuk mendapatkan membran yang berprestasi tinggi iaitu membran yang

mempunyai kadar pemisahan yang tinggi dan kadar pemilihan yang tinggi dalam

masa yang sama. Ini kerana membran yang mmpunyai kadar pemisahan yang tinggi

akan mempunyai kadar pemilihan yang rendah dan begitulah sebaliknya. Oleh

kerana itu, polimer campuran diperkenalkan bagi menagatasi masalah tersebut.

Dalam kaedah ini, kebaikan yang ada pada dua polimer digabungkan menjadi dalam

satu bahan. Dalam kajian ini, empat larutan pekat yang berbeza iaitu 25%

polyethersulfone (PES), 25% polysulfone (PSF), 20% polyethersulfone 5%

polysulfone (PES/PSF) dan 5% polyethersulfone 20% polysulfone (PES/PSF)

disediakan untuk menyediakan asymmetric membran. Teknik yang digunakan ialah

pembalikan fasa kering/basah. Dua jenis membran dihasilkan daripada semua sampel

membran iaitu bersalut dengan agen salutan polydimethylsiloxane (PDMS) dan tidak

bersalut. Prestasi semua membran diuji dengan alat penyerapan gas menggunakan

gas oksigen (O2) dan nitrogen (N2) tulen. Daripada keputusan yang diperolehi,

campuran polymer PES/PSF menunjukkan keputusan yang baik daripada yang lain,

dimana kadar serapan untuk O2 ialah 19.93 GPU dan N2 ialah 14.95 GPU manakala

kadar pemilihan O2/N2 ialah 1.33. Kadar pemilihan yang rendah diperolehi dengan

menggunakan larutan pekat primary polymer PES dan kadar pemilihan O2/N2 ialah

1.12 dimana kadar pemisahan untuk O2 ialah 91.84 GPU dan N2 ialah 82.07 GPU.

Kadar pemilihan mununjukkan tidak banyak perbezaan pada jumlah polymer 25%.

Hanya jumlah yang kecil untuk polymer yang kedua ditambahkan kepada polymer

yang pertama untuk menghasilkan campuran polymer. Hasil membran kemudiannya

akan dianalisa untuk mengenal pasti struktur permukaan dan keratan rentas membran

tersebut dengan menggunakan Scanning Electron Microscopy (SEM). Keratan rentas

menunjukkan liang bagi campuran polymer adalah kecil berbanding primary polymer

manakala struktur permukaan membran yang bersalut adalah lebih licin berbanding

yang tidak bersalut. Daripada kajian ini, didapati campuran dua jenis polymer

menunjukkan peningkatan terhadap prestasi membran.

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSRTACT v

ABSTRAK vi

TABLE OF CONTENT vii

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF SYMBOLS xv

LIST OF ABBREVIATIONS xvi

1 INTRODUCTION

1.1 Background of the Study 1

1.2 Problem Statement 3

1.3 Objective of the Study 4

viii

1.4 Scope of the Study 4

2 LITERATURE REVIEW

2.1 Definition of Membrane 5

2.2 History of Gas Separation 6

2.3 Membrane Modules 7

2.3.1 Plate-and Frame Modules 7

2.3.2 Spiral Wound Modules 8

2.3.3 Hollow Fiber Modules 9

2.3.4 Tubular Modules 11

2.4 Membrane Materials 12

2.4.1 Polymeric Membranes 12

2.4.2 Ceramic and Zeolite Membrane 13

2.5 Type of Membrane 14

2.6 Advantages and Disadvantages Polymer Membrane 15

2.6.1 Advantages of Membrane Technology 15

2.6.2 Disadvantages of Polymer Membrane 16

2.7 Oxygen/Nitrogen for Membrane Separation 16

2.8 Parameter in Gas Separation System 17

2.8.1 Permeability of the Membrane 17

2.8.2 Selectivity of the Membrane 18

2.9 Polymer Blend 18

ix

2.9.1 Effect of Blending Polymer to the Membrane 18

3 METHODOLOGY

3.1 Research Design 20

3.2 Materials 21

3.2.1 Polysulfone (PSF) 21

3.2.2 Polyethersulfone (PES) 22

3.2.3 N-Methyl-2-Pyrrolidone (NMP) 23

3.2.4 Water 24

3.2.5 Methanol 25

3.2.6 Polydimethylsiloxane (PDMS) 26

3.2.7 N-hexane as Coating Agent Solvent 27

3.2.8 Oxygen and Nitrogen as Test Gas 28

3.3 Preparation of Dope Formulation 29

3.4 Turbidity Titration Test 30

3.5 Preparation of Membrane Casting 31

3.6 Membrane Coating 32

3.7 Membrane Characterization 32

3.7.1 Membrane Testing Using Gas Permeation Unit 32

3.7.2 Morphology of Membrane Using Scanning

Electron Microscopy (SEM)

34

x

4 RESULT AND DISCUSSION

4.1 Turbidity Titration for Dope Formulation 35

4.2 Effect of Different Polymer Concentration on Uncoated

Membrane for O2/N2 Separation

37

4.3 Effect of Different Polymer Concentration on Coated

Membrane for O2/N2 Separation

44

5 CONCLUSION AND RECOMMENDATION

5.1 Conclusion 51

5.2 Recommendation 52

REFERANCES 54

APPENDICES

Appendix A1 57

Appendix A2 58

Appendix A3 59

Appendix A4 60

Appendix A5 61

xi

LIST OF TABLES

TABLE NO. TITLE PAGE

3.1 Physical properties of polysulfone 21

3.2 Physical properties of water 24

3.3 Physical properties of methanol 25

3.4 Physical properties of polydimethylsiloxane (PDMS) 26

3.5 Physical properties of n-hexane 27

3.6 Physical properties of oxygen and nitrogen 28

4.1 Comparison of dope formulation before and after turbidity

titration test

36

4.2 Performance of uncoated membrane for O2/N2 separation 37

4.3 Performance of coated membrane for O2/N2 separation 44

xii

LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Schematic diagram permeation of membrane 5

2.2 Schematic drawing of plate and frame module 8

2.3 Schematic drawing of spiral wound module 9

2.4 Illustrated design of hollow fiber module, shell side feed 10

2.5 Illustrated design of hollow fiber module bore side feed 11

2.6 Typical tubular module design 11

2.7 Schematic drawing of defect sealing on selective layer 12

2.8 Schematic drawing of two layer composite membrane 13

2.9 Illustrated of cross sections of asymmetric membrane 14

2.10 Illustrated of cross sections for asymmetric membrane 15

3.1 Research design 20

3.2 Polysulfone structure 21

3.3 Polyethersulfone structure 22

3.4 N-Methyl-2-pyrrolidone structure 23

3.5 Water structure 24

3.6 Methanol structure 25

3.7 Polydimethylsiloxane (PDMS) structure 26

3.8 N-hexane structure 27

3.9 Dope solution preparation vessel 30

3.10 Membrane casting unit 31

3.11 Gas permeation unit 33

4.1 Selectivity versus pressure of uncoated membrane for

O2/N2 separation

38

xiii

4.2 Permeability versus pressure of uncoated membrane for

O2/N2 separation

38

4.3 Image of cross section for uncoated primary polymer

membrane 25% PES

40

4.4 Image of cross section for uncoated primary polymer

membrane 25% PSF

40

4.5 Image of cross section for uncoated blend polymer

membrane contain of 20% PES + 5% PSF

41

4.6 Image of cross section for uncoated blend polymer

membrane contain of 20% PSF + 5% PES

41

4.7 Image of surface structure for uncoated primary

polymer membrane 25% PES

42

4.8 Image of surface structure for uncoated membrane for

primary polymer membrane 25% PSF

42

4.9 Image of surface structure for uncoated blend polymer

membrane contains of 20% PES + 5% PSF

43

4.10 Image of surface structure for uncoated blend polymer

membrane contains of 20% PSF + 5% PES

43

4.11 Selectivity versus pressure of coated membrane for

O2/N2 separation

45

4.12 Permeability versus pressure of uncoated membrane for

O2/N2 separation

46

4.13 Image of cross section for coated primary polymer

membrane 25% PES

47

4.14 Image of cross section for coated primary polymer

membrane 25% PSF

47

4.15 Image of cross section for coated blend polymer

membrane contain of 20% PES + 5% PSF

48

4.16 Image of cross section for coated blend polymer

membrane contain of 20% PES + 5% PSF

48

4.17 Image of surface structure for coated primary polymer

membrane 25% PES

49

xiv

4.18 Image of surface structure for coated primary polymer

membrane 25% PSF

50

4.19 Image of surface structure for uncoated blend polymer

membrane contains of 20% PES + 5% PSF

50

4.20 Image of surface structure for uncoated blend polymer

membrane contains of 20% PSF + 5% PES

51

xv

LIST OF SIMBOLS

Q -Flowrate of supplied gas

A -Area

P -Trans membrane pressure

α -Selectivity

-Permeability of O2

-Permeability of N2

xvi

LIST OF ABBREVIATIONS

PES Polyethersulfone

PSF Polysulfone

PVDF Polyvinylidene diflofide

PP Polypropylene

PI Polyimide

NMP N-Methyl-2-Pyrrolidone

PDMS Polydimethylsiloxane

GPU Gas Permeation Unit

O2 Oxygen

N2 Nitrogen

SEM Scanning Electron Microscopy

CHAPTER 1

INTRODUCTION

1.1 Background of Study

Nowadays, membrane technology for gas separation and purification process

has been interesting. This is mainly due to relatively higher reliability, energy

efficiency and lower capital cost than other conventional gas separation process (Paul

et al and Stern, 1994).

Enriched nitrogen production from air, hydrogen separation in ammonia

plants and refineries, removal of carbon dioxide from natural gas, removal of volatile

organic compound such as ethylene or propylene from mixture with light gases such

as nitrogen in polyolefin purge gas purification and water vapor removal from air are

the most widely practice separations (Baker, 2000; Ghosal et al, 1994; Zolandz et al,

1992).

Membranes have a small footprint where space is limit or where portability.

These make them ideal for use in application on offshore platforms, aboard aircraft

and refrigerated shipping containers (Baker, 2000).

2

Many commercial polymeric membrane materials that have good chemical,

thermal and mechanical stability is such as polysulfone (PSF), polyethersulfone

(PES), polyvinylidene diflofide (PVDF), polypropylene (PP) and nylon

Polymeric materials such as polysulfone (PSF), polyethersulfone (PES) and

polyimide (PI) gives high selectivity coefficient and acceptable permeability value

for separation of gas mixture (Vu, 2001).

The permeability coefficient will vary from one gas to the next depends on a

given polymer and its property that allows the polymer to separate gas mixture.

Oxygen (O2) is always more permeable than nitrogen (N2) in all polymers.

Ratio of O2 to N2 permeability, the selectivity varies from 1.6 to 7.8 with given

materials. As the permeability of polymer to oxygen increase, its selectivity will be

decrease (Freemen, 1999; Robeson, 1991).

One of the methods to improve the properties of a polymer is by blending

with another polymer those posses some desired physical and chemical properties.

By using this blending polymer method give ideal separation factor for O2/N2 (Ismail

et al, 2008). Polymer blending method establish as excellent candidate membrane for

separation of gaseous mixture in industrial level. Thus, this method can develop in

perspective for future commercial application (Kapantaidakis et al, 2002).

3

1.2 Problem Statement

Gas separation with polymer membrane is rapidly becoming a mainstream

technology. The main problem in membrane technology is hard to find high

performances with both selectivity and permeability. Most of membranes selectivity

is inversely proportional with permeability.

PSF and PES are high performance engineering polymer. It has good

stability, permeability, selectivity, high critical pressure of plasticization and low cost

(Ding et al and Ismail et al, 2008; Li et al, 2004; Kapantaidakis et al, 2002).

Polymers with higher gas permeability have lower selectivity (Kapantaidakis,

1999; Robeson, 1991). This fact becomes a factor for looking towards polymer

blending methods to combine the properties of different materials and as versatile

tool to combine the beneficial properties of two or more components in one single

material (Li et al, 2001; Park et al, 2000).

Therefore, to overcome the problem, by blending the polymer is one of the

attractive of tuning the performance of a membrane to achieve the desire for

selectivity and permeability of polymer membrane.

4

1.3 Objective of the Study

Based on problem statement, the objectives of this study are listed as

following:

1. To develop asymmetric membrane for O2/N2 separation.

2. To compare the membrane performance of difference polymer loading in

casting solution.

1.4 Scope of the Study

Several scopes that have been outlined in order to achieve the objective of

this study are as following:

1. Make a performance comparison between primary polymers with blended

polymer using permeability test.

2. Test the performance of uncoated and coated membrane using O2 and N2

gases as a test gas.

3. Characterize the membrane morphology using Scanning Electron Microscopy

(SEM).

CHAPTER 2

LITERATURE REVIEW

2.1 Definition of Membrane

Membrane is as a barrier between two fluids where one of the fluids passes

the membrane faster than others. Hence, separation occurs. The two fluids will

separated into a retentate and a permeate. Retentate is part of the fluid does not pass

through the membrane whereas permeate is the part of the fluid that passes through

the membrane as show in Figure 2.1 (Mulder, 1996; Baker, 2000 and Naylor, 2004).

Figure 2.1: Schematic diagram permeation of membrane

6

2.2 History of Gas Separation

Study of gas separation has a long history but it has become major industrial

application of membrane technology only during the past 20 years (Baker, 2000). On

1866, Thomas Graham gave first description of the solution-diffusion model by

which the penetrant first dissolve in the membrane and then diffused through by the

same process as that occurring in liquids. He demonstrated that atmospheric air could

be enriched from 21 % and 41 % oxygen using a natural rubber membrane. He also

showed that the permeation rate will effect by the thickness where permeation rate of

the gas decrease as the film thickness increase. His work on porous membrane led to

Graham’s law of diffusion (Baker, 2000 and Naylor, 2004).

Gas separation by polymer was observed by Mitchell in 1891 who found

India rubber films permeated CO2 faster than hydrogen (Naylor, 2004). End of

nineteenth and early twentieth century’s, the ability of gas to permeate membrane has

no industrial or commercial use but the concept is used as theoretical tool to develop

physical and chemical theories such as Maxwell’s kinetic theory of gas (Baker,

2000).

From 1943 to 1945, for the first time Graham’s law of diffusion is used for

separation of uranium gas isotopes for uranium enrichment. U235

F6 is separate from

U238

F6. This project is part of Manhattan project (Baker, 2000 and Naylor, 2004).

The separation plant, the first large scale membrane that use for gas separation built

in Knoxville, Tennessee and for the next 40 years become world largest membrane

separation plant (Baker,2000).

In 1940 to 1950, the foundation of modern theories of gas permeation is laid

by Barrer, van Amerongen, Stren, Meares and others academic studies (Baker, 2000

and Naylor, 2004). The previous law, Graham’s law of diffusion is still accepted for

gas transport through membrane. Despite the availability of interesting polymer, to

make useful separation membrane systems from these polymers, membrane

fabrication technology is not sufficiently advance at that time (Baker, 2000).

7

Late 1960, techniques developed to produce high flux anisotropic, large

surface area, thin and defect free polymeric membrane for reverse osmosis and

provided the basis for modern membrane gas separation technology early 1970

(Baker, 2000 and Naylor, 2004). Cellulose acetate for gas dehydration and gas

separation are the first polymer to be commercialized. The problem to commercial

the gas separation membrane is to economically package large area of membrane.

Bray and Westmoreland provided a solution in 1968 the development for reverse

osmosis of the spiral wound module. Led to the large scale introduction of gas

separation process is due to the development of hollow fibres by Dow and DuPont in

between 1968 to 1971. General Electric developed polycarbonate/silicon rubber

copolymer was developed for oxygen enrichment of air (Naylor, 2004).

In 1980, Masanto has led to the recent world wide surge in interest in gas

separation systems by success in commercializing its Prism membrane which

polysulphone with a sealing layer of polydimethylsiloxane for hydrogen sepration

(Baker, 2000 and Naylor, 2004). Membrane plant to remove carbon dioxide from

methane was built in mid 1980 by Cynara, Separex and Gas Membrane Systems.

Although need to face low natural gas price in the 1990, this application grown over

the years. At the same time, Dow launched Generon, the first commercial membrane

system for nitrogen separation from air. Dow, Ube and DuPont develop materials

with improved selectivities since made membrane produce nitrogen was cost

competitive (Baker, 2000).

2.3 Membrane Modules

2.3.1 Plate-and-Frame Modules

Plate-and frame modules are one of the earliest modules of membrane

system. Membrane, feed spacers and product are layered together between two end

8

plates. The feed mixture is forced across the surface of the membrane. A portion

passes through membrane, enters the permeate channel, and makes its way to a

central permeate collection manifold (Baker, 2000 and Naylor, 2004). Figure 2.2

show schematic drawing of plate and frame module.

Figure 2.2: Schematic drawing of plate and frame module

2.3.2 Spiral Wound Modules

The spiral wound modules is the next logical step from flat membrane. It is in

fact a plate-and frame system wrapped around a central collection pipe, in a similar

fashion to a sandwich roll. Membrane and permeate side spacer material are then

glued along three edges to built a membrane envelope. The feed side spacer

separating the top layer of the two flat membranes also acts as a turbulence promoter

(Baker, 2000 and Naylor, 2004). This module is shown schematically in Figure 2.3.

9

Figure 2.3: Schematic drawing of spiral wound module

2.3.3 Hollow Fiber Modules

Hollow fiber membrane modules are formed in two basic geometries. The

first is the shell side feed design illustrated in Figure 2.4. A loop or a closed bundle

of fibers in contained in a pressure vessel. The system is pressurized from the shell

side. Permeate passes through the fiber wall and exits through the open fiber ends.

This design is easy to make and allows very large membrane areas to be contained in

an economical system. Because the fiber wall must support considerable hydrostatic

pressure, the fibers usually have small diameters and thick walls, typically 50 m

internal diameter and 100 to 200 m outer diameter (Baker, 2000 and Naylor, 2004).

10

Figure 2.4: Illustrated design of hollow fiber module, shell side feed

The second type of hollow fiber module is the bore side feed type illustrated

in Figure 2.5. The fibers in this type of unit are open at both ends, and the feed fluid

is circulated through the bore of the fibers. To minimize pressure drop inside the

fibers, the diameter are usually larger than those of the fine fibers used in the shell

side feed system and are generally made by solution spinning. These called capillary

fibers that used in ultrafiltration, pervaporation and some low to medium pressure

gas application. Feed pressures are usually limited to below 150 psig (Baker, 2000

and Naylor, 2004).

11

Figure 2.5: Illustrated design of hollow fiber module bore side feed

2.3.4 Tubular Modules

Tubular modules are now generally limited to ultrafiltration application, for

which the benefit of resistance to membrane fouling due to good fluid

hydrodynamics outweighs their high cost (Baker, 2000). Typically, membranes are

placed inside a porous stainless steel, ceramic or plastic tube with the diameter of the

tube that generally more than 10 mm. the number of tube put together in the module

may vary from 4 to 18, but is not limited to this number as shown in Figure 2.6

(Baker, 2000 and Naylor, 2004).

Figure 2.6: Typical tubular module design

12

2.4 Membrane Materials

2.4.1 Polymeric Membrane

Most gas separation processes require that the selective membrane layer be

extremely thin to achieve economical flux. Typical membrane thicknesses are less

than 0.5 m and often less than 0.1 m. Early gas separation membranes were

adapted from the cellulose acetate membrane for reverse osmosis (Baker, 2000).

Gas separation membranes are sensitive to minor defect shown in Figure 2.7,

such as pinholes in the selective membrane layer, than membranes used in reverse

osmosis or ultrafiltration. Small defect can highly decrease the selectivity of gas

separation membranes. For early developer, the sensitivity of gas separation

membranes to defects becomes a serious problem. Moreover, few defects are very

difficult to avoid during membrane preparation and module formation. So that,

coating is the solution to plugged membrane defect by apply thin layer of coating

agent such as silicon rubber to the membranes (Baker, 2000).

Figure 2.7: Schematic drawing of defect sealing on selective layer