DESIGN AND DEVELOPMENT OF A PERVAPORATION MEMBRANE SEPARATION MODULE

Weihua Xu

A thesis submitted in conformity with the requirements for the Degree o f Master of Applied Science Graduate Department of Mechanical and Industrial Engineering University of Toronto

@Copyrightby Weihua Xu 2001

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permission.

autorisafion.

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DESIGN AND DEVELOPMENT OF A PERVAPORA-TION-MEmRANE-SPARATIONMODULE A thesis subrnitted in confodty with the requirements

for the Degree of Master of Applied Science Graduate Department of Mechanical and Industrial Engineering University of Toronto 2001

ABSTRACT This thesis contributes to the design and development of a new pervaporation membrane separation module based on axiomatic design theory and Design for X methodology. The overall design pmcess consists of needs generation, task analysis, knowledge preparation, design methodology selection, conceptual design, detailed design, working drawings, manufacturing arrangement, prototyping and design evaluation. The conceptual design was executed on four levels to form the basic configurations and features under the guidance of axiomatic design theory. Thereafter, the detailed design was perfonned based on Design for X methodology. The design incorporates the customer requirements, cost, manufactunng, performance, structure, maintenance, reliability, schedule and human factor considerations, etc. Numerous innovative design features have been incorporated in the module and have been made to obtain the best combination of various design concepts which have been validated by prototyping. Recommendations for the further improvement of the module are addressed.

ACKNOWLEDGMENTS 1 would like to thank Professor Ron D. Venter for providing me with the opportunity to

work in this project. His inspiration and guidance have been essential to my educational and career oriented pursuits.

My sincere thanks are expressed to Ian McGregor and Darren Lawless of Fielding Chernical Technologies Inc., for their creative thinking, program management, critical design review and financial investment.

My sincere gratitude is also due to Materials and Manufacturing Ontario and Michael D. Burgoyne for the financial support via the interact program. Working with Mark Nye was not on1y educational, but refreshing. Mark's help with the manufacturing of the prototype and jig was much appnciated. Thanks to Brenda Fung, Administrator of the MIE Graduate Studies Office, for her consistent support over the past few years. To al1 the friends and coworkers 1 met while studying at the University of Toronto, thank you for your friendship and support. Finally, 1 would like to thank for my family, Yan, rny wife for sharing wealth and woe with me. Her love and support dunng the last two years have been beyond compare; to my parents for their encouragement; to Jeanne and Matthew, my lovely kids for the great joy they provide.

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TABLE OF CONTENTS

1.2

General Statement and Research Objectives ........................................ .... .... .. ... . ... .3

1.3

Overview of the Thesis ...............................................................

CHAITER 2

MEMBRANE

. .. .. ......................4

PERVAPORATIONmmmmmmam~mmmm*mmm~mmmmmmmm*mmmmmmmmmmmmmmammmmammammmmmmma

. .. . . .... ......... .

7

2.1

Description of Pervaporation Separation ......................................

2.2

Pervaporation Membranes ........................................... . .....

2.3

Separation Mechanism of Pervaporation Membranes ....................................................... 8

2.4

Specifications of Pervaporation Membranes ............................................................. 9

7

. . .. . ... ..... .. .... .... ...... 8

2.4.1

Membrane Selectivity ............................... .. . .

... ... . . . ... . . . . .. ....... .... . .. . 10

2.4.2

PermeslteFlux .......,,,...........................................................

.................................... 10

2.5

Configuration of Pervaporation Rocess .........................................

2.6

Various Pervaporation Membrane Separation Modules ..................................................13

2.6.1 Plate-and-Frarne Modules.........,........................ .. 2.6.2

Hollow-FiberModules

. . . . . . .. . .. . 10

........... . .. . . ... . .. . 13

..................................... . . ............................. .............. 14 iv

2.6.3 Spiral-Wound Modules ........................................................................................... 15 =a-......

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Tubular Module ...... ......................................................................

2.6.5

............... 17 FCT Module .............................................................................................................. 18

2.6.6

Cornparison of Pervaporation Modules..................................................................... 19

2.6.4

CHAPTER 3

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OVERVIEW OF DESIGN THEORIES

21

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3.1

Introduction...................................................................................................................... 21

3.2

Overview of Design Methodologies .............................................................................2 2

3.3

Axiomatic Design Theory ............................................................................................24 Design Axioms ....................................................................................................... 2 5 Design Equation .................................................................................................... 2 5 Uncoupled Design ..............................................................................................2

6

Decoupled Design............................................................................................. 2

7

Coupled Design ......................................................................................................2 8 Constrains ............................................................................................................... 28 Task Decomposition and Hierarchy ......................................................................... 2 8

Corollaries ................................................................................................................3 0 Theorems ................................................................................................................... 31 3.4

Design for X .................................................................................................................... 32

3.4.1

Definition of DFX ....................................................................................................32

3.4.2

Principles of DFX ...................................................................................................... 33

3.4.2. L

Ptocedures of DFX .............................................................................................. 34

3.4.2.2

Tools of DFX ...................................................................................................

3.4.3

3 5

Benefits from DFX ............................................................................................... 3

CHA.Pl'ER 4

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CONCEFIVAL DESIGN AND ANALYSIS oooomoooomooooooomomooooooooooooooooaooaomoooomo 37

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Introduction ...................................................................................................................... 37

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.......................

4.2

EHect of the Pervaporation Rocess Conditions ....................................................... 3

4.3

Conceptual Design Pmcess of the Pervaporation Module............................................... 41

8

4.3.1

Lever O-Task Definition and hplementation ...................................................... 4 5

4.3.2

Level 1-General Functions and Physical Solutions .................................................. 45

4.3.3

Level 2-Major Functions and Physical Solutions.....................................................47

4.3.3.1

Conceptual Design of the Perrneate Generator ...............................................4 7

4.3.3.2 Conceptual Design of the Penneate Removing..................................................5 3

4.3.4

Level3-DetailedConceptualDesign ......................................................................54

4.3.4.1

Conceptual Design of Maximizing the Membrane Area ....................................55

4.3.4.2

Conceptual Design of the Disk Membrane Support..........................................5 8

4.3.4.3

Conceptual Design of the Sealing ......................................................................6 2

4.3.4.4 Conceptual Design of Minimizing the Flow Restriction ....................................64 4.4

Summary ............................................................................................................6

CHAPI'ER 5

DETAILED DESIGN AND ANALYSIS

8

.......................................................70

Introduction .................................................................................................................... 70 Design of the Permeate Flow Velocities..........................................................................71

Design of the Separate Disk Etements............................................................................7 4 Design of the Channel Configuration .............................................................................. 76 Design of the Built-in Membrane Spacers .................................................................7 8 Design of the Segmented Disk Joints ..........................................................................8 2 Design of the Membrane Disk Hubs ................................................................................87 Design of the Central Removal Tube.............................................................................. 91 Design of the Membrane Disk Reinforcements............................................................... 95

5.10 . .

Plastic Material Selection ........................ ................................................................... 9 8 ........

510.1

Specificationsof the Plastic Components ............................................................... 98

5.10.2

GeneralDescriptionofPolymers........................................................................ 9 9

5.10.3

Cornparison of Typical Polp e r s ............................................................................ 99

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5.1 1

Design for Assembly and Disassembly ....................................................................... 102

5.12

RototypingofthePervaporationModule.................................................................. 104

5.13

Sumrnary ...................................................................................................................... 107

CHAITER 6 ASSEMBLY JIG DESIGN

........,... ..........................................................108

Introduction .................................................................................................................... 108

FRs of the Membrane Disk Jig ......................................................................................108 Disk Holding Assembl y Design................................................................................... 110 Roller Assembly Design ................................................................................................1 1 1 Design of the Base .........................................................................................................1 1 1

CHAPTER 7 CONCLUSIONS......................................................................................... 112 ... 7.1

Sumrnary of Results .......................................................................................................112

7.2

Recommendation for Future Work ................................................................................114

REFERENCES

.......................................................................................................................127

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LIST OF TABLES -L

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Table 2.1

Cornparison of Pervaporation Modules .................................................................... 20

Table 3.1

Overview of Design for X ............................................................................. .......3

Table 3.2

What Does a DFX Tool Accomplish? ...................................................................... 36

Table 5.1

Cornparison of Typical Thennoplasts ..................................................................... LOO

Table 5.2

Cornparison of Typical Thermosets..................................................................... 101

Table 5.3

Cornparison between the Real Module and its Prototype ....................................... 106

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LIST OF FIGURES .

F i p 2.1

Pervaporation Membrane Separation Schematics ................................................... 7

Figure 2.2

Vacuum Driven Pervaporation ................................................................................ 11

Figure 2.3

Temperature Gradient Driven Pervaporation .......................................................... 11

Figure 2.4

Carrier Gas Pervaporation ....................................................................................... Il

Figure 2.5

Pewaporation with a Condensable C h e r .............................................................. 12

Figure 2.6

Pervaporation with a Two-phase Permeate and Partial Recycle ............................. 12

Figure 2.7

Pewaporation with Fractional Condensation of the Pemeate .................................12

Figure 2.8

A Plate-and-Frame Membrane Module ..................................................................14

Figure 2.9

Monsanto Prism Closed-end Module ......................................................................15

Figure 2.10

A Capillary (spaghetti) Module ............................................................................. 15

Figure 2.1 1

Spiral-wound Membrane Module ..........................................................................16

Figure 2.12

Four4eaf. Spiral-wound Module ........................................................................ 17

Figure 2.13

A Tubular Module .............................................................................................

Figure 2.14

FCT Pervaporation Module Layout ....................................................................... 19

Figure 3.1

Block Diagram of Design M e s s ...........................................................................21

Figure 3.2

Design Mapping Process Illustration .................................................................... 25

Figure 3.3

Hierarchical Structure. Task Decomposition and Zig-zag Mapping .......................29

Figure 4.1

Hierarchy of Functional Requirements....................................................................43

Figure 4.2

Hierarchy of Design Parameters ............................................................................. 44

Figure 4.3

Cornparison between Glue and Mechanicd Seals..................................................5 6

Figure 4.4

Illustration of Disk Structure Instability ................................................................ 59

Figure 4.5

Possible Disk Frarnes............................................................................................... 61

Figure 4.6

Penneate Gas Fiowing Mechanism in a Mesh Spacer ............................................-65

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Figure 4.7 - d

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Permeate Pressure Pattern between Channels ......................................................... 66 . .

....

Figure 4.8

Built-in Mesh Spacer Concept ................................................................................67

Figure 5.1

Membrane Disk Element ..................................................................................... 7 5

Figure 5.2

Comparison of the Polar Parabola Channels and the Straight Channels ................. 77

Figure 5.3

Membrane Disk with Spiral Channels .....................................................................78

Figure 5.4

Dot Pattern of the Membrane Spacer................................................................... 8 1

Figure 5.5

V Shape Grove Pattern of the Membrane Spacer ....................................................81

Figure 5.6

Circle Shape Grove Pattern of the Membrane Spacer .............................................81

Figure 5.7

Joints with Bolts and Nuts ....................................................................................... 84

Figure 5.8

Spacer Joints ........................................................................................................ 8 4

Figure 5.9

Aluminum Strap Joining ..........................................................................................86

Figure 5.10

Configuration of Membrane Disk Hub ................................................................. 8 8

Figure 5.11

Membrane Disk Hub Configuration ......................................................................89

Figure 5.12

Central Structure of the Membrane Separator Unit ...............................................94

Figure 5.13

Reinforcement Clip Configuration ................................................................... 9 6

Figure 5.14

Reinforcement Rig Configuration .........................................................................96

Figure 5.15

Reinforcement Clip Installation.........................................................................97

Figure5.16

Collar Torching Mechmisnt ................................................................................103

Figure 5.17

Assembly and Disassembly of a Reinforcement Clip ......................................... 104

Figure 6.1

Configuration of Membrane Disk Jig ...............................................................109

Figure 6.2

Positional Structure of the Disk Inner Penphery ................................................... 1IO

Figure App-A- 1 Two Membrane Cell Assembly (Plastic Disk) ...........................................1 1 6 Figure App-Ad

Two Membrane Ce11 Assembly (Steel Disk. Prototype) .............................. 117

Figure App-B-1

Central Collar .............................................................................................. 119

Fig~reApp-B-2 . . . . . .

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Sepmte Disk Element.................................................................................1 2 0 -

.

Figure App-B-3

Pin Washer.................................................................................................... 121

Figure App-B-4

Reinforcement Clip.................................................................................... 122

Figure App-C- l

Pervaporation Module Cornponents ............................................................ 124

Figure App-C-2

Pervaporation Module Assembly ................................................................ 124

Figure App-C-3

Raw Membrane Steel Disk Plate .................................................................. 125

Figure App-C-4

Membrane Separation Cell ........................................................................... 125

Figure App-C-5

Jig in Action (Top View) ............................................................................. 126

Figure App-C-6

Jig in Action (Side View) ............................................................................126

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LIST OF APPENDIXES a

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APPENDIXES A

Selected Assembly Dniwings .................................................................... 115

APPENDIXES B

Selected Component Drawings .................................................................. 118

APPENDIXES C

Selected Pictures .........,.........,., ............................................................ 123

NOMENCLATURE AND ACRONYMS

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Roman LRtters Element of the design matrix Active surface area of the membrane Concentration of the solvent component which has lower volatility Concentration of the solvent component which has higher volatility Diarneter of the disk hub Inner Diameter of the center tube Diameter of the membrane support disk Membrane flux rate Number of the channels in each membrane disk Number of the disk membrane cells in a pervaporation module S t e m pressure at the temperature of 100 OC Permeate pressure in the pervaporation module at the temperature of LOO OC Volumetnc permeate flow Total cross section area of the channels on the membrane disk Thickness of the steel disk Maximum temperature in the pervaporation module Volume per pound steam at the pressure of Po Volume per pound steam at the pressure of Pi Velocity of the permeate flow in the disk channels Velocity of the permeate flow in the center tube Width of the outer periphery seals Width of the disk channels xiii

Greek Letters ~embraneselectivity

Acronyms

CE

Concurrence Engineering

DFX

Design for X

DP

Design Parameter

FCT

Fielding Chemical Technology Inc.

FR

Functional Requirement

PA

Isopropyl Alcohol

PVA

Pervaporation

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CHAPTER 1

1.1

INTRODUCTION

Background and Motivation Pervaporation is a membrane separation process used to separate mixture of dissolved

solvents. In recent years there has k e n increased interest in the use of pervaporation membrane separation techniques for the selective separation of organic liquid mixtures, because of its high separation efficiency and flux rates coupled with potential savings in energy costs. Systematic studies of membrane phenornena can be traced to the eighteenth century philosopher scientists. Early investigators experimented with any type of diaphragm available to them, such as the bladders of pigs, cattle or fish and sausage casings made of animal gut. In later work collodion membranes were preferred. By the early 1930s micro-pomus collodion membranes were commercially available. During the next 20 years this early micro-filtration

membrane technology was expanded to other polyrners. Membranes found their first significant applications in the filtration of drinking water sarnples at the end of World War II. By 1960. thetefore, the elements of modem membrane science had been developed. But membranes were used in only a few laboratones and small industrial applications. Membranes suffered from four problems that prohibited their widespread use: they were too unreliable, too slow, too unselective, and too expensive. Partial solutions to each of these problems have been developed during the last 30 years. and as a result there is a surge of interest in membrane-based separation techniques. The 20-year period from 1960 to L980 produceci a tremendous change in the status of membrane technology. Using the techniques such as interfacial polymerization or multi-layer composite casting and coating, it is now possible to make membranes as thin as 0.1 ,un or less.

In 1980s GFT, a small German engineering company, introduced the first commercial -

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pervaporation systems for dehydratioi of aÏcohol. Membrane process techniques can be classified into membrane formulation and membrane pervaporation separation modules. The former is to develop and produce various membranes and to exploit the separation mechanisrn of pervaporation membranes. The latter focuses on the design and development of various membrane separators such that the potential of pervaporation membranes is maximized with minimum cost, weight and size.

With the developrnent of new pol yrner matenals and membranes, poor membrane performance is no longer a problem. In this situation, a good pervaporation separator plays an important role to maximize the membrane performance. Although t k r e are a number of different pervaporation separators available in today's market, most of them suffer from some comrnon problems, such as high cost, which inhibit their widespread use.

U.S.,Europe and Japan are the major countries active within pervaporation membrane industry. Fielding Chemical Technologies Inc. (FCT)is a medium size company located in Mississauga, Ontario, Canada. Their mission is to be a world leader in chemical separation technologies and to provide the leadership in environmental practices so that companies can safely use and Ruse chemicals. As the largest chemical recycling company in Canada, FCT is a Canadian pioncer in the industriat application of membrane sepamtion technologies. FCT not

only systematically explored the pervaporation membrane formulation, membrane separation mechanisms and membrane applications, but also developed the fiat generation of FCT pervaporation membrane module for the deh ydration of PAlwater mixture. This membrane module has been used by FCT for the testing of various membranes. FCT's experience shows that a pervaporation module plays an important role in excavating the performance of a pervaporation membrane. The existing FCT pervaporation

module has been validated by a large number of tests over the past few years. Some innovative & - -

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design concepts have been successful~yproven. However, some weaknesses has been identified in the application, such as limited production capacity, over weight, structure defects and sealing problem. etc. Over the past one year, there have been a numkr of exploratory meetings between FCT and the creative design team from the University of Toronto. The discussions focused on launching a project to design and develop a new generation of pervaporation membrane separation modules to boost market. This new module is specially required to have higher production capacity to overcome this limitation of the earlier modules. Moreover, the new module should build on and extend the approved design concepts as much as possible. University of Toronto undertwk the project and has king collaborated with FCT on the design and development of the new module, under the support of MM0 interact program. This thesis details the entire design process performed for the project requirements described above.

General Statement and Research Objectives Engineering design is the key technical ingredient in the product realization process, and the means by which new products are conceived, developed and brought to market. Design is also a creative process which is an essential feature of the human king's ability to survive and prosper. Based on the first generation of FCT module, a new concept module is proposed in this thesis for the chemical separation business. This new module should inherit the proven design concepts in the baseline module as much as possible. Besides, the defects identified in earlier prototype modules should be avoided. Such a challenge could not be completed by regular design approaches based on detailed drawing in isolation of the actual pervaporation process. First, a thorough understanding of chemical pervaporation separation techniques was required.

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Second1y, a comprehensive design and analy sis process was undertaken, including needs L

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generationi t a & &aiy&, knowledg& preparation, design methodology selection, conceptual design, detailed design, working drawings, manufactunng arrangement, prototyping and design evaluation. Finally, the design is a creative process based on the designer's experience, with the help of certain design theones and methodologies. Since the last decade, a relatively new field of research which has emerged to promote the understanding of design and referred to and known design theory and methodology. On the one hand, engineering product design is seeking the guidance of design theory. On the other hand, there is a need to evaluate and verify various design methodologies developed recently. Axiomatic design theory developed ai MIT by Suh, Nakazawa, Bell, Gossard et. al. is one of the most systematic design theones. The axiomatic design approach defines design as the creation of synthesized solutions that satisfy perceived needs through the mapping between functional requirements and design parameters. Axiomatic design theory offers the means by which good and bad design is distinguished and optimum design solutions are selected. Design for X is a concurrent design concept by which the product realization prwess is

organized. The design pmcess based on Design for X uses, wherever possible, information and knowledge about al1 the issues in a product life. This thesis contributes to the bRdging between the latest design methodotogies and r

practical design example. The Axiomatic Design Theory in conjunciion with Design for X has been selected to guide the design and development of a novel pervaporation module.

Overview of the Thesis This thesis consists of seven Chapters and two Appendixes. In Chapter 1, the background and general statement are presented. 4

The understanding of the pervaporation separation technique is essentid for the *

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development of a pervapor&on module. In Chapter 2, various pervaporation membranes are introduced and the membrane separation mechanism is explained. Then current pervaporation process is described and different pervaporation modules are compared to understand the advantages and disadvantages of different design concepts. The earlier versions of the FCT module are presented; these are particularly important as the new design is based on the established working success of the design. Chapter 3 is the overview of the design theoties and methodologies. Over the past decade, axiomatic theory has been developed by rnany researches. There are numerous publications dedicated to this theory and axiomatic design has become one of the most systematic of the emerging design theones. Thus it is possible to systematically introduce the axiomatic theory in this thesis. Unfortunately, Design for X (DFX)is a methodology still under development; there is no unique design method suitable for al1 of the design goals, Le. "Xs". It is very therefore difficult to demonstrate the overall methodology conveniently. However. the author will summaxize the process of DFX such that it can be followed for the subsequent detailed design. The conceptual design of the pervaporation module is addressed in Chapter 4. The

cvrtceptuat design witt start from the identification of the effect of pervaporatim process conditions, since module design is to m a t e a process condition which can maximize the membrane potential. Under the guidance of axiomatic design theory, the conceptual design is perfomed on four levels. The main configuration and features of the module are detennined

during the conceptual design phase. The detailed design process follows the conceptual design. Chapter 5 describes the details of the components and assemblys individually. DFX is employed to set the design goals. The

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engineering drawings are generated in the detailed design phase as well. Finally, the prototyping -- -- - - - - -process is presented to evaluate the design concepts. A

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In Chapter 6, a membrane disk jig, as important equipment to facifitate the assernbly of

the membrane disks is designed and detailed. Conclusions and recommendations for future work are addressed in Chapter 7. In the Appendix A and B, the selected assembly drawings and component drawings are enclosed for reference.

CHAPTER 2

2.1

MEMBRANE PERVAPORATION

Description of Pervaporation Separation Pervaporation is a membrane process used to separate mixture of dissolved solvents. The

process is shown schematically in Figure 2.1. A liquid mixture contacts one side of a noneporous permselective membrane; the permeate is removed as a vapor from the other side. Transportation through the membrane is induced by the difference in partial pressure between the liquid feed solution and vapor permeate. The permeate undergoes a phase change, from liquid to vapor, during its transport through the membrane barrier.

Feed Mixture

Permeate Figure 2.1

Gas

Pervaporation Membrane Separation Schematics

2.2

Pervaporation Membranes

. The family of pervaporation membranes pnmaril y consists of symmetrical membranes, - -

asymmetric membranes and composite membranes. Cerarnic and metal membranes and liquid membranes are also the member of this family, but they are not popular in industries. Syrnrnetrical membranes are unifomly isotropic throughout. The membrane can be porous or dense, but the permeability of the membrane material does not change from point to point within the membrane. Typical asymmetic membranes have a relatively dense, thin surface layer supported on an open, often micropomus substrate which has the s m e material as the surface layer. The surface layer generally performs the pervaporation separation and is the principal bamer for the flow through the membrane. The open support layer provides mechanical strength. Composite membranes comprise a porous support layer with a thin dense coated layer on top of it. This top layer is made of a different matenal from the suppon layer and this support layer is often applied on a fabric non-woven. Composite membranes are one of the most popular pervaporation membranes used in the chemical industries.

2.3

Separation Mecbanism of Pervaporation Membranes Pervaporation separation mechanisms have been studied by a large number of researches

for a long time. There are different opinions on how selectivity and transport could be explained in a pervaporation membrane system. Binning et al. [32] suggested that the selectivity took place in a boundary layer between the liquid zone and the gas zone in the membrane. Michaels et al. [33] interpreted the selectivity as a result of sieving by the polyrner crystals. Schrodt et al. 1341

suggested that hydrogen bondings between polymer and solvent components plays an important d e . Long [35] considered that the diffusion and concentration gradients in the different solvent 8

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components were the goveming factors. Matsuura et al. 136, 37) regarded the pervaporation --

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mechanism as a combination of reverse osmosis (RO)separation, followed by evaporation and vapor transport through the capillary pores on the surface layer of a RO membrane. Yoshikawa et al. [38,39,40,41, 421 explained that specific and selective separation of substances through membranes may be realized by differences in strength of hydrogen bonding interaction w hic h leads to selective separation through the membranes. Although pervaporation transport mechanism can be explained in different ways. most people agree that the transport of the permeate through a pore-free permselective film involves three successive steps as follows: a) Upstrearn partitioning of the feed-components between the flowing liquid mixture and the swollen upstrearn layer of the membrane. b) Diffusion of the penetrants through the unevenl y-swo!len pemselective bamer, c) Permeate desorption, which takes place at the downstream surface of the film.

In this thesis, the project present focuses on the pervaporation membrane separation devices, instead of pervaporation membranes. Therefore, the three separation processes above

are good enough to guide the design and development of the pervaporation membrane separation module.

2.4

Specifications of Pervaporation Membranes The behavior of a pervaporation membrane used to separate a given binary A-B liquid

mixture is characterized by two parameten: Selectivity and Flux.

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Membrane Se1ectiMty

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Membrane selectivity is defined as follows:

Where

a - Membrane selectivity

Ci- Concentration of component which has higher volatility Ci - Concentration of component which has lower volatility

2.4.2

Permeate Flux Penneate flux (J) through the membrane is defined as the amount of permeate per

effective membrane surface area and tirne unit, specified in Kglh mZ. In most commerical applications, penneate flux is the most important specification of membranes. A higher flux improves the pmcess economics.

2.5

Configuration of Pervaporation Process Maintaining a vapor pressure gradient across the membrane produces transport through

pervaporation membranes. The vapor pressure gradient used to produce a flow across a pervaporation membrane can be generated in a number of ways. Figure 2.2-2.7 illustrates several configurations of the pervaporation membrane separation processes. The first two are introduced below only for simplicity. Figure 2.2 shows a vacuum driven pervaporation. Vapor penneate is sucked out by using

a vacuum pump, maintaining a pressure gradient across the membrane. The use of a vacuum pump speeds up the permeate transportation. Figure 2.3 illustrates a temperature gradient dnven

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pervaporation without any vacuum pumping. The vapor permeate is driven out by condensation.

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This system is simple, but the permeate transport speed is lidted by the condensation efficiency. In FCT, the standard configuration combined the vacuum dnven and temperature

gradient driven approaches. which takes the advantages of both systems. The heater improves the membrane separation efficiency. The transportation of the vapor permeate is speeded up by vacuum pumping. Liquid

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Feed

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Retentate

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Permeate

Vapor

Figure 2.2

Vacuum Driven Pervaporation

Liquid

Fe ed

C

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Retentate

Permeo te

Heater

liquid

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Vapor Condenser

Figure 2.3

Temperature Gradient Driven Pervaporation

Liquid

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Feed -

Retentate

Condenser

Heater

Vapor Permeate liquid

Nonecondensable c a r r i e gas

Figure 2.4

Carrier Gas Pervaporation 11

Liquid Feed

{ y R e t e n t a t e?////////////////i

Condenser

Vapor

Permea t e Evaporator

Decanter

Iiquid Imiscibie Liquid c a r r i e r

Figure 2.5

Pervaporation with a Condensable Carrier

Liquid

- -1

Feed

Retentate

Vapor

I

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I Permea t e

Decanter

Figure 2.6

Liquid

Pervaporation with a Two-phase Pemeate and Paitial Recycle

Feed

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Retentate

I Vapor

Condenser

t.

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(y First fraction

Figure 2.7

Condenser 1 at T2