MEMBRANE PROCESS CURVE MAPS...4 PROPERTIES OF MEMBRANE RESIDUE CURVE MAPS 29 4.1 Stationary Points...

MEMBRANE PROCESSDESIGN USING RESIDUECURVE MAPS

MEMBRANE PROCESSDESIGN USING RESIDUECURVE MAPS

MARK PETERSDAVID GLASSERDIANE HILDEBRANDTCentre of Material and Process Synthesis (COMPS)University of the Witwatersrand Johannesburg, South Africa

SHEHZAAD KAUCHALISchool of Chemical and Metallurgical EngineeringUniversity of the Witwatersrand Johannesburg, South Africa

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Library of Congress Cataloging-in-Publication Data:

Membrane process design using residue curve maps / Mark Peters ... [et al.].

p. cm.

Includes bibliographical references and index.

ISBN 978-0-470-52431-2 (cloth)

1. Membrane separation 2. Diffusion. 3. Pervaporation. 4. Gas separation membranes.

I. Peters, Mark, 1981-

TP248.25.M46M44 2011

660’ .28424–dc22

2010019515

Printed in the United States of America

oBook ISBN: 978-0-470-91003-0

ePDF ISBN: 978-0-470-91002-3

ePub ISBN: 978-0-470-92283-5

10 9 8 7 6 5 4 3 2 1

www.copyright.comhttp://www.wiley.com/go/permissionwww.wiley.com

CONTENTS

PREFACE xi

ACKNOWLEDGMENTS xiii

NOTATION xv

ABOUT THE AUTHORS xix

1 INTRODUCTION 1

2 PERMEATION MODELING 7

2.1 Diffusion Membranes 8

2.1.1 Gas Separation 8

2.1.2 Pervaporation 11

2.2 Membrane Classification 13

3 INTRODUCTION TO GRAPHICAL TECHNIQUESIN MEMBRANE SEPARATIONS 15

3.1 A Thought Experiment 15

3.2 Binary Separations 16

3.3 Multicomponent Systems 20

3.3.1 Mass Balances 21

3.3.2 Plotting a Residue Curve Map 23

v

4 PROPERTIES OF MEMBRANE RESIDUE CURVE MAPS 29

4.1 Stationary Points 29

4.2 Membrane Vector Field 30

4.3 Unidistribution Lines 31

4.4 The Effect of a-Values on the Topology of M-RCMs 32

4.5 Properties of an Existing Selective M-RCM 34

4.5.1 Case 1: When the Permeate Side Is at Vacuum

Conditions (i.e., pP � 0) 344.5.2 Case 2: When the Permeate Pressure Is Nonzero

(i.e., pP > 0) 36

4.6 Conclusion 38

5 APPLICATION OF MEMBRANE RESIDUE CURVE MAPSTO BATCH AND CONTINUOUS PROCESSES 41

5.1 Introduction 41

5.2 Review of Previous Chapters 44

5.3 Batch Membrane Operation 45

5.3.1 Operating Leaves in Batch Permeation 45

5.3.2 Material Balances 46

5.3.3 Permeation Model 48

5.3.4 Operating Regions: Nonselective Membranes 48

5.3.5 Operating Regions: Selective Membranes 50

5.4 Permeation Time 52

5.5 Continuous Membrane Operation 54

5.5.1 Nonreflux Equipment 54

5.5.2 Reflux Equipment 58

5.6 Conclusion 64

6 COLUMN PROFILES FOR MEMBRANECOLUMN SECTIONS 65

6.1 Introduction to Membrane Column Development 66

6.1.1 Relevant Works in Membrane Column Research 67

6.2 Generalized Column Sections 68

6.2.1 The Difference Point Equation 70

6.2.2 Infinite Reflux 71

6.2.3 Finite Reflux 74

vi CONTENTS

6.2.4 CPM Pinch Loci 76

6.3 Theory 80

6.3.1 Membrane Column Sections 80

6.3.2 The Difference Point Equation for an MCS 81

6.3.3 Permeation Modeling 82

6.3.4 Properties of the DPE 84

6.4 Column Section Profiles: Operating Condition 1 85

6.4.1 Statement 85

6.4.2 Mathematics 85

6.4.3 Membrane Residue Curve Map 85

6.5 Column Section Profiles: Operating Condition 2 87

6.5.1 Statement 87


6.5.3 Column Profile 88

6.5.4 Analysis 89

6.5.5 Pinch Point Loci 93

6.5.6 Further Column Profiles 94

6.5.7 Direction of dT 96

6.5.8 Direction of Integration 96

6.5.9 Crossing the MBT Boundary 97

6.6 Column Section Profiles: Operating Conditions 3 and 4 97

6.6.1 Statement 97


6.6.3 Column Profile 98

6.6.4 Pinch Point Loci 99

6.6.5 Analysis of Column Profile 100

6.6.6 Pinch Point 102

6.6.7 Further Column Profiles 102

6.6.8 Variations in XD and rD 104

6.7 Applications and Conclusion 105

7 NOVEL GRAPHICAL DESIGN METHODS FORCOMPLEX MEMBRANE CONFIGURATIONS 107

7.1 Introduction 108

7.2 Column Sections 110

7.2.1 Definition 110

CONTENTS vii

7.2.2 The Difference Point Equation 111

7.2.3 Vapor–Liquid Equilibrium and Permeation Flux 113

7.2.4 Column Profiles 113

7.3 Complex Membrane Configuration Designs: General 114

7.3.1 Overview 114

7.3.2 Petlyuk Membrane Arrangement 114


7.4 Complex Membrane Configuration Designs:

Operating Condition 1 117

7.4.1 Statement 117



7.4.4 Requirements for Feasibility 120

7.4.5 Analysis and Behavior of Column Profiles 121

7.4.6 Feasible Coupled Columns 124

7.5 Complex Membrane Configuration Designs:

Operating Condition 2 132

7.5.1 Statement 132



7.5.4 Feasibility 134

7.6 Complex Membrane Configurations:

Comparison with Complex Distillation Systems 138

7.7 Hybrid Distillation–Membrane Design 138

7.7.1 Overview 138


7.7.3 Feasibility 141

7.8 Conclusion 150

8 SYNTHESIS AND DESIGN OF HYBRIDDISTILLATION–MEMBRANE PROCESSES 151

8.1 Introduction 152

8.2 Methanol/Butene/MTBE System 153

8.2.1 Design Requirements 155

8.3 Synthesis of a Hybrid Configuration 156

viii CONTENTS

8.4 Design of a hybrid configuration 159

8.4.1 Column Sections of Hybrid Configuration 159

8.4.2 Degrees of Freedom 161

8.4.3 Generating Profiles for Hybrid Columns 163

8.4.4 Comparing Feasible Design Options 164

8.4.5 Attainable Region 164

8.5 Conclusion 167

9 CONCLUDING REMARKS 169

9.1 Conclusions 170

9.2 Recommendations and Future Work 171

9.3 Design Considerations 172

9.3.1 Processes for Which Membrane Separations

Are Particularly Suitable 172

9.3.2 Processes for Which Membrane Operations Are

Unsuitable 173

9.3.3 Pressure Difference as a Design Consideration 174

9.3.4 Effect of Reflux in Membrane Columns 175

9.4 Challenges for Membrane Process Engineering 176

REFERENCES 177

APPENDIX A: MemWorX USER MANUAL 183A.1 System Requirements 183

A.2 Installation 184

A.3 Layout of MemWorX 184

A.4 Appearance of Plots 186

A.5 Step-by-Step Guide to Plot Using MemWorX 186

A.6 Tutorial Solutions 192

APPENDIX B: FLUX MODEL FOR PERVAP1137 MEMBRANE 201

APPENDIX C: PROOF OF EQUATION FOR DETERMININGPERMEATION TIME IN A BATCH PROCESS 203

APPENDIX D: PROOF OF EQUATION FOR DETERMININGPERMEATION AREA IN A CONTINUOUSPROCESS 207

CONTENTS ix

APPENDIX E: PROOF OF THE DIFFERENCEPOINT EQUATION 209

E.1 Proof Using Analogous Method to Distillation 209

E.2 Proof Using Mass Transfer 213

INDEX 217

x CONTENTS

PREFACE

It is the intention of this book to introduce the reader to new, exciting and

novel methods of designing and synthesizing membrane-based separation

processes. Initially developed by the authors in fulfillment of postgraduate

(PhD) research, these methods provide a unique way of analyzing membrane

systems. This book is a monograph (of sorts) documenting the various

aspects of the research done. Some of this work has already appeared in

reputable scientific journals and has also been presented at numerous con-

ferences. By capturing thiswork in the formof a book, rather than a thesis only,

it is hoped that the research presented here will generate interest, planting a

seed that will grow.

While selectivemembranes are useful in that they are able to perform high-

purity separations, they can be very costly to fabricate. However, the work

displayed here shows that basic, nonselective membranes are also a viable

option for achieving useful separations. What’s more, the nonselective

membranes are more robust—making them cheaper and allowing for a

reconsideration of the design procedure.

The contents of this book are aimed at undergraduate and postgraduate

students, research academia, engineers and scientists in industry involved in

the process design, as well as membrane specialists. The book explains the

ideas and conceptualizes them by incorporating tutorials and worked exam-

ples. A computer-aided program, entitled MemWorX, written by the authors

and fellow postgraduate students, is included to assist the reader with the

xi

contents of the book. MemWorX is not intended as a design tool, but rather a

learning aid, and should be used in a supplementary manner with the book

material.

MARK PETERS

DAVID GLASSER

DIANE HILDEBRANDT

SHEHZAAD KAUCHALI

Johannesburg, South Africa

xii PREFACE

ACKNOWLEDGMENTS

We, the authors, wish to thank the following postgraduate students for their

efforts and significant contribution to the preparation of the book and CD-

ROM: Craig Griffiths, Neil Stacey, Chan Yee Ma, Aristoklis Hadjitheodorou,

Ronald Abbas, Nik Felbab, and Daniel Beneke. Their inputs have been

extremely valuable, enhancing the overall outcome of this work. A special

thanks to Darryn van Niekerk for his contribution in preparing the cover

artwork.

Several organizations have supported this work, both directly and indi-

rectly, and we are grateful to them. These include the University of the

Witwatersrand, Johannesburg, South Africa; The Academic and Non-Fiction

Authors’ Association of South Africa (ANFASA); The National Research

Foundation (NRF) of South Africa; and Sasol Technology for their financial

contributions.

MARK PETERS

DAVID GLASSER

DIANE HILDEBRANDT

SHEHZAAD KAUCHALI

xiii

NOTATION

Scalar quantities represented in italics.

Vector quantities represented in bold italics.

SYMBOLS

A Membrane area m2

A0 Dimensionless membrane area —An Normalized area mol/s

B Bottoms flow rate mol/s

c Number of components —

D Distillate flow rate mol/s

F Feed flow rate mol/s

J Membrane flux mol/s�m2J Vector of fluxes mol/s�m2Ji Flux of component i through the membrane mol/s�m2ki Parameter value for component i (see Appendix A)

L Liquid flow rate mol/s

n Number of theoretical stages in a distillation CS —

p0i Saturation pressure of component i Pa

P Permeate flow rate (continuous) mol/s

P0i Permeability of component i mol�m/s�m2�Pa_P Permeate removal rate (batch) mol/sR (continuous) Retentate flow rate mol/s

xv

R (batch) Retentate holdup mol

r Ratio of pressures (flux model) —

rD Reflux ratio —

S Separation vector —S Side-draw flow rate mol/s

sr Split ratio (hybrid design—see Section 8.4.2) —

t Time s

TF Feed temperature�C

V Vapor flow rate mol/s

x Residual fluid molar composition —

x Retentate composition —XD Difference point —y Permeate composition —y Vapor phase molar composition —

GREEK LETTERS

aDij Relative volatility for distillation —

aMij Ratio of permeabilities, or membrane selectivity —

b(A) Ratio of RT to R(A) —D Net molar flow in a column section mol/sd Thickness of the membrane md Difference vector —ci Liquid phase activity coefficient for component i —pP Permeate (low) pressure PapR Retentate (high) pressure Pat Dimensionless time —

SUBSCRIPTS

Symbol Designates

Acc Accumulated amount

B Bottom

D Distillation

F Feed

i Component i

j Component j

M Membrane separation

P Permeate

R Retentate

T Top

xvi NOTATION

SUPERSCRIPTS

Symbol Designates

D Distillation

M Membrane separation

O Initial conditions� Local composition

ABBREVIATIONS

AR Attainable region

CPM Column profile map

CS Column section

DCS Distillation column section

DE Differential equation

DPE Difference point equation

D-RCM Distillation residue curve map

MBT Mass balance triangle

MCS Membrane column section

M-RCM Membrane residue curve map

MTBE Methyl tertiary-butyl ether

NRTL Nonrandom two liquid

RCM Residue curve map

SP Stationary point

VLE Vapor–liquid equilibrium

NOTATION xvii

ABOUT THE AUTHORS

MARK PETERS obtained his undergraduate degree in Chemical Engineeringcum laude in 2003 and his PhD in 2008 from the University of the

Witwatersrand, Johannesburg, South Africa. The topic of his thesis,

entailing the development of graphical tools for membrane process design,

has formed the basis of this book. Mark has spent time at the University of

Illinois at Chicago (UIC), Chicago, Ilinois, USA as a research student. He

has authored four scientific articles in the field of membrane separation and

has presented work at numerous internationally recognized conferences.

He previously worked as a research process engineer at Sasol Technology,

focusing on Low Temperature Fischer–Tropsch (LTFT) Gas-to-Liquids

(GTL) conversion. He is currently a Separations Consultant and Research

engineer at the Centre of Material and Process Synthesis (COMPS), based

at the University of the Witwatersrand.

DAVIDGLASSER is a personal Professor ofChemical Engineering and directorof the Centre ofMaterial and Process Synthesis (COMPS) at the University

of the Witwatersrand, Johannesburg, South Africa. He obtained his BSc

(Chemical Engineering) from the University of Cape Town and his PhD

from Imperial College in London. Along with Diane Hildebrandt, he

pioneered the work in the Attainable Region (AR) approach for process

synthesis and optimization. He has been awarded an A1 rating as a scientist

in SouthAfrica, by theNational Research Foundation, the central research-

funding organization for the country. He has been awarded the Bill

Neale–May Gold Medal by the South African Institution of Chemical

xix

Engineers (SAIChE), as well as the Science for Society Gold Medal of

the Academy of Sciences of South Africa for his research work. He has

also been awarded the inaugural Harry Oppenheimer Gold Medal and

Fellowship. He has authored or coauthored more than 100 scientific papers

and was editor-in-chief of the new book Series on Chemical Engineering

and Technology, published by Kluwer Academic Publishers of The

Netherlands. He has authored a chapter published in Handbook of Heat

andMass Transfer Volume4, Advances in ReactorDesign andCombustion

Science. He has also served as President of the South African Institution of

Chemical Engineers. He has worked in a very wide range of research

areas, including optimization, chemical reactors, distillation, and process

synthesis.

DIANE HILDEBRANDT is the codirector for the Centre of Material and ProcessSynthesis (COMPS) at the University of theWitwatersrand, Johannesburg,

South Africa. She obtained her BSc, MSc, and PhD from the University of

the Witwatersrand. She has authored or coauthored over 70 scientific

papers and has supervised 40 postgraduate students. She has been both

a plenary speaker and invited speaker at numerous local and international

conferences. In 1998, Diane became the first woman in South Africa to be

made a full professor of Chemical Engineering when she was appointed as

the Unilever Professor of Reaction Engineering at the University of the

Witwatersrand. In 2003, she became the first woman professor of chemical

technology in The Netherlands when she was appointed as a part time

Professor of Process Synthesis, University of Twente, The Netherlands. In

2005, shewas recognized as aworld leader in her area of research when she

was awarded an A rating by the National Research Foundation. She has

been the recipient of numerous awards, including the Bill Neale–MayGold

Medal from the South African Institute of Chemical Engineers (SAIChE)

in 2000, and Distinguished Women Scientists Award presented by the

Department of Science and Technology (DST) South Africa.Most notably,

in 2009, she was the winner of the African Union Scientist of the year

award. She has worked at Chamber of Mines, Sasol and the University of

Potchefstroom and has spent a sabbatical at Princeton.

SHEHZAAD KAUCHALI obtained his PhD at the School of Chemicaland Metallurgical Engineering, University of the Witwatersrand,

Johannesburg, South Africa. He is currently a full time senior academic

and the director of the Gasification Technology & Research Group at the

university. Shehzaad’s thesis developed process synthesis tools for reactor

and separation networks. He has developed expertise in the areas of reactor

network synthesis, hybrid membrane–distillation design and gasification

technologies. Shehzaad has spent ten months at Carnegie Mellon

xx ABOUT THE AUTHORS

University in Pittsburg, Pennsylvania USA as a research scholar. Shehzaad

completed a sabbatical, in the capacity of visiting professor, at the Indian

Institute of Technology (IITB), Powai, Mumbai, India. Shehzaad has

coauthored over ten publications in the field of chemical engineering and

has cosupervised some theses for masters and doctoral degrees. Shehzaad

has been a consultant with the Centre of Material and Process Synthesis

(COMPS) and has consulted for Sasol, AECI, deBeers Diamonds, Element

Six, Pratley, and the Paraffin Association of Southern Africa.

ABOUT THE AUTHORS xxi

CHAPTER 1

INTRODUCTION

Separation processes are fundamentally important in the chemical industry.

It is inevitable that during any chemical process, be it continuous or batch, the

need for effective separation will arise. There are a variety of separation

options available.However, distillation has proved to be themost effective and

commonly used method, especially for the separation of mixtures containing

compoundswith relatively lowmolecularweights, such as organic substances.

Other efficient separation techniques are absorption and liquid–liquid

(solvent) extraction. In recent decades, membrane permeation has come to

the fore as a successful method of separating mixtures, both gaseous and

liquid.

One would like to have available a technique to select the appropriate

method of separation to achieve the required product specifications. This

chapter will begin to address this need, laying the foundation for the rest of the

book.

Membranes have been developed for various separation applications.

Examples of these include, among others, reverse osmosis, electrodialysis,

pervaporation, and gas separation. Rautenbach and Albrecht (1989) discuss

each of these. The aim of this book is not to reiteratewhat numerous texts have

discussed previously. Rather, the reader is referred to this, and other texts (such

as Geankoplis, 1993; Hoffman, 2003; Drioli and Giorno, 2009), which give

Membrane Process Design Using Residue Curve Maps, First Edition.Mark Peters, David Glasser, Diane Hildebrandt, and Shehzaad Kauchali.� 2011 John Wiley & Sons, Inc. Published 2011 by John Wiley & Sons, Inc.

1

more detailed appraisals of each individual membrane application. In order

to demonstrate design and synthesis techniques, only diffusion membranes

(e.g., gas separation and pervaporation membranes) will be considered in

this book, but the method developed can be adapted and applied to the other

kinds of membranes.

In diffusionmembrane separation, a high-pressure fluidmixture comes into

contact with amembrane, which preferentially permeates certain components

of the mixture. The separation is achieved by maintaining a lower pressure

(sometimes vacuum) on the downstream, or permeate, side of the membrane.

The remaining high-pressure fluid is known as the retentate. Figure 1.1a,b

depicts basic batch and continuous diffusion membrane separation units,

respectively. A more detailed discussion of membrane process operation is

given in the book where appropriate. Gas separation involves the diffusion of

a gaseous mixture, whereas pervaporation is a separation process where one

component in a liquid mixture is preferentially transported through the

membrane and is evaporated on the downstream side, thus leaving as a vapor.

These processes are discussed in more detail in Chapter 2.

The conventional way of analyzing membrane separators is to ask what

permeate composition can be achieved for a particular feed, as in the experi-

ments conducted by Van Hoof et al. (2004) and Lu et al. (2002). Furthermore,

the flux of a particular component through the membrane is also reported as a

function of the feed in these and similar experiments. However, it must be

remembered that the flux of any of the components may not necessarily remain

the same and may vary as permeation proceeds down the length of the

membrane (continuous operation). Therefore, the conventional information,

although accurate, is insufficient, especially when it comes to designing

industrial-scalemembrane separators, aswell as sequencing of such equipment.

When examining how the other, more established, separation processes are

analyzed, it can be seen that the methods used for membranes are somewhat

ineffective. In distillation, as well as single-stage flash separations, one never

reports how either the top or bottom products are related to the feed, but rather

Figure 1.1. (a) Batch and (b) continuous diffusion membrane units.

2 INTRODUCTION

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