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
Copyright � 2011 by John Wiley & Sons. All rights reserved.
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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
6.5.2 Mathematics 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
6.6.2 Mathematics 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
7.3.3 Material Balances 116
7.4 Complex Membrane Configuration Designs:
Operating Condition 1 117
7.4.1 Statement 117
7.4.2 Mathematics 117
7.4.3 Column Profiles 119
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
7.5.2 Mathematics 132
7.5.3 Column Profiles 133
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
7.7.2 Material Balances 140
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