Liquid Membranes. Theory and Applications

198 Pages·1987·3.47 MB·English

by  Richard D. Noble and J. Douglas Way (Eds.)

Liquid Membranes
In Liquid Membranes; Noble, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
In Liquid Membranes; Noble, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
347
A C S SYMPOSIUM S E R I E S
Liquid Membranes
Theory and Applications
Richard D. Noble, EDITOR
National Bureau of Standards
J. Douglas Way, EDITOR
National Bureau of Standards
Developed from a symposium presented at
the 8th Rocky Mountain Regional Meeting
of the American Chemical Society
in Denver, Colorado,
June 8-12, 1986
American Chemical Society, Washington, DC 1987
In Liquid Membranes; Noble, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Library of Congress Cataloging-in-Publication Data
Liquid membranes.
(ACS symposium series, 0097-6156; 347)
"Developed from a symposium presented at
the 8th Rocky Mountain Regional Meeting of the
American Chemical Society in Denver, Colorado,
June 8-12, 1986."
Includes bibliographies and indexes
1. Liquid membranes—Congresses.
I. Noble, R. D. (Richard D.), 1946- . II. Way,
J. Douglas. III. American Chemical Society.
IV. American Chemical Society. Rocky Mountain
Regional Meeting (8th: 1986: Denver, Colo.) V. Series.
QD562.I63L57 1987 660.2'842 87-18684
ISBN 0-8412-1407-7
Copyright © 1987
American Chemical Society
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PRINTED IN THE UNITED STATES OF AMERICA
In Liquid Membranes; Noble, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
ACS Symposium Series
M. Joan Comstock, Series Editor
1987 Advisory Board
Harvey W. Blanch
University of California—Berkele
Alan Elzerman W. H. Norton
Clemson University J. T. Baker Chemical Company
John W. Finley James C. Randall
Nabisco Brands, Inc. Exxon Chemical Company
Marye Anne Fox E. Reichmanis
The University of Texas—Austin AT&T Bell Laboratories
Martin L. Gorbaty C. M. Roland
Exxon Research and Engineering Co. U.S. Naval Research Laboratory
Roland F. Hirsch W. D. Shults
U.S. Department of Energy Oak Ridge National Laboratory
G. Wayne Ivie Geoffrey K. Smith
USDA, Agricultural Research Service Rohm & Haas Co.
Rudolph J. Marcus Douglas B. Walters
Consultant, Computers & National Institute of
Chemistry Research Environmental Health
In Liquid Membranes; Noble, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Foreword
The ACS SYMPOSIUM SERIES was founded in 1974 to provide a
medium for publishing symposia quickly in book form. The
format of the Series parallels that of the continuing ADVANCES
IN CHEMISTRY SERIES except that, in order to save time, the
papers are not typeset but are reproduced as they are submitted
by the authors in camera-ready form. Papers are reviewed under
the supervision of th
Advisory Board and ar
symposia; however, verbatim reproductions of previously pub
lished papers are not accepted. Both reviews and reports of
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types of presentation.
In Liquid Membranes; Noble, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Preface
LIQUID MEMBRANE TECHNOLOGY is coming of age. The chapters in this
book indicate the renewed and widespread activity in this field. This
renaissance has come about because of the following factors: better
understanding of carrier chemistry for carrier-mediated transport, better
support materials such as ion-exchange membranes, an increasing number
of applications, and better predictive capabilities. Commercialization of this
technology for both gas- an
indicates its highly advance
objective of this book is to present state-of-the-art papers on various
aspects of this technology that can assist either the novice or practitioner.
The text covers liquid- and gas-phase separation, emulsion and immobilized
liquid membranes, theory, experimentation, and applications.
Putting this book together has been particularly satisfying for us
because, as the saying goes, the time is right. The increased activity in the
field coincides with the completion of the text. Our timing was fortuitous
and a little lucky. We have also been fortunate to get the authors to
contribute their work and add to the ultimate success of this book. This
book was also completed in spite of a six-month sabbatical in Italy (R.D.N.)
and a job change (J.D.W.). Our desire to turn out a good piece of work
overcame these and other obstacles. We hope that, after you use the book,
you agree that the effort was worthwhile.
A special thanks to Susan Robinson and the ACS Books Department
staff for a job well done. An excellent typing performance was accom
plished by Terry Yenser and Vicky Vivoda of the Word Processing group at
the National Bureau of Standards.
We also acknowledge the support of Madhav Ghate and Lisa Jarr of
Morgantown Energy Technology Center through DOE Contract No.
DE-AI21-86MC23120.
RICHARD D. NOBLE J. DOUGLAS WAY
National Bureau of Standards SRI International
Center for Chemical Engineering Chemical Engineering Laboratory
Boulder, CO 80303 Menlo Park, CA 94025
May 1987
ix
In Liquid Membranes; Noble, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Chapter 1
Liquid Membrane Technology
An Overview
Richard D. Noble and J. Douglas Way1
National Bureau of Standards, Center for Chemical Engineering, Boulder, CO 80303
Liquid membrane technology is introduced and is identi
fied as a subset of membrane science. A tutorial sec
tion discusses configurations, transport mechanisms,
experimental techniques and a survey of basic theoret
ical approaches
branes which combin
as extraction or absorption with stripping are discus
sed. The chapters to follow in this volume are summa
rized and the subject of each is placed in perspective
to the field of liquid membrane technology.
Tutorial
A membrane can be viewed as a semi-permeable barrier between two
phases. This barrier can restrict the movement of molecules across
it in a very specific manner. The membrane must act as a barrier
between phases to prevent intimate contact. The semi-permeable na
ture is essential to insuring that a separation takes place.
There are two points to note concerning this definition.
First, a membrane is defined based on what i t does, not what i t is.
Secondly, a membrane separation is a rate process. The separation
is accomplished by a driving force, not by equilibrium between
phases (JO.
By extending our definition of a membrane, we can include liq
uids. If we view a membrane as a semipermeable barrier between two
phases, then an immiscible liquid can serve as a membrane between
two liquid or gas phases. Different solutes will have different
solubilities and diffusion coefficients in a liquid. The product of
these two terms is a measure of the permeability. A liquid can yield
selective permeabilities and, therefore, a separation. Because the
diffusion coefficients in liquids are typically orders of magnitude
higher than in polymers, a larger flux can be obtained.
1Current address: SRI International, Chemical Engineering Laboratory,
Menlo Park, CA 94025
This chapter is not subject to U.S. copyright.
Published 1987, American Chemical Society
In Liquid Membranes; Noble, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
2 LIQUID MEMBRANES: THEORY AND APPLICATIONS
Liquid membranes can be prepared in two different configura
tions (see fig. 1). A liquid can be impregnated in the pores of a
porous solid for mechanical support. This form is commonly known as
an immobilized liquid membrane (ILM). In the alternate configura
tion, the receiving phase is emulsified in an immiscible liquid mem
brane. This type of liquid membrane is known as a liquid surfac
tant, or emulsion liquid membrane (ELM).
An ILM can be made in at least three different geometries. A
planar or flat geometry is very useful for laboratory purposes. For
industrial purposes a planar geometry is not very effective since
the ratio of surface area to volume is too low. Hollow fiber and
spiral wound modules can be used to provide high surface area to
volume ratios. Surface area to volume ratios can approach 10,000
m2/m3 for hollow fiber and 1000 m2/m3 for spiral wound modules (2).
Way et al. (3) discuss the criteria for selecting supports for ILMs.
There are two primary problems associated with the use of ILMs
Solvent loss can occur. Thi
tion, or large pressure difference
support structure. Also, carrier loss can occur. This loss can be
due to irreversible side reactions or solvent condensation on one
side of the membrane. Pressure differences can force the liquid to
flow through the pore structure and leach out the carrier.
Ion exchange membranes (IEMs) have recently been studied as a
means for overcoming the above problems (£). The carrier is the
counter ion in the IEM. The carrier is bound in the membrane by
ionic charge forces. The IEM is a nonporous polymer which is
swelled by the solvent. Because the IEM is nonporous, no "short
circuiting" occurs i f the membrane loses solvent. The carrier also
remains bound in the membrane. The membrane can be resolvated and
continue performing without a loss in capacity
Emulsion liquid membranes are also known as double emulsions.
Two immiscible phases are mixed with a surfactant to produce an emul
sion. This emulsion is then dispersed in a continuous phase. Mass
transfer takes place between the continuous phase and the inner
phase through the immiscible (membrane) phase. Figure 1 shows both
an ILM and an ELM.
In both purification and recovery applications the ELM must be
demulsified into two immiscible phases after the extraction step of
the process. This is commonly accomplished by heating, application
of electric fields (5), or centrifugation. The liquid membrane
phase containing the surfactant and carrier will be recycled to the
emulsion preparation step while the internal phase of the emulsion
containing the concentrated solute will undergo further purification
in a recovery process or treatment and disposal in a purification
process. Such a continuous process is shown in Figure 2.
The major problem associated with ELMs is emulsion stability.
The emulsion must be formulated to withstand the shear generated by
mixing during the extraction but must be broken to remove the inter
nal phase and reformulate the emulsion. This requires an additional
process step and additional energy inputs. Consequently, this pro
cess has limited potential applications to recovery of products with
high added value or to pollution control, where process efficiency
and degree of separation may be more important than the cost of the
process.
In Liquid Membranes; Noble, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
1. NOBLE AND WAY Overview of Technology 3
Impermeable Boundaries
Support
Containing
Liquid Membrane
Permeate Permeate
,which is solvent!
Rich Fluid Lean Fluid
containing
the carrier,
complex, and
other species
"Semi-permeable
Boundaries
Figure 1. Immobilized and emulsion liquid membranes.
(Reproduced from Ref. 23.)
Addition of
LM Components
Inner Phase
Emusifier Recovered
Components
of the LM
(carrier,
surfactant, etc.)
Wastewater
Inner Phase
(recovery,
disposal)
Mixer Settler
Purified Water
Figure 2. Flowsheet of an emulsion liquid membrane extraction
process.
In Liquid Membranes; Noble, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.