Electrochemical Cell Design

396 Pages·1984·13.475 MB·English

by  S. N. Chatterjee (auth.), Ralph E. White (eds.)

Electrochemical
Cell Design
Electrochemical
Cell Design
Edited by
Ralph E. White
Department of Chemical Engineering
Texas A&M University
College Station, Texas
PLENUM PRESS • NEW YORK AND LONDON
Library of Congress Cataloging in Publication Data
Main entry under title:
Electrochemical cell design.
"Selected contributions from a symposium on recent advances in electrochemi
cal cell design, held March 27-31,1983, in Houston, Texas"-T.p. verso.
8ibliography: p.
Includes index.
1. Electrolytic cells-Congresses. 2. Electric batteries-Congresses. I. White,
Ralph E.
QD568.E44 1984 621.31'242 84-11710
ISBN-13: 978-1-4612-9723-9 e-ISBN-13: 978-1-4613-2795-0
001: 10.1007/978-1-4613-2795-0
Selected contributions from a symposium on Recent Advances in
Electrochemical Cell Design, held March 27-31, 1983, in Houston, Texas
© 1984 Plenum Press, New York
Softcover reprint of the hardcover 1s t edition 1984
A Division of Plenum Publishing Corporation
233 Spring Street, New York, N.Y. 10013
All rights reserved
No part of this book may be reproduced, stored in a retrieval system, or transmitted
in any form or by any means, electronic, mechanical, photocopying, microfilming,
recording, or otherwise, without written permission from the Publisher
PREFACE
This book consists essentially of a collection of papers that
were contributed to a national meeting held in Houston, Texas, in
1983. The papers contained herein cover a wide range of electro
chemical engineering topics and should serve as useful starting points
in the design of electrochemical cells.
The editor would like to thank the authors for their contribu
tions and patience and the typists, Mrs. Susan 'Firth and Mrs. Jeri
Saulsbury, for their efforts. Also, the editor would like to thank
Mr. T. Nguyen and Ms. M. A. Nictrolson for their help in preparing the
index of this book.
R.E. White
v
CONTENTS
Design and Development of Electrochemical
Chlor-Alkali Cells • • • • • • • • • 1
S. N. Chatterjee
A Simple Model of a Diaphragm - Type Chlorine Cell 25
R. E. White, J. S. Beckerdite, and J. Van Zee
Design Principles for Chlorine Membrane Cells 61
K. H. Simmrock
Hydroxyl Ion Migration, Chemical Reactions, Water Transport
and Other Effects as Optimizing Parameters in Cross-,
Co- and Countercurrently Operated Membrane Cells for
the Chlor/Alkali Electrolysis .•••••••.•••• 89
K. H. Simmrock
Hydraulic Modelling as an Aid to Electrochemical Cell Design. 115
I. Wardle
Calculating Mechanical Component Voltage Drops in
Electrochemical Cells • • • • 123
I. Wardle
Electrolysis Cell Design for Ion Exchange Membrane
Chlor-Alkali Process • • • • • • • • • • • • 135
M. Seko, A. Yomiyama, and S. Ogawa
Experiences with a Bench-Scale Electrochemical Plant • 161
R. D. Goodin, R. E. W. Jansson, and R. J. Marshall
Economic Driving Force in Electro-Organic Synthesis 175
R. E. W. Jansson
Design of SU Modularized Electrochemical Cells • 197
A. Bjareklint, L. Carlsson, and B. Sandegren
vH
viii CONTENTS
Electrochemical Techniques for the Extraction of Heavy Metals
in Industry: Concepts, Apparatus and Cost • • • • 207
W. Samhaber
The Design and Application of Rotating Cylinder Electrode
Technology to Continuous Production of Metal • • • • 225
N. A. Gardner and F. C. Walsh
Shunt Current Control in Electrochemical Systems -
Theoretical Analysis • • • • • • • 259
P. G. Grimes, R. J. Bellows, and M. Zahn
Shunt Current Control Methods in Electrochemical
Systems - Applications • • • • • • • • • • 277
P. G. Grimes and R. J. Bellows
A Simple Model of Exxon's Zn/Br2 Battery. • •••••• 293
J. Van Zee, R. E. White, P. G. Grimes, and R. J. Bellows
. . . . . . .
A Finite Element Model of Bipolar Plate Cells 311
J. W. Holmes and R. E. White
Changes in Overall Ohmic Resistance Due to
. . . . . . . . . .
Migration/Diffusion of Electrolytes 337
K. H. Lim and E. I. Frances
Mathematical Model for Design of Battery
Electrodes: Lead-Acid Cell Modelling 357
W. G. Sunu
Extension of Newman's Numerical Technique to
. . . . .
Pentadiagonal Systems of Equations • • • • • • 377
J. Van Zee. G. Kleine. R. E. White, and J. Newman
Index 391
DESIGN AND DEVELOPMENT OF ELECTROCHEMICAL CHLOR-ALKALI CELLS
S. N. Chatterjee
Durgapur Chemicals Ltd.
Calcutta, India
ABSTRACT
The gradual development of electrochemical chlor-alkali processes
is described. The processes described are as follows: diaphragm,
mercury and membrane. These processes are compared and various design
and selection factors are given for a variety of membrane processes.
INTRODUCTION
The manufacture of chlor-alkali by an electrochemical process is
an old industry. The first diaphragm process was commissioned in 1886
and has undergone a slow evolution since then. Cell amperage has
increased gradually with time from 1 KA to 100 KA. The main drawback
of the diaphragm cells of early days was a large anode/cathode gap to
accomodate diaphragm swelling resulting in high energy consumption,
low concentration of caustic soda, and high chloride impurity in the
caustic soda, which made it unsuitable for some industries like
production of Rayon, etc. This necessitated the development of the
mercury cell process. The technology of mercury cells even up to the
mid-fifties was not very advanced when compared to that of the
eighties. With improved cell design, energy consumption and other
2 S.N.CHATTERJEE
operating costs have been brought down considerably. The technology
of both cells was improved further by the use of dimensionally stable
metallic anodes in 1968.
Due to a large increase in oil prices between 1973 and 1980 and
stringent effluent regulations, a new chlor-alkali technology was
needed. As a result of research and development in pilot plant
studies throughout the world, the first chlor-alkali membrane cell was
commissioned in 1975. There is presently a continuous effort from
every corner to further bring down energy consumption, capital cost,
and operating cost in commercial membrane cells. DC energy consump
tion of 4000 kWh/ton in the mid-fifties, for instance, was brought
down to 2200 kWh/ton in 1983.
Diaphragm Cells
Up to the early seventies all diaphragm-type electrolyzers were
equipped with graphite anodes and asbestos diaphragms. In the course
of time the design became even more sophisticated. The bottom was ~f
complicated form. A 10 - 12mm electrode gap was kept to accomodate
diaphragm swelling. The maximum specific load was around 1.5 KA/m2•
The compact and nearly cubic form of the electrolyzer, which resulted
in high current density in the steel cathode, had to be reinforced by
copper bus bars in order to reduce the thermal load and energy losses.
The introduction of metal anodes with improved diaphragms removed
these limitations resulting in reduction of the electrode gap to 3 -
4mm. A smaller electrode has necessitated closer fabrication
tolerances for the anode.
One of the improved diaphragm cell designs is the UHDE HU type
cell design. This (see Table 1) is based on the idea of keeping the
cell rows and the current and product paths short in order to reduce
DESIGN OF CHlOR-AlKALI CEllS 3
Table 1.
u
Electrolyzer Anode Diaphragm (V)
General Graphite Asbestos 0.9 - 1.0 4.4 - 4.6
General Metal Asbestos 0.5 - 0.6 3.6 - 3.8
Hooker H4 Metal HAPP 0.40 3.38
UHDE HU Metal HAPP 0.36 3.30
*
Cell electrical resistance factor in the equation U 2.36 + KI with
I in KA.
Table 2. Cell Characteristics: Kuhera SK 330 Cell
Current density, amp/sq m 2,340
Cell voltage 3.3
Current efficiency, % 96.5
DC kWh/metric ton, NaOH 2,292
Diaphragm life, days 200 to 400
Catholyte conc., % NaOH 11 - 12
NaCI02 in catholyte, % 0.002 - 0.01
the conductor and piping requirements and to save space. Also the
by-pass switch for this cell system is in an advantageous position
below the row of cells. In addition, a polymer modified asbestos dia
phragm (HAPP) developed by Hooker is used in the HU type electro
lyzers. This diaphragm is dimensionally stable, and its high
mechanical stability increases its service life from 200 to 500 days
depending on the brine purity. The low K value of 0.36 in Table 1 for
the HU type electrolyzer has not been surpassed apparently by any
other diaphragm electrolyzer using the same anodes and diaphragms.
Improved diaphragms offer several other advantages such as: (a) less
resistance to cell room upsets; (b) lower hydrogen in chlorine gas;
(c) ease of recovering spent diaphragm material; (d) better reproduci
bility of cell performance throughout the operating period; (e) longer
diaphragm life during storage; and (f) twice the diaphragm life
compared to standard asbestos. Kuhera Chemical Industry has developed
a cell which uses a molded asbestos diaphragm and operates at 330 KA
(see Table 2 for performance).
4 S. N. CHATTERJEE
Some of the additional developmental work taking place for
further improvement in diaphragm cell technology is:
(a) catalytic coating of cathodes to reduce hydrogen over
voltage;
(b) microporous diaphragms which have the possibility of the
elimination of asbestos, improved current efficiency and
higher caustic strength;
and (c) dynamic gel diaphragm having the potential of ion exchange
functions in a diaphragm cell at much lower cost than mem
brane cells.
Mercury Cell
For the last 25 years there has been rapid growth in electrochem
ical chlor-alkali technology. This has been achieved by improving the
design concept to optimize industrial production techniques
superceding the technology up to the 1950's. For our discussion in
this paper we shall consider mercury cells up to the fifties as older
cells.
Reduction of investment cost became necessary in the following
areas: (a) cells; (b) mercury inventory; (c) graphite requirement;
(d) bus bar requirement; and (e) civil work. Attention was also di
verted to reduction of operating cost by lower graphite and mercury
consumption, lower bus bar loss and less down time of the plants.
Design in the follOwing areas was significantly improved:
(a) Current Density and Mercury Inventory - The arrangement of
cathodic discs in older cells was replaced by bare bottom
cells. This altered design concept necessitated higher
current density and a higher slope of the cell from 0.5% to
even 1.5%. These changes resulted in reduction of energy
consumption and mercury inventory. Mercury inventory,
cathode surface area and cell house area per ton of caustic