shaposhnik1997 (1)

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MEMBRANE
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ELSEVIER
Journal of Membrane Science 136 (1997) 35-39
An early history of electrodialysis with permselective membranes
V.A. S h a p o s h n i k a, K. K e s o r e b'*
aDepartment of Analytical Chemistry, Faculty of Chemistry, Voronejh State University, 1, University Place, 394693 Voronejh,
Russian Federation
blnstitute of Technical Chemistry and Macro-molecular Chemistry, Martin-Luther-University Halle-Wittenberg, 06108 Halle~S, Germany
Received 12May 1997; accepted 10 June 1997
Abstract
This paper outlines the main stages in the history of electrodialysis, from the discovery of the method in 1890 to the
development of the fundamental principles of matter-separation and chemical conversions. The evolution of electrodialysis is
closely bonded to the birth of the concept considering the presence of fixed charges and mobile counter-ions in ion exchange
membranes. The main and basic role of the idea about alternating anion exchange membranes and cation exchange
membranes in multi-compartment apparatus (1940) has been described here. Attention has been devoted as well to the
synthesis of anion-permeable membranes from anion exchange resins and cation-permeable membranes from cation exchange
resins (1950). An analysis of the results of the early applications of electrodialysis which has received much development in
the past years, has been also presented.
Keywords: Electrodialysis; Permselective membranes
Electrodialysis with ion exchange membranes
represents one of the most important membrane methods, which deals with the problems of desalination of
salted waters, waste water minimization, production
of ultra-pure water, concentration of dilute solutions,
separation of electrolytes and non-electrolytes and
with the production of acids and alkalis from their
salts [1]. Electrodialysis is a well proven technology
with a multitude of systems operating worldwide. In
Europe electrodialysis dominates as a desalting process with total plant capacity exceeding that of
reverse-osmosis and distillation [2]. Electrodialysis
*Corresponding author. Fax: +49 345 5527163.
0376-7388/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved.
PII S 0 3 7 6 - 7 3 8 8 ( 9 7 ) 0 0 149-X
is also applied for whey-, organic acid- and sugar
demineralization, amino acid and blood treatments,
mineral acid concentration, preparation of isotonic
solutions and wine stabilization. The deep ecological
aspect of this method implies favourable forecasts for
its future.
In 1995 the volume commemorating the 100th issue
of the Journal of Membrane Science pleased its readers through the publication of classical works on
membrane methods but unfortunately, there was no
mention of electrodialysis. However, the editor of this
special issue, K.W. B6ddeker [3], noted the start of
development of electrodialysis in the 1930s, remembering the work of Meyer and Strauss [4] in which the
basic principles of modern electrodialysis had been
proposed.
36
V.A. Shaposhnik, K. Kesore/Journal of Membrane Science 136 (1997) 35-39
Fig. 1. Scheme of the first electrodialysis apparatus. [8].
Prognosing the future is, first of all, an operation on
the past. The bigger the period of time analysed, the
more exact the result we can achieve. In relation to
this, we would like to focus on the fact that electrodialysis has a much earlier history than that usually
acclaimed by several authors.
Electrodialysis is a combination method. One of its
components is dialysis, proposed for the separation of
water and alcohol first by Nollet [5] and later on for the
separation of true and colloidal solutions by Graham
[6]. The other component is electrolysis [7].
Electrodialysis as a method combining electrolysis
and dialysis was proposed for the first time in 1890 by
Maigrot and Sabates [8]. The aim of their work was to
demineralize sugar syrup. Fig. 1 shows the scheme of
the first electrodialysis apparatus. The frames were
made out of wood, the plastic age lying still in future
then. The electrodes were made out of carbon and
permanganate paper serves as membrane. A direct
electric current was supplied by a dynamo. The middle
electrode acted as the common anode. Sugar syrup
was poured through the anodic compartment. On
turning on the dynamo potassium, sodium, magnesium and calcium cations were carried away by the
electric current from the anodic compartment to the
cathodic one. This resulted in the purification (demineralization) of the sugar syrup in the anodic compartment. In order to prevent the precipitation of sparingly
soluble hydroxides, the reaction medium was controlled using litmus paper. The electrodialysis process
was stopped when the litmus turned blue. Cassel and
Kempe [9] applied this method to purify molasses,
syrups and sugar solutions. The particularity in their
work was the addition of salt solution to the cathodic
solution, causing an alkaline reaction to take place
under hydrolysis. This, in turn, prevented the hydrolysis of the desired products by the acids formed
during the anodic reaction.
However, the term 'electrodialysis' was not used in
the patents considered above. It was proposed for the
first time in the patent of Schollmeyer in 1900 [10],
whose aim was to purify sugar syrup through the same
method but using soluble zinc or iron anodes with
simultaneous ozonation of the solutions. Kollrepp and
Wolf [11] continued to use the term electrodialysis in
their patent describing an improvement of the method
for the purification of sugar syrup through the solubility of a sparingly soluble salt of lead, obtained
during the use of a soluble lead anode.
The first article about electrodialysis which
appeared in a scientific journal was published in
1903 by Morse and Pierce [12]. Evaluating the first
works on electrodialysis, Schlrgl [13] assumed that
uncharged and non-selective membranes were used
there. An analysis of those publications allows us to
state that the membranes used had a small concentration of fixed ions and were still very far from ideal
selective membranes. But they were not totally inert.
New ideas came from the biologists Loeb and
Beutner [14], who discovered the selective permeability of apple skin to cations during a study on the
dependence of electrode potentials from the concentration of electrolyte solutions. They demonstrated
that the nature and type of the anion did not influence
the magnitude of the electrode potentials, but at the
same time the charge number and type of cations
caused a significant impact on it. Remembering the
old apple which was picked by Eva from the tree of
knowledge and the one which brought Newton to the
universal law of gravitation, we can conclude that
those wishing to make beautiful discoveries must put
their attention first of all on the wise apple. Studying
the flow of a direct current through membranes of
collodion, permanganate-impregnated paper and gelatine, Bethe and Toropoff [15] found that there was a
deviation from neutrality in the solution at the mem-
V.A. Shaposhnik, K. Kesore/Journal of Membrane Science 136 (1997) 35-39
brane surface. We would like to put some more light
on this acidification found at the cathodic side and on
the alkalination occurring at the anodic side. Today, in
view of modem representation these results can be
interpreted as the exceeding of the limiting current
density on the membrane, proving the existence of a
difference in the transport numbers of ions in the
membrane and in the solution. The excess of the
electrical current over the limiting value is transferred
by hydroxonium ions, formed during the non-reversible dissociation of water molecules at the solution/
membrane interface. This causes a decrease in the pH
of the diffusion boundary layer at the cathodic side and
an increase in the pH at the anodic side. As such, this
gives us the base to make conclusions about the
selective permeability of these membranes for cations.
Furthermore, Bethe and Toropoff found that the walls
of the pores have non-mobile negative charges and
that there was an excess of mobile charges inside the
pores, compensating the charges of the non-mobile
ones. Indeed, the mobile ions carry the electrical
charges through the membrane under the application
of a gradient of an electric potential across the membrane system.
The synthesis of semi-permeable membranes was a
first related to trials dealing with the modelling of
biological membranes. It was easier to measure
the transport number, electrical conductivities and
membrane potentials for synthetic membranes. The
pioneering start of research on model membranes was
laid down by Michaelis, studying the properties of
collodion membranes [1,16]. The membranes used in
his early works had low electro-chemical activities.
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37
Nevertheless, they were more selective in respect to
cations, having weak acidic carboxylic ions as ionogene groups. Anion selective membranes were
obtained during the adsorption of proteins on collodion membranes.
Generalizing the results of his precedents and of his
own experiments, Teorell [17-19] developed the theory of charged membranes. According to this theory a
selective membrane is considered as a homogeneous
phase in which the fixed ions, mobile counter-ions and
the mobile co-ions having the same charge sign as the
fixed ones are uniformly distributed. Under this consideration, the membranes selectively permeable to
cations had negatively charged fixed ions and membranes selectively permeable to anions had positively
charged fixed ions. The concentration of co-ions was
limited by the electrostatic repulsion from the fixed
charges of the membrane, which corresponded to the
earlier thermodynamical theory of membrane equilibrium developed by Donnan [20]. The further development of this theory was practised by Meyer and
Sievers [21], Sollner [16] and Schl6gl [13].
Theoretical research on the electrochemistry of
membranes opened the way for the progress in electrodialysis. The use of the first electrodialysers with 3
compartments emerged in the works of Pauli [22]. The
mixture to be separated was fed into the middle
compartment from which the cations migrated into
the cathodic compartment and anions into the anodic
compartment. The first monograph on electrodialysis
came out, explaining clearly the electrodialysis process [23]. Nevertheless, only one type of membrane
was used in the electrodialysers of that time.
A
KA
KA
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b
Fig. 2. Migration of ions in a system of alternating membranes, a - before the action of an electric current, b - after the action of an electric
current, where • represents an anion and 0 a cation. [4].
38
V.A. Shaposhnik, K. Kesore/Journal of Membrane Science 136 (1997) 35-39
Manegold and Kalauch [24] used for the first time
permselective anion exchange and cation exchange
membranes in a 3-compartment electrodialysis apparatus. Desalination took place in the middle compartment. An outstanding work by Meyer and Strauss [4],
in which the properties of alternating cation exchange
and anion exchange membranes were presented.
Fig. 2 shows the process of ion transport in a 6compartment electrodialysis cell. In (Fig. 2 (a)) during the absence of the action of an electric current,
there is an uniform distribution of cations and anions
in the compartments of the apparatus. Under the
application of an electric field, with the passage of
a direct electric current through the solution, a beautiful symmetrical process starts taking place. During
this process the cations move towards the cathode and
the anions in the opposite direction towards the anode.
For example, with numbering of compartments done
from left (anodic compartment) to right, the anions
from the second compartment migrate towards the
anodic compartment through the anion-permeable
membrane and the cations migrate towards the
cathode through the cation-permeable membrane. As
a result of this, desalination takes place in the second
compartment. During the electro-migration towards
the cathode, cations from compartment 2 meet an
anion-permeable membrane in their way which separates compartments 3 and 4. This membrane stops
further migration of the cations towards the cathode.
Consequently, the cations gather in the solution in
compartment 3. On the other side there is an electromigration of anions from compartment 4 into the
solution in compartment 3. This electro-migration is
limited by the presence of a cation-permeable membrane separating compartments 2 and 3. Consequently,
there is concentrating of ions in the compartment 3. In
this way, the multi-compartment electrodialysis of
Meyer and Strauss [4] allowed to carry out the concentration as well as the desalination of electrolyte
solutions without the danger that the products enter
into a chemical reaction with the electrodes in the
electrodialyser. Even more important to note is that the
same expense of electrical energy is needed for carrying out the electrode processes in the multi-compartment electrodialyser as in the three compartment
apparatus.
Subsequently this led to an increase in the number
of compartments in the apparatus with alternating
cation-permeable and anion-permeable membranes
to hundreds of membranes and compartments, under
which all the even-numbered compartments fulfilled
the function desalination and all the odd ones- that
of concentrating, in respect to the above described
electrode positions and numbering.
The realization of the principle of alternating
cation-permeable and anion-permeable membranes
in multi-compartment electrodialysis became possible
after the manufacture of selective membranes from
ion exchangers. First, it started after the work of Juda
and Mc Rae [25] and also simultaneously after that of
Kressman [26]. Soon after this the basic principle of
electrochemistry of ion-exchange membranes and the
basic directions of electrodialysis with ion-exchange
membranes were worked out: purification, desalination of weak electrolytes with low dissociation constants, and of non-electrolytes; concentration of
solutions; synthesis of acids and bases from their salts;
reactions of double chemical conversion; methods for
the separation of ions according to their mobilities,
magnitude and sign of charge and to their differences
in the capabilities to form complexes [1]. Soon, a very
fruitful idea of filling the compartments of the electrodialyser with ion exchange granules was born,
which principally expanded the first and original
concepts about the possibilities of electrodialysis,
allowing to work in economically and ecologically
desirable improved ways for the deep desalination of
dilute solutes [27,28].
That was relatively a short period, but a period
of high stress and breakthroughs, during which the
most important versions of the application electrodialysis were worked out. In this way ended the
early period of development of electrodialysis - a
method which has to occupy a place among the
most important and determining technologies of the
twenty-first century.
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