ISSN 1070-4272. Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 3, pp. 461! 463. + Pleiades Publishing, Inc., 2006.
Original Russian Text + V.P. Greben’, I.G. Rodzik, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 3, pp. 468! 471.
AND POLYMERIC MATERIALS
Mg/Na Selectivity of Sulfonic Cation-Exchange Membrane
Modified with Poly(4-Vinyl-N-Propylpyridinium) Bromide
V. P. Greben’ and I. G. Rodzik
Institute of Chemistry, Far-Eastern Division, Russian Academy of Sciences, Vladivostok, Russia
Received October 4, 2005
Abstract-Mg/Na selectivity of sulfonic cation-exchange membrane modified with poly(4-vinyl-N-propyl-
pyridinium) bromide by surface electrodeposition, influenced by the electrodialysis conditions, is studied.
Cations can be separated by electrodialysis with a
cation-exchange membrane using various techniques.
The most practicable approach involves complexation
of cations of one or several sorts with formation of
compounds poorly penetrable through the membrane.
In particular, Na and K ions were separated by elec-
trodialysis in the presence of 18-crown-6 as a strong
complexant for potassium . Silver was separated
from zinc and copper in the presence of EDTA .
Malonic, oxalic, and citric acids were used as com-
plexants in separating Cu, Ni, and Co . The draw-
back of this approach is in a large consumption of
Another approach involves bulk or surface modifi-
cation of the membrane by soaking in solutions of
reagents, which are mostly high-molecular-weight
cationic surfactants or complexants. For example, im-
pregnation of a cation-exchange membrane with
crown ethers increases the permeability with respect
to alkali cations as compared to alkaline-earth ele-
ments, and also to Na relative to K . Modification
with polyethylenimine was used to increase the proton
transfer relative to that of divalent cations . The
most widely used method is modification of cation-
exchange membranes by direct introduction of re-
agents into the solution to be electrodialyzed. In this
case, the modifier, having, as a rule, a positive charge,
e.g., cyclodextrin , polyethylenimine [7, 8], or
crown ether , is electrodeposited on the membrane
surface from the side of the solution being dialyzed,
thus increasing the transmembrane transfer of alkali
metals as compared to alkaline-earth elements.
All the above-mentioned methods require regular
repeated modification of membranes, because of
gradual desorption of modifiers from the surface.
Therefore, it is advisable to chemically bind a modi-
fier to the membrane. Takata et al.  have bound
polyethylenimine to the surface of cation-exchange
membranes through interaction with sulfochloride
groups introduced into the membrane.
In this study we examined the effect of modifica-
tion of MK-40L membrane with poly(4-vinyl-N-prop-
ylpyridinium) bromide (PVPPB) on the Mg/Na selec-
tivity of transmembrane transport.
The selectivity coefficient of transmembrane trans-
is written as
are the transport numbers of
Mg and Na cations across the membrane and c
, Mg and Na concentrations in the solution
The cell and the procedure of determination of the
transport numbers of the cations were the same as in
. The middle compartment of the cell between an
ideally selective anion-exchange membrane and the
investigated cation-exchange membrane was charged
with 0.25 N NaCl + 0.25 N MgCl
with or without
addition of PVPPB. Three different procedures were
used for modification of the cation-exchange mem-
(1) The membrane was held for a fixed time in
a PVPPB solution, washed with distilled water several
times for 335 s, and arranged in the cell. The middle
compartment was filled with the NaCl and MgCl