I n d . Eng. Chem. Res. 1994,33, 96-101
96
SEPARATIONS Ion Transport through Monovalent-Anion-PermselectiveMembranes Guido Saracco*and Maria Chiara Zanetti Dipartimento di Scienza dei Materiali e Ingegneria Chimica, Politecnico di Torino, C.so Duca degli Abruzzi, 24, 10129 Torino, Italy
This paper analyzes the separation properties of monovalent-anion-permselectivemembranes, manufactured and commercialized for edible salt production from seawater. Experimental data from the separation of S042-from C1- ions are used to verify the reliability of a new theory based on kinetic concepts, and compared with those of a previously studied separation ( C 2 0 4 W l - ) . In both cases, the proposed model fits data satisfactorily, contrary to the classical solution-diffusion model (based on thermodynamic principles), which cannot account for the strong dependency of the measured separation factors on the electric current density applied; the new proposed model may be thus regarded as a good tool for process design purposes.
Introduction Edible-grade sodium chloride can be obtained from seawater by electrodialytic preconcentration (up to 200220 g/L) followed by evaporative crystallization. This production route has been performed in Japan since the early 1970s. Meanwhile this technology has been exported to other countries (i.e., Korea, Taiwan, and Kuwait) so that about 1.2 million tons of salt per year are nowadays produced in the world according to this procedure (Bauer and Strathmann, 1990). The membranes employed for this purpose have to be monovalent-ion-permselective, namely be capable of separating monovalent ions (Na+,C1-) from divalent ions (Ca2+, Mg2+,S042-).The rejection of divalent ions is important for two reasons: (a) their content has to be quite low in edible-grade salt; (b) their presence in the concentrate promotes irreversible scaling of the membranes (i.e., precipitation of salts such as, for example, Cas04 on the membrane surface). Different methods were tested for the production of these permselective membranes. Some researchers tried to suppress the transport of divalent ions by the introduction of some exchange groups, having a strong affinity for these ions, into the membrane (Yamane et al., 1961; Onoue et al., 1961). However, divalent ions became irreversibly bound to the introducedexchange groups, thus making this method almost ineffective. Attempts were also made to decrease the charge density on the membrane surface, but results were poor (Hani and Nishihara, 1961; Mihara et al., 1969). Anisotropic membranes were then developed in which a thin layer with a high cross-linking density was synthesized upon a non-permselective membrane support (Yawataya, 1962; Hani et al., 1966; Gunjima and Sugano, 1973). The thickness of this layer was optimized so as to reduce divalent-ion transport without unacceptably increasing the electric resistance of the membranes. This method is nowadays industrially adopted for manufacturing all commercial anion-exchange membranes permselective toward monovalent anions (Sata, 1992). Finally, the fixation of a thin surface layer, carrying charges of the same sign of those of the permeating ions,
* To
whom correspondence should be addressed. E-mail:
[email protected]. 0888-5885/94/2633-0096$04.50/0
was performed either by impregnation or coating with a promoting reactant mixture (Glueckauf and Kitt, 1956; Mihara et al., 1970; Tsuda et al., 1978; Shimasaki et al., 1987;Sata et al., 1989;Sata and Izuo, 1989),or by dynamic accumulation, on the membrane surface, of ionic macromolecules added to the solution fed to the electrodialyzer (Azeki et al., 1972; Tanaka and Seno, 1981). In any case this charged layer affects the permeability of divalent ions by rejecting them more intensively than monovalent ones through electrical repulsion forces. Nowadays industriallyproduced cationic membranes, permselective to monovalent cations, are manufactured following this last procedure (Sata, 1992). Particularly, Tokuyama Soda Co. produces monovalentcation-permselective membranes (Neosepta CMS)(Sata et al., 1989), prepared by synthesizing a thin cationiccharged layer on their surface, and also monovalent-anionpermselective membranes (Neosepta ACS) carrying a surface layer of a highly cross-linked resin (Gunjima and Sugano, 1973). In both cases the surface films are responsible for divalent ion repulsion. We have recently studied the potentials of these membranes in the recovery treatment of industrial wastewaters (Saracco et al., 1993; Saracco and Onofrio, 1993). Attention is here focused on ion transport through monovalent-anion-permselectivemembranes and modeling thereof. In fact, while transport phenomena through monovalent-cation-permselectivemembranes have been studied to some extent, there is a surprising lack of literature about monovalent-anion-permselectivemembranes concerning this topic. The separation between SOr” and C1- ions was experimentally tested. The obtained findings are here presented and compared with those of a previously studied separation [ C Z O ~ ~ /(Saraccoet C~al., 199313on the basis of an original theory. The consequent modeling approach was developed mainly to account for kinetic phenomena, which were found to influence markedly the separation efficiency of the membranes.
Experimental Section Our experimental setup was a modified, continuously operable version of the commercially available model TS2-10 by Tokuyama Soda Co. equipped with Neosepta ACS 0 1994 American Chemical Society
Ind. Eng. Chem. Res., Vol. 33, No. 1, 1994 97 Table 1. Experimental Results: SOdZ-/C1-Separation 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
25 25 25 25 25 30 30 30 30 30 30 35 35 35 35 35
25.1 18.3 44.2 24.5 48.6 17.97 44.5 44.5 18.06 17.82 44.45 17.65 43.1 17.02 16.9 30.5
3.71 3.68 3.65 3.52 3.73 3.68 3.72 3.65 3.31 3.37 3.69 3.65 3.61 3.40 3.29 3.69
and CMS membranes. The structure of ACS membranes is composed of a PVC internal tissue giving mechanical stability to the membrane which is coated upon it via the so-called "paste method" (Mizutani et al., 1975). A highly cross-linkedlayer is then deposited accordingto procedures described in Yamane et al. (1963). More details about the properties of these membranes can be found in Tokuyama Soda (1989), while some information about their rather complex chemical composition is given in Yamane et al. (1964). A detailed description of the electrodialyzer and of the employed membranes was reported in Saracco et al. (1993). The membrane stack was composed of 10 pairs of cells for a total membrane surface of 0.2 m2. The diluate and the concentrate were kept in two separate reservoirs. The intermembrane chambers, provided with static turbulence promoters, were fed in parallel with diluate and concentrate alternatively. The solutions were conveyed to the membrane stack from the diluate and the concentrate reservoirs using separate pump-arounds. In accordance with industrial practice these solutions were forced to flow with a linear velocity of about 6 cm/s along the membranes. Polarization phenomena give rise to ion concentration gradients at the membrane-solution interfaces. The consequent concentrations variations were proved to be comparatively small and thus negligible for the interpretation of the experimental data (Saracco et al., 1993). The pH and temperature of each solution, as well as the applied current density and the electric potential difference over the membrane stack, were monitored and controlled at setpoint values within ranges of industrial interest (Bauer and Strathmann, 1990). The solution continuously fed to the diluate tank had a fixed composition: NaCl = 40 g/L; Na2S04 = 5 g/L. These concentrations were chosen equal to those adopted for the Cz042-/Cl-separation (Saracco et al., 1993), so as to set a proper basis for a comparison. Moreover, they are close to those typical of seawater. The effective composition of the solution flowing in the diluate loop could be varied, within certain limits (see Table l), by changing the flow rate of the above feed solution, at given hold-up and current density values. The higher the feed flow rate, the higher the saline content in the diluate reservoir. The composition of the concentrate was allowed to reach a steady-state value as long as the solution permeating the membranes was flushing the corresponding tank. Each run was stopped when stationary conditions were reached (typically after 20 h of operation).
887 1191 1222 1502 737 773 1186 1177 1523 1617 934 1303 1569 1686 1867
5.34 1.65 5.24 2.10 4.57 0.955 1.65 7.57 16.4 3.52 7.44 2.17 18.96 21.1 12.9
120.3 160.1 163.7 201.3 100.0 103.8 159.4 159.7 208.5 217.6 127.1 175.2 215.3 231.5 253.7
33.4 59.6 33.5 54.9 33.0 67.7 58.9 28.5 17.6 38.1 25.9 50.3 16.6 15.6 17.5
32.1 59.5 34.4 50.2 32.3 74.2 54.7 25.4 18.6 38.6 25.6 46.2 16.1 15.1 20.9
The content of sulfates in the diluate and in the concentrate (in this last case arising from the escape of these ions through the membranes) was determined via a gravimetric method [Bas04 precipitation (Treadwell, 1966)l. The NaCl concentrations, dominating the saline content of both solutions, were deduced from conductivity measurements.
Results The separation efficiency of the membranes can be represented by a separation factor defined as follows:
C d and C m are the concentrations of divalent and monovalent ions in the diluate, while J d and Jm are the respective molar flow rates through the membranes. These flow rates could be derived on the basis of simple mass balances. We measured the variation of the separation factor versus the main parameters which proved to affect it in a significant way, in order of importance: the effective current density imposed i, the ratio between the ion concentrations in the diluate c d c d , and the operating temperature. i, could be easily calculated from J d and Jm values. The experimental results of the 16 runs performed are listed in Table 1. These results are substantially consistent with the product characterizations from the membrane manufacturer, which are given only for standard values of temperature, current density, and ion concentration (Tokuyama Soda, 1989). At first glance one can readily appreciate the major role played by the current density upon a, a likely sign of nonequilibrium phenomena affecting the separation. For example, runs 1 and 4 were performed at almost constant temperature and diluate composition values, getting a marked decrease of the separation factor (from 46.6 to 33.5) when the current density was almost doubled. Similar considerations can also be drawn for other couples of runs (i.e., 8 and 11, 9 and 10, 12 and 14).
Modeling
Data interpretation through an adequate modeling approach is somewhat complex owing to the variety of transport phenomena taking place simultaneously in monovalent-anion-permselective membranes (Figure 1). Anions are transported via the imposed current density i from the diluate to the concentrate. A small escape of Na+ ions in the opposite direction, also pushed by the
98 Ind. Eng. Chem. Res., Vol. 33, No. 1, 1994
i
Diluate
I
Concentrate
monovalent
I 1. Oanotic transport of water 2. Electro-osmotic transport of water 3. Electric transport sf ions 4. transport of ions 5. Partial rejection of diualent ions
Figure 1. Transport phenomena in an anion-exchange membrane. (- -) Minor flow rates; (-) major flow rates.
-
electric current, is unavoidable due to the imperfect cation repulsion of the membranes (co-ionleakage). Water moves toward the concentrate either because of direct osmosis or via electroosmotic transport as ion-solvating molecules. Ions potentially move from the concentrate to the diluate due to pure diffusion. Finally, divalent-ion rejection mechanisms take place on the membrane surface. Any attempt to take into account each one of these transport mechanisms in a complex modeling setup results in an overwhelming task. Things are further complicated by the formerly described heterogeneous structure and composition of the membranes. In a simplifying effort, one should take into consideration only the phenomena that markedly control the separation, neglecting those of minor importance. In this context, the classical approach to the modeling of ion transport through ionic membranes is based on the so-called solution-diffusion model developed by Teorell in the early 1950s (Teorell, 19511, on the grounds of the thermodynamic theory of the Donnan-exclusion potential (Donnan and Guggenhein, 1932). A quasi-equilibrium condition is assumed to be verified at the interface between the membrane and the diluate. The concentrations of the generic ion i inside (tagged) and outside (untagged) the membrane are linked by the following expression (valid in case of a 1:l electrolyte in dilute aqueous solution):
ci = K
e g The equilibrium constant KW is related to the activity coefficients of the ion i inside and outside the membrane as well as to the concentration of fixed charges of the membrane itself. Ions, once in the membranes, are assumed to move accordingto the Nernst-Planck equation, while the Einstein relationship is used to link diffusion coefficients to electric mobilities (Hwang and Kammermeyer, 1975). This modeling fails when applied to our separation data mainly because of its inability to account for the dependency of the separation factor on the applied current density. A more elaborate modeling based on the thermodynamics of irreversible processes (De Groot and Mazur, 1984)can in principle consider the effect of current density, the variety of the interactions between the ions and the membrane, and the complex structure of the membrane
permselectbe membraneI lcryer bulk Figure 2. Qualitative potential profiles and apparent activation energies of anions in an anion-exchange membrane.
itself. The practical applicability of irreversible thermodynamics is however hampered by the major difficulties in the experimental measurement of a great number of independent interaction, diffusion, resistance, and frictional coefficients. If a thermodynamic approach fails, a kinetic one may be helpful. Therefore we developed a kinetic model based on apparent activation energy concepts. The existence of nonequilibrium phenomena in the permeation through monovalent-cation-permselective membranes was already proposed by Sata (1973) and Timashev (1991). Similar theories have been frequently used to solve other problems of dynamic electrochemistry Le., the Butler-Volmer expression of the electrode overpotential for the discharge of ions from electrolytic solutions, the Mott-Cabrera equation linking the current flowing in solid electrolytes to the applied electric field, etc. (Atkins, 1978)l. We assumed that the thin permselective layer imposes different potential energy barriers (i.e., apparent activation energies) w d and W,, to the permeation of divalent and monovalent anions, respectively (Figure 2). The ion concentrations inside and outside the membrane are assumed to be linked by an expression similar to the one by Teorell:
where Ki is now a kinetic constant, accounting for the existence of a potential barrier, Wi, or for the molar thermal energy of the ions (RT),or, which is most important, for the electric energy they possess as a consequence of the imposed effective current density ie (zi is the valency of the generic ion i, F is the Faraday number, and R1 is the electric resistance of the highly cross-linked film). Due to their electric and thermal energy, ions pass over the potential energy barriers imposed by the highly-cross linked layer. The permselectivity toward chloride ions arises from the much lower value of W, compared to that of w d . Provided the entire permselectivity is given to the membranes by the considered layer and no further separation occurs in the bulk of the membrane, we can set (4) and finally derive an expression of the separation factor
Ind. Eng. Chem. Res., Vol. 33, No. 1, 1994 99 0.5 1 0.4 -0.3 -0.2 -0.1 -r s , o
I
1
I
I
I
I
I 0.85
1.4 1.2 I
..
I 1 .
-0.1 --0.2 --0.3 .-0.4 .-
1.6 1
1
0
I
Y 1
I
--- - - - - - -
;**m*&--
0.8
1.1
I
0.6
0.4 4 0.25
1
1
1
1
1
0.35
0.45
0.55
0.65
0.75
iJT (A.K-1.m-2)
-0.5 ’I
Figure 4. Data dependency on effective current density and their fitting by the proposed model. C 2 0 4 W l -separation: (- - -) model; ( 0 ) experimental data. SOrZ/C1- separation: (-) model; ).( experimental data.
Assuming Separation SO,z/C1C20rZ/Cl-
A -3.078 -1.255
B (K)
C (K-A-l.m2)
1703 1523
-1.729 -1.494
D 0.952 0.270
as a function of the main variables of interest:
which in logarithmic terms becomes In a = A + B T1 + C1f + D l n
(2)
(6)
The data listed in Table 1were fitted by the least squares method, neglecting the dependency of R1 on temperature. Table 2 lists the thereby obtained values of the constants in eq 6, together with those derived from the previously studied C204W1- separation (Saracco et al., 1993). On the basis of these figures, the values of the separation factor could be estimated as a function of T, i,, and Cm/Cd, and are reported in the last column of Table 1.
Discussion Adeviation parameter 6 can be defined in order to assess the model accordance to experimental data: 6=
amod - aexp
(7)
a0.p
6 values are plotted in Figure 3 as a function of aerpfor both separations. For the system S04VCl- the absolute value of 6 is always lower than 137% ,except for run 16; for the C20r2-/C1- separation 6 is always lower than 5 % . The standard deviation, defined as U=
(&y2
(8)
is 0.083 for the so42-/c1- separation and 0.031 for the C2O4%/Cl-one. This has to be regarded as a good approximation from an engineering viewpoint. The reliability of the model is particularly encouraging as regards the capability of accounting for the effect of i,.
eq 6 can be rewritten in the form
Y = -C(i$T) (10) Figure 4 shows the variation of Y vs iJT as it can be derived from either the experimental data or the model. The model fits satisfactorily the experimental data of both separations. Estimations of the electric resistance of the layer R1, directly proportional to the slope of both model lines, can be easily derived as 1.29 and 1.49 Q.cm2for the C Z O ~ ~ - / C ~ and the S042-/C1-separations, respectively. These values are quite close to each other, as should be expected. The slight difference may eventually be explained with a different interaction of sulfate and oxalate ions with the permselective layer. Moreover R1 values are consistent with the electric resistance of the entire membrane [=2.5 Qcm2(Tokuyama Soda, 1989)l. From the interpolation constant B the potential barrier difference ( w d - Wm)can be estimated as 14.2 kJ-mol-l, a slightly higher value than that obtained for the oxalate/ chloride separation (12.7 kJ*mol-l). In fact the rejection of Sod2-ions was a bit stronger than that of C204% ions, as demonstrated by the higher CY values measured for the system so42-/c1- in comparable conditions. The used membranes were indeed optimized especially for S042-repulsion in order to overcome the abovementioned problems of scale formation during the production of edible salt from seawater. Yamane et al. (1964) noticed that when monovalentanion-exchange membranes as the ones we employed were dipped and equilibrated with seawater, the ratio sod2-/ C1- in the examined membranes was much lower than that in seawater itself. This is a likely index of the low solubility of the sulfate ions in the resin constituting the membrane layer. Equilibrium-controlled separation mechanisms, parallel to kinetic-controlled ones, may be enabled, owing to this low solubility, especially when operating at low current densities. This might be also suggested by the value n = 1.95 (derived for the coefficient D listed above), which is quite close to the value 2 of the Teorell expression (Teorell, 1951). From the data of the c2042-/c1- separation the same parameter is equal to 1.27, a value much closer to 1 (first-order kinetics). A sort of intermediate regime between an equilibriumand a kinetic-controlled one may be governing both separations. Nonetheless a dependency on i, can only be
100 Ind. Eng. Chem. Res., Vol. 33, No. 1, 1994
described by means of kinetic concepts and not by equilibrium ones. Final considerations can be drawn concerning the values of the interpolation coefficients listed in Table 2. The value of A, rather different for the two systems, probably has to be regarded as a mere fitting parameter, not directly linked to any further experimental evidence. From the B coefficients, estimates of the difference w d - W,, could be derived, obtaining reasonable values. The reliability of these data is however limited by the narrow range of variation of (l/T). In fact temperature in electrodialysis can be varied only between 298 and 313 K. The lower limit is imposed by an excessive increase of the electric resistance of the membrane stack, while the upper limit is related to membrane degradation problems. Keeping a constant temperature value, the terms related to A and B Coefficients in expression 6 could be grouped in a single overall fitting parameter. Concerning C and D parameters, things are rather different. Their values appear reliable since they are based on a comparatively wide excursion of (Q T ) and (cdc d ) , respectively. Moreover, they are related to specific experimental features such as the electric resistance of the permselective layer under operating conditions and the solubility of the ions in the membranes (i.e., relevance of equilibrium-controlled phenomena). Perhaps, simple and specific experiments (i.e., R1 determination, solubility measurements) might lead to a confident estimation of C and D values for different systems than those studied, with no need of extensive separation studies.
Conclusions The performance of commerciallyavailable monovalentanion-permselective membranes (Neosepta ACS by Tokuyama Soda Co.) was tested as regards the separability of S042-from C1- ions. The experimental data were compared to those of a previously studied separation ( C Z O ~ ~ / C on~the - ) basis of a kinetic-based theoretical approach. The thereby derived model allowed to satisfactorily account for the dependency of the separation factor on the applied current density (the main parameter affecting it). The traditionally employed solution-diffusion model could not be used due to its inability to describe this dependency. Moreover, the proposed model gives a relatively accurate prediction of the separation factor a for both systems. This, on the one hand, suggests its possible wider applicability to other separation cases and, on the other hand, makes this model a potentially attractive tool for engineering design purposes. In fact, plants for edible salt production from seawater are generally designed in multiple-stage systems. The stages are fed consecutively with the diluate, whose monovalent-ion concentrations are progressivelydepleted while those of divalent ions increase. Therefore the separability of these ions becomes, stage after stage, more and more critical. The use of progressively lower operating current densities can help to keep the separation factor sufficiently high, as long as the ratio CdCd decreases. Moreover,lower current densities would limit the energy dissipations exactly where the electric resistance is increased by the low saline content of the diluate (last stages). However, low current densities require large membrane areas for a given NaCl production. This needs an optimization. A model that could confidently predict the variation of the separation factor vs the current density is needed for
this purpose, especially if the amount of available experimental data is not extensive. In the specific field of edible salt production from seawater, the experience gained during decades of application, the very wide amount of data available, and the tough competition among the producers (Tokuyama Soda, Asahi Glass, etc.) lead to highly developed process and plant designs. Rather than in this context, the developed model might be particularly helpful for plant design purposes whenever new separations are studied using monovalent-ion-permselective membranes (e.g., in the recovery treatment of an industrial wastewater). For instance, the application of the model to the design of a multiple-stage electrodialytic plant for Na&204/NaCl separation was recently reported in another paper by the authors (Saracco and Onofrio, 1993).
Nomenclature A, B, C, D = fitting parameters E , C = ion concentration inside the membrane and in the
diluate [mol.L-lI F = Faraday constant = 96 480 coulomb.equir1; i = current density [A-m-21 J = molar flow rate of ions through the membranes [mol.h-l] Kw = equilibrium constant K = kinetic constant K , = preexponential kinetic constant n = model exponent N = number of runs for each separation R = ideal gas constant = 8.314 Jamol-1K-1 R1= electricresistance of the highly cross-linkedlayer [Q.m2]T = temperature [K] z = ion valency W = apparent activation energy [kJ.mol-l] Y = model variable Greek Letters a = separation factor
6 = deviation parameter (T = standard deviation Subscripts e = effective exp = experimental i = generic ion i m = monovalent ion mod = modelistic d = divalent ion
Literature Cited Atkins, P. W. Physical Chemistry;Oxford University Press: Oxford, UK, 1978. Azeki, S.; Yamamoto, H.; Nagabuka, S.; Akiyama, M.; Itami, Y. Treatment for Giving Low Permeability of Bivalent Cation to Cation Exchange Membranes by Adding Reagent of Feed Sea Water. Bull. SOC.Water Sci. 1972,26,38-49. Bauer, B.;Strathmann, H. Ion Exchange Membranes. Presented at the 8th European Summer School on Membrane Science, Gargnano, Italy, Sept 17-21,1990. De Groot, S. R.; Mazur, P. Non-Equilibrium Thermodynamics; Dover: New York, 1984. Donnan, F.; Guggenheim, E. A. Die genaue Thermodynamik der Membrangleichgewichte. Z . Phys. Chem. 1932,162,346360, Glueckauf, E.; Kitt, G.P. A New Electrolytic Separation Technique Using Semipermeable Membranes. J. Appl. Chem. 1966,6,511516. Gunjima, T.;Sugano, Y. Jpn. Pat. 48-34999, 1973. Hani, H.;Nishihara, H. Jpn. Pat. 3164,April 14, 1961. Hani, H.;Nishihara, A.; Oda, Y. US Pat. 3,276,991,Oct 4, 1966.
Ind. Eng. Chem. Res., Vol. 33, No. 1, 1994 101 Hwang, S. T.; Kammermeyer, K. Membranes in Separations; Techniques of Chemistry 12;Wiley: New York, 1975. Mihara, K.; Misumi, T.; Yamagoehi, Y.; Miyauchi, H.; Tsuzura, K. Jpn. Pat. 8985,April 25, 1969. Mihara, C.; Misumi, T.; Miyauchi, H.; Ishida, T. Jpn. Pat. 19,980, July 8, 1970; Jpn. Pat. 30,693,Oct 5, 1970. Mizutani, Y.; Kusumoto, K.; Mizumoto, Y. US Pat. 3,868,314,1975. Onoue, Y.; Mizutani, Y.; Yamane, R.;Takasaki, Y. Studies on IonExchange Membranes. 11. Selectivity of Cation Exchange Membranes for NaCl-CaC12 System. J. Electrochem. SOC.Jpn. 1961, 30,156158, Saracco, G.; Onofrio, M. Electrodialytic Recovery of NaCl and NazC204 from an Electrolytic-Titanium-Leaching Solution by Means of Permeoselective Membranes. Proceedings of the First International Conference on Recycling, Geneva, CH, 1993; Hexagon Ltd.; Copenhagen, Vol. 111, pp 153-165. Saracco, G.; Zanetti, M. C.; Onofrio, M. Novel Application of Monovalent-Ion-PermselectiveMembranes to the Recovery Treatment of Industrial Wastewater by Electrodialysis. Ind.Eng. Chem. Res. 1993,32, 667-662. Sata, T. Properties of a Cation-Exchange Membrane. Adsorbed or Ion Exchanged with HexadecylpyridiniumChloride. Electrochim. Acta 1973,18,199-203. Sata, T. (Tokuyama Soda Co. L a . ) Private communication, 1992. Sata, T.; Izuo, R. Modification of the Transport Properties of Ion Exchange Membranes. XII. Ionic Composition in Cation Exchange Membranes with and without a Cationic Polyelectrolyte Laver at Eauilibrium and During- Electrodialysis. J. Membr. Sci. 1989,45,269-224. Sata,T.; Izuo,R.;Takata, K. Modificationof the Transport Properties of Ion Exchange Membranes. IX. Laver Formation on a Cation Exchange Membrane by Acid-Amide Bonding, and Transport Properties of the Resulting Membrane. J.Membr. Sci. 1989,45, 197-208.
Shimasaki, H.; Ihara, M.; Mizutani, Y. Modification of Cation Exchange Membrane by Grafted Poly-(4-vinylpyridinium Chloride). J. Appl. Polym. Sci. 1987,34,1093-1108. Tanaka, Y.; Seno, M. Treatment of Ion Exchange Membranes to Decrease Divalent Ion Permeability. J. Membr. Sci. 1981,8,116 127. Teorell,T. Zur quantitativen Behandlung der Membranpermeabilitat. 2.Elektrochem. 1951,55,460-469. Timaehev, S . F. Physical Chemistry of Membrane Process; Ellis Horwood: New York, 1991. Tokuyama SodaCo. Neoseptalon-Exchange Membranes; Catalogue No. 89020500,1989. Treadwell, F. P. Chimica Analitica; F. Vallardi editore: Milano, 1966; Vol. 2,p 515. Tsuda,S.; Misumi,T.; Murakoehi,M. Jpn. Pat. 44,155,Nov27,1978. Yamane, R.; Mizutani, Y.; Onoue, Y. Studies on Ion-Exchange Membranes. IV. Permselectivity of Anion Exchangers for NaClNap904 System. J. Electrochem. SOC.Jpn. 1961,30, 220-223. Yamane, R.;Mizutani, Y.; Motomura, H.; Izuo, R. Studies on Ion Exchange Membranes. XXI. Preparation of sodz Non-permselectiveAnion Exchange Membranes. J.Electrochem. SOC.Jpn. 1964,32 (3),134-142. Yawataya, T. Thinly Reaii Coated Cation-ExchangeReain Membrane with Permselectivitybetween Uni-and Di-Valent Cations. Dechema Monogr. 1962,47,501-514. Received for review June 4,1993 Revised manuscript received September 16, 1993 Accepted September 22,1993.
Abstract published in Advance ACS Abstracts, November 15, 1993. @
