formance and confirm that the sample capillary is responsible to a certain extent for the effect, the noted improvement is insufficient to justify this approach as a technique for overcoming the inferior performance chanacteristics of unheated FID’s. In conclusion it would appear that heated type FID’s are required for accurate real-time concentrations and modal mass automotive measurements. Acknou ledgrnents The author gratefully acknowledges the interest and cooperation shown by J. Blanke and R. E. Belcher of Beckman Instruments, Inc., during the course of this program. Literature Cited (1) Blades, A . T . , J Chromatog S e i , 11,251-5 (1973)
( 2 ) Sternberg, J . C., Gallaway, W. S., .Jones, D. T. L., “tias Chromatography,” N . Brenner, .J. E. Callen, M . D. Weiss, Eds., pp 231-67, Academic Press, New York, N.Y., 1962. (3) Mohan, P., General Motors Proving Ground. private communication, 1973. (4) Jackson, M . W., General Motors Research Laboratories, ibid., 1971. (5) Johnston, M . , Beckman Process Instruments Division, ibid., 1971. (6) Siegel, R. D . , J Air Pollut. Contr. A s s . , 22,845-53 (1972). (7) Wagner, T. O., SAE Paper KO. 700338, Society of Automotive Engineers, National Air Transportation Meeting, New York, N.Y., 1970. Receiied for reuieu, December 5, 1973. Accepted April 24, 1974. Mention of commercial products is for identification on/> and does not constitute endorsement or recommendation for use. Work supported under contract from the Vehicle Emi,ysions Laborator?, of General Motors Procing Ground.
Selectivity of Strongly Basic Anion Exchange Resins for Organic Anions Michael Semmens”.’ and John Gregory Department of Civil a n d Municipal Engineering, University College London, London WC1, England
Exchange equilibria between chloride and a series of carboxylate ions are presented for a variety of strong-base anion exchange resins. Six polystyrene resins differing widely in structure, type, and cross-link density were examined. The carboxylate ions ranged from butyrate to decanoate; within this range, no significant electrolyte sorption or uptake of free acid occurred so that sorption was accounted for entirely by ion exchange. All of the resins showed a regular increase in selectivity for carboxylate as the chain length of the latter increased and values for the standard free energy change for the transfer of a methylene group from aqueous solution to the resin phase have been estimated for each resin. Despite the differences in structure and cross-link density all resins yielded a value of approximately -2200 J mol-I; a similar value obtained from independent selectivity data available for the exchange between hydrogen and a series of alkyl ammonium ions. These results confirm earlier reported results and support the conclusion that hydrophobic interaction between the resin matrix and the hydrocarbon chains of the carboxylates is responsible for the increasing selectivity. One of the most important characteristics of strongly basic anion exchangers is their high selectivity for certain large organic ions, which may be desirable or undesirable depending upon their application. For instance, advantage is taken of the resins’ selectivity for organics in the study and characterization of organic color in natural waters ( I ) , for the removal of color from products in the food processing industry (2), and in large varieties of organic and biochemical separation processes (3). However, the same characteristic is responsible for the problems of organic fouling ( 4 ) whenever these resins are used in the demineralization of surface waters-a problem of major concern in water treatment practice. Present address, Department of Civil Engineering, University of Illinois, Urbana, Ill. 61801. 834
Environmental Science & Technology
The research into organic fouling like the vast literature on organic separations is mainly of a n empirical nature, and comparatively little effort has been made to investigate systems which will develop a n understanding of the interactions that give rise to the observed behavior. In this study, the exchange of a series of carboxylate ions for chloride on a variety of strongly basic anion resins has been investigated, and a n attempt has been made to indicate which factors are operative in determining resin selectivity. Experimental Resins. Six commercially available strong-base anion exchangers were studied. The properties of the various resins are summarized in Table I. The resins were first cleaned by alternate treatments with hot water and cold methanol and conditioned with alternate treatments of 1M NaOH and 1 M HC1. Capacities were measured by elution of chloride with NaN03 and subsequent argentometric titration with potassium chromate indicator. Resin samples were stored in deionized water and were not allowed to dry. Reagents The purest available forms of n-butyric, n-hexanoic, noctanoic, n-nonanoic, and n-decanoic acids (at least 98% pure) were obtained from B.D.H. Ltd., England. These compounds were used without further purification. Analar potassium chloride, sodium nitrate, potassium hydroxide ampuls, and hydrochloric acid ampls were also obtained from B.D.H. Ltd. Stock solutions (0.1N) of the potassium salts of the carboxylic acids were made by neutralizing the appropriate weight of acid with the contents of a volumetric ampul of potassium hydroxide. Dilution water was distilled and deionized. Equilibration Procedure The apparatus used was similar to that of Kressman and Kitchener ( 5 ) , with a plastic mesh resin container
that could be rotated in the solution. Rotation of the container was a t 900 rpm to give a rapid flow of solution through the resin and ensured thorough mixing of the solution. The solution vessel was equipped with platinum electrodes so that the conductance of the solution could be followed during equilibration. The electrodes were connected to a Wayne-Kerr Bridge B 221, with Auto-Balance Adaptor AA 221, the signal from the latter being fed to a Servoscribe RE 511.20 chart recorder. Solutions used contained potassium carboxylate and potassium chloride, the total concentration being fixed a t 10 meq/l. The equivalent fraction of carboxylate varied from 0.2-1.0 (i.e., 2 to 10 meq/l.), and the solution volume was always 250 ml. A known amount of chloride-form resin (3-8 meq, depending on expected uptake of carboxylate) was placed in the mesh container and lowered into the solution of least carboxylate concentration in a series. The resin was rotated a t 900 rpm and the uptake of carboxylate was followed conductometrically. During exchange of carboxylate for chloride, conductance of the solution increased since the equivalent conductance of the chloride ion is considerably greater than that of any of the carboxylates used. For each carboxylate, a calibration curve was obtained so that the composition of the solution could be determined from conductance readings. This method is, of course, only valid when the carboxylate is removed from solution entirely by ion exchange. Several times the chloride level in solution was checked independently by titration with standard silver nitrate solution, and the results were always in close agreement with the values obtained from conductance readings. Since solution p H was always greater than six it is unlikely that significant uptake of free acid occurred. From the recorded conductance trace it could easily be seen when equilibrium had been attained and the final reading gave the composition of the equilibrium solution and, hence, the amount of carboxylate removed from solution. Information on exchange kinetics was also obtained by this method, b u t apart from noting that equilibration for all the ions could be achieved in 7 hr or less, only equilibrium results will be considered here. After each equilibration, the resin sample was stirred in the next solution, containing a higher fraction of carboxylate, and the new equilibrium condition was established. The resin was not regenerated to the chloride form between equilibrations and, thus, the amount of carboxylate exchanged each time had to be added to give a cumulative resin concentration. The final solution contained initially 10 meq/l. carboxylate and, after stirring in this solution, the resin was regenerated with NaCl solution. In some cases, the equilibration was carried out in the reverse order-i.e., exchanging chloride for carboxylate to check the reversibility of the exchange. M o s t of the experiments were carried out a t a temperature of 25 f O.O5"C, although a few were conducted a t higher and lower temperatures.
Resu Its The equilibrium results are presented in the form of X , against X A plots, where X I is the equivalent fraction of carboxylate in the resin and X A the equivalent fraction in solution. If A is preferred, the equilibrium curve is negatively curved and lies above the diagonal, and if the chloride is preferred, the curve is positively curved and lies below the diagonal. In this way, the distribution of carboxylate between resin and solution can easily be seen. Figure 1 shows the curves obtained for the various resins with carboxylates containing 4, 6, 8, 9, and 10 carbon atoms. The figure shows that similar selectivity curves were obtained for all the resins and that in all cases resin
selectivity increased with increasing chain length of the organic ion. The equilibrium curves may be used to calculate separation factors, for given conditions. The separation factor is defined (6) as:
and will generally depend upon total solution concentration and X.A.For the present case of uni-univalent exchange, the separation factor is numerically equal to the molal selectivity coefficient, given by:
where >!dl and Mc:l are molal concentrations of carboxylate and chloride in solution, and bars indicate corresponding quantities in the resin. By use of Equation 2, resin
Table I. Resin Characteristics Percentage crosslinkage Typea
Resin
Matrix
Manufacturer
Deacidite FF-IP isoporous Deacidite FF-IP isoporous Deacidite FF-IP isoporous Deacidite N-IP isoporous Deacidite K-MP rnacroporous
2-3
1
Polystyrene Perrnutit
3-5
1
Polystyrene Perrnutit
7-9
1
Polystyrene Perrnutit
7-9
2
Polystyrene Perrnutit
-
1
Polystyrene Perrnutit
I RA-910
-
2
Polystyrene Rohrn & Haas
= Type 1,resins contain trimethylamine functional groups, whereas Type 2 resins contain dimethylethanolamine groups.
0
0
0,5
1.0
0
XA e Butyrate o Nonanoate
0.5
I.o
XA
v Hexonoote A Deconoate
o Octanoate
Figure 1. Ion exchange equilibria at 25°C between chloride and carboxylate ions for a variety of strong-base polystyrene resins Volume 8. Number 9, September 1974
835
selectivities have been calculated from the equilibrium curves in Figure 1 for X q = 0.5. The results are tabulated in Table I1 to enable easy comparison of the resins. The results of temperature variation studies on exchange equilibria for butyrate and octanoate systems are shown in Figure 2 for the N-IP resin. The results indicate that the selectivity for the organic ions is increased slightly by increasing the temperature. The influence of solution concentration was demonstrated for the octanoate system with the FF-IP (7-9%) resin and solutions of 10-2M and 4 X lO-3M total ionic strength. The equilibrium curves obtained are presented in Figure 3, and show that selectivity increased when solution concentration increased over this range.
Discussion Many factors may affect resin selectivity for carboxylate ions (7-9), and some of the possible interactions of significance are outlined below. For simplicity the interactions may be divided into two sections: (1) those involving the nonpolar hydrocarbon chain and (2) those involving the polar carboxylic group. (1) Interactions Involving the Hydrocarbon Chain (Nonpolar). (a) Water-water interactions. Water molecules are largely covalent in nature and tend to hydrogen bond to one another in pure water. Varying degrees of interaction are possible and a water molecule may hydrogen bond to a maximum of four neighboring molecules. As the degree of association between molecules increases, the water becomes more “structured.” In dilute solution, the introduction of a nonpolar solute tends to promote hydro-
-Octanoate
A, I
Resin
N-IP
:
XA
I .o
0.5 XA Figure 2. Temperature variation studies
.-
,i n
I
-4 x 1 0 ’ Solution ~~
0
I
-
IC‘M
Solution
Resin = F F - I P ( 7 - 9 % ) Temperoture = 2 5 O C
I
0.5 -
Oclanoote
- Chloride I.o
XA
Figure 3. The effect of solution concentration octanoate-chlo-
ride equilibria 836
Environmental Science & Technology
gen bonding among the neighboring water molecules, thereby giving rise to an increase in water structure (10, 11). The decrease in entropy associated with the increase in water structure is unfavorable and tends to exclude nonpolar solutes from solution. There is good reason to believe that the water surrounding an alkyl chain is more structured than free water and that the degree of structuring increases as chain length increases (12). The water inside the resin, however, is likely to be very different in structure from that in-the dilute external solution (13).The water content of the resin is restricted by the extent to which the matrix is able to swell which is, in turn, dependent upon the cross-linking. A medium crosslinked resin will, in the swollen form, contain only about 50% water and this water is confined within the narrow pores and channels of the hydrophobic organic matrix. The diameters of the pores and channels vary with the degree of cross-linking. Pore sizes have been crudely estimated for resins with 1, 2 , and 4% cross-linking as 3, 1.5, and 1 nm on the basis of interchain distances in the rodlike polyelectrolyte model of Fuoss et al. (14). The hydrophobic nature of the organic matrix should tend to promote water-water interactions and increase water structure within the resin, but this effect is more than offset by the large number of fixed ionic groups and their counterions. The limited amount of water must satisfy the competing hydration demands of these ions, and as there is considerably less water per ion available than in the dilute external solution, much of the water within the resin may be expected to be involved in ion-water interactions. Water-water interactions within the resin are therefore physically limited in the extent to which they may occur and are hindered by the disruptive effect of such a large number of ions. The effect a hydrocarbon chain has on the surrounding water within the resin phase is thus significantly reduced and transfer of the hydrocarbon chain to the resin phase results in an overall increase in entropy. As the hydrocarbon chain increases in length, this interaction becomes increasingly more favorable. (b) Hydrophobic interactions (15) between the hydrocarbon chains and the resin matrix may occur (12). These would depend strongly upon the nature of the matrix, perhaps also upon charge density but very little upon crosslink density. (c) When the previous interactions do not occur, it is possible that carboxylate ions in the resin might interact hydrophobically with each other, to give structures analogous to micelles in bulk solution (16, 17). Another tendency with increasing chain length would be toward a greater effect of swelling pressure, due to the increasing size of the resin for the carboxylate, and would be more significant with higher crosslinking (18). (2) Interactions Involving the Polar Group. (a) The intense electric field around an ion or polar group attracts and polarizes a shell of water molecules. The water molecules in this tightly bound shell are referred to as electrostricted molecules. The mare intense the electric field surrounding the ion, the larger the size of the electrostricted shell becomes and the more strongly the ion is hydrated. Thus a small ion, such as lithium, has a large electrostricted shell whereas larger ions which create less intense electric fields have smaller electrostricted hydration shells and in some cases have none. As mentioned above the amount of water within the resin phase is limited and ions in the resin will not be hydrated to the same extent as ions in the dilute external solution. Following the theory of Diamond et a1 (13), all ions will favor the dilute solution where they may satisfy their hydration requirement; however, this preference will be greater for the more
Table II. Measured Selectivity Coefficients Koa at XA = 0.5 Organic ion
Butyrate Hexanoate Octanoate Nonanoate Decanoate
K-MP
IRA-910
0.12 0.32 1.41
0.13 0.27 1.13
6.7
9.0
-
-
N-IP
FF-IP, 2-3%
0.15
-
0.38 1.82 4.55 11.5
0.63 2.60 5.26 14.4
FF-IP, 3-5T0
FF-IP, 7-9T0
0.13 0.25 1.00 2.22 7.30
0.26 0.70 1.94 5.20
-
strongly hydrated ions and the weakly hydrated ions will be “forced” into the resin. (b) The reduction in the degree of ionic hydration within the resin brings about a corresponding increase in the strength of electrostatic interactions since ionic charges are not screened as effectively as they are in the dilute external solution. Rice and Nagasawa (19) have estimated that the dielectric constant within a resin is approximately 30 but may be lower for resins with higher charge density. Effect of Functional :Type From Table I1 it is seen that the type 2 , N-IP resin showed markedly higher selectivities for all the carboxylate ions than the type 1, FF-IP resin of similar cross-link density. The larger ethanolic groups in the type 2 resin must be responsible for this difference. It has also been shown that type 2 resins are more selective toward phosphate (20) and nitrate (21) ions in exchange with chloride ions than their type 1 counterparts. These results may be explained using the theory of Eisenman (22). As the functional group increases in size the electrostatic interactions become less important in determining Selectivity. The nonhydrated radii of the nitrate, phosphate, and the carboxylate group are all greater than that of the competing chloride ion. Therefore, the electrostatic interaction between the chloride and the functional group is likely to be more significantly Ieduced, which gives rise to the observed increase in selectivity for the above ions. Influence of Cross-lifi king Comparing the selectivities of the FF-IP resins for the carboxylates, shown in Table 11, it is apparent that selectivity increases with decreasing cross-link density. As the cross-link density of a resin decreases, the following changes occur: (1) the swelling pressure decreases, ( 2 ) the average pore size increases, and (3) the resin absorbs more water. Clearly the reduced swelling pressure may be responsible for the increase in selectivity since the carboxylate ions are considerably larger than the competing chloride ions and would therefore swell the resins to a greater extent. As will be shown below, however, swelling pressure considerations are not responsible for the observed behavior. Limited access of the larger carboxylate ions to all the exchange sites in the more highly cross-linked resins may also account for the observations; however, this is considered unlikely since it was demonstrated that all resins could be completely converted to the decanoate form. It is, therefore, suggested that the variation in selectivity with cross-linking results from the changes brought about by the increased amount of water within the resin. As the water content of the resin increases the resin phase becomes more like the dilute external solution. The differences in water structure between the resin and the dilute external solution are reduced, and it is likely that the hydrocarbon chain-water interactions will become less important in determining selectivity. The additional water also reduces ielectrostatic interactions and the ion-
water interactions which contribute to resin selectivity. Of these two changes, the changes in water structure cannot account for the observed increase in selectivity with decreased cross-linking since it would support the opposite finding. The explanation for the observed behavior most probably lies, therefore, with the influence of cross-linking on the interactions involving the polar group. For the lower members of the carboxylate series nonpolar interactions are of little significance, and selectivity is principally influenced by interactions involving the polar carboxylate group. Thus the observed low selectivities for butyrate and hexanoate indicate that the resins prefer the chloride ion to the carboxylate group. From section 2(a) this might be interpreted as the preference of the more strongly hydrated carboxylate for the dilute external solution. Alternatively from 2(b) it may result from more favorable interactions between the partially “dehydrated” chloride ion and the functional groups of the resin. Whichever explanation is chosen the preferred ion, chloride, will be favored by an increase in resin cross-linking which thus accounts for the observed behavior. Influence of Solution Concentration From Figure 3 the lower selectivity for the octanoate ion in the 0.004 molar solution may result from the increased preference of the strongly hydrated carboxylate group for the more dilute external solution. The influence of solution concentration upon resin selectivity may be viewed as analogous to the influence of resin cross-linking, in respect of the ion-water interactions. Dilution is equivalent to an increase in resin cross-linking, since both increase the differences in water structure and ionic hydration between the phases. Conversely, an increase in solution concentration is tantamount to a decrease in resin cross-linking. Since the observed increase in resin selectivity for the octanoate ions with decreasing cross-linking arises principally from ion-water interaction, it follows that selectivity will increase with solution concentration. Influence of Chain Length As the hydrocarbon chain length of the anion increases beyond butyrate, the character of the carboxylic group (e.g., pH value) will not change significantly and so the increased affinity must, therefore, arise from interactions involving the hydrocarbon chain. If we use the values from Table 11, when loglo Kc.1” is plotted against n, the number of carbon atoms in the carboxylate ion, for the resins, values for n ? 8 lie on reasonably straight lines. Example curves are drawn in Figure 4. Although Kcl” is not a thermodynamic equilibrium constant, it is possible to relate the slope of these lines to the standard free energy of transfer of a methylene group from aqueous solution to resin. If we consider the resin as a separate phase (12), different standard states of the ions in the resin and bulk solution are assumed. At equilibrium, the free energy of exchange between chloride and carboxylate is given by:
where p a o and pcl0 are the standard chemical potentials of carboxylate and chloride ions in bulk solution, a4 and a(1 the corresponding activities a t equilibrium. As before, are bars indicate quantities in the resin phase. 8, and the partial molal volumes in the resin and I1 the swelling pressure of the resin. Introducing the molal selectivity coefficient from Equation 2 and activity coefficients, y 4, ~ C I etc.: ,
v(.~
Volume 8. Number 9 . September 1974
837
If attention is restricted to the change in with chain length of the carboxylate ion, then all the chloride terms can be ignored. Also, it is reasonable to assume that the activity coefficient ratio, TA/YA, will not change appreciably with chain length, provided the hydrocarbon interactions are included in the term ( p a o - ~ A O ) , which is the standard free energy change for the transfer of carboxylate from aqueous solution to resin phase, AGAO. Hence, Values of RT 6(ln K(-,A)/Gnmay be estimated from the slopes of the lines in Figure 4. Values so obtained are presented below in Table 111. All of the polystyrene resins give a value for RT 6(ln K&)/Gn. of approximately 2200 J mol-I, apart from K-MP which yields a slightly lower result. The last term in Equation 5 cannot be calculated accurately as there is very little information available on swelling pressures in conventional resins and none for macroporous resins. However, when we take the swelling pressures in Table IV as approximate values for conventional resins and assume the partial molar volume per methylene group to be 16 ml mol-I, although this is the value in water ( 2 4 ) , the swelling pressure for the isoporous resins may be estimated.
Table I l l . Values Obtained for RT6(ln Resin
Kc1")/6n
Value obtained, J mol-1
2150 i 150 2200 i 150 2200 i 150 150 2200 2200 i 150 1950 =k 150
N-IP FF.IP (2-3%) FF-I P (34%) FF.IP (7-9%) I R A 910 K.M P
*
Table IV. Variation of 6vA/6n with Cross-linking Resin percent cross-linking
Approximate swelling pressure (25), bars
6Va/6n, J mol-1
2-3 3-5 7-9
0 50 150
+ 75 +250
0
Although the estimated swelling pressure contributions, in Table IV,may be contained within the margins of experimental error it is unlikely when five resins, including IRA 910, all yield the same result for RT 6(ln K(+)/6n. This result suggests that swelling pressure effects are negligible for all the resins with the possible exception of K-MP. The only comparable data for exchange on polystyrene resin are the results of Starobinets and Chizhevskaya (23). These researchers measured the selectivity of Dowex 50 containing 2% and 8% cross-linking for a series of alkylammonium ions. When we take their results for aqueous solution only (they measured the selectivity in a range of aqueous methanol mixtures), a similar plot to Figure 4 may be drawn for the alkylammonium ions as shown in Figure 5. The slopes of these plots are identical and yield a value for RT 6(ln K H ~ ) / of G ~2100 J mol-1. These results therefore support the results obtained with the carboxylates and also confirm that the swelling pressure term in Equation 5 is indeed negligible. It is interesting to compare these values with others reported for the transfer of hydrocarbon chains out of aqueous solution. An incremental value of AG.10 of about -2500 J mol-I has been obtained for the adsorption of surfactants a t an air-water interface, while the slightly larger values of -3400 and -3100 J mol-1 have been obtained a t the oil-water interface (26, 27). It is apparent that the values obtained for six quite different resins and values obtained by Starobinets et al. are similar and close to the corresponding value obtained for adsorption a t the air-water interface. Calorimetric data would be valuable for a detailed interpretation of these results but the temperature variation studies suggest that AH would be small. Some interpretation in terms of the mechanisms l ( a ) and l ( b ) is warranted, however. It is felt that hydrophobic interactions between the carboxylate chain and the resin matrix are primarily responsible for the increase in resin selectivity with chain length. This conclusion stems from the fact that hydrophobic interactions are not affected significantly by the degree of cross-linking, as noted above, and they therefore more readily account for the constant results obtained with resins of varying cross-link density. This is not to suggest that water-water interactions do not contribute to selectivity however. Substantial evidence suggests they do, but the magnitude of water-water interactions arising from the hydrocarbon chain in the resin phase would have to be ,
,
0 Dowex
2
,
,
,
,
50 x 2
0 Dowex 50 x 8 0 -FF-
0 ---FF-IP
iP (2-3%)
(3-5%)
I
RT log K;
-
RT lop K21
4
-I
n
n
- Number of Carbon Atoms in the Carboxylate
Figure 4. Variation of logla K C I A with carboxylate chain length for the FF-IP resins
838
Environmental Science & Technology
5
6
7
8
9
- Number of Carbon
Atoms in the Alkylommonium Ions
Figure 5 . Variation of log,o K H (~x . 4 = 0.5) with the chain length of alkylammonium ions for two Dowex resins. From the data of Starobinets and Chizhevskaya (23)
constant in order to explain the above results. One could argue that the water structure within the resin phase is so strongly influenced by the resin matrix and functional groups that the introduction of a long-chain carboxylate has little influence upon the degrees of water-water interactions even in resins with low cross-link densities. However, in the absence of more detailed thermodynamic data this seems unlikely and it is more likely that water-water interactions would occur to a greater extent in more dilute highly swollen resins. Thus it appears that the extent of water-water interaction contribution to selectivity is limited to the removal of the hydrocarbon chain from the dilute external solution. Hydrophobic interactions between the resin matrix and the hydrocarbon chain would minimize interaction between the hydrocarbon chain and the resin water, and would therefore be affected very little by the increased water content of highly swollen resins. No association between carboxylate ions was observed in the polystyrene resins and so l ( c ) did not contribute in any way to resin selectivity. However, earlier reported results (17) show that carboxylate association is of major importance in determining selectivity for certain acrylic resins. L i t e r a t u r e Cited (1) Grigoropoulos, S. G., Smith, J. W.. in “Organic Compounds in Aquatic Environments,” S. J. Faust and J . V. Hunter, Eds., Marcel Dekker, New York, N.Y., 1971. (2) Parker, K . J., “Ion Exchange in the Sugar Industry,” Chem. Ind., 20, 782 (1972). (3) Colman, C., K r e s m a n , T . R. E., Eds., “Ion Exchange in Organic and Biochemistry,” Interscience, New York, N.Y., 1957. (4) Ward, R. F., “Organic Fouling of Strongly Basic Anion Exchange Resins,” PhD Thesis, Washington University, S t . Louis, Mo., June 1964. (5) Kressman, T. R. E., Kitchener, J . A., “Cation Exchange with a Synthetic Phenolsulphonate Resin. Part 111. Equilibria with Large Organic Cations, J. Chem. S O C . ,1949, p 1208. (6) Helfferich, F., “Ion Exchange,” p 153, McGraw-Hill, New York, N.Y., 1962. (7) Chu, B., Whitney, D. C., Diamond, R. M., “On Anion-Exchange Selectivities,” J. Inorg. Nucl. Chem., 24, 1405 (1962).
(8) Marinsky, J . A., Ed., “Ion Exchange,” Vol. I, Marcel Dekker. New York, N.Y., 1966. (9) Ibid., Vol. 11, 1969. (10) Frank, H . S., Wen, W. Y., “111. Ion Solvent Interaction. Structural Aspects of Ion-Solvent Interaction in Aqueous Solutions: A Suggested Picture of Water Structure,” Discuss. Faraday. Soc., 24, 133 (1957). (11) Nemethy, G., Scheraga, H . A,, “Structure of Water and Hydrophobic Bonding in Proteins. 11. Model for the Thermodynamic Properties of Aqueous Solutions of Hydrocarbons,” J. Chem. Phys., 36,3401 (1962). (12) J . Feitelson, Ref. 9, p 135. (13) Diamond, R. M., Whitney, D. C., in Ref. 8, p 277. (14) Fuoss, R. M., Katchalsky, A., Lifson, S., “The Potential of an Infinite Rod-Like Molecule and the Distribution of Counter Ions,” R o c . N a t . Acad. Sci., 37, 579 (1951). (15) Nemethy, G., Angew. Chem. Int. Ed., 6,195 (1967). (16) Richter, G., 2. Phys. Chem., 12,247 (1957). (17) Gregory, J., Semmens, M . J., “Sorption of Carboxylate Ions by Strongly Basic Anion Exchangers,” J. Chem. S O C . ,Faraday Trans. I., 68, 1045 (1972). (18) Gregor, H. P., “A General Thermodynamic Theory of Ion Exchange Process,”J. A m e r . Chem. S O C . 70,1293 , (1948). (19) Rice, S. A,, Kagasawa, M.,“Polyelectrolyte Solutions,” p 461, Academic Press, New York, N.Y., 1961. (20) Gregory, J . , Dhond, R. V., “Anion Exchange Equilibria Involving Phosphate, Sulphate and Chloride,” Water Res., 6, 695 (1972). (21) Roberts, G. O., Miller, J . R., “Effects of Chemical and Physical Structure on Anion Exchange Equilibria in Quaternary Ammonium Ion Exchangers,” “Ion Exchange in the Process Industries,’’ S.C.I. Symposium, London, 1970. (22) Reichenberg, D., in Ref. 8, p 227. (23) Starobinets, G . L., Chizhevskaya, A. B., “Exchange of n Alkylammonium Ions for Hydrogen and Lithium Ions in Aqueous Methanol Solutions,” Russ. J . Phys. Chem., 41 ( 8 ) , 1135 (1970). (24) Corkill, J. M., Goodman, J. F., Walker, T., Trans. Faraday. S O C . 63, , 768 (1967). (25) Ref. 6, p 112. (26) Davies, J. T., Rideal, E . K., “Interfacial Phenomena,” p 158, Academic Press, New York, N.Y., 1973. (27) Watanabe, A., Tamai, H., Kolloid Z., 216, 587 (1971). Received for recieu: December 10, 1973. Accepted M a y 6, 1974. Work supported by the Science Research Council
Volume 8, Number 9, September 1974
839
