Ind. Eng. Chem. Res. 1987,26, 2437-2441
2437
Reddy, K. A,; Doraiswamy, L. K. Chem. Eng. Sci. 1969, 24, 1415-1426. Shelstad, K. A.; Downie, J.; Graydon, W. F. Can. J. Chem. Eng. 1961, 39, 201-204. Shriner, R. L.; Fuson, R. C.; Curtin, D. L. F. Systematic Zdentification of Organic Compounds, 5th ed.; Wiley-Interscience: New York, 1964; p 253. Temkin, M. K. Zhur. Fiz. Khim. 1957, 31, 3-26. Tomas, E.; Brahm, J.; Jottrand, R. Stud. Surf. Sci. Catal. 1980, G(Cata1. Deact.), 353-361. Vaidyanathan, K.; Doraiswamy, L. K. Chem. Eng. Sci. 1968, 23, 537-550. Volta, J. C.; Turlier, P.; Trambouge, Y. J. Catal. 1974, 34, 329-337. Yoshida, F.; Ramaswami, Y.; Houghen, 0. A. AZChE J . 1962, 8, 5. Weisz, P. B. 2.Phys. Chem. 1957, 11, 1.
Cozzi, D. Chim. Znd. 1942,24, 351-354. Fedevich, E. V.; Zhiznevskii, V. M.; Morkii, E. M., Zhur. Khim. Abstr. 1970, 38, 1189; Chem. Abstr. 1970, 73, 120013k. Gershbein, L. L.; Pines, H.; Ipatieff, V. N. J. Am. Chem. SOC.1947, 69, 2888-2893. Goodwin, L. F. J. Am. Chem. SOC.1920,42, 39-45. Hinshelwood, C. N. The Kinetics of Chemical Change; Oxford University Press: London, 1947; pp 203-222. Juusola, J. A.; Mann, R. F.; Downie, J. J. Catal. 1970, 17, 106-113. Laidler, K. J. Chemical Kinetics, 2nd ed.; McGraw-Hill: New York, 1965; pp 274-278. Mars, P.; Van Krevelen, D. W. Chem. Eng. Sci. 1954,3 (Spl. Suppl.), 41-59. Messinger, J. Ber. 1888, 21, 3366-3372. Mezaki, R.; Kittrel, J. R. Can. J. Chem. Eng. 1966, 44, 285-288. Pshezhetskii, S. Ya.; Kamentskaya, S. A. Zhur. Fiz. Khim. 1949,23, 136-155. Pshezhetskii, S. Ya.; Kamentskaya, S. A. Sbornik. 1955,406; Chem. Abstr. 1955, 52, 16021.
Received for review June 10, 1986 Revised manuscript received June 2, 1987 Accepted July 20, 1987
Sorption of Water from Alcohol-Water Mixtures by Cation-Exchange Resins Joseph A. Sinegrat and Giorgio Carta* Department of Chemical Engineering, University of Virginia, Charlottesuille, Virginia 22901
Equilibrium and mass-transfer rates of uptake of water from alcohol-water mixtures by an ionexchange gel have been obtained experimentally for a strong, sulfonic acid type, ion-exchange resin (Amberlite IR-120 Plus) in various ionic forms. Ethanol-water, 2-propanol-water, and 2-butanol-water mixtures have been considered with the sodium, potassium, and magnesium forms of the resin. The results for water sorption from liquid mixtures in a range of concentrations up to 10 mol % water show considerable selectivity for water, and the intrinsic separation factor between water and the alcohols investigated ranged from 49.7 to 437.5, depending upon the nature of the resin counterions and of the organic component. Mass-transfer rates were found to depend strongly upon the counterion and were highest for the potassium form of the resin. Effective intraparticle difcm2/s. This system is potentially useful fusivities for water were found to be of the order of 1X for the separation of mixtures of alcohols and water and for the removal of trace amounts of water from less polar organic solvents. The chief advantage over conventional adsorbents is the ease of thermal regeneration, which can be carried out at temperatures as low as 100 "C. Removal of small amounts of water from organic liquids is an important step in many industrial operations. Production of fuels from rectified spirits, such as ethanol for example, requires almost complete removal of water. This operation is often complicated by the formation of azeotropes. Typically, azeotropic or extractive distillations are used for such separations. These processes are energy intensive and expensive, because of the high reflux ratio and large number of stages required for nearly complete separation. In recent years, the need for renewable energy sources as alternatives to fossil fuels has greatly stimulated the search for more efficient separation techniques in this area. For instance, dehydration of ethanol by adsorption on molecular sieves has shown considerable promise. The adsorbent in this case can be quite selective for water, exhibiting in some cases almost no competition from the organic component as in the case of 3-A molecular sieve zeolites (Teo and Ruthven, 1986). Water is generally bound very strongly to the adsorbent in these cases, requiring high regeneration temperatures. As a consequence, the process may be rather energy intensive unless special arrangement are made to store and reuse the heat of adsorption (Garg and Ausikaitis, 1983; Garg and Yon, 1986). 'Present address: Lever Research Inc., Edgewater, NJ 07020.
0888-5885/8~/2626-2437$01.50/0
Water sorption by polysaccharide adsorbents has been considered as an alternative, and industrial applications of corn grits to dehydrate ethanol vapors have been proposed (Ladisch et al., 1984). A t temperatures of 50-100 O C , cornmeal, cellulose, and starch do not sorb alcohol vapors to a great extent (Hong et al., 1982; Rebar et al., 19841, and removal of the sorbed water can be carried out with a dry purge gas at temperatures of 100-110 "C (Bienkowski et al., 1986). The ability of ion-exchange resins to sorb water vapor has been investigated rather extensively in the past with respect to equilibrium and mass-transfer characteristics (Dole and McLaren, 1947; Gregor, 1951; Gregor et al., 1952; Boyd and Soldano, 1953; Sundheim et al., 1953; Westermark, 1960; Helfferich, 1962). Sorption of water from nonaqueous mixed liquids or vapors has received, however, much less attention, and the few studies addressed primarily swelling phenomena of sorbents in contact with liquids of very high water concentrations (Gregor et al., 1955; Ruckert and Samuelson, 195.7; Marcus, 1973; Helfferich, 1962). The practical use of sulfonic acid type cation-exchange resins as sorbents for liquid-phase organics-water separations has been described by Wymore (1962) for the separation of azeotropic mixtures and for the removal of traces of water from nonpolar solvents such 0 1987 American Chemical Society
2438 Ind. Eng. Chem. Res., Vol. 26, No. 12, 1987
as l,l,l-trichloroethane. Dowex 50 cation-exchange resin was used in Wymore's studies, providing good drying performance and great ease of regeneration, which could be carried out at low temperatures (110-140 "C). In breakthrough-type experiments with the potassium form of Dowex 50 X 8, residual amounts of water in organic liquids were below 5 X lo+ g/g for nonpolar liquids such as, for example, trichloroethane and below about 5 X g/g for ethanol-water mixtures. The equilibrium uptake of water from these solutions varied with the ionic form of the resin and in general was comparable with that of conventional solid desiccants. Swelling of the resin was limited because of the relatively small amounts of water sorbed. To obtain data necessary to assess the viability of drying processes using ion-exchange resins, we investigated the equilibrium and mass-transfer characteristics of sorption of water by a sulfonic acid type cation-exchange resin from ethanol-water, 2-propanol-water, and 2-butanol-water mixtures. Water concentration, nature of the organic component, and ionic form of the resin have been varied in an investigation of their effects upon the equilibrium distribution of water between liquid and gel phases, upon water sorption capacity, and upon the rate of approach to equilibrium in a stirred batch system.
Experimental Methods and Materials Materials. The cation-exchange resin Amberlite lR-120 Plus (Rohm and Haas Co., Philadelphia, PA) was used as the sorbent in this study. The resin is a sulfonated styrene-divinylbenzene copolymer with 8% degree of crosslinking. The ion-exchange capacity of the resin was determined by letting a sample of the resin in the hydrogen form equilibrate with an excess volume of 0.1 N aqueous sodium hydroxide containing 50 g of sodium chloride per liter of solution (Rohm and Haas,1979). After equilibrium was attained, the excess sodium hydroxide was titrated with 0.1 N hydrochloric acid. The ion-exchange capacity was thus found to be 5.30 f 0.08 mequiv/g of dry resin the hydrogen form. The water content of resin fully swollen in distilled water at 30 "C was found to be 1.00 f 0.03 g of water/g of dry resin. The particle size distribution of unswollen resin beads was measured microscopically. The average diameter of the dry resin beads was found to be 0.52 mm, and the standard deviation of the distribution was 0.09 mm. Prior to use, the resin was converted to the desired ionic form by equilibrating it with excess volumes of 1 N solutions of NaCI, KC1, and MgClz prepared from analytical reagent grade salts (Fisher Scientific). The resin was then dried in a vacuum oven (Precision Scientific) at 115 "C and stored in a desiccator. Mixtures of alcohols and water were prepared by using distilled, deionized water and analytical grade anhydrous alcohols (Fisher Scientific). Concentrations of water in alcohol-water mixtures were determined by the Karl Fischer titration method using a potentiometric apparatus consisting of an Orion 701A ionanalyzer as the source of a 1-mA polarizing current. The potentiometric titrations were carried out in a stirred titration vessel with a volume of 100 mL. The titration vessel could be purged by a stream of dry nitrogen and was equipped with a dual-platinum electrode (Schott-Gerate, Pt140). The Karl Fischer reagent (Fisher Scientific) was dispensed to the titration cell with an automatic buret (Fisher, Model 395). This system allowed water to be determined with an accuracy of 5% in standard solutions of methanol and ethanol containing 0.2-200 g of water per liter of mixture. The total amount of liquid (alcohol and water) taken up by a resin sample in equilibrium with an alcohol-water solution was determined gravimetrically
a r
I
& ' sample Q
/I Figure 1. Cross section of experimental apparatus for batch uptake rate measurements.
from the weight lost by the resin sample upon drying it at 115 "C. Excess liquid trapped between resin particles was quickly removed by centrifugation prior to drying. The resin sample attained constant weight (f1%) in 5 h. However, a period of 36 h was used as a standard drying time. Equilibrium Studies. Sorption equilibrium was determined at 30 "C by means of batch equilibration experiments. Alcohol-water mixtures with a mole fraction of water ranging from 0.002 to 0.10 were used. Amounts of dry resin (1-10 g) in the desired ionic form were placed in contact with known volumes of alcohol-water mixtures (50 or 75 mL) in 100-mL Erlenmeyer flasks sealed with rubber septa. The flasks were immersed in a constant temperature bath at 30.0 f 0.5 "C (Haake Co., Model D1-19) and shaken for 6 h (the time to reach equilibrium). Samples of the liquid (0.1-0.5 mL) were then withdrawn with a syringe and analyzed with the Karl Fischer potentiometric technique. The amount of water present in the resin was calculated from the difference between the initial and equilibrium concentrations in the liquid phase. The total mass of liquid (alcohol plus water) held by the resin at equilibrium was determined gravimetrically as described above. Mass-Transfer Studies. The rates of water uptake by the resin at 30.0 f 0.5 "C were measured in a 5.7-cm-i.d. cylindrical contactor (Figure 1)constructed of Plexiglas. Ports to introduce liquid and resin samples and purge the contactor with dry nitrogen were provided on the top plate. The dry resin samples (5-10 g) and anhydrous alcohol (100 mL) were introduced into the contactor and allowed to equilibrate for 6 h under a dry nitrogen atmosphere. The mixture was agitated with a 1-in., three-blade propeller at loo0 rpm. A Hall-effect magnetic sensor and a frequency meter (Heath-Zenith, Model SM-2420) were used to measure the stirrer speed. Samples of dry resin having a particle diameter of 0.50 f 0.09 mm obtained by using standard sieves were used for these experiments. Water (typically 1 mL) was then quickly introduced into the contactor with a syringe to yield a mixture with an initial mole fraction of water in the range 0.01-0.05. The alcohol-water mixture outside the particles was periodically sampled with a syringe. The liquid samples withdrawn (0.1-0.3 mL) were analyzed with the Karl Fischer technique. The amount of water in the resin at each time was determined from a material balance.
Results and Discussion Equilibrium Sorption Isotherms. The results of equilibrium sorption measurements at 30 f 0.5 "C are presented in Figures 2-5. The amount of water taken up by the resin per gram of dry resin, q,, and the mole fraction of water in the fluid held by the resin, Y, (=moles of water/(moles of ,water + moles of alcohol)), were deter-
Ind. Eng. Chem. Res., Vol. 26, No. 12, 1987 2439 1
012
010;
0
006 008 010 &,mole fraction of water in fluld phase 002
004
002
004
006
008
010
012
Xw, m l e fraction of water in fluid phase
Figure 2. Equilibrium isotherms showing water sorption capacity for ethanol-water mixtures. Lines are calculated according to eq 2. T = 30 "C. 1.01
"0
012
Figure 4. Equilibrium isotherms showing water sorption capacity for potassium form of resin. Lines are calculated according to eq 2. T = 30 "C.
1
: 0
0.41
2
2o 0
0.02 &mde
004
006
0.08
010
012
fraction of water in fluld phase
Figure 3. Equilibrium distribution of water between resin and fluid phases. Lines are calculated according to eq 1. T = 30 "C.
mined. These quantities are shown in Figures 2-5 as functions of the mole fraction of water in the liquid phase outside the resin, X,. Figure 2 shows the amount of water sorbed from ethanol-water mixtures for the sodium, potassium, and magnesium forms of the resin. Figure 3 shows the corresponding resin-phase composition. The ionic form of the resin affected the equilibrium uptake of water, q,, which is maximum for the sodium form among the three forms investigated. The selectivity for uptake of water relative to ethanol was also affected by the ionic form and again was highest for the sodium form. The hydrogen form of the resin was used only in preliminary experiments because, although it appeared to be effective in sorbing water, it swelled excessively in organic solvents and degraded rapidly when heated for regeneration, thus hindering practical applications. Sorption capacities and sorbate-phase compositions for 2-propanol-water and 2-butanol-water mixtures are given in Figures 4 and 5 for the potassium form of Amberlite IR-120 Plus. The results for ethanol-water are also shown in these figures for a comparison. Both capacity and selectivity for water are greater for 2-propanol- and 2-butanol-water than for ethanol-water mixtures. The resin functionality may be regarded as an acid permanently attached to an insoluble elastic matrix. As described by Westermark (1960), the initial hydration of the resin may be interpreted as the result of ion-dipole interactions between water and the resin counterions. Hence, water tends to solvate the counterions and the fixed ionic functional groups in much the same way as salts are
oi
002
l 004
006
008
010
0\2
Xw, mole fraction of water in fluid phase
Figure 5. Equilibrium distribution of water between resin and fluid phases for potassium form of resin. Lines are calculated according to eq 1. T = 30 "C.
solvated in free solutions. Because chemical cross-linking of the resin matrix prevents the polymer from dissolving, the net result at equilibrium is a balance of solvation or osmotic forces and the elastic forces of the polymeric network. The selectivity and sorption capacity depend upon the solvation characteristics of the counterions and fixed ionic groups, the electrostatic repulsion between neighboring ionic groups, the polarity and dielectric constants of the organic solvent, and the degree of cross-linking of the resin. These factors may result in opposite effects (Helfferich, 1962). The less polar the solvent, the weaker is the solvation tendency of the ions and the smaller the total uptake of liquid should be. The lower the dielectric constant, the stronger is the electrostatic interaction between ions of opposite charge and thus the lower is the osmotic activity of the ions in the resin and their solvation tendency. As the dielectric constant is reduced, however, electrostatic repulsion between fixed charges becomes stronger and swelling of the resin may increase with increased liquid uptake. From our experimental observations, for monovalent counterions, the sorption capacity appears to be somewhat greater for the sodium form than for the potassium form of the resin, and this order is in agreement with the hydration numbers of the two ions. The water uptake, however, appears to be lower for the magnesium form of the resin than for the sodium and potassium forms, despite considerably larger hydration number of the magnesium
2440 Ind. Eng. Chem. Res., Vol. 26, No. 12, 1987 Table I. Equilibrium Parameters for Equations 1 and 2 (30 "C) A S B solvent ionic form K 1.82 7.61 Na 93.5 ethanol 1.37 7.86 ethanol K 83.6 13.8 Mg 49.7 1.53 ethanol 2.50 12.6 2-propanol K 333.8 8.24 K 437.5 1.92 2-butanol
/" / o
1
In g of H,O/g of dry resin. ~
ion. To explain this phenomenon, it is perhaps possible to speculate that water is held in the resin in two forms: that of hydration water, which is tightly bound to the ions, and that of more mobile "free water" (Helfferich, 1962). In this case, the observed greater uptake for the sodium and potassium forms may be attributed to the contribution of free water which does not in general parallel the hydration order of the ions. In addition, it is possible that in a mixed alcohol-water system, alcohol molecules occupy the solvation shell of magnesium ion in competition with water. In this case, both the capacity and the selectivity for sorption of water by the resin would be reduced as observed. The sorption capacity and selectivity for water are, as it would be expected, distinctly greater for mixtures of water with 2-propanol and water with 2-butanol, which are less polar and have a lower dielectric constant than ethanol. Within the composition range investigated experimentally, the selectivity can be adequately described by a constant separation factor isotherm given by KXW Y, = 1 + (K - l)X, where X, and Y, are the mole fractions of water in the fluid outside the resin and in the liquid held by the resin, respectively. K is the selectivity coefficient or intrinsic separation factor between water and the alcohol. The equilibrium uptake of water at 30 "C may be empirically correlated with the mole fraction of water, X,, by means of the expression
where qw is the mass of water sorbed per unit mass of dry resin and A and B are characteristic of each alcohol-water system. The numerical values of K , A , and B determined from a nonlinear least-squares fit of the experimental data for each system are given in Table I. As shown in Figures 2-5, the fit is quite good, and these expressions could be used for process calculations, such as the estimation of breakthrough times in fixed bed operation. Batch Uptake Results. Experimental results for the rate of uptake of water from ethanol-water mixtures are shown in Figure 6 in terms of fractional approach to saturation as a*functionof time for the sodium, potassium, and magnesium forms of Amberlite IR-120 Plus at 30 "C. Experimental conditions and parameters determined from analyses of these results are summarized in Table 11. Consider an isothermal batch system in which a number of identical resin particles are immersed in a well-mixed finite volume of fluid. At time t = 0, the fluid phase is subjected to a step increase in mole fraction of water from 0 to XWo.As uptake of water by the resin proceeds, the fractional approach to saturation of the resin, f = qw/qw*, may be calculated from f
=
x,o - x, x,o - x,*
(3)
Ethand-Water 3 Na form
1 I
t , min
Figure 6. Experimental uptake curves showing fractional approach to saturation versus time for ethanol-water mixtures. Lines are calculated according to eq 4 and 5. Points from runs 1,5, and 7 are shown. T = 30 O C . Table 11. Summary of Experimental Uptake Rate Measurements (30 "C)a run ionic form rpm q,*, g/g A D,/R2, s-* De, cm2 s-' 1 K 1000 0.044 0.22 5.5 X 3.4 X lo-' 3.3 X lo-' 2 K 1000 0.25 5.3 X 0.039 0.22 5.7 X 10" 3.6 X lo-' 3 K 1000 0.029 3.3 X lo-' 4 K 600 0.041 0.20 5.2 X 5 Na 1000 0.039 0.27 1.5 X 9.6 X 1.1 X lo-' 0.037 0.27 1.7 X 6 Na 1000 0.028 0.12 9.6 X lo4 6.0 X lo4 7 Mg 1000 6.9 X lo4 0.040 0.13 1.1 X 8 Mg 1000
" R = 0.025 cm.
where XWoand X,* are respectively the initial and equilibrium mole fractions of water in the liquid phase. qw* is the amount of water (in gram/gram of dry resin) that will ultimately be held by the resin when equilibrium is reached. For the ethanol-water system if the water mole fraction in solution does not exceed a value of about 0.05, the equilibrium uptake may be considered to be correlated in a virtually linear manner with water concentration (with a deviation of less than 5%). Volume changes of the resin particles may be neglected because of the small amounts of water and alcohol taken up the resin. Under these conditions, neglecting external mass-transfer limitations and assuming that the transport process within the resin particles may be represented by a constant effective diffusivity, the fractional approach to saturation in the batch sorption system may be calculated from (Ruthven, 1984) f=1-6
I
n=1
exp (-pn2De.t / R 2 ) 9A/(l - A) + (1- A)p;
where the p n values are given by the non-zero roots of (5) A = (XWo- Xw*)/Xwois the fraction of water initially present in the batch system which is ultimately taken up by the resin when equilibrium is reached. Values of A were between 0.12 and 0.27 in our runs. An external masstransfer coefficient of about 3 X lo9 cm/s was estimated from available correlations for mass transfer to small drops and particles in baffled agitated contactors (Cussler, 1984). This value is sufficiently high that the mass-transfer process may be estimated to be entirely controlled by internal resistances, except during the very first instants
Ind. Eng. Chem. Res., Vol. 26, No. 12, 1987 2441 of a run. Furthermore, additional evidence that external mass-transfer resistance was not important was given by the fact that the uptake curves were found to be essentially coincident at reduced agitation rates. Values of the effective diffusivity of water in resin saturated with alcohol were determined by a nonlinear least-squares fit of the experimental uptake data with curves calculated according to eq 4 and 5 for the Na, K, and Mg forms of the resin. Rather large differences in sorption rates clearly result with different counterions. The effective diffusivity is greatest for the potassium form of the resin, followed by the sodium and by the magnesium forms. Again, it may be speculated that in the case of magnesium, the uptake process is rather slow because water is held largely in the form of tightly bound hydration shells. In the case of potassium and sodium, the water uptake process is faster as a greater fraction of water is held in the form of more mobile free water. Because sodium has a hydration number considerably greater than potassium and holds water more tightly, the uptake rate is greater for the potassium form than for the sodium form of the resin. These results are in qualitative agreement with the breakthrough behavior observed by Wymore (1962). The values of the effective diffusion coefficients, however, are very low as,in this case, diffusive transport takes place through a cross-linked polymer matrix which is essentially unswollen in the alcohol solvents. When equilibrium was achieved at the end of a transient uptake experiment, the amount of water adsorbed was about 0.04 g/g of dry resin. This value is to be compared with that of about 1 g/g of dry resin, for resin particles fully swollen in distilled water for which diffusivities 5-10 times larger are found. Faster uptake would probably be exhibited by macroreticular or macroporous resins. However, at the same time, these resins would yield lower performance in terms of selectivity for adsorption of water from the liquid phase, because a greater amount of alcohol would be trapped in the intraparticle pores. Concluding Remarks We have investigated experimentallythe uptake of water from alcohol-water liquid mixtures by a sulfonic acid type, polystyrene-divinylbenzene ion-exchange resin. The resin exhibits high selectivity for water and considerable sorption capacity. Selectivity and capacity are dependent upon the ionic form of the resin and the nature of the organic solvent. Transient batch uptake experiments have provided estimates of effective diffusion constants for sorption of water from ethanol-water mixtures. The sorption rate is strongly dependent upon the counterion, and the initial uptake can be described approximately in terms of a simple particle diffusion model with effective diffusivities of cm2/s. the order of 1 X The quantitative results reported here confirm the potential use of ion-exchange resins for drying alcohol-water mixtures and should provide guidance for a technical and economic evaluation of process applications. Although we have not conducted a systematic study of thermal regeneration of the resin, virtually complete regeneration could be accomplished in an oven at 110 “C. No appreciable
degradation or loss of capacity was observed for the alkali metal forms of the resin even during repeated sorptionregeneration cycles. Nomenclature A = constant in eq 2, g/g of dry resin B = constant in eq 2 De = effective diffusivity, cm2/s f = fractional approach to saturation, eq 3 K = selectivity coefficient, =Y,(1 - X , ) / ( l - Y,)X, pn = eigenvalue, eq 5 q, = amount of water sorbed, g/g of dry resin R = particle radius, cm t = time, s X, = mole fraction of water in fluid phase Y, = mole fraction of water in fluid held by the resin Greek Symbol A = fraction of sorbate initially present in a batch system which is adsorbed at equilibrium Superscripts
*
= equilibrium value
0 = initial value Registry No. Amberlite IR-120 Plus, 78922-04-0; H 2 0 , 7732-18-5; H&CH,OH, 64-17-5; (H&)ZCHzOH, 67-63-0; H&CHZ(OH)CHCH,, 78-92-2.
Literature Cited Bienkowski, P. R.; Barthe, A,; Voloch, M.; Neuman, R. N.; Ladish, M. R. Biotechnol. Bioeng. 1986,28, 960. Boyd, G. E.; Soldano, B. A. 2.Elektrochem. 1953,57, 162. Cussler, E. L. Diffusion, Mass Transfer in Fluid Systems; Cambridge University Press: New York, 1984; p 230. Dole, M.; McLaren, A. D. J. Am. Chem. SOC. 1947, 69, 651. Garg, D. R.; Ausikaitis, J. P. Chem. Eng. Prog. 1983, 79, 60. Garg, D. R.; Yon, C. M. Chem. Eng. Prog. 1986, 82, 54. 1951, 73, 642. Gregor, H. P. J. Am. Chem. SOC. Gregor, H. P.; Nobel, D.; Gottlieb, M. H. J. Phys. Chem. 1955,59, 10.
Gregor, H. P.; Sundheim, B. R.; Held, K. M.; Waxman, M. H. J. Colloid Sci. 1952, 7, 511. Helfferich, F. G. Ion Exchange; McGraw-Hill: New York, 1962; p 104. Hong, J.; Voloch, M.; Ladisch, M. R.; Tsao, G. T. BiotechnoL Bioeng. 1982, 24, 725. Ladisch, M.; Voloch, M.; Hong, J.; Bienkowski, P.; Tsao, G. T. Ind. Eng. Chem. Process Des. Dev. 1984, 23, 437. Marcus, Y. “Ion-Exchange in Non-Aqueous and Mixed Solvents”, In Ion Exchange and Solvent Extraction; Marinsky, J. A., Marcus, y., Eds.; Marcel Dekker: New York, 1973; Vol. 4, p l. Rebar, V.; Fischbach, E. R.; Apostopoulos, D.; Kokini, J. L. Biotechnol. Bioeng. 1984, 26, 513. Rohm and Haas Co. “Amberlite Ion Exchange Resins Laboratory Guide”, Technical Bulletin, 1979; Philadelphia, PA. Ruckert, H.; Samuelson, 0. Acto Chem. Scand. 1957, 11, 303. Ruthven, D. M. Principles of Adsorption and Adsorption Processes; Wiley: New York, 1984; p 170. Sundheim, B. R.; Waxman, M. H.; Gregor, H. P. J. Phys. Chem. 1953, 57, 974. Teo, W. K.; Ruthven, D. M. Ind. Eng. Chem. Process Des. Dev. 1986, 25, 17. Westermark, T. Acta Chem. Scand. 1960, 14, 1858. Wymore, C. E. Ind. Eng. Chem. Prod. Res. Deu. 1962, 1, 173. Received for review June 16, 1986 Revised manuscript received April 27, 1987 Accepted August 18,1987
