1620
Vol. 47.No. 8
INDUSTRIAL AND ENGINEERING CHEMISTRY
least over the temperature range investigated, one expression is as good as the other. The rate of the change of dielectric constant with temperature as determined by the logarithmic expression is equal to -be,/T2. SUNIMARY
The addition of certain Group IV oxides to barium titanate in concentrations from 0 t o 50 mole % markedly reduces the dielectric constant of ceramics prepared therefrom over the temperature range 30” to 170’ C. The dissipation factor is not greatly changed from that of pure barium titanate. Analysis of dielectric constant data above the Curie temperature for these ceramics showed that either the Curie-Weiss law or a given exponential function is applicable. It is not possible to choose between the two functions because of the limited accuracy of the experimental data. ACKNOWLEDGMENT
The authors thank Ray Pepinsky and coworkers at the Pennsylvania State University foi preparation of the x-ray diffraction patterns, Joseph Thompson, for taking the phase contrast photomicrographs, Frieda Herreshoff for aid in preparing graphs, and John Hickman for encouragement during the course of this work. LITERATURE CITED (1) Berberich, L. J., and Bell, M.E., J. A p p l . Phys., 11, 681 (1940).
(2) Berlincourt, D. A., and Jaffy; H., Brush Laboratories, “Research on Barium Titanate, 6th Progress Report, No. 515-6, May 1954.
Blattner, W., Kanzig, W., and Merz, W., Helv. P h y s . Acta, 22 35 (1949).
Brajer, E. J., Jaffe, H., and Kulcsar, F.,Chicago Meeting, Acoustical Society, Paper E2, October 1951. DeBretteville, A. P., Jr., Ceram. Age., 54, 363-4, 376-9 (1949). Devonshire, A. F., Phil.Mag., 4 0 , 1040 (1949). Donley, I€. L., R C A Rev., 9 , 218 (1948). Garcia-Verduch, A., and Lindner, R., Arkiv K e m i , 5, 313 (1953), Jonker, G. H., and Van Santen, J. H., Chem. Weekblad, 43, 672 (1947).
Kittel, C., “Introduction to Solid State Physics,” Wiley, Ncw York, 1953. Lichtenecker, K., and Rother, K., Physik. Z.. 32, 255 (1931) Mason, W. P., Bell Labs. Record, 2 7 , 2 8 5 (1949). Megaw, H. D., T r a n s . Faraday Soc., 4ZA, 224 (1947). Reddish, W., Plessner, W., and Jackson, W., Tbid., 42A, 245 (1947).
Roberts, S.,P h y s . Rev., 71, 890 (1947). Ibid., 7 5 , 9 8 9 (1949).
Rushman, D. F., and Strivens, M. A., Trans. Faraday Soc.. 42A, 231 (1947).
Statton, W. O., J. Chem. Pkus., 19, 33 (1951). Taylor, A., Horizons, Inc., Cleveland, Ohio, “Piezoelectric Material for High Power Underwater Sound Transducers,” NObsr-63108, Index No. NE-051248, January 1954. Van Santen, J. H., Trans. Faraday Soc., 42A, 249 (1947). Von Hippel, A., Breckenridge, R. G., Chesley, F. G., and Tisaa. L., IND. ENG.CHEM.,38, 1097 (1946). Wul,B., J . P h y s . (U.S.S.R.), 10, 95 (1946). Wul, B. M., and Goldman, I. M.,Compt. rend. acad. scz. (U.R.S.S.),4 9 , 177 (1945).
Wyckoff, R. W. G., “Crystal Structures,” Chap. IV, “Compounds RXa,” Interscience, New York, 1948. RECEIVED for review February 2, 1954.
ACCEPTEDFebruary 24, 1956.
NEL Professional Contribution No. 12.
Sulfate-Bisulfate Equilibrium on Anion Exchange Resins R. E. ANDERSON, W. C. BAUMAN, AND D. F. HARRINGTON Physical Research Laboratory, The Dow Chemical Co., Midland, Mich.
T”
sulfate salts of the quaternam ammonium anion exchange resins are able t o adsorb strong mineral acids from solution. This ability of the resin sulfates to act as weaklv basic resins was observed both by the authors and by Kraus and others, who have published brief communications ( 3 , 4). This phenomenon offers a new method for the removal of strong arids from certain mixtures of solutes without requiring chemical regeneration of the resins. The equilibrium existing among hydrogen, sulfate, and bisulfate ions in a solution oE sulfuric acid is a function of the total molar concentration of sulfuric acid. Sherrill and Noye8 ( 5 ) determined the ionization of sulfuric acid conductometrically a t a number of concentrations up to 0.05M. If the molar concentrations of the three ions formed are plotted on logarithmic paper against the molarity of sulfuric acid present, essentially linear relationships are found. The data of Sherrill and Noyes may thus be extrapolated easily to 0.1M sulfuric acid and qualitatively to 1M sulfuric acid. When an anion exchange resin is placed in a solution, all of the anion species present compete for sites on the resin. The composition of the resin at equilibrium is determined by the relative selectivities shown for the different anions and their relative equivalent concentrations in solution. The relative equivalent concentrations of sulfate and bisulfate ions in sulfuric acid solu-
tion are shown in Figure 1. The equivalent fractions of total anion equivalents in solution which are sulfate ions, X , and which are bisulfataions, 1 - X , are shown as a function of the sulfuric acid molarity, M . The solid lines of Figure 1 are from the data of Sherrill and Noyes ( 5 ) and the dashed lines are a qualitative extrapolation. If sulfate and bisulfate ions are the only anions present, the equilibrium existing with a quaternary resin may be represented as : 2RHSOi SOa-- S 2HSO4&SO4 (1)
+
+
The selectivity expression for this equilibrium when expressed in terms of X and the equivalent fraction of total anion equivalents held by the resin which are sulfate ions, X r , becomes:
I n Equation 2, K ,
sei-
HSOa
is the selectivity coefficient of the resin
for sulfate ion over bisulfate ion defined in terms of concentrations (6). As activity coefficient ratios are not available for most of the species present, Equation 2 can be used only as a first approximation. Cr is the total capacity of the resin phase expressed as equivalents per liter. C is the concentration of total cation or anion equivalents in the solution phase at equilibrium. If
August 1955
INDUSTRIAL AND ENG INEERING CHEMISTRY
hydrogen ions are the only cations present, C is equal t o the hydrogen ion concentration a t equilibrium. This can be obtained from a plot of the Sherrill and Noyes data, if the concentration of sulfuric acid a t equilibrium is known. The term C./C arises from the fact t h a t the exchange is between monovalent and divalent ions ( 2 ) . It can be seen from Equation 2 that as the total normality of the solution phase, C, becomes small, the apparent selectivity of --
the resin for sulfate ions, K , so:
HSOr
C
X 4 becomes large.
c
In Equation 2, the term
.
.. .
for separating strong acids from weak acids, water-soluble organic materials, and certain salts, without need for chemical regenerants
chloride potentiometrically with silver nitrate in the presence of sulfuric acid.
K
C(1
- X ) 2 is dependent solely upon the
total molar concentration of sulfuric acid in solution a t equilibrium, M . Therefore, this quantity can be obtained from a titration of the equilibrium solution phase through use of the Sherrill and Soyes data.
Presenting a n interesting method..
This
effect, is thus added to the mass action effect of the larger equivalent fraction of sulfate ions present in dilute sulfuric acid shown in Figure 1. The result is that the resin is driven to the sulfate form in dilute sulfuric acid solutions and to the bisulfate form in concentrated acid solutions.
1621
SAMPLE CALCULATIONS
For sample 1 the following dnta were obtained. acid molarity a t equilibrium,
X'
Similarly, the ratio ( 1 - X')2 can be
obtained by analysis of the equilibrium resin phase. The quantity 1 - XT is the ratio of bisulfate ions on the resin to total ions on the resin. The bisulfate may be readily determined by titration with sodium hydroxide and the total ions by standard total capacity methods. Since Cr is essentially constant and approximately unity for the resin used, K , sei- X Cr was treated
Total sulfuric
M
= 0
From plot of Sherrill and Xoyes data [H+] = C [HSOI-I [SO,--]
= 0.0113 = 0.0027 = 0,0043
0071
Total milliequivalent,s of H + extracted from resin = 0.667 Tot,al milliequivalents of resin capacity = 5,906
Xr
ESO&
=
0 887
as a single value and determined experimentally over a range of equilibrium acid concentrations. EXPERIMENTAL
About 500 ml. of Dowex 1-X8, C1-, was placed in a filter and rinsed with dilute sodium sulfate solution until there was essentially no chloride ion i n the effluent. The resin was then rinsed with water until the effluent was free of sulfate. Five samples were made up containing 5.0 ml. of the conditioned resin (tapped volume under water), 10 t o 25 ml. of water, and 25 to 75 ml. of either 0.2N or 0.05N sulfuric acid. No attempt was made to set the initial concentration closely. The samples were shaken overnight. Aliquot samples of the liquid were titrated with standard sodium hydroxide to a p H of 7.0 to determine the total sulfuric acid molarity, M .
z
0.88'7 so;- x ~(0.113)* - K p ~ s ~ ; _s04 x = 0.059 KcESO;
X 0.0043 cr x 2~-
(0.0027)2
cr
RESULTS Sample No.
M
C
These results are plotted in Figure 2 as X ' vs. M
0 - / - -
c
6 -
-- ---
LL
2W
4 -
J
2
3
2 -
w
DISCUSSION
Figure 2 shows the equilibrium compositions of Dowex 1 when placed in a solution of sulfuric acid. The solid curve represents the case K , X Cr = 0.07, which approximates the experiHSO4
I .OOl M
.01 M
I
I
0.1 M
lIIl1. I.OM
HZS%
Figure 1.
Anions present in sulfuric acid
The resin was transferred to a centrifuge vessel equipped with a porous glass disk and a thimble to receive the remaining solution, and was centrifuged a t 2000 r.p.m. for 3 minutes to remove the interstitial water. The centrifuged resin was transferred to a special funnel consisting of a length of glass tubing 1 / ~inch in outside diameter equipped with a sintered disk. Half normal sodium chloride solution was passed through the resin and the effluent was collected in a 100-ml. volumetric flask. The volume of effluent was made up t o 100 ml. and aliquots were titrated with sodium hydroxide to a p R of 7.0. The total milliequivalents of hydrogen in the effluent were taken as the total milliequivalents of bisulfate ion on the resin. The total capacity was determined by rinsing the resin sample with deionized water and titrating the
mentally determined points. I n solutions more than 0.5M in sulfuric acid the resin is largely in the bisulfate form, while in Polutions less than 0.OlM the resin is largely in the sulfate form. In addition, the majority of the change-over takes place in a fairly narrow concentration range. The selectivity coefficient-resin normality product, K , X C; HSO;
increases over the range of resin composition investigated. Refinement of Equation 2 by inclusion of activity coefficients, if available, would probably give more elegant results. However, the extent of the variatioh is not so great as that reported for the chloride-hydroxide exchange on Dowex 2 (6). This phenomenon is general in ion exchange equilibrium and has received considerable attention in the case of cation exchange. Kraus reported that the selectivity of the resin for sulfate apparently fell off very markedly in very dilute solutions, with the result that regenera-
INDUSTRIAL AND ENGINEERING CHEMISTRY
1622
tion of the resin with water was accompanied by a pronounced tailing of acid. One obvious source of error which could occur in the equilibrium measurements described above is the presence of free sulfuric acid occluded in the resin. This effect would become more serious at higher concentrations. A rough calculation based on Donnan exclusion data for typical electrolytes (E) indicated that the error would be negligible a t acid concentrations below 0.1iV. At higher concentrations the presence of free acid in the resin would lead to high values for bisulfate in the resin and low values for XI. The trend of the data is just the opposite. This error might be circumvented at higher concentrations by determining the total sulfate removed from the resin and comparing this with the total capacity of the resin.
.e
-
.6
--
.4
-
.2
-
X'
\
'\
'.
.\
-1
I
I
I
I
I I I I I I
I
I I I I l l
Vol. 47, No. 8
This value is only approximate, since several assumptions were made in calculation, but serves to indicate the error in the published value of 6.1. APPLICATION
This phenomenon offers a new ion exchange method for removing sulfuric acid from solution, which does not require an.v regenerant other than water. If sulfuric acid is passed into a column of Dowex 1 in the sulfate form, the resin composition changes toward the bisulfate form-the stronger the acid the more completely the resin is converted. This reaction is essentially RzS04
+ HzSO4
+
2RHSOa
Thus the free acid is removed from solution as long as there is sulfate-form resin available to react. The maximum theoretical capacity of the resin in this process can be seen t o be one half of the resin's total exchange capacity. Regeneration is accomplished by simply passing water (a sulfuric, acid solution of infinite dilution) through the bed and reversing the equilibrium. A second look a t this process will show that i t is not limited to removal of sulfuric acid from solution but will work for any strong acid-for example, hydrochloric. While rigorous treatment of the case when a third anionic component such as chloride is present cannot be given here, in a qualitative way much the same conditions exist as before. This may be visualized by assuming that the hydrochloric acid displaces sulfate ion from the first resin with which it comes in contact and is therefore preceded by a sulfuric band in which conditions are identical with the previous case. I n this instance the net result is
RrS04
+ HCl
+
+ RC1
RHSO4
This reaction is accompanied by the additional reaction An alternative method of determining the order of magnitude of K Ofor the sulfate-bisulfate exchange would be by combining the selectivity coefficients given by Wheaton and Bauman (6) for the sulfate-chloride and bisulfate-chloride exchanges. These coe5cients may be combined to give the desired coefficient by the expression:
At a solution normality of 0.1 and a resin composition of F = 0.5 the values obtained from Wheaton and Bauman's paper are:
RHSOd
+ HCl
+ RC1
+ HzS04
As a result, the sulfate and bisulfate ions are completely displaced from the upper portions of the ion exchange bed. Therefore, in order to regenerate the bed to the sulfate form the water wash must be passed through the bed in the direction opposite to the original acid flow. The bed is regenerated upflow if exhaustion was carried out down flow, and vice versa. 1.345 ~~MAXlMUM==ll.O WT % G L Y C E R O L
c1-
E
Kc~so4
Kos0T- X c1
Therefore K c H i z i - X Cr = 0.1 X
GI
c
-
-
1 6.1
RESIN. IOqcc.OOWEX I-XB, S O i , 50-100 M E S H
= 1.6
50%
F E E D : 25ml. ! I O % GLYCEROL H,SO,
(63* -
X 1.6 = 0.0043
This value is much too low as compared with the experimental value of approximately 0.1. The value of 6.1 was determined in 0.1N sulfuric acid under the assumption that essentially all of the sulfur would be present as bisulfate ions at this concentration. However, Figure 1 shows that only about 50% of the anion equivalents are bisulfate in 0.1N sulfuric acid and the value of 6.1 can be assumed to be in considerable error. Working backwards from the present determination, a more reasonable value for the bisulfate-chloride exchange would be:
1.335
1.333
I331
c II pd 0
I
100
200
300
400
VOLUME
Figure 3.
500
600
OF E F F L U E N T
* I
700
I
800
900
IC
(ml.1
Separation of glycerol and sulfuric acid on a resin sulfate
Because this acid sorption process must compete with conventional ion exchange using either strong or weak base resin and with the ion exclusion process ( 7 )in some instances, it is necessary to set forth its specific limitations and advantages. Its most serious limitation is that the acid removed from the resin during regederation must be more dilute than that originally sorbed by
August 1955
INDUSTRIAL AND ENGINEERING CHEMISTRY
the refiin. The acid eluted from the resin cannot have a maximum concentration of much above O . B N and will probably be considerably less. This also implies that very dilute acid cannot be picked u p efficiently by this process. These limitations immediately exclude the method from the field of water conditioning and limit i t to chemic.al processing of mixtures. The process is suit.able for removal of strong acids from aqueous solutions of nonelectrolytes. I n such cases both this method and the ion exclusion method offer the advantage over conventional methods of eliminating t.he cost of chemical regenerants and often both may be applica,bie t,o a given problem. I n many cases, however, one or the ot,her has a definite advantage. Specifically, acid adsorption on a resin sulfate may be used where the separation by ion exclusion is verj. difficult because the size or nature of the nonionic prohibit)s it8 entering the resin phase. The use of a resin sulfate is not Puitable for separations involving amines, since they react with the sulfate form of the resin. Both methods are of limited use for work with phenols because of the excessive sorbability of such compounds ( 1 ) . Even in cases where both the anion sulfate and ion esciusion methods are applicable, the relative concentrations of acid and nonionic in the mixture ma:dictate n-hich method is most suitable. Figure 3 shows a separation using a resin su!fate. Dowes 1-58, C1-, 50 to 100 mesh) was converted t o the sulfate form hy treating it columnwise with 0.liW sodium sulfate solution until no chloride ion was present in the effluent and then rinsed. One hundred milliliters of this sulfate-form resin was placed in a buret,type column. Twenty-five milliliters of a solution containing 10% glycerol and 10% sulfuric acid was washed through this column a t a n initial flow rate of 1 ml. per minute. A plot of the refractive index of the effluent versus the volume of the effluent is shown in Figure 3. A complete s e p r a t i o n was obtained. The glycerol was quantit,atirel>-recovered in 40 ml. The flow rate was increased to 3 mi. per minute after the glycerol had been recovered. Over 807' of the acid was removed from the resin in a volume of 460 ml. and the effluent was free of acid after an additional volume of 650 ml. This extreme dilution of the acid rules out its direct recoverv. Figure 4 shows a separation in which the regeneration rinsc must be carried out upflo~-. Fifteen milliliters of a solution containing 10% ethylene glJ-col and 10% hydrochloric acid was washed through a column of resin similar to that used above. All of the glycol was recovered in less than 60 ml. of effluent, free of acid. The flow of wat,er \vas then reversed and the hydrochloric acid was completely removed from the resin in a volume of 1200 ml. Other pairs which haye been separated with the resin sulfate include: Sulfuric acid-ethyl alcohol Sulfuric acid-acetic acid Sulfuric acid-glucose Ethylenedisulfonic acid-ethylene glycol Chloroaretic acid-acetic acid Xelson and Kraus ( 4 )discuss the separation of weak and strong acids by resin sulfates. Another application discussed by Kraus, Nelson, and Baxter ( 3 ) is the separation of sulfuric acid from metal sulfates by this method. The applicability of the process can be widened to the removal of salts of strong acids from solutions of nonionic materials by the use of two ion exchange beds in series. If the solution is first
1623
passed through a bed of sulfonic acid-type cation exchange resin in the hydrogen form, the salt is converted to a free acid which can be picked up by a subsequent bed of resin sulfate and thus separated from the nonionic solute. If the two-bed system is rinsed countercurrent to the exhausting flow, the acid removed from the resin sulfate bed will regenerate the cation bed. The degree of utilization of this weak acid for the regeneration of the cation bed depends upon the type of cations originally removed from solution. As complete utilization can only be approached, some additional sulfuric acid must be used. The amount of acid required will be less than an amount equivalent to the salt removed-the minimum acid required for regeneration in conventional hydrogen exchange operations.
0.6 F-
1
R E S I N : 100 cc SO4.
t
.;i
w 0
a
0.5
0.
FEE0
15 m i
DOWEX I-XB 50-100M E S H
{
I I
10% E T H Y L E N E
0.I
0
L I 963 200
TOTAL
I 400
VOLUME OF E F F L U E N T
I 600
I BOO
,1000 1200
(rnl.)
Figure 4. Separation of ethylene glycol and hydrochloric acid on a resin sulfate
Several other polyvalent anion salts of the quaternary resins have been investigated in this laboratory and by Kraus and others ( 4 ) . While some of the other polyvalent systems investigated have shown adsorption of acid, none of them have lent themselves to satisfactory regeneration with water, as does the suifate-bisulfate system. Similarly, in extending the sulfate-bigulfate system to the use of a weak-base polyamine resin (Dowex 31, the sulfate form of the resin was effective in adsorbing actids but the regeneration with water tailed out very badly. Khile the use of the quaternary ammonium resin sulfate for the adsorption of acids is limited in scope, it offers the process engineer one additional tool for the never-ending job of reducing processing costs. LITERATURE CITED (1) Anderson, R. E., and Hansen, R. D., 1x0. ENG. CHEM.,47, 71
(1955).
( 2 ) Bauman, W. C . , and Eichhorn, J., J . Am. Chem. SOC.,69, 2830 (1947). (3) Kraus, K. A., Nelson, F., and Baxter, J. F., Ibid., 75, 2768
(1953). (4) Nelson, F., and Kraus, K. A , , I b i d . , 77, 329 (1955). (5) Sherrill, M. S., and Noyes, A. A., Ibid., 48, 1861 (1926). (6) Wheaton, R. LI., and Rauman, W C., 1x0. ENG. CHEM.,43, 1088 (1951). (7) Ibzd., 45, 228 (1953). RECEIVED for review November 1, 1954. ACCEPTED February 23, 1955. Presented a t the Gordon Research Conference on Ion Exchange, New Hampton, N. €I., June 1953, and at a meeting of the Midland Section, AMERICAN CHEMICAL SOCIETY.
