6
JOHN A . BISHOP
(2) HEISIG,G. B.: Ind. Eng. Chem., Anal. Ed. 8, 149 (1936). (3) LANNUNG, A.: Z . physik. Chem. A161, 265 (1932). (4) LASCZYNSKI, 8. VON:Ber. 27, 2285 (1894). (5) LOYD,E., BROWN,C. B., GLYNWYN, D., BONNELL, R., AND JONES,W. J.: J. Chem. SOC. 1928, 658. (6) MACY,R., AND THOMAS, E. W.: J. Am. Chem. SOC. 48, 1547 (1926). (7) WADSWORTH, A. E., AND DAWSON, H. M.: J. Chem. SOC.129, 2784 (1926). (8) WALDEN,P. T.: Z. physik. Chem. 66, 712 (1902).
COVALENT ADSORPTION ON BASE-EXCHANGE RESINS. I
THEADSORPTION OF MONOBASIC ACIDS JOHN A. BISHOP' Chemical Laboratory, University of Delaware, Newark, Delaware Received July 26, 19.@
Since the pioneering work of Adams and Holmes (1) on the use of resins as base exchangers, a large number of patents have been obtained describing resinous and carbonaceous base-exchanging materials. On the theoretical side of this type of adsorption, the first attempts t o investigate the phenomena were made by Bhatnagar and coworkers (3, 4) and by Broughton (2, 5 ) . Walton (9, 10) and Nachod (6, 7) have discussed and summarized the results on cation exchangers. Comparatively little investigation has been made of the adsorption of anions except chloride and sulfate (2, 6, S ) , aside from the early work of Bhatnagar. The problem may be considered as one involving the formation of covalent bonds between the nitrogen of the resin and the hydrated proton of the acid, the anion being retained by electrostatic attraction as in the neutralization of ammonia by an acid. EXPERIMENTAL
A . Materials The adsorbent used in this series was Amberlite IR-3, obtained from the Resinous Products and Chemical Company through the courtesy of Dr. F. J. Myers. It was sized by sieving through No. 20 on No. 40 U. S. Standard sieves. It was then freed from soluble impurities by extraction with water, using a Soxhlet extractor, until a colorless extract was obtained. The residue was dried a t 110°C. and stored over calcium chloride. This treatment resulted in a material which did not discolor distilled water. The acids used mere either Baker's C.P. grade or from the Eastman Kodak Company. 1
Present address: Moravian College for Women, Bethlehem, Pennsylvania.
ADSORPTION ON BASE-EXCHANGE RESINS.
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B. Swelling of resins As mentioned by Walton (10) and in operating directions for using the resins as water purifier, the dry resins adsorb water to a great extent, resulting in swelling. In another series of experiments it was found that the samples as prepared above would pick up about half their weight of water. Since the amount of resin used was small compared with the amount of solution, no correction has been made in the calculations for this effect.
C. Adsorption experiments Five-gram samples of Amberlite were weighed into tightly stoppered bottles and shaken with 200 ml. of acid solution. Samples were taken at intervals and TABLE 1 Rate c adsorption of acids TIME IN HOURS..
. ... ...... .. . .
CH&OOH (0.0459 M ) * . CHaCOOH (0.0845 M ) . . CHaCOOH (0.492 M) .. . CHzClCOOH (0.0546 M) CHClzCOOH (0.0469 M ) CHC12COOH (0.0748 M) HC1 (0.0498 M ) . . . . . . . . HC1 (0.1401 M). . . . . . . . (C0OH)z (0.1360 M).. .. Tartaric acid (0.0961 M )
*M
-
2
4
0.20 0.39 0.83 0.83 0.78 0.92 0.94 1.87 2.32 0.15
0.28 1.14 1.31 1.20
6
Y
-0.26 0.43 0.99 1.12 0.91 1.19 2.46 2.82 0.31
10
24
0.36 0.48 1.04 1.19 1.18 1.21 1.19 1.33 1.21 1.60 1.76 1.25 1.31 1.38 1.42 2.64 2.74 2.98 3.02 0.52 0.91
0.30
0.29 0.45
0.31
48
72
98
-- -0.37
0.44 0.55
1.11 1.22 1.92 1.46 3.04 1.18
1.19 1.36 1.92 1.49 2.84 2.84 1.24
= initial molarity of t h e acid solutions.
analyzed by titration of the acid. A curve was plotted to determine the equilibrium point. The rate results are summarized in table 1 and plotted in figure 1. The equilibrium data are summarized in table 2 and plotted in figure 2. For comparison Bhatnagar’s results for the adsorption of organic acids on m-phenylenediamine resin are plotted in figure 3, from the data given by him in tables VI1 and VI11 in paper IV of his series (4). In the case of Bhatnagar’s data, all adsorption was from an initial concentration of 0.01 molar. DISCUSSION O F RESULTS
The adsorption of acids on nitrogen-containing resins may for the most part be regarded as a species of salt formation, in which both resinous base and the resulting salt are insoluble in water. The extent of salt formation should be a function of the strength of the acid adsorbed, the usual hydrolysis of the salt being greater for weak acids than for strong. Since the basic properties of the resin are presumably weak, there will be hydrolysis even in the case of strong acids.
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JOHN A. BISHOP
If RN is taken as the formula for the resin base, and HA as the general formula for the monobasic acid adsorbed, an equilibrium relation may be developed by
100
TIME
IN HOURS
FIG.1. Rete of adsorption of acids on Amberlite TABLE 2 Adsorption equilibria o n Amberlite IR-5* ACID
CH&OOH..
.. . . . . . . . . . . .
X
-
0.44 0.55 1.11 CH&lCOOH.. .... . . . . . . . 1.20 CHClzCOOH............. 1.36 1.92 H C l . . . . . . . . . . . . . . . . , . . . . 1.49 2.48 (COOH),. . . . ... . . . . . . . . . , 3.04 Tartaric acid.. . . . . . . . . . . . 1.24
Me
0.0349 0.0707 0.454 0.0156 0.0129 0.0258 0.0125 0.0691 0.0600 0.0651
CA = c,
Ka
1.75 X 1.75 X 1.75 X 1.5 x 3.3 X 3.3 X
10-6
8.19 11.03 28.1 82.9 1W2 99.2 10-2 166.5 125 691 400 6.5 X 7g.3 1.1 X 10-6 10-6 10-3
X X X
x X X
x x X X
a -+ LOG CECA
1.8265 2.0828 2.8974 10-4 3.8371 lo-* 3.9930 l W 4 4.4428 10-4 4.1938 10-4 5.6790 lW4 5.2041 loT4 3.7986
1 f LOG
x
0.6435 0.7404 1.0453 1.0792 1.1335 1.2833 1.1732 1.4533 1.4829 1.0934
M , = molarity of the acid solutions a t equilibrium; X = adsorption in millimoles per gram of adsorbent; C, and
CA
= concentrations of hydrogen ion and cation, respectively, a t equilibrium.
the following sequence, in which X represents millimoles of resin salt per gram of resin, and T represents total millimoles of resin base. (T - X ) , therefore,
ADSORPTION ON BASE-EXCHANGE RESINS.
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8 t LOG CH*CA
FIG.2. Equilibrium adsorption of acids on Amberlite TABLE 3 Adsorption equilibria on m-phenylenediamine resin
x x 104
ACID
‘A
8f
E
LOG
e&,
4 f LOG
x
.-
CHsCOOH . . . . . . . . . . , . . . . . . . . CHzClCOOH.. ... . . . . . . . . . . . . CHClzCOOH CClZCOOH.. ....... . . . . . . . . . . CHzCNCOOH . . . . . . . . . . . . . . . . CHzOHCOOH.. CHzNHzCOOH . . . . . . . . . . . . . . CzH6COOH CzH4ClCOOH. . , . . . . . . . , . . . . . CzH40HCOOH. . . . . . . . . . . . . . .. CzHrNHzCOOH . . . . . . . HCOOH ..................... n-C3H?COOH.. . . . . . . . . . . . . . ..... . . (COOWz Malonic acid.. . . . . . . . . . . . . . Succinic acid.. . . . . . . . . . . . . . . . Aconitic acid.. . ,... . . . . . . . . . .
. ..
X
=
3.15 6.25 7.75 8.26 6.70 3.56 0.25 3.15 4.95 3.35 1.61 3.37 2.28 7.74 6.83 4.72 8.00
3.495 x 16.28 X 21.60 x 17.3 X 20.87 X 2.45 X 0.0182 X 2.475 X 20.86 X 2.418 X 0.0275X 10.89 X 3.306 x 21.4 x 15.98 X 5.583 X 6.67 X
10-4 10-4
lo-‘ lW4
lW4 lW4
10-4 10-4
lW4 lW4
1.1052 2.4232 2.6689 2.4762 2.6390 0.7776 -3.4795 0.7871 2.6386 0.7669 -3.1220 2.0744 1.0386 2.6608 2.4071 1.4937 1.6482
0.4983 0.7959 0.8887 0.9167 0.8261 0.5519 -0.6021 0.4983 0.6946 0.5250 -0.2068 0.5270 0.3578 0.8887 0.8344 0.6739 0.9031
adsorption in millimoles per gram of adsorbent;
CH and CA = concentrations of hydrogen ion and cation, respectively, a t equilibrium.
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JOHN A. BISHOP
C C ~ ~ O H
0.90-
ACONITGe
e.
0.50. % c3
0
44.
-4-
0.00-
-0.50I
I
If the relationship expressed in equation 5 could be plotted for a variety of acids, the result would be a straight line on which all monobasic acids should
ADSORPTION ON BASE-EXCHANGE RESINS.
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fall, the slope being the acidity function of the resin base in terms of millimoles per gram. The exact value of T is difficult to determine experimentally, being complicated by the fact that some of the adsorption on this type of gel may be nonacidic (8). The relationship map be expressed in a manner similar t b the Freundlich equation, with the limitations which apply to that equation: n Log
x = Log
+ Log CH'CA
(6)
The usefulness of this method of approach may best be judged by a consideration of figures 2 and 3. The most striking thing about these two graphs is the fact that acids of such varying strengths are caused to fall so close to a straight line over an ion concentration varying 100,000 fold. The second is that the slope seems to be the same for both graphs. This would indicate that the treatment is justified and that the difference in adsorptive capacity is due to the greater number of basic groups in each gram of the Amberlite. Since the comparison is between monobasic acids, and since the experimental activity coefficients of some of them are not available, activities were not used, although their use would increase the accuracy. The activities of the two hydrochloric acid solutions mere calculated, the resulting changes being toward a smaller ion product, moving the larger hydrochloric acid concentration definitely closer to the line as drawn. The use of a straight line through all the acids in figures 2 and 3 gives a method by which the approximate adsorption of monobasic acids on a given resin may be determined by use of the points for a strong acid and a weak acid. A more exact relationship may be developed by rearranging and differentiating equation 5 .
Ka+'(T- x)= X/CH'CA Z
