1098
S. L. CUYPA, MQNISHA BOSE, AND S. K. MUKHERJEE
(4) BANGHAW FARHOLBY, AND MOHAMED: Proc. Roy. SOC. (London) A147,t52 (1934). (5) RANGHAU AND FRANKLIN: Trans. Faraday Soe. 42B, 299 (1946). (6) BANGHAM A N D MAWS:Proc. Conf. Ultrafine Structure of Coals and Cokes, Brit. Coal Utilisation Research Assoc. 1944, 118. (7) BANGHAM AND RAZOUK: Proc. Roy. SOC.(London) A166,572 (1938). (8) F A K H O U AND ~ YWAHBA:Nature 146, 63 (1940). (9) GREGG:J. Chem. SOC.1942, 696. [IO) GREGGA N D i M ~ Trans. ~ ~ Faraday ~ : SOC.44, 123 (1948). (11) HAINESA N D MCIKTOSH: J . Chem. Phys. 16, 28 (1947). et al.: J. Chem. Phys. 14, 117, 311 (1916). (12) HARKINS (13) Infernational Criticat Tables, Vol. IV, p. 21. McGraw-Hill Book Company, Inc., New Tork (1928). (14)KEMBALL: Proc. Roy. SOC.(London) A190, 117 (1947). (15) MAGGS:Trans. Faraday SOC.42B, 254 (1946). (16) RILEYAXD NELSON:Proc. Phys. SOC.(London) 67, 477 (1945). (17) SUHOFIELD A N D R I D E A L : h 0 r . Roy. SOC. (London) A109, 57 (1925).
I O S EXCHANGE I N SYSTHETIC RESINS 8 . L. GUPT.4, MONISHA BOSE,
AND
5. K. MUKHERJEE'
University College of Scietice and Technology, Calcutta, India Received November 88, 1949 INTRODUCTION
The study of synthetic resins has attracted the attention of a large number of investigators because of the vast promises these materials have shown in respect of their industrial applications. One of the most important uses to which the synthetic resins have been put in recent times is based upon their power of exchanging both anions and cations from electrolytic solutions. This property of synthetic resins, first observed by Adams and Holmes (I), was previously known to be possessed by siliceous zeolites, the bentonites and many other minerals, and the carbonaceous zeolites prepared by the sulfonation and oxidat,ion of complex organic materials such as coal or lignite. The reaction between phenols and aldehydes in the presence of a catalyst, leading to the formation of synthetic resins, is not understood in all its details. Three stages are generally distinguished in the condensation of phenol and formaldehyde in the presence of alkali (8). The chemistry of each of the stages has been carefully studied with a view to elucidating the mechanism of the reactions. For the purpose of the present investigation, however, reference to this aspect of the problem is not particularly relevant. But it must be pointed out that cured resin is cross-linked in three dimensions and has a high but undetermined molecular weight. The phenol-form1 At present a post-doctorate research worker in the Department of Soils, University of Missouri, Columbia, Missouri, with n fellowship from Calcutta CniverBity, C:ilruttn. India.
LOX EXCHhNGE IN SYXTHETIC RESINS
1099
aldehyde condensation products possess acidic properties and the power to react with bases and all cations. These are known as the cation-active resins. The anion-active resins are similarly formed by the condensation of amines with formaldehyde (1). They evidently have the same structure as the phenolformaldehyde resins, except that the amino groups take the place of hydroxyl groups. The elucidation of the physical structure of the amorphous condensation products of phenol and formaldehyde, called the “phenoplasts,” has been largely developed by Houwink (8). Ion-exchange resins Ion-exchange resins constitute a special type of the synthetic resins described above. Adams and Holmes (1) found that only polyhydric phenols when condensed with formaldehydegave resins which exhibited exchange capacity, whereas monohydric alcohols did not. The work of Akeroyd and Broughton (2) and of Bhatnagar, Kapur, and Puri (5), however, showed that even monohydric phenol resins possess exchange capacity. Introduction of further acidic groups like the sulfonic acid group increased the exchange capacity (16). Holmes (1) prepared anion-exchange resins by the condensation of aromatic amines, such as aniline or m-phenylenediamine, with formaldehyde. However, the condensation may proceed both on the ring and through the amino group, and a low exchange capacity as reported by Broughton and Lee (7) will be obtained. Patented anionexchange resina generally use polyamines, so that a more strongly hasic material is produced. All condensation products do not necessarily possess ion-exchange properties. The exchange spots in the resin structure are created as a result of the presence of certain functional groups. These may be radicals or groups like SOaH, CHISOIH, COOH, OH, and KHt, which act optimally a t definite pH ranges (16). Mechanism of exchange process The reaction between resins and electrolytes may be either molecular or exchange adsorption. The true base-exchange character of the reactions between the hydrogen or sodium derivative of the phenol-sulfonic acid type resin and calcium chloride was demonstrated by Myers and Eastes (17);Akeroyd and Broughton (2), on the other hand, showed that, unlike exchange reaction, the adsorption of alkalis by a phenol-formaldehyde resin was an extremely slow process, requiring about a week’s time to come to equilibrium. They assumed that the hydroxyl hydrogen of the acid is replaced by the -CaOH group. Theoretically, therefore, a monohydric phenol and a dihydric phenol should combine with 8.9 and 15.5 millimoles, respectively, of calcium per gram of resin. Their experiments actually confirmed these values. Evidence for both physical adsorption and ion exchange exists. Beaton and Furnas (4)found that the exchange of copper for hydrogen in a carbonaceous resin is best interpreted as a function of pH. Griessbach’s (11) data on the neutralization of a nuclear sulfonic acid resin with alkalis show that the nature of the cation of the base has an appreciable effect on the features of the neutralization
1100
S. L. GUPTA, MONISHA BOSE, AND S. K. MUKHERJEE
curve. Explanations for these differences were sought in the activities of the ions, hydration effects, and ionic sizes in the same way as they occur in siliceous exchangers (20). In the case of anion-exchange resins, the reactions were found to be markedly different from the cation-exchange resins. Thus Broughton and Lee (7), experimenting with aniline-formaldehyde and m-phenylenediamine-formaldehyde resins, observed low values for the adsorption of sulfuric and hydrochloric acids compared with the theoretical anion-exchange capacities of the resins. However, the equilibrium was attained much more quickly than in the case of cationexchange systems. Edwards, Schwartz, and Boudreaux (lo), in their experiments on the adsorption of acids by a m-phenylenediamine-formaldehyde resin, estimated the total acid as well as the anion concerned and concluded that the whole molecule of the acid is adsorbed. They found no adsorption of chloride from neutral and basic salt solutions. However, a greater adsorption of sulfuric acid than hydrochloric acid was observed by various investigators. The result was explained by Edwards et al. (10) by assuming that for each molecular unit of the resin a molecule of the acid is adsorbed and not in equivalent amounts. The experimental data of Kunin and Myers (13) did not entirely correspond to this assumption and they thought that some specific forces might be operative. Kunin and Myers, working with two anion exchangers of high and low capacities, observed that equilibrium for all practical purposes was attained in about 5-6 hr. and that the adsorption proceeds according to Freundlich’s isotherm. Great practical significance is attached to the dynamic method of studying the exchange capacities by means of percolating solutions through columns packed with resin. The results obtained by such experiments confirm the general conclusions of the equilibrium method. The work reported here has been confined t o the equilibrium method alone. EXPERIMENT.4L
Materials Since the composition of most of the ion exchangers available in commerce is not definitely known, and since it was desirable for the purpose of the present investigation to h o w the component parts and the functional groups, the following resins were prepared in the laboratory according to the methods of Adams and Holmes (1): (1) resorcinol-formaldehyde resin; (2) m-phenylenediamine-formaldehyde resin. The 2-mm. sieved material of the resorcinol-formaldehyde resin represented the coarse fraction. Finer fractions mere separated from a portion of the coarse resin by passing through 100- and 200-mesh sieves (Tyler’s series). The m-phenylenediamine-formaldehyde resin was lightly powdered, and the sample passing through 28 mesh and retained by 48 mesh was the coarse fraction. Two other fine fractions were separated from a portion of the coarse resin, viz.: (1) passing through 48-mesh and retained by 100-mesh sieves and (8) passing through 100-mesh sieves.
ION EXCHAXGE IN SYNTHETIC RESINS
1101
Methods The reaction between the acid resin and alkalis was studied by adding known volumes of excess standard alkali to weighed amounts of resin kept in wellstoppered Jena bottles, which were shaken for definite periods of time in an endto-end shaker. After allowing the solid matters to settle, an aliquot portion of the supernatant liquid free from suspended matter, but usually colored, was titrated either directly or, by adding excess of standard acid, back-titrated with standard alkali using phenolphthalein or Wesselow’smixed indicator. The reaction between the amine resin and the acids was similarly studied by adding excess of the acid and either titrating the residual acid after reaction or estimating the anion in the clear supernatant liquid. The amount of alkali or acid adsorbed was expressed in milliequivalents per 100 g. of the sample and has been termed the “exchange capacity (E.C.) .” Sodium was estimated either gravimetrically (3) as triple acetate, h’aZn(UOz)3, (CZH302)8, or volumetrically (9) by titrating the solution of the triple acetate with standard alkali, using phenolphthalein as indicator. Barium was determined as barium sulfate. Calcium was precipitated as calcium oxalate and titrated in a sulfuric acid medium with standard potassium permanganate solution. Potassium was precipitated as K2NaCO(SO2)8 (14), treated with standard potassium permanganate solution acidified with sulfuric acid, the excess permanganate reduced with excess oxalic acid or sodium oxalate solution, and the excess oxalic acid titrated with standard potassium permanganate solution. Ammonium ion was estimated after nesslerization by comparing the color developed with standard ammonium chloride solution. Chloride was estimated potentiometrically with standard silver nitrate solution, using the silver-silver chloride electrode. A Leeds & Korthrup type K potentiometer was used for E.M.F. measurements. Sulfate ion was estimated as barium sulfate, oxalate ion by titration with standardized potassium permanganate solution, and phosphate ion volumetrically after precipitating as ammonium phosphomolybdate (19). RESULTS BND DISCUSSION
Reaction between acid resin and bases The results of alkali interaction with the coarse resorcinol-formaldehyde resin are presented in table 1. The shaking was continuous in an end-to-end shaker. From experiments 1 to 3 it will be seen that by increasing the time of contact from 5 to 15 days, the exchange capacity (E.C.) shows an increase from 547 to 622 milliequiv. In the last experiment the ratio of resin to the total amount was nearly the same, but the concentration was lower, whereas the time of interaction was considerably increased. By doing so the E.C. shows an appreciable increase.
The nature of reacting alkali Colloidal acids of the siliceous clays are known to give a higher value of the exchange capacity when titrated with baryta than with sodium hydroxide (15). A comparison was, therefore, made of the values obtained with sodium hydroxide
1102
S. L. QUPTA, MONISHA BOSE, AND S. K. MUKHERJEE
and baryta. In the case of baryta all precautions were taken to prevent contact for any length of time with carbon dioxide of the air. The results given in table 2 will show that baryta gives a higher value than caustic soda. These results include measurement of the exchange capacity with sodium hydroxide and baryta, using samples of resin II(a) and II(b), sieved through a 200-mesh sieve. It will be seen that with both baryta and caustic soda appreciably higher values have been obtained in the case of the finer fractions.
Reactions with bases in the presence of neutral salts Although the excess alkali was appreciably high, the concentration of the cation in question may conveniently be increased by using strong solutions of the neutral salts. In the case of colloidal hydrogen clays, where the reaction between the TABLE 1 Reaction of alkali with coarse resorcinol-formaldehyde resin OF
KO.
V O L U OF ~ NaOH ADDED
PEEIN
TIME OF CONTACI
EXCEANGS CAPACITY
days
millicquio.
5
547 605 622 657 706
1. . . . . . . . . . . . . . . . . . 2. . . . . . . . . . . . . . . . . . . . .
7 15 12 25
3. . . . . . . . . . . . . . . . . . . 4.... .................... 5, ........................
Effect of nature of the alkali on the exchange capacitv NO.
1
WBIGETOPPSEIN
1
\'OLUYE OF BASE ADDED
0.5 0.5085 0.2755 0.5877
(coarse) (coarse) (200 mesh) (200 mesh)
TIME OF COXTACT
days
grams
I(a),. . . . . . . . . . . . . (b). . . . . . . . . . . . . . II(a).. . . . . . . . . . . . . . (b). . . . . . . . . . . . . .
I
85 50 50 75
cc. cc. cc. cc.
of 0,1198 N of 0.1163 N of 0.1187 N of 0.1153 N
NaOH Ba(OH)z Na0H Ba(OH)z
15 15 6
6
1
EXCHANGI CAPAClN
ni/liEpuk.
622 911 709 1004
hydrogen and the added cations was one of exchange in character, the neutralizable acidity increased to a very high value when the titration was carried out in the presence of a high concentration of neutral salts (15).The results with the resins are given in table 3. It will appear from these data that the presence of salts increases the E.C. But sodium hydroxide in the presence of sodium chloride gives a higher relative increase in the E.C. than baryta in the presence of barium chloride. These observations are similar t o those made with hydrogen clays (15).
Exchange of cations adsorbed from bases The amounts of cation adsorbed by the acid resin from the bases were determined by washing the treated resin residue with alcohol and replacing the adsorbed cations with 0.1 N hydrochloric acid. Before leaching with hydrochloric
1103
ION EXCHANGE I N SYSTHETIC RESIXS
acid the residue was kept in contact with the acid for about 5-7 days and shaken occasionally. I t will appear from the results given in table 4 that the amounts of adsorbed sodium or barium brought back by exchange with hydrogen ions are much less than what corresponds to alkali adsorption. It has been noticed that the excess
_____ VO 1I
ThBLE 3 Eflect of neutral salts on the ezchange capacity ~
WEIGHT OB RESI\
grams
0.4688 0.4350 0.6434 0.462
I
(coarse) (200 mesh) (coarse) (200 mesh)
'
75 cc. 75 cc. 75 cc. 75 cc.
of of of of
0.0945 N 0.0945 N 0.1153 N 0.1153 A'
~~
EXCHATGP C \PACITY
VOLUME OF ALKALI
-_
+ +
m*i!rrqu,i~
NaOH 2 N XaC1 NaOH 2 N NaCl Ba(OH)S N BaCla Ba(0H)z N BaClz
+ +
832 864 965 1079
TBBLE 4 Exchange of cations adsorbed f r o m bases so.
I
1
WEfG73TOPPESlS
grams
1
TIME OF
soarnoN
0 5 (coarse) 0 4688 (coarse)
3
0 4350 (200 mesh)'
10
4
0 5877 (200 rnesh)l 0 6434 (coarse)
6 10
~
CXCHASGEABLE CATlOh'
miliiequio miliisquir.
1 2
5
EXCEASG :APACITY4LKALI AD
Y O L U l I E OF ALKALI
d;
10
85 cc. of 0.1198 N 75 cc. of 0.0945 N NaCl 75 cc. of 0.0945 N NaCl 75 cc. of 0.1153 N 75 cc. of 0.1153 N N BaCL 75 cc. of 0.1153 N AT BaCll
NaOH iXaOH NaOH
+2N +2N
Ba(OH)Z Ba(OH)2
+ Ba(OH)? +
623 832
480 420
864
400
1004 965
832 768
1079
748
TABLE 5 Solt~bilization o f the resin bu alkali
alkali after treatment with the resin was colored brown, owing obviously to the solubilization of the polymerized resin. The resin made soluble in this way could be precipitated with acid and its weight determined. It was found in one experiment (acid resin and sodium hydroxide) that about 20.5 per cent of the original sample was rendered soluble by caustic soda treatment, as the figures in table 5 will show.
1104
S. L. GUPTA, MONISHA BOSE, AND S. K . MUKHERJEE
If we consider the following structural unit of resin and assume that the hydrogen ions at the exchange spots are hydrated as H80+,the theoretical exchange capacity of the resin becomes equal to 1220 milliequiv. per 100 g. OH
Assuming then that the soluble fraction has this theoretical exchange capacity, its contribution would amount to 251 milliequiv. This amount of sodium recovered from the soluble portion when added to that estimated in the residue makes the total equal to 862, a value much closer to the observed exchange capacity. The solubilization does not, however, appear to be a breakdown process, but merely suggests a vigorous reaction of the alkali with the exchange resin followed by a strong dispersion of the sodium resinate almost in its ultimate structural unit. In fact, one of us (S.L.G.) has made a number of potentiometric TABLE 6 Exchange of cations from barium acetate solution WEIGHT OF COARSE PBSIN
NO.
grams
1.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
0.4786 .! ,;
0.4178 0.4661
-1
1 BARIUM ADSOPBED FPOM BWWACETATE
1
milliequiv.
I
207 216 221
titrations with the colloidally dispersed resins and found that the theoretical value indicated above could be approached thereby.
Exchange of cations from salts It is clear from what has been observed so far that the interaction of acid resin with alkali is somewhat complicated by the solubilization effect. It was, therefore, of interest to see how salts interact with the acid resins. The samples of resins were progressively leached with 500 cc. of a neutral normal barium acetate solution and the amounts of adsorbed barium ion estimated. The results given in table 6 show that the values of the adsorbed barium ion from barium acetate solutions are much less than the exchange capacity determined by alkali interaction. The resins, as already mentioned, are at their optimum reactivity a t definite pH ranges. The weakly acidic nature of the resorcinol-formaldehyde resin requires that it should be active in the alkaline range. The low value of adsorbed barium ion from the neutral barium acetate solution may partly be due to this factor. Interaction between sodium hydroxide and acid resin obtained by heating for diflerent periods of time An apparent reason for the solubilizing effect of the acid resin described in the last section is possibly the degree of polymerization of the final product of con-
1105
10s EXCHANGE IK SYNTHETIC RESINS
densation of resorcinol and formaldehyde during the last stage of the treatment, i.e., curing. The time of curing the resin, Le., the heat treatment, was therefore varied from 0 to 10 hr. All the previous experiments were with the sample heated for 10 hr. Table 7 gives the results obtained with coarse samples (2 mm. sieve) of the resin heated for 0, 2, 4,6, and 10 hr., respectively. The mixtures of acid resin and excess alkali were shaken for 100 hr. over a period of 9 days. It will be seen that with the exception of the sample heated for 4 hr. the exchange capacity increases with the period of heating. The color of the solutions after the alkali treatment indicated in column 3 is more intense with the sample heated for 10 hr. TABLE 7 Effect of heating on the exchange capacity of a n acid Teain I I K E 01 H B A R N G
hours
No heating 2
i
4
6 10
-I
COLOB OF SOLUTION
PXCEANGE CAPACITY
nillicquic.
497 856 784 910 1003
~-
i, i
Slightly colored Slightly colored Slightly colored Slightly colored Highly colored
TABLE 8 Effect of heating on the exchange capacity of a n acid Yesin V n e r samples) fM OF UXATINQ
hours
No heating 2 4
6 10
I
BXC5ANGE CAPACIN
100-mesh sample mnillicauiw.
842 653 923 735 952
I
1W- to ZW-mesh sample milliquiw,
792 869 949 839 1067
Each of the above samples was again powdered in an agate mortar and sieved through 100-mesh and 200-mesh sieves. Two portions of the samples were separately collected, one passing through 100-mesh and the other passing through 100-mesh but retained by 200-mesh sieves. These samples were then kept in a desiccator for one month to enable all the samples to come to the same equilibrium state with respect to free moisture. The results of alkali adsorption are given in table 8. There is a tendency for the exchange capacity to increase with the period of heating, but there is not much regularity. I t is likely that the amounts of fine fraction having various grades of fineness present in the different samples are not the same, particularly because the grinding cannot usually be so controlled as to produce products having the same size distribution in all the samples. However, in the samples passing through 100-mesh but retained by 200-mesh sieves (column 3, table €9, the different sized particles are distributed within a narrower
1106
S. L. GUPTA, MONISH.4 BOSE, AND S. K. MUKHERJEE
range. The exchange capacities of these samples show a tendency to increase with the hours of heating, except for the sample heated for 6 hr. The relative intensity of color of the solutions after alkali treatment was nearly the same as that with the coarse samples. Catzon exchange i n resinates
Whatever be the mechanism of reaction between alkali and acid resin, it has become apparent that a true exchange process cannot be clearly envisaged. Such complications are expected to be absent in the interaction between resinates and neutral salts. The exchange reaction was studied with sodium and barium resinates, which were prepared by adding the requisite amounts of the hydroxides to the acid resin. Symmetry values determined against various cations are given in table 9. TABLE 9 Cation exchange i n resinates
____ Sodiuin resin Sodium resin Sodium resin Sodiuin resin Sodiuni resin
+ HC1 + KCl + NH&I + CaClt + BaClt
__
I I
Colorless Orange Light orange Faint yellow Faint yellow
I l
I
Exchanged
84 0 70 S 74 s 88.7 859
Adsorbed
~-
93.7 71 7 73.6 89.1 89.2
1107
ION EXCHANQE I N SYNTHETIC RESINS
standard sodium hydroxide solution. The residual resin was washed free from electrolytes, kept in contact with 0.1 N sodium hydroxide for about 5 days, and leached with the alkali solution in order to displace the adsorbed anion. The reTABLE
10
Chloride-ton content of the supernatant liquid before and after the exchange
1
1
__
__
VOLUME OP
i
SYSIEM
0.1729 h' AgNO, REQUIRED BY 5 CC.
OF THE CHLORlDX SOLUTION
After exchange
Before exchange
cc.
cc
+ HC1 Sodium resin + KCl Sodium resin + NHICl Sodium resin + CaCl? Barium resin + NH&l Barium resin + NaCl
1
Sodium resin
1.439 1.460 1.444 1.410
1 444 1.444 1444 1 444 1 444 1 444
~
1
1.500 1.459
TABLE 11 Anion ezchange with m-phenylenediamine resin
-
NO
SYSTEM
ANION ADS 0E B E D FROM ACID SOLUTION
ANION XSPLACED
hours
milliequip..
nriUicquiu.
68
407
384
Yellow
68
412
434
Yellow
68
245
160
Faint yellow
68
249
160
Faint yellow
68
433
432
Very faint yellow
68
280
277
Very faint yellow
68
277
27i
Very faint yellow
68
378
68
380
?IYE OF SHAKISO
BY
NaOH
COLOX OF SUPERNATANT LIQUID
~
1
la 2 2a
3 4 4a
5
+ + + + + + +
0.3174 g. resin 50 cc. of 0.1375 N HsSOd 0,1686 g. resin 50 cc. of 0.1375 N HzSOr 0.1762 g. resin 50 cc. of 0.096 N HC1 0.2244 g. resin 50 cc. of 0.096 N HC1 0.2786 g. resin 50 cc. of 0 . 1 N HzC204 0.2072 g. resin 50 cc. of 0 . 1 N HaPo, 0.2165 g. resin 50 cc. of 0 . 1 N HaPOl 0.1392 g. resin (100 mesh) 50 cc. of 0.1375 N
+
Yellow
HzSOI 5a
0.4564 g. resin (100 mesh) 50 cc. of 0.1375 N
+
HzSOI
sults of these determinations are presented in table 11. Experiments 1 to 4a were done with 40- to 100-mesh samples. The figures are means of duplicate experiments.
1108
8. L. GUPTA, MONISHA BOSE, AND S. K. MUKHERJEE
The results indicate that with the phosphoric and oxalic acids the exchange is probably anionic, since the amounts adsorbed are completely replaceable by another anion, viz., OH. In the case of sulfuric acid and, more markedly, hydrochloric acid the anions appear to possess a stronger binding with the resin residue. Edxards et al. (10) and Bishop (6) concluded from their experiments that hydrochloric and sulfuric acids are molecularly adsorbed by the amine resins. They confirmed this conclusion from their observation that no anion is adsorbed from neutral or alkaline solutions. Kunin and Myers (13), however, concluded that the anionic resins (they actually used Amberlite IR-4B) do exhibit anion exchange and suggested that since the exchange spots of amine resins become active only in acid solutions no adsorption from neutral or alkaline solution is possible. The observations made in the present investigation show clearly that, at least in acid solutions, adsorption from phosphoric and oxalic acid solution is an anionexchange process. In the more strongly acidic solutions of sulfuric acid, and more particularly hydrochloric acid, perhaps molecular or maybe very strong anionic adsorption takes place. I t will no doubt be difficult to decide between anionic exchange from acid solutions and molecular adsorption. No adsorption from a neutral 1 N sodium sulfate solution could be observed, however, even on prolonged interaction with the salt. Another important point to be noticed in the case of amine resins is that the maximum exchange capacity obtained with either sulfuric acid or oxalic acid is only about one-fourth of the theoretical value. Similar results have also been reported by others (16). The theoretical value has been calculated on the basis that two amino groups for each unit structure are available for anionic exchange (cf. page 1104). To explain the low value (7) suggestions have been made to the effect either that polymerization involves these amino groups or that amino groups are blocked by steric hindrance. From our observations on cation-exchange resins, we found that particle size was an important factor which determined the accessibility of the exchange spots. The resin samples used in the above experiments are very coarse (48-100 mesh) and the samples used by other investigators are also of a similar texture. Using a colloidally dispersed amine resin and taking recourse to potentiometric titrations with acids, one of us (S.L.G.) has been able to approach the theoretically calculated value. The results will be published elsewhere. SUMMARY AND CONCLUSIONS
A resorcinol-formaldehyde cation-exchang e resin and a m-phenylenediamine anion-exchange resin Rere used for the present investigation. The reaction between the acid resin and alkali was studied by adding known amounts of alkali and, after definite periods of time, analyzing the alkaline supernatant liquid. The exchange capacity thus obtained is determined by the following factors: the time of contact, the relative proportions of the solid and solution phases, the fineness of the resin, and the nature and concentration of the alkali. Baryta gives under identical conditions a higher value of the acidity or exchange capacity than sodium hydroxide. The presence of a high concentration of neutral salt increases the total neutraliaable acidity. The amounts of cation adsorbed
ION EXCHANQE IN SYNTHETIC RESINS
1109
from either alkali or salts are much less than the exchange capacity obtained by way of estimation of the alkali consumed. A decrease in the time of heating during the process of curing the resin causes an appreciable reduction in exchange capacity. The symmetry values of the resin salts or the resinates of sodium and barium were determined against different cations. Chloride-ion concentration before and after the reaction of the added chlorides was the same, showing absence of molecular adsorption. The exchange of cations is equivalent and the cations show the lyotrope effect. The total exchange capacity of the anion-exchange resin is about one-fourth of the theoretical value, but shows a small lyotrope effect in its reaction with hydrochloric, sulfuric, oxalic, and phosphoric acids. REFERENCES (1) ADAMS AND HOLMES: J . SOC.Chem. Ind. 64, 1-6T(1935). AND BROUGHTON: J. Phys. Chem. 42, 343 (1938). (2) AKEROYD J. Am. Chem. SOC.66. 1625 (1928). (3) BARBERAND KOLTHOFF: AND FURNAS: Ind. Eng. Chem. 99, 1500 (1941). (4) BEATON KAPUR,AND PURI: J. Indian Chem. SOC.18, 679 (1936). (5) BAATNAGAR, (6) BISHOP:J. Phys. Chem. 60,6 (1946). AND LEE: J. Phys. Chem. 43, 737 (1939). (7) BROUGHTON High Polymers. VII. Phenoplasts. Interscience Publishers, Inc., New York (8) CARSWELL:
(1947). (9) DOBBING AND BYRD:J. Am. Chem. SOC.69, 3288 (1931). (10) EDWARDS, SCHWARTZ, AND BOUDREAUX: Ind. Eng. Chem. s1, 1462 (1940). Quoted by Myers (16). (11) GRIESSBACH: J. Phys. Chem. 86, 2217 (1932). (12) JENNY: (13) KUNINAXD MYERS:J. Am. Chem. SOC.69, 2874 (1947). (14) MILNE:J. Agr. Sci. 19, 541 (1929). AND BAGCHI: Indian J. Agr. Sci. 10, 303 (1942). (15) MITRA,MUKHERJEE, (16) MYERS:Advances i n Colloid Science, Vol. I, p. 317. Interscience Publiahers, Inc., New York (1942). (17) MYERSAND EABTES:Ind. Eng. Chem. 81, 1138 (1939). (18) PALMER:Ezperimenlal Physical Chemistry. Cambridge University Press, London (1941). (19) TREADWELL AND HALL:Analytical Chemistry, Vol. 11, p . 516. The Macmillan Company, New York (1945). (20) WIEGNERAND JENNY:Kolloid-2. 42, 268 (1927).
