Equilibrium and Column Behavior of Exchange Resins STRONG BASE ANION EXCHANGE RESIN ,
ROBERT KUNIN AND FRANCIS X. MCGARVEY
Resinous Products Division, Rohm & Haas C o m p a n y , Philadelphia,P a . Until recently, the anion exchange resins that have been available have been of the weak base type functioning as anion exchangers only in acid media. The recent availability of a strong base type of anion exchange resin (Amberlite IRA-400) has widened the scope of anion exchange operations so that anion exchange may now extend to neutral and alkaline media as well as acid media. The results of studies on the equilibria and column characteristics of these new resins are presented.
A
\
SULFURIC ACID IN I I N KpSOI
B HYDROOMRIC ACID IN I I N KCI 0 NITRIC ACID IN I/N “0,
T
HE applications of ion exchange, particularly anion exchange, have been limited because of the unavailability of an eschange substance having strong base characteristics that permit the exchange of anions in neutral and alkaline media and also permit the adsorption or exchange of anions of very weak acids. The recent availability of Amberlite IRA-400, a resinous type anion exchange substance, has overcome this deficiency and has extended the field of ion exchange operations. Since the equilibria and column characteristics of resins of this type are considerably different from the conventional weak base type anion exchangers, an extensive study of these properties was undertaken.
01
I
I
ACID -0
I
I
I
2 3 4 3 (MILLIEQUIVbLENTS PER QRAMI
1. Titration Curves Amberlite IRA-400
Figure
of
EXPERIMENTAL PROCEDURE
The Amberlite IRA-400 chosen for this study was supplied as a spherelike particle having an effective size of 0.41 mm. and .uniformity coefficient of 1.55. The resin was thoroughly regenerated a t first in a column using a 4% solution of sodium hydroxide and thoroughly rinsed with distilled water until the effluent was neutral to phenolphthalein. The regenerated resin was filtered and stored in a glass jar for further use. In this moist state, the resin had a moisture content of 5Oy0 and contained 3.2y0 nitrogen on a dry basis. The total capacity of the resin was determined as follows: A 5-gram (wet) sample was leached with 1 liter of 4y0 sodium hydroxide and then leached free of alkali with distilled water. One liter of a 5% sodium sulfate solution was then passed through the resin and an aliquot of the filtrate titrated with standard 0.1 K hydrochloric acid. The capacity as determined in this manner is referred to as the “total salt splitting” capacity and does not include any capacity that may be present as a result of a weakly basic nitrogen. The capacity as determined by this procedure yielded a value of 2.0 milliequivalents per dry gram. The titration curves and equilibrium studies were obtained using the methods described by Kunin and Myers (2). Column studies were carried out in 1.0-inch (inside diameter) Pyrex tubes containing 250 ml. of resin supported by acid- and alkali-washed Ottawa sand. All studies were conducted a t room temperature. Unless specified, the regeneration flow rate was 0.134 ml. per ml. resin per minute. The exhaustion flow rate was 0.268 ml. per ml. of resin per minute.
late > iodide > nitrate > chromate > bromide > thiocyanate > chloride > formate > hydroxyl > fluoride > acetate. As would be expeoted, the position of the hydroxyl ion is diferent from that for the less basic Amberlite IR-
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f 6-
P
3’-
4B.
- BC A
1
0
WITER O O l N POTASSIUM OnLDRlDE I O N POTASSILM CHLORIDE
I
1
L
I
-
RESULTS
EQUILIBRIUM STUDIES.The strong base character of this resin type is clearly indicated by the titration curves in Figuces 1 and 2. The effect of ionic strength is similar to that already
Quantitative application of the RothmundKornfeld (3) relationship t o these data are ment
Figure 2. Titration Curves of Amberlite IRA-400 with Hydrochloric Acid at Various Ionic Strengths
1265
found for the exchange equili-
bria ( 1 ) . Fair agreem e n t was obtained
1266
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 41, No. 6
for the exchange of univalent ions (Table I, Figure 4),but as in the case of cations, exchange of ions of unequal charge exhibited little agreement. The slope for the mass action relationship approaches unity for ions of similar size and charge as in the c a w for the hydrovvl and fluoride ions.
w-
10
MP
Ill
I
I
Figure 4.
I
I
I
lOd-
I
I
9
lW%,EFFICIENCY SOMUM*OXALATE SODIUM HYDROGEN TARTRATE
SOJklJ’
FORMATTE
---
SODIUM ACETATE
*4O
2olP 10
V
I
I
I
O
l
COLCAIX STUDIES. The column behavior of Aniberlite IRA400 is described in Figures 5 to 10. Although previous studies of anion exchangers have been devoted to the adsorption and exchange of ions in acid media, these studies include exchange rcactions in acid, neutral, and basic media. The concentration histories of the column experiments in the hydroxyl (resin hydroxide versus sodium chloride or sulfat,e) cycle and chloride (resin chloride versus sodium sulfate) cycle arc described in Figure 9 as a function of regeneraiion level. For these and subsequent experiments, t,he regenerant chosen was a 4% sodium hydroxide solution. The hydroxyl cycle indicat e5 that the neutral salt splitting ability of the strong base anion exchange is remarkable and approaches almost complete coni-ersion a t higher regeneration levels, I t the lower regeneration levels, leakage of incomplete removal or exchange is noticeablr,. Lcalcage of the sulfat,e ion occurs a t a much lover regenerat,ion level than that of the chloride ion. The chloride-sulfate cycle as described in Figure 5 (lower! ’ illustrates the ease 1%-it’h which the chloride ion may be replaced by the sulfate ion. Leakage of sulfate ion during t,his cycle is only apparent a t regeneration levels that are low. The exchange of sulfate ions by chloride ions, although urifavored by the equilibrium, yields a capacity but one half of the reverse reaction. The p H of the effluent during the chloride cycle was practically neutral (6.5 to 9.0) during all t8he cycles. In contrast, weakly basic anion exchangers exhibit a pT1 2 to 3 effluent throughout the cycle because of hydrolysis. The effect of regenerant type is adequately described in Figure 6. Ammonium hydroxide is much too weak a base for t h e regeneration of the strongly basic cation exchanger. Although
__1
IO I 1
0
2 SYMMETRY VALUE
(MILLIEPUIULENTS ADDED
Figure 3.
I
PER
ABLE
I.
EQUILIBRIU\f COSSTAXTS F O R
HYDROXYL Iors
I
3
MILLIEQUIVALENT DRY
Exchange Equilibria for Univalent Ions
Upper, H.alide-hydroxide exchange. Lbper center. Thiocyanate, nitrate, arsenate-hydroxyl exchange. Lower center. Oxalate, tartrate, formate, acetate-hydroxyl exchange. Lnwar. Sulfate, chromate, citrate, phosphate-hydroxyl exchange.
EXCHANGE 0 1
AXBERLITEIRA-400
(OH)s = K c ( -(-4)s ) P
RESIN)
Equilibria of Amberlite IRA-400
IS
~OEUR Ion
r-
c1Br1-
?io3scs-
COOHC~HIOC
(.4)11
X, 1.13 2.93 6.8
9.0
8.6 6.3 1.8 0.8
Slopr
0.94
0.75 0.58 0.35
0.69 0.65 1 4 -.> 0 4:)
INDUSTRIAL AND ENGINEERING CHEMISTRY
June 1949
EXHAUSTANT. CURVE
REG LEVEL
1267
0 01 N SODIUM CHUlRlDE AVERAGE%REMDIAL
EQ / LITER I21 201
92 0
0 271
975
A \
I
6 )
I i NOCI OR No,sO, 001 N NOCI OR N02SOa
REGENERANI' EXHAUSTANT,
EXMAUSTAW L
0 01 NORMAL HOC1
V
xi.
BlCARgKlPiTE BN
562 5 1 4
b c
101 0'
E
10 I
20 VOLUME
Figure 5. Upper. Lmoer.
-
x) I 40 I 40 Eo I 70 I OF EFFLUENT PER VOLUME OF RESIN
80 I
Column Behavior of Amberlite IRA-400
For chloride-hydroxyl as function of regeneration l e v e l . For chloride-sulfate rxchange a s function of regeneration level.
the data in Figuie 6 indicate sodium carbonate to be almost as efficient as caustic, Figure 7 indicates that the use of sodium carbonate as a regenerant yields a resin that is partly in the carbonate and partly in the bicarbonate state rather than in the hydroxyl form. Data for the exchange of the carbonate and bicarbonate ions by the sulfate and chloride ions are reported in Figures 7 and 8. The adsorption of hydrochloric, sulfuric, and phosphoric acids and weak acids such as phenol, silicic, hvdrogen sulfide, and hydrocvanic acids is summarized in Table 11 The adsorption of the sulfide ions and cyanide ions was awomplished with no leakage (le36 than 1 p p.m.).
OF AMBERLITEIRA-400 TABLE 11. CAPACITY ACIDS
Acid Hvdrochloric Sulfuric
Ionization Constant m
Hydrosulfuric Phenol Hydrocyanic Silicic
VARIOUS
Capacity (Break Through), Equivalent/I,iter 0 47
kl = m k2
Phosphoric
FOR
=
kl = kz = k3 = ki = kg =
2 x 10-2 1 . 1 x 10-2 2 X 10-7 3 . 6 x 10-13 9 . 1 X 10-8
0.47 0.51 (dibasic) 0.84 (tribasic)
1.3 X
0.51 0.41 1.36
=
k
= 7 2 X 10-10
10-10
DISCUSSION
The results obtained in this study are of interest from two points of view. First, they definitely illustrate the existence of anion exchange rather than acid adsorption in anion exchange
0 , R5
1.2 X-10-15
k
rates of exchange or the strong base anion exchange resin are as high as for the sulfonic acid exchangers of similar particle size. DEIONIZATION. Figures 10 and 11 describe the use of Amberlite IRA-400 with the sulfonic acid cation exchange resin Amberlite IR-120 for the deionization of aqueous solutions. Figure 10 illustrates the two column (Amberlite IRA-400 and IR-120) system in which the anion exchanger precedes the cation exchanger. This arrangement is designated as "reverse" deionization. Figure 11 describes the deionization of aqueous solutions utilizing a mixture of Amberlite IRA-400 and the sulfonic acid cation exchanger Amberlite IR-120. Utilization of the resin mixture in a batch procedure is designated as a mixed bed operation I t is interesting t o note that both procedures, impossible to achieve prior to the advent of strong base anion exchange resins, perform as efficiently as the conventional procedu re.
The adsorption and exchange of the nitrate ion (Figure 9) indicate an unusually high degree of binding in that the regeneration efficiency is low. I n fact, high regeneration levels of 10% sodium chloride are necessary for regeneration of the nitrate form of the resin. RATEOF EXCHAXGE. The rate of exchange or this resin type has been studied in flowing systems. Table I11 shows that the
TABLE111. EFFECTOF REGEKERATIOS AMI FLOW
RATESON Regeneration Rate, MI./MI./Min. 0.134 0.134 0.134 0.134 0,067
0 134 0 268 0.636 1.34
EXHAUSTION IRA-400
CObUalIi BEHAVIOR OF h f B E R L I T B IN THE CL--OH - CYCLE
Exhaustion Rate MI./Ml./kIin. 0.134 0.268 0.536 1.34 0.268
0.268 0.268 0.268 0.268
Equivalent/Litel Capacity, 0.39 0.39 0.39 0.38 0.38 0.38 0.38 0.39 0.38
Vol. 41, No. 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
1268
RESISTMICE EFFLUENT FROM IR 120 BED
2
/
I
I W B O H A T E ION
b
WLUME OF EFFLUENT PER VOLUME OF RESIN
Figure 8. Column Behavior of Amberlite Chloride IRA 400 for Bicarbonate Exchange
-
-
IIESISTANQ EFFLUMTFROM I R A 4 0 0 E€D
?!
-4 X
6
&
!A
iJ FA V O U U E Of E F F W N T PER MLUME OF
Eb
R r n
Figure 10. Reverse Deionization of 0.009 N Sodium Chloride with Amberlite IRA-400 and Amberlite 1R-120
WHERE Y
x'
* OH'OR SO: a
EXHAUSTANTS
0-RE4?EGER 4
i
b k
5
SQl,NO;,OR GI. 0 01 NORMAL NoGI. NOnSO., AND NlNOJ
; ;1
9
io
11
I
'
Figure 9. Capacity of Amberlite IRA-400 as a Function of Regeneration Level
resins. Alt,hough t.he results for weakly basic anion exchangers could be interpreted on an anion exchange basis, the fact that ion exchange for these resins was limited to acid media made it rather difficult to distinguish betxveen anion exchange and molecular acid adsorption for t'hose systems involving the hydroxyl form of the resins. The difference in the ion exchange behavior of the two anion exchange resin types centers predominantly about the ease with which the hydroxyl ion can be exchanged, or iri other words the basic strength of the active basic groups. This increased basicity permits the adsorption of such weak acids as boric, cyanic, hydrogen sulfide, carbonic, phenol, and silicic. Secondly, a comparison of t,he column behavior of the strong base anion exchanger and the strong acid cation exchangers reveals many similarities. The concentration histories (C/C, curves) for the strong base anion exchanger (hmberlite IR-4-400) in the hydroxyl cycle is similar to those for the hydrogen cycle of a sulfonic acid cation exchanger, The exchange behavior for the exchange of the anions of different valence (bivalent and monovalent) such as t,he chloride-sulfate exchange is analogous from all aspects t o the calcium-sodium exchange in the strongly acidic sulfonic acid type of cation exchangers. Froin the viewpoint of economics of operation, the use of a strong base exchanger for the removal of acids that can bc removed by a weak base exchanger is unwarranted. A strong base exchanger requires a strong base for regeneration a t regeneration levels that is much less efficient than those required for a weaker base anion exchanger. It is, therefore, obvious that the more economic utilization of an anion exchanger requires the choice of the resin ha.ving the loivesl basicity sufficiently great
Figure 11. Mixed Bed Batchwise Deionization by Amberlite IR-120 and IRA-400
to perform adequately. However, for such applications in which an anion of a weak base must be adsorbed or in which the deionization must be accomplished without, t,he formation of acid or at neutralit,y, one must employ a strong base exchanger either in R reverse deionization technique or in a batchwise mixed bed operation. LITERATURE CITED
(1) Boyd, G . E., andSchubert, J.. J . Am. Chem,.SOC., 69, 2818 (1947). ( 2 ) Kunin, R., and Myers, R. J.,I b i d . . 69, 2874 (1947). (3) Rothmund, V., and Kornfeld. G., 2 . anorg. allgem. Chern., 103, 129 (1918). (4) Wiklander, L., Ann. R o y . A g r . CoZZ. Sweden, 14, 1 (1946). RECEIVED August 17, 1918. Presented before the Diviaion of Industrial and 1':ngineering Cheiriistry a t the 114th Neeting of the AXERICANCHEUICAL SOCIETY,Washington, D. C.
