(Equilibrium and Column Behavior of Exchange Resins)
CARBOXYLIC, WEAK ACID TYPE, CATION EXCHANGE RESIN ROBERT KUNIN AND RUTH E. BARRY Resinous Products Division, Rohm & Haas Company, Philadelphia, P a . T h e equilibrium and column characteristics of sulfonic acid types of cation exchange resins have been adequately described i n the literature, but relatively little has been published concerning the behavior of a unifunctional carboxylic type cation exchange resin. Equilibrium studies and titration curves of the carboxylic type cation exchange resin, Amberlite IRC-50, show the weak acid characteristics of this tj-pe of exchanger. Results of the investigation on equilibrium, column behavior, and rates of exchange of Amberlite IRC-50 are presented.
amino acids and the recovery of other nitrogen bases such as quinine, nicotine, thiamine, etc. Mattson (5) has determined some basic ion exchange data for natural sponge in which the exchange activity was attributed t o carboxylic acid groups. In addition to the foregoing investigations, several investigators (1)
A
LTHOUGH the equilibrium and column characteristics of sulfonic acid types of cation exchange resins have been adequately described in the literature (6, 8 ) , comparatively little has been published concerning the behavior of a unifunctional, carboxylic type of cation exchange resin. Griessbach ( 9 ) has described the titration curve of Wofatit C, a phenolic type of carboxylic acid cation exchange resin and Wieland (7) has described the separation of basic amino acids utilizing the same resin. More recently, Winters and Kunin (9) have utilized the carboxylic exchanger, Amberlite IRC-50, for the separation of
W N l l W UCI
I
I
3c
1,
b
I
1
I
zI
4I
I
,
I
I
SYMMETRY !
6 MILLIEWIVALENTS
I
10 12 14 WOHle ADDED PER FRAM DRY RESlN 8
Figure 3. Cation Exchange Equilibria in Sodium-Calcium and Sodium-Magnesium Cycles of Amberlites IR-105 and IRC-50
16
Figure 1. Titration Curves of Amberlite IRC-50
1269
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
1210
0012
-
oalc-
,/'
0
!
1: omsz 0006
I
-
/
I 0'4
'
08
I
1
12 SYMMETRY
1
lb
'
20
/
2+-
Figure 4 . C a t i o n Exchange Equilibria i n Hydrogen C y c l e of A m b e r l i t e IRC-50
VOI. 41, No. 6
calcium and hydrogen ions is shown in Figures 3 to 5 along with a comparison o the equilibria for the SUIfonic acid groups. The data indicate a consid crable difference betmeen the equilibria involving the exchange of ions a t the carboxyl group and those a t the sulfonic acid group The greatest diffprences, of couise, arc' noted for tho-(. equilibria involving the hydrogen ion. Apparently, the carboxyl 4 groupexhibitsarnarkcd affinity for the hydroJB-lO"Cn,'Vs~gen ion indicating that thiq ion is exchanged v, ith great difficultybut 08 I2 6 LO 24 may exchange othci SYMMETRY i o n s r e a d i l y mhcii Cation E x c h a n g e Equilibria in bound to a carbox71 Cycle of Amberlites 1R-105 a n d IRC-50 group The calcium i o n exhibits s i m i l a r but to a .vioiierties. . lesser extent. h comparison 01 the ion exchange equilibria of t h r carboxylic and sulfonic acid groups is summarized in Table I. The comparison is merely on an empirival basis-Le., a comparison of the extent of exchange at a symnic't>ry ratio (4)of unity. C o ~ r r BEHAVIOR. ~s As in the cquilibriuni studies, the colurmi behavior of Amberlite IRC-50 was studied in both the sodium and hydrogen cycles. I n the sodium-calcium (or magnesium) cycle (water softening) the results (Figure 6) are in good agreement with those of t'he equilibrium study. \\'hereas the softening ability of the carboxyl group is most efficient, the regeneration efficiency utilizing brine solutions is most inefficient. The strong affinity of the carbosyl group for calcium ions prevents an efficient regeneration. I n the hydrogen cycle, t,he weak acid character of the exchanger restricted the influents that could be studied to basic solutions. Salts such as sodium chloride, calcium chloride, and magnesium chloride were ineffect,ive. Figures 7 to 10 describe the results obtained for sodium hydroxide, sodium carbomte, sodiuiii bicarbonate, and calcium bicarbonate solutions of varying coilcentration and a t varying flow rates. As would be expected, the capacity of the exchanger, as determined by an arbitrary leakage end point of 10yoincreases wit,h increasing basicity of t'he solution-Le., sodium hydroxide, sodium carbonate, and sodiuin bicarbonatme. Owing t,o the increased affinity of the carhosyl / -
, , 04
Figure 5 . Hydrogen
have studied the ion exchange behavior of cellulose, oxycellulose, alginic acid, proteins, etc.-substances having carboxylic acid activity. Ailthoughthese investmigationshave been informative, considerable information is lacking for the equilibrium and column characteristics of the exchange reactions occurring at the carboxyl group I t is for this reason t,hat this invcstigation was undertaken. EXPERIMENTAL PROCEDURE
The resin chosen for this study was -%mberliteIRC-50, a bead type carboxylic acid carion exchanger having a n effective size of approximately 0.4 mm. (diameter) and a uniformity coefficient of 1.6. The hydrogen form of the resin was prepared by leaching the resin with 1 N hydrochloric acid and rinsing with distilled water until a neutral effluent vias obtained. The sodium and calcium forms of the resin were prepared by treating the hydrogen form of the resin with an excess of either sodium or calcium hydroxide. The resins were then rinsed free of excess hydroxide. with distilled water. The equilibrium studies \\-ere conductcd in a manner similar to the procedure ut,ilized by Kunin and Myers ( 4 ) for the anion exchange resins, substituting standard alkali for the standard acid solutions. Equilibrium w a s considered to be complete after 2 weeks of intermittent shaking. The column st,udies were carried out in 1.O-inch (inside diameter) Pyrex tubes containing 100 ml. of resin supported either on Ottawa sand or porous glass plates. Sodium and calcium were determined by the uranyl zinc acetate and oxalate methods, respectively. pH measurements were made of the suspensions using a glass electrode assembly after rinsing the electrodes with small portions of thv snpcrriatant liquid. K E:SU LTS EQUILIBRIU\f STCDIIX Thc weak acid character of Amberlite IRC-50 is cltAarly indicated by the titration curves with potassium hydroxide, and calcium hydroxide (Figure 1). The capacity at the point of inflection (10 niilliequivalents per gram) compares favorably with the total capacity (10 milliequivalents per gram) as determined by equilibrating a sample of the hydrogen form of the resin with an excess of standard alkali. For comparison purposes, Figure 2 exhibits the titration curve of a sulfonic acid cation exchange resin, iimberlite IR-105. The nature of the equilibria for the sodium and calcium ions, sodium and magnesium ions, sodium and hydrogen ions, and
__ Per Cent Exchange ~ (Symmetry ~ = _ 1) Na+ +++ lCa-' \Ig++ R - S a + H+ R Ca + H* R - h a + Ca++ R - S a + Mg-' R-Ca + h-a+ R-H R-H R-H
Amberlite IRC-SO 0.004 0.004 0,012 90 00
sa
55 10
lmberlite IR-120
_
June 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
group for calcium ions, calcium bicarbonate solutions are more readily neuWBERLITE I R C - Y I tralized thansodium bicarbonate solu/ tions. The effectsof such variables as particle size, concentration, and flow rate upon the column performances of Amberlite IRC-50 in the hydrogen form are similar [Figures 8, 9 (right), and 101. An increase in any of these three variables results in an Figure 6 . C o m p a r i s o n of S o f t e n increased leakage i n g C h a r a c t e r i s t i c s of Carboxylic and break-through and S u l f o n i c Acid C a t i o n E x c h a n g e Resins c a p a c i t y . These factors indicate a marked sensitivity of the hydrogen form of the carboxyl exchanger towards rate. T h e marked affinity of the carboxyl group for the hydrogen ion results in a high acid regeneration efficiency even at acid concentrations as low as 1%. Figure 11 describes the course of a regeneration of the sodium and calcium forms of Amberlite IRC50 utilizing dilute solutions of hydrochloric and sulfuric acids. Although the sulfuric acid regeneration of the calcium form of Amberlite IRC-50 results in calcium sulfate dehydrate (Cas04 .2H20) precipitation, no loss in capacity is noted as in the case of the strong acid sulfonic acid cation exchangers. ,
I
TABLE11. COMPARISON OF RATES OF EXCHANGE FOR CARBOXYLIC AND SULFONIC h C I D CATION EXCHANGE RESINS Equilibrium Attainment Time 7 days 2 minutes 2 minutes 2 minutes
Equilibrium RCOOH KOH RSOsH 4- KOH RCOONa CaCh RSOaNa CaCb
+ ++
~
dpparent Density, Gram/MI. 0.40 0.435
0.30 0.500
RATESOF EXCHANGE.Although true kinetic measurements n ere not made, a comparison was made of the rates of exchange for the carboxylic exchanger and sulfonic acid cation exchanger by comparing the time necessary t o attain equilibrium under comparable conditions of particle size and concentration. A summary of this comparison is given in Table 11. For those exchange equilibria t h a t involve the salt forms of the resins, equilibrium attainment was rapid for both resin types. However, for tbe equilibria involving the hydrogen modification, the equilibrium time for the carboxyl exchange resin was very high, whereas the sulfonic acid exchanger exhibited results similar t o those for the corresponding salt form. DISCUSSION
T h e results obtained in this study of the exchange propertics of a carboxylic cation exchange resin are of considerable interest when compared with the knowledge of the cation exchange behavior of the more widely studied sulfonic acid exchangers. The results become more significant if one views these cation exchange resins as macroelectrolyte molecules consisting of a large multicharged nondiffusible anion whose charge is satisfied by small diffusible cations. I n e n these cations are the hydrogen ions, the extent of dissociation of the hydrogen ion depends largely upon the strength of acid formed between the exchange group and t h e hydrogen ion. Since carboxylic acids are usually weak acids, the differences observed for the equilibrium involving the hydrrgen forms of the carboxylic and strongly acidic sulfonic 1
I "I
40, /NaHCO,
m-
1271
I0006 NI Y
3
35-
as 10
-
i
SOLUTION : NDOR
,L-+----i--L
IO
15
2 5 --+*-&&2
2,--I 0
R A T E : 0.133 ML PER ML
/
5-
0
CAPACITY iEOUIVALENTS PER LITER]
CAPACITY [EQUIVALENTS
F i g u r e 7 . C o l u m n P e r f o r m a n c e of A m b e r l i t e IRC-50 t o w a r d s S o d i u m Bicarbonate, S o d i u m C a r b o n a t e , and S o d i u m Hydroxide
Pm
MN.
,
/ I
CONOENTRATION {NMIMALITYI
PER LITER)
F i g u r e 9. Effect o f Concentration on C o l u m n P e r f o r m ance of A m b e r l i t e IRC-50
Ea-
70.x
60-
s
;
50-
*
X 40-
49-
30-
XI-
M-
20-
IO
€0-
-
10 I
I
L
!
0
I
I
1
I
I
J
1272
INDUSTRIAL AND ENGINEERING CHEMISTRY
----
I d
toL
___-
----
I
100 % OF THEORETICAL
~
I 2 3 4 REOEHERATION LEVEL LEOUIVALENTS HISO.
Figure 11.
5 PER LITER)
Regeneration of Amberlite
IRC-50 with Sulfuric Acid
acid cation exchange resins are readily explained on an acid strength basis. Since the carboxylic group of Ainberlite IRC-50 forms a weak acid, the hydrogen ion has a strong affinity for tho oxygen of this group and is very difficult t o replace. On the other hand, since most other ions form strong electrolytes with the carboxyl group, the hydrogen ion is able t o replace these cations very readily. The differences observed in the sodium-calcium and sodiummagnesium exchange equilibria for the carboxylic and sulfonic acid exchangerq are similar to the behavior of soluble sulfonic and carboxylic acid electrolytes. The polybasic carboxylic acids exhibit a sequestering ability for the dibasic alkaline earth cations whereas the corresponding salts of sulfonic acids are true strong electrolytes. apparently this property of the carboxyl group carries over to the resinous carboxyl cation exchangers and may account for the unusual ability of Amberlite IRC-50 t o adsorb calcium ions in preference to the sodium ion. A41though this property of the carboxyl exchanger, Amberlite IRC-50, enables the resin to soften water efficiently in the presence of a large excess of sodium salt, the equilibrium is such t h a t regeneration with brine 1s highly inefficient. -4lthough the rate data were rather meager, the fact t h a t in the hydrogen cycle the rate decreased as the acidity of the functional group decreased and the fact that in the sodium cycle the rates of both the carboxylic and sulfonic type resins are comparable are highly significant. These results indicate that the rate of exchange is dependent upon the degree of dissociation of the cation exchange micelle Since a swelling of the resin gel structure accompanies the transition of the weak electrolyte form of the resin to the strong electrolyte form, the increased rate of cxchange may be attributed t o a n increased rate of diffusion. The column performance of Amberlite IRC-50 in both the
Vol. 41, No. 6
sodium and hydrogen cycles is consistent, with the equilibrium and rate data. I n the sodium cycle, the resin is capable of adsorbing most cations which in turn may readily be eluted with a minimum of acid. I n the hydrogen cycle, the resin is capable only of adsorbing cations present as hydroxides, carbonates, bicarbonates, or as salts (borates and silicates) whose corresponding acids are not sufficiently acid t o cause the p H to drop below p H 4 to 5 during the exhaustion. As the p H drops below 4.0, the competitive activity of the hydrogen ions is such that only hydrogen ions are adsorbed. The chief advantages of a carboxylic cation exchanger over a sulfonic acid exchanger depend upon the application. For the removal and recovery of cations of alkalies, carbonates, bicarbonates, silicates, borat'es, etc., the carboxylic exchanger will function as well as a sulfonic acid exchanger and may be fully regenerated much more efficiently with acid than the strongly acidic sulfonic acid exchangers. The carboxylic cation exchanger permits one to remove the undesirable calcium bicarbonat,e in waters without the formation of mineral acids from the sulfate and chloride salts. This application is of considerable interest t,o the beverage industry. The carboxylic exchanger may also be used for deionization purposes in conjunction with other exchangers. If a dilute solution is passed through a strong base anion exchanger in the hydroxyl form ( 3 ) , the salts will be converted t o their corresponding hydroxides which may then be removed by the carboxylic exchanger. For the conventional scheme of deionization, the use of the carboxylic exchanger before the sulfonic acid exchanger enables one to deionize m t e r s cont'aining bicarbonates more economically since carboxylic exchangers may be more efficiently regenerated with sulfuric acid and will not be hindered by the calcium sulfate precipitation t h a t markedly reduces t,he capacit.y of sulfonic acid exchangers. I n essence, the carboxylic cation exchanger serves as a solid buffer for exchange reactions in a manner analogous t o soluble weak acids and their salts in homogeneous solution reactions. LITERATURE CITED
(1) Davidson, G. F.,and Nevell, T. P., J . TestiZeInst., 39, T 5 9 (1948). Griessbach, R., Beiheft Z . V e l . deut. Chem. 31, Angew. Chem.,
(2)
52, 215-19 (1939). ( 3 ) Kunin, It., and McGarvey, F. X., IKD.ENG.CHEX.,41, 1265 (1949). (4) Kunin, R.,and Meyers, R. J., J . Am. Chem. Soc.. 69, 2874 (1947). ( 5 ) Mattson, S., Ann. AQT.Coll. Sweden, 10, 56 (1942). (6) Myers, R. J., Advances in CoZZoidSci., 1, 317-51 (1942). (7) Wieland, T., Be?., 77, 539 (1944). (8) TViklander, L., Ann. Rog. Aor. Coll. Sweden, 14, 1 (1946). (9) Winters, J. C., and Kunin, R., IND. ESG.CHEX, 41,460 (1949).
RECEIVED September 10, 1948. Presented before the Division of Industrial and Engineering Chemietry at the 114th hIeeting of the AYERICANCHEYIC A L Socmry, JVashington, D. C.
Volumetric Behavior of Benzene J. W. GLANVILLE .AND B. H. SAGE California Institute of Technology, Pasadena, Calif'. T h e specific volume of benzene was determined at seven temperatures lying between 100' and 460' F. and for pressures between vapor pressure and 10,000 pounds per square inch. The results are presented in tabular form.
T""
,vapor pressure, critical constants, and volume of benzenc as saturated liquid and saturat>edgas were determined by Young (9). This work was supplemented by later investigations o f the vapor pressure at relatively low temperatures ( 7 , 8).
The influence of pressure and temperature upon the volume and refractive indcx of this compound was studied by Gibson and Kincaid ( 3 ) . Limited inforination concerning the heat capacity mas obtained by Burlew (2). Gillilarid and Lukes ( 4 ) measured directly the effect of pressure upon the enthalpy of benzene. These investigations serve to establish the volumetric behavior a t low pressures. It would be possible t o calculate the specific volume at higher pressures from the enthalpy-pressure measurements of Gillilund and Lukes if volumetric data were available
