A practical procedure was developed in the laboratory for DTPA recovery and concentration. The process may be best visualized by examination of Figure 9, which indicates a flowsheet and material balance based on an ion exchange (150 cubic feet of Dowex 50-X4, 50 to 75 mesh) crystallization recovery process. Contaminated DTPA is fed at low concentration to a n acid form cation exchange resin which: because of the amphoteric nature of the DTPA, sorbs DTPA as an amine salt. Elution with NHa solution a t a higher equivalent concentration results in a concentration of the DTPA and a simultaneous separation of metal contaminants. These contaminants appear a t the tail end of the DTPA wave as the pH rises with the appearance of the ammonium salts. T h e ion exchange product is a solution supersaturated with DTPA at room temperature which will crystallize with agitation to produce a very clean, easily filterable crystalline product. Typically about 90% of DTPA will crystallize from a 4% aqueous solution. T h e filtrate containing about 0.5% D T P A may be recycled to a subsequent resin loading cycle. T h e crystalline DTPA product may be redissolved in aqueous NHP for reuse in the yttrium purification process.
Acknowledgment
T h e authors acknowledge the particular contributions of the following individuals in the analytical aspects of the project: T. M. Hess, J. F. Bartel, E. L. McLaughlin, P. P. North, and B. R. Loy. References (1) Harder, R., Chaberek, S., J. Inorf. €3 Nuclear Chem. 11,
197 (1959). (2) Russell, R. G., Pearce, D. LV.. J . Am. Chem. SOC.65, 595 (1 943). (3) Schwarzenbach, G., Gut, R., Anderegg, G., Helc. Chim. Acta 37, 937 (1954). (4) Spedding, F. H., Powell. J. E., LVheelwright, E. J., J . Am. Chem. SOC.76, 612 (1954). (5) Ibid..78. 34 11956). (6) Speddiig, F: H.,’ Voight, A. F., Gladrow, E. M., Sleight. N. R., Ibid., 69, 2777 (1947). (7) Tomkins, E. R.. Mayer, S. W., Ibid., 69, 2859(1947). ( 8 ) Wheelwright, E. J.. Spedding, F. H., Ibid., 75, 2529 (1953).
RECEIVED for review March 13, 1961 ACCEPTED September 1, 1961 Presented in part, Division of Inorganic Chemistry, 133rd Meeting ACS, San Francisco, Calif., April 1958.
REVERSIBLE SORBENTS FOR ORGANIC ACIDS AND AMINES R O G E R N . S A R G E N T A N D DONA L. G R A H A M
The Dow Chemical Go., Midland, Adich.
Resins of low ion exchange capacity are shown to be excellent and reversible sorbents for organic acids and amines. The low capacity cation exchange resins are used for the sorption of organic acids and are regenerated with caustic, whereas the corresponding anion exchangers are used for the sorption of amines and are regenerated with acid. Since these resinous sorbents contain fixed ionic groups which exhibit the Donnan exclusion forces of repulsion, they are quantitatively and more rapidly regenerated than i s charcoal, thus providing a good method for the con-
centration and recovery of the solute from dilute aqueous solutions.
As with charcoal, the presence of ionic solutes
in the feed solution generally enhances the sorptive power of the resins so that a larger capacity can be realized. Other comparisons with charcoal have been made to enable the reader to choose the proper sorbent for his particular problem.
, for the removal of CHARCOtL organic solutes from aqueous solution, is usually very AN
EXCELLEST
SORBENT
difficult to regenerate (reactivate) for reuse. In the case of organic acid or amine sorption, regeneration is greatly facilitated by the conversion of the sorbed acid or amine to an ionic species which has a lower affinity for the charcoal phase. Regeneration is still far from complete for phenolics, the higher 56
l & E C PROCESS D E S I G N A N D D E V E L O P M E N T
carboxylic acids, and the higher amines because of the van der Waals forces of attraction between the organic ion and the charcoal. Incomplete regeneration reduces the sorption capacity of the charcoal and causes leakage of the solute during the next sorption cycle. Strongly basic anion exchange resins have been shown to be good sorbents for phenol ( 2 , 3 ) . Methods for the regeneration of these resins have been proposed (2-5), but they suffer from being slow, incomplete, and/or costly. Samuelson (7) found that molecular sorption of carboxylic acids on cation exchange resins increased with decreasing capacity, and Rieman (6) has used both cation and anion exchangers of low ion exchange capacity for the sorption of phenol. His study was limited to sorption only on resins cross linked with 8% divinylbenzene (DVB). T h e study presented herein was initiated to determine the optimum properties of a resin for the sorption of phenol. Emphasis was necessarily placed upon the ease with which the resin could be regenerated with caustic. T h e scope of the problem was later broadened to include carboxylic and amino acids when very favorable results were obtained for the phenol work. An investigation was also made tu determine to what extent amines could be sorbed on low-capacity anion exchange resins for removal and recovery problems. Analogously, these resins could be regenerated by the conversion of the sorbed amine to its hydrochloride by treatment with dilute HC1. Finally, a n investigation was conducted to determine the degree of sorption of both the organic acids and amines an charcoal. Information concerning the reversibility of the sorption was obtained for comparison with the low-capacity resin sorbents.
Table 1.
Capacity (H+), D V B , Meq./Dry W'ater Content, % 7c Gram (H') (Na+) 2 5.29 88.0 73.1 2 2.73 68.0 60.5 2 2.17 62.0 57.9 2 1.58 48.2 46.8 1 .Ob 40.9 38.5 2 Nonporous copolymer, 0 . 0 % H20 Porous copolymer, 8 0 . 0 % HzO 1 1.62 61 . I 57.5 4 1.66 42.0 37.7 8 1.68 34.2 30.0 1.37 2 47.7 47 2 1.37 . .7 2 1.37 47.7 2 1.37 47.7 1.37 47.7 2 2 1.37 47.7 2 1.37 47.7 2 1.37 47.7 2 1.37 47.7 2 1.37 47.7 2 1.37 59.3d 2 1.37 47.78
Run AVOvo.
A
B C D E F G H I J K
~~
hi N 0 P
Q
R S T U V
Batch-Equilibrium Sorption Experiments
Ionic Form of Resin Na + Na Na Na + Na + None None Na + Na + Na + H+
Acid Sorbed Phenol Phenol Phenol Phenol Phenol Phenol Phenol Phenol Phenol Phenol Propionic Valeric Caprylic Malonic Succinic Adipic Benzoic Phenol Propionicb Phenylalaninec Caprylicd Caprylic'
Soh. concn."
0,0936 0.0406 0.0419 0.0314 0,0427 0.100 0.0914 0.0360 0.0416 0.0402 0.445 0.330 0.0505 0.469 0.494 0.439 0,244 0.312 0.0704 0.0215 0.0125 0.0289
+
H+ H+ H+ H+ H+ H+ HT H+ NHI' H+ H+ H+
+
A t Equilibrium Resin conma 0,0955 0.985 1.24 2.04 2.42 0.00 1.52 1.52 2.46 3.06 1.465 5.94 18.1 0.418 0,573 1.01 9.23 7 . . 77 .. 9.64 18.6 15.6 4.74 ~
Kd 1.02 24.2 29.6 65.0 56.7 0.00 167 42.3 59.2 76.1 3.29 18.0 357.0 0.89 1. I 6 2.34 37.8 24.9 137.0 863.0 254 0 164.0
a M g . phenol per gram water in solution or resin phase. Sorbed from saturated solution of (NH4),S04(in this run resin was partially in .VH4 A form). Abnormally high Kd due to protonation (ion exchange) with resin. Wt. methanol in resin phase (sorbed from 1007, methanol). e Wt. 70methanol (sorbed from 707, methanol).
e
Of ever increasing importance to economical chemical processing is the recovery of valuable solutes from dilute industrial process or waste streams. From a pollution standpoint, the chemical industry has also had to expend a relatively larger effort in recent years in the reduction of obnoxious wastes. T h e repetitive cyclic sorption methods illustrated herein should be quite useful for removal and recovery problems concerning organic acids and amines.
Experimental Resins. Resins of low cation exchange capacity were prepared by the sulfonation of styrene-DVB copolymers of spherical form, 30 to 50 mesh, 1 to 8% DVB. The sulfonation was carefully controlled to introduce the functional groups uniformly throughout the bead. The cross linkage, exchange capacity, and water content of the resins are listed in Table I. Type I anion exchange resins of low capacity were prepared by the amination (with trimethylamine) of specially chloro-
Table II.
h'o
.
-4 B C D E F G H I J K L M N a
Type and Cross Linkage 1-xl Couolvmer -X2 1- x 2 1- x 2 1- x 2 1- x 2 1- x 2 Dowex 1-X2 resin 1-X4 1-X8 2-x2 Dowex 2-X8 resin 3-X2 Dowex 3-X4 resin I
,
methylated copolymer beads, 50 to 100 mesh. T h e chloromethylation was controlled to ensure that the functional groups were evenly distributed throughout the resin matrix. Similarly prepared were the strongly basic Type I1 (aminated with dimethylethanolamine) and the weakly basic polyaminetype resins. Properties of the finished resins are listed in Table 11. Procedures. Both batch equilibrium and dynamic columnar sorption data were obtained. In the batch equilibration studies, a weighed (5- to 9-gram) sample of wet-centrifuged resin was shaken with a known volume (50 to 100 ml.) of a solution of the organic acid or amine to be sorbed. After 10, 45, and 100 minutes of shaking, 2-ml. aliquots of the solution phase were withdrawn for analysis. Phenolics, aniline, and benzylamine were determined by standard bromination titration, oxidation with dichromate ( 8 ) , or ultraviolet absorption methods, depending upon the concentration. Other organic acids and amines were determined
Batch-Equilibrium Sorption Experiments with Aniline
Capacity, .tfeq. /Dry Gram (GI-) 0.76 0.00 0.24 0.92 1.23 1.61 2.59 4.28 1.45 0.94 1.43 3.59 4.67 5.50
Water Content, % (Cl-) 36.5 0.00
21.430.2 37.6 47.3 59.7 75.0 31.5 19.6 39.0 36.5 20.0 36.8
WetCentrvuged Resin Used, Grams 7.5363 7 . 6898 ... 8.1240 7.2209 7.9787 8.1351 8,6264 8.3553 7,4246 8.0679 7.1463 8.1156 6.8732 7.4857
Soh. Concn., 70 0.0135
n- , n_ _9_ ~_ 5
0.0927a 0.0153 0.0289 0.0262 0.0289 0,0566 0,0148 0.011oa 0.0244 0.0314 0.0383a 0.0276
Kd
116.0
>
' 4.07 126 89.8 37.7 23.8 6.43 122 >256.0 55.5 36.9 >58.5 47.8
IVot at equilibrium at 700 minutes.
VOL. 1
NO. 1
JANUARY
1962
57
by acid-base titration. coefficient, K d ,where K,j =
Equilibrium values of the distribution
solute concentration in water inside resin phase solute concentration in interstitial solution at equilibrium
were calculated (Tables I and 11) from the knowledge of the initial concentration and volume of the solution phase, the water content of the resin, and the final (equilibrium) concentration of the solution phase. Column sorption data were also obtained by the passage of a solution of the organic acid or amine downflow through beds of the resin a t a specified linear flow rate (expressed in gallons per minute per square foot of bed area). Usually, a t or just before the breakthrough point of the solute, the bed was regenerated with caustic (for removal of sorbed acids) or acid (for removal of amines): followed by water to rinse the ionized solute from the interstitial solution of the bed. T h e quantity of caustic or acid required for regeneration was equal to a slight excess over the quantity of solute sorbed, plus the quantity of resin in the hydrogen or hydroxide form, if any. Following the water rinse the bed was used for the next sorption and regeneration cycle. Breakthrough and regeneration curves were obtained by the collection and analysis of small fractions of effluent from the column. T o determine the effects of the counter anion which occupies the exchange site on the rrsin, and the effect of concentration of the feed solution, benzylamine breakthrough curves were determined on the resin bed used above. The conditions used and the results of these runs are given in Table 111. Following each sorption run, the bed was regenerated with excess mineral acid and rinsed with water.
Results and Discussion
Phenol Sorption. Figure 1 shows the breakthrough curves for a 100-p.p.m. solution of phenol on the star,dard ion exchange resins and their low-capacity analogs. The strongly basic anion exchangers sorb more phenol than the strongly acidic resins of low ion exchange capacity but are considerably more difficult to regenerate because of the exchange reaction that occurs when phenol is converted to the strongly held phenate ion. For this reason, sorption of phenolics and car-
I c
I
----
i
I
/
00;
/--/
-I
,’It+
z W
n 1
0
10
20
30
40
B E D VOLUMES OF E F F L U E N T
Figure 1. Phenol breakthrough curves obtained with 25-cc. beds (38.2 cm. X 0.654 sq. cm.) at 0.5 gallon per minute per square foot and aqueous 100-p.p.m. phenol feed LA. I-B.
Il-A. ILB.
58
Dowex 50W-X8, 5.2 meq. p e r d r y gram, 53% HzO, H + form Low-capacity sulfonic acid resin, 1.23 meq. p e r d r y gram, 43.8% HzO, H form Dowex 1-X8, 3.5 meq. per d r y gram, 42.4% HzO, CI- form Low-capacity type I quaternary amine resin, 1.61 meq. p e r d r y gram, 47.3% HzO, CI-form
l&EC PROCESS DESIGN AND DEVELOPMENT
Table 111. Breakthrough Curves for Benzylamine Ionic Feed BreakBenzylamine Sorbed: Concn., through Form of No. Resin % Point, T’B ‘tlg. 1 c10.01 15.9 38.8 2 c10.1 6.8 160.0 1 0 3 0 650 0 3 c10 1 7 9 188 0 4 37035 so4-* 0 1 3 9 87 5
boxylic acids was conducted only on the sulfonated cation exchange resins. The speed of phenol sorption in Runs A through J of Table I was determined by removing and analyzing small aliquots of the solution phase at various times during the batch equilibrations. As expected, the sorption rate was related to the porosity (water content) which, in turn, is a function of the cross linkage and capacity of the resin. For example, the very porous resin used in R u n H attained equilibrium in less than 20 minutes; whereas the highly cross-linked resin, R u n J, and a resin of very low capacity, R u n E, required more than 100 minutes to reach equilibrium with the solution phase. Rapid sorption kinetics and good handling characteristics were exhibited by the 2y0 DVB resins, which were found to have a phenol sorption maximum between the exchange capacity of 1.3 and 1.5 meq. per dry gram. A resin having the optimum cross linkage (2y0DVB) and capacity (1.37 meq. per dry gram) was then prepared and used for Runs J through U in which other organic acids were sorbed. I t was necessary to use the hydrogen form of the resin (HR) for the sorption of aliphatic carboxylic acids (H,4) to prevent exchange : NaR HA = H R NaT A -
+
+
+
This exchange did not occur with phenol because its ionization constant is 10-’0. T h e use of the hydrogen form facilitates molecular sorption of the relatively stronger acids such as the aliphatic carboxylic acids (pK = 3 to 5) by virtue of the common ion effect which lowers the degree of ionization of the acid in the resin phase. Table I also shows the beneficial effect (upon the sorption of propionic acid, R u n S) exerted by the presence of a salt such as (SHJzS04 in the solution from which the acid is to be sorbed. Since the salt is partially excluded from the resin phase, the sorption of propionic acid is enhanced when the ionic strength of the solution phase is increased. The propionic acid is therefore salted out ( 8 ) of the solution phase. Organophilic acids, such as caprylic acid, can be sorbed from hydrophilic nonaqueous solvents such as methanol (Runs U and V). When water is absent, however, the rate of sorption is slow even though the resin is more highly swollen by methanol than by water. This is probably due to the time necessary to desorb several molecules of methanol to accommodate one molecule of caprylic acid. The function of the ion exchange groups on the resin is twofold : First, solvation of the groups causes the resin to swell and make the sites on the resin matrix available for sorption. A large number of these groups decreases sorption. Sorption on the unswollen copolymer (Run F) is negligible because the effective surface area available is very small in comparison with a porous copolymer (Run G) which has the maximum number of sorption sites available. Like charcoal, the porous copolymer will sorb a larger quantity of the solute than the ion exchange resins that could be prepared therefrom, but quantitative regeneration is difficult in most cases.
0
5
3.2
-
2.0
-
2.4
-
2.0
-
1.6
-
1.2
-
0.8
/ @
/
0.4 ALANINE
CAPRYLIC
0.3
PROPIONIC IN SAT'D. ( N H 4)2S04
/
B
rr
BENZOIC
-1
2
w n
t / a,'
P R O PIONIc
0.2
0.1
- 0.4 0
- 0.0 0
2
4
6
8
IO
12
14
BED V O L U M E S O F E F F L U E N T
16
Figure 3. Sorption and elution of phenol on a 25-cc. bed (38.2 cm. X 0.654 sq. cm.) of low-capacity resin, 1.23 meq. per dry gram, N a + form
NUMBER OF C A R B O N ATOMS
Figure 2. Within a given homologous series, distribution coefficient increases logarithmically with number of carbon atoms in acid molecule
Cycle: 21.6 VB 100-p.p.m. phenol feed, followed by 2.0 ml. o f 1.ON N a O H and a water rinse, a11 a t 0.5 gallon per minute per square foot
Data taken from Runs K-T, Table I
Second, the presence of these ion exchange groups facilitates quantitative regeneration (removal of the sorbed organic acid as its salt), since the ions are excluded from the resin phase by virtue of the Donnan exclusion principle. Thus, the anions of most organic acids cannot be sorbed to any appreciable extent, and most organic solutes such as propyl and higher alcohols, ethers, and the like, which do not form anions, cannot be readily removed from the resin phase. Figure 2 shows a logarithmic increase in the distribution coefficient with the number of carbon atoms in the chain for the homologous series of mono- and dicarboxylic acids. Evidently, the relatively poor sorption exhibited by the dicarboxylic acids is due to the lack of a dangling hydrocarbon tail through Lvhich sorption can take place. Figure 3 illustrates a sorption and regeneration cycle that could be used for the removal, concentration, and/or recovery of phenol from a 100-p.p.m. aqueous solution. T h e bed was a resin in the sodium form. At the flow rate used, 17.0 bed volumes (V,) of phenol-free effluent were collected up to the breakthrough point. At 21.6 V,, the feed was discontinued and N a O H passed through the bed, followed immediately by water. The quantity of caustic used was slightly in excess of the amount necessary to convert the sorbed phenol to its sodium salt. Table I\' shows the results of this and similar runs for aqueous phenol feeds of various concentrations. M'hen the hydrogen form of the resin was used, an additional 13.4 meq. of caustic were required to convert the resin to the sodium form before regeneration was possible. Higher loadings, lower caustic requirements, no heating effects (of neutralization), and higher concentration factors can be obtained by sorption on the sodium form. Concentration factors (on a molar basis) : .%veragephenate concentration in entire regeneration effluent Feed concentration
of about 40 and 14 have been obtained with feeds of 100 and 4000 p.p.m., respectively. Therefore, if the regeneration effluent from a bed loaded with a 100-p.p.m. phenol feed is
0.05
c
I
0.02 0.01
1;
(SALT)
L II
II
Table IV.
Feed Concn., P.P.M. Phenol 100 4000 100 1200 8590
Phenol Sorption Data Caustic
Ionic Form,of Reszn
Na + Na +
H+ H+ H+
VOL.
Breakthrough Point, VB 17.0 6.1 11.5 7.2 3.3
1
NO.
1
Phenol Sorbed, Meq. 0.53 6.4 0.4 2.8 11.2
JANUARY
Reqd. f o r Regen., Meq. 0.53 6.4 13 8 16.2 24.6
1962
59
I20 O-CHLOROPHENOL
100
a
\
a
80
CHLOROPHENOL
P-CHLORO/ PHENOL
2-
$
60
PHENOL
W
/
I:
40 20
A
0
20
0
80
60
40
100
I20
BED V O L U M E S OF E F F L U E N T
Figure 5. Breakthrough and regeneration curves for 100p.p.m. solutions of phenolic compounds in 3270 HCI using 10.0-cc. beds (43.5 cm. X 0.230 sq. cm.) of resin, 1.37 meq. per dry gram, 30 to 50 mesh, H + form Beds were regenerated with caustic a t points shown b y dashed lines. Flow rate was 0.5 gallon per minute per square foot
2 1.0 z 0
s
0.8
0
0.6 PHENYLALANINE (SATD. N a p S O 4 )
LL
0.4
z
z0
0.2
m
LL
0.0
4
0
I2
8
16
20
24
28
32
36
40
44
BED VOLUMES OF E F F L U E N l
Figure 6. Breakthrough curves for phenylalanine sorbed from aqueous 0.05% solution and from 0.05% solution in saturated Na2S04 on N a + form and for aqueous 0.05% valeric acid on the H+ form 0.5 gallon per minute per square foot, 10-cc. beds (44.0 cm. sq. cm.), 1.37 meq. per dry gram, 30 to 50 mesh
X 0.227
yr; W z
V
I
I-W (6)
3 0
5
0
0
20
80 TIME, MIN.
40
60
Figure 7. Sorption of aniline on various anion exchange resins in CI- form
100
I
I
I
I
I
2
3
4
" I 5
D R Y WEIGHT C A P A C I T Y , MEQ. / G R A M
