Sorption of Phenols by Anion Exchange Resins M. G. CHASANOV', R. ICUNIN, AND F. MCGARVEY Rohm & Haas Co., Philadelphia, Pa. ARIOUS adsorbents have been studied in the past in connection with phenolic waste treatment. Amiot ( 1 ) and Chaplin (6) examined activated carbon for this purpose. Kunin and McGarvey (9) reported that phenol could be removed from solution by means of a strong base anion exchange resin. This process was considered to be one of typical ion interchange. Anders ( 8 ) showed that a weakly basic anion exchanger, Wofatit M, could also remove phenol from aqueous solution. The exchange beds could be regenerated using butyl acetate and methanol. Anderson and Hansen (3) have recently completed a survey of phenol adsorption on strongly basic resins. Their work was confined t o 0.1N phenol solutions and elution with methanol. With these previous studies in mind, i t was decided to evaluate the removal of phenols from synthetic solutions and from typical industrial wastes by means of some of the newer commercially available resins.
volume of effluent through the resin a t the point of the first detection of phenol by the Gibbs method (8) which Gibbs reported had a sensitivity of a t least one part in 20,000,000. The phenolic concentration in the effluent (at breakthrough) increased sharply t o above the allowable limits for stream pollution. The effect of flow rate, phenol concentration, total ionic strength, and p H on capacity and leakage were investigated. Methods for regeneration of phenol exhausted resin beds were also considered. STRONG BASE ANION EXCHANGE RESINS-CHLORIDE FORM
The results obtained from the percolation of a 300 p.p.m. aqueous phenol solution (pH 5.9) through beds of the various strong base anion exchange resins are summarized in Table I.
Table I. Phenol Removal from Aqueous Solution by Chloride Form Quaternary Anion Exchange Resins Influent: 300 p p.m. phenol (pH 5 9) at a gal /min./cu f t rate Breakthrough Point Capacity, Resin Vol./Vbl. Lb. Phenol/Cu. Bt. IR.4-BOO 7 0 13 IRA-401 6 0 11 IRA-410 4 0 08 IRA-411 8 0 15
PHENOL REMOVAL PROCEDURES
The removal of phenolic materials by ion exchange resins may be ascribed to two processes. I n the case of strong base anion exchange resins in the hydroxyl form, the phenols are removed primarily by exchanging for hydroxyl ions. For weak base anion exchangers in the free amine forms and strong base anion exchange resins in the salt forms, the pickup of phenolics is a chemisorption. For this study Amberlites IRA-400, IRA-410 and their more porous analogs, IRA-401 and IRA-411, respectively, were employed as the strong base anion exchange resins; Amberlite IR-4B and a series of experimental resins A, B, C, and D were selected as the weak base anion exchange resins. Amberlite IR-4B, resin A, and resin B contained both primary and secondary amine groups, while resins C and D had tertiary amine structures. The weak base anion exchange resins were employed in their free amine forms, and the strong base resins were used in both the hydroxyl and chloride forms. Samples of resin were placed in glass columns with 1-inch inside diameters t o the depth of 24 inches. These columna contained fritted glass plates on which the resins were supported. Various phenolic materials in aqueous solution were percolated through these beds. T h e phenolics were standardized by the bromide-bromate method (IO). The effluent was analyzed for phenol linkage by means of the Gibbs reagent (8). Whenever the chloride form of the resin was employed the effluent was also analyzed for the amount of chloride present. I n the case of the actual industrial waste liquors, the phenolic concentration was determined by the 4-aminoantipyrene method (6) and the results were reported as p.p.m. dichlorophenol (DCP). The ionized solids content of the wastes was determined by percolation of the waste liquor through the hydrogen form of Amberlite IR-120 and titration of the effluent with 0.1N caustic t o a phenolphthalein end point. Some of the waste liquors were highly colored and in order t o analyze for phenols fractions were distilled and the D C P content was measured with a n Evelyn Colorimeter using a 560 mp filter (Paminoantipyrene method). The primary objective of the present study was t o estimate the capacity of the resin for various phenols at low leakages; therefore, the break-through point for a resin was chosen as the 1
Amberlite IRA-41 1 exhibited the greatest capacity of the group of resins; however, the others did not differ markedly in this respect. Negligible amounts of chloride were present in the effluents, indicating t h a t no appreciable exchange took place. A solution of 570 sodium chloride was used as a regenerant without success. As was indicated by Anders (E?), organic solvents could be used, but this was not considered t o be a practical solution for a waste problem. However, further experimentation revealed that a solution of alkaline hypochlorite, followed by a brine wash restored the sorptive capacity for phenol. Due to the higher capacity of Amberlite IRA-411, it was decided to evaluate the other variables using this resin. Effect of Flow Rate on Phenol Capacity of Amberlite IRA-411 (Cl). Since the best column result8 are obtained a t near equilibrium conditions it was decided t o determine the form of the sorption isotherm and t o use that t o estimate the upper limits for phenol sorption obtainable for this system. The results obtained by equilibrating 10-gram samples of Amberlite IRA-411 ( C l ) with solutions of varying phenol concentrations are given in Table 11. The samples were allowed to shake for 24 hours followed by sampling and continued equilibration for another
Table 11. Equilibrium Sorption of Phenol on Amberlite IRA-411 (Cl) Concentration, hIgm. Phenol/Liter Original S o ht ion Final 118 55 236 79 142 460 212 704 1000 298 2000 432
Present address, Army Chemical Center, Aberdeen, Md.
305
M g . Phenol Adsorbed per
Grams Dry Resin 0.69 1.75 3.62 5.36 7.80
17.4
306
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 28
voi. 48, NO. 2
Effect of Various Phenols on Sorption by Amberlite IRA-41 1
(Cl). Since the sorptive capacity might not be independent of 24 I
_1
-
4. w
04
c-0 2 4
V
-I 0
X W
v)
-20
c _I a 0
5
0 2
-30
n L . L L
"2
-40
0
01
_I
0 08
-50
0 06 -60
004
-7 0 0 02 0
4
2
6 pH
Figure 2.
OF
8
10
12
14 -8
SOLUTION
Phenol breakthrough capacity of A m b e r l i t e IRA-411 (chloride) as function of pH
resonance with the resin matrix and the substituents on the nitrogen which would result, in little hydrogen bonding of molecular phenol and certainly none for t,he phenolate ion. Further, the work of Herbert Brown (4)indicates that for amines of comparable base strengths the less hindered amines react faster and involve lower activation energies. Since the sorption mechanism is a function of the basicity of molecular phenol and the amine it, is not surprising that the PI-I should affect the binding of phenol on the amine ion exchange resins. In the acid region, the amount of ionized phenolate ion present is very limited since the dissociat>ionconstant for phenol is only 10-10; for alkaline pH values, the phenol exists in the diwociated state as the phenolate ion; a t intermediate and neutral p H values, molecular phenol and phenolate ion exist in varying ratio depending on the dissociation constant
Furthermore, consider the expression for the amine
r
R
R g
i
H
.
Figure 3.
Correlation of phenol capacity with phenolate-phenol ratio
not available in the salt form. For high p l I regions the phenolate ion is present in large quantities arid t,he amine phenol capacity lvould be increased. The mechanism for sorption on the quaternary ammonium ion exchange resins when in the chloride form is not easily demonstrated by the hydrogen bonding theory. I n the first place, the sorption is a function, a t least to some degree, of the type of quaternary exchanger used and t o the porosity of the exchanger. Amberlite I R A 4 1 0 and Arnberlite IRA4-411 are similar with respect t o the nature of the quaternary ainine group; however, Amberlite IRA-41 1 is more porous than Amberlite IRA-410 and has about twice the capacity a t breakthrough. This is not a function of diffusion rate since the rate of exchange for these resins is considerably greater than the flow rate used for exhaustion. No similar result was observed with Amberlite IRA-400 and Amberlite I R A 4 0 1 which exhibited similar capacities. Those exchangers have a higher degree of basicity than have Amberlite IRA-410 and Amberlite IRA-411. It is possible that basicity may have a considerable effect on t,his sorption although steric effects must not be overlooked especially since porosity would affect the freedom of t'he exchange t o orient itself for a chemical reaction. The effect of p H values on the sorption with quaternary arnmoniuin anion exchange resins is quite complex. The primary reaction is related to the amount of phenolate ion in the solution. The data have been plotted in Figure 2. If it is assumed that ihe process is largely
(Ra)NfC1-
R~--~-H1
LOGIOPHENOL C A P A C I T Y , (LBS/FT.3 )
J
Thus the free base form ratio decreases immensely with the hydrogen ion concentration. Since a t low p H virtually no phenolate ion is present and only molecular phenol is present a marked decrease in phenol capacity should be expected because the electrons available for bonding in the free amine form are
+ GO-
c1-
- IT+ -+ (R3K)+O-+
the amount of phenolate present, liecomes
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1956
Table X. Stability of Quaternary Anion Exchange Resins in Static Treatment with Alkaline Hypochlorite
-
Resin IRA-400 IRA-401 IRA-410 IRA-411
Table XI.
Capacity, Me./Gram Original total Total Quaternary 2.70 3.72 3.89 2.75 3.60 3.48 1.84 3.52 3.04 0.86 2.91 1.06
Capacity Remaining YoOriginal Total Quaternary 96 70 97 76 87 53 67 30
Stability Tests on Amberlite IRA-4111 C1 for Hypochlorite Rejuvenation
Strength NaOCl Cycle No.
0.1
Original Phenol Capacity Retained, % 0.2 0.4 1.0 1.6 2.25 110 100 IJU
Residual quaternary capacity, me./ gram
1.92
120 120
0.31
125 120 48 31 0.20
110
70 34 28
0.17
A log log plot of the relationship between (@O-)/(@OH)and +OH capacity of IRA-411-C1 is shown in Figure 3. The data empirically approximates a straight line which has the form: ,@-/+OH = cap”. The slope n, is found t o be 4.4and since the affinity of the phenolate ion is very great a t high p H values, it is probable that actual anion interchange occurs a t p H values of 12 and greater. This is certainly true for the hydroxyl cycle. Figure 3 indicates that when the phenolate ratio increases, the phenol capacity also increases. Industrial Applications. The use of anion exchange resins, particularly the quaternary ammonium types, appears practical for phenol removal on an industrial scale. The process could be relatively simple and could be carried out in readily available equipment. Perhaps the chief advantage of ion exchange over other methods is in the size of equipment necessary for large volumes of wastes containing low concentration of phenol. Extraction, chlorination, and other methods are a t a disadvantage due t o the retention times needed t o complete the reaction. Extraction and ion exchange have the common problem of not destroying the phenolics but only removing them from the stream. Similarly the regenerant from the exchanger and the spent extractant must be treated t o remove the phenol either by oxidation or by some other procedure. I n either case phenol recovery could also be attempted. Before any definite conclusion can be reached as t o the economic feasibility of the ion exchange process, it is necessary t o evaluate the stability of the resin for the hypochlorite treatment. This was done experimentally by contacting the exchanger for prolonged periods in the presence of varying amounts of alkali hypochlorite. A 2.25% solution of sodium chloride in 1% sodium hydroxide was employed. I n a static test, samples of the resins were placed in this solution for 6 months and the resins evaluated t o determine changes in quaternary capacity. These results are tabulated in Table X. No change in particle appearance was observed and no breakdown in particle size was observed. Since hypochlorites degrade the quaternary amines by an oxidative step resulting in relatively small changes in the total capacity but marked reduction in strong base capacity, one might expect temporarily increased capacity for phenol after treatment with hypochlorite followed by a gradual decrease as the amine groups were completely destroyed. A series of runs was undertaken t o determine the life expectancy and also t o find if hypochlorite concentration had a marked influence on rapacity. Studies were carried out with Amberlite IRA-411 (Cl), the most unstable resin in the series. The resin was saturated with 300 p.p.m. phenol, regenerated with hypochlorite in 1% caustic, rinsed with salt, and exhausted with phenol again. These results are summarized in Table XI.
309
These results show that dilute hypochlorite solutions are effective only after long periods of contact with the resin; which would be prohibitive from a practical standpoint. I n the cases of the higher regeneration levels a t 3 t o 4 hours contact time, the rise in capacity predicted does occur, followed by a gradual decrease. The results indicate that after 25 cycles, resin rejuvenated with 0.5 t o 1.5% NaOCl are still usable and have greater capacities than initially. It is doubtful that the chloride form of the quaternary anion exchanger is suitable for industrial operation since a hypochlorite treatment would be required at each cycle. At a 0.4% strength, a life of 60 t o 80 cycles (by extrapolation) is predicted. The cost of regenerating one cubic foot is estimated at 50 cents per cubic foot. Since the resins cost about $50 t o $60 per cubic foot, a fixed cost must be added which makes the process very uneconomical. The utilization of hydroxyl form of the resin, however, appears more promising since increased capacity is found and the hypochlorite treatment is needed only once in five cycles. An estimate of the cost for an ion exchange phenol process t o treat a 10,000-gallon-per-day waste of the composition shown as type C can be made from the information a t hand. If daily regeneration is required, a unit must remove Lb. +OH = 10,000 X 8.33
(g)
= 2.58 lb./day
The capacity for phenol at such a concentration on Amberlite IRL4-411has been found t o be 0.012 lb. +OH/cu. ft. 2.58 Volume resin required = -- = 215 cu. ft. 0.012 Since the flow rate through this bed would be 10,000215 = 0.032 gal./cu. ft./min. F = 24 10,000 6o 215 - 1440 the capacity would be higher than the one used by about 150%. The cost breakdown predicted would be Cost regenerant: 5 X 215 lb. NaOH a t $0.03/lb. = 1075 X 0.03 = $32.30/day Assume $0.50/cu. ft./cycle for NaC10 = 0.50 X 215 (1/5) = $21.50,fday Resin loss: 215 X $60.00 ( l / m X = $12,000 (l/aoo) = $43.05 X 100 = -21500 $5.90 Unit depreciation = 215 = 365 X 10 3650 Total $102.75/day
The cost is quite dependent on the phenol to mineral acidity ratio, so t h a t the same cost would result if ten times the phenol were t o be removed. By careful operation with a recirculation of the effluent t o increase the p H of the influent, it is probable that the cost could be reduced by as much as 50%. Although the cost is about 50 t o 100 times higher than normally reported for bacteriological treatment, the resin operation requires about 1/50 t o 1/100 of the space required for bacteriological filters and is particularly effective in removing traces of phenol. LITERATURE CITED (1) (2) (3)
Amiot, R., Compt. rend. 197, 325 (1933). Anders, H., Gas-u.-Wasserfuch 92, No. 17, ( G a s ) 238 (1951). Anderson, R. E., and Hansen, R. D., IND. ENG.CHCM.4 7 , 71 (1955).
(4) Brown, H., presented at Conference on lMechanisms of Organic Reactions at Northwestern University, August 1950. (5) Chaplin, R., J . Phys. Chem. 36, 909 (1932). (6) Emerson, E. I., J . Org. C h m . 8, 417 (1943). (7) Freymann, R., Ann. chim. 1 1 , 11-72 (1939). (8) Gibbs, €I., J. Biol. C h m . 72, 649 (1927). (9) Kunin, R., and McGarvey, F. X., IND. ENQ. CHEW41, 1265 (1949). (10)
Scott, W., “Standard Methods of Analyses,” 4th ed., vol. 11, p. 2253, Van Nostrand, New York, 1944.
RECEIVED for review J u l y
8, 1954.
ACCEPTED October 5 , 1055
