INDUSTRIAL AND ENGINEERING CHEMISTRY
734
ACKNOWLEDGMENT
The authors wish t'o express their appreciation to H. W. Grote of the Universal Oil Products Co., McCook, Ill., for assistance in obtaining data.
(1) Adams, B. A,, a n d Holmes, E. L., J . SOC.Chem. Ind., 54, 1-6T
S.P a t e n t
development
(3) B a u m a n n , W. C., and Eichorn, J., J . Am. CIwm. SOC.,69, 2830-6 (1947). (4) International Critical Tables, Voi. VI, p. 152, Ke\\, York,
RIcGraw-Hill Book Co. (5) Jones and Bradshaw, J . Am. Chem. SOC.,55, 1800 (1933). (6) Kohlraush and Heydweiller, 2. p h y s i k . Chem.. 14, 317 (1894). (7) K u n i n , R., a n d IlcGarvey, F. X., IXD.ENG.CHEK, 41, 1265 (1949). (8) Ibid., 43, 734 (1981).
LITERATURE CITED
(1935). ( 2 ) Baumnnn, TT'. C., U .
Vol. 43, No. 3
2,466,675 (April 12, 1949).
'"
(') Smitl ''' Patent 23171340S(A'ug. 29, 1939). (10) Swain, R. C., Ibid., 2,285,750 (June 9, 1942).
RECEIVED March 23, 1950.
Monobed eionizatio Ion Exchange Resins ROBERT KUNlN
AND
FRANCIS X. MCGARVEY
ROHM & HAAS CO., PHILADELPHIA, PA.
w a t e r may be deionized with ion exchange resins by any one of three methods. The first, conventional deionization, requires conversion of the electrolytes into the corresponding acids by passage through a cation exchange resin bed and then adsorption of the acid by passage through an anion exchange resin bed. The second method, reverse deionization, requires conversion of the electrolytes into the corresponding bases by passage through an anion resin bed and then adsorption of the bases by passage through a cation exchange resin bed. The third method, monobed deionization, involves simply passage of the solution through a single bed containing an intimate mixture of the two resins. Because the monobed technique offers many advantages from an
economic and technical point of view over the other two techniques, a thorough investigation w7as conducted. It was found that several combinations of commercial ion exchange resins may be used to conduct the monobed deionization technique. The resin combinations are such t h a t they may be separated, regenerated, and remixed in a single column unit. Several combinations are able to produce w-ater having the quality of conductivity w-ater in but a single pass through a monobed. Other monobed combinations were investigated and their spheres of application indicated. This study is of significance in that i t has shown how many of the difficulties and objections to the conventional double-bed deionization techniques can be overcome.
T
volves the passage of the electrolyte solution through a column containing an intimate mixture of the anion exchanger in the hydroxyl form and t'he cation exchanger in the hydrogen form. For the majority of water supplies, the convent'ional method requires the cation exchanger to be of the strongly acid type-Le., sulfonic acid cation exchanger. The anion exchanger may he either a weak or a strong base. For the reverse deionization method, the anion exchanger must be a strong base; however, the cation exchanger may be either a strong or a weak acid. The completeness of deionization by either the conventional or the reverse procedure depends upon the total concentration of electrolyt,es in the water and upon the degree of regeneration of the leading exchanger column, inasmuch as the degree of conversion of the electrolytes into their corresponding acids or bases is dependent, upon these variables. I t is, therefore, obvious that in order to achieve a high degree of deionization a t economic regeneration levels, a multiple series of alt,ernating columns of anion and cation exchangers may he required. The number of columns in series Till depend, of course, upon the concentrat'ion of solution and the regeneration levels chosen. Because the installation of a series of exchanger columns requires a large capital investment and is difficult to operate, the achievement of complete deionization in a single column of rpsinous exchangers wvould be a considerable improvement. It is obvious that a column containing an intimate mixture of the regenerated anion and cation exchanger corresponds to a large
HE utilization of ion exchange resins for the removal of
electrolytes from aqueous media has been practiced extensively for more than a decade in both the laboratory and large scale industrial operations ( 6 , 7 ) . Although this operation has been conducted successfully, its scope has been limited in certain cases because of several factors: capital investment, concentration limitations, effluent quality limitations, intermittent operation difficulties, and intermediate pH changes during operation. These difficulties stem from two sources: chemical equilibria associated with the nature of the ionic groups of the exchanger, and physical nature of the resins. The nature of the equilibria of ion exchange reactions is such t h a t removal of ionic constituents from a solution may be accomplished by several methods (1-3, 8): conventional deionwation, reverse deionization, and monobed deionization. The conventional method involves the conversion of the salts of the water into their corresponding acids by passage through a column of a cation exchanger in the hydrogen form, preferably a strongly acidic one. The acids are then passed through a column of an anion exchanger in which they are adsorbed. The reverse deionization method depends upon the conversion of the electrolytes into their corresponding bases or hydroxides by passage through a column of a strongly basic anion exchanger in the hydroxyl form. The resulting solution IE then passed through the column of cation exchanger in the hydrogen form. The third method (8-11), monobed deionization, merely in-
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
March 1951 INFLUENT AND
AIR VENT
ION EXCHANGE RESINS INVESTIGATED
+--ACID A N D R I N S E WATER t l N F L U E N T AND ALKALI DISTRIBUTOR
~
'Q///
735
T h e i o n e x c h a n g e resins chosen for this study are reported in Table I. The systems studied included: strong acid and strong base, strong acid and weak base, weak acid and strong base, and weak acid and weak base. D I P P I N G CONDUCTIVITY CELL
MONOBED APPARATUS AND TECHNIQUE
+EFFLUENT
The apparatus utilized in this study is shown in Figure 1. The cation exchange resin was charged t o the unit up to the point of the lower (acid) distribution system. The required amount of anion exCOMPRESSEB changer was c h a r p d t o t h e -COMPRESSED AIR AIR 4 unit and placed above the -+ E F F L U E N T cat2ion exchanger. The watm Figure 1. Laboratory Monobed Experimental Apparatus level was then brought t o a point 1 inch above the resin bed. The resins were mixed bv charging compressed air ( 7 . 5 cubic feet per square foot pe*r number of alternating columns in series and can therefore achieve minute) into the bottom of the unit. After mixing, the resin bed a degree of deionization that would necessitate a series of many was rinsed under pressure so as t o displace the adsorbed air. alternating columns of either the conventional or reverse deThe course of a run was followed by conductivity and p H measurements using flowing cells. At the conclusion of an exhaustion ionization schemes. However, the utilization of such a procerun, the resin bed was backwashed until the bed had expanded dure would be impracticable unless the resinous mixture could be 100% and permitted to remain in "teeter" until the resin comseparated and regenerated in the same unit. In order to acponents had separated. At this point, the resins were regencrcomplish these requirements, a hydraulic separation of the resin ated. The alkali was introduced a t a rate of 1 gallon per cubic foot per minute and the waste regenerant was permitted t o flow components is essential. From simple physical considerations, over the cation exchanger. The bed was rinsed and then acid it is obvious t h a t t h e resin components must differ in specific gravity or in particle size. The former is preferred, because a large difference in particle size will result in wide differences in rate between the two resin components and possibly in a high pressure drop across the unit. The availability of several types of ion exchanger resins having the proper densities has made it possible t o study the various aspects of monobed deionization in a practical manner.
1
*
CATION
EXCHANGER
1
+ pR@
'c
s
During the initial phases of this study, i t was felt that a combination of a strongly acidic and basic resin was required for the monobed operation because of certain equilibrium and rate considerations. In order to verify this, several experiments were conducted, using a mixture consisting of a strong acid cation exchange resin (Amberlite IR-100) and a weak base anion exchange resin (Amberlite IR-4B). The first results obtained with this system apparently verified the original assumption. However, further studies indicated that such systems could effect deionization if a proper ratio of resins was chosen so that the rate and equilibrium differences between the anion and cation exchanger could be balanced. Because of these results, a thorough investi- ' gation was conducted on various ion exchange resin mixtures.
TABLEI. IONEXCHANGE RESINSSTUDIEDIN MONOBED DEIONIZATION True Density Total Capacity w Z e r , Resin Resin Type Me./g. Me./ml. G./M1. Amberlite IR-100 Strong acid cation exchanger 1.7 0,60 1.30 Amberlite IR-120 Strong acid cation exchanger 4.5 2.00 1.38 Amberlite I R C 50 Weak acid cation exchanger 10.5 4.50 1.25 Amberlite IR-4B Weak base anion exchanger 10.0 3.50 1.25 Amberlite IR-45 Weak base anion exchanger 5.5 2,OO 1.15 Amberlite IRA-400 Strong base anion exchanger 2.8 1 .'OO 1.15 Amberlite IRA-410 Strong base anion exchanger 2.8 1.00 1.15 '
IR-120: I R A - 4 0 0 ( I : 2 VOLUME RATIO
14
EXPERIMENTAL WORK
-
4
1 12
-
10
6-
INFLUENT: DELAWARE RIVER WATER 6-
F L O W : 4gal./+t.yrnin.
4-
2-
0
20
40
60
80
PERCENT OF RUN
Figure 2. Performance of Strong Acid-Strong Base Ion Exchange Resin Monobed System
236
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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Vol. 43, No. 3
MONOBED AND CONVENTIONAL D . I . ( N a INFLUENT)
D.1
~ - C O N Y E N T I O N A t 12qNOyD
D.1
5102 T.A.
