46
January, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
47
S
*
I N C E the pioneering work of Adams and Holmes (8) on the synthesis of ion exchange resins, rapid progress has been made in the improvement of these resinous exchangers and their application to a variety of chemical processes (1). Synthesis of resins showing marked ion exchange properties from a wide variety of raw materials .has clarified the nature of the exchange reaction and has made it possible to define the essential requirements for a good exchange material: (a) a highly cross-linked structure to ensure insolubility; (a) a multiplicity of ion active groups-e.g., SOaH, COOH, OH groups for cationic exchange, and amine groups for anionic exchange. The breadth of application of the ion exchange process will depend to a large extent upon the degree of success in increasing the density of these ion active groups with maintenance of sufficient cross linking for Flow in G o l l o n s I S q . Ft./Min. stability and insolubility. The phenol-formaldehyde condensation produces a n excellent cross-linked structure for ion exchange Figure 1. Pressure Drop in Downflow Operation in a 52-Inch Bed materials. Ion active groups, either cationic or of Nuclear Sulfonic Acid Resin anionic, may be introduced during the condensation reaction or. in some cases. by aftertreatment of a standard phenol-formaldehyde resin (10). I n the cation exFor most exchange applications, such as water softening and change field, resins may be produced of all three basic typesdemineralization, only the sulfonic acid grouping is active. sulfonic acid, carboxylic acid, and polyhydric phenol (7’). The However, the wet phenate form has shown promise in the removal latter two types may find some specialty applications such as for of weak acids, such as HzS, COZ, and substituted phenols, from buffer filters in the neutral p H range or in chemical processing gases and oils. The weak acid is converted to the water-soluble where their high selectivity for hydrogen, calcium, and magsodium salt, which remains in the wet granules. nesium ions may be used to advantage. I n the fie14 of water The nuclear sulfonic acid groups are very stable to hydrolysis softening, dealkalizing, and demineralizing, resins of the sulfonic at elevated temperatures in the presence of either acid or alkali. acid type are preferable because of their high acidity and ready The resin has shown no color, throw, no loss in capacity, and no reversibility in the sodium-calcium exchange. These sulfonic acid breakdown of the particles when operated on either the acid or resins are of two types: nuclear sulfonic acid in which the SOsH groups are directly connected to the benzene ring, and w-sulfonic acid in which the active group is -CH2SO,H. An improved ion exchange resin of the nuclear sulfonic acid type (Dowex-30) is the subject of this paper. It is a condensation product of 0- and p-phenolsulfonic acid with formaldehyde, as described by Wassenegger and Jaeger (10). Its composition is
with some of the SOJI groups replaced by a -CH2-
cross link.
PHYSICAL AND CHEMICAL PROPERTIES
The resin is produced in the form of hard black granules of irregular shape. A typical mesh analysis, as shipped in the wet sodium form, is: 69.8% on 20 mesh, 14.2% on 30 mesh, 8.1% on 40 mesh, 5.0% on 50 mesh, 2.9% through 50 mesh. I n its wet form it weighs 50 pounds per cubic foot and contains approximately 55% moisture. The density of the wetted granules is 1.30 and of the dried granules, 1.67. An operating bed of the resin contains about 38% free space. The material i s hard and shows little packing on downflow operation. The pressure drop on downflow operation of a 52-inch bed a t various flow rates is given in Figure 1. These results were obtained with a bed classified by thorough backwashing. The expansion of a bed of this resin on backwashing increases with a n increasing backwash rate in the following manner: 8.6% at 3 gallons per square foot per minute, 17.2% a t 4 gallons, 31.0% at 5 gallons. The resin contains phenolic groups and nuclear sulfonic acid groups, both of which possess ion exchange activity. However, the phenolic groups become active only at p H values above 9.5, the conversion to thephenate salt being very slow below p H 11.5.
0
1.0
2 .o
3.0
4.0
5.0
6.C
C C. 2 N N A O H
Figure 2.
_x-x-x-x-x-x______-_____ _.._.._.._.._.. _._._._._._._ a
pH Titration Curves Designation.
E resin A renip C ream R resin Decationiaed sreenisnd 5 grama of resin except for greensand.
Active Group -SOiH -CHrSOsH -COOH -OH (20 9.)
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
48
Vol. 38, No. 1
complete salt removal in water demineralization even on waters of high salt content. Griessbach (7) gave p H titration curves for resins of various types (Figure 2). Figure 3 is the corresponding curve for the improved resin discussed in this paper. This titrated capacity represents the total available sulfonic acid capacity of the resin and agrees closely with the total sulfur analysis (2.92 pounds per cubic foot sulfur content, equivalent to 13y0 _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _-_- -_- - - - - ------ of the dry weight), This total capacity is equivalent to 32,000 grains of calcium carbonate per cubic foot. Titrated Capacity : As with all exchange materials, the operating 32,000 G r u i n s C o C 0 ~ l capacity is dependent upon the quantity of regenCu. Ft. erant used, the concentration of the regenerant, the rate of flow of the regenerant and rinse water, C C. 2 N N a O H the temperature of the regenerant solution, and, 0 ,.o e.o J.o 5.0 6.0 7.0 8.0 9.0 100 to a lesser extent, upon the concentration of salts in the raw water and its rate of flow. Attempts Titration Curve for 5 Grams of Improved Nuclear Figure 3. have been made to develop the funct,ionality of this Sulfonic Acid Resin operating, OP break-through, capacity on the total capacity, the static equilibrium constants of the resin for the ions involved, and the speed of exchange or the rate of sodium cycle below 9.5,pH a t temperatures tip to 2120 fi'. some softening of the particles and loss in capacity are obtained in diffusion of ions through the resin lattice (6). This theoretical sodium cycle operation a t combined high p H and high temperawork has been most valuable in indicating qualitatively the properties of high exchange capacity, high exchange speed, and low tures. However, one unit has operated in t'he hydrogen cycle on water of 10.0-10.5 p l I a t 150-180" F. for over 100 cycles without exchange selectivity for one ion over another, which are desirable in the ideal exchange resin. However, the variables involved in any breakdown or loss in capacity. the value of the operating capacity are so numerous that the The resin, because of its highly cross-linked structure, is insoluble in all organic or inorganic liquids and is infusible. Decalculation of this value for any one set of operating conditions would be more laborious than the experimental evaluation. composition of the dry acid form starts a t about 200" C. As with other organic exchange agents, the resin is decomposed by Data on the operat'ing capacity of this resin has been obtained in both the acid and sodium cycles in laboratory glass columns of 1 strong oxidizing agents, such as chlorine, bromine, HCr04, etc. inch diameter with a bed depth of 29 inches. The method used Weaker oxidizing agents, such as oxygen, sulfuric acid, Fe+++, follows closely the one outlined by the American Water Worlis show no detrimental effect. Even nitric acid is without appreciAssociation ( 5 ) . The results are shown for a water containing able effect at room temperature and below 10% concentration. 10 grains per gallon calcium and 5 grains per gallon magnesium ION EXCHANGE PROPERTIES (as CaCOa) a t a flow rate of 5 gallons per square foot per minute. Resins of the nuclear sulfonic type show the highest acidity of Regeneration was effected by 5 % sodium chloride, 4% hydrochloric acid, and 2y0 sulfuric acid a t such a rate that the regenerall ion exchange resins tested. Single-pass contacting of a 6ant was added during 30 minutes and rinsed a t this same rate for foot bed with strong sodium chloride solution has produced as high as 10% hydrochloric acid solutions. This property ensures an additional 30 minutes. The end point of each run was taken at 1 grain per gallon hardness. Parallel runs were made on samples of exchange materials of other types for the sake of comparison. The data are present'ed in Figures 4, 5, and 6 .
;; 3 0
-. 3
0
K)
0 0 0
0
25
ln
.-C U
&
20
.-0 Y
.-c r. 15
c .0 0
Q 0
0 CII
.E
10
e (Y
n 0.5
0
Lbs. NaCL p e r Kilograin COCO3 ,
Figure 4.
I. 0
Removed
Operating Capacity of Ion Exchange Materials in Sodium Cycle
0
5
0
0.5
1.0
Lbs. HCL P e r Kilograin C o c o 3 R e m o v e d
.
Figure 5. Operating Capacity of Ion Exchange Material in Acid Cycle with HCI Regeneration
t
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1946
49
proved nuclear sulfonic acid resin to determine its stability. I n one of them a 6-inch depth of resin was operated in a 6-minute water-softening cycle for 8500 cycles. I n the second test individual particles of resin were carried through a Zminute watersoftening cycle for 40,000 cycles. I n both tests saturated sodium chloride was used as a regenerant in order t o give the resin particles the maximum osmotic force shock-Le., a rapid swelling and shrinking of the particles caused by osmotic force changes with changing salt concentration. Experience indicates that this swelling and shrinking is the usual cause of particle splitting during operation of ion exchange resins. After each of the tests the nuclear sulfonic acid resin had shown no physical degradation or loss in exchange capacity.
25
I 0
I
I
I
0.5 Lbr. HgSO4 Per Kilograin Go GO3 Removed
1.0
~
Figure 6. Operating Capacity of Ion Exchange Materials in Acid Cycle with H2SO4 Regeneration
Both sodium chloride and hydrochloric acid regeneration of this nuclear sulfonic acid resin give a n operating capacity closely approaching the total available capacity a t high regenerant dosages. This feature appears to be common for most exchange matcrials of the resinous gel type (8),and indicates a high rate of diffusion of ions through the gel structure. The exchange speed in the Na-H exchange in 0.01 N chloride solution is shown in Figure 7 for a batch system with rapid agitation as determined by conductivity. The equilibrium state is attained in about 2 minutes. The exchange rate is much lower for the aluminum silicates, either natural or synthetic. Natural greensand has a cation content equivalent t o about 100,000 grains of calcium carbonate per cubic foot of which only about 3% is available for exchange. Synthetic aluminum silicates have been produced of lower density and higher water content than greensand, so that about 40% of their total capacity of 25,000 grains of calcium carbonate per cubic foot is available in the softening cycle ( 4 ) . Predominance of a surface reaction with greensand led early investigators to treat the ion exchange reaction as one of adsorption (9). Work with the newer exchange resins has indicated clearly that the exchange is a true chemical exchange of ions between liquid and aolid phases and is controlled by mass action laws ( 3 ) . The failure of sulfuric acid to give a regenerant efficiency and operating capacity comparable to sodium chloride or hydrochloric acid is not yet fully understood. Concentrations of sulfuric acid higher than 2% give pronounced precipitation of calcium sulfate. This limitation on concentration may cause lower regenerant efficiency because of the increased selectivity of the resin for calcium and magnesium ions a t low acid concentrations. It is also possible that the acidity of the second hydrogen in sulfuric acid is too low to regenerate effectively the strongly acid nuclear sulfonic acid groups in this resin. LIFE TESTS
.4number of factors may contribute to the deterioration of an ion exchange material during service. High temperature, oxidizing agents, high acidity, alkalinity, or brine concentration may destroy either the primary resin structure or the ion active groups. Rapid changes in salt concentration, excessive bed packing, or attrition may split the particles into fines. Water turbidity or supersaturation may lead to a fouling of the resin particles. Bacterial growths may feed on the resin. .Resistance t o many of these deteriorating factors may be determined by laboratory tests; others can only be checked by field tests. Two accelerated laboratory tests have been run on this im-
I2
24
36
48
6Q
72
84
96,100
Figure 7. Speed of Exchange in the Conversion of N a Form to H Form a t 0.01 N Chloride Concentration
This resin has been installed in a boiler feed water purification plant for three years. In this application it softens a limetreated river water a t 8-9 pH and maximum temperature of 100' F. from 60-70 p.p.m. calcium carbonate hardness to less than 1p.p.m. The resin has shown no volume loss, no increase in flnes, and no loss of total capacity during this period. After 2.5 years of operation the operating capacity had dropped 15-20% because of fouling of the particles with ferric hydroxide and calcium carbonate. Acid treatment has been used to clean the resin and has restored the operating capacity to its initial value. Tests also indicate that this resin could have been cleaned effectively by a backwash a t 6-8 gallons per square foot per minute, but insufficient head room was available in the commercial units. The photograph on page 46 shows this installation, A second installation has operated in the acid cycle for water demineralization for three years. This demineralization unit reduces the salt content of Midland city water from 200 to less than 2 p.p.m. Hydrochloric acid is used as regenerant. Full operating capacity has been maintained throughout this period. An analysis of a resin sample taken after 20 months of service 'showed identical particle size and capacity as the original resin. A third installation was made for experimental purposes in the softening cycle; it handled a surface water containing up to 100
'
50
INDUSTRIAL AND ENGINEERING CHEMISTRY
p.p.m. turbidity a t 140-150" F. Saturated sodium chloride was used as regenerant, also at about 150' F. Although the unit gradually lost operating capacity to the extent of about 25% in 15 months because of resin fouling, no degradation of the resin occurred. Treatment with 1570 hydrochloric acid t o remove the accumulation of ferric hydroxide and complex silicates restored the original capacity. An unexpected result in all of these units has been a marked reduction in turbidity of the water being softened or demineralized. Water containing 5-10 p.p.m. turbidity which has passed through sand filters of 40-80 mesh will be reduced t o 1-2 p.p.m. turbidity in passing through a resin of 12-30 mesh. Surface water of 50-100 p.p.m. turbidity may be reduced to 15-20 p.p.m. The resin appears to coagulate the colloidal particles, possibly because of its high concentration of ionic charges. This clar5cation is advantageous for both boiler feed water and for municipal supplies. LITERATURE CITED
(1) Adams, B. A. [to Ocean Salts (Products) Ltd.], Brit. Patents 536,266 and 541,450 (1941) ; Johnsen, H. (to Norsk 1.iydro
Vol. 38, No. I
Electric), Norwegian Patent 59,035 (1938) ; Findlay, D. M. (to U.S.Rubber Co.), U. S. Patent 2,261,021 (1941). (2) Adams, B. A., and Holmes, E. L., J. SOC.Chem. Id., 54, 1-6T (1935); Brit. Patents 450,308-9 (1936) and 474,361 (1937); French Patents 796,796-7 (1936); U. S. Patents 2,104,501 (1938), 2,151,883 (1939), and 2,191,853 (1940). (3) Akeroyd, E. I., and Broughton, G., J . Phys. Chent., 42, 343
(1938). EXG.CHEM.,19,446 (1927). (4) Behrman, A. S., IND. (5) Committee on Water Works Practice, J . Am. Water Worke ASSOC., 35, 721-50 (1943). 6)Furnas, C. C., and Beaton, R. H., IND.ENQ.CHEM.,33, 1500 (1941); Thomas, H. C., J. Am. Chem. SOC.,66, 1664 (1944). (7) Griessbach, R., Ueber die Herstallung und Anwendung neuerer Sustausch adsorbienten, inbesonders auf Rarzbasis", Verlag Chemie, Berlin, 1939; abstd. in Angcw. Chem., 52, 215-19 (1939). (8) Myers, R. J., and Eastes, J. W., IND.ENG.CHEM.,33, 1204 (1941). (9) Thompson, J . Roy. A g r . SOC.Engl., 11, 313 (1850); 13, 123 (1852). (10) massenegger, H., and Jaeger, K. (to L G . Farbenindustrie), U S. Patent 2,204,539 (1940). PRESENTEDbefore the fall, 1945, Meeting-in-Miniature of the Midland Section. AMERICANCHEMICAL SOCIETY.
Kinetics of Sucrose Crystallization J
SUCROSE-NONSUCROSE SOLUTIONS ANDREW VAN HOOK Natural Resources Research Institute, University of Wyoming, Laramie, Wyo. The effects of the most commonly occurring nonsucrose constituents of cane and beet juices on the crystallieation velocity of sucrose were investigated. These materials invariably depress the rate of adjustment of sucrose solutions when conditions are similar to those encountered in sugar boiling and crystallizing. The activity interpretation previously proposed explains the effects of these contaminants in a qualitative way when they are present singly or in combinations which imitate real molasses.
A
QUAKTITATIVE understanding of the crystallizing behavior of massecuites should develop from a kinetic interpretation of the crystalliaation of sucrose from pure solutions and from synthetic sirups. Velocity data and mechanism for pure sucrose solutions have already been discussed in previous papers of this series (24, a5) as well as the effects of common electrolytes. The present paper supplements the list of salts already considered ($66)and presents additional data on the effects of various substances which are likely to be found in cane and beet juices. I n most cases the concentrations of impurities considered are greater than those usually found in ordinary final molasses. A static technique was used for most of the results presented. The procedure consists of seeding the sirup, which has previously been adjusted t o the proper conditions, and following the rate of adjustment refractometrically. It has already been demonstrated (24, 85) t h a t this method gives essentially the same values for pure sucrose as do methods involving the actual measurements of growing crystals, and the procedure is more convenient and rapid. With impure solutions the same agreement prevails out to the usual limit of impurity when single constituents are considered, but at extremely low velocities the usual procedure, in which the smear adjusts directly on the refractometer prism, gives velocities lower than methods in which stirring is involved.
This same difference is suggested by the observation that deviations from monomolecularity with unstirred solutions are more pronounced as the purity decreases. These variations, however, are all beyond the three-quarter life period of reaction and are therefore of little significance in the evaluation of rate constants; they may be important in ascertaining the mechanism of crystallization from impure solutions. It is well recognized that the p H of a sirup has a tremendous effect on the crystallization velocity of sucrose (6,10, 16). An acid condition causes a diminished rate t o a variable extent on account of inversion. From p H 6-8 the r&es are reproducibly constant; above 8 the values are again decreased variably. A development of color is associated with this change. A p H of 7-8 was therefore adopted as standard in these investigations, and was realized by the addition of acid or base when necessary, This was preferred to the use of buffered solutions in order t o avoid salt effects. VELOCITY OF CRYSTALLIZATION
The general behavior of synthetic sirups is demonstrated with the results for raffinose shown in Figure 1. The concave curvature is significantly maintained on a semilog plot, as discussed later in connection with Figure 5 . The same type of result was obtained when invert sugar and betaine were the impurities; in no case, at 30" C. or higher, was a n increase in velocity observed at small concentrations of nonelectrolytes (7, l a ) . However, a t 16' C. and an initial sucrose concentration equivalent t o sucrose/ (sucrose water) = 0.685, relative velocities of 1.30 in the presence of 0.4 gram of raffinose per 100 grams of water, 1.21 in the presence of 1.0 grams betaine per 100 grams water, and 1.11with 1.0 grams invert per 100 grams water, were obtained. At higher concentrations of impurities the relative velocities of crystallization were diminished and a t higher temperatures these maxima also disappeared. This general behavior is exactly what is ex-
+
