Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 150-157
150
Osmotic Shock Stability of Ion-Exchange Resins Wllllam M. Alvlno' end Michael C. Skrlba Westinghouse R&D Center, Pittsburgh, Pennsylvania 15235
Robert Kunln 13 18 Moon Drive, Yardley, Pennsylvania 19067
In this paper, the effect of osmotic pressure on the stability of ion-exchange resins was studied. Over 160 batches of 33 different resins from U.S. and foreign manufacturers were evaluated. The ion-exchange resins were alternately cycled between solutions of different ionic strength so as to create osmotic pressure gradients within the beads. The resistance of the resins to osmotic shock was measured in terms of thek abllity to resist cracking and fracturing. Macroporous resins are much more resistant than gel resins and show much less variability among batches of resin. Considerable variability exists among batches of the same resin and between resins and manufacturers.
Introduction Ion-exchange materials have been used in various and sundry ways. For most of these applications, the users want to ensure themselves that a resin of the highest quality is chosen for its intended use. No one test exists at the present time that can be used to evaluate the quality of the resin beads for all applications. As a result, many types of tests (Jabsco Pump Test, 1968; Chatillon Test, 1977; Kunin, 1972; Golden and Irving, 1972) have been devised for this purpose. These tests usually measure the resistance of the ion-exchangeresin to physical degradation due to chemical and mechanical shock. We became involved in the evaluation of ion-exchange resins as a result of Westinghouse's interest in the recovery of uranium from acid leach liquors. The primary concern was how long the ion-exchange resins would last in such an environment and what kind of test could be used to measure the quality of incoming batches of resin. An extensive research program was begun to examine the chemical and mechanical stability of ion-exchange resins. Results of this research were reported earlier (Alvino, 1980, 1981). Initially, a number of tests were studied to determine their utility for measuring the resistance of ion-exchange resins to osmotic shock. One of these tests was selected as being most suitable for screening candidate resins. This paper deals with the application of this test method for the evaluation of Type I anionic-exchange resins. (Type I resins are strong base anion-exchange materials with benzyl trimethylammonium functional groups.) Over 160 batches of 33 resins from four US.and five foreign suppliers were evaluated. These materials included both strong and weak base gel and macroporous resins. Osmotic Shock. The physical forces imposed on ionexchange resins arise from hydraulic pressure as in flowing streams in deep beds, from osmotic pressure resulting from volume changes with a change of electrolyte and electrolyte concentration, and from purely mechanical forces as in pumping resin slurries or backwashing a column for classification. These forces are strong enough to cause cracking and breakage of the resin beads. Ion-exchange resin beads can be considered as porous membranes and as such readily allow diffusion to take place into and out of the bead by the process of osmosis. Osmotic flow occurs from the more dilute solution toward
the more concentrated solution and continues, theoretically, until the concentrations are the same on both sides of the membrane. Consider an ion-exchange bead swollen with water and surrounded by a more concentrated electrolyte. Passage of the water from the bead into the electrolyte will occur causing the resin bead to shrink. If the situation were reversed whereby the swollen bead contained the more concentrated electrolyte, the bead would expand. The least external pressure required to prevent the flow of solvent through the membranes is the osmotic pressure. This volume expansion and contraction imposes strains on the resin, and those beads with internal stresses or weak structure will succumb to the effects of repeated size change by breaking down into finer particles or by developing cracks that further weaken the resin bead.
Experimental Section Resin Identification. Ion-exchange resins from four U S . manufacturers (Dow Chemical, Rohm & Haas, Diamond Shamrock, and Ionac) and five foreign manufacturers (in Italy, Netherlands, Japan, France, and Germany) were evaluated. All of the US. and foreign resins are based on a styrene-divinylbenzene matrix and all have a quaternary ammonium functional group except where noted. The resins are all anion-exchange materials and are representative of the commonly used gel and macroporous type materials. In order not to advertise one manufacturer's resin over another, the exact identification code and batch number is not given. The resins are identified as strong or weak gel and/or macroporous resins. The manufacturers are identified by the capital letters A-I, the resins are identified by numbers 1, 2, 3, ..., etc., and the batch is coded with small letters. For example, Ala means manufacturer A, resin 1, batch a. Osmotic Shock Test Description. The osmotic shock test (OST) consists of alternately contacting the ion-exchange resin beads with hot 20% by weight H2S04and cold deionized water for the required number of cycles. Resin attrition is measured in terms of sphericity, perfect beads, and whole perfect beads. A schematic of the OST is shown in Figure 1. The test procedure is as follows: About 10-15 mL of resin (chloride form) is placed in a coarse fritted glass disk Gooch crucible (60 mm high with an i.d. of 41 mm) and soaked in deionized water at room temperature for 2 h. After soaking, the resin-filled Gooch
0196-4321/83/1222-0150$01.50/0Q 1983 American Chemical Society
Ird. Eng. Cham. Prod. Res. Dev., Vol. 22. No. 1. 1983 151
Whole Perfeot Beads (WPB). A Combined Measure of Bead Fragmentation and Cracking. This determination is made from multiplying the sphericity by the perfect beads and is a global measure of the percent of beads that passed the test without any effect on them. % sphericity X % perfect beads = % whole perfect beads (3)
Figure 1. Schematic of OST apparatus.
Figure 2. Inclined plane.
crucible is p l e d on the vacuum flask and the resin is: (1) vacuum drained for 5 s and soaked in cold deionized water (10-12 "C) for 15 s; with the resin in place and after closing the stopcock, the vacuum gauge read 26 in. Hg; during vacuum draining, the free air flow through the system is 16 L/min a t 16 in. Hg; (2) vacuum drained for 5 s and soaked in hot 20% H2S0, (60-63 'C) for 15 8; with the resin in place and after closing the stopcock, the vacuum gauge read 26 in. Hg; during vacuum draining, the free air flow through the system is 16 L/min at 16 in. Hg; (3) carried through steps 1 and 2 for 10 cycles; (4) converted back to the chloride form by immersing in excess 10% NaCl solution a t ambient temperature; (5) washed with deionized water and vacuum drain; (6) dried at 5100 "C until beads are free rolling (30 min); (7)measured for sphericity, perfect beads, whole perfect beads. Sphericity ( S ) . A Measure of Bead Fragmentation. Pour the dried free-flowing beads down an inclined plane 80 that the beads flow down the plane without interfering with each other (see Figure 2). The beads that roll, as well as those that remain on the plane, are collected separately and weighed. Sphericity is calculated as weight of beads rolling off plane S= x loo (1) total weight of beads Perfect Beads (PB). A measure of the amount of noncracked spherical beads. The beads that roll off the inclined plane are then examined microscopically 10-30X magnification to determine cracked and uncracked beads. A portion of the beads are placed in a 0.5 in. diameter ring and then the number of uncracked beads is counted. This procedure is repeated until 500 to loo0 beads have been examined. The percent perfect beads is calculated as number of perfect beads % PB = x 100 (2) total number of beads
Results and Discussion b i n Evaluation in the OST Test. Multiple batches of various types of resin from all manufacturers were evaluated in the OST. The results of these tests for each batch of resin from each manufacturer are reported in Table I. It is clear from the data reported in Table I that there is considerable variation in the stability of different batches of the same resin. Comparison of S, PB, WPB Values before and after OST. A number of batches of different resins were examined. S,PB, and WPB were measured before and after the OST in order to determine the sensitivity of the resins to the conditions of osmotic shock. Table I1 presents these data. It appears that the OST is sensitive in detecting weak batches of gel resins but does not appear to differentiate between strong and weak batches of macroporous resins. Statistical Analysis. Variance between the results of the OST by different groups prompted an investigation into the source of this parameter. The OST was run on 14 replicates from the m e batch of resin. These data are shown in Table 111. It was observed that this variance in whole perfect bead values was greater when the resin had a large number of cracked beads. When only a few cracked beads were present this variance decreased and the precision of the test results increased. It was concluded that if the resin is strong, the test is relatively precise, but a weak resin will give widely scattered data. It should be noted that even though considerable variation can be expected, those resins tested by one group of testers that did not pass the OST also did not pass when tested by the other group. (The criterion for passing the OST was a WPB 2 go%.) The source of the variability was traced to sampling. In order to minimize this error and increase the precision of the test, a larger number of beads should be examined in separating cracked from uncracked ones. This would increase the precision more than running replicate osmotic shock tests. However, in order to halve the standard deviation one would have to increase the counting by the square of the number of counts. Presently, we count five separate portions of beads from one sample. These are approximately 200 beads per count so that squaring the number of counts we obtain 25. This means that we would need to count 5000 heads to halve the standard deviation. Despite the variability of results obtained in the OST, the method is useful for distinguishing between strong and weak batches of gel-type resins. Mode of Fracture. T w o types of fracture occurred when the resin was subjected to the OST test. These failure modes are identified as fragmentation (beads breaking into pieces) and cracking (development of cracks in beads). In general we find that the gel resins are more susceptible to cracking than the macroporous resins. However, if a gel resin is weak, the sphericity values can be quite low, indicating that the resin fragments easily. A good gel resin, on the other hand, will probably not fragment, but could be susceptible to cracking. The effects of osmotic shock on bead cracking and fragmentation for gel and macroporous resins are shown in Figures 3 and 4.
152
Ind. Eng. Chem. Prod. Res. Dev., Vol.
22, No. 1, 1983
Table I. OST Test Results mfg
resin
A
1
batch
size
type
1 4 x 20
strong base gel
16 X 30 16 X 40
strong base macro
1 6 X 30
strong base macro
1 6 x 50
weak base macro
1 6 X 50 1 6 x 30
weak base macro
g
a
1 6 X 20
strong base gel
a b C
B C
2 3
d e f g a a b C
4
a b C
d e 5
f a b C
C
5
d e f
h i
B
6
b C
d e f g
h i j
k 1 m n 0
P q
1 6 x 30
r
S
B
6
t
1 4 x 30
strong base gel
20 x 40 20 X 50 1 6 X 30
strong base gel
20
strong base gel
u V W
B
7 8
X
ba C
d e B
9
f a b
X
50
C ti
e
B B
10 11
a
a b
20 X 50 16 x 35
strong base gel strong base macro
1 6 X 35
strong base macro
1 6 X 50 1 6 x 40
strong base gel
C
d e f
B
D
11
h I
j
k 1
C C
12 13
a a
S
PB
WPB
93 92 95 88 77 97 82 88 98 98 97 89 95 92 95 93 95 99 99 98 99 99 98 97 97 96 99 95 99 85 98 97 89 98 97 93 95 98 91 98 98 92 96 99 97 92 99 97 97 99 99 88 82 99 97 98 35 85 50 87 76 99 99 99 99 99 97 99 99 99 99 99 99 98 99 82
94 57 72 83 64 86 60 99 99 99 99 99 99 98 99 99 99 99 99 99 99 99 99 98 98 99 99 86 99 98 98 58 66 99 86 76 94 69 32 71 65 86 85 76 96 88 98 99 99 99 99 93 89 99 99 91 86 85 89 66 76 92 99 99 99 99 99 99 99 99 99 99 99 98 99 94
87 52 68 73 49 83 49 87 98 98 96 98 94 90 94 92 94 99 99 98 99 99 98 94 95 95 98 82 98 84 96 56 59 97 84 71 90 68 29 69 64 79 82 76 96 81 97 97 97 99 99 82 73 99 96 90 30 72 44 58 57 91 99 99 99 99 96 99 99 99 99 99 99 97 99 78
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 1, 1983 153
Table I (Continued) ~
mfg
resin
batch
size
type
S
PB
WPB
C
14
a b
16 X 40
strong base macro
16 X 40
strong base macro
20 x 40 20 x 40 16 X 30 16 x 30
strong base gel
j
1 6 X 30
strong base gel
1 m n
16 X 30
strong base gel
1 6 x 40 16 X 20
strong base gel
97 86 85 88 85 83 95 89 91 92 92 84 89 86 80 90 97 90 89 82 83 91 85 87 91 84 86 91 95 99 99 93 88 97 99 98 96 99 98 99 93 98 98 99 99 99 99 99 99 99 98 98 98 92 92 99 99 97 99 88 97 99 95 98 99 99 100 97 99 99 99 99 99 100 100 100
99 98 99 99 99 99 99 99 99 99 99 99 99 99 95 99 99 99 98 99 99 99 99 96 99 99 99 96 98 99 99 98 95 98 99 98 97 98 98 99 95 96 97 99 98 98 99 98 99 97 98 99 99 97 91 99 99 99 99 99 91 99 95 95 13 97 94 80 99 92 99 99 99 99 99 99
97 84 85 88 85 83 85 89 91 91 91 84 89 86 76 89 96 90 87 81 82 91 85 83 90 83 85 87 93 99 98 92 84 95 98 96 93 97 97 99 98 95 96 98 98 98 99 98 99 96 97 98 98 90 84 99 99 97 99 87 88 99 90 93 12 96 94 78 99 91 98 99 99 99 99 99
C
d e f g h 1
j
k 1 m n 0
C
14
P 9 r S
t
u V W
X
Y z Zl
D D
15 16
D
17
a a b a b C
d e f g h 1
k
D
17
0
P q r S
t
u V
D D
18 19
D D
20 21
a a b a a b C
D D E
E F G
22 23 24 25 26 27 28
a a a a a b a b
20 20 14 20 20 16 16 20 20
x X
X X X X X X
30 40 20 40 50 50 50 40 40
strong base macro
20 X 30
weak base macro strong base macro strong base gel strong base macro strong base macro strong base macro strong base macro
20 X 30 20 X 30
strong base macro strong base macro
x
C
d e G G
29 30
a
a b C
d e
154
Ind.
€ne. Chem. Rod. Res. Dev..
Table I (Continued) mfg resin H 31
Vci. 22. No. 1. IS83
batch
size
a
16 x 40
strong base gel
16 x 40
strong base gel strong base gel
99 98 99 99 98 97 96 97 95 96 97 98 95
b C
I
d e f a a b
32 33
J
C
d e f
Table 11. Comparison of Resin Roperties Before and After OST before mfg resin batch S PB WPB S A 1 a 98 9 7 93 ~.99 ~
~~
b C
d e f g
6
a
b C
d e f g h
8
a b C
9
d a b
14
a
C
b C
17
a b C
30
a b C
d
97 99 98 99 99 98 99 95 99 91 92 85 97 93 99 99 89 99 99 99 97 81 86 81 93 87 96 99 99 99 99
99 99 99 99 99 99 99 99 99 94 98 94 99 99 99 99 94 97 98 99 98 96 98 99 99 98 99 99 99 99 99
~~
96 98 98 98 99 97 99 95 99 86 90 80 97 92 99 99 84 97 98 98 95 78 85 80 92 85 95 99 99 99 99
92 95 88 77 97 82 99 95 99 85 97 89 97 93 99 88 82 98 35 85 87 81 87 84 93 88 98 99 99 99 98
PB 99 96 95 95 98 99 89 98 99 96 97 98 96
S
type
WPB 98 94 95 94 96 95 86 95 94 93 94 96 91
Table 111. Statistical Data on OST" after PB WPB 94 .~ 117 57 52 72 68 83 73 64 49 86 83 60 49 99 98 86 82 99 99 98 84 58 56 66 59 86 84 76 71 99 99 93 82 89 73 91 90 86 30 72 85 66 58 98 80 96 83 99 83 98 92 95 84 98 97 99 99 99 99 99 99 98 96
We have found for our application that those resina that score consistently above 95% in all batches tested are an indication of the g w d quality of that batch of resin. It should be mentioned that this is an arbitrary value based on one's needs and that other limitscould be used to defme 'good" or "bad" resins, depending upon the particular ion-exchangeoperation. While resistance to osmotic shock is important, it should not be the only criterion for choosing an ion-exchange resin for a given application. Evaluation of Resin Types The data in Table I were condensed by averaging the values of S,PB, and WPB obtained for all resin batches of a given type of resin. These data are presented in Table IV. The range of values, the average value, the standard deviation, and number of tests for each resin are shown in this table. In addition, a brief description of some of the resin properties is given. Gel Resins. There is considerable variance in the resistance of the gel resins to osmotic shock. This variation is seen both among batches of the same resin from the
%
sample 1 2 3 4 5 6 7 8 9 10 11 12 13 14
mean 0
95% CI ( 0 x 1.96) (I
%
perfect
whole perfect
sphericity
beads
beads
96.2 96.2 96.0 95.5 95.5 94.6 92.4 92.5 95.9 95.5 95.1 95.4 93.7 95.7 95.0 1.21 92.5-97.5
84.9 80.1 86.5 77.1 86.8 83.0 82.0 89.0 78.1 87.3 83.4 85.8 84.2 89.1 84.1 3.75 76.7-91.4
81.6 77.0 83.1 73.7 82.9 78.6 75.8 82.3 74.9 83.4 79.3 81.8 78.9 85.3 80.1 3.56 72.9-86.9
%
Mfg B, resin 6.
OST
PLVRCEL RESIN Resin 6. m fg 5
Goo0 G€l RESIN Resin 17,mfg D
srq MACRO" Resin 14. mfg
RESIN
C
2:;:*:
.. :; , ;,' &. .,_ .-:.p;. %,,'>.~!\:'> tY, I
L
;.:.,
t',:
.
Figure 3. Bead cracking after 10 osmotic shock cycles.
same manufacturer and between different manufacturers of gel type resins (see Table V). The differencesobserved in the resins made by different manufacturers seem reasonable; however, the differen- observed between batches
Ind. Eng. Chem. Prod, Res. Dev., Vol. 22, No. 1, 1983 155
t
k
oooooooooomoooooooooooooooooooooo
~ ~ ~ m m m m m m m m m * d d d m * ~ m d ~ ~ m d d d d m d d d ~ x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x
d w w w C D w o w o o w w w w o o w w w o o o w ~ o o o o o o w w w
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0)
a
h c
.-E
E M
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150 lnd. Eng. chem.Rod. Res. De% Vol. 22. No. 1. 1983
Table V. Gel Resins. OST Results mfg resin S PB A
B
B B B C
c -
D D D D D D
E H 1
J
1 6 8 9 10 12 13 ..
15 16 17 18 19 20 24 31 32 33
77-97 85-99 82-99 35-87 99 99 R_291 95-99 88-99 98 92 99 99 98-99 96 95-98
OST
WPB
57-94 32-99 89-99 66-89 92 99
48-87 29-98 73-99 30-72 91 99 7R .87 93-99 84-99 98 84-90 98 99 95-98 86 91-95
9 4 ..
96 98-99 95-99 99 91-97 99 99 97-99 89 96-99
POOR GEl RESIN
GOOD GEL RESIN Resin 17,mfg D
MACROPOROUS RESIN Resin 11, mfg 8
Table VI. Macroporous Resins. OST Results mfc resin S PB WPB 2 3 4 5
A A A
A
B C D
D
D E F F G G G
11 14 21 22 23 25 26 27 28 29 30
88 98 92 98-99 95-99 80-97 99 88 97 95 98 99 97-99 99 99-100
99 99 98
87 98 90
99 96-97 99 99 91 95 9s .. 13 80-99 98 98-99
96-99 76-97 99 87 88 90
MACROPOROUS RESIN Resin 14, mfg C
..
..
Figure 4. Bead fragmentation after 10 osmotic shock cycles.
93 ..
12 78-99 98 98-99
of the same resin from the same manufacturer suggest quality control problems during manufacture of the resins. Although multiple batches of resin from a l l manufacturers were not tested, it is clear that weak batches of gel resins can be detected by use of an osmotic shock test. Under osmotic shock conditions, these resins break down by cracking (see PB values). However, some of the very weak resins will also fragment, as indicated by the low S values. Macroporous Resins. These materials are quite resistant to the effects of the osmotic shock test. However, if a very weak batch of resin is made, the OST can detect it. Note resins 27 and 28, manufacturer F and G,in Table VI. In the gel resins, cracks would develop within the resin beads. These cracks were readily observed because of the transparency of the resin. The macroporous resins are opaque and cracks are often difficult to detect. Nevertheless, when cracking does occur, it appears as a fissure in the bead. Sometimes we observed a splitting of the outer surface of the beads (see Figure 5). For the most part, the quality of the macroporous resins (as consistent with different batches and manufacturers) is very good. Comparison of Gel a n d Macroporous Resins. In order to compare the overall resistance of the gel and macroporous resins to osmotic shock, the data for each type of resin were combined and treated statistically. The average values for S, PB, WPB, the standard deviation, and variance for the combined batches of gel and macroTable VII. Comparison of Gel and Macroporous Resins S gel resins
macroporous resins
x
0
93.9 93.9
9.4 5.7
V 89 32
Figure 5. Splitting of macroporous ion-exchange resin after 10 osmotic shock cycles: mfg D, resin 23.
porous resins are reported in Table VII. The corresponding data for each resin are also reported in Table VIII. There is less variance among the macroporous resins than among the gel resins. The average sphericity values for the two types of resin are essentially equivalent, but there is more scatter in the data obtained for the gel resins. The sphericity is a measure of bead fragmentation. Its value depends on the amount of broken beads present in the resin batch as it is shipped from the manufacturer plus any additional beads broken after it is subjected to the osmotic shock test. It is important to note that sometimes the S values before and after the OST were the same, indicating that bead fragmentation did not occur under osmotic shock conditions. Gel resins are more susceptible to cracking than are the macroporous resins. (Compare the PB values in Table PB
x 90.6 98.1
WPB
(I
V
x
12.7 2.6
162 6.7
85.8 93.1
(I
16.3 5.6
sample V
size
268 32
88 77
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 1, 1983 157
Table VIII. Statistical Calculations for Sampled Data
PB
S resin 1 3 4 5 6 8 9 11 14 16 17 19 21 28 30 31 33
x
0
V
x
89 97.6 93.1 98 95.6 93.8 66.6 98.7 87.6 97 97.4 92 98.3 98.8 99.6 98.3 96.3
6.7 0.47 2.1 1.0 3.5 6.5 20.5 0.59 4.1 2 2.6 0 0.9 0.9 0.48 0.74 1.1
45 0.2 4.8 1.0 12.8 42.4 423 0.35 17 4 7.2 0 0.8 0.96 0.24 0.5 1.2
74 99 98.8 98.7 83.6 95 80.4 98.9 98.6 98.5 97.8 94 99 92.4 99 97 97.3
0
WPB V
13.1
173
0.3 0.4 16.9 4.1 8.4 0.27 0.94 0.5 1.1 3 0 6.6 0 1.7 1.1
0.1 0.1 285 17.3 70.6 0.07 0.88 0.25 1.4 9 0 44.2 0 3 1.2
VII.) The internal structural differences between the two types of resin probably account for the differences observed in their cracking behavior. Both types of resins are porous; however, due to differences in the synthesis, the macroporous resins contain much larger pores than the gel resins. Because of this, they are better able to dissipate osmotic pressure gradients that can develop in the ion-exchange process. These large pores are not present in the gel resins and considerable force is exerted within the beads. This force cannot be dissipated easily and, if the resin beads are weak, the pressure developed can cause cracking and eventually fracture of the beads. An estimate of the degree of property variance among batches of the same resin and between resins and manufacturers can be obtained from the data on Table VIII. The data are self-explanatory and point out the need for carefully choosing a resin to ensure that it is physically strong enough for its intended application. The standard deviations are quite high when there is a large number of cracked beads (PB value is low). Conclusions Ion-exchange resins are susceptible to cracking and fracturing when exposed to an environment where osmotic pressure gradients are created within the resin beads. A measure of the stability of the resin beads can be obtained by cycling the resin between solutions of different ionic strengths. In this type of test, the susceptibility of the beads to fracturing is measured and quantified in terms of properties defined as sphericity, perfect beads, and whole perfect beads.
x
U
V
sample size
66 97.3 93.6 97.3 80.4 89.8 52.2 98.5 84.1 96 95.8 91.5 98.3 91.6 99 95.3 93.8
14.9 0.9 2.4 1.9 17.0 9.5 14.2 0.94 15.5 3 3.6 7.5 0.9 7.2 0 1.3 1.5
222 0.8 5.8 3.7 290 91.8 201 0.9 242 9 13.2 56.2 0.8 53 0 1.8 2.4
7 3 6 9 23 6 5 12 27 2 22 2 3 5 5 6 6
The major mode of resin fracture under osmotic shock is bead cracking (development of internal cracks within the resin beads) rather than fragmentation. This type of fracture is more common with the gel resins. While the development of internal cracks is itself not detrimental to the exchange function of the resin, these cracks could weaken the material and cause it to fragment. Fragmentation of the resin would lead to increased packing density and higher pressure drops in flowing systems. In summary, our test results indicate that ion-exchange resins in general show a marked propensity to physical deterioration under severe osmotic shock conditions. It is further indicated that screening tests should be developed in order to differentiate between strong and weak batches of resin. These screening tests should be of such a nature as to simulate the environment (mechanical, osmotic, or both) in which the ion-exchange resin is to be used. Literature Cited Alvino, W. M. Ind. Eng. Chem. Prod. Res. D e v . I W O a , 19. 271; IWOb, 19, 276; 1980c, 19, 282; 1980d, 19, 624; Alvino, W. M. Ind. Eng. Chem. Prod. Res. Dev. 1981, 2 0 , 391. Chatillon Test (Crush Strength), Dow Chemical Co., Midland, M I , Analytical Method No. 258, 1977. Golden, T. S.; Irving, J. Chem. Ind. 1972, 1 , 837. Jabsco Pump Test, Dow Chemical Co., Midland, M I , Analytical Method No. 14, 1968. Kunin, R. "Ion Exchange Resins", R. E. Krieger: New York, 1972; Chapter 16.
Received f o r review April 19, 1982 Reuised manuscript received August 9, 1982 Accepted October 6, 1982
