Growlhr in Subculture.
KMnOl I10 P.P.M.1
Treotment Time.
Control
Hour9
pH 6.0
pH
7.0
pH 8.5
15 m m
1
I
2
Figure 3. Effect of pH on durotion of treatment required to kill Chlorella pyrenoidoso (Wis. 2005)
ment time required for algicidal activity. The results of the test are presented in Figure 3 as a photograph of filtered subcultures The data indicate that pH had very little effect on the loxicity of potassium permanganate to Chlorella under these conditions. The toxicity of 10 p p.m of Potassium Permanganate even be slightly enhanced at PH 6.0 and Over the at PH 7 0, but more tests would be necessary to check this.
recover and grow when removed from the treatment medium or when the copper is lost from the immediate environment of the algae. Practical comparisons of the algicidal activity of potassium permanganate, Armazide, and Algimycin MT-4 would have to be made on an economic basis, as each product exhibits algicidal properties as tested here. The pH value of the testing medium does not appear to have any great effect between p H 6.0 and 8.5 a n the algicidal properties of potassium permanganate. The importance of algicidal testing by the treatment and subcultures technique used here should be emphasized when considering the use of a chemical under conditions in which it would be difficult to maintain a continuous supply of the chemical in the environment of the algae. A chemical that can kill algae after a certain contact time would have a greai advantage over a chemical that must be present a t all times to prevent the growth of algae. Although potassium permanganate is a n oxidizing agent and can be used u p in time by chemical reactions with algae, as long as sufficient chemical (10 p.p.m.) is added to a cooling tower installation and it is maintained for or 6 hours, enough chemical would be absorbed during this short exposure to cause the death of the algae. this of permanganate the color of the treated WaIer could be used to indicate when additional amounts of the chemical would be required to maintain the desired concentration. However, in installations where droplets of permanganate colored water might be dispersed by the wind, the use of such a chemical might be limited because of possible corrosive action of the concentrated droplets.
Discussion
Comparative toxicity tests have shown that potassium PPI. manganate is a n algicidal agent, as compared to the algistatic properties of copper sulfate. This means that algae treated with sufficiently high concentrations (10 p.p.m.1 of potassium permanganate for a long enough time (2 to 6 hours) will not recover a n removal from the treatment medium or on removing or losing the chemical by dissipation from the treatment medium. In contrast, algae of the type tested here when treated with 10 p.p.m. of copper sulfate for up to 24 hours will
literature Cited
(1) Allen, M. B., Arch. Mikrobiol. 17, 34 (1952). (2) Antonides, H. J., ~ ~ " n ew. r , s.,~ p Microbiol. p ~ 9, 572 (1961). (3) Fitzgerald, G. P., Ibid., 7, 205 (1959). (4) Fitzgerald, G. P., Faust, S. L., [hid., 11, 345 (1963). (5) Fitzgerald, G. P., Faust, S . L., Wnto Scmo,q Wmkorks 110, 296 (1963). RECEI~ED for review December 13, 1963 ACCEPTED February 17, 1964
A CONTOUR MAP OF ANION EXCHANGE
RESIN PROPERTIES R0BE RT E
. A NDE RS0N
Phyical Resmorch Lohorotory, The Oolu Chemical Co., Midiand, Mich
Quaternary ammonium anion exchange resins ore made by chloromethylating and subsequently aminating styrene-divinylbenzene (DVB) copolymer. The chloromethylation reaction does not hove well defined limits. In addition, methylene bridging can occur which alters the topology of the polymer. As a result, resins of a wide range of properties can be mode from a given copolymer composition by changing the chloromethylotion conditions. In addition, resins of apparently identical properties can be made from copolymers of widely different DVB contents. An equation is derived correlating the volume capocity, weight capacity, and moisture content of these resins. From this, o contour map is developed that shows how these properties develop during the chloromethylotion and whot range of properties con be obtained when starting with a copolymer of given DVB content. SULFONATED styrene-divinylbenzene resins, introduced around 1945, gave for the first time an ion exchange material of relatively well defined cornposition and controllable properties such as cross-linkage, shape, size, and capacity. The introduction of the quaternary ammonium resins produced by the chloromethylation and subsequent amination of the same type of copolymer bead was an extension heyand the cation
THE
exchange development. These resins have a considerably more complex nature than their cation exchange counterparts. The quaternary ammonium group is more organic-like than the sulfonic group, and anions present a much broader spectrum of properties than cations. Beyond this, a structural complexity arises inherently in the preparation. The conversion of a styrene-DVB copolymer to a cation VOL 3
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CHLOROMETHY L A T I O N
CH,Cl SULFONATION AM IN AT ION
...CH,-CH--.
CHzCl
Figure 1 . Conversion of styrene-DVB copolymer to cation exchange resin
exchange resin involves one straight forward reaction-sulfonation (Figure 1). With a reasonable amount of art, the sulfonation can be carried out to the extent of one sulfonic group per benzene ring. on the average, and no one yet has announced any success in sulfonating to a higher degree than this. Side reactions appear to be minimal: thus many of the properties after sulfonation directly reflect those of the copolymer. O n the other hand, the conversion of a styrene-DVB copolymer to a quaternary ammonium resin involves two consecutive reactions (Figure 2), a t least one of which: chloromethylation, does not show any well defined limit, and has a major side reaction which can drastically alter the topological structure of the polymer network (Figure 3). Thus, the final properties of the resin depend on both the properties of the original copolymer and the subsequent reactions carried out on it. ?'he original papers on the quaternary ammonium resins, while pointing out the possibility of these complicating factors, dealt only \vith standard commercial resins of set properties: or limited themselves to reaction conditions that minimized the complicating side reaction (5: 6 ) . Source and Treatment of Data
I n attempting to optimize a commercial resin, a \vide variety of preparation variables was evaluated. Three properties were chosen for correlating the data accumulated : dry weight capacity. \vet volume capacity. and water content. T h e data were limited to 'l'ype I resins-- that is, resins made by reacting trimethylamine with chloromethylated styrene-DVB copolymer beads. Data Lvere obtained on about 300 batches representing a wide range of catalyst systems and reaction conditions. The starting copolymers ranged from a cross-linkage of 1 to 247, DVB. Any resin in which one of the three properties appeared questionable was omitted. Since these data represent the brork of several different men over a period of about six years, some scatter Lrould be expected. Again. since some of the batches represent very unusual reaction conditions. there is the definite possibility of nonuniform chloromethylation and('or amination. This nonuniformity can be either from bead to bead within a batch or even within the individual beads. I n spite of these uncertainties, the mass of the data fell into a well defined pattern when plotted as \ret volume capacity us. dry Lveight capacity: the per cent \rater being written beside each point. Tie lines rrere then drawn through areas of constant lvater content. These tie lines. or isograms, are shoum on a reduced scale in Figure 4. T h e shaded portions represent the approximate distribution of the data. The fact that these isograms approximate straight lines converging to the origin suggested that the relationship could be expressed b y a simple algebraic equation. 86
Figure 3. Formation of methylene bridges during chloromethylation
Figure 2 . Conversion of styreneDVB copolymer to anion exchange resin
l&EC PRODUCT RESEARCH A N D DEVELOPMENT
Algebraic Correlation
The requirement is to express the water content in terms of the wet volume and dry weight capacities. The dry weight capacity, Q E , is the number of equivalents of exchange sites.!, per unit weight of dry resin, s, in this work expressed as milliequivalents of chloride ion per dry gram. (Capacities were determined after conditioning the resin Lvith dilute HC1 and rinsing with water until the washings were free from chloride ion. The strong base and total exchange capacities of these Type I resins were found to agree within 1 to 2 7 , as made. This difference increases considerably as they age in use.) It is the reciprocal of the equivalent Ireight of the resin and as such is a measure of the degree of substitution of quaternary ammonium groups in the polymer. The wet volume capacity, Qo, is the number of milliequivalents of chloride ion, f ? per milliliter of fully \vater-s\rollen resin, as measured in a graduate after tapping. This capacity per unit volume is the upper limit of a resin to d o useful \rork in a conventional column use. The Lvater content, 11.'. expressed as per cent of sample iveight. is the amount of water, g , held by a fully swollen, chloride-form resin after centrifugation. Previous \vork has shoivn that many properties of ion exchange resins, such as rate of diffusion and ionic selectivity, are closely related to the water content of the resin. Thus:
QW
=
f/s
Qo
=
f;u
1.1' = g/(s
2
2.0
L
0.4
1
(1)
+ g) x 100
02
0
0.5
I
0
1.5 0,.
2 0 2.5 D R Y WEIGHT
3.0
3.5
4.0
4
5
5 0
C A P A C I T Y , meq l g
Figure 4. Empirically determined water isograms for anion exchange resins
W, W A T E R C O N T E N T ,
T h e tapped volume, u , is related to the weights, s and g, by 0
s L' = Ps
+
~-g
+ up
where empirical density factor for the solids: the density of water, and is the fraction of void volume in the sample p g is
Substituting the values of r ' : s. and g from Equations 1 , 2. and 3 into Iqiiation 4 and simplifying gives
3.0
3.5
%
30
40
1.8 -
c
p s is an
20
2.0
(4)
Po
10
2
E
1.6
E
1.4
E
1.2
-cross-linked tvhile s\vollen in a good solvent. the crosslinking is essentially strain-free, and the polymer \vi11 tend to remain in its s\vollen configuration even Lvhe.1 the solvent is replaced by a poor solvent. .4 similar behavior could be VOL. 3
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87
W, WATER CONTENT, 7, 0 20
D
40
E
+
1.6
v
1.6
E
. t
1.4 t
F-
1.4
1.2
3 1.2 a
0 4
1.0
1.0
z
0.8
2>
0.8
' 0.6
c
0.6
w
I:-I
46
I .8
I. B
s
Yo
2.0
2.0
t
W, WATER CONTENT, 20
W
W
.
5z 0.4
0.4
0
CT
0.2
0.2
0
D
0
0.5
1.0
1.5
ow.
Figure 6.
DRY
2.0
2.5
WEIGHT
3.0
CAPACITY,
3.5
4.0
4.5
5.0
meq./d.
Resin properties attainable with an X 2 copolymer
expected in the chloromethylation reaction since the methylene cross-links are introduced while the polymer is swollen. However, this additional cross-linking causes the polymer to contract. This can be observed during the chloromethylation and is reflected in the increase in Q D observed in the final resin. Apparently, the methylene cross-linking is not introduced randomly. Since the methylene bridging reaction is very dependent on the proximity of aromatic rings, it is probable that the reaction will take place where two polymer chains are intertwined. Once such a new cross-link is formed, it increases the probability that another .link will occur in the same vicinity. This would lead to accelerated. localized cross-linking which would contract the polymer.
0
0.5
1.5
1.0 Ow,
2.0 2.5 3.0 3.5 4.0 DRY W E I G H T CAPACITY, rneq./g.
45
5.0
Figure 7. Resin properties attainable with copolymers of varying DVB content
Data from a couple of 5 1 resins and for a XO.5 resin are also noted on Figure 7. High values of Qlc were obtained and, although one of these resins was made with a highly active catalyst system. they show little tendency to form methylene bridges because of the dilute nature of the copolymer. Yore that the value of Qu of approximately 5 meq. per gram is well over the value for monosubstitution on the aromatic polymer unit of 4.73 meq. per gram. ,These points establish the lower limit of the attainable areas for these lo\s cross-linked resins. Methylene bridging can be induced by chloromethylation of these copolymers in a partially swollen state and the properties boosted into the area above this lo\ver limit. Thus, just as it is possible to obtain widely different resins from a given copolymer. it is also possible to obtain apparently identical resins from M idely different copolymers.
Effect of Copolymer Cross-linkage
An area similar to that for the X2 copolymer exists for each copolymer composition, the size and shape depending on the initial cross-linking. Figure 7 shows areas obtained with X4 and X7.5 copolymers based on much more limited data. As the X number increases. the areas become more restricted. This is due to a balance of factors. T h e minimum Q t obtained is higher since the copolynier is not as free to swell even before methylene bridging starts. T h e maximum Q w is lower perhaps reflecting some steric hindrance. More importantly. the methylene bridging reaction starts a t a lower value of Q w because the aromatic rings are closer together and are in a position to react more frequently. Copolymers of high divinylbenzene are difficult to convert to quaternary ammonium resins because methylene bridging sets in a t a very low degree of chlorornethyl substitution. Jones has shown this same effect in the chloromethylation of linear polystyrene where cross-linking is a function of concentration ( 3 ) . The very limited data for resins made from copolymers of 10ypD\'B and higher are sho\vn. At these high initial crosslinkages. differences in the DVB content appear to play a minor role in determining the properties of the resins. There is no longer a n y indication of an appreciable loop area. While the d a t a are far from conclusive, the X2. 5 4 ,and X7.5 copolymers all appear tu have a common upper limit on their areas, Lvhich is also the same line in which the resins made from the X10 and higher copolymers fall. 88
l&EC PRODUCT RESEARCH A N D DEVELOPMENT
Advantages of Methylene Bridging
Controlled use of the methylene bridging reaction to change the polymer structure during the synthesis of anion exchange resins greatly increases the range of properties available. The major use of these resins is in the demineralization of water, and a major factor in their performance is the relative efficiency with which they can be regenerated to the hydroxide ion form with sodium hydroxide. This efficiency is essentially a function of the selectivity of the resin for mineral-acid anions over hydroxide: the lo\ser this selectivity, the more efficient the regeneration. Chu, 'rvhitney. and Diamond have sho1z.n that this selectivity is closely related to the amount of water surrounding the quaternary ammonium groups ( 7 ) . Consequently, a resin of high homogeneous water content shows a more efficient use of sodium hydroxide in a demineralization cycle than does a resin of lower water content, the wet volume capacities being roughly equal. If the desired high water content is obtained by starting with a copolymer of low DVB cross-linkage and a conventional chloromethylation, the resin has a low wet-volume capacity, is soft. and undergoes large volurnr changes when subjected to osmotic forces. However, use of a low DVR copolymer and controlled methylene bridging can lead to a resin of acceptable wet-volume capacity (1.25 meq. per i d . ) and \yarer content (ca. 55%)) and the resulring good operating efficiencies in demineralization cycles. By careful control of the preparation conditions, it is possible to
obtain a t the same time resins which are very tough physically arid have a reasonable osmotic volume change. For applications other than demineralization: a n entirely diff'erent set of resin properties may be required. I n decolorization cycles, a high \vet-volume capacity may be disadvantageous because the resin may show such a high selectivity for the anionic color bodies that it in time picks u p more than it can accomrriodate volume-wise and is ruptured. t\gain> in sonic difficult separations, as in the anionic complexes of the transuranium elements, a delicate balance among the factors of selectivities. diffusion rates. and mechanical properties of the resin must be obtained. At present, the ideal resin properties for any such application can be found only by experimentation. Ho\vevrr! Figures 5 to 7 provide a convenient tool for correlating such data and setting meaningful specifications on the resin needed. Other Implications of Methylene Bridging
A number of variables are involved in the chloromethylation reaction. Among these are: time and temperature. amount and compo>ition of catalyst, amount and purity of chloromethylmethyl ether, and presence of other solvents. Juggling these interrelated variables and the copolymer cornposi tion to obtain a desired point on Figure 2 is still an empirical process. There certainly is not a unique set of conditions for each point of the map, even starting \vith a given copolymer composition. 'This possibility of variability places a heav)- responsibility on the resin manufacturer to produce resin reproducibly within well defined spccifications. T\vo of the three gross properties discussed here must be specified. A chart such as Figure 5 presents a convenient quality control tool in that placing limits on t ~ v oof the properties defines a n area of acceptability.
Literature Cited
l ' h e fact that resins of identical Qtc: Qc: and Tt' can be made from tvidely differing copolymer compositions raises interesting questions as to ho\v other properties of the resin will reflect this difference in polymer topology. Ion selectivities correlate roughly \vith water content. Osmotic volume changes are extremely sensitive to small changes in resin topology to the point of appearing almost erratic. No other Lvork on such variations are reported in the literature. Certainly attempts to d o prrcise physical-chemical measurements on quaternary ammonium resins must note these topological complications.
(1) C h u , B.. IYhitney, D. C., Diamond, R. M., J . Inorg. N u c l . Chem. 24, 1405 (1962). (2) ,Helfferich, F., "Ion Exchange," p. 75, McGraw-Hill, New Eork, 1962. (3) Jones. G. D.. Ind. Eng. Chem. 44,2686 (1952). (4) Lloyd. \V,G.: Xlfrey, T., Jr., J . Poly. Scz. 62, 301 (1962). (5) Pepper. K. LY., Paisley, H. M.. Young. M. A . . J . Chem. Soc. 1953, p. 4097. (6) \$'heaton, K. M., Bauman, \Y. C., Ind. Eng. Chem. 43, 1088 (1951). RECEIVED for review September 30, 1963 ACCEPTED February 3, 1964
A M M O X I D A T I O N OF ISOBUTYLENE I N A COATED T U B E W I L L I A M
F . B R I L L A N D JOSEPH
H . F I N L E Y
Petro-Tex Chemical Corf , F.WC Chemical Research and Deuelojment Center, Prtnceton, 'Y J . Isobutylene, oxygen, and ammonia react at
500" C. on passing through
a tube coated with a catalytic metal
oxide. Under the most favorable conditions, 80% of the isobutylene reacted forms methacrylonitrile, methacrolein, and acetonitrile. Ammoxidation in a coated tube i s characterized b y good ammonia utilization and tolerance to high reactant concentrations. Over molybdenum oxide, the reaction rate i s dependent upon oxygen concentration and independent of isobutylene and ammonia concentrations. The ammoxidation of methacrolein was investigated and the possible role of aldehyde intermediates in the ammoxidation of olefins considered.
HE first reported reaction of olefins and ammonia in the Tpresence of oxygen t o yield unsaturated nitriles ( 4 ) described the oxidation of isobutylene (2-methylpropene). Subsequent Lvork on this reaction, now generally known as amnioxidation, has been concerned almost exclusively with propylene and has led to the development of some excellent catalysts (9) for this olefin. Furthermore. information concerning the possible mechanism of the reaction has been obtained ( 7 ) 7). Initial attempts in our laboratories to develop a process for thr production of methacrylonitrile led to the discovery that amnioxidation proceeded readily on passing isobutylene through a n unpacked tube: the inside surface of \yhich had catalytic activity. Good methacrylonitrile selectivities and efficient utilization of ammonia, under the proper conditions:
coupled with the absence of local overheating, made the coated tube reactor appear to be superior to a fixed bed for studying reaction variables. Experimental
Reactor. T h e reactors consisted of 24-inch tubes of 304 stainless steel, Vycor, or ceramic, 22-mm. internal diameter, heated by a Hevi-Duty Rlultiple unit furnace. Gases were metered from calibrated rotameters through a manifold to the head of the reactor. Temperatures recorded in this report are the maximum temperatures measured in a thermowell: placed down the center of the reactor. T h e effluent was sampled immediately belo\v the heated portion of the reactor. through a sampling port lagged with heating tape, using an insulated syringe kept a t 160' C. VOL. 3
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