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Ind. Eng. Chem. Prod. Res. Dev. 1883, 22, 272-276
Brown, R. A. Batteries Today, 1080, 76(2/3), 85. Cammarota, V. A., Jr. "Zinc-Mineral Commodity Proflles MCP-l2", US. Dept. of the Interior, Bureau of Mines: Washington, DC, May 1978. Cammarota, V. A., Jr. "Mlnerals Yearbook, 1980"; U.S. Bureau of Mines, U S . Government Prlnting Office: Washington, DC, 1981; p 883. Cammarota, V. A. Jr.; Babltzke, H. R.; Hague, J. M. "Mineral Facts and Problems", US. Bureau of Mines Bull. 687, U.S. Dept. of the Interior, Bureau of Mlnes: Washington, DC, 1975; pp 1223-1238. Coliart, A.; Tombras, C. P., Ind. Res. Dev., 1982, 24(2), 170. Dyson, W. H.; Schreier, L. A.; Shoiette, W. P.; Salklnd, A. J. J . Electrochem. Soc., 1088, 775, 588. EIC Corporation "A Survey of Metallurgical Recycllng Process"; Argonne National Laboratory Report ANLIOEPM-79-2, Argonne, IL, March 1978. Avail. NTIS. Gordon, A. R. "Symposium on Advances In Extractive Metallurgy, 1977"; Jones, M. J., Ed.; Institute of Mining and Metallurgy: London, 1977; p 153. Hoare, J. P. "The Electrochemistry of Oxygen", Interscience: New York, 1988. Kellogg, H. H. "Lead-Zlnc-Tin '80, Proceedings, TMS-AIME World Symposlum on Metallurgy and Environmental Control", Las Vegas, NV, Feb 1980; Cigan, J. M.; Mackey, T. S.; O'Keefe, T. J., Ed.; The Metallurgical Society of AIME: New York, 1980; p 28. Ketchum, E. C. U.S. Patent 592055, Oct 19, 1897. Klunder, K. W.; Katz, M. J. Batteries Today, 1080, 76(2/3), 107. Klein, M.; Dube, D. "Deslgn and Cost Study of NickeVZlnc Batteries for Eiectrlc Vehicles"; Argonne National Laboratory Report, ANL-K76-3541-1, Argonne, IL, 1976. Avail. NTIS. Knobler, R.; Moore, T. S.; Capps, R. L. Errmetall., 1970, 32, 109. McCullough, J. G. "Lead-Zlnc Update", Rausch, D. 0.; Stephens, F. M.; Marlacher, B. C. Ed.; Society of Mining Engineering: New York, 1977; p 331. Meek, R . L. "Proceedings, Extractive Metallurgy Division of AIME, Symposium"; Cleveland, Dec 1968, Henrie, T. A,; Bakder, D. H. Ed.; AIME: New York, 1989; p 306.
Meek, R. L. Gulf South Research, New Orleans, LA, personal communication, Feb 1981. Meisel, G. M. J. Metals, 1074, 28, 25. Mining Mag. 1070, 740, 551. Opie, W. R. AMAX Inc., Carteret, NJ, personal communlcation, Feb 1981. Pallanche, R. A. "Zinc, The Sclence and Technology of the Metal, its Alloys and Compounds"; Champion Herbert, Ed.; Reinhold Publishing Corp.: New York, 1959; p 103. Pooley, F. D.; Wheatley, B. I.; Blackmore, R.; Jones, H. Processing, 1081, 27(2), 38. Radtke, S. F. "Lead-Zinc Update"; Rausch, D. 0.; Stephens, F. M.; Mariacher, B. C. Ed.; Society Of Mining Engineering: New York, 1977. Schlechten, A. W.; Thompson, A. P. "Klrk-Othmer Encyclopedia of Chemical Technology", 2nd ed.;Mark, H. F.; McKetta, J. J.; Othmer, D. F. Ed.; Interscience: New York, 1970; Voi. 22, p 555. USBM "Minerals and Materiais/A Monthly Survey"; U.S. Bureau of Mines; Washington, DC, Feb 1980. USBM "Mlnerals and Materlals/A Monthly Survey"; U S . Bureau of Mines; Washlngton, DC, Jan 1982. Wedow, H., Jr.; Kulsgaard, T. H.; Heyl, A. V.; Hall, R. B. " U S Mineral Resources, U S . OeOlOglCal Survey Professional Paper 820", Brobst, D. A,; Pratt, W. P. Ed., U.S. Government Prlnting Office: Washington, DC, 1973; p 697. Yao, N. P.; Christianson, C. C.; Elliott, R. C.; Lee, T. S.; Miller, J. F. "Proc. EVC Expo '80 Conf."; St. Louis, MO, May 1980, Paper 8029, Electric Vehicle Council: Washington, DC, 1980. Yao, N. P.; Mlller, J. F. "Lead-Zinc-Tin '80. Proceedlngs, TMS-AIME World Symposium on Metallurgy and Environmental Control"; Las Vegas, NV. Feb 1980; Cigan, J. M.; Mackey, T. S.; O'Keefe, T. J., Ed.; The Metallurgical Society of the AIME: New York, 1980; p 871.
Received for review July 20, 1982 Accepted October 22, 1982
Application of Weak Magnetic Fields To Influence Rates and Molecular Weight Distributions of Styrene Polymerization Nlcholas J. Turro Department of Chemistry, Columbia University, New York, New York 10027
The efficiency of emulsion polymerization and the average molecular weight of the polymers formed are found to be significantly increased by the application of laboratory magnetic fields when photoinduced Initiation is sensitized by oil-soluble ketones, but not when aqueous soluble thermal initiators are employed. No magnetic field effects are observed for photoinitiited polymerization of styrene in toluene solution. These results are interpreted in terms of the postulate that for oil-soluble photoinitiators, micellized radical pairs are produced at the initial stages of polymerization and that micellized triplet pairs are required for the effective operation of external magnetic field effects because the efficiency of radical escape out of the micelle aggregate in the early stages of polymerization is significantly influenced by the application of weak magnetic fields.
Introduction The Basis for Sizable Magnetic Field Effects in Organic Reactions in Solution. The extreme weakness of achievable magnetic effects in the energetic sense requires that a kinetic (rates) rather than a thermodynamic (energy)basis be found (Atkins, 1976; Atkins and Lambert, 1975) if magnetic fields are to influence chemical reactions. Such a basis is available in the Zeeman splitting of magnetic states of radical pairs. The most commonly encountered example of the latter is the triplet radical pair (3RP)that is commonly produced by photoexcitation of ketone photoinitiators (Turro, 1978). The absorption of light does not cause a change in magnetic properties of the absorbing molecule; only electron orbital occupancy is changed (Turro, 1978). Since most organic molecules are singlets (spins paired) in their ground states, absorption produces an electronically excited singlet state. The orbital uncoupling of the electrons facilitates the change in ori0196-4321/83/1222-0272$01.50/0
entation of an electron spin and its associated magnetic moment, so that most excited singlet ketones convert quite efficiently to triplet (spins unpaired) ketones. The triplet ketone is a rather metastable state and may persist for s in the absence of a deactivation reaction or quenching process. The triplet of a ketone consists of three magnetic states that possess identical energies and which rapidly interconvert in the absence of an applied laboratory field. The common reactions of a ketone triplet are homolytic cleavage to produce a triplet radical pair (eq 1)or hydrogen abstraction which also produces a triplet radical pair (eq 2). R-CO-R R-CO-R
hu
hu
0 1983 American
3R-C0
+R
3R-COH-R
(homolytic cleavage)
+X
Chemical Society
(1)
(hydrogen abstraction) (2)
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 2, 1983 273 b t b
T H E STATES OF A SPIN CORRELATED RADICAL PAIR
SCAVENGABLE
RANDOM THE T R I P L E T STATE(S1 A
r
>
RADICALS
THE SINGLET STATE
FREE
PRIMARY GEMINATE PAIR
Hz
Tt
T-
s
TO
Figure 1. Vector model of the triplet and singlet states of a radical pair (or diradical). The direction of an arbitrary magnetic field H, is used as an orienting directing direction about which the electron spin vectors precess.
PRIMARY SECONDARY SOLVENT GEMINATE SEPARATED PAIR PAIR
Figure 3. Schematic representation of pathways to form primary geminate (caged) pairs, primary solvent separate pairs, secondary geminate (caged) pairs, and random free radicals. @
WATER
MOLECULE
DETERGENT MOLECULE
eOi
TYPICAL IONIC DETERGENTS
S
S
CH~(CH~),,SO NO@ ~
when o < when a > &ii Figure 2. Schematic representation of the Zeeman interaction j3gH on the energetic separation of T+, T-,and To.When the Zeeman interaction is small relative to other interactions (such as the hyperfine interaction whose strength is given by a, the hyperfine splitting constant), the triplet and singlet states are energetically degenerate and all three triplet sublevels interconvert with the singlet state. When j3gH is large relative to a, only To S intersystem crossing occurs. The effect of BgH is to energetically split T, from S and thereby inhibit intersystem crossing from or to these sublevels.
-
In eq 1and 2 the triplet ketone is shown producing caged, geminate triplet radical pairs (denoted by the bar over the radical pair). Like the ketone triplet, these triplet radical pairs consist of three magnetic states of identical energy in the absence of an applied field. The three states are shown pictorially in Figure 1. When a magnetic field is applied to a sample containing the triplet radical pairs, one of the three is raised in energy, (T,), one of the three is lowered in energy (T-),and one of the three remains unchanged in energy (To). Furthermore, since the singlet state, S, has no net magnetic moment (spins paired) its energy is unchanged by application of a magnetic field. This means that S has the same energy as T+,T-, and To in the absence of magnetic field, but in the presence of a magnetic field, only To and S possess identical energies (Figure 2). This difference in the energies of S and [T, and T-] when a field is present provides a ready basis for magnetic field effects on the cage reactions of triplet radical. Cage Reactions of Radical Pairs. Cage reactions of radical pairs generally fall into two classes: combination and disproportionation. However, it has been established that as a rule only singlet radical pairs can undergo cage reactions. The reason for this rule is that the molecular products of combination and disproportionation are singlets. Because the Law of Spin Conservation must be maintained during an elementary process, such as a combination or disproportionation, it follows that the immediate precursors of such cage products must be singlet radical pairs. However, in the photolysis of ketones, as we have seen, triplet radical pairs are typically produced initially. This means that there must be a conversion of the caged triplet radical pair into the singlet radical pair (a
inside
SDS
TOPOLOGICAL MODEL OF MICELLE
bound0 r y
Figure 4. Schematic model of micelle aggregates formed by addition of HDTCl or SDS to water.
process called intersystem crossing) before a cage reaction can occur. In homogeneous solutions the triplet radical pair has another option to intersystem crossing and cage reaction: separation of the radical fragments and the formation of random free radicals (Figure 3). The latter are the active species responsible for initiation of polymerization. Given now that (1)application of a magnetic field will prevent T, and T- from intersystem crossing to S, and (2) triplet radical pairs become reactive free radicals if they do not intersystem cross, we have a basis for magnetic field effects on the efficiency of initiation of polymerization: Under the proper conditions the efficiency of initiation of polymerization by a triplet radical pair will increase when a magnetic field is applied to the sample. What are the "proper" conditions? Basically, the necessary conditions are that the "triplet" nature of the radical pair must be preserved for a period of time that is long enough for the To S intersystem crossing mechanism to occur (Kaptein, 1975). Typically, this time is of the to lo-' s. However, in common organic solorder of vents, the rate of separation of triplet radical pairs into s. This means free radicals is of the order of 10-l' to that the ordinary solvent cage provided by typical solvent molecules is too weak to contain the triplet radical pair for a long enough period of time to allow for intersystem crossing. For magnetic effects to be significant, the radical pair must be contained in a "super cage" that can maintain the fragments for a long enough period of time for To S intersystem crossing to occur. Micelle aggregates, which are formed by the addition of ionic detergents to water (Figure 4), provide such a su-
-
-
274
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 2, 1983 WHEN
WHEN
,H = O ( T H E
EARTH'S MAGNETIC F I E L D )
> a
Figure 6. Reaction scheme for the photolysis of dibenzl ketone in micellar solution. The encircled species represent micellized molecules or radicals.
Figure 5. Schematic representation of the influence of a laboratory magnetic field on the efficiency of the cage reaction of a triplet radical pair in a micelle. In the earth's field ISC from Tt and Toto S is maximal and the fraction a of triplet radical pairs undergo cage combination. When the applied field is strong enough to inhibit T, S ISC, the fraction of cage combination (in the limit) decreases to a / 3 .
-
percage environment for triplet radical pairs. The time for escape of small organic molecules or radicals from a The basis typical micelle is of the order of lo4 to for a magnetic field effect on triplet radical pairs in micelles goes as follows (Figure 5): In the absence of magnetic field, all three triplet levels will intersystem cross to S and a large cage effect will occur (in the limit 100% cage). When a magnetic field is applied, up to two-thirds of the triplet pairs (T, and TJ will not be able to cross to S and therefore will not be able to undergo cage reactions. Instead, these radical pairs will form free radicals that are effective in initiating polymerization. Thus, the efficiency of initiation of polymerization may be varied considerably if the proper conditions are met. Now the question arises as to the magnitude of the magnetic field needed to render T, and T- inert to intersystem crossing. Here we have a pleasant surprise: magnetic fields of the order of those produced by ordinary magnetic stirrer bars (50-500 G ) are sufficient! Thus, T, and T- are typically completely inhibited from intersystem crossing to S a t fields of several hundred gauss. We now give some actual examples of magnetic field effects on polymerization of styrene and show that the rate of polymerization and the molecular weight of the polymer produced are significantly influenced by the application of weak magnetic fields. Photoinitiation by Dibenzyl Ketone (DBK). The photolysis of deaerated solutions of DBK in aqueous micellar solutions has been shown to proceed predominantly via an initial homolytic a-cleavage of the TIstate, followed by decarbonylation and coupling of benzyl radicals to yield 1,2-diphenylethane (DPE) in the absence of radical scavenger (Figure 6). The cage effect (defined as the yield of cage product, DPE, relative to DBK disappearance in the presence of radical scavenger in water) in aqueous micellar hexadecyltrimethylammonium chloride (HDTCI), is -32% at earth's magnetic field and -17% at 500 G. It has been proposed that a magnetic field increases the efficiency of escape of radicals from radical pairs produced in micellar aggregates by inhibiting the competing geminate cage recombination (Turro et al., 1980, 1981). Figure 7 shows that relatively weak external magnetic fields can dramatically influence the average molecular
I'
;1
01 0
IO00
do0
3d00
-'
5&0
4d00
MAGNETIC FIELD-
(GI
Figure 7. Magnetic field dependence of the average molecular weight (determined by viscosity measurements) of polystyrene produced by emulsion polymerization photoinitiated by dibenzyl ketone.
3
6
12
9
RETENTION VOLUME
I
15
mil-
Figure 8. Typical size exclusion chromatograms of polystyrene pfoduced by EP in the earth's field (-0%, dashed line), and in a moderately strong magnetic field of 5000 G (solid curve).
weight (M,) of polymer photoinitiated by DBK in the emulsion polymerization of styrene ( T w o et al., 1980; for experimental details see Turro et al., 1983). From the figure it is seen that for photochemical initiation of polymerization by DBK (a) molecular weights (lo6)achieved are comparable to those achieved by employing conventional water soluble thermal initiators such as persulfates, (b) the average molecular weight (MI) of the isolated polystyrene increases by a factor of 5 with increasingly field strength, and that the major effect of magnetic field is in the range of 0-500 G. The isolated yield of polymer formed in comparable periods of irradiation also varies with magnetic field in a manner that is qualitatively the same as MI; i.e., polymer yields are higher (for a given dose of irradiation) as the field is increased between 0 and 500 G. It was also found that neither the MI of polymer produced by water-soluble thermal initiator sodium persulfate nor
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 2, 1983 275
0”
h v . INITIATOR TOLUENE
MICELLE SWOLLEN WITH MONOMER
WATER INITIATOR
0
3
6
9
R E T E N T I O N VOLUME (mil
12
\
Figure 9. Typical size exclusion chromatograms of polystyrene produced by solution polymerization of styrene (-0 G, solid curve, 5000 G, dashed curve).
the oil-soluble thermal initiator azobis(isobutyronitri1e) varied with application of an external magnetic field. Figure 8 shows a typical size exclusion chromatogram of the polystyrene produced in emulsion polymerizations of styrene with sodium dodecyl sulfate (SDS) as a micelle-forming surfactant and DBK as a photoinitiator. The solid curve shows the characteristic higher molecular weight fraction produced in the presence of a magnetic field and the lower molecular weight fraction produced in the earth’s magnetic field (-0.5 G ) . Figure 9 shows results that are typical of solution polymerization of styrene: relative to EP, lower molecular weight polymer is produced and the molecular weight is not influenced by magnetic field up to field strengths of 10000 G . In order to determine which stage of polymerization is most sensitive to external magnetic field effects, polymerization was initiated at one magnetic field and then field strength was changed after the initiation step was completed. For example, if the polymerization were initially allowed to proceed to -20% conversion in the earth‘s field and then a magnetic field were applied, the M,values observed were identical with those obtained when the entire polymerization is conducted in the earth‘s magnetic field. Conversely, if the polymerization was initially allowed to proceed to -20% conversion in a magnetic field, the M,values observed were identical with those of 5000 G. Thus, the initial stage of polymerization completely determines the M,characteristics of the product. Discussion An idealized schematic description of a conventional thermal emulsion polymerization (Blackley, 1975) is shown in Figure 10. Aqueous-solubleinitiators are employed so that initiation will typically involve entry of a singlet radical into a monomer swollen micelle. The rate of termination is relatively slow compared to propagation because it requires the entry of a second radical (shown in Figure 10) or association of two growing polymer chains. When an oil-soluble initiator is employed, radicals are produced in pairs (Figure 11)resulting in a competition between chain termination and escape of a radical from the propagating locus. If escape occurs, then the resulting situation is qualitatively equivalent to that produced by an aqueous soluble initiator, Le., a single radical in a propagating locus. Three idealized stages are considered as occurring during a conventional emulsion polymerization (Figure 12): (I) an initial stage in which the loci of initiation of polymerization are micelles swollen with monomer molecules, during which (a) dispersed monomer droplets serve as a
I
MONOMER DROPLET
POLYMER MICELLE
IN
‘
15
DETERGENT MOLECULE
/
’
\
\
‘
I
/
\
POLY M ERI 2 AT ION T E RMlNATE D
POLYMER PARTICLE SWOLLEN WITH MONOMER
Figure 10. Schematic representation of the conventional mechanism for EP initiated by a water soluble initiator. See text for discussion.
Figure 11. Schematic representation of the reaction pathways for radical pairs in EP during the initial stages of polymerization.
II
+ + CONVERSION
“/e
I
-
IL
m D
Micelle
Polymer Par t i d e
Polymer Particle
M
Monomer Droplet
Monomer Droplet
Figure 12. Schematic representation of the conventional stages of EP. See text for discussion.
reservoir of monomer molecules, (b) “nuclei” of growing polymer particles are produced in micelles, and (c) toward the end of which (10-2070 conversion of monomer) the number and size of growing polymer particles increase and the number of micelles decreases because detergent molecules become preferentially adsorbed on growing polymer
Ind. Eng. Chem. Prod. Res. Dev. 1983,22, 276-279
276
particles which swell with monomer that is available from the dispersed droplet reservoir; (11) a second stage during which (a) the major growth of polymer occurs as the volume of monomer swollen polymer particles increases and the volume of monomer reservoir decreases, and (b) the loci of polymerization are considered to be exclusively the polymer particles; (111)a final stage during which the monomer disappears completely and the unreacted monomer exists only in swollen particles. What is the mechanistic basis of the magnetic field effect and at what stage(s) of the polymerization does it operate? From recent work (Turro and Kraeutler, 1980) on cage reactions of triplet radical pairs in micelles, we postulate that it is the Zeeman splitting of the Ti triplet levels from the singlet level (Figure 5) which causes the magnetic field effect by decreasing Ti S intersystem crossing, and thereby allows for an increase in the efficiency of radical escape. A more efficient escape of radicals simultaneously allows a more efficient initiation of polymerization and formation of a greater number of polymer particles (by reducing the extent of radical pair combination in micelles), a more efficient overall initiation (by escaping radicals which enter other micelles), and a less efficient termination (by inhibiting the extent of combination of propagating radicals and initiator radicals). This postulate is consistent with the relatively low magnetic fields needed to influence polymerization, because fields of the order of 500 G are sufficient to suppress intersystem crossing in typical carbon-centered radical pairs.
-
Conclusion
Emulsion polymerization photoinitiated by DBK is subject to external magnetic field effects. The observed average molecular weight increase which occurs upon ap-
plication of laboratory magnetic field results from a more efficient escape of a radical from the radical pairs produced at the early stage of polymerization. The conventional aqueous soluble thermal initiator (sodium persulfate) or an oil-soluble initiator that thermolyzes or photolyzes to produce micellized singlet radical pairs [AIBN] does not display significant external magnetic field effects on the emulsion polymerization. Triplet radical pairs generated from oil-soluble initiators, however, provide a proper starting point for the observation of significant magnetic field effects. Acknowledgment
The author thanks the National Science Foundation and the Air Force Office of Scientific Research for their generous support of this work. This paper is based on material presented in a lecture a t the Middle Atlantic Regional Meeting of the American Chemical Society at the University of Delaware, April 1982. Registry No. Styrene, 100-42-5. Literature Cited Atkins, P. Chem. i3r. 1978, 214-218. Atkins, P.; Lambert, T. P. Ann. Rep. Chem. SOC.A 1975, 72, 76-88. Blackiey, D. C. "Emulsion Polymerization"; Wlley: New York, 1975. Kaptein, R. Adv. Free Radical Chem. 1975, 5 , 319-380. Turro, N. J. "Modern Molecular Photochemistry"; Benjamin/Cummlngs: Menlo Park, CA, 1976. Turro, N. J.: Kraeutler, B. Acc. Chem. Res. 1980, 13, 369-377. Turro, N. J.; Chow, M.-F.; Chung, C.J.; Tung, C.-H. J . Am. Chem. SOC. 1980, TOZ, 7391-7393. Turro, N. J.; Chow, M.-F.; Chung, C.J.: Tanlmoto, Y.; Weed, G. C. J. Am. Chem. SOC. 1981, 103, 4574-4576. Turro, N. J.; Chow, M.-F.; Chung, C.J.; Tung, C.-H. J . Am. Chem. SOC. 1983, in press.
Received for review July 26, 1982 Accepted November 22, 1982
Removal of Nitrogen Compounds from Lubricating Oils C. A. Audeh Mobil Research and Development Corporation, Princeton, New Jersey 08540
Anhydrous hydrogen chloride adsorbed on a solid is an effective reagent for reducing the nitrogen content of lubricating oil base stocks to very low levels. This removal of nitrogen compounds is selective, does not change the sulfur content of the stock, and improves color and oxidative stability. Although many solids may be used for adsorbing HCI gas, the efficiency of nitrogen removal with respect to the amount of HCI adsorbed depends on the solid support. Amorphous silica-alumina cracking catalyst is the solid support of choice and can be regenerated for reuse without loss of HCI adsorptive capacity. The adsorbed HCI substantially removes an equimolar amount of nitrogen compounds from the base stock. Dehydrated base stock is processed without solvent, at about 100 O C . An HCI guard after the denitrogenation step is included to ensure that the product oil is acid free. Since this is an adsorptive technique, oil containing small amounts of nitrogen could be easily processed with a minimum of loss.
Introduction
Nitrogen-containing compounds are found in crude oils in various amounts and are usually concentrated in the heavier distillates. For example, McKay and Latham (1975) have shown that high-boiling distillates obtained from crude oils of varying origins contain twice the weight percent of basic compounds, determined as nitrogen, as the lower boiling distillates. In catalytic processing of
distillates nitrogen compounds are not desirable and affect catalyst activity. Both color instability of processed oils and formation of gums and lacquers during the storage and use of oils and fuels have also been related to the presence of nitrogen compounds, even in trace amounts (Oswald and Noel, 1961; Katzmark and Gilbert, 1967). For these reasons, the removal of nitrogen from distillates and products is desirable.
0196-4321/83/1222-0276$01.50/00 1983 American Chemical Society
