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smaller than 1pm, possible distortion of droplet size by the cover slip, and limited sample size.
Conclusions Droplet-size distributions and the corresponding surface areas of water-in-oil emulsions prepared under a wide range of conditions were measured with a particle sizer. The emulsions were uniquely and reproducibly characterized. Hydrocarbon solvents studied included decane, toluene, and IPS. The emulsifier speed ranged from 9OOO to 22 0oO rpm, the emulsification time from 1to 4 min, and the aqueous weight percent from 30 to 60%. Although these emulsions were prepared for use in ELM systems, the technique coule be applied to emulsions which arise in other applications. Emulsifier speed and emulsification time had the greatest effect on the surface area created. In more viscous hydrocarbon solvents, however, the aqueous weight percent became a controlling factor on the amount of surface area produced. Three variables (speed, time, and weight percent) were adequate for predicting the surface area created over the ranges studied. In low-viscosity hydrocarbons, a synergistic effect existed between speed and time of emulsification. Highest surface areas were obtained for high emulsifier speeds and long emulsification times. The breadth of the droplet-size distribution increased under these conditions. Emulsions with higher internal surface areas extracted copper faster than those with lower internal surface areas. This result agrees with the data of Frankenfeld et al. (1981) and Hayworth (1981) but is in conflict with the resulh of Teramoto et al. (1983a). The data of Teramoto et al. do not permit normalization for external surface area, and therefore, comparisons are difficult. The effect of internal
surface area on mass transfer is currently the subject of a more detailed study. Acknowledgment The authors gratefully acknowledge the laboratory support of Shari Hanson and Erlinda Kiefel. Literature Cited Bock,J.; Kleln, R. R.; Vaiint, P. L., Jr.; Ho, W. S. Preprint from AIChE Annual Meeting, New Orleans, LA, 1981. Bock, J.; Vaiint, P. L., Jr. Ind. Eng. Chem. Fundam. 1982, 21, 417-22. Box, G. P.; Hunter, W. 0.;Hunter, J. S. "Statlstlcs for Experiments"; Wliey: New York, 1978; Chapter 10. Boyadzhlev, L.; Bezenshak, E. J . Membr. Sci. 1883, 14, 13-18. Cahn, R. P.; U, N. N. Sep. Sci. 1974, 9 . 505. Frankenfeld, J. W.; Cahn, R. P.; Li, N. N. Sep. Sci. Techno/. 1881, 16(4), 385-402. Gu, 2.; Kurzeja, R. D.; Wasan, D. T.; Li, N. N. "Interfacial Phenomena in Metal Ion Extractlon by Liquki Membranes from Wastewater Containing Ligands", Paper No. 5 4 , 75th Annual AIChE meeting, Washington, DC, Nov 1983. Hayworth, H. C. CHEMTECH 1981, 6, 342-346. Hayworth, H. C.; Ho, W. S.; Burns, W.A,, Jr.; Li, N. N. Sep. Sci. Techno/. 1883, 18(8),493-521. Kim, K.; Chol, S.; Ihm, S. Ind. Eng. Chem. Fundam. 1983, 22. 167-172. Li, N. N. US. Patent 3410794, 1988. Martin, T. P.; Davies, G. A. Hydrometa//urgy 197W1977, 2, 315-334. Teramoto, M.; Sakal, T.; Yanagawa, K.; Ohsuga, M.; Mlyake, Y. Sep. Sci. Techno/. l983a, 18(8),735-764. Teramoto, M.; Takihana, H.; Shlbutanl, M.; Yuasa, T.; Hara, M. Sep. Sci. Techno/. 1983b, 18(5),397-419. Teramoto, M.; Takihana, H.; Shlbutanl, M.; Yuasa, T.; Miyake, Y.: Teranishi, H. J . Chem. Eng. Jpn. 1981, 74(2), 122-128. Terry, R. E.; Ll, N. N.; Ho, W. S. J . Membr. Sci. 1982, 10, 305-323. Volk, W. "Applied Statistics for Engineers"; McGraw-Hili: New York, 1989; pp 235-259. Volkei, W.; Haiwachs, W.; Schugerl, K. J . Membr. Sci. 1980, 6 , 19-31. Weiss, S.: Grlgorlav, V.; Muhl, P. J . Membr. Sci. 1882, 12, 119-129. Yagodin, G.; Lopukhln, Y.; Yurtov, E.; Guseva, T.; Serglenko, V. "Extraction of Blood from Cholesterol Using LiquM Membranes"; Proceedings, International Solvent Extraction Conference, Denver, CO, 1983.
Received for review August 24, 1984 Accepted December 20, 1984
Slow Release Herbicide Formulation Based on Castor Oil and Its Derivatives Shukla Bhattacharya, Shyamal K. Sanyal, and Ram N. MukherJea' Process Engineering and Technology Laboratory, Chemical Engineering Department, Jadavpur University, Calcutta 700032, India
Castor oil and its polyol derivatives have been used as a matrix to prepare controlled-release (2,4dichlorophenoxy)acetic acid (2,4-D) formulations, and their release characteristics have been studied both in vivo and in vitro. The initial release rate has been found to be dependent on the hydrophilicity of the formulations. The pH of the hydrolysis also strongly affects the release characteristics; the release rate increases sharply in the alkaline range (pH 10). Cross-linking via carbamate linkage has been found to retard the release rate. Compared to formulations based on natural or synthetic polymer matrices, such castor oii-based preparations are likely to be more suitable for agricultural applications requiring shorter release period of the toxicant.
Introduction Controlled release herbicide formulations are gaining increasing importance in an effort to reconcile chemical control of weeds with the need for preservation of environmental quality. So far most of the activities have been directed toward formulations in which the pesticide is physically dissolved or dispersed in a polymer matrix (Cardarelli, 1976; Kydonieus, 1980). Herbicide 14ACEB1 is one such controlled-release formulation in which butoxyethanol ester of 2,4-D is dispersed in natural rubber for aquatic weed control (Bille et al., 1971; Zweig, 1977). An increasingly attractive approach to designing new
o 196-432 11851 i224-0274$0 1.5010 0
controlled-release systems is that of attaching the agent by covalent or ionic bond to a macromolecule as a pendent group wherefrom the active agent is released by hydrolytic and enzymatic bond cleavage. Of the various possible reaction paths, the most attractive system from the ecological standpoint might be the one that is based on a naturally occurring biodegradable substrate with which the pesticide is attached through labile bonds. Neogi and co-workers (Neogi, 1970; Allan et al., 1971; Neogi and Allan, 1974) reacted 2-methyl, 4-chlorophenoxyacetic acid with kraft lignin and Douglas fir bark and 2,4-D with cellulose and the formulations were reported 1985 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 2, 1985
to be active in lettuce seed germination s t d y . Allan (1970; 1971; 1974; 1968) has combined the herbicide with forest, agricultural, and other waste products which include bark, cellulose, lignins, corncobs, chitin, alginic acid, and oat hulls. These are reacted either directly with the pesticide or via a bridging group. Allan et al. (1977a) later compared the release of 2,4-D from differently substituted a-cellulose formulations using laboratory and bioassay techniques. The acid chloride of 2,4-D has also been reacted with unmodified, cyanoethylated, and cross-linked starches in pyridine. Hydrolysis studies reported that the combination liberated varying amounts of 2,4-D and 2,4-D esters by both ester and glycosidic bond cleavage (Mehltretter, 1974). In reactions of herbicide derivatives with natural polymers, a multitude of side reactions may occur which drastically alter the resulting polymer structure from that predicted from analogous organic reactions on small molecules, greatly affecting the release profile (McCormick et al., 1983). Incomplete solubility of the natural polymer and heterogeneous reaction conditions often decrease the yield. Moreover, unreacted herbicide is often difficult to remove during purification, and this obviously interferes with subsequent activity studies. Because of these experimental difficulties, only a very few of the reported formulations have been thoroughly characterized. Lichatowitch (McCormick and Lichatowitch, 1979) reported a number of polymeric pesticide formulations using naturally occurring polysaccharides under homogeneous reaction conditions utilizing the solvent system N,N-dimethylacetamide and LiCl or LiBr salt. Only a few formulations have progressed beyond laboratory evaluation. A controlled release herbicide (Allan et al., l972,1973,1975,1976,1977b, 1978) with long period of release, primarily intended as a reforestation aid, has been successful in field trials. However, controlled-release formulations to be used successfully in agriculture should have a shorter period of release. In the present study castor oil and its derivatives have been selected as matrices for developing slow-release 2,4-D formulations. Castor oil has the proper functionality for attaching pendent groups, and the presence of a double bond in it offers the potential to increase its hydrophilicity required for efficient release of the active agent in aqueous medium. It is possible to change the amount of hydroxy functionality of the product to the desired extent by altering the reactants and the reaction conditions. Thus starting with castor oil and its chemically modified derivatives it is possible to synthesize controlled-release formulations having short to long range release characteristics. Moreover, castor oil is known to hydrolyze to ricinoleic acid and glycerol with no apparent environmental consequences (Sjogren, 1975). The present investigation describes in detail the synthesis of 2,4-D esters of castor oil and castor oil based polyols. The effect of increasing molecular weight through carbamate linkage has also been included in the study. The effect of change in pH of the hydrolysis medium on release rate has been investigated in detail. The biological effectiveness of the prepared formulations has been evaluated by laboratory bioassay technique. Experimental Section Materials and Methods. (a) (2,4-Dichlorophenoxy)acetic acid (2,4-D) was recrystallized from benzene, castor oil (containing over 82% triglyceride of ricinoleic acid; its fatty acid composition: saturated acid 0.5%, hydroxy acid 90%, oleic acid 0.5%, and 9,12-octadecanoic acid 3.0%) was freed from free fatty acid by standard procedure.
275
Toluene diisocyanate (8020 Bayer) was used as received; acetic anhydride (E. Merck), pyridine (E. Merck), thionyl chloride (BDH), and other solvents used were distilled and dried before use. (b) Preparation of Polyols from Castor Oil. Epoxidation of castor oil was carried out with peracetic acid prepared from hydrogen peroxide and acetic anhydride. Peracetic acid solution was placed in a three-necked flask equipped with a mechanical stirrer, thermometer, and dropping funnel. The castor oil was added during 30 min at 20-25 "C. The reaction was continued for an additional 3 h. The resulting mixture was treated with dilute H2S04 at 40 "C for 1 h and kept overnight. (c) Preparation of 2,4-D Esters of Castor Oil/Polyols. The acid chloride of 2,4-D was prepared by refluxing (2,4-dichlorophenoxy)aceticacid with thionyl chloride. The excess thionyl chloride was removed by distillation. Pyridine solution of castor oil/castor oil polyols was taken in a three-necked flask fitted with a mercury-sealed mechanical stirrer. The flask was purged with pure dry nitrogen gas, and (2,4-dichlorophenoxy)acetylchloride in dry benzene was added dropwise with cooling and with continuous stirring. The temperature was raised gradually and reflux continued for 4 h. Benzene and excess pyridine were removed by distillation under reduced pressure. The oily mass was poured into cold water and then extracted with ethyl acetate. The ethyl acetate extract was washed with dilute sodium bicarbonate solution to remove unreacted 2,4-D and then with water, dried over anhydrous sodium sulfate, filtered, the solvent was removed, and the sample was dried over Pz05under vacuum for 72 h. Preparation of Cross-Linked Carbamate Derivatives. A 25% solution (benzene/ethyl acetate 6:l) of the polyol, partially esterified with 2,4-D, was taken in a two-necked flask and reacted with the 10% solution of the required amount of toluene diisocyanate in the same solvent mixture under stirring and nitrogen purging at 55-65 "C for 4 h. The product was cooled to room temperature and kept overnight. Benzoyl chloride was used as an inhibitor. Analytical Methods. To find the hydroxyl value, the method of Ogg et al. (1945) was follwed. The active agent content was determined from chloride estimation by the standard Carius method (Carius, 1860). The relative viscosity was determined from the efflux time of 10% acetone solution by use of an Ostwald viscometer. A Perkin-Elmer M 297 spectrometer was used to determine the IR spectra. Release Study. Hydrolysis Study at Different pH. A release study was carried out for each formulation by taking weighed amounts of the herbicide samples, containing 25 mg of releasable 2,4-D, in five conical flasks to which 100 mL of distilled water (pH 6.7) was added. The flasks were shaken mechanically in a water bath at 25 "C for different periods of time. After a week a definite amount of liquid WPS withdrawn from the flask marked for the first week. 'rhe released 2,4-D in water was extracted with ether, the extract ether was removed, and the concentration of 2,4-D was determined spectroscopically at 565 nm by complexing with chromotropic acid in presence of concentrated H2S04(Marquardt and Luce, 1951). Similar procedures were followed for 2, 3, 4, and 5 weeks, respectively, for each of the six formulations. Similar hydrolysis study was carried out in acidic (pH 4) and alkaline (pH 10) media for each of the formulations for the same length of time. Leachate Analysis from Soil Column. The leaching characteristics of the herbicide formulations were deter-
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Table I. Physical Characteristics of Castor Oil-Based Pendently Bound Herbicide Formulations
sample COD EP-1 EP-2 EP-3 EP-2T EP-3T
description 2,4-dichlorophenoxv acetate of castor oil 2,4-dichlorophenox; acetate of castor oil poly01 2,4-dichlorophenoxy acetate of castor oil poly01 2,4-dichlorophenoxy acetate of castor oil poly01 TDI reaction product of castor oil poly01 ester, EP-2 TDI reaction product of castor oil poly01 ester, EP-3
appearance red oil brown pasty mass brown pasty mass brown pasty mass brown brown
herbicide w t % 28 50 40 28 30 20
re1 visc 10% soln in acetone 1.5 1.5 1.6 1.8 insol insol
hydroxyl value 15.1 27.4 160.0 336.6
?
/
a ' d e n e g i s:cyam'e
Tr.: i_
r-
D-ZIQC
C H ~
C
Figure 1. Probable reaction scheme.
mined with a soil (clay-loamtype containing 0.69% organic matter) filled glass tube of 5 cm diameter and 20 cm height. The soil column was settled by the addition of water. The herbicide formulations containing 30 mg of the active agent were placed on top of the soil column and 25 mL of distilled water was applied daily to the tubes. The leachates were collected weekly by providing water jet suction to the outlet of the column and they were analyzed for 2,4-D content of the effluent. A control column containing free 2,4-D was similarly analyzed. Laboratory Bioassay. Petri dishes of 5 cm radius containing soil of 2 cm thickness were used for bioassay experiments. The soil was at first treated with the herbicide formulations at a dose (Goutam 1982-83) of 80% active principle/700 L of water/hectare (10 000 X 10000 cm2)96,48, and 24 h before sowing. Ten sunflower seeds were placed on the soil of each Petri dish at the same time. Controls containing no herbicide and untreated 2,4-D were similarly prepared. After 21 days, germinated root structures and weight of the plant materials were compared with those of the controls.
Results and Discussion The six formulations containing pendent 2,4-D prepared for this study are listed in Table I. Besides the 2,4-D ester of unmodified castor oil (COD), three esters of castor oil polyol with 2,4-D (EP-1, EP-2, and EP-3) were formulated by varying the extent of esterification as indicated by the hydroxyl values of these samples. Two more samples (EP-2T and EP-3T) were prepared by reacting EP-2 and EP-3, respectively, with toluene diisocyanate. A probable scheme for 2,4-D esterification, poly01 formation, and carbamate preparation is given in Figure 1. The percent concentration of active agent increased with the extent of esterification of castor oil poly01 from 28% in EP-3 to 50% in EP-1. It is also found that the ester obtained from castor oil is a reddish brown oil, and while the consistency of the castor oil poly01 ester changed to a pasty mass, the
14
21 TIME IN DAYS
28
A 35
Figure 2. Cumulative concentration of 2,4-D released with time (neutral medium).
products obtained by cross-linking the reactive free hydroxyl groups of these poly01 esters with TDI are insoluble solids, indicating an increase in molecular weight. The reaction of free hydroxyl groups of castor oil poly01 esters of 2,4-D (EP-2 and EP-3) with TDI was confirmed by taking IR spectra of EP-2T and EP-3T, which shows absorbance characteristic for carbamates (1790-1800, 3340, and 1050-1210 cm-'), besides those for ester and aromatic ring (1735,1480, and 1600 cm-l), while that of EP-2 and EP-3 indicated absorbance for free hydroxyl groups (3500 cm-') as well as those for ester and aromatic rings. Figure 2 shows the cumulative release of 2,4-D from different formulations with time. It is evident from Figure 2 that the lower molecular weight formulations released herbicide much more rapidly than the cross-linked urethane system. EP-3 is characterized by a rapid initial release in the first week which is consistent with its lower degree of substitution and consequently higher degree of hydrophilicity. With COD having the same degree of substitution as EP-3 but negligible residual hydrophilicity, the rate of release fell much below that of EP-3. With EP-1, EP-2, and EP-3 the rate of release in the first week was in the reverse order of the degree of substitution EP-1 < EP-2 < EP-3. The observation confirms the view that hydrophilicity plays an important role in controlling the release. Since each herbicide molecule released by hydrolysis gives rise to a free hydroxyl group, the hydrophilicity of EP-1 increased considerably with time and at the end of the second week its rate of release was close to
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 2, 1985 277
I
7
14
21 TIME IN DAYS
-
28
35
Figure 3. Cumulative concentration of 2,4-D released with time (acid medium).
that of EP-3, surpassed that of EP-2 after the third week, and ended up with maximum amount of herbicide released in five weeks time. The decrease in release rate with EP-3 and EP-2 may be due to the collapse of the secondary structure of the hydrolyzed molecule through reformation of hydrogen bond or ether bond which renders the particle surface more difficult to penetrate for the water molecule (McCormick et al., 1981). Diffusion may also play an important role in controlling the release rate. Since the mass of EP-3 is almost twice as great as EP-1 (for the same amount of releasable herbicide), 2,4-D has a longer path for diffusion which may account for the observed final rate. As was expected, the cross-linked system EP-3T had much lower release rates because of the inaccessibility of the pesticide-matrix ester bond to the water molecule. With EP-3 having more residual hydroxyl groups, the extent of cross-linking on reaction with toluene diisocyanate is expected to be much more than in the case of EP-2. Consequently, the release of 2,4-D is much more restricted in case of EP-3T than in the case of EP-2T. It is found from Figure 3 and 4 that the release rate is pH dependent. The increase in the rate of release in an acid medium was lower compared to that in the alkaline medium, which may be due to the cleavage of the glyceride ester bond. The carbamate linkage is also unstable in an alkaline medium. The behavior of the formulations in actual soil conditions underwent minor variation, where the maximum efficiencywas shown by EP-2 both in the soil column study (Figure 5) as well as in the bioassay (Figure 6). The hydrolytic cleavage of the herbicide in soil was made complicated by simultaneous attack of soil microbes and enzymes. The microbial and enzymatic cleavage may appear to be directly proportional to the degree of substitution, i.e., the amount of the active material per milligram of the formulation. The higher release rate in case of EP-2 compared to EP-1 and EP-3 can be accounted for by considering the higher degree of substitution in EP-2 compared to EP-3, which was supplemented further by ita higher degree of hydrophilicity compared to EP-1. That
7
21
14
35
28
TIME I N DAYS-
Figure 4. Cumulative concentration of 2,4-D released with time (alkaline medium). 60
I
I
j:
7
21
I4 TIME IN DAYS
28
Figure 5. Cumulative concentration of 2.4-D released with time (soil leachate).
002
w : , 0 01 E
n
C itrol 2,L-D
iP-2
EP-3
.P-3T
COD
SAMPLES
Figure 6. Effect of pre-emergent spray on dry weight of 21 day old sunflower seedling; the white, shaded, and hatched areas refer to spraying before 24, 48, and 96 h, respectively.
the soil microbes play an important part was evident from the considerable increase in the release rate from the cross-linked formulations and here also the rate was related to the degree of substitution. While with free herbicide
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Ind. Eng. Chem. Prod. Res. Dev. 1985,
more than 80% of the active matter was lost through leaching in only three weeks, in the case of the prepared herbicide formulations the loss was much less. The maximum loss was found to be around 50% in case of EP-1 in four weeks time. In the laboratory the maximum growth inhibition was exhibited by EP-2, which may be due to the maximum amount of the releasable toxicant available from this formulation during the three-week period. The difference in bioactivity among EP-2, EP-3, and EP-1 narrowed down when the soil was treated with the formulations 96 h before sowing, which increased the availability of the minimum effective level of free herbicide. The bioactivity of the cross-linked formulations was found to be unsatisfactory during this short period of the experiment, but EP-2T showed phytotoxicity comparable to free 2,4-D when the soil was treated with it 96 h before sowing. Natural or synthetic polymer-based formulations, so far reported, require a longer release period, and thus, although they are suitable for forestry, they are not applicable in agriculture. Formulations, having a shorter period of release, particularly during the maximum growth period of the plant, are important in agriculture. The foregoing results indicate that controlled-release 2,4-D formulations based on castor oil and its derivatives can be tailored to have a wide range of release characteristics which may find applications in agriculture. Moreover, homogeneous reaction conditions in preparing the formulations in the present case led to better yield and greater purity of the products in contrast to earlier preparations in a heterogeneous medium using natural or synthetic polymers. Acknowledgment The authors thank Drs. S. P. Moulik and S. Gupta, Department of Chemistry, Jadavpur University, for analytical assistance, Ashish Chakraborty, Department of Agriculture, Calcutta University, and Chandan Guha of this department for bioassay and other assistance. Thanks are also due to Anker Industries Pvt., Ltd., Calcutta, for a free gift of 2,4-D samples. One of the authors (S.B.) is indebted to West Bengal Science and Technology Com-
24,278-283
mittee for a Research Fellowship. Registry No. 2,4-D, 94-75-1.
Literature Cited Allan, G. G.; Chopra, C. S.; Neogi, A. N.; Wilkins, R. M. Nature (London) 1971, 234, 349. Allan, G. G. Canadian Patent 855 181, 1970. Allan, G. G. Canadian Patent 863310, 1971. Allan, G. G. U.S. Patent 3813236, 1974. Allen, 0. G. French Patent 1544406, 1968. Alian, G. G.; Beer, J. W.; Cousin, M. J. ACS Symp. Ser. 1977a, N0.53, 94. Allan, G. G.; Beer, J. W.; Cousin, M. J. "Proceedings, Symposium on Controlled Release Pesticide"; Oregon State Unlverslty, Corvailis, OR, 1977b; p 19. Allan, G. G.; Beer, J. W.; Cousin, M. J.; Powell, J. C. Tappi 1978, 61(1), 33. Allan, G. G.; Chopra, C. S.; Russell, R. M. Int. Pest Control 1972, 14(2), 15. Alian, G. G.; Chopra, C. S.; Maggl, M. W.; Neogi, A. N.; Wilklns, R . M. Int. Pest Control 1973, 15(3), 8. Allan, G. G.; Cousin, M. J.; MeConneil, W. J.; Powell, J. C.; Yahiaoui, A. "Proceedings, Symposium on Controlled Release Pesticide"; University of Akron, Akron, OH, 1976; p 7-15. Alian, G. G.; Frledhoff, J. F.; Powell, J. C. Int. Pest Conhol 1975, 17(2), 4. Bille, S.;Mohsdorf, S. F.; Cardarelii. N. F. "Annual Rep 11, Development of Slow-release Herbickle for Controlling Aquatic plants"; university of Akron, Product Development Lab., July 1971. Cardarelll, N. "Controlled Release Pesticides Formulations", C.R.C. Press: Cleveland, OH, 1976. Carlus, L. Ann. 1860, 116, 1. Goutam, B. ASPEE, 19th Annual Report 1982-1983. Kydonleus, A. F. "Controlled-Release Technologies: Methods, Theory and Applications"; CRC Press: Boca Raton, FL, Vol. I and 11, 1980. Marquardt, R. P.; Luce, E. N. Anal. Chem. 1951, 2 3 , 1484. McCormlck, C. L.; Anderson, K. W.; Hutchinson, B. H. JMS-Rev. Macromol. Chem. Phys. 1982-83, c22(1), 58. McCormlck, C. L.; Anderson, K. W.; Pelezo, J. A.; Lichatowkch, D. K. "Controlled Release of Pesticides and Pharmaceuticals", D. H. Lewis, Ed.; Plenum: New York, 1981. McCormick, C. L.; Lichatowitch, D. K. J. Polym. Sci., Polym. Lett. Ed. 1979, 17, 479. Mehltretter. C. L.; Roth, W. B.; Weakley, F. B.; McGuire, T. A,; Russell, C. R . Weed Sci. 1974, 22(5),415. Neogi, A. N. Ph.D. Dlssertation, Unlverslty of Washington, 1970. Neogl, A. N.; Allan. G. G. "Controlled Release of Blolcgicaily Actlva Agents", Tanquary, A. C.; Lacey, R. E., Ed.; Plenum: New York, 1974; pp 195-224. OggsC. L.; Porter, W. L.; Willits, C. 0. Ind. Eng. Chem. Anal. Ed. 1945, 17, 394-397. Sjogren. R. D. "Proceeding, Symposium on Controlled Release Pesticide"; Wright State University, Dayton, OH, 1975. Zweig, G. ACS Symp. Ser. 1977, No. 5 3 , 37-53.
Received for review June 7 , 1984 Revised manuscript received September 4, 1984 Accepted December 3, 1984
Propylene Polymerization Kinetics in a Semibatch Reactor by Use of a Supported Catalyst Norman F. Brockmeler" and John B. Rogan Research and Development Department, Amoco Chemicals Corporation, Napervllle, Illinois 60566
A mathematlcal model is developed and compared with two others for tracing the progress of propylene polymerization with titanium-based supported catalyst in a semibatch slurry reactor. Previously published Montedison laboratory reaction results are the basis for comparing the three model equations that describe the isotactic polymer yield as a function of operatlng conditions. The model equations are distinguished by the exponential order of the catalyst decay kinetics: first order, 1.5 order, and second order. The first-order model provides the most accurate correlation for reaction times of zero to 2 h. The second-order model provides an accurate correlation from 0.5 to 15 h. The 1.5-order catalyst decay model developed by Amoco Chemicals provides an accurate correlation from 2 to 15 h and, in contrast to the other two models, eliminates the need for stochastic procedures to determine the two major catalyst parameters: the catalytic rate constant and the decay half-life. For the 1.5-order model, the activation energies for the temperature effect on the catalyst rate constant and half-lives are 15 600 and 14 600 cal/g-mol, respectively.
The use of highly active supported transition-metal catalysts provides a basis for developing new and improved 0196-4321/85/1224-0278$01.50/0
processes for the manufacture of isotactic polypropylene (PP). Most of the supported catalysts of commercial in0 1985 American Chemical Society
