269
Ind. Eng. Chem. Prod. Res. Dev. 1985, 24, 269-274 e,,
e, e, e,
= instantaneous elastic displacement, m = asymptotic elastic displacement, m = value of e for t' = 0, m = radial displacement common to both lip and shaft when
t ' = tu', m { = E / E 2 = c o l e m dimensionless 7 = viscous constant of the dash-pot of
the three-parameter solid, Ns/m X = radial displacement of the lip points not in contact with the shaft, m = time derivative of X, m/s u = force applied to the three-parameter solid, N u = time derivative of u, N/s
= 7/& 8 9,\kM = phase shift angles, rad Q = u2,rad2/s2 w = angular velocity of the shaft, rad/s wcr = angular velocity at which E L = 0, rad/s T
L i t e r a t u r e Cited Flirgge, W. "Viscoelasticity", 2nd ed.; Sprlnger-Veriag: New York, 1975. Ishlwata. H.; Hirano, F. "Proceedings of the 2nd Fluid Sealing Conference"; BHRA Fluid Engineering, Cranfield, England, April 6-8, 1964 Paper H2, pp 17-32.
Kanaya, T.; Inoue, H.; Shlmotsuma, Y. "Proceedings of the 10th Fluid Sealing Conference"; BHRA Fluid Engineering, Innsbruck, Austria, April 3-5, 1984; Paper K2, pp 439-449. Muller, H. K.; Ott,0. W. "Proceedings of the 10th Fluid Sealing Conference"; BHRA Fluid Engineering, Innsbruck, Austria, April 3-5, 1984; Paper K3, pp 451-466. Prati, E. Tribol. Lubr. l W l a , 76 (l), 4-11 (in Italian), Prati, E. Triboi. Lubr. 188lb, 76 (4), 139, 147 (in Italian). Prati, E. "Proceedings of the 6th National Congress AIMETA"; University of Genova, Italy, Oct 7-9, 1982; pp 151-162 (in Italian). Prati, E. "Proceedings of the 10th Fluid Sealing Conference"; BHRA Fluid Engineering, Innsbruck, Austria, April 3-5, 1984a; Paper C3, pp 123-138. Prati, E. "Proceedings of the 7th National Congress AIMETA"; University of Trieste, Italy, Oct 2-5, 1984b; pp 417-428 (in Italian). Schuck, 0.; Muller, H. K. "Proceedings of the 9th Fluid Sealing Conference"; BHRA Fluid Engineering, Noordwijkerhout, Netherlands, April 1-3, 1981; Paper D1, pp 103-110. Volgt, U. Msschinenbautechnik 1975, 24, 35-39. Voigt, U.; Troppens, D. Maschinenbautechnik 1S75a, 24, 64-67. Voigt, U.; Troppens, D. Maschlnenbautechnik 1975b, 24, 259-262.
Received for review October 1, 1984 Accepted December 3, 1984
This study was supported financially by the Italian National Council of Research.
Influence of Preparation Parameters on Internal Droplet Size Distribution of Emulsion Liquid Membranes Gregory J. Hanna' and Kevln M. Larson Center for Chemical Engineering, National Bureau of Standards, Boulder, Colorado 80303
Droplet-size distributions and the corresponding surface areas for emulsions prepared for emulsion liquid membranes were measured by differential X-ray sedimentation. The water-in4 emulsions were prepared with toulene, decane, and an isoparaffinic solvent. The surface area was measured as a function of hydrocarbon solvent, emulsifier speed, time of emulsification, and aqueous weight loading. The surface area increased with increasing speed and time of emulsification, and it decreased with aqueous weight loading. Speed, time, and weight loading were all significant at the 95 % level or better. Several interactions between variables were also significant. Emulsions formed with the lube-oil base were quite viscous at high aqueous loadings which limited the creation of surface area. Typical values of the surface area ranged from 3.0 to 8.0 m2/cm3of aqueous phase. The effect of surface area on mass transfer rate was demonstrated with a copper extraction system.
Introduction
Emulsion liquid membranes (ELMS)have been studied extensively since they were first reported by Li (1968). In addition to metals such as copper (Volkel et al., 1980; Martin and Davies, 1976-1977; Frankenfeld et al., 1981; Teramoto et al., 1983a), uranium (Bock and Valint, 1982; Hayworth et al., 1983), mercury (Weiss et al., 1982; Boyadzhiev and Bezenshek, 19831, and cobalt (Gu et d., 1983), extractions have been carried out on phenol (Cahnand Li, 1976; Terry et al., 1982; Kim et al., 1983),cresol (Teramoto et al., 1983b), amines (Teramoto et al., 1981), and even cholesterol from blood (Yagodin et al., 1983). All of the systems listed above require a water-in-oil emulsion to separate and concentrate the component of interest. These emulsions can be prepared in many ways, and it is often difficult to compare results from one investigation to another because no data which adequately characterize the emulsion are available. One way to characterize emulsions and ELM systems is by measuring the surface area. Emulsion liquid membranes have two important surface areas which must be determined (see Figure 1). The external surface area (ESA) is produced when the emulsion is dispersed in the This article
continuous (or external) phase. The shear field of the impeller causes the emulsion to form drops (called globules) which are approximately 1mm in size. The internal surface area (ISA) is created in the emulsifier, and the internal droplets are approximately 1pm in size. External surface area is usually measured photographically. Internal droplet sizes are qualitatively determined with a light microscope, but droplets less than 1pm in size are diffuse and difficult to measure. For this reason, internal droplet sizes are usually reported as 1-3 pm, 1-10 pm, and so on because droplets smaller than 1 pm appear diffuse under the microscope. Bock et al. (1981) used a commercial particle sizer to characterize emulsion droplet size but reported no details. In order to adequately characterize an emulsion, the internal droplet size distribution and the formulation recipe must be reported. There is also evidence which indicates that the internal droplet size affects the mass transfer rate. Frankenfeld et al. (1981) observed different extraction rates for emulsions with different internal droplet sizes. A Japanese corporation licensed ELM technology for extraction of ammonium, mercury, chromium, cadmium, and copper ions from wastewater. They experienced initial difficulty
not subject to U S . Copyright. Published 1985 by the American Chemical Society
270
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 2, 1985
Table I. Factorial Table for Emulsion Preparation expt A B 1 a + b + ab + + C ac bc + abc + +
+
AB
+ -
+ +
I
-
+
-
Membrane
30 1
3
External Phase
Internal Phase , Droplets (0 1-5 pm)
Oil Surfactant
+
-Emulsion Globules
Figure 1. Enlarged diagram of emulsion liquid membrane system.
in reproducing the high extraction rates and yields because the ISA in their emulsions was lower than in the emulsions used by the licensor (Hayworth, 1981). Recently, Teramoto et al. (1981) found no difference in the extraction rate of copper by emulsions of varying internal droplet size. In this paper, we present a technique which can be used to give reliable, reproducible measurements of the internal droplet size distribution for emulsions used in ELM formulations. A variety of emulsions were characterized as a function of aqueous weight percent loading and emulsifier speed and time. Data demonstrating the effect of the ISA on mass transfer are also presented.
Experimental Section Experimental Design. The factorial method of statistical experimental design (Volk, 1969; Box et al., 1978) offers advantages to researchers when several variables combine to produce a response. In addition to requiring the least number of experiments to determine the response from a particular variable, the factorial method reveals variables which act in combination to produce a response which is different from the sum of the individual responses. A three-variable, two-level factorial experimental matrix was constructed to evaluate the effects of emulsifier speed, emulsification time, and aqueous phase loading. The high (+) and low (-) values are given in Table I. Complete factorial designs were carried out for emulsions prepared with an isoparaffinic solvent (IF'S; approximately 0.04 Pa.s) and toluene. Emulsion Preparation. All emulsions were prepared in 200-g batches in a commercial blender. The surfactant was a polyamine and the carrier was a @-hydroxyoxime. The surfactant concentration was 2.0% and the carrier concentration was 2.5%. The remaining 95.5% of the membrane phase was either IPS, reagent grade toluene, or technical grade decane. The three components of the organic phase were weighed and well mixed prior to being added to the blender. The aqueous phase was 12% or 15%
BC
ABC
+
-
+ + + +
60
DISPERSION OF LM EMULSION 0 1 - 2 "
AC
High (+I and Low (-) Values high low 19000 10 500
variable emulsifier meed ( A ) aqueous weight % ( B ) emulsification time (C)
-
C -
units rPm weight % minutes
sulfuric acid and was prepared from concentrated sulfuric acid and deionized water immediately prior to emulsification. Emulsions were prepared as 30-60% aqueous phase. The internal and membrane phases were added to the blender and emulsified for 1to 4 min at different speeds. The speed of the blender was controlled with a variable AC transformer. All reported percents are on a w/w basis. Internal Droplet Size Measurement. A commercial differential X-ray sedimentation particle sizer was used without modification to measure the internal droplet size distribution of the emulsion. Twenty milliliters of emulsion was diluted with IPS or toluene until the concentration of aqueous droplets in the sample was between 10 and 15%. For emulsions with aqueous loadings in the 5040% range, a double-dilution technique was required to ensure that no agglomerated droplets were present in the final emulsion. Samples were stirred with a glass rod for 30 s at each stage of the dilution to ensure complete droplet separation. Each experiment required 9-30 h to produce a size distribution. The temperature of the cell and compartment was 309 K. Blank solutions (membrane phase with no aqueous phase present) were prepared with surfactant concentrations in the range of 1.2-1.5%. Qualitative droplet-size measurements were made with a light microscope equipped with a 35-mm camera. Mass Transfer Measurements. One liter of a 500. ppm CuS04solution was stirred in a 2-L reaction flask at 365 rpm. The flask was equipped with a 7.5-cm square plexiglass window for photographing globule size distributions and a 4-mm sidearm for withdrawing samples. Two hundred forty grams of emulsion was added to the stirred flask, and extraction continued for 20-35 min. Aqueous samples were withdrawn every 2 to 5 min and analyzed by atomic absorption spectrophotometry. A small plug of glass wool was placed at the entrance to the sidearm to prevent emulsion globules from being pulled into the samples. Globule Size Measurement. Photographs were taken with a 35-mm camera equipped with a bellows, auto-winder, and 135-mm and 80-mm macro lenses. A flash unit was positioned 15' from vertical above the window. The steep angle of the flash shadowed the globules on one side to make analysis easier. The photographs were taken on IS0 400 or I S 0 125 black and white print film and enlarged to approximately 40 X 50 cm. A ruler was placed in the flask and photographed prior to each extraction to scale the photographs. The flash duration was l/lmo to 1/2m s depending on the f-stop, which varied from 16 to 45.
The globules on each photograph were measured with an image analyzer interfaced to the laboratory computer. At least 500 globules were measured before the Sauter
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 2, 1985 271 C
a) Toluene emulsions
Table 11. Mean Effects and Significance Levels for Factorial Design Experiments
A
~
I
2,!3.7+2,7.6
-
E
5.27 4.96
A
/ C
b) I P S emulsions
t
a. Factorial Design with Toluene variable or interaction mean effect signif level A 3.85 0.01 B -0.20 0.10 C 2.21 0.01 AB -0.095 a AC 1.59 0.01 BC 0.065 a ABC -0.050 a
_-.-
b. Factorial Design with IPS variable or interaction mean effect signif level A 1.30 0.01 B -2.06 0.01 C 1.02 0.01 AB -0.78 0.01 AC -0.03 a BC -0.40 0.05 ABC 0.07 a Used to compute an error-variance term.
Figure 2. Internal surface area (m2/cm3)from factorial design experiments: A = emulsifier speed; B = aqueous wt %; C = emulsification time.
mean diameter was calculated. The Sauter mean diameter (d32)is defined as
Ed3 d32 = (1) Ed2 Results and Discussion The response from each experiment was the internal surface area per cubic centimeter. The ISA also gives a measure of how finely divided the droplets are. The Sauter mean diameter is related to the surface area per cubic centimeter by d32 = 6/(area/cm3) (2) Figure 2 contains the results for the emulsions prepared with toluene and IPS. The responses are plotted as corners of a cube, and their locations are determined by the level of each of the three variables. The mean effects and significance levels for all variables and interactions are listed in Table 11. The total effect for each variable was obtained by adding the responses according to the signs in Table I (Volk, 1969; Box et al., 1978). For example, the A effect was calculated by adding the responses from experiments a, ab, ac, and abc and subtracting the responses from experiments 1, b, c, and bc. The mean effect is the total effect divided by 2n-1,where n is the number of variables. The effects of emulsions prepared with toluene are contained in Table IIa. The effect of emulsifier speed (variable A ) was very large, which indicated that increases in speed produced large increases in the internal surface area. The time effect ( C ) indicated that longer emulsification times favored higher surface areas. The large speed-time interaction (AC) implied that increasing the speed and time together produced a larger surface area than would be predicted by combining the effects of increasing the speed or the time individually. The three smallest mean squares (AB, BC, and ABC) were averaged to determine the error variance. F ratios were calculated to determine the significancelevel of the other effects. The A and C effects and the AC interaction were significant at the 0.01 level (99% confidence). The aqueous weight percent ( B ) effect was significant a t the 0.10 level (90% confidence).
i
c
i
1
ir o ol , l , l j z
1
2
3
4
5
EMULSIFICATION TIME, min
Figure 3. Effect of emulsificationtime on internal surface area. All emulsions were 60% aqueous in IPS and emulsified at 19000 rpm.
The results for IPS emulsions are reported in Table IIb. The internal surface area formed with IPS emulsions was influenced by the preparation parameters differently from the toluene emulsions. Speed (A) and time ( C ) were positive effects, but the largest effect was the negative effect of the aqueous weight percent (B). High aqueous weight percent emulsions had larger average droplet sizes than their corresponding low weight percent counterparts. The speed-time (AC)and ternary (AB)interactions were averaged to determine the error variance. Speed ( A ) , weight percent (B),time (C),and the speed-weight percent interaction (AB) were significant at the 0.01 level. The weight percent-time (BC) interaction was significant at the 0.05 level. The error variance for the IPS system was half that of the toluene system (see Volk (1969) for a detailed discussion of variance analysis). The magnitudes of the effects can be compared between Tables IIa and IIb to determine the relative importance of variables in each system. The toluene system was more dependent on speed and time than the IPS system, and the IPS system was most heavily influenced by the aqueous weight percent. The aqueous weight percent was of much less importance for the toluene emulsions, but the speed-time interaction was important. In both cases, the ternary interactions were not significant. In addition to the multivariable factorial experiments, single-variable experiments for emulsification time axid emulsifier speed were conducted. Figure 3 is a plot of
272
Ind. Eng. Chem. Prod. Res. Dev.. VoI. 24, NO.2, I985
2;
" 12
'
'
16
'
'
20
'
'
24
2 1, , , , , , , , 0
, , , , , , , ,
,
,
\
,
L
10
100
I 0.1
EQUIVALENT SPHERICAL DIAMETER. pm
BLENDER SPEED. krom
Figure 4. Effect of emulsifier speed on internal swface area; emulsification time 3 min.
I
0
Figure 5. T y p i d partide sizer chart. Emulsion preparation: 60% aqueous in IPS,emulsified 3 min at 19000 rpm.
r
internal surface area vs. emulsification time for IPS emulsions. The aqueous weight loading was 60%. The internal surface area reached a plateau after 2 min, and additional emulsification produced no additional surface area. Emulsions prepared with toluene did not exhibit a plateau effect for emulsification times up t o 4 min. The viscosity of the 60% aqueous loading/IPS system limited the production of surface area and produced a plateau in the graph. Figure 4 is a plot of internal surface area vs. emulsifier speed for toluene and IPS emulsions. In the range of 9000-22000 rpm, the emulsion systems responded very differently to increases in emulsifier speed. The surface area in the toluene systems was still increasing linearly at the maximum speed obtainable with the emulsifier for both the 30- and 60-wt % loadinps. Internal surface areas for IPS emulsions prepared with 30% aqueous loadings increased linearly with increasing emulsifier speed up to 13500 rpm and then leveled off. The increase in ISA observed in the 60% aqueous/IPS system was an order of magnitude less than the increase observed in the other three systems. Emulsions prepared with either toluene or decane exhibited little change in viscosity compared to the viscosities of the component phases. Both hydrocarbon solvents produced emulsions with similar internal surface area properties. The results from the factorial and single variable experiments clearly indicated that increasing the speed and/or time of emulsification favored higher internal surface area (or smaller droplets). The distribution of droplets was significantlywider at higher speeds and longer times, but the low viscosity of the emulsion allowed creation of additional surface area at long times or high speeds. The aqueous weight percent had a slightly detrimental effect on the surface area created. The viscosity of emulsions prepared with IPS was considerably higher than the viscosity of either the hydrocarbon or aqueous phases. The high viscosity limited the creation of additional surface area a t longer times and higher speeds, especially for emulsions which were 60% aqueous. The results from the IPS factorial experiments support these observations. The largest effect for IF'S emulsions was the aqueous weight percent. The high viscosity of the 60% aqueous emulsions overpowered all other factors and inhibited the creation of additional surface area. The leveling effect seen in Figures 3 and 4 is due to the increased viscosity of the emulsions, and the interaction terms also reflect the effect of the weight percent. Emulsions prepared with IPS at 30% aqueous exhibited behavior similar to decane or toluene up to 13500 rpm. The separate fadorial designs for IPS and toluene were also combined as a Z4 factorial design with choice of hy-
z
DROPLET SIZE,
pm
DROPLET SIZE.
pm
Figure 6. Distributions by number and surface area from the chart in Figure 4.
drocarbon as the fourth variable. Unfortunately, the effects obtained were difficult to interpret. Some ternary interactions were as significantas primary variables, which clouded the statistical significanceof the important effects. The difficulties associated with the larger factorial matrix can be partially understood by examining Figure 4. The speed effect depends on the choice of solvent and the weight percent loading (a ternary interaction) and the weight percent effect depends on the choice of hydrocarbon and the speed (also a ternary interaction). The two separate designs were more easily interpreted because the ternary interaction terms did not arise. The surface area created depends on the emulsion viscosity and not the viscosity of the hydrocarbon component alone. The emulsion viscosity under shear would be an ideal variable choice, but the type of hydrocarbon and the aqueous weight loading both affect the emulsion viscosity. Therefore, choice of hydrocarbon was a poor variable for the fadorial design, and the IPS and toluene systems were analyzed separately. The particle sizer chart output gave the range of diameters present in each emulsion. A typical chart is reproduced in Figure 5, and the corresponding distributions by number of droplets and by surface area contribution are given in Figure 6. Distributions ranged in breadth from 0.75-2 to 0.5-5 pm, and longer emulsification times and higher emulsifier speeds favored broader distributions. The ISA was determined from a point-by-point averaging/integration procedure from the particle sizer chart (see Figure 5). An average size was selected for each
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 2, 1985 273 Table 111. Conditions and Data for Mass Transfer Experiments exDt 1 2 ~
system
Re, cm
init concn, ppm 445 435
A
B
0.066 0.061
5 min 0.656 0.793
Emulsion Preparation Conditionsa System A: emulsify 2 min at 10500 rpm System B: emulsify 2 min at 19OOO rpm
~~
degree of extraction 10 min 0.854 0.938
30 min 0.996 0.995
I.S.A. = 2.0 m2/cm3 I.S.A. = 12.0 mZ/cm3
=Both systems were 60% aqueous (15% H2S04)and 40% organic (2.0% surfactant, 2.5% carrier, 95.5% decane). 1.o
I
I
I
A-
I
1
1
I 20
0
E- o
0.OOll
0
I
4
I
8
I
12
16
I
8 Figure 7. Copper extraction rates for different internal surface areas. Internal surface areas were approximately 2.0 m2/cm3(system A) and 12.0 mz/cm3 (system B).
mass-percentage level up to 98%. The number of droplets and corresponding surface area was then computed using a basis of 1 cm3 of aqueous phase. The sum of all the percentage levels produced the total ISA. Selecting average values for the S curve a t the small end of the scale is difficult and introduces error into the data. The magnitude of the error can be as large as 3-5%. Effect on Mass Transfer. Figure 7 is a plot of copper concentration vs. dimensionless time for two extraction systems. Time was nondimensionalized according to (3) where De, the effective diffusivity of the carrier complex was estimated from (Teramoto et al., 1983a) to be 8.0 X lo4 cm2/s and R, is half the Sauter mean diameter for the emulsion globules. Systems A and B had internal surface areas of 2.0 m2/cm3 and 12.0 m2/cm3, respectively. All other experimental conditions were the same for both systems. The emulsions of system B extracted copper much more rapidly than those of system A during the first 15 min. The degree of extraction, however, was approximately equal for the two systems after 30 min. Degree of extraction was defined as (Co - C)/Co, where Co is the initial copper concentration and C is the concentration at any time. The important experimental conditions and extraction data are summarized in Table 111. The rates were reproducible to within 5 % . Membrane breakage (or leakage) is probably responsible for the leveling effect observed in the extraction rates of system B emulsions. Frankenfeld et al. (1981) presented mass transfer data for a copper hydroxy oxime system using emulsions with average droplet sizes of 14,7, and 2 pm. The mass transfer rate increased with decreasing droplet size. The data were not normalized to account for external surface area. Teramoto et al. (1983a) recently claimed that sonication of the emulsion (changes in internal surface area) did not affect the mass transfer rate of copper, but they used a
different hydroxy oxime carrier. Again, the data were not normalized to account for the external surface area. The data from the present study clearly indicate that the mass transfer rate is influenced by the internal droplet size. The emulsions of group A had average diameters of 4 pm, and the emulsions of group B had average diameters of 0.9 pm. The mass transfer rates observed in group B were substantially faster than those observed in group A, but the degree of extraction was not affected by the internal droplet size. The results suggest that the ISA can influence mass transfer rates, and a successful model must be able to account for this effect. Further studies are necessary before the reason for the effect on mass transfer can be fully understood. Measurement of the external surface area is extremely important in characterization of ELM systems. It is impossible to compare mass-transfer data without first normalizing the rates to the available surface area. The preparation of the emulsion can have a large effect on the external surface area created. Since most emulsions are prepared at a constant surfactant loading, decreasing the internal droplet size distributes the surfactant over a greater surface area. The decrease in interfacial surfactant concentration causes a corresponding increase in interfacial tension (Teramoto et al., 1983b). If the agitator speed in the contacting tank is held constant, the external surface area created is smaller for emulsions with higher interfacial tension. Therefore, identical emulsion compositions and contacting conditions can produce systems with different external surface areas. Emulsions created with high internal surface area are also more susceptible to breakage because the interfacial surfactant concentration is lower. The mass transfer data reported in this study suggest that slight breakage occurred in system B emulsions near the end of the 30-min extraction. System B emulsions prepared with 5% surfactant loadings (instead of the normal 2%) did not exhibit the curvature seen in Figure 7. The extraction rate continued linearly up to the end of the experiment, which confirms the hypothesis that breakage is responsible for the leveling of the extraction rate in the high ISA emulsions. Error and Reproducibility. The method of residuals was applied to the responses in Tables IIa and IIb to determine if the variance in the data was due to an omitted variable or to randomness (see Box et al. (1978) for a detailed discussion of residuals). The residual analysis indicated that only randomness was responsible for the scatter in the data. Experiments were repeated periodically to check the values obtained and were consistently reproduced within 5 % . Although the precision of the ISA measurements was 5 % , the accuracy was somewhat more difficult to determine. A direct comparison between the microscope and particle sizer always produced qualitative agreement for size ranges, but quantitative comparison was of limited value due to the errors inherent in the photographic technique. These errors include diffuse images for droplets
274
Ind. Eng. Chem. Prod. Res. Dev. 1005, 2 4 , 274-278
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
