1926
I n d . E n g . C h e m . Res. 1991,30, 1926-1931
Ohtauka, Y.; Tomita, A. Calcium Catalysed Steam Gasification of Yallourn Brown Coal. Fuel 1986,65, 1653-1658. Ohtauka, Y.; Kuroda, Y.; Tamai, Y.; Tomita, A. Chemical Form of Iron Catalysts during the C0,-Gasification of Carbon. Fuel 1986, 65,1476-1478. Ohtsuka, Y.; Tamai, Y.; Tomita, A. Iron-Catalyzed Gasification of Brown Coal at Low Temperatures. Energy Fuels 1987a,I , 32-36. Ohtsuka, Y.; Hosoda, K.; Nishiyama, Y. Rate Enhancement and in Situ Desulfurization by Iron-Calcium Catalyst in the Gasification of Coal Char. J . Fuel SOC.Jpn. 1987b,66, 1031-1036. Schafer, H. N. S. Factors Affecting the Equilibrium Moisture Contents of Low-Rank Coals. Fuel 1972,51, 4-9. Schafer, H. N. S. Organically Bound Iron in Brown Coals. Fuel 1977, 56, 45-46. Suzuki, T.; Mishima, M.; Takahashi, T.; Watanabe, Y. Catalytic Steam Gasification of Yallourn Coal Using Sodium Hydridotetracarbonyl Ferrate. Fuel 1985,64, 661-665.
Takarada, T.; Nabatame, T.; Ohtauka, Y.; Tomita, A. New Utilization of NaCl as a Catalyst Precursor for Catalytic Gasification of Low-Rank Coal. Energy Fuels 1987,I , 308-309. Takarada, T.; Nabatame, T.; Ohtauka, Y.; Tomita, A. Steam Gasification of Brown Coal Using Sodium Chloride and Potassium Chloride Catalysts. Ind. Eng. Chem. Res. 1989,28, 505-510. Tomita, A,; Ohtsuka, Y.; Tamai, Y. Low Temperature Gasification of Brown Coals Catalysed by Nickel. Fuel 1983,62, 150-154. Tomita, A,; Yuhki, Y.; Higashiyama, K.; Takarada, T.; Tamai, Y. Physical Properties of Yallourn Char during the Catalyzed Steam Gasification. J . Fuel SOC.Jpn. 1985,64, 402-408. von Bogdandy, L.; Engell, H.-J. The Reduction of Iron OresScientific Basis and Technology (Engl. ed.); Springer-Verlag: New York, 1971; p 243.
Received for review September 24, 1990 Accepted May 2, 1991
Sorption and Desorption of Organic Compounds by Synthetic Polymeric Sorbents Jiii Hradil* and Frantisek Svec Institute of Macromolecular Chemistry, Czechoslovak Academy of Sciences, 162 06 Prague 6, Czechoslovakia
Valerie V. Podlesnyuk, Ruslan M. Marutovskij, Lev E. Friedman, and Natalia A. Klimenko Institute of Colloid Chemistry and Chemistry of Water, USSR Academy of Sciences, Kiev, USSR
The sorption and desorption of organic compounds by synthetic polymeric sorbents of various compositions were investigated by use of a model with a bidisperse structure. The diffusion coefficients in transport macropores and polymer bulk of the sorbent were determined on the basis of similarity by using the method of statistical moments. Conclusions regarding regularities of the sorption process were drawn from an analysis of the calculated values. Synthetic polymeric sorbents of various types are quite widely used in the sorption of organic compounds from aqueous solutions (Weber and Vliet, 1981; Kaedling et al., 1983; Bender, 1985; Urano et al., 1984; Kunin, 1977; Gustafson et al., 1968). Application of this group of sorbents not only allows a high degree of retention of various compounds to be achieved but also makes possible separation of sorbed compounds in the regeneration of the sorbents (Crook et al., 1975; Podlesnyuk and Klimenko, 1988). Problems involved in the optimization of the adsorption-desorption process in the case of polymeric sorbents require the knowledge not only of sorption equilibria but also of the sorption kinetics, which is the basis of the study of the nonequilibrium process. The kinetics of sorption and desorption by polymeric sorbents has not been sufficiently investigated. Thus, for example, in some studies (Rees and An, 1979; Marton et al., 1981) the adsorption kinetics was described by using the homogeneous sorbent model without bearing in mind special features of the inner structure of these materials. Such procedure is a mere approximation without any possibility of interpretation of kinetic data. Conditions of the preparation of macroporous sorbents (Kun and Kunio, 1968) allow us to assume that they have a bidisperse structure consisting of macropores, micropores, and the polymer bulk. The objective of this study is an interpretation of experimental results obtained in the investigation of the adsorption-desorption process using the sorbent model with a bidisperse structure and a quantitative analysis of regularities that control this process using the adsorption of nitrobenzene by sorbents of various types and their 0888-5885191/ 2630-1926$02.50/0
elution desorption by 2-propanol as an example.
Experimental Section The sorbents used were macroporous methacrylate copolymers (IMC CSAS, Prague), Wofatit Y-59 (FRG), and Polysorb 40/100 (USSR). Methacrylate copolymers G-5, G-60, and G-70 are hydrophilic copolymers of glycidyl methacrylate ( 5 6 0 , and 70 wt 70;GMA) and ethylene dimethacrylate (EDMA) obtained by the suspension radical copolymerization in the presence of porogens cyclohexanol and dodecanol in the rat,io 9:l. Sorbent fractions 0.25-0.50 and 0.8-1.20 mm were used in the measurements. Polymer samples denoted with -VS were swollen 24 h in dioxane, washed with a 5-fold amount of methyl alcohol and diethyl ether, and dried at room temperature and reduced pressure of 1.3 kPa. Polymer samples denoted with -HYDR were hydrolyzed with a 3-fold amount of 1 mol/L H2S04at 80 "C for 3 h, washed with distilled water methyl alcohol, and diethyl ether, and dried at 100 OC and 1.3 kPa for 48 h. Wofatit Y-59 is a copolymer of styrene (ST),divinylbenzene (DVB),and acrylic acid methyl ester (MA). The commercial sample was produced at the Bitterfield (FRG) chemical factory (Kaedling et al., 1983). Sieve fractionated fractions 0.4-0.5 and 0.63-1.00 mm were used in the measurement. Polysorb 401100 is a hydrophobic styrene-divinylbenzene copolymer, obtained by the suspension polymerization in an inert solvent, light petrol BR-1, containing 40 w t 70&vinylbenzene. 0 1991 American Chemical Society
Ind. Eng. Chem. Res., Vol. 30, No. 8, 1991 1927 Table I. Characterirticr of Sorbents v a Sfb P,C R,d grain size, sorbent commition m f / n m / a nm nm mm G-70 CMA-EDMA i.l3 30 75.3 0.30 G-60 1.47 56 52.5 0.30 G-5 0.81 367 4.4 40 0.19
-
a
N
E
e
1I
E It
0-
0.50
Wofatit ST-DVB-MA Y-59 Polysorb ST-DVB 40/100
0.63
410
3.1
30
1.16
150
15.5
70
0.22 0.40 0.20 0.40
o0w+-2 '
a Specific pore volume from cyclohexane regain measurement. bSpecific surface area. eMean pore radius calculated according to equation p = 2000V /S dMean pore radius determined from the adsorption isotherm (hfesnyuk, 1981).
.
Some properties of the sorbents are summarized in Table I. The specific surface area values of polymeric sorbents were determined by the low-temperature adsorption of argon (for Polysorb 40/100) and nitrogen (for methacrylate copolymers). Those for Wofatit Y-59 were taken from the literature (Kaedling et al., 1983). The specific volumes of pores were determined from the cyclohexane regain and the adsorption isotherm of the standard (p-chloroaniline) from an aqueous solution by employing a method described elsewhere (Podlesnyuk and Levchenko, 1981). Prior to use, the sorbent was extracted with organic solvents ethyl alcohol and acetone. The sorbents Wofatit Y-59 and Polysorb 40/100 were also washed with water. The sorbent G-5 was dried in vacuo after extraction. Chemically pure nitrobenzene, aniline, p-chloroaniline, and phenol are used as the adsorbates at 25 O C . The concentration of adsorbates in water and 2-propanol solutions was determined spectrophotometrically. The adsorption and desorption kinetics of nitrobenzene was followed in an apparatus of standardized dimensions (Kasatkin, 1971), provided with a four-propeller stirrer. The nitrobenzene solution was prepared directly in the apparatus. The weighed amount of the sorbent was introduced after the conditions had been stabilized. The adsorption process was followed by observing the decrease of the nitrobenzene concentration in the solution; samples used in the concentration measurements were taken in regular intervals until equilibrium was established. In the investigation of the desorption kinetics the sorbent used had been isolated by filtration from an aqueous solution of nitrobenzene and then introduced into the apparatus containing a certain volume of 2-propanol (500 mL). Desorption was followed by observing the increase in the concentration of nitrobenzene in solution. Again, the samples were taken in regular intervals until equilibrium was established. Standard stirring during both sorption and desorption was provided electronically.
Sorption of Organic Compounds by Sorbents Earlier, we investigated the sorption of substituted phenols by macroporous methacrylate copolymers (Hradil et al., 1986). This study was focused on the sorption of low-molecular-weightcompounds (nitrobenzene, aniline, p-chloroaniline, and phenol) and larger molecules of nonionogenic surface active compounds-[oligo(ethyleneoxy)]benzenes (Triton X-100, X-305, and X-405). The sorption of organic compounds from solutions by polymers is given by the participation of specific and nonspecific interactions and by their competition with the solvent. The nonspecific interactions correspond to weak van der Waals forces and are related to the electron polarizability of the sorbate; the specific interactions involve
4 1
6
I 8
I1
0J
c,mmol/l I
n
d
I
I
I
b /I
I
0
1
20
40
60 80 c, mmol I I
100
Figure 1. (a) Sorption isotherm of nitrobenzene from water on G-5
(x), Wofatit Y-59 (o),and Polysorb (+). (b) Sorption isotherm of nitrobenzene from 2-propanol on G-5 (X), Wofatit Y-59 (O), and Polysorb 40/100 (+I.
dipole-dipole interactions, formation of hydrogen bonds, and the like and depend in the first place on dipole moments of the sorbate. If the specific interactions predominate over the nonspecific ones, the sorbed compound is dissolved in the polymer (Hradil et al., 1986). A comparison between the magnitudes of sorption related to the unit surface on polar methacrylate sorbents (G-70) shows that the largest covering is observed with sorbates having a low electron polarizability. The dependence on dipole moments is less statistically significant. In nonpolar sorbents the effect of substitution is effaced. High sorption values suggest that hydrophobic interactions of the nonpolar skeleton and of the aromatic part of the sorbate become operative in this case. The competitive role played by the solvent during sorption from water indicates that the sorbed amount of compounds related to the surface unit of the sorbent decreases with increasing polarity of the sorbent. In the sorption from 2-propanol the sorption on G-5 and Polysorb 40/100 in fact are close to each other (Figure 1). In the case of the sorption of nitrobenzene from 2propanol the situation is different, however, because the less polar solvent does not complete so much with the polar methacrylate sorbent (Figure lb) by its interaction with the sorbate. The fact that micropores play a decisive role in the sorption is also documented by a comparison between the magnitude of sorption by the sorbents G-5and G-5-VS, for which the content of micropores was increased by employing a physical procedure (Table 11), which holds for low-molecular-weightcompounds and particularly for surface-active compounds (Figure 2). If the less polar oxypropyl groups were replaced by more polar 1,2-dihydroxypropyl groups by hydrolysis (sorbents G-60-HYDR and G-70-HYDR), the sorption decreased, which is yet another proof of the prevalent hydrophobic interaction.
1928 Ind. Eng. Chem. Res., Vol. 30, No. 8, 1991 Table 11. Sorption Capacity of Some Polymeric Sorbents sorbent G-5 G-5-VS G-60 G-60-HYDR G-70 G-70-HYDR Wofatit Y-59 Polysorb 40/100 active charcoal a Maximal
nitrobenzene 0.9 0.9
sorption capacity a,, mmol/g p-chloroaniline phenol Triton X-100 1.41 1.97 0.31 1.46 5.13 0.60 0.25 1.38 0.28 0.25 0.23 0.081 0.25 0.16 0.25 0.16 2.14 5.19 0.46 1.51 1.86 0.46 3.11 3.82 0.43
aniline 1.74 1.74 0.95 0.95
3.31 1.9 3.85
1.86
Triton X-305 0.30 0.74 0.061 0.085 0.040 0.040
Triton X-405 0.22 0.32 0.00 0.00 0.098 0.098
sorption capacity calculated acording to the Dubinin isotherm (Koganovskaya, 1977).
a
N
0
I
1
1
2
c, mmolli
2 N
E
4
0
E
I
-i
/
0 0
0
1
I
&+-+
-
2
1
c,mmol/l
2
Figure 2. (a) Sorption of Triton X-100 (O), X-305 (+), and X-405 ( X ) on G-5. (b) Sorption of Triton X-100 (O),X-305 (+), and X-405 (x) on G-5-VS.
The methacrylate copolymer G-5 is particularly suitable in the sorption of surface-active compounds, where its sorption capacity exceeds both that of the styrene-divinylbenzene copolymer and that of active charcoal. The degree of covering observed with the more lightly cross-linked copolymers G-70 and G-60(Figure 3) is higher than that observed with G-5, which suggests that, along with adsorption, the compounds dissolve in the polymeric less cross-linked matrix. During the sorption of Triton X-305 by the copolymers G-60, G-70,and G-5 the sorption isotherms passed through a maximum. This phenomenon was interpreted by the formation of micelles, as follows from changes of surface tension with growing concentration of Triton X-305. Micelles pass into solution, if the association energy (U-) exceeds the adsorption energy (-AQ (Figure 3b). Morphology of Sorbents. The inner morphology of the sorbents was investigated a t the grain section by scanning electron microscopy. Two types of pores were detected: the primary porosity is formed by agglomerates of spherical particles having the gel structure; the secondary porosity is composed of gaps between the agglomerates which can be regarded as transport channels. In
0
I 1
1 c,mmoill
2
Figure 3. (a) Sorption of Triton X-100 on methacrylate copolymers with different cross-linking (G-70 (+), (3-60 (X), and 95 (0)). (b) Sorption of Triton X-305 on methacrylate copolymer with different cross-linking (G-70 (+), G-60 ( X ) , and 95 (0)).
the first approximation the particles of the sorbent are spherical, and it may be assumed that there are no contacts between the globules. Under these conditions the mass transfer in the sorbent having the bidisperse structure proceeds in the following way: adsorption, where the process begins in the transport pores (diffusion coefficient 0;)and continues in the micropores (diffusion coefficient D J ;desorption, in which the transfer proceeds in the same way, Le., it begins in the macropore region (diffusion coefficient Dd) and then continues in the micropores (diffusion coefficient Due to the known morphology, the sorbent model with the bidisperse structure was chosen for the investigation of the adsorption kinetics of nitrobenzene (Figure 4). Theory of Adsorption. Assuming a linear adsorption isotherm, adsorption of a compound from a certain volume is described by equations related to the kinetics of adsorption by the bidisperse structure in the following form (Voloshchuk et al., 1974a,b):
Ind. Eng. Chem. Res., Vol. 30, No. 8, 1991 1929
Here, a(r,t) and c(r,t) are local concentrations of the sorbed compound and of the compound in the liquid phase inside the sorbent; A is the fraction of pores of the sorbent in the volume unit of the sorbent; r is Henry's adsorption constant according to the sorption isotherm; 7, is the time of diffusion relaxation in the polymer region equal to ro2/D,; ro is the radius of the globule; D, and Di are the diffusion coefficients in the polymer and transport pores, respectively; co is the initial concentration of the adsorbate; u, is the volume of the spherical particle of the sorbent; and = 2 X u is the solution volume in the apparatus, &P1nm.
When examining the reverse procedure of the adsorption kinetia, i.e., in the determination of the parameters Di and D, from experimentally determined kinetic curves (Figure 4), we used the methods of statistical moments. The first-order statistical moment M1 is the area of the curve demarcated by the coordinates, the straight line y = a/a, = 1, and the kinetic curve; a, is the equilibrium concentration in the apparatus having the volume c,. If we determine statistical moments for two grain sizes of the sorbent having the radii R1 and R2, relations can be obtained for the calculation of the time of diffusion relaxation in the primary and secondary porous structures 7, and T~ (Voloshchuk et al., 1974a,b) for the case of sorption from a certain volume:
7,
=
li%f1,1(1
+ a) = Ti,l
7
l t c ( r , a ) $( t - a 0
200
400 t, s Figure 4. Kinetics of sorption of nitrobenzene from water by G-5. Conditions: sorbent particle diameter 0.25-0.5 (01, 0.8-1.2 (X); sorbent weight 1.7321 g; volume of solvent; concentration of nitrobenzene 2.95 mmol/L. 100
300
Table 111. Diffusion Coefficients of Sorption of Nitrobenzene by Some Polymeric Sorbents Ri, losTi, 1&,, lO'ODi, low,, sorbent r. mm s s z, cmz/s cmz/s G-5 140 0.19 7.2 9.1 0.56 6.6 1.8 0.15 0.50 51.2 16.1 0.36 Wofatit 450 0.22 13.4 24.8 0.65 Y-59 0.4 44.9 0.36 5.4 85.3 0.94 11.0 0.58 Polysorb 150 0.20 40/100 0.40 22.7 0.87
transport pores and micropores, respectively. The diffusion coefficients of desorption can also be determined by using the method of moments. Using the similarity principle given by Zolotarev and Pilipenko (1979), which defines the relationship between models of sorption and desorption processes after the substitution a' = cyo - cy and c' = co - c in (8)-(12), we obtain a form corresponding to the system of equations describing the adsorption kinetics:
(7)
where T , = rt/D,, q = Rt(1+ r)Di,and cy = u,I'/u,. From relations 5 and 7 and using the known values of ro, Ri, r, u,, and up we obtain D, and Di. Theory of Desorption. In a manner similar to relations 1-7 and with assumption of a linear isotherm of desorption (without including sorption on walls of the transport pores), desorption can be described in terms of the relations
a=
- 2 0
)
da
= 0, a(r,O) = ao, c(r,O) = co
a2
El
cy
6r
=
r,c
(15)
= 0, a'(r,O)= 0, c'(r,O) = 0 r=O
up(c0 - C ?
=
l,
(a'+
C?
dun
(16) (17)
In order to determine the kinetic parameters of desorption with new variables, it is necessary to consider the first statistical moment of kinetic curves for a grain of various radii, R1 and R2,which leads to relations (5)-(7). In the desorption the quantity y is defined by the relation
(9)
(11)
where in addition to the symbols given above a, denotes the initial amount of the compound sorbed, r d is Henry's constant of the desorption isotherm, Td = ro2/Dd,and Di,d and Dd are the diffusion coefficients of desorption of
where a, and c, correspond respectively to the sorption and concentration values of the desorbed compound in the solid state for t m. By employing this procedure based on the method of moments and using experimentally obtained kinetic curves, it is possible to calculate kinetic parameters of adsorption from aqueous solutions, Di and D,, and of desorption of sorbents by solvents, Di,d and Dd. Sorption and Desorption Processes in Polymers. Results of the investigation of the kinetics of adsorption of nitrobenzene from aqueous solutions on various poly-
-
1930 Ind. Eng. Chem. Res., Vol. 30, No. 8, 1991 Table IV. Diffusion Coefficients of SorDtion of Nitrobenzene
sorbent (3-5 Wofatit Y-59 Polysorb 40/100
mm 0.19 0.50 0.45 0.22 0.40
8
s
e.
cm2/s
0.45 3.2 0.7 2.2
0.4
0.48 0.12
1.6
cm2/s 3.8
0.2
0.19
1.2
5.6
1.0
8.5
r d
1
0.66
0.20
0.6
0.40
2.3
0.07
0.6
0.50 0.20
meric sorbents and summarized in Table 111. Those obtained for the kinetics of desorption with 2-propanol from sorbents saturated with nitrobenzene are given in Table IV. The parameters cg and t d represent the degree of bidispersity of the system: 7,
t,
=, Ta = Ti,a
td=-
Td
+
Ti,d
Their values characterize the necessity of assuming a bidiserpse structure in the adsorption-desorption process. An analysis of the values of the parameter t, during the adsorption of various sorbents leads to a conclusion that in the case of Polysorb 40/100 with a given particle size the decisive role is played by the mass transfer in the primary porous structure. On the other hand, with the sorbents G-5 and Wofatit Y-59 the contributions of both types of mass transfer in the polymer bulk and pores are comparable, which is connected with a much larger mean radius of the agglomerates forming the primary porous structure of Polysorb 40/100. As can be seen from the sorbed amount of surface-active compounds having various degrees of cross-linking (Figure 3), the degree of covering of polymer surfaces increases with decreasing surface area. This suggests that organic compounds dissolve in the polymer. Hence the low values of the diffusion coefficients (D,= (0.36-1.3) X cm2/s), determined assuming the diffusion model through the micropores, corresponds to diffusion in the polymer bulk. This is also confirmed by the values of the diffusion coefficients in desorption. During sorption of organic compounds the polymeric sorbents behave as polydisperse systems composed of transport macropores (P 150 nm), micropores (P I 15 nm), and polymeric mass-globules having radii between 6 and 76 nm. Under the same conditions, the decisive role in all cases of desorption with large sorbent is played by the mass transfer in the transport pores. It is of importance that in the case of desorption the diffusion coefficients in the primary porous structure are higher by 2 orders of magnitude than those in the adsorption from aqueous solutions. High values of the coefficient D, in the desorption are obviously related to the increasing motive power of the process due to the considerably higher solubility of nitrobenzene in 2propanol (mixing liquids). This is reflected in the parameters of the adsorption isotherms, r, from an aqueous solution and 2-propanol, which differ by several orders of magnitude. An analysis of the values of the adsorption coefficient Da shows that, with decreasing values of the parameter I?, i.e., with decreasing sorption of the organic compound on the sorbent, the values of the coefficient D, and the rate of the process in the polymer structure increase, in accordance with the values obtained for the sorption of various compounds on Polysorb 40/100. According to the values summarized in Table 111, a decrease in the sorption ability of an organic compound
-
(nitrobenzene) from 2-propanol during the desorption is accompanied by an increase in the diffusion coefficients in the polymer bulk, D d . The overall rate of the process also increases. It should be mentioned that the diffusion coefficients Di differ for various sorbents used in adsorption and desorption, which may be due to the different porous structure of the sorbents. In desorption, the diffusion coefficients Di,d (Table IV) have more or less the same values, probably due to the decisive influence of properties of the solvent on the rate of the desorption process. Conclusions The results show that the sorption of low-molecularweight compounds by polymeric sorbents depends not only on their chemical composition but also on the morphology of the porous structure. It was proved that, particularly in the case of polymers cross-linked to a lower degree and having as a consequence a smaller inner surface, organic compounds dissolve in the polymer bulk. In the adsorption-desorption processes the polydisperse structure consisting of macropores, micropores, and polymeric globules was considered, and the corresponding diffusion coefficients were determined by use of this model. Nomenclature A = fraction of macropores of the sorbent in the volume unit of the sorbent a, = initial amount of the compound sorbed a, = sorption value of the desorbed compound in the solid state for t m c, = initial concentration of the adsorbate c, = concentration value of the desorbed compound in the solid state for t m Da, Di = diffusion coefficients in the micropores and transport pores, respectively M, = first-order statistical moment-the area of the curve demarcated by the coordinates R1,R2 = grain sizes of the sorbent ro = radius of the globule u, = volume of the spherical particle of the sorbent up = solution volume in the apparatus
-
-
Greek Symbols 1' = Henry's adsorption constant according to the sorption
isotherm
rd = Henry's constant of the desorption isotherm c,,
td 7i
= degree of bidispersity of the system = time of diffusion relaxation in the primary and sec-
ondary porous structures, respectively Literature Cited Bender, H. Entfernung Organischer Schadstoffe aus Abwasser. Galuanotechnic 1985, 76, 721. Crook, C. A,; McDonel, R. P.; McNalty, J. T. Removal and Recovery of Phenols from Industrial Waste Effluents with Amberlite XAD Polymeric Adsorbents. Ind. Eng. Chem. Prod. Res. Deu. 1975,14, 113.
Gustafson, R. L.; Albright, R. L.; Heiser, J. Adsorption of Organic Species by High Surface Area Styrene-Divinylbenzene Copolymers. Ind. Eng. Chem.-Prod. Res. Deu. 1968, 7, 107. Hradil, J.; Wojacyziiska, M.; Svec, F.; Kolarz, B. N. Sorption of Phenols on Macroporous Methacrylate Copolymers Containing Ethyleneamine Groups. React. Polym. 1986, 4, 277. Kaedling, J.; Walther, H. J.; Bohm, R.; Helming, R. Elimination von Wasser Schadstoffen durch Makroporose Adsorberpolymere. Wiss. 2. Tech. Uniu. Dresden 1983, 32, 159. Kasatkin, L. G. Basic Process and Apparatus in Chemical Technology. Chimiya, Moscow 1971, 784. Koganovskaya, A. M.; Levchenko, T. M.; Kiritsenko, V. A. Sorption of Solubilized Compounds. Nauk. Dumka, Kiev 1977, 223.
Znd. Eng. Chem. Res. 1991,30,1931-1936 Kun, K. A.; Kunin, R. Macroreticular Resins. Formation of Macroreticular Styrene-Divinylbenzene Copolymers. J. Polym. Sci. A-1 1968, 6, 2689. Kunin, R. Polymeric Adsorbents for Treatment of Waste Effluents. Polym. Eng. Sci. 1977, 17, 58. Marton, G.;Szokonza, L.; Havas-Dencs, J.; Illes, 2s. Removal of Organics from Waste Water by Macromolecular Resins 11. Separation of two Components by Liquid Adsorption. Hung. J. Znd. Chem. (Vesprem) 1981,9, 263. Podlesnyuk, V. V.; Levchenko, T. M. Adsorption Properties of Styrene-Divinylbenzene Copolymers. Chim. Tekh. Vody 1981,3,327 (in Russian). Podlesnyuk, V. V.; Klimenko, N. A. Experimental Methods of Adsorbents Recovery. Chim. Tekh. Vody 1988,10,303 (in Russian). Rees, G. H. V.; An, L. Use of Amberlite XAD-2 Macroreticular Resin for the Recovery of Ambient Base Levels of Pesticides and Industrial Organic Pollutants from Water. Bull. Enuiron. Contam. Toxicol. 1979, 22, 761. Urano, X.;Kano, H.; Tabceta, T. The Reversibilities of the Adsorption and Desorption of Organic Compounds in Water. Bull. Chem. SOC.Jpn. 1984,57, 2307.
1931
Voloshchuk, A. M.; Dubinin, M. M.; Erashko, I. T. Structure of Microporous Adsorbents and Kinetia of Physical Adsorption 2. Evaluation of Diffusion Coefficientsof Benzene and +Pentane in Micropores of Carbon Adsorbents. Zzu. Akad. Nauk. USSR Ser. Khim. 1974a, 1943. Voloshchuk, A. M.; Zolotarev, M. M.; Illin, V. I. Using the Method of Statistical Moments for Determination of Internal Diffusion Coefficients in Adsorbents with Bidisperse Porous Structure and Linear Adsorptions Isotherms. Zzu. Akad. Nauk. USSR Ser. Khim. 1974b, 1250. Weber, W. J.; W e t , B. M. Synthetic Adsorbents and Activated Carbons for Water Treatment. J.Am. Water Works Assoc. 1981, 73, 420. Zolotarev, P. P.; Pilipenko, A. I. Conection between Process of Adsorption and Desorption in Particles with Bidisperse Porous Structure. Izv. Akad. Nauk USSR Ser. Khim. 1979, 1188 (in Russian).
Received for reuieu October 1, 1990 Revised manuscript received May 1 , 1991 Accepted May 8,1991
Rheology of Oil in Water Emulsions with Added Kaolinite Clay Yuhua Yan, Rajinder Pal,' and Jacob Masliyah* Department of Chemical Engineering, University of Alberta, Edmonton, Canada T6G 2G6
T h e present paper deals with the rheological measurements of oil in water emulsions with added kaolinite clay. T h e percent oil concentration, solids-free basis, was varied up to 70% by volume. T h e volume fraction of clay was varied up to 0.2 based on the total volume. T h e clay/emuIsion mixtures displayed shear thinning behavior. Yield stress was observed, and its value increased with clay volume fraction and with oil concentration. The shear stress versus shear rate data could be fitted by the Casson model for low oil concentrations (below 40%) and by the Herschel-Bulkley model for higher oil concentrations. On the basis of the experimental data,a correlation was developed to evaluate the relative viscosity of the clay/emulsion mixtures, where the relative viscosity was defined as the ratio of the viscosity of clay/emulsion mixtures to that of emulsions alone. A viscosity equation was also developed for calculating the viscosity of clay/emulsion mixtures.
Introduction Crude oil is often produced in the form of an oil/ water emulsion. Both oil in water (O/W) and water in oil types of emulsions are produced depending upon the reservoir conditions. Quite often the produced emulsions also carry some solids, mainly sand and clays. Solids content in the emulsions is normally low, although higher concentrations are encountered occasionally. The knowledge of the rheological properties of emulsions with added solids is important for the design and operation of production gathering facilities and emulsion pipelines. In the available literature, the rheological properties of solids suspensions and of oil/water emulsions have been studied extensively (see van Olphen (1977)for clay suspensions and Sherman (1970)and Pal (1987)for emulsions). However, little work has been reported on the flow behavior of emulsions with added solids. Following the study on the rheology of oil in water emulsions with added silica sand, glass beads, and polystyrene particles (Pal and Masliyah, 1990;Yan et al., 1991a,b),the present study investigates the effects of kaolinite clay addition to oil in water emulsions.
* Author
t o whom correspondence should be addressed. Present address: Department of Chemical Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.
Experimental Section Materials. The oil used was a refined mineral oil (Bayol-35),having a density of 780 kg/m3 and a viscosity of 2.4 mPa-s at 25 "C. The prepared emulsions were oil in water type; Le., the oil droplets formed the dispersed phase and the aqueous emulsifier solution formed the continuous phase. The emulsifier used to stabilize the emulsions was Triton X-100,a nonionic-type emulsifier. The concentration of the emulsifier was kept at 1% by volume, based on the aqueous phase. The clay used was kaolinite Hydrite-Flat D supplied by Georgia Kaolin Company. The median diameter of the dry clay particles was 5 pm. Experimental Procedure. The clay particles were first dispersed in the 1% Triton X-100water solution in an 1-L beaker. To ensure a good dispersion of the clay particles, shear was applied by a Gifford-Wood homogenizer (model 1-LV),which is a rotor and stator type mixer. Then, a known volume of oil was slowly added to the clay suspension while shear was applied. The mixture of clay and oil was continuously sheared for another 10-15 min after the completion of the oil addition. The mixing speed of the homogenizer was carefully chosen to avoid air entrainment and at the same time maintain a fairly high shear. Rheological measurements were carried out by use of a coaxial cylinder viscometer (Contraves Rheomat 115)
0888-5885/91/2630-1931$02.50/00 1991 American Chemical Society
