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Some experimental observations on recirculating semi-batch foam columns
Chemical
EngineeringScience
ooO9-2509/8S $3.00 + .OO Pergamon Press Ltd.
Val.40,No. 7, pp. 1305-l 308, 1985
Printed in Great Britain.
Some
experimental
observations
(Received
on recirculating
31 October
1983; accepted
1.
800
ml
200
ml distd.
3.
4.85
glycerine
+
Tempe-
rature
Viscosity
Density
(OK)
(Nsm '2)
(Kg.0'3)
299.5
1984)
1. Experimental conditions
system
2.
columns
(i) Number of recirculation cells Figure 1 depicts the kind of recirculation patterns observed in all the experiments mentioned in Table 1. The other gas-liquid contactor in which recirculation has been observed and investigated is the bubble column. For columns with low height to diameter ratio (L/D), more than one recirculation cell has been found side by side[13]. For higher L/D, the columns have exhibited one recirculation cell[ 14, 151. Predictions have also been made that, for high L/D columns, multiple cells could exist one above the other[l6, 17. Such multiple cells have been observed when adverse temperature gradient is imposed upon the column[lS]. The longitudinal dispersion in a bubble column with a single cell has also been estimated[l9]. However, recirculation in foam columns have so far exhibited only a single cell as depicited in Fig. 1. Even a 140 cm high (Experiment No. 15) and 15 cm x 15 cm semi-batch foam column has exhibited only a single recirculation cell. Moreover, in bubble columns, it is mainly the liquid that recirculates and bubbles start recirculating only when the
EXPERLMENTAL Recirculating semi-batch foam was generated in a foam column described earlier(l21. The experimental procedure and the liquid holdup measurement technique were also the same as described earlier[l2]. Aqueous glycerol solutions with Teepol as the foaming agent were used as the foaming liquids. Experimental parameters varied were the liquid viscosity, the surfactant concentration, the superficial gas velocity and the clear liquid height. Table 1 lists the experimental conditions for various experiments.
Expt * No.
18 April
foam
RESULTS AND DISCUSSION Results of the various experiments are presented below under three separate sections.
Cellular foams have many possible uses[l-51. They also occur on distillation and absorption trays@-81. Consequently, over the past few decades, they have attracted considerable engineering attention. When foam on a sieve tray gets converted into froth, some recirculation occurs which has been reported in the literature B-1 11. This paper presents substantially more experimental observations on recirculating semi-batch foam columns. These observations pertain to the following three hitherto unreported aspects of foam columns: (i) number of recirculation cells; (ii) critical liquid holdup at the foam-gas interface; and (iii) effect of clear liquid height on the liquid holdup profiles.
Table
semi-batch
0.060
1200
water+
Superficial air velocity
Vo+me
(ma 'lar102) 0.85
1000
12.0
1.33 1.33
loo0
22.5 31.0 45.3
2.00
im im
5.
2.3.0
2ooo
Teepol
+
-6.
800
ml
glycerin
7.
200
ml
distld.wster+
8,
4
ml
Tcepol
300
0.062
1200
Foam Height
(U102)
4.
ml
of
39.0
1.00
1470
14.2
1.70
1470
21.0
1.70
2ooo
27.0
9.
1.70
2250
28.5
10,
2.50
2230
33.0
11.
800
ml
glycerin
920
11.8
12.
2M
ml
distld.water+
+
297.5
0.066
1850
17.0
13.
2.5
ml
Teepol
2150
18.3
3.50
1400
17.5
7.4
1750
140.0
1200
14. 15.
300 7a3
ml.glycerin ml distld.
+ 0.46
CES 40:1-R
ml
+ water
298.5
0.0028
1090
Teepol
1305
1.80
1306
Shorter Communications GZiS
36 r---
out
71
I
,-Ecrit
t t
t
Foam- gas interface
-
:I
! Indicates
foam
height 1
Symbol
F 0 A M
Liquid POOL
I
I
I
= 0.032
Expt.
no.
.
6
0
7
I ,.“.a” ---- 0’
-
tt
GdS in
Fig. 1. Recirculation patterns in a semi-batch foam column. liquid recirculation velocity is higher than the bubble rise velocity. In the recirculating foam columns, however, the downward movement of bubbles at the wall could be easily seen. It is the foam that recirculates and not the continuous phase alone. It should be noted that these observations are confined to a limited range of superficial air velocity. The superficial air velocity has not been varied, for any given system, by more than 2.5 times. This is because the foam regime itself is confined to this limited range. At lower velocities, there is very little foam formed and at higher velocities the interface between the liquid pool and foam is not visible, thus suggesting preponderance of froth rather than foam. (ii) Critical The
when
liquid hoidup at the foam-gas
that reaches
view
it
boundary
a single thinning liquid film breaks a critical thickness has been well
Indicates
foam
Symbol
9
L
6 0.02
0.04
0.06
O.oB Liquid
0.10
holdup,
0.12
0.u
0.16
E C-1
Fig. 3. Liquid holdup profiles in recirculating semi-batch foam columns. investigated[20, 211; and models have also been suggested to predict this critical film thickness[20,21]. It has also been conjectured that films in the foam break when they have thinned to a certain critical thickness[22,23]. However, no evidence either for or against this conjecture has been reported so far. Our findings suggest that this conjecture is very likely to be correct. Figures 2-4 report the typical experimentally obtained liquid holdup profiles for recirculating semi-batch cellular foam columns for the conditions given in Table 1. Each of these figures is for a different gas-liquid system. The family of curves in each figure was obtained with different values
height
Expt.no.
_
201
~6crit
= 0.0375
t
t I
Indicates Symbol
foam
height
Expt.
*
11
0
12
no.
8
I
1
0.04
I
I
0.06 Liquid
holdup,
0.08 6
I
0.x)
(-1
Fig. 2. Liquid holdup profiles in recirculating semi-batch foam columns.
Liquid
holdup,
E t-J
Fig. 4. Liquid holdup profiles in recirculating semi-batch foam columns.
Shorter Communications of clear liquid height and superficial gas velocity. These figures indicate that, given a gas-liquid system, foams of different heights break at the foam-gas interface at more or less the same liquid holdup. This holdup is designated as ccn, in the figures. The results Figs. 224 are for systems with high viscosity (62 x 10-3Nsm-2). Similar results were also obtained for systems with low viscosity (2.8 x 10-‘Nsm-2). Only final values of cat for the low viscosity systems are reported here (Fig. 5). Figure 5 reports the observed dependence of etit on surfactant concentration. It is evident that for both low as well as high viscosity systems the L_+ decreases, as the surfactant concentration increases. This is expected, as the surface rigidity of the foam films would increase with the increase in the surfactant concentration. In fact, Ivanov et ~I.[241 have reported similar observations for single liquid films. Their results are reproduced in Fig. 6. However, it should be noted that the critical film thicknesses reported by Ivanov et al., are of the order of IO-’ m. On the other hand, the films at the foam-gas boundary were visibly much thicker. The film thickness at the foam-gas interface calculated from the models on the liquid holdup of foam[l2,23] also come out to be two orders of magnitude higher than that of Ivanov et al. The reason, of course, is clear. Ivanov et al.‘s films were small (radius 10m4m) and were studied in an environment relatively free from disturbances. Whereas foam films at foam-gas interface are continuously subjected to vibrations, as the gas has to disengage and liquid drops have to fall back onto the semi-batch foam. This view that the theories suggests present of film rupture[20, 21,24,25] are not adequate for foam films, as they pertain to only isolated films and neglect the role of the environment. Figure 5 also brings out the effect of viscosity of the c,,. It is evident that the decrease in L,~, as the surfactant concentration increases, is sharper for low viscosity system. It can also be inferred from Fig. 5. that the ectiit increases, as the viscosity increases. This latter inference, however, is through extrapolation of the data, as it is not possible to experimentally vary the viscosity substantially without simultaneously changing the surfactant concentration. (For low viscosity systems, the high surfactant concentration does not permit semi-batch operation. And for high vis-
1307
)-
I
I
I
System
I
with
C~2H250H
0.0062 0.0125 0.020
,-
I_~
1
2
Surfactant
I
I
I
I
3
4
5
6
concentration,
vlscoslty (Nsm2)
volume) in water
0.0028
+
TWPOl V. (by
voLume)
glycerine distld.
in water
+
x0.062
Tcepol
Fig. 5. Dependence
(M)
cosity systems, the low surfactant concentration does not yield any foam at all.) It should also be noted that the results of present investigation point only towards the presence of a critical liquid holdup and not towards the presence of a critical film thickness. However, as the liquid holdup and film thickness are closely linked, it is believed that the present evidence also points favourably towards the idea of critical film thickness at the foam-gas interface.
distld.
I
2 Teepol
Csx106
Fig. 6. Dependence of the critical film thickness on the surfactant concentration: data of Ivanov el al. [24].
glycerine
I
stabilized
Film radius (m)x102
I-
System
1
I
films
Experimental
30 ‘1. (by
80
I
: Aniline
concentratlon,Cs(mI.m31x
10’
of critical liquid holdup on surfactant concentration
1308
Shorter Communications
(iii) E&cl of clear liquid height on the liquid holdup profiles Figures 24 also bring out another fact. They show that the clear liquid height (or the volume) of the foaming liquid has an appreciable effect on liquid holdup profiles in recirculating semi-batch foam columns. Up to a certain point, liquid holdup of the foam increase as the clear liquid height increases. After that, the increases in clear liquid height does not have any noticeable effect on the liquid holdup. These trends are similar to those reported by Takahashi et al.1261 for the effect of clear liauid height on the froths on sieve-trays. CONCLUSIONS The study has led us to conclude
that: (i) The recirculating semi-batch foam columns have only one recirculation cell. (ii) Semi-batch foams break at the foam-gas boundary at a certain critical liquid holdup which is characteristic of the gas-liquid system. (iii) Clear liquid height of the foamed liquid affects the liquid holdup profiles of semi-batch recirculating foam columns. Department of Chemical Engineering Indian Institute of Science Bangalore-560012, India
DILIP DESAI R. KUMAR*
REFERENCES
[I] Rubin E. and Gaden E. L., Jr., New Chemical Engineering Separation Techniques, (Edited by Schoen H. M.) p. 319. Interscience, New York 1962. [2] Lemlich R. (Ed.), AcLForptive Bubbk Separation Techniques. Academic Press, New York 1972. [3] Bikerman J. J., Foams. Springer-Verlag. New York 1973. [4] Aker, R. J. (Ed.), Foams. Academic Press, New York 1976. [S] Jackson J., Br. Chem. Engng 1963 B(5) 319. [6] Zuiderweg F. J. and Harmens A., Chem. Engg Sci., 1958 9 89. *Author
to whom correspondence
should be addressed.
[71 Fane A. G. and Sawistowski H., Distillntion 1969, p. 1:8. Institute of Chemical Engineers, London 1969. PI Biswas J. and Kumar R., Chem. Engng Sci. 1981 36(9) 1547. r91 Ho G. H., Muller R. L. and Price R. G. H., Distillation 1969, p. 2:10. Institute of Chemical Engineers, London 1969. I101 Porter K. E., Transport Phenomena, (Edited by Rottenberg P. A.) P. 6:95. Institute of Chemical Engineers, London 1965. [Ill Porter K. E., Davies B. J. and Wong P. F. Y., Tram Inst. Chem. Engrs 1967 45 T265. ]121 Desai D. and Kumar, R., Chem. Engng. Sci., 1983 38 (9) 1525. [I31 Beek W. J., Symp. on Two-Phase Flow, F401 University of Exeter 1965. [I41 Rietema K. and Ottengraf S. P. P., Trans. Inst. Chem. Engrs 1970 48 T54. 1151 Whalley P. B. and Davidson J. F., Inst. Chem. Engrs,flnst. Mech. Engrs, Symp. on Multi-Phase FIow Sysfems, J5. Institute of Chemical Engineers/Institute of Mechanical Engineers, London 1974. iI61Joshi J. B. and Sharma M. M., Trans. Ins?. Chem. Engrs 1979 57 244. 1171 Joshi J. B. and Sharma M. M., Trans. Inst. Chem. Engrs 1982 60 256. [181 Rietema K., Chem. Engng Sri. 1982 37(8) 1125. 1191 Mashelkar R. A. and Ramachandran P. A., Trans. Inst. Chem. Engrs 1975 53 274. Scheludko A., Advun. Cofloid Interface Sci. 1967 1 391. t::; Clunie J. S., Goodman J. F. and Ingram B. T., Surface and CoIZoid Science (Edited by Matiievic) Vol. 3. WilevInterscience, New York 1971. _ ’ ]22] Hartland S. and Barber A. D., Trans. Insr. Chem. Engrs 1974 52 43. ]231 Barber A. D. and Hartland S., Trans. Insr. Chem. Engrs 1975 53 106. 1241 Ivanov I. B., Radoev B., Manev E. and Scheludko A., Trans. Faraday Sot. 1970 66 1262. [251 Maldarelli C., Jain R. K.. Ivanov I. B. and Ruckenstein E., J. Colloid Inferface Sci. 1980 78(l) Il8:- ~~~~~~_-____ P61 Takahashi T., Miyahara T. and Shimixu K.. J. Chem. Engng Japan, 1974 7(2) 75.
EngineeringScience
ooO9-2509/8S $3.00 + .OO Pergamon Press Ltd.
Val.40,No. 7, pp. 1305-l 308, 1985
Printed in Great Britain.
Some
experimental
observations
(Received
on recirculating
31 October
1983; accepted
1.
800
ml
200
ml distd.
3.
4.85
glycerine
+
Tempe-
rature
Viscosity
Density
(OK)
(Nsm '2)
(Kg.0'3)
299.5
1984)
1. Experimental conditions
system
2.
columns
(i) Number of recirculation cells Figure 1 depicts the kind of recirculation patterns observed in all the experiments mentioned in Table 1. The other gas-liquid contactor in which recirculation has been observed and investigated is the bubble column. For columns with low height to diameter ratio (L/D), more than one recirculation cell has been found side by side[13]. For higher L/D, the columns have exhibited one recirculation cell[ 14, 151. Predictions have also been made that, for high L/D columns, multiple cells could exist one above the other[l6, 17. Such multiple cells have been observed when adverse temperature gradient is imposed upon the column[lS]. The longitudinal dispersion in a bubble column with a single cell has also been estimated[l9]. However, recirculation in foam columns have so far exhibited only a single cell as depicited in Fig. 1. Even a 140 cm high (Experiment No. 15) and 15 cm x 15 cm semi-batch foam column has exhibited only a single recirculation cell. Moreover, in bubble columns, it is mainly the liquid that recirculates and bubbles start recirculating only when the
EXPERLMENTAL Recirculating semi-batch foam was generated in a foam column described earlier(l21. The experimental procedure and the liquid holdup measurement technique were also the same as described earlier[l2]. Aqueous glycerol solutions with Teepol as the foaming agent were used as the foaming liquids. Experimental parameters varied were the liquid viscosity, the surfactant concentration, the superficial gas velocity and the clear liquid height. Table 1 lists the experimental conditions for various experiments.
Expt * No.
18 April
foam
RESULTS AND DISCUSSION Results of the various experiments are presented below under three separate sections.
Cellular foams have many possible uses[l-51. They also occur on distillation and absorption trays@-81. Consequently, over the past few decades, they have attracted considerable engineering attention. When foam on a sieve tray gets converted into froth, some recirculation occurs which has been reported in the literature B-1 11. This paper presents substantially more experimental observations on recirculating semi-batch foam columns. These observations pertain to the following three hitherto unreported aspects of foam columns: (i) number of recirculation cells; (ii) critical liquid holdup at the foam-gas interface; and (iii) effect of clear liquid height on the liquid holdup profiles.
Table
semi-batch
0.060
1200
water+
Superficial air velocity
Vo+me
(ma 'lar102) 0.85
1000
12.0
1.33 1.33
loo0
22.5 31.0 45.3
2.00
im im
5.
2.3.0
2ooo
Teepol
+
-6.
800
ml
glycerin
7.
200
ml
distld.wster+
8,
4
ml
Tcepol
300
0.062
1200
Foam Height
(U102)
4.
ml
of
39.0
1.00
1470
14.2
1.70
1470
21.0
1.70
2ooo
27.0
9.
1.70
2250
28.5
10,
2.50
2230
33.0
11.
800
ml
glycerin
920
11.8
12.
2M
ml
distld.water+
+
297.5
0.066
1850
17.0
13.
2.5
ml
Teepol
2150
18.3
3.50
1400
17.5
7.4
1750
140.0
1200
14. 15.
300 7a3
ml.glycerin ml distld.
+ 0.46
CES 40:1-R
ml
+ water
298.5
0.0028
1090
Teepol
1305
1.80
1306
Shorter Communications GZiS
36 r---
out
71
I
,-Ecrit
t t
t
Foam- gas interface
-
:I
! Indicates
foam
height 1
Symbol
F 0 A M
Liquid POOL
I
I
I
= 0.032
Expt.
no.
.
6
0
7
I ,.“.a” ---- 0’
-
tt
GdS in
Fig. 1. Recirculation patterns in a semi-batch foam column. liquid recirculation velocity is higher than the bubble rise velocity. In the recirculating foam columns, however, the downward movement of bubbles at the wall could be easily seen. It is the foam that recirculates and not the continuous phase alone. It should be noted that these observations are confined to a limited range of superficial air velocity. The superficial air velocity has not been varied, for any given system, by more than 2.5 times. This is because the foam regime itself is confined to this limited range. At lower velocities, there is very little foam formed and at higher velocities the interface between the liquid pool and foam is not visible, thus suggesting preponderance of froth rather than foam. (ii) Critical The
when
liquid hoidup at the foam-gas
that reaches
view
it
boundary
a single thinning liquid film breaks a critical thickness has been well
Indicates
foam
Symbol
9
L
6 0.02
0.04
0.06
O.oB Liquid
0.10
holdup,
0.12
0.u
0.16
E C-1
Fig. 3. Liquid holdup profiles in recirculating semi-batch foam columns. investigated[20, 211; and models have also been suggested to predict this critical film thickness[20,21]. It has also been conjectured that films in the foam break when they have thinned to a certain critical thickness[22,23]. However, no evidence either for or against this conjecture has been reported so far. Our findings suggest that this conjecture is very likely to be correct. Figures 2-4 report the typical experimentally obtained liquid holdup profiles for recirculating semi-batch cellular foam columns for the conditions given in Table 1. Each of these figures is for a different gas-liquid system. The family of curves in each figure was obtained with different values
height
Expt.no.
_
201
~6crit
= 0.0375
t
t I
Indicates Symbol
foam
height
Expt.
*
11
0
12
no.
8
I
1
0.04
I
I
0.06 Liquid
holdup,
0.08 6
I
0.x)
(-1
Fig. 2. Liquid holdup profiles in recirculating semi-batch foam columns.
Liquid
holdup,
E t-J
Fig. 4. Liquid holdup profiles in recirculating semi-batch foam columns.
Shorter Communications of clear liquid height and superficial gas velocity. These figures indicate that, given a gas-liquid system, foams of different heights break at the foam-gas interface at more or less the same liquid holdup. This holdup is designated as ccn, in the figures. The results Figs. 224 are for systems with high viscosity (62 x 10-3Nsm-2). Similar results were also obtained for systems with low viscosity (2.8 x 10-‘Nsm-2). Only final values of cat for the low viscosity systems are reported here (Fig. 5). Figure 5 reports the observed dependence of etit on surfactant concentration. It is evident that for both low as well as high viscosity systems the L_+ decreases, as the surfactant concentration increases. This is expected, as the surface rigidity of the foam films would increase with the increase in the surfactant concentration. In fact, Ivanov et ~I.[241 have reported similar observations for single liquid films. Their results are reproduced in Fig. 6. However, it should be noted that the critical film thicknesses reported by Ivanov et al., are of the order of IO-’ m. On the other hand, the films at the foam-gas boundary were visibly much thicker. The film thickness at the foam-gas interface calculated from the models on the liquid holdup of foam[l2,23] also come out to be two orders of magnitude higher than that of Ivanov et al. The reason, of course, is clear. Ivanov et al.‘s films were small (radius 10m4m) and were studied in an environment relatively free from disturbances. Whereas foam films at foam-gas interface are continuously subjected to vibrations, as the gas has to disengage and liquid drops have to fall back onto the semi-batch foam. This view that the theories suggests present of film rupture[20, 21,24,25] are not adequate for foam films, as they pertain to only isolated films and neglect the role of the environment. Figure 5 also brings out the effect of viscosity of the c,,. It is evident that the decrease in L,~, as the surfactant concentration increases, is sharper for low viscosity system. It can also be inferred from Fig. 5. that the ectiit increases, as the viscosity increases. This latter inference, however, is through extrapolation of the data, as it is not possible to experimentally vary the viscosity substantially without simultaneously changing the surfactant concentration. (For low viscosity systems, the high surfactant concentration does not permit semi-batch operation. And for high vis-
1307
)-
I
I
I
System
I
with
C~2H250H
0.0062 0.0125 0.020
,-
I_~
1
2
Surfactant
I
I
I
I
3
4
5
6
concentration,
vlscoslty (Nsm2)
volume) in water
0.0028
+
TWPOl V. (by
voLume)
glycerine distld.
in water
+
x0.062
Tcepol
Fig. 5. Dependence
(M)
cosity systems, the low surfactant concentration does not yield any foam at all.) It should also be noted that the results of present investigation point only towards the presence of a critical liquid holdup and not towards the presence of a critical film thickness. However, as the liquid holdup and film thickness are closely linked, it is believed that the present evidence also points favourably towards the idea of critical film thickness at the foam-gas interface.
distld.
I
2 Teepol
Csx106
Fig. 6. Dependence of the critical film thickness on the surfactant concentration: data of Ivanov el al. [24].
glycerine
I
stabilized
Film radius (m)x102
I-
System
1
I
films
Experimental
30 ‘1. (by
80
I
: Aniline
concentratlon,Cs(mI.m31x
10’
of critical liquid holdup on surfactant concentration
1308
Shorter Communications
(iii) E&cl of clear liquid height on the liquid holdup profiles Figures 24 also bring out another fact. They show that the clear liquid height (or the volume) of the foaming liquid has an appreciable effect on liquid holdup profiles in recirculating semi-batch foam columns. Up to a certain point, liquid holdup of the foam increase as the clear liquid height increases. After that, the increases in clear liquid height does not have any noticeable effect on the liquid holdup. These trends are similar to those reported by Takahashi et al.1261 for the effect of clear liauid height on the froths on sieve-trays. CONCLUSIONS The study has led us to conclude
that: (i) The recirculating semi-batch foam columns have only one recirculation cell. (ii) Semi-batch foams break at the foam-gas boundary at a certain critical liquid holdup which is characteristic of the gas-liquid system. (iii) Clear liquid height of the foamed liquid affects the liquid holdup profiles of semi-batch recirculating foam columns. Department of Chemical Engineering Indian Institute of Science Bangalore-560012, India
DILIP DESAI R. KUMAR*
REFERENCES
[I] Rubin E. and Gaden E. L., Jr., New Chemical Engineering Separation Techniques, (Edited by Schoen H. M.) p. 319. Interscience, New York 1962. [2] Lemlich R. (Ed.), AcLForptive Bubbk Separation Techniques. Academic Press, New York 1972. [3] Bikerman J. J., Foams. Springer-Verlag. New York 1973. [4] Aker, R. J. (Ed.), Foams. Academic Press, New York 1976. [S] Jackson J., Br. Chem. Engng 1963 B(5) 319. [6] Zuiderweg F. J. and Harmens A., Chem. Engg Sci., 1958 9 89. *Author
to whom correspondence
should be addressed.
[71 Fane A. G. and Sawistowski H., Distillntion 1969, p. 1:8. Institute of Chemical Engineers, London 1969. PI Biswas J. and Kumar R., Chem. Engng Sci. 1981 36(9) 1547. r91 Ho G. H., Muller R. L. and Price R. G. H., Distillation 1969, p. 2:10. Institute of Chemical Engineers, London 1969. I101 Porter K. E., Transport Phenomena, (Edited by Rottenberg P. A.) P. 6:95. Institute of Chemical Engineers, London 1965. [Ill Porter K. E., Davies B. J. and Wong P. F. Y., Tram Inst. Chem. Engrs 1967 45 T265. ]121 Desai D. and Kumar, R., Chem. Engng. Sci., 1983 38 (9) 1525. [I31 Beek W. J., Symp. on Two-Phase Flow, F401 University of Exeter 1965. [I41 Rietema K. and Ottengraf S. P. P., Trans. Inst. Chem. Engrs 1970 48 T54. 1151 Whalley P. B. and Davidson J. F., Inst. Chem. Engrs,flnst. Mech. Engrs, Symp. on Multi-Phase FIow Sysfems, J5. Institute of Chemical Engineers/Institute of Mechanical Engineers, London 1974. iI61Joshi J. B. and Sharma M. M., Trans. Ins?. Chem. Engrs 1979 57 244. 1171 Joshi J. B. and Sharma M. M., Trans. Inst. Chem. Engrs 1982 60 256. [181 Rietema K., Chem. Engng Sri. 1982 37(8) 1125. 1191 Mashelkar R. A. and Ramachandran P. A., Trans. Inst. Chem. Engrs 1975 53 274. Scheludko A., Advun. Cofloid Interface Sci. 1967 1 391. t::; Clunie J. S., Goodman J. F. and Ingram B. T., Surface and CoIZoid Science (Edited by Matiievic) Vol. 3. WilevInterscience, New York 1971. _ ’ ]22] Hartland S. and Barber A. D., Trans. Insr. Chem. Engrs 1974 52 43. ]231 Barber A. D. and Hartland S., Trans. Insr. Chem. Engrs 1975 53 106. 1241 Ivanov I. B., Radoev B., Manev E. and Scheludko A., Trans. Faraday Sot. 1970 66 1262. [251 Maldarelli C., Jain R. K.. Ivanov I. B. and Ruckenstein E., J. Colloid Inferface Sci. 1980 78(l) Il8:- ~~~~~~_-____ P61 Takahashi T., Miyahara T. and Shimixu K.. J. Chem. Engng Japan, 1974 7(2) 75.