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A new system for the measurement of effective interfacial area in agitated liquid—liquid contractors by the chemical method
ChemicolEngineering Science, 1973, Vol. 28. pp. 2089-2092.
A new system for the measurement
Pergamon Press 1973.
Printed in Great Britain
of effective interfacial area in agitated liquid-liquid the chemical method
contactors by
(Received 2 October 1972)
THE EFFECTIVE interfacial area is an important variable which determines the capacity of an agitated liquid-liquid contactor. Also, for the design of liquid-liquid contactors involving chemical reaction, it is necessary to know the values of continuous phase mass transfer coefficient and effective interfacial area separately [ I]. The chemical method of measuring interfacial area in liquid-liquid contactors was suggested by Nanda and Sharma[2]. It was found that extraction of esters such as butyl formate, amyl formate etc., which are sparingly soluble in water, into aqueous solutions of sodium hydroxide, can be conveniently adopted for measuring effective interfacial areas in liquid extraction columns. This method has been employed by a number of workers to obtain values of effective interfacial area in a variety of liquid-liquid contactors [3- 111. Esters of chloroacetic acid, dichloroacetic acid, oxalic acid etc., which are sparingly soluble in water, have also been employed. However, the esters of acids other than formic acid pose some health hazards and these materials have to be handled with great care. It was thought desirable to develop other systems which can be employed to cover a still wider range of process variables and which may be more convenient in some respects. Gehlawat and Sharma[lZ] have studied the kinetics of absorption of isobutylene in aqueous solutions of sulphuric acid in the range of acid concentration from 49.5 to 71.0 per cent (wt/wt). Sankholkar and Sharma[l3] have studied the kinetics of absorption of isoamylene (2-methyl-2-butene) in aqueous solutions of sulphuric acid in the range of acid concentration from 61.5 to 75.0 per cent (wtlwt). (Extraction of the above olefins into aqueous sulphuric acid is industrially important). The absorption of isobutylene and isoamylene was found to be accompanied by a fast pseudo-first order reaction. The value of the pseudo-first order rate constant was found to be a strong function of the concentration of sulphuric acid. The value of the pseudo-first order rate constant for the above olefins was found to vary from lo2 to lo8 set-’ in the range of acid concentration covered by the authors. Thus, it should be possible to employ extraction of an olefin, with a structure akin to that of isobutylene, into aqueous solutions of sulphuric acid, to obtain values of effective interfacial area in a variety of contactors. Isoamylene has a low boiling point (38.5”C) and hence it was thought desirable to use an oletin having a higher boiling point. Diisobutylene (2,4,4-trimethyl2-pentene) appeared to be an attractive olefin. The sulphuric acid concentration was selected in the range of 72-77 per cent (wt/wt) (68 per cent sulphuric acid can also be
employed). The solubility of diisobutylene in water at 30°C is very low (of the order of lo-* g mole/cm3) and hence ah the conditions which are necessary for the validity of the chemical method for the measurement of effective interfacial area will be satisfied. (Ihe theoretical aspects of the chemical method have been discussed by Nanda and Sharma[2] and Sharma and Danckwerts[l4] and will not be repeated here). It was first thought that pure diisobutylene may be contacted with sulphuric acid but this idea was rejected as it would be very impracticable to follow the extent of the reaction accurately. Since the solubility of diisobutylene in water is inordinately low, it can be mixed with any appropriate organic liquid, which does not react with sulphuric acid, without introducing any resistance in the diisobutylene phase. The course of the extraction can then be conveniently followed by noting the fall in the concentration of diisobutylene in the organic phase. Toluene, monochlorobenzene and 1,2,4-trichlorobenzene were thought to be useful diluents for the initial study. Thus, when the organic phase constitutes the dispersed phase, the properties of the dispersed phase can be varied over a wide range by a judicious selection of the diluent. However, when aqueous sulphuric acid is used as the dispersed phase, the properties of the dispersed phase can be varied only over a limited range. The differences in the properties of the organic phase and the aqueous acid phase are very large and hence large variations in the properties of the dispersed and continuous phase can be realised by interchanging the phases. Since the specific rate of extraction of diisobutylene is expected to be very low, it may be possible to carry out batch experiments in a reasonable batch time even in a mechanically agitated contactor, without any substantial change in the properties of both the phases and without any significant decrease in the dispersed phase hold up. Some preliminary experiments in a mechanically agitated contactor indicated that the phase separation occurred rapidly after the agitation was stopped. MATERIALS Diisobutylene (2,4,4-trimethyl-2-pentene), toluene, monochlorobenzene and 1,2,4-trichlorobenzene were obtained from firms of repute. Sulphuric acid used was of commercial grade. Aqueous solutions of sulphuric acid were prepared with deionised water.
2089 C.E.S. Vol. 28 No. I1 -L
ANALYSIS The extent of reaction was followed by noting the fall
in the concentration of diisobutylene in the organic phase. This can be conveniently carried out chromatogmphically. An F and M Model 720 Dual Column Programmed Temperature Gas Chromatogmph was used. The components of organic phase were analysed by 6 mm, id. 3 m long copper column packed with 10 per cent Carbowax 20 M on Chromosorb-W. EXPERIMENTAL Stirred cells It is necessary to know the value of the specific rate of extraction of diisobutylene for the measurement of effective interfacial area. Diisobutylene dissolved in toluene or monochlorobenzene was contacted with an aqueous solution of sulphuric acid in stirred cells of known interfacial area. Most of the experiments were carried out in a 95 cm i.d. glass stirred cell. The design of the stirred cell was similar to that used by Gehlawat and Sharma[lZ]. In view of the low specific rate of extraction of diisobutylene, the experimental runs were made from 10 to 40 hr. In all the cases, the aqueous phase was below the organic phase. Both the phases were stirred, so as to renew the interface continuously without disturbing the interface significantly. The stirrer having two sets of blades one above the other, was so adjusted that the lower edge of upper set of blades and the upper edge of lower set of blades were just above, and below the interface, respectively. In some experiments, the speed of stirring was varied from 25 to 50revlmin to study the effect of speed of stirring on the specific rate of extraction of diisobutylene. Agitated contactor A 10.6cm i.d. vessel was used, which was provided with four vertical baffles, each one-tenth the diameter of the tank, mounted against the tank wall at right angles to it and spaced at 90” intervals around the tank. A fourbladed straight paddle impeller of glass with a diameter of 4.7 cm was used. Most of the experiments were carried out with the organic phase as the dispersed phase. Here a known amount of aqueous sulphuric acid was charged to the previously cleaned contactor. The organic phase (consisting of diisobutylene mixed with either toluene, monochlorobenzene or 1,2,4-trichlorobenzene) was then added carefully without significantly disturbing the interface between the two liquids. The speed of agitation was varied from 500 to 1200rev/min. In most cases, the batch experiments were carried out for a period of 15-30min. It was observed that at the end of the experiment the temperature was practically the same as at the beginning. The phase separation was found to occur in less than 90 set after the cessation of agitation. In the case of 77 per cent (wt/wt) sulphuric acid, it was observed that a small amount of diisobutylene was converted to oligomer. Some experiments were also carried out with 72 per cent (wt/wt) aqueous sulphuric acid as the dispersed phase. The continuous phase was a mixture of diisobutylene and monochlorobenzene. The speed of agitation was varied from 600 to 1500 revlmin. In view of the large volume of organic phase, the batch experiments were carried out for a period of 2-5 hr in order to get a significant decrease in the concentration of diisobutylene in the organic phase. The phase
2090
separation was found to occur in less than 30 set after the cessation of agitation. RESULTS AND DISCUSSION Stirred cells The specific rate of extraction of diisobutylene into aqueous sulphuric acid of a particular concentration was found to be independent of the speed of stirring in the range of 25-50revlmin (Fig. 1). The specific rate of extraction was also found to be proportional to the mole fraction of diisobutylene in the organic phase (Fig. 2). Thus, the extraction of diisobutylene in aqueous sulphuric acid solutions is accompanied by fast pseudo-first order reaction. The relevant values of specific rate of extraction, g mole/cm* set, are reported in Table 1.
2.0Speed
of stirring,
rev/min
Fig. 1. Effect of speed of stirring on the specific rate of extraction of diisobutylene from diisobutylene-toluene mixture into 77% (wt/wt) aqueous sulphuric acid in the stirred cell, at 3O”C, 0 mole fraction of diisobutylene = 0.71, 0 mole fraction ofdiisobutylene = 0.38.
Mole
fraction
of
diisobutylene
Fig. 2. Effect of concentration of diisobutylene on the specific rate of extraction of diisohutylene from diisobutylenetoluene mixture, into 77% (wt/wt) aqueous sulphuric acid, at 30°C.
Shorter Communications Table 1. Specific rates of extraction of diisobutylene into aqueous solutions of sulphutic acid in the stirred cell (temperature = 30°C) Concentration H,SO,
of
Organic phase (% wtlwt)
Diisobutylene-toluene
13.35
77
0.71 0.38 0.21
6.15 3.32 1.91
Diisobutylene-monochlorobenzene
12.01
72
0.48
1.05
I
I
1100
1300
1 700
900
Speed of ogitotion,
I50 1500
revlmin
Fig. 3. Effect of speed of agitation on the effective interfacial area in the agitated liquid-liquid contactor (Temp. = 30°C). Dispersed phase
Continuous phase
Fractional dispersed phase hold up (average)
DIB-T (75% wtlwt DIB)
77% (wtlwt) H,SO,
0.09
DIB-MCB (50% wt/wt DIB)
72% (wtlwt) H,SO,
0.09
DIB-1,2,4-TCB (30% wt/wt DIB)
72% (wtlwt) H,SO,
0.09
72% (wtlwt) H,SO,
DIB-MCB (35% wtlwt DIB)
0.30
DIB = diisobutylene
MCB = monochlorobenzene
T
TCB = trichlorobenzene.
= toluene
Agitated
Specific rate of extractionx log, (g mole/cm2 set)
(g mole/l.)
0 500
Mole fraction of diisobutylene in the organic phase
results in changing both the density as well as the viscosity of the dispersed phase. The values of effective interfacial area obtained with 72 per cent (wtlwt) aqueous sulphuric acid as the dispersed phase and diisobutylene-monochlorobenzene as the continuous phase are also plotted against the speed of agitation in Fig. 3, for an average dispersed phase hold up of 30 per cent. The values of effective interfacial area obtained in this case with a dispersed phase hold up of about 30 per cent are quite low as compared to those obtained with aqueous sulphuric acid as the continuous phase, for which the dispersed phase hold up was about 9 per cent. This is probably due to the fact that the properties of the continuous phase exercise a dominating influence on the dispersion characteristics. The properties of the continuous phase can be varied by a proper choice of the diluent. Further work is proposed to be carried out with a variety of diluents to cover a wide range of properties. It is also planned to develop another system, namely a-methyl styrene aqueous sulphuric acid, as this system is expected to allow further variations in the properties of the system. CONCLUSIONS The extraction of an olefin like diisobutylene, diluted with substances like toluene, monochlorobenzene, 1,2,4trichlorobenzene etc., into aqueous solutions of sulphuric acid (72-77 per cent (wtlwt)) can be conveniently employed for the measurement of interfacial area in mechanically agitated contactors. For contactors where the effective interfacial area is expected to be much lower than that in the case of mechanically agitated contactor, lower olefins like isoamylene, 2-methyl-2-pentene, etc. can be employed. It is reported that isoamylene from the C5 fraction of naphthacrackers is recovered by selective extraction in aqueous sulphuric acid solutions[ 151. The data from the commercial columns coupled with the data of Sankholkar and Sharma [ 131 can perhaps give the values of effective interfacial area in the above industrial contactors. Acknowledgement-One of us (DSS) wishes to thank the University Grants Commission for an award of a scholarship which enabled this work to be carried out.
contactor
The values of effective interfacial area obtained in the various experiments, with an average organic dispersed phase hold up of 9 per cent, are plotted against the speed of agitation in Fig. 3. The interfacial area varies linearly with the speed of agitation. This observation is in agreement with that of Femandes and Sharma[3]. A change over from monochlorobenzene to 1,2A+ichlorobenzene as a diluent
D. S. SANKHOLKAR M. M. SHARMA Department of Chemical University of Bombay Matunga Road Bombay-l 9 India
209 1
Technology
Shorter Communications REFERENCES SHARMA M. M., Chem. Age India 1962 13 335. t:; NANDA A. K. and SHARMA M. M., Chem. Engng Sci. 1966 21707. 131 FERNANDES J. B. and SHARMA M. M., Chem. Engng Sci. 1967 22 1267. 141 FERNANDES J. B. and SHARMA M. M., Chem. Engng Sci. 1968 23 9. PI SHARMA M. M. and NANDA A. K., Trans. In&n. Chem. Engrs 1968 46 T44. [61 PURANIK S. A. and SHARMA M. M., Chem. Engng Sci. 1970 25 257. [71 de SANTIAGO M. and TRAMBOUZE P., Chem. Engng Sci. 197 126 1803. PI de SANTIAGO M. and BIDNER M. S., Chem. Engng Sci. 197126 175. [91 ONDA K., TAKEUCHI H. and TAKAHASHI M., Kagaku Kdgaku 197135 22 1. [lOI SHAH A. K. and SHARMA M. M., Can. J. Chem. Engng 197 149 596. 120,197268 124. [Ill FERNANDESJ.B.,A.Z.Ch.E.Symp.Ser.No. iI21 GEHLAWAT J. K. and SHARMA M. M., Chem. Engng Sci. 1968 23 1173. iI31 SANKHOLKAR D. S. and SHARMA M. M., Chem. Engng Sci. 1973 28 49. iI41 SHARMA M. M. and DANCKWERTS P. V., Brit. Chem. Engng 1970 15522. D. K., PATINKIN S. H. and SANFORD R. A., Petrol Ref. 1960 39 229. [IV FOSTER R. L., WUNDERLICH ChemicalEngineering
Science,
1973, Vol. 28. pp. 2092-2093.
Pergamon Press.
Printed in Great Britain
Gas absorption with second order reaction-comparison factor equations
of approximate
enhancement
(Received 13 October 1972) IF A DISSOLVED gas C undergoes an irreversible secondorder reaction of Iinite speed with a dissolved reactant B, it is known that the governing differential equations cannot be solved analytically. But Van Krevelen and Hoftijer [ I] showed that the following implicit equation could be fitted to the numerical solutions for film model within about 10 per cent:
and the Kishinevskii equation [ 121: E=
1+*{I
-exp
a
(-0.65X@-)}(Y
(3)
where I
.
The Van Krevelen equation, i.e. Eq. (I), gives E as an implicit function of relevant parameters hence E cannot be calculated simply. On the other hand Porter and Kishinevskii equations are explicit, but their validities have not been
where
,,,f =
D&P -;
E,=(l+-$-$
k,*
320
Here E is the enhancement factor and E, is the enhancement factor corresponding to instantaneous reaction. A number of workers [2-41 have used Eq. (I) for penetration theory case by using the following equation for E1 Et=
t
x Colculoted . Calculated
from Kishinvskii’s aquatin from Puter~ equofion
160-
so-
e+-$g
40E
as this procedure has some justification[2,4]_ Numerical solutions for the penetration-theory case have been given by Perry and Pigford[5], by Brian ef al.[4] and by Pearson[6]. Observations of Brian et al.141 showed that Eq. (I) approximately represents all the numerical data and the error does not exceed 12 per cent. Equation (1) is now widely known and textbooks of gas absorption[7-91 recommend it for design purposes. Alper[ IO] has pointed out that two more less well known explicit equations are available in the literature. These are the Porter equation [ 1 l] :
20-
IO 8 6
10-
5-
M-pA.1 I I
I 5
I
I
I
I
I
I
IO
20
40
60
160
320
E,
E= l+(E,-]){I-exp-[(VM-l)/(E,-I)]}
(2)
2092
Fig. 1. Comparison of approximate equations.
I
640
A new system for the measurement
Pergamon Press 1973.
Printed in Great Britain
of effective interfacial area in agitated liquid-liquid the chemical method
contactors by
(Received 2 October 1972)
THE EFFECTIVE interfacial area is an important variable which determines the capacity of an agitated liquid-liquid contactor. Also, for the design of liquid-liquid contactors involving chemical reaction, it is necessary to know the values of continuous phase mass transfer coefficient and effective interfacial area separately [ I]. The chemical method of measuring interfacial area in liquid-liquid contactors was suggested by Nanda and Sharma[2]. It was found that extraction of esters such as butyl formate, amyl formate etc., which are sparingly soluble in water, into aqueous solutions of sodium hydroxide, can be conveniently adopted for measuring effective interfacial areas in liquid extraction columns. This method has been employed by a number of workers to obtain values of effective interfacial area in a variety of liquid-liquid contactors [3- 111. Esters of chloroacetic acid, dichloroacetic acid, oxalic acid etc., which are sparingly soluble in water, have also been employed. However, the esters of acids other than formic acid pose some health hazards and these materials have to be handled with great care. It was thought desirable to develop other systems which can be employed to cover a still wider range of process variables and which may be more convenient in some respects. Gehlawat and Sharma[lZ] have studied the kinetics of absorption of isobutylene in aqueous solutions of sulphuric acid in the range of acid concentration from 49.5 to 71.0 per cent (wt/wt). Sankholkar and Sharma[l3] have studied the kinetics of absorption of isoamylene (2-methyl-2-butene) in aqueous solutions of sulphuric acid in the range of acid concentration from 61.5 to 75.0 per cent (wtlwt). (Extraction of the above olefins into aqueous sulphuric acid is industrially important). The absorption of isobutylene and isoamylene was found to be accompanied by a fast pseudo-first order reaction. The value of the pseudo-first order rate constant was found to be a strong function of the concentration of sulphuric acid. The value of the pseudo-first order rate constant for the above olefins was found to vary from lo2 to lo8 set-’ in the range of acid concentration covered by the authors. Thus, it should be possible to employ extraction of an olefin, with a structure akin to that of isobutylene, into aqueous solutions of sulphuric acid, to obtain values of effective interfacial area in a variety of contactors. Isoamylene has a low boiling point (38.5”C) and hence it was thought desirable to use an oletin having a higher boiling point. Diisobutylene (2,4,4-trimethyl2-pentene) appeared to be an attractive olefin. The sulphuric acid concentration was selected in the range of 72-77 per cent (wt/wt) (68 per cent sulphuric acid can also be
employed). The solubility of diisobutylene in water at 30°C is very low (of the order of lo-* g mole/cm3) and hence ah the conditions which are necessary for the validity of the chemical method for the measurement of effective interfacial area will be satisfied. (Ihe theoretical aspects of the chemical method have been discussed by Nanda and Sharma[2] and Sharma and Danckwerts[l4] and will not be repeated here). It was first thought that pure diisobutylene may be contacted with sulphuric acid but this idea was rejected as it would be very impracticable to follow the extent of the reaction accurately. Since the solubility of diisobutylene in water is inordinately low, it can be mixed with any appropriate organic liquid, which does not react with sulphuric acid, without introducing any resistance in the diisobutylene phase. The course of the extraction can then be conveniently followed by noting the fall in the concentration of diisobutylene in the organic phase. Toluene, monochlorobenzene and 1,2,4-trichlorobenzene were thought to be useful diluents for the initial study. Thus, when the organic phase constitutes the dispersed phase, the properties of the dispersed phase can be varied over a wide range by a judicious selection of the diluent. However, when aqueous sulphuric acid is used as the dispersed phase, the properties of the dispersed phase can be varied only over a limited range. The differences in the properties of the organic phase and the aqueous acid phase are very large and hence large variations in the properties of the dispersed and continuous phase can be realised by interchanging the phases. Since the specific rate of extraction of diisobutylene is expected to be very low, it may be possible to carry out batch experiments in a reasonable batch time even in a mechanically agitated contactor, without any substantial change in the properties of both the phases and without any significant decrease in the dispersed phase hold up. Some preliminary experiments in a mechanically agitated contactor indicated that the phase separation occurred rapidly after the agitation was stopped. MATERIALS Diisobutylene (2,4,4-trimethyl-2-pentene), toluene, monochlorobenzene and 1,2,4-trichlorobenzene were obtained from firms of repute. Sulphuric acid used was of commercial grade. Aqueous solutions of sulphuric acid were prepared with deionised water.
2089 C.E.S. Vol. 28 No. I1 -L
ANALYSIS The extent of reaction was followed by noting the fall
in the concentration of diisobutylene in the organic phase. This can be conveniently carried out chromatogmphically. An F and M Model 720 Dual Column Programmed Temperature Gas Chromatogmph was used. The components of organic phase were analysed by 6 mm, id. 3 m long copper column packed with 10 per cent Carbowax 20 M on Chromosorb-W. EXPERIMENTAL Stirred cells It is necessary to know the value of the specific rate of extraction of diisobutylene for the measurement of effective interfacial area. Diisobutylene dissolved in toluene or monochlorobenzene was contacted with an aqueous solution of sulphuric acid in stirred cells of known interfacial area. Most of the experiments were carried out in a 95 cm i.d. glass stirred cell. The design of the stirred cell was similar to that used by Gehlawat and Sharma[lZ]. In view of the low specific rate of extraction of diisobutylene, the experimental runs were made from 10 to 40 hr. In all the cases, the aqueous phase was below the organic phase. Both the phases were stirred, so as to renew the interface continuously without disturbing the interface significantly. The stirrer having two sets of blades one above the other, was so adjusted that the lower edge of upper set of blades and the upper edge of lower set of blades were just above, and below the interface, respectively. In some experiments, the speed of stirring was varied from 25 to 50revlmin to study the effect of speed of stirring on the specific rate of extraction of diisobutylene. Agitated contactor A 10.6cm i.d. vessel was used, which was provided with four vertical baffles, each one-tenth the diameter of the tank, mounted against the tank wall at right angles to it and spaced at 90” intervals around the tank. A fourbladed straight paddle impeller of glass with a diameter of 4.7 cm was used. Most of the experiments were carried out with the organic phase as the dispersed phase. Here a known amount of aqueous sulphuric acid was charged to the previously cleaned contactor. The organic phase (consisting of diisobutylene mixed with either toluene, monochlorobenzene or 1,2,4-trichlorobenzene) was then added carefully without significantly disturbing the interface between the two liquids. The speed of agitation was varied from 500 to 1200rev/min. In most cases, the batch experiments were carried out for a period of 15-30min. It was observed that at the end of the experiment the temperature was practically the same as at the beginning. The phase separation was found to occur in less than 90 set after the cessation of agitation. In the case of 77 per cent (wt/wt) sulphuric acid, it was observed that a small amount of diisobutylene was converted to oligomer. Some experiments were also carried out with 72 per cent (wt/wt) aqueous sulphuric acid as the dispersed phase. The continuous phase was a mixture of diisobutylene and monochlorobenzene. The speed of agitation was varied from 600 to 1500 revlmin. In view of the large volume of organic phase, the batch experiments were carried out for a period of 2-5 hr in order to get a significant decrease in the concentration of diisobutylene in the organic phase. The phase
2090
separation was found to occur in less than 30 set after the cessation of agitation. RESULTS AND DISCUSSION Stirred cells The specific rate of extraction of diisobutylene into aqueous sulphuric acid of a particular concentration was found to be independent of the speed of stirring in the range of 25-50revlmin (Fig. 1). The specific rate of extraction was also found to be proportional to the mole fraction of diisobutylene in the organic phase (Fig. 2). Thus, the extraction of diisobutylene in aqueous sulphuric acid solutions is accompanied by fast pseudo-first order reaction. The relevant values of specific rate of extraction, g mole/cm* set, are reported in Table 1.
2.0Speed
of stirring,
rev/min
Fig. 1. Effect of speed of stirring on the specific rate of extraction of diisobutylene from diisobutylene-toluene mixture into 77% (wt/wt) aqueous sulphuric acid in the stirred cell, at 3O”C, 0 mole fraction of diisobutylene = 0.71, 0 mole fraction ofdiisobutylene = 0.38.
Mole
fraction
of
diisobutylene
Fig. 2. Effect of concentration of diisobutylene on the specific rate of extraction of diisohutylene from diisobutylenetoluene mixture, into 77% (wt/wt) aqueous sulphuric acid, at 30°C.
Shorter Communications Table 1. Specific rates of extraction of diisobutylene into aqueous solutions of sulphutic acid in the stirred cell (temperature = 30°C) Concentration H,SO,
of
Organic phase (% wtlwt)
Diisobutylene-toluene
13.35
77
0.71 0.38 0.21
6.15 3.32 1.91
Diisobutylene-monochlorobenzene
12.01
72
0.48
1.05
I
I
1100
1300
1 700
900
Speed of ogitotion,
I50 1500
revlmin
Fig. 3. Effect of speed of agitation on the effective interfacial area in the agitated liquid-liquid contactor (Temp. = 30°C). Dispersed phase
Continuous phase
Fractional dispersed phase hold up (average)
DIB-T (75% wtlwt DIB)
77% (wtlwt) H,SO,
0.09
DIB-MCB (50% wt/wt DIB)
72% (wtlwt) H,SO,
0.09
DIB-1,2,4-TCB (30% wt/wt DIB)
72% (wtlwt) H,SO,
0.09
72% (wtlwt) H,SO,
DIB-MCB (35% wtlwt DIB)
0.30
DIB = diisobutylene
MCB = monochlorobenzene
T
TCB = trichlorobenzene.
= toluene
Agitated
Specific rate of extractionx log, (g mole/cm2 set)
(g mole/l.)
0 500
Mole fraction of diisobutylene in the organic phase
results in changing both the density as well as the viscosity of the dispersed phase. The values of effective interfacial area obtained with 72 per cent (wtlwt) aqueous sulphuric acid as the dispersed phase and diisobutylene-monochlorobenzene as the continuous phase are also plotted against the speed of agitation in Fig. 3, for an average dispersed phase hold up of 30 per cent. The values of effective interfacial area obtained in this case with a dispersed phase hold up of about 30 per cent are quite low as compared to those obtained with aqueous sulphuric acid as the continuous phase, for which the dispersed phase hold up was about 9 per cent. This is probably due to the fact that the properties of the continuous phase exercise a dominating influence on the dispersion characteristics. The properties of the continuous phase can be varied by a proper choice of the diluent. Further work is proposed to be carried out with a variety of diluents to cover a wide range of properties. It is also planned to develop another system, namely a-methyl styrene aqueous sulphuric acid, as this system is expected to allow further variations in the properties of the system. CONCLUSIONS The extraction of an olefin like diisobutylene, diluted with substances like toluene, monochlorobenzene, 1,2,4trichlorobenzene etc., into aqueous solutions of sulphuric acid (72-77 per cent (wtlwt)) can be conveniently employed for the measurement of interfacial area in mechanically agitated contactors. For contactors where the effective interfacial area is expected to be much lower than that in the case of mechanically agitated contactor, lower olefins like isoamylene, 2-methyl-2-pentene, etc. can be employed. It is reported that isoamylene from the C5 fraction of naphthacrackers is recovered by selective extraction in aqueous sulphuric acid solutions[ 151. The data from the commercial columns coupled with the data of Sankholkar and Sharma [ 131 can perhaps give the values of effective interfacial area in the above industrial contactors. Acknowledgement-One of us (DSS) wishes to thank the University Grants Commission for an award of a scholarship which enabled this work to be carried out.
contactor
The values of effective interfacial area obtained in the various experiments, with an average organic dispersed phase hold up of 9 per cent, are plotted against the speed of agitation in Fig. 3. The interfacial area varies linearly with the speed of agitation. This observation is in agreement with that of Femandes and Sharma[3]. A change over from monochlorobenzene to 1,2A+ichlorobenzene as a diluent
D. S. SANKHOLKAR M. M. SHARMA Department of Chemical University of Bombay Matunga Road Bombay-l 9 India
209 1
Technology
Shorter Communications REFERENCES SHARMA M. M., Chem. Age India 1962 13 335. t:; NANDA A. K. and SHARMA M. M., Chem. Engng Sci. 1966 21707. 131 FERNANDES J. B. and SHARMA M. M., Chem. Engng Sci. 1967 22 1267. 141 FERNANDES J. B. and SHARMA M. M., Chem. Engng Sci. 1968 23 9. PI SHARMA M. M. and NANDA A. K., Trans. In&n. Chem. Engrs 1968 46 T44. [61 PURANIK S. A. and SHARMA M. M., Chem. Engng Sci. 1970 25 257. [71 de SANTIAGO M. and TRAMBOUZE P., Chem. Engng Sci. 197 126 1803. PI de SANTIAGO M. and BIDNER M. S., Chem. Engng Sci. 197126 175. [91 ONDA K., TAKEUCHI H. and TAKAHASHI M., Kagaku Kdgaku 197135 22 1. [lOI SHAH A. K. and SHARMA M. M., Can. J. Chem. Engng 197 149 596. 120,197268 124. [Ill FERNANDESJ.B.,A.Z.Ch.E.Symp.Ser.No. iI21 GEHLAWAT J. K. and SHARMA M. M., Chem. Engng Sci. 1968 23 1173. iI31 SANKHOLKAR D. S. and SHARMA M. M., Chem. Engng Sci. 1973 28 49. iI41 SHARMA M. M. and DANCKWERTS P. V., Brit. Chem. Engng 1970 15522. D. K., PATINKIN S. H. and SANFORD R. A., Petrol Ref. 1960 39 229. [IV FOSTER R. L., WUNDERLICH ChemicalEngineering
Science,
1973, Vol. 28. pp. 2092-2093.
Pergamon Press.
Printed in Great Britain
Gas absorption with second order reaction-comparison factor equations
of approximate
enhancement
(Received 13 October 1972) IF A DISSOLVED gas C undergoes an irreversible secondorder reaction of Iinite speed with a dissolved reactant B, it is known that the governing differential equations cannot be solved analytically. But Van Krevelen and Hoftijer [ I] showed that the following implicit equation could be fitted to the numerical solutions for film model within about 10 per cent:
and the Kishinevskii equation [ 121: E=
1+*{I
-exp
a
(-0.65X@-)}(Y
(3)
where I
.
The Van Krevelen equation, i.e. Eq. (I), gives E as an implicit function of relevant parameters hence E cannot be calculated simply. On the other hand Porter and Kishinevskii equations are explicit, but their validities have not been
where
,,,f =
D&P -;
E,=(l+-$-$
k,*
320
Here E is the enhancement factor and E, is the enhancement factor corresponding to instantaneous reaction. A number of workers [2-41 have used Eq. (I) for penetration theory case by using the following equation for E1 Et=
t
x Colculoted . Calculated
from Kishinvskii’s aquatin from Puter~ equofion
160-
so-
e+-$g
40E
as this procedure has some justification[2,4]_ Numerical solutions for the penetration-theory case have been given by Perry and Pigford[5], by Brian ef al.[4] and by Pearson[6]. Observations of Brian et al.141 showed that Eq. (I) approximately represents all the numerical data and the error does not exceed 12 per cent. Equation (1) is now widely known and textbooks of gas absorption[7-91 recommend it for design purposes. Alper[ IO] has pointed out that two more less well known explicit equations are available in the literature. These are the Porter equation [ 1 l] :
20-
IO 8 6
10-
5-
M-pA.1 I I
I 5
I
I
I
I
I
I
IO
20
40
60
160
320
E,
E= l+(E,-]){I-exp-[(VM-l)/(E,-I)]}
(2)
2092
Fig. 1. Comparison of approximate equations.
I
640