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Experimental studies on the effect of ultrasonic waves on single drop liquid–liquid extraction
Ultrasonics - Sonochemistry 40 (2018) 11–16
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Experimental studies on the effect of ultrasonic waves on single drop liquid–liquid extraction
MARK
⁎
Javad Saien , Sana Daneshamoz Department of Applied Chemistry, Bu-Ali Sina University, 65174 Hamedan, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords: Liquid–liquid extraction Ultrasound Circulating drops Hydrodynamics Mass transfer
The influence of ultrasonic waves on hydrodynamics and mass transfer of circulating drops in liquid–liquid extraction process was studied. The recommended chemical systems of toluene–acetic acid–water with mass transfer resistance mainly in the organic phase, and cumene–isobutyric acid–water in the aqueous phase were used. An extraction column, equipped with an ultrasonic emitter of 35.40 kHz real frequency and 0.37 mW/cm2 intensity, was employed. The ultrasound properties were measured using the hydrophone standard method. Drops terminal velocity was comparable with the Grace model. In mass transfer study, significant enhancement was revealed in overall mass transfer coefficient for different drop sizes and for the both mass transfer directions by using ultrasonic waves. The average and maximum enhancements were, respectively, 20.8 and 31.7% for toluene–acetic acid–water, and 40.3 and 55.1% for cumene–isobutyric acid–water. Small drops exhibited a higher enhancement percentage. Regarding the mass transfer direction, the system of cumene–isobutyric acid–water with continuous to dispersed phase direction, was benefited more as the consequence of creating effective agitation in continuous phase than in dispersed phase.
1. Introduction Liquid–liquid extraction, a prevalent separation method, has found many applications in different industries. The industrial extractors involve two major types of mixer-settlers and columns. Columns are most conventional equipments for higher inputs and for adjusting contact of phases by drops, which are produced by distributors and provide a wide contact area. Up to now, the influence of several parameters and operating conditions have been studied on the hydrodynamics and mass transfer of drops in different extraction columns. Recent works include investigations on the influence of contaminants [1], aqueous phase pH [2], presence of salts [3], temperature [4], presence of nanoparticles both with single drop investigations [5–7] and swarm of drops [8,9] and nanoparticles in the presence of magnetic field [10]. However, among these investigations, the lack of a fascinating phenomenon in process intensifying and also a flexible alternative parameter for energy efficient processes by “ultrasonic waves”, is still distinctive while it is attainable. Applying ultrasound waves, have been found efficient in diverse chemical, medical, biological and food industries [11,12]. Many phenomena may result from propagation of ultrasonic waves into a fluid and particularly into a liquid medium. The most important favorite impacts of ultrasound in mass and heat transfer are due to
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Corresponding author. E-mail address: [email protected] (J. Saien).
http://dx.doi.org/10.1016/j.ultsonch.2017.06.020 Received 16 March 2017; Received in revised form 25 June 2017; Accepted 25 June 2017 Available online 27 June 2017 1350-4177/ © 2017 Elsevier B.V. All rights reserved.
acoustic streaming and acoustic cavitation. Acoustic streaming arises further gradients in momentum by ultrasonic waves, and thereby the fluid currents will be more established. Acoustic cavitation, on the other hand, is a phenomenon that may arise from the dissipation of ultrasonic waves into a liquid. It is the formation, growth, oscillation and powerful collapse of gas bubbles into a liquid. Some experimental results and photographic studies show the impact of a collapsing cavitation bubbles could last 10−7 s and reaching a local pressure of up to 193 MPa. This cavitation explains many phenomena involved in chemistry, biology, engineering and so forth [13,14]. Ultrasound waves are often classified according to their frequency or power. The classification can be roughly expressed with respect to the application as following [14–16]:
• Low frequency ultrasound, between 20 and 100 kHz waves are de-
•
fined as “power ultrasound” devoted to the study of high-intensity applications. Indeed, it is usually transferred at a high power level (a few tens of Watts). Power ultrasound finds uses in various processes like cleaning, plastic welding, sonochemistry, homogenization, extraction and so forth. It is also generally used for heat and mass transfer process intensification. Intermediate frequency range of 100 kHz–1 MHz, is less used than power ultrasound to promote transport phenomena.
Ultrasonics - Sonochemistry 40 (2018) 11–16
J. Saien, S. Daneshamoz
Nomenclature
Greek Symbols
c C d E Eo¨ g H
γ Δ μ ρ
k Kod M NPG Re T t ut We
viscometer constant concentration drop diameter (mm) extraction fraction Eötvös dimensionless number, Eo¨ = g Δρd 2/ γ standard gravity (m/s2) dimensionless group defined by Grace et al. H= (4/3)Eo¨ M−0.149 (μc / μ w )−0.14 dispersed and continuous phase local mass transfer coefficient (μm/s); viscometer constant overall dispersed phase mass transfer coefficient (μm/s) Morton dimensionless number, M= gμc4 Δρ / ρc2 γ 3 inverse of Morton dimensionless number drop Reynolds number (Re = ρcutd/μc) temperature (°C) drops contact time and efflux time in viscometer (s) drops terminal velocity (m/s) drop Weber number (We = dut2 ρc / γ )
interfacial tension (mN/m) difference viscosity (mPa·s) density (kg/m3)
Subscripts c d f i od w
continuous phase dispersed phase final value initial value overall dispersed phase water
Superscripts ∗
• High frequency ultrasound of above 1 MHz, is considered as “low
equilibrium
in KOH solution where the reaction between them was performed. The results indicate that mass transfer coefficient on silicon surface in the reactor with ultrasound was higher and mass transfer coefficient increased with increasing the ultrasound power. However, mass transfer coefficient did not increase steadily with the frequency. In the condition of ultrasound power of 50 W, the maximum enhancement was at 60 kHz and the minimum at 80 kHz. Concerning liquid–liquid contact, recent applications are mainly concerned on dispersion of a liquid phase small droplets in another phase under ultrasound assistance until the initial heterogeneous liquid–liquid system is made uniform. This process is known as “homogenization” or “emulsification” and is a well-documented process in both the analytical and industrial fields. However, mass transfer between two immiscible phases is arguable if one considers the ability of this form of energy to form stable emulsion. Probably for this reason, analytical chemists have been reluctant to test ultrasound as a means for improving liquid–liquid extraction (LLE). In fact, ultrasound application may cause stable emulsions that results in long times phase separation, generally non-favorable in practice [21].Despite these attempts, no investigation has been made on applying ultrasound in liquid–liquid extraction columns. The device can provide a desired vibration and agitation in a column for mass transfer intensification. The aim of this study was therefore to investigate the hydrodynamic and mass transfer of different single drops in a liquid–liquid extraction column equipped with low intensity ultrasonic irradiation. Two chemical systems of toluene–acetic acid–water and cumene–isobutyric acid–water were used for this aim. Both systems are well-known and recommended for liquid–liquid extraction investigations. The most prominent difference of these chemical systems is the slope of equilibrium curves. In the former system with a rather high interfacial tension, mass transfer resistance exists mainly in the organic dispersed phase (Kod ≈ kd), whereas in the latter system with medium interfacial tension, there is mass transfer resistance mainly in the aqueous continuous phase (Kod ≈ kc).
power ultrasound” (usually less than 10 W), does not affect the medium of propagation. Consequently, it is especially used for medical diagnosis or nondestructive material control.
In this regard, different kinds of reactors and contactors are equipped with ultrasound devices. Among the several types of sonicator systems, mostly bath and probe–types are used [15]. With respect to the desired uniform and diffusive vibration in fluids, a variety of investigations have been conducted on the subject of ultrasonic assisted mass transfer in gas–liquid, solid–liquid and liquid–liquid transfer cases. In the work of Riera et al. [17], concerning on CO2 supercritical extraction of oil from different substrates, it was reported that power ultrasound would enhance mass transfer as a result of producing small scale agitation. In their work a transducer working with frequency of about 20 kHz and power of 50 W, located inside a high-pressure extractor, caused an increase of 30 and 20% in the kinetic and the oil extraction yield, respectively. In addition, they introduced this technique as an inimitable applied manner for producing agitation, because exerting mechanical stirrers was not available in their set-up. In a similar work, the effect of operational parameters for extracting oil from adlay seed, in an ultrasound assisted supercritical fluid extraction was investigated by Hu et al. [18]. They reported that ultrasonic waves create vibration and an enhancement of about 14% was achieved in the extraction. In gas–liquid operations, Asgharzadehahmadi et al. [19] employed a contactor equipped with an ultrasonic horn. The effect of ultrasonic intensity on volumetric gas–liquid mass transfer coefficient as a function of gas flow rate and temperature was investigated. It was reported that during augmentation of ultrasonic power, mass transfer coefficient was increased and reached a maximum value with 320–360 W power; however, further increase was led to a decrease in mass transfer as a result of uncontrolled temperature rise (caused by high ultrasonic dissipation) and gas hold up in the system. In the field of solid–liquid operation, Jiao et al. [20] presented a new computational quantitative model for enhancing mass transfer coefficient in the presence of ultrasound in a sonochemical reactor working with the frequencies within 40–100 kHz and power range of 10–50 W. They studied the impact of more effective parameters of ultrasonic power and frequency as well as other parameters including temperature, transducer diameter and distance between reactor and transducer (filled with fresh water). A piece of solid silicon was placed
2. Experimental 2.1. Chemicals To perform experiments, the used chemicals were: toluene (mass purity > 99.9%), acetic acid (> 99.9%), isobutyric acid (> 99.5%), cumene (> 99.5); all of them from Merck Company. Fresh deionized water (with conductivity of 0.08 µS/cm) were obtained from a 12
Ultrasonics - Sonochemistry 40 (2018) 11–16
J. Saien, S. Daneshamoz
drop transient velocity, the location for determining initial drop concentration was considered at 6.5 cm above the nozzle tip. Having traveled about 40 mm, drops motion was observed to reach steady state. To determine initial concentration, drops were collected at the same distance of 6.5 cm above each nozzle tip in a separate small column, provided with the same nozzle and drop sizes. The same operating conditions of the main column were dominant in the small column. The syringe and the connection tube to the nozzle tip were first filled with toluene + acetic acid (5 wt%) or pure cumene to produce drops. The column was then filled with the continuous phase. After preparing each run, the ultrasonic device were turned on as soon as drops started to travel through the column, and while ultrasound working, drops were captured at top of the column. Each experiment was repeated under the same conditions while ultrasound device was turned off. To determine the size of drops, the syringe pump was initially calibrated with respect to the specified volume scale on the calibration syringe. Having the flow rate, besides the number of generated drops per a specified period, the drop size was easily calculated. For both the systems with and without ultrasound, the contact time of drops from the initial to the collection point was measured several times by stopwatch and the average time was accounted in the calculation. According to the measured average time, the terminal velocity of drops was obtained. Distance between two subsequent drops was adjusted typically more than 50 mm apart with a dispersed phase flow-rate range within 45–120 mL/h. All experiments were conducted at the ambient temperature of 20 ± 2 °C. It is worth noting that temperature was constant when column was irradiated by ultrasound. The column temperature was measured by a digital thermometer during the experiments.
deionizer and used as continuous phase. In order to analyze the collected samples, the standard 0.1 N sodium hydroxide titrant (Merck) was used. 2.2. Physical properties The physical properties of the both toluene–acetic acid–water and cumene–isobutyric acid–water systems, at 20 °C, are given in Table 1. Densities were measured using a self-adjustable temperature densitymeter (Anton Parr DMA 4500, Austria) equipped with automatic viscosity correction with uncertainty of ± 0.05 kg/m3. Calibration of the apparatus was carried out with dry air and deionized water prior to experiments. Interfacial tensions were measured with the drop weight method based on the equation [22]:
γ=
V Δρ g 2πrf (r / 3 V )
(1)
where V is a drop volume falling off a capillary into the organic phase; Δρ is the density difference between aqueous and organic phases, g and r are the acceleration of gravity and capillary outer radius (4.68 mm in this study), respectively, and f (r / 3 V ) is a constant which can be obtained from empirical relations. Lee et al. [23] have proposed a seven order polynomial fit equation for this constant, valid for the range of 0.0 < r / 3 V < 1.2. For measuring viscosity, an Ubbleohde viscometer was used. The equation for viscosity, according to Poiseville’s law, is
c μ = ρ ⎛kt − ⎞ t⎠ ⎝
(2)
where μ, ρ and t are dynamic viscosity, density, and efflux time and k and c are the viscometer constants, obtained by measurements on deionized water and toluene. 2.3. Set-up and operating procedure
2.4. Calibration of the column ultrasonic performance
The schematic of the experimental set-up is illustrated in Fig. 1. A Pyrex glass column (11.4 cm diameter and 51 cm height) was used as the contactor. The ultrasonic emitter was fitted to the column at about 12.4 cm above the nozzle tip. It was since the most mass transfer occurs during initial travelling times of drops in continuous phase coincident with a high driving force. The ultrasonic transducer worked at real frequency of 35.40 kHz, acoustic pressure of 740.9 Pa and actual intensity of 0.37 mW/cm2 (measured by hydrophone method). Low ultrasound irradiation power will decrease the extent of cavitation formation in the liquids [24].In order to generate various drops, different size glass nozzles, located at the bottom of the column were used. The dispersed phases was either toluene (with 5 wt% acetic acid) for the toluene–acetic acid–water system or pure cumene for the system of cumene–isobutyric acid–water. Continuous phase was water for the former system and water with 2.5 wt% isobutyric acid for the latter system. Experiments were conducted in the mass transfer direction of dispersed to continuous phase (d → c) with toluene–acetic acid–water system and continuous to dispersed phase (c → d) with cumene–isobutyric acid–water system. The organic phase, in each system, was held in a glass syringe, using an adjustable syringe pump (JMS SP-500, Japan) and flowed through a glass nozzle into the column to produce drops while the column was filled with continuous phase (5.2 L). For the purpose of capturing nearly 1 mL of dispersed phase at the top of the column, after transporting 33 cm distance from initial point, drops were collected with a small inverted glass funnel attached to a pipette and vacuum bulb. The interfacial area in the funnel was minimized at the level of the pipet inlet by occasionally pulling drops into the pipet. In each series of experiments, samples were taken in the both cases of with and without ultrasonic irradiation and were kept in closed tubes for immediate analysis by titration with NaOH (0.1 N). Either acetic acid or isobutyric acid concentration was determined in this way. To avoid the effect of unsteady mass transfer during drop formation and
Calibration of acoustic properties in the column was carried out using hydrophone method with calibration frequency range between 1 kHz and 1 MHz and by means of a 25 mm diameter sensor [25–27]. A polyvinylidene difluoride (PVDF) type hydrophone (PA124, Precision Acoustics Ltd, Dorchester, Dorset, UK) was located in front of the ultrasonic transducer in the column, filled with water. Ultrasonic signals, measured by the hydrophone was transferred into a digital oscilloscope (TNM Electronics Ltd, 20080, Iran) and then to a computer (Intel Pentium IV, 3.00 GHz, Taiwan) to record and process the received signals. Fast Fourier transform (FFT) analysis was used to obtain the frequency content of the captured signals. Each signal comprised a huge number of data points. MATLAB software version 7.0.1 using FFT function was employed for signal processing [25–27]. The measured signal amplitude versus frequency is shown in Fig. 2. The fundamental frequency appeared at 35.40 kHz. The corresponding intensity and acoustic pressure were obtained as 0.37 mW/cm2 and 740.9 Pa. During hydrophone test, there are environmental noises that appear in the measurements. Therefore, background noises were considered and measured prior to the main measurements.
Table 1 The range of physical properties of the used chemical systems at 20 °C. Chemical system
Phase
ρ (kg/m3)
μ (mPa·s)
γ (mN/m)
Toluene–acetic acid–water
Continuous dispersed Continuous Dispersed
998.20 867.21 1000.2 862.86
1.002 0.584 1.178 0.910
32.46
Cumene–isobutyric acid water
13
18.29
Ultrasonics - Sonochemistry 40 (2018) 11–16
J. Saien, S. Daneshamoz
Fig. 1. Details of experimental setup.
(dc) at which oscillation begins [28], as:
dc = 0.33μc0.30 γ 0.43ρc−0.14 Δρ−0.43
(in c.g.s units)
(3)
where μc and ρc are the continuous phase viscosity and density, respectively. There are also a number of criteria for drops circulation as: – dimensionless group, H, defined by Grace et al. [29]:
H= (4/3)Eo¨M−0.149 (μc / μ w )−0.14 g Δρd 2/ γ
and M= where Eo¨ = mensionless numbers.
(4)
gμc4 Δρ / ρc2 γ 3
are Eötvös and Morton di-
– drops Weber number (We = dut2 ρc / γ ) , – drops Reynolds number(Re = ρcutd/μc) and – Re/NPG−0.15 ratio, where NPG is the inverse of the Morton number [29]. Fig. 2. Acoustical spectrum obtained from FFT of signals obtained for the ultrasonic extraction column.
In these formulas, d is drop size, ut is terminal velocity and indices c, d and w stand for continuous, dispersed and water cases. The corresponding values of the above criteria as well as the circulating extreme values are given in Table 3 for the both chemical systems. The obtained experimental terminal velocities are compared with those predicted by Grace et al. [29]. For the system of toluene–acetic acid–water, terminal
3. Results and discussion 3.1. Hydrodynamic investigations Different ranges of drops size, for the both chemical systems, are presented in Table 2. By applying ultrasonic field, no change was appeared in the size of drops. It is due to no impact of the used ultrasonic waves on drops formation and size. Beside of this, for the both chemical systems, terminal velocity did not change remarkably with the ultrasonic irradiation since the employed frequency and intensity caused no alteration on buoyancy and other parameters involved in the drops hydrodynamic.On the whole, circulating conditions were dominant for the generated drops with respect to the equation of the critical drop size
Table 2 Drops size (in mm) produced from different nozzles. Chemical system
Toluene–acetic acid–water Cumene–isobutyric acid–water
14
Nozzle No. 1
2
3
4
5
2.82 2.63
3.14 3.22
3.63 3.45
3.78 3.57
3.99 4.16
Ultrasonics - Sonochemistry 40 (2018) 11–16
J. Saien, S. Daneshamoz
Table 3 Different criteria and values to indicate circulating drops in this work. Chemical systems
Toluene–acetic acid–water Cumene-isobutyric acid–water
Criterion 2 < H < 59.3
We < 3.58
Rec/(NPG0.15) < 20
200 < Rec < 500
d < dc (mm)
16.23 < H < 32.43 17.19 < H < 43.77
0.58 – 1.22 1.05 – 2.84
6.29 – 10.83 7.49 – 15.53
229.9 – 396.1 190.7–395.4
2.82–3.99 < 9.0 2.63–4.16 < 7.60
coefficient was much increased when assisted with ultrasound. The average and maximum enhancements of 40.3 and 55.1% in the mass transfer rate was achieved as a consequence of induced deep agitation and micro-turbulence in the mass transfer resistive continuous phase. It is also notable that small drops were benefited more due to a higher adjacent concentration driving force whereas a less inside circulating was relevant. From Figs. 4 and 5, it is obvious that ultrasound system did cause higher mass transfer enhancement in cumene–isobutyric acid–water system compared to the other one. When the column is irradiated and the propagated waves are conducted into continuous phase, the provided micro-turbulence would be more feasible for continuous phase than dispersed phase since the continuous phase with a large and opening area is more prone to the induced agitation than drops with closed and limited area and to which agitation is reached via the continuous phase.
velocities are partially lower than calculated values from Grace model; however, for the system of cumene–isobutyric acid–water, there is an excellent agreement between measured and calculated values (Fig. 3). 3.2. Mass transfer investigations The initial acetic acid concentrations in toluene–acetic acid–water system were within the range of (3.80–16.50) g/L and final concentrations within the ranges of (1.87–6.15) and (2.18–7.80) g/L, respectively, with and without ultrasound utilization. In cumene–isobutyric acid–water system, initial isobutyric acid concentrations were within the range of (5.37–15.92) g/L and final concentrations within the ranges of (21.23–22.02) and (18.94–21.19) g/L, with and without ultrasound, respectively. Considering mass transfer during the measured contact time, t; the overall mass transfer coefficient, Kod, can be calculated from the following equation:
K od = −
d ln(1−E ) 6t
4. Conclusions
(5)
where E is the extraction fraction calculated from:
E=
In this study, the influence of ultrasound on liquid–liquid extraction by circulating drops was investigated. Two chemical systems with different properties and mass transfer resistance were examined in an extraction column equipped with ultrasonic transducer. In hydrodynamic study, it was revealed that ultrasound irradiation provided no change in drop size, contact time and terminal velocity. Terminal velocities were partially lower than those predicted by the Grace model for the toluene–acetic acid–water system while a good agreement was relevant for the cumene–isobutyric acid–water system. The column temperature was remained constant during irradiation. In mass transfer study, ultrasonic irradiation caused a significant enhancement in mass transfer coefficient for both the systems (average enhancement of 20.8% and 40.3%, respectively). This achievement can be attributed to the known ultrasonically induced small scale agitation and turbulence in the media. Concerning mass transfer resistance, ultrasonic waves assisted more the cumene–isobutyric acid–water system (mass transfer resistance mainly in aqueous phase), indicating the more effective agitation and micro-convection in the continuous phase. Small drops exhibited a higher enhancement in this regard. Obviously, this work provides an advancement for the liquid–liquid extraction process of
Cdi−Cdf Cdi−Cd∗
(6)
where Cdi, Cdf and Cd∗ are initial, final and the equilibrium solute concentrations of drops contacting with continuous phase, respectively. Basically, the extraction fraction is the ratio of the amount of material transferred to the maximum amount transferable, and the overall mass transfer coefficient obtained from Eq. (5) is in fact an overall timeaveraged mass transfer coefficient. Drops contact time for toluene–acetic acid–water system was within (3.31–4.03) s and for cumene–isobutyric acid–water system, within (2.95–3.82) s. For dispersed to continuous phase mass transfer direction Cd∗ is zero, since the surrounded continuous phase was pure water (5.2 L) and even if solute transfer to water was completed, the solute content in this phase was not significant. In the cumene–isobutyric acid–water system, for continuous to dispersed phase mass transfer direction, the value of Cd∗ was considered from the previously provided equilibrium data at 20 °C [30]. For the system of toluene–acetic acid–water with mass transfer direction of d → c, obtained Kod values were within (114.9–142.1) and (87.2–120.2) µm/s with and without ultrasound, respectively. For this system, the variation of overall mass transfer coefficient versus drop size, is presented in Fig. 4. Compared with no ultrasonic, mass transfer rate was enhanced when ultrasound system was used. The average and maximum mass transfer enhancements were 20.8 and 31.7%. This is due to effective agitation caused by propagation of ultrasound waves in the column so that in addition to the coherent continuous phase, the moving drops in which mass transfer resistance lies, are also influenced by the waves. Meanwhile, for the both states of with and without ultrasound, Fig. 4 shows that mass transfer coefficient increases with drop size. Indeed, drops tend to higher internal circulation or turbulence as their size increases, and therefore, easier mass transfer per unit time was expected. With the other system of cumene–isobutyric acid–water (mass transfer direction of c → d), the obtained Kod values were within (208.8–267.3) and (134.5–267.3) µm/s, with and without ultrasound, respectively. The variation of this parameter for different nozzles is presented in Fig. 5. It is seen that for all generated drops, mass transfer
0.12 0.11
ut (m/S)
0.10 0.09 0.08 0.07
experimental (toluene–acetic acid–water) Grace Eq
0.06
experimental (cumene–isobutyric acide–water ) Grace Eq
0.05
2.0
2.5
3.0
d (mm)
3.5
4.0
4.5
Fig. 3. Variation of terminal velocity of the generated drops versus their size.
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Ind. Eng. Chem. Res. 51 (2012) 7364–7372. [5] J. Saien, M. Zardoshti, Mass transfer intensification of nanofluid single drops with effect of temperature, Korean J. Chem. Eng. 32 (2015) 2311–2318. [6] S.S. Ashrafmansouri, M. Nasr Esfahany, The influence of silica nanoparticles on hydrodynamics and mass transfer in spray liquid–liquid extraction column, Sep. Purif. Technol. 151 (2015) 74–81. [7] J. Saien, R. Hasani, Hydrodynamics and mass transfer characteristics of circulating single drops with effect of different size nanoparticles, Sep. Purif. Technol. 175 (2017) 298–304. [8] A. Bahmanyar, N. Khoobi, M.R. Mozdianfard, H. Bahmanyar, The influence of nanoparticles on hydrodynamic characteristics and mass transfer performance in a pulsed liquid–liquid extraction column, Chem. Eng. Process. Process Intensif. 50 (2011) 1198–1206. [9] A. Bahmanyar, N. Khoobi, M.M.A. Moharrer, H. Bahmanyar, Mass transfer from nanofluid drops in a pulsed liquid–liquid extraction column, Chem. Eng. Res. Des. 92 (2014) 2313–2323. [10] J. Saien, H. Bamdadi, S. Daliri, Liquid–liquid extraction intensification with magnetite nanofluid single drops under oscillating magnetic field, J. Ind. Eng. Chem. 21 (2015) 1152–1159. [11] J.A. Gallego Juárez, Power ultrasonics: new technologies and applications for fluid processing, in: K. Nakamura (Ed.), Ultrasonic Transducers, Elsevier, 2012. [12] J. Gallego-Juárez, K. Graff, Power Ultrasonics, Woodhead Publishing, Oxford, 2015. [13] E.A. Neppiras, Acoustic cavitation, Phys. Rep. 61 (1980) 159–251. [14] M. Legay, N. Gondrexon, S. Le Person, P. Boldo, A. Bontemps, Enhancement of heat transfer by ultrasound: review and recent advances, Int. J. Chem. Eng. (2011) 1–17. [15] I. Bendicho Lavilla, Applications of ultrasound-assisted metal extractions, in: I. Wilson (Ed.), Encyclopedia of Separation Science, Academic Press, London, 2000. [16] J.D.N. Cheeke, Fundamentals and Applications of Ultrasonic Waves, CRC Press, 2012. [17] E. Riera, Y. Golas, A. Blanco, J. Gallego, M. Blasco, A. Mulet, Mass transfer enhancement in supercritical fluids extraction by means of power ultrasound, Ultrason. Sonochem. 11 (2004) 241–244. [18] A.J. Hu, S. Zhao, H. Liang, T.Q. Qiu, G. Chen, Ultrasound assisted supercritical fluid extraction of oil and coixenolide from adlay seed, Ultrason. Sonochem. 14 (2007) 219–224. [19] S. Asgharzadehahmadi, M. Davoody, R.A. Ghotli, A.A.A. Raman, R. Parthasarathy, Effect of ultrasonic irradiations on gas–liquid mass transfer coefficient (kLa); experiments and modelling, Measurement 79 (2016) 119–129. [20] Q. Jiao, X. Tan, J. Zhu, Numerical simulation of ultrasonic enhancement on mass transfer in liquid–solid reaction by a new computational model, Ultrason. Sonochem. 21 (2014) 535–541. [21] M.L. de Castro, F. Priego-Capote, Ultrasound assistance to liquid–liquid extraction: a debatable analytical tool, Anal. Chim. Acta 583 (2007) 2–9. [22] J. Saien, M. Kharazi, S. Asadabadi, Adsorption behavior of long alkyl chain imidazolium ionic liquids at the n-butyl acetate + water interface, J. Mol. Liq. 212 (2015) 58–62. [23] B.B. Lee, P. Ravindra, E.S. Chan, A critical review: surface and interfacial tension measurement by the drop weight method, Chem. Eng. Commun. 195 (2008) 889–924. [24] S.G. Gaikwad, A.B. Pandit, Ultrasound emulsification: effect of ultrasonic and physicochemical properties on dispersed phase volume and droplet size, Ultrason. Sonochem. 15 (2008) 554–563. [25] H. Hasanzadeh, M. Mokhtari-Dizaji, S.Z. Bathaie, Z.M. Hassan, Evaluation of correlation between chemical dosimetry and subharmonic spectrum analysis to examine the acoustic cavitation, Ultrason. Sonochem. 17 (2010) 863–869. [26] H. Hasanzadeh, M. Mokhtari Dizaji, S.Z. Bathaie, Z.M. Hassan, V. Nilchiani, H. Goudarzi, Enhancement and control of acoustic cavitation yield by low-level dual frequency sonication: a subharmonic analysis, Ultrason. Sonochem. 18 (2011) 394–400. [27] A. Hajnorouzi, R. Afzalzadeh, F. Ghanati, Ultrasonic irradiation effects on electrochemical synthesis of ZnO nanostructures, Ultrason. Sonochem. 21 (2014) 1435–1440. [28] R.E. Treybal, Mass Transfer Operations, McGraw-Hill, New York, 1968. [29] A.H.P. Skelland, Interphase mass transfer, in: J.D. Thornton (Ed.), Science and Practice of Liquid-Liquid Extraction, Oxford Science Puplications, New York, 1992. [30] J. Saien, M. Norouzi, Salting-out effect of NaCl and KCl on the liquid–liquid equilibrium of water + 2-methylpropanoic acid+(1-methylethyl)-benzene system at several temperatures, J. Chem. Eng. Data 56 (2011) 2892–2898.
with ultrasound
140
without ultrasound
Kod (µm/s)
130 120 110 100 90 80
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
d (mm)
Fig. 4. Variation of overall mass transfer coefficient with drop size with and without ultrasound for toluene–acetic acid–water system.
280
with ultrasound
260
without ultrasound
Kod (μm/s)
240 220 200 180 160 140 120
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
d (mm)
Fig. 5. Variation of overall mass transfer coefficient with drop size with and without ultrasound for cumene–isobutyricacid–water system.
systems with different physicochemical properties. Acknowledgments The authors wish to acknowledge Bu Ali Sina University – Iran for providing the financial support to carry out this project. References [1] J. Saien, M. Riazikhah, S.N. Ashrafizadeh, Comparative investigations on the effects of contamination and mass transfer direction in liquid−liquid extraction, Ind. Eng. Chem. Res. 45 (2006) 1434–1440. [2] J. Saien, S. Daliri, Mass transfer coefficient in liquid-liquid extraction and the influence of aqueous phase pH, Ind. Eng. Chem. Res. 47 (2008) 171–175. [3] J. Saien, F. Ashrafi, Mass transfer enhancement in liquid− liquid extraction with very dilute aqueous salt solutions, Ind. Eng. Chem. Res. 48 (2009) 10008–10014. [4] J. Saien, S. Daliri, Mass transfer from single drops and the influence of temperature,
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Ultrasonics - Sonochemistry journal homepage: www.elsevier.com/locate/ultson
Experimental studies on the effect of ultrasonic waves on single drop liquid–liquid extraction
MARK
⁎
Javad Saien , Sana Daneshamoz Department of Applied Chemistry, Bu-Ali Sina University, 65174 Hamedan, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords: Liquid–liquid extraction Ultrasound Circulating drops Hydrodynamics Mass transfer
The influence of ultrasonic waves on hydrodynamics and mass transfer of circulating drops in liquid–liquid extraction process was studied. The recommended chemical systems of toluene–acetic acid–water with mass transfer resistance mainly in the organic phase, and cumene–isobutyric acid–water in the aqueous phase were used. An extraction column, equipped with an ultrasonic emitter of 35.40 kHz real frequency and 0.37 mW/cm2 intensity, was employed. The ultrasound properties were measured using the hydrophone standard method. Drops terminal velocity was comparable with the Grace model. In mass transfer study, significant enhancement was revealed in overall mass transfer coefficient for different drop sizes and for the both mass transfer directions by using ultrasonic waves. The average and maximum enhancements were, respectively, 20.8 and 31.7% for toluene–acetic acid–water, and 40.3 and 55.1% for cumene–isobutyric acid–water. Small drops exhibited a higher enhancement percentage. Regarding the mass transfer direction, the system of cumene–isobutyric acid–water with continuous to dispersed phase direction, was benefited more as the consequence of creating effective agitation in continuous phase than in dispersed phase.
1. Introduction Liquid–liquid extraction, a prevalent separation method, has found many applications in different industries. The industrial extractors involve two major types of mixer-settlers and columns. Columns are most conventional equipments for higher inputs and for adjusting contact of phases by drops, which are produced by distributors and provide a wide contact area. Up to now, the influence of several parameters and operating conditions have been studied on the hydrodynamics and mass transfer of drops in different extraction columns. Recent works include investigations on the influence of contaminants [1], aqueous phase pH [2], presence of salts [3], temperature [4], presence of nanoparticles both with single drop investigations [5–7] and swarm of drops [8,9] and nanoparticles in the presence of magnetic field [10]. However, among these investigations, the lack of a fascinating phenomenon in process intensifying and also a flexible alternative parameter for energy efficient processes by “ultrasonic waves”, is still distinctive while it is attainable. Applying ultrasound waves, have been found efficient in diverse chemical, medical, biological and food industries [11,12]. Many phenomena may result from propagation of ultrasonic waves into a fluid and particularly into a liquid medium. The most important favorite impacts of ultrasound in mass and heat transfer are due to
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Corresponding author. E-mail address: [email protected] (J. Saien).
http://dx.doi.org/10.1016/j.ultsonch.2017.06.020 Received 16 March 2017; Received in revised form 25 June 2017; Accepted 25 June 2017 Available online 27 June 2017 1350-4177/ © 2017 Elsevier B.V. All rights reserved.
acoustic streaming and acoustic cavitation. Acoustic streaming arises further gradients in momentum by ultrasonic waves, and thereby the fluid currents will be more established. Acoustic cavitation, on the other hand, is a phenomenon that may arise from the dissipation of ultrasonic waves into a liquid. It is the formation, growth, oscillation and powerful collapse of gas bubbles into a liquid. Some experimental results and photographic studies show the impact of a collapsing cavitation bubbles could last 10−7 s and reaching a local pressure of up to 193 MPa. This cavitation explains many phenomena involved in chemistry, biology, engineering and so forth [13,14]. Ultrasound waves are often classified according to their frequency or power. The classification can be roughly expressed with respect to the application as following [14–16]:
• Low frequency ultrasound, between 20 and 100 kHz waves are de-
•
fined as “power ultrasound” devoted to the study of high-intensity applications. Indeed, it is usually transferred at a high power level (a few tens of Watts). Power ultrasound finds uses in various processes like cleaning, plastic welding, sonochemistry, homogenization, extraction and so forth. It is also generally used for heat and mass transfer process intensification. Intermediate frequency range of 100 kHz–1 MHz, is less used than power ultrasound to promote transport phenomena.
Ultrasonics - Sonochemistry 40 (2018) 11–16
J. Saien, S. Daneshamoz
Nomenclature
Greek Symbols
c C d E Eo¨ g H
γ Δ μ ρ
k Kod M NPG Re T t ut We
viscometer constant concentration drop diameter (mm) extraction fraction Eötvös dimensionless number, Eo¨ = g Δρd 2/ γ standard gravity (m/s2) dimensionless group defined by Grace et al. H= (4/3)Eo¨ M−0.149 (μc / μ w )−0.14 dispersed and continuous phase local mass transfer coefficient (μm/s); viscometer constant overall dispersed phase mass transfer coefficient (μm/s) Morton dimensionless number, M= gμc4 Δρ / ρc2 γ 3 inverse of Morton dimensionless number drop Reynolds number (Re = ρcutd/μc) temperature (°C) drops contact time and efflux time in viscometer (s) drops terminal velocity (m/s) drop Weber number (We = dut2 ρc / γ )
interfacial tension (mN/m) difference viscosity (mPa·s) density (kg/m3)
Subscripts c d f i od w
continuous phase dispersed phase final value initial value overall dispersed phase water
Superscripts ∗
• High frequency ultrasound of above 1 MHz, is considered as “low
equilibrium
in KOH solution where the reaction between them was performed. The results indicate that mass transfer coefficient on silicon surface in the reactor with ultrasound was higher and mass transfer coefficient increased with increasing the ultrasound power. However, mass transfer coefficient did not increase steadily with the frequency. In the condition of ultrasound power of 50 W, the maximum enhancement was at 60 kHz and the minimum at 80 kHz. Concerning liquid–liquid contact, recent applications are mainly concerned on dispersion of a liquid phase small droplets in another phase under ultrasound assistance until the initial heterogeneous liquid–liquid system is made uniform. This process is known as “homogenization” or “emulsification” and is a well-documented process in both the analytical and industrial fields. However, mass transfer between two immiscible phases is arguable if one considers the ability of this form of energy to form stable emulsion. Probably for this reason, analytical chemists have been reluctant to test ultrasound as a means for improving liquid–liquid extraction (LLE). In fact, ultrasound application may cause stable emulsions that results in long times phase separation, generally non-favorable in practice [21].Despite these attempts, no investigation has been made on applying ultrasound in liquid–liquid extraction columns. The device can provide a desired vibration and agitation in a column for mass transfer intensification. The aim of this study was therefore to investigate the hydrodynamic and mass transfer of different single drops in a liquid–liquid extraction column equipped with low intensity ultrasonic irradiation. Two chemical systems of toluene–acetic acid–water and cumene–isobutyric acid–water were used for this aim. Both systems are well-known and recommended for liquid–liquid extraction investigations. The most prominent difference of these chemical systems is the slope of equilibrium curves. In the former system with a rather high interfacial tension, mass transfer resistance exists mainly in the organic dispersed phase (Kod ≈ kd), whereas in the latter system with medium interfacial tension, there is mass transfer resistance mainly in the aqueous continuous phase (Kod ≈ kc).
power ultrasound” (usually less than 10 W), does not affect the medium of propagation. Consequently, it is especially used for medical diagnosis or nondestructive material control.
In this regard, different kinds of reactors and contactors are equipped with ultrasound devices. Among the several types of sonicator systems, mostly bath and probe–types are used [15]. With respect to the desired uniform and diffusive vibration in fluids, a variety of investigations have been conducted on the subject of ultrasonic assisted mass transfer in gas–liquid, solid–liquid and liquid–liquid transfer cases. In the work of Riera et al. [17], concerning on CO2 supercritical extraction of oil from different substrates, it was reported that power ultrasound would enhance mass transfer as a result of producing small scale agitation. In their work a transducer working with frequency of about 20 kHz and power of 50 W, located inside a high-pressure extractor, caused an increase of 30 and 20% in the kinetic and the oil extraction yield, respectively. In addition, they introduced this technique as an inimitable applied manner for producing agitation, because exerting mechanical stirrers was not available in their set-up. In a similar work, the effect of operational parameters for extracting oil from adlay seed, in an ultrasound assisted supercritical fluid extraction was investigated by Hu et al. [18]. They reported that ultrasonic waves create vibration and an enhancement of about 14% was achieved in the extraction. In gas–liquid operations, Asgharzadehahmadi et al. [19] employed a contactor equipped with an ultrasonic horn. The effect of ultrasonic intensity on volumetric gas–liquid mass transfer coefficient as a function of gas flow rate and temperature was investigated. It was reported that during augmentation of ultrasonic power, mass transfer coefficient was increased and reached a maximum value with 320–360 W power; however, further increase was led to a decrease in mass transfer as a result of uncontrolled temperature rise (caused by high ultrasonic dissipation) and gas hold up in the system. In the field of solid–liquid operation, Jiao et al. [20] presented a new computational quantitative model for enhancing mass transfer coefficient in the presence of ultrasound in a sonochemical reactor working with the frequencies within 40–100 kHz and power range of 10–50 W. They studied the impact of more effective parameters of ultrasonic power and frequency as well as other parameters including temperature, transducer diameter and distance between reactor and transducer (filled with fresh water). A piece of solid silicon was placed
2. Experimental 2.1. Chemicals To perform experiments, the used chemicals were: toluene (mass purity > 99.9%), acetic acid (> 99.9%), isobutyric acid (> 99.5%), cumene (> 99.5); all of them from Merck Company. Fresh deionized water (with conductivity of 0.08 µS/cm) were obtained from a 12
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J. Saien, S. Daneshamoz
drop transient velocity, the location for determining initial drop concentration was considered at 6.5 cm above the nozzle tip. Having traveled about 40 mm, drops motion was observed to reach steady state. To determine initial concentration, drops were collected at the same distance of 6.5 cm above each nozzle tip in a separate small column, provided with the same nozzle and drop sizes. The same operating conditions of the main column were dominant in the small column. The syringe and the connection tube to the nozzle tip were first filled with toluene + acetic acid (5 wt%) or pure cumene to produce drops. The column was then filled with the continuous phase. After preparing each run, the ultrasonic device were turned on as soon as drops started to travel through the column, and while ultrasound working, drops were captured at top of the column. Each experiment was repeated under the same conditions while ultrasound device was turned off. To determine the size of drops, the syringe pump was initially calibrated with respect to the specified volume scale on the calibration syringe. Having the flow rate, besides the number of generated drops per a specified period, the drop size was easily calculated. For both the systems with and without ultrasound, the contact time of drops from the initial to the collection point was measured several times by stopwatch and the average time was accounted in the calculation. According to the measured average time, the terminal velocity of drops was obtained. Distance between two subsequent drops was adjusted typically more than 50 mm apart with a dispersed phase flow-rate range within 45–120 mL/h. All experiments were conducted at the ambient temperature of 20 ± 2 °C. It is worth noting that temperature was constant when column was irradiated by ultrasound. The column temperature was measured by a digital thermometer during the experiments.
deionizer and used as continuous phase. In order to analyze the collected samples, the standard 0.1 N sodium hydroxide titrant (Merck) was used. 2.2. Physical properties The physical properties of the both toluene–acetic acid–water and cumene–isobutyric acid–water systems, at 20 °C, are given in Table 1. Densities were measured using a self-adjustable temperature densitymeter (Anton Parr DMA 4500, Austria) equipped with automatic viscosity correction with uncertainty of ± 0.05 kg/m3. Calibration of the apparatus was carried out with dry air and deionized water prior to experiments. Interfacial tensions were measured with the drop weight method based on the equation [22]:
γ=
V Δρ g 2πrf (r / 3 V )
(1)
where V is a drop volume falling off a capillary into the organic phase; Δρ is the density difference between aqueous and organic phases, g and r are the acceleration of gravity and capillary outer radius (4.68 mm in this study), respectively, and f (r / 3 V ) is a constant which can be obtained from empirical relations. Lee et al. [23] have proposed a seven order polynomial fit equation for this constant, valid for the range of 0.0 < r / 3 V < 1.2. For measuring viscosity, an Ubbleohde viscometer was used. The equation for viscosity, according to Poiseville’s law, is
c μ = ρ ⎛kt − ⎞ t⎠ ⎝
(2)
where μ, ρ and t are dynamic viscosity, density, and efflux time and k and c are the viscometer constants, obtained by measurements on deionized water and toluene. 2.3. Set-up and operating procedure
2.4. Calibration of the column ultrasonic performance
The schematic of the experimental set-up is illustrated in Fig. 1. A Pyrex glass column (11.4 cm diameter and 51 cm height) was used as the contactor. The ultrasonic emitter was fitted to the column at about 12.4 cm above the nozzle tip. It was since the most mass transfer occurs during initial travelling times of drops in continuous phase coincident with a high driving force. The ultrasonic transducer worked at real frequency of 35.40 kHz, acoustic pressure of 740.9 Pa and actual intensity of 0.37 mW/cm2 (measured by hydrophone method). Low ultrasound irradiation power will decrease the extent of cavitation formation in the liquids [24].In order to generate various drops, different size glass nozzles, located at the bottom of the column were used. The dispersed phases was either toluene (with 5 wt% acetic acid) for the toluene–acetic acid–water system or pure cumene for the system of cumene–isobutyric acid–water. Continuous phase was water for the former system and water with 2.5 wt% isobutyric acid for the latter system. Experiments were conducted in the mass transfer direction of dispersed to continuous phase (d → c) with toluene–acetic acid–water system and continuous to dispersed phase (c → d) with cumene–isobutyric acid–water system. The organic phase, in each system, was held in a glass syringe, using an adjustable syringe pump (JMS SP-500, Japan) and flowed through a glass nozzle into the column to produce drops while the column was filled with continuous phase (5.2 L). For the purpose of capturing nearly 1 mL of dispersed phase at the top of the column, after transporting 33 cm distance from initial point, drops were collected with a small inverted glass funnel attached to a pipette and vacuum bulb. The interfacial area in the funnel was minimized at the level of the pipet inlet by occasionally pulling drops into the pipet. In each series of experiments, samples were taken in the both cases of with and without ultrasonic irradiation and were kept in closed tubes for immediate analysis by titration with NaOH (0.1 N). Either acetic acid or isobutyric acid concentration was determined in this way. To avoid the effect of unsteady mass transfer during drop formation and
Calibration of acoustic properties in the column was carried out using hydrophone method with calibration frequency range between 1 kHz and 1 MHz and by means of a 25 mm diameter sensor [25–27]. A polyvinylidene difluoride (PVDF) type hydrophone (PA124, Precision Acoustics Ltd, Dorchester, Dorset, UK) was located in front of the ultrasonic transducer in the column, filled with water. Ultrasonic signals, measured by the hydrophone was transferred into a digital oscilloscope (TNM Electronics Ltd, 20080, Iran) and then to a computer (Intel Pentium IV, 3.00 GHz, Taiwan) to record and process the received signals. Fast Fourier transform (FFT) analysis was used to obtain the frequency content of the captured signals. Each signal comprised a huge number of data points. MATLAB software version 7.0.1 using FFT function was employed for signal processing [25–27]. The measured signal amplitude versus frequency is shown in Fig. 2. The fundamental frequency appeared at 35.40 kHz. The corresponding intensity and acoustic pressure were obtained as 0.37 mW/cm2 and 740.9 Pa. During hydrophone test, there are environmental noises that appear in the measurements. Therefore, background noises were considered and measured prior to the main measurements.
Table 1 The range of physical properties of the used chemical systems at 20 °C. Chemical system
Phase
ρ (kg/m3)
μ (mPa·s)
γ (mN/m)
Toluene–acetic acid–water
Continuous dispersed Continuous Dispersed
998.20 867.21 1000.2 862.86
1.002 0.584 1.178 0.910
32.46
Cumene–isobutyric acid water
13
18.29
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Fig. 1. Details of experimental setup.
(dc) at which oscillation begins [28], as:
dc = 0.33μc0.30 γ 0.43ρc−0.14 Δρ−0.43
(in c.g.s units)
(3)
where μc and ρc are the continuous phase viscosity and density, respectively. There are also a number of criteria for drops circulation as: – dimensionless group, H, defined by Grace et al. [29]:
H= (4/3)Eo¨M−0.149 (μc / μ w )−0.14 g Δρd 2/ γ
and M= where Eo¨ = mensionless numbers.
(4)
gμc4 Δρ / ρc2 γ 3
are Eötvös and Morton di-
– drops Weber number (We = dut2 ρc / γ ) , – drops Reynolds number(Re = ρcutd/μc) and – Re/NPG−0.15 ratio, where NPG is the inverse of the Morton number [29]. Fig. 2. Acoustical spectrum obtained from FFT of signals obtained for the ultrasonic extraction column.
In these formulas, d is drop size, ut is terminal velocity and indices c, d and w stand for continuous, dispersed and water cases. The corresponding values of the above criteria as well as the circulating extreme values are given in Table 3 for the both chemical systems. The obtained experimental terminal velocities are compared with those predicted by Grace et al. [29]. For the system of toluene–acetic acid–water, terminal
3. Results and discussion 3.1. Hydrodynamic investigations Different ranges of drops size, for the both chemical systems, are presented in Table 2. By applying ultrasonic field, no change was appeared in the size of drops. It is due to no impact of the used ultrasonic waves on drops formation and size. Beside of this, for the both chemical systems, terminal velocity did not change remarkably with the ultrasonic irradiation since the employed frequency and intensity caused no alteration on buoyancy and other parameters involved in the drops hydrodynamic.On the whole, circulating conditions were dominant for the generated drops with respect to the equation of the critical drop size
Table 2 Drops size (in mm) produced from different nozzles. Chemical system
Toluene–acetic acid–water Cumene–isobutyric acid–water
14
Nozzle No. 1
2
3
4
5
2.82 2.63
3.14 3.22
3.63 3.45
3.78 3.57
3.99 4.16
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Table 3 Different criteria and values to indicate circulating drops in this work. Chemical systems
Toluene–acetic acid–water Cumene-isobutyric acid–water
Criterion 2 < H < 59.3
We < 3.58
Rec/(NPG0.15) < 20
200 < Rec < 500
d < dc (mm)
16.23 < H < 32.43 17.19 < H < 43.77
0.58 – 1.22 1.05 – 2.84
6.29 – 10.83 7.49 – 15.53
229.9 – 396.1 190.7–395.4
2.82–3.99 < 9.0 2.63–4.16 < 7.60
coefficient was much increased when assisted with ultrasound. The average and maximum enhancements of 40.3 and 55.1% in the mass transfer rate was achieved as a consequence of induced deep agitation and micro-turbulence in the mass transfer resistive continuous phase. It is also notable that small drops were benefited more due to a higher adjacent concentration driving force whereas a less inside circulating was relevant. From Figs. 4 and 5, it is obvious that ultrasound system did cause higher mass transfer enhancement in cumene–isobutyric acid–water system compared to the other one. When the column is irradiated and the propagated waves are conducted into continuous phase, the provided micro-turbulence would be more feasible for continuous phase than dispersed phase since the continuous phase with a large and opening area is more prone to the induced agitation than drops with closed and limited area and to which agitation is reached via the continuous phase.
velocities are partially lower than calculated values from Grace model; however, for the system of cumene–isobutyric acid–water, there is an excellent agreement between measured and calculated values (Fig. 3). 3.2. Mass transfer investigations The initial acetic acid concentrations in toluene–acetic acid–water system were within the range of (3.80–16.50) g/L and final concentrations within the ranges of (1.87–6.15) and (2.18–7.80) g/L, respectively, with and without ultrasound utilization. In cumene–isobutyric acid–water system, initial isobutyric acid concentrations were within the range of (5.37–15.92) g/L and final concentrations within the ranges of (21.23–22.02) and (18.94–21.19) g/L, with and without ultrasound, respectively. Considering mass transfer during the measured contact time, t; the overall mass transfer coefficient, Kod, can be calculated from the following equation:
K od = −
d ln(1−E ) 6t
4. Conclusions
(5)
where E is the extraction fraction calculated from:
E=
In this study, the influence of ultrasound on liquid–liquid extraction by circulating drops was investigated. Two chemical systems with different properties and mass transfer resistance were examined in an extraction column equipped with ultrasonic transducer. In hydrodynamic study, it was revealed that ultrasound irradiation provided no change in drop size, contact time and terminal velocity. Terminal velocities were partially lower than those predicted by the Grace model for the toluene–acetic acid–water system while a good agreement was relevant for the cumene–isobutyric acid–water system. The column temperature was remained constant during irradiation. In mass transfer study, ultrasonic irradiation caused a significant enhancement in mass transfer coefficient for both the systems (average enhancement of 20.8% and 40.3%, respectively). This achievement can be attributed to the known ultrasonically induced small scale agitation and turbulence in the media. Concerning mass transfer resistance, ultrasonic waves assisted more the cumene–isobutyric acid–water system (mass transfer resistance mainly in aqueous phase), indicating the more effective agitation and micro-convection in the continuous phase. Small drops exhibited a higher enhancement in this regard. Obviously, this work provides an advancement for the liquid–liquid extraction process of
Cdi−Cdf Cdi−Cd∗
(6)
where Cdi, Cdf and Cd∗ are initial, final and the equilibrium solute concentrations of drops contacting with continuous phase, respectively. Basically, the extraction fraction is the ratio of the amount of material transferred to the maximum amount transferable, and the overall mass transfer coefficient obtained from Eq. (5) is in fact an overall timeaveraged mass transfer coefficient. Drops contact time for toluene–acetic acid–water system was within (3.31–4.03) s and for cumene–isobutyric acid–water system, within (2.95–3.82) s. For dispersed to continuous phase mass transfer direction Cd∗ is zero, since the surrounded continuous phase was pure water (5.2 L) and even if solute transfer to water was completed, the solute content in this phase was not significant. In the cumene–isobutyric acid–water system, for continuous to dispersed phase mass transfer direction, the value of Cd∗ was considered from the previously provided equilibrium data at 20 °C [30]. For the system of toluene–acetic acid–water with mass transfer direction of d → c, obtained Kod values were within (114.9–142.1) and (87.2–120.2) µm/s with and without ultrasound, respectively. For this system, the variation of overall mass transfer coefficient versus drop size, is presented in Fig. 4. Compared with no ultrasonic, mass transfer rate was enhanced when ultrasound system was used. The average and maximum mass transfer enhancements were 20.8 and 31.7%. This is due to effective agitation caused by propagation of ultrasound waves in the column so that in addition to the coherent continuous phase, the moving drops in which mass transfer resistance lies, are also influenced by the waves. Meanwhile, for the both states of with and without ultrasound, Fig. 4 shows that mass transfer coefficient increases with drop size. Indeed, drops tend to higher internal circulation or turbulence as their size increases, and therefore, easier mass transfer per unit time was expected. With the other system of cumene–isobutyric acid–water (mass transfer direction of c → d), the obtained Kod values were within (208.8–267.3) and (134.5–267.3) µm/s, with and without ultrasound, respectively. The variation of this parameter for different nozzles is presented in Fig. 5. It is seen that for all generated drops, mass transfer
0.12 0.11
ut (m/S)
0.10 0.09 0.08 0.07
experimental (toluene–acetic acid–water) Grace Eq
0.06
experimental (cumene–isobutyric acide–water ) Grace Eq
0.05
2.0
2.5
3.0
d (mm)
3.5
4.0
4.5
Fig. 3. Variation of terminal velocity of the generated drops versus their size.
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Ind. Eng. Chem. Res. 51 (2012) 7364–7372. [5] J. Saien, M. Zardoshti, Mass transfer intensification of nanofluid single drops with effect of temperature, Korean J. Chem. Eng. 32 (2015) 2311–2318. [6] S.S. Ashrafmansouri, M. Nasr Esfahany, The influence of silica nanoparticles on hydrodynamics and mass transfer in spray liquid–liquid extraction column, Sep. Purif. Technol. 151 (2015) 74–81. [7] J. Saien, R. Hasani, Hydrodynamics and mass transfer characteristics of circulating single drops with effect of different size nanoparticles, Sep. Purif. Technol. 175 (2017) 298–304. [8] A. Bahmanyar, N. Khoobi, M.R. Mozdianfard, H. Bahmanyar, The influence of nanoparticles on hydrodynamic characteristics and mass transfer performance in a pulsed liquid–liquid extraction column, Chem. Eng. Process. Process Intensif. 50 (2011) 1198–1206. [9] A. Bahmanyar, N. Khoobi, M.M.A. Moharrer, H. Bahmanyar, Mass transfer from nanofluid drops in a pulsed liquid–liquid extraction column, Chem. Eng. Res. Des. 92 (2014) 2313–2323. [10] J. Saien, H. Bamdadi, S. Daliri, Liquid–liquid extraction intensification with magnetite nanofluid single drops under oscillating magnetic field, J. Ind. Eng. Chem. 21 (2015) 1152–1159. [11] J.A. Gallego Juárez, Power ultrasonics: new technologies and applications for fluid processing, in: K. Nakamura (Ed.), Ultrasonic Transducers, Elsevier, 2012. [12] J. Gallego-Juárez, K. Graff, Power Ultrasonics, Woodhead Publishing, Oxford, 2015. [13] E.A. Neppiras, Acoustic cavitation, Phys. Rep. 61 (1980) 159–251. [14] M. Legay, N. Gondrexon, S. Le Person, P. Boldo, A. Bontemps, Enhancement of heat transfer by ultrasound: review and recent advances, Int. J. Chem. Eng. (2011) 1–17. [15] I. Bendicho Lavilla, Applications of ultrasound-assisted metal extractions, in: I. Wilson (Ed.), Encyclopedia of Separation Science, Academic Press, London, 2000. [16] J.D.N. Cheeke, Fundamentals and Applications of Ultrasonic Waves, CRC Press, 2012. [17] E. Riera, Y. Golas, A. Blanco, J. Gallego, M. Blasco, A. Mulet, Mass transfer enhancement in supercritical fluids extraction by means of power ultrasound, Ultrason. Sonochem. 11 (2004) 241–244. [18] A.J. Hu, S. Zhao, H. Liang, T.Q. Qiu, G. Chen, Ultrasound assisted supercritical fluid extraction of oil and coixenolide from adlay seed, Ultrason. Sonochem. 14 (2007) 219–224. [19] S. Asgharzadehahmadi, M. Davoody, R.A. Ghotli, A.A.A. Raman, R. Parthasarathy, Effect of ultrasonic irradiations on gas–liquid mass transfer coefficient (kLa); experiments and modelling, Measurement 79 (2016) 119–129. [20] Q. Jiao, X. Tan, J. Zhu, Numerical simulation of ultrasonic enhancement on mass transfer in liquid–solid reaction by a new computational model, Ultrason. Sonochem. 21 (2014) 535–541. [21] M.L. de Castro, F. Priego-Capote, Ultrasound assistance to liquid–liquid extraction: a debatable analytical tool, Anal. Chim. Acta 583 (2007) 2–9. [22] J. Saien, M. Kharazi, S. Asadabadi, Adsorption behavior of long alkyl chain imidazolium ionic liquids at the n-butyl acetate + water interface, J. Mol. Liq. 212 (2015) 58–62. [23] B.B. Lee, P. Ravindra, E.S. Chan, A critical review: surface and interfacial tension measurement by the drop weight method, Chem. Eng. Commun. 195 (2008) 889–924. [24] S.G. Gaikwad, A.B. Pandit, Ultrasound emulsification: effect of ultrasonic and physicochemical properties on dispersed phase volume and droplet size, Ultrason. Sonochem. 15 (2008) 554–563. [25] H. Hasanzadeh, M. Mokhtari-Dizaji, S.Z. Bathaie, Z.M. Hassan, Evaluation of correlation between chemical dosimetry and subharmonic spectrum analysis to examine the acoustic cavitation, Ultrason. Sonochem. 17 (2010) 863–869. [26] H. Hasanzadeh, M. Mokhtari Dizaji, S.Z. Bathaie, Z.M. Hassan, V. Nilchiani, H. Goudarzi, Enhancement and control of acoustic cavitation yield by low-level dual frequency sonication: a subharmonic analysis, Ultrason. Sonochem. 18 (2011) 394–400. [27] A. Hajnorouzi, R. Afzalzadeh, F. Ghanati, Ultrasonic irradiation effects on electrochemical synthesis of ZnO nanostructures, Ultrason. Sonochem. 21 (2014) 1435–1440. [28] R.E. Treybal, Mass Transfer Operations, McGraw-Hill, New York, 1968. [29] A.H.P. Skelland, Interphase mass transfer, in: J.D. Thornton (Ed.), Science and Practice of Liquid-Liquid Extraction, Oxford Science Puplications, New York, 1992. [30] J. Saien, M. Norouzi, Salting-out effect of NaCl and KCl on the liquid–liquid equilibrium of water + 2-methylpropanoic acid+(1-methylethyl)-benzene system at several temperatures, J. Chem. Eng. Data 56 (2011) 2892–2898.
with ultrasound
140
without ultrasound
Kod (µm/s)
130 120 110 100 90 80
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
d (mm)
Fig. 4. Variation of overall mass transfer coefficient with drop size with and without ultrasound for toluene–acetic acid–water system.
280
with ultrasound
260
without ultrasound
Kod (μm/s)
240 220 200 180 160 140 120
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
d (mm)
Fig. 5. Variation of overall mass transfer coefficient with drop size with and without ultrasound for cumene–isobutyricacid–water system.
systems with different physicochemical properties. Acknowledgments The authors wish to acknowledge Bu Ali Sina University – Iran for providing the financial support to carry out this project. References [1] J. Saien, M. Riazikhah, S.N. Ashrafizadeh, Comparative investigations on the effects of contamination and mass transfer direction in liquid−liquid extraction, Ind. Eng. Chem. Res. 45 (2006) 1434–1440. [2] J. Saien, S. Daliri, Mass transfer coefficient in liquid-liquid extraction and the influence of aqueous phase pH, Ind. Eng. Chem. Res. 47 (2008) 171–175. [3] J. Saien, F. Ashrafi, Mass transfer enhancement in liquid− liquid extraction with very dilute aqueous salt solutions, Ind. Eng. Chem. Res. 48 (2009) 10008–10014. [4] J. Saien, S. Daliri, Mass transfer from single drops and the influence of temperature,
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