Novel Approach of Producing Oil in Water Emulsion Using

Article pubs.acs.org/IECR

Novel Approach of Producing Oil in Water Emulsion Using Hydrodynamic Cavitation Reactor Kiran A. Ramisetty, Aniruddha B. Pandit, and Parag R. Gogate* Chemical Engineering Department, Institute of Chemical Technology, Mumbai-40019, India ABSTRACT: The present work reports the use of venturi-based hydrodynamic cavitation reactor for the preparation of stable submicron emulsions. Different types of cavitating devices such as circular venturi and slit venturi have been used in this study. Effect of different operating parameters such as inlet pressure and number of passes of the emulsion through the cavitating zone on the droplet size and the stability of emulsion has been investigated. Emulsion of coconut oil in water has been chosen as the model system. Two types of emulsifying agents, namely, Tween 80 and Span 80, were used for the preparation of the emulsions, and the effect of emulsifying agent volume fraction on the emulsion droplet size has been illustrated. Zetasizer has been used to measure the droplet size and distribution of internal phase of emulsion. It has been established that the inlet pressure affects the droplet size of emulsion favorably due to the enhanced cavitational intensity with increasing inlet pressures. Among the two types of venturi investigated in the work, slit venturi showed pronounced effect on droplet size reduction as compared to the circular venturi with the requirement of lower number of passes for the formation of stable emulsion. The present work has, for the first time, illustrated the enhanced effectiveness of hydrodynamic cavitation-based emulsification approach for the preparation of stable emulsions with controlled droplet size distribution illustrating the dependency on the type of the cavitating device.

1. INTRODUCTION Preparation of emulsions with droplet size possibly in the nano and submicron range is an important requirement in various manufacturing processes though the process is highly energy intensive. The applications in the food and pharmaceutical industries (as drug carriers for controlled delivery) are controlled by the droplet size distribution, as well as stability, because the properties and the activity are dependent on the droplet size distributions. Apart from food and pharmaceutical applications, oil-in-water emulsions can also have significant interest in petroleum industries, polymer processing, as well as cosmetic applications. Generally, lower size emulsions can be obtained with the help of a high energy rotor-stator system, high pressure homogenization, and ultrasonic generators1 though all these operations are significantly energy intensive leading to enhanced processing costs. In a recent study, hydrodynamic cavitation based on a liquid whistle reactor has been reported for the preparation of nanoemulsions with low energy input compared to the conventional processes.2 Hydrodynamic cavitation has a size reduction mechanism similar to that of ultrasonic cavitation, though the ultrasonic generators/processors are generally suitable for small scale operations and are found to be more energy intensive.3 Hydrodynamic cavitation is produced by pressure variation in a flowing liquid, which can be obtained by using geometric constrictions such as orifice and venturi. When the liquid passes through the constriction, kinetic energy/velocity increases at the expense of the local pressure. When the local pressure at the throat or vena contracta falls below the vapor pressure of the fluid at the operating temperature, liquid flashes, generating a number of vaporous cavities.4,5 The generated cavities travel downstream of the constriction and finally collapse or implode as a result of the pressure recovery. The extreme transient conditions generated in the vicinity and within the collapsing cavitational bubbles can be the controlling mechanism for the © 2014 American Chemical Society

size reduction of the emulsion to the nanoscale or the submicron scale depending on the cavitational intensity, similar to the ultrasound induced emulsification. Parthasarathy et al.2 investigated the use of Liquid Whistle Hydrodynamic Cavitation Reactor (LWHCR) for the generation of palm oilbased submicron emulsions, and this has been claimed as the first study to report the emulsification performance of LWHCR. In another work on hydrodynamic cavitation-based emulsification, w/o/w multiple emulsion has been prepared using inlet pressures over the range from 100 to 200 psi.6 Overall, it can be said that there have been only limited studies reporting the use of hydrodynamic cavitation for emulsification as compared to the commonly used ultrasound-based reactors. Hydrodynamic cavitation offers the advantage of being able to process high volumes in a continuous operation. As the setup typically consists of a displacement pump/centrifugal pump followed by a geometric constriction, scale up is relatively easy, as the energy efficiencies of pump are expected to be higher at a larger scale of operation. It may have some limitations in terms of lower cavitational intensity to produce very small size emulsions compared to ultrasonic emulsification, but the process is noise free and can produce large quantity of emulsion in an energy efficient manner. Although hydrodynamic cavitation has been used successfully for a variety of applications ranging from nanomaterial synthesis to wastewater treatment,7,8 the preparation of nano and submicron emulsion has not been studied extensively, and hence, the present work forms an important contribution to this field. In the present study, the emulsification of oil-in-water emulsions has been Received: Revised: Accepted: Published: 16508

July 10, 2014 September 30, 2014 October 2, 2014 October 2, 2014 dx.doi.org/10.1021/ie502753d | Ind. Eng. Chem. Res. 2014, 53, 16508−16515

Industrial & Engineering Chemistry Research

Article

(HC1) at the throat and slit venturi with width of 6 mm and height of 1.9 mm (HC2) at the throat. The experiments were carried out over different operating pressures developed by the positive displacement pump ranging from 1 to 20 bar dependending on the type of cavitating device used in the main line. The variation in the liquid flow rate affects the number of passes of the liquid through the cavitating zone, which also decides the degree of emulsification, and hence, in addition to the inlet pressure, the effect of number of passes has also been investigated. Based on the number of passes and inlet pressure, the energy consumption also changes, and some discussion in this regard has been presented, as this directly impacts the processing costs. The temperature of the emulsion during experiments was kept constant in the range from 38 to 40 °C by circulating cooling water through the jacket of the holding tank.9 The hydraulic characteristics of the cavitating device have been established using the dimensionless number described as the cavitation number (Cv), which can be expressed as follows:

investigated using the hydrodynamic cavitation based on venturi and the dependency on the type of cavitating device; additionally, the operating parameters have been illustrated.

2. MATERIALS AND METHODS 2.1. Materials. Coconut oil in water has been chosen as the oil-in-water emulsion system to study the emulsification using hydrodynamic cavitation. Coconut oil (procured from Marico India Pvt. Ltd.) has been used as an internal phase. Tween 80 (HLB = 15) and Span 80 (HLB = 4.3) obtained from SD FineChem. Ltd. Mumbai, India, were used as emulsifying agents to reduce the interfacial tension between oil and water. 2.2. Hydrodynamic Cavitation Reactor. The experiments were performed using hydrodynamic cavitation setup, which has a 20-L capacity holding tank with a positive displacement pump of power rating 1.1 kW. The schematic representation of the experimental setup is shown in Figure 1.

Cv = 2(P2 − Pv)/ρV 2

where P2 is the fully recovered downstream pressure, Pv is the vapor pressure of the liquid at the operating temperature, and V is the local velocity of the liquid.9 2.3. Experimental Procedure. Preliminary experiments were conducted with varying volume fraction of emulsifying agents to get the required HLB (Hydrophilic Lipophilic Balance) value for the formation of stable emulsion, and it was established that the prepared emulsions with HLB values of 9, 10, 11, and 12 were very stable when subjected to the destabilization techniques such as electrolyte addition and freeze thaw test. The HLB values have been calculated using Griffin formula10 and are indicative of the content of the internal phase in the final emulsion under stable conditions. Based on these results, average HLB of 10 has been chosen for the experiments to study the effect of number of passes and the geometry of cavitating device on the droplet size of emulsion. Emulsifying agent fractions such as 0.05, 0.09, and 0.12 have been used to study the effect of interfacial tension on the emulsion droplet size using different cavitating devices and number of passes. In the present work, the coconut oil is the internal phase of the emulsion and the amount of oil addition has been quantified in terms of the fraction of oil added to the total amount of emulsion. The effect of different values of internal phase volume fractions, 0.1, 0.2, 0.3, and 0.4, on the droplet size and stability of emulsion has also been investigated. In a typical experiment, the two-phase mixture was taken in the holding tank and passed through the cavitation zone. The inlet pressure has been noted using pressure gauge located before the cavitating device (Figure 1). Initially, emulsion has been prepared by passing it through the circular venturi with an internal phase volume fraction of 0.1 and an emulsifying agent volume fraction of 0.05. The water−Tween 80 mixture has been added to the holding tank initially and coconut oil−Span 80 mixture has been added slowly as the liquid circulates through the cavitating device. Time of emulsification has been considered after the complete addition of all the internal phase to the continuous phase. Regular samples of emulsion were withdrawn from the sampling port provided in the main line at intervals of 10 min to check the droplet size distribution and polydispersive index (PDI) of the emulsion. The stability of the emulsion was also checked by keeping some samples for

Figure 1. Schematic representation of hydrodynamic cavitation reactor setup. P1, P2: Pressure gauges 1 and 2. V1, V2, V3: Control valves 1−3.

The configuration has three control valves (V1, V2, and V3) to control the flow through the main line, which also accommodates the cavitating device. The bottom of the tank is connected to the suction line of the pump, and the recirculation loop has two branches designated as main line and bypass line. The main line consists of a flanged connection that houses the cavitating device. The positive displacement pump used in the work has the provision to change the flow rate by adjusting the number of piston strokes per unit time. To control the liquid flow through the main line, an additional valve is also provided in the bypass. Care has been taken to avoid any introduction of air into the liquid by terminating both the mainline and bypass line well inside the tank, below the liquid level. Figure 2 shows the two types of cavitating device used in this work viz. a circular venturi having a 2-mm hole

Figure 2. Schematic representation of cavitating devices. 16509

dx.doi.org/10.1021/ie502753d | Ind. Eng. Chem. Res. 2014, 53, 16508−16515


Article

extended period without any changes. All the experiments were carried out by varying one parameter at a time. The number of passes of the emulsion through the cavitating device has been given in Table 1. Flow rate through the

distribution of the droplet size in an emulsion. A PDI value of about 0.08 indicates the monodispersivity of droplets, and value above 0.7 is indicative of broad range of droplet size distribution.11

Table 1. Number of Passes of 5 L of Emulsion Recirculated through Circular and Slit Venturi

3. RESULTS AND DISCUSSION 3.1. Effect of Operating Pressure on the Droplet Size of Emulsion. The effect of the inlet pressure has been studied at three inlet pressures of 5, 10, and 20 bar for the circular venturi for each volume fraction of the internal phase. The results are given in Figure 3. A substantial decrease in the mean droplet diameter has been observed at higher inlet operating pressure, which can be attributed to higher cavitational intensity due to an increase in the number of cavitational events resulting into an increased turbulence and shear. Cavitational events and intensity of cavity collapse (intensity of shock wave and turbulent shear) are directly proportional to the cavitation number, which is inversely proportional to the velocity of the emulsion passing through the venturi. High inlet pressure results in an increase in the velocity of the emulsion at the geometric constriction, finally reducing the cavitation number. It is important to calculate the energy dissipation for each case as this transpires into the processing costs, and hence, the dissipated energy for each inlet pressure has been calculated to compare the variation in the droplet size with power dissipation per unit volume of the emulsion. Experiments were conducted at different inlet pressures with same compositions of emulsifying agent volume fraction and internal phase volume fraction with an objective of isolating the effect of pressure. At 5 bar pressure, the droplet size was observed to be 711 nm after 10 min treatment through the hydrodynamic cavitation reactor. At 10 bar inlet pressure, the droplet size was 332 nm after 10 min of treatment time, and it was subsequently reduced to 200 nm at 30 min of emulsification. After this time, there was no further decrease in droplet size. At 20 bar inlet pressure and 416.67 W of dissipated power, the droplet size reduced to 233 nm in 10 min, confirming that the increase in inlet pressure from 10 to 20 bar was not that effective as compared to increase in the pressure from 5 to 10 bar. As the pump discharge pressure is increased, there is an increase in the degree of cavitation in terms of number of cavitational events and its collapse intensity. As the cavitational activity increases, the amplitude of the interfacial instability increases, which increases the number of droplets. With an increase in the pump discharge pressure, the rate of energy dissipation in the system also increases, contributing to the size reduction. PDI for the prepared emulsions at different inlet pressure was measured using zetasizer. PDI was observed

no. of passes for circular venturi

no. of passes for slit venturi

time (min)

5 bar

10 bar

20 bar

1 bar

2 bar

3 bar

4 bar

5 bar

10 20 30 40 50 60 70 80 90 100 110 120

13 26 39 52 65 78 91 104 117 130 143 156

18 37 55 73 92 110 128 147 165 183 202 220

25 50 75 100 125 150 175 200 225 250 275 300

8 17 25 33 42 50 58 67 75 83 92 100

22 43 65 87 108 130 152 173 195 217 238 260

27 53 80 107 133 160 187 213 240 267 293 320

32 63 95 127 158 190 222 253 285 317 348 380

40 80 120 160 200 240 280 320 360 400 440 480

hydrodynamic cavitation setup at different pressure had been calibrated earlier for the different pump discharge pressures to obtain the number of passes of liquid through the cavitation zone. The obtained results for velocity and cavitation number have been given in Table 2 for the circular venturi and in Table 3 for the case of slit venturi. It can be seen that, with an increase in the inlet pressure, there is an increase in the flow rate of the liquid and also a corresponding decrease in the cavitation number. For all the experimental runs, cavitation number has been observed to be less than 1, which confirms the formation of cavitational events with significant intensity, which can create significant mechanical shear and shock-wave, due to which the internal phase (oil) breaks into smaller droplets. The calculations for the energy consumptions are given in Appendix 1. 2.4. Analysis. A Malvern Zetasizer nano-ZS has been used to measure the droplet size of emulsion. The droplet size has been measured, after taking sample of emulsion in small vials. During the analysis, all the samples were diluted 800 times with continuous phase water. Intensity average hydrodynamic diameter has been used to quantify the average droplet size and measurements were performed in triplicate. The Z-average diameter11 has been considered as the average diameter of the droplets. PDI, which is a dimensionless number having typical range from 0.1 to 1, has been used to determine the degree of

Table 2. Energy and Cavitation Number Calculations for Circular Venturi circular venturi inlet pressure (bar)

flow rate (LPH)

3 5 7 10 12 15 17 20

370 390 450 550 610 665 700 750

flow rate (m3/s) 1.028 1.083 1.250 1.528 1.694 1.847 1.944 2.083

× × × × × × × ×

10−04 10−04 10−04 10−04 10−04 10−04 10−04 10−04

diam. (m) 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002

area (m2) 3.14 3.14 3.14 3.14 3.14 3.14 3.14 3.14

× × × × × × × ×

velocity at throat (m/s)

P2

Pv

cavitation no. (Cv)

32.73 34.5 39.81 48.66 53.96 58.83 61.92 66.35

101325 101325 101325 101325 101325 101325 101325 101325

4242 4242 4242 4242 4242 4242 4242 4242

0.18 0.16 0.12 0.08 0.07 0.06 0.05 0.04

10−06 10−06 10−06 10−06 10−06 10−06 10−06 10−06 16510

ΔP (Pa)

energy (W)

× × × × × × × ×

30.83 54.17 87.5 152.78 203.33 277.08 330.56 416.67

3.00 5.00 7.00 1.00 1.20 1.50 1.70 2.00

1005 1005 1005 1006 1006 1006 1006 1006



Article

Table 3. Energy and Cavitation Number Calculations for Slit Venturi slit venturi inlet pressure (bar)

flow rate (LPH)

flow rate (m3/s)

1

250

6.9444 × 10−05

2 3 4 5

650 800 950 1200

0.00018056 0.00022222 0.00026389 0.00033333

area (m2)

velocity at throat (m/s)

P2

Pv

Cv

ΔP

1.14 × 10−05

6.09

101325

4242

5.23

100000

9.72

10−05 10−05 10−05 10−05

15.84 19.49 23.15 29.24

101325 101325 101325 101325

4242 4242 4242 4242

0.77 0.51 0.36 0.23

200000 300000 400000 500000

36.11 66.67 105.56 166.67

diam. W = 6 mm, h = 1.9 mm

1.14 1.14 1.14 1.14

× × × ×

energy (W)

Figure 4. Comparison of effect of time of emulsification on droplet size for slit and circular venturi.

Figure 3. Effect of inlet pressure on emulsion droplet size at varying times of emulsification for circular venturi.

case of slit venturi. The results are attributed to the enhanced power dissipation in the case of slit venturi (166.67 W) compared to circular venturi where the power dissipation was 54.17 W. The cavitation number observed was also less in the case of slit venturi as compared to the case of circular venturi at constant 5 bar inlet pressure. The flow rate was also more in the case of slit venturi, which gives a higher number of cavitational events9 to disintegrate the droplets to lower size. Also, due to the higher flow rate, the liquid will experience the cavitating conditions for a longer duration when the same processing time is chosen. It can also be observed from Figure 4 that 5 bar pressure with slit venturi and 10 bar pressure with circular venture gives similar droplet sizes, as is also confirmed on the basis of similar levels of energy dissipation as 166.67 W and 152.78 W, respectively. Thus, it can be established that slit venturi gives better effects in terms of the emulsion characteristics as compared to the circular venturi, and this can be attributed to the increased number of recirculation passes through the cavitating zone. 3.2. Effect of Number of Passes at Constant Pump Discharge Pressure. The effect of the number of passes of liquid through the cavitating zone on dispersed phase droplet size has been investigated at constant pump discharge pressure. It has been reported that the increase in the number of passes decreases the droplet size of multiple emulsion of w/o/w and also leads to the formation of stable emulsion.6 The variation in dispersed phase droplet size with time of emulsification and hence the number of passes has been depicted in Figure 5. It has been observed that the dispersed phase droplet size decreases with an increase in the number of passes of the solution. As the number of passes increases, the degree of exposure to the cavitating conditions increases, leading to beneficial effects.12 It has been also observed that an increase in the number of passes decreases the droplet size until a certain optimum value, beyond which no effect has been observed for all the cases of emulsification. On the other hand, a certain minimum number of passes has also been found to be required

to decrease with an increase in the operating inlet pressure, which indicates the uniform distribution of the internal phase droplets. Visual observation also confirmed that the appearance of the emulsion turned from white to translucent with an increase in the operating pressure, meaning that a stable emulsion was formed. The studies over extended periods also confirmed the formation of stable emulsions. Emulsification with the passage of oil and water phase through slit venturi has also been studied under conditions of different inlet pressures. In the case of slit venturi, it has been observed that at low operating pressures of 1, 2, 3, 4, and 5 bar, the flow rate of the liquid was more as compared to the circular venturi. The flow rates of the emulsion through slit venturi have been given in Table 3 for different operating pressures. Due to an increase in the flow rate, the number of passes of the emulsion through slit venturi also increases when the processing time is kept the same. For the case of slit venturi, initial experiments were performed using the same volume fractions of emulsifying agent and the internal phase at 1 bar pressure. It has been observed that the emulsion formation is very poor and unstable emulsion has been obtained. Even if the flow rate is more at 1 bar pressure, the energy supplied was not enough to mix the solution completely. The cavitation number at this pressure is very high (about 5.23), as shown in Table 3, which possibly results in no cavitation and has practically no effect on the formation of emulsion. Thus, it can be said that a certain minimum energy dissipation is required for the formation of stable emulsion and subsequent reduction in the droplet size. Emulsification with slit venturi at 5 bar inlet pressure has been compared with the emulsification using circular venturi and the obtained results have been given in Figure 4. It can be easily seen that the droplet size reduced over 2 times for the case of slit venturi as compared to circular venturi at 5 bar pressure. After 10 min of emulsification, it has been observed that droplet size is 711 nm in the case of circular venturi and 310 nm in the 16511



Article

reduce the polydispersity. There is a formation of nonuniform droplets in the emulsion initially, which are subsequently reduced to the fine droplets as the number of passes increases resulting in enhanced cavitational event contribution to drop breakage. If we consider the mean droplet size, 5 min of emulsification results in a mean droplet size of 1245 nm, which is decreased to 711 nm after 10 min of emulsification. This clearly confirms the fact that the breakage of droplet is dependent on the number of passes. The droplet size decreased to 266 nm after 70 min of emulsification, and there was no further decrease, which indicates that there was no effect of hydrodynamic cavitation on the droplet size beyond an optimum emulsification time. This is expected, as the final emulsion and droplet size will be in equilibrium with local maximum energy dissipation rate. For 10 bar inlet pressure, the droplet size has been observed to reduce from 332 to 215 nm within 30 min of emulsification. Subsequent treatment with an increase in the number of passes and processing time showed no effect on the droplet size. For 20 bar inlet pressure, it was observed that 20 min of processing time gives a stable droplet size of 199 nm. This clearly shows that there is a combined effect of both the number of passes and inlet pressure of liquid where higher values until optimum gives more stable emulsion with lower droplet size. The emulsion appeared as translucent and more stable, based on the stability studies using visual observation and storage over extended time periods. In the case of slit venturi, it has been also observed that droplet size reduced with an increase in the number of passes, as shown in Figure 8. 3.3. Effect of Internal Phase Volume on Droplet Size of Emulsion. It can be expected that, as the internal phase volume fraction increases, a higher amount of energy is required for the disintegration of the dispersed phase into fine droplets. Considering this, experiments to study the effect of internal phase volume have been performed using higher inlet pressure of 20 bar, and the obtained results are depicted in Figure 9. It can be observed that the droplet size increased with an increase in internal phase volume fraction from 0.1 to 0.4. The emulsifying agent volume fraction used in the study was kept constant at 0.055. The cavitational events occurring in the aqueous phase of emulsion release energy near the surface of the internal phase (coconut oil) resulting in breakage into smaller droplets.13 As the internal phase volume increases, efficiency of these cavitational events to disintegrate the

Figure 5. Comparison of effect of number of passes on droplet size for slit and circular venturies.

to get required emulsion characteristics. For circular venturi, at 5 bar inlet pressure with 5 min of emulsification, around 7 passes of emulsion through the cavitating device are obtained, but these are inadequate and result in the formation of an unstable emulsion. The mixing and shear effects generated due to these conditions are not sufficient to form a stable emulsion. To reduce the droplet size, exposure to more number of cavitational events is required such that sufficient energy dissipation is obtained. It can be seen from Figure 6, the PDI is 1 for 5-min emulsification time, which indicates the nonuniform distribution of the droplets. As the time of emulsification and the number of passes increases, the PDI decreases and the droplet size distribution becomes narrower. The droplet size distribution depicted in Figure 7 for the 5 bar inlet pressure and circular venturi can be used to clearly understand the effect of number of passes. From the figure, it can be seen that the mean droplet size decreases from 1245 to 405 nm and PDI decreased from 1 to 0.515 with increasing number of passes until a processing time of 30 min. Droplet size distribution changes from the bimodal distribution to unimodal distribution over this period. Mean droplet size also shifted toward lower size. Two peaks have been observed in the case of smaller time of emulsification, which indicates that the cavitational events occurring in the emulsion, which are stochastic in nature, are low in number and not capable of breaking the droplets to

Figure 6. Droplet size distribution and PDI at 5 bar inlet pressure and different time of emulsification from 5 min to 30 min for circular venturi. 16512



Article

Figure 7. Variation in the droplet size distribution and PDI at 5 bar inlet pressure with time of emulsification from 35 to 120 min for circular venturi.

Figure 8. Variation in the droplet size and PDI with time of emulsification for circular venturi at 5 bar pressure.

It has been also observed that as the internal phase volume fraction increases, time of emulsification to get the stable emulsion also increases. For internal phase volume fraction as 0.4, time required to get stable emulsion with size of 307 nm was about 100 min whereas for the lower volume fraction of 0.3, 0.2 and 0.1, the required time were lower at 80, 40, and 20 min, respectively. The obtained results confirm that the internal phase volume fraction has significant effect on the emulsion characteristics in terms of the processing time as well as the mean droplet size. At low internal phase volume fraction of 0.1, the prepared emulsion appeared translucent at 10 min of emulsification, and it was opaque for internal phase volume fraction of 0.4 at similar processing time and need nearly 100 min to obtain similar quality emulsion (translucent). 3.4. Effect of Emulsifying Agent Loading on Droplet Size. Tween 80 and Span 80 have been used to reduce the interfacial tension between the oil and water interface. The mixture has been added to get the required HLB value of 10 for the formation of stable emulsion. Effect of emulsifying agent concentration has been studied at constant volume fraction of internal phase and inlet pressure for the reactor. As the emulsifying agent volume fraction increases, the droplet size has been observed to decrease as shown in Figure 10. The presence of emulsifying agent decreases the interfacial tension, and hence, the shear forces required to break up the droplets into

Figure 9. Effect of internal phase volume fraction on droplet size at different times of emulsification.

droplets decreases and it requires a higher number of collapsing events (higher energy) to further reduce the droplet size to a possible minimum. This hypothesis has been confirmed on the basis of the fact that as the internal phase fraction increases from 0.1 to 0.4, droplet size increased from 233 to 620 nm for 10 min of emulsification. 16513



Article

Overall, it has been demonstrated for the first time that adjusting the hydrodynamic cavitation operating conditions such as type of cavitation device, emulsifying agent fraction and inlet pressure allows a generation of unimodal size distribution with lower average size of the droplet.

■

APPENDIX 1

Cavitation Number and Energy Calculations for Venturi

Inlet fluid pressure = 301325 Pa

Downstream pressure (P2) = 101325 Pa Vapor pressure of water at 30 °C (Pv) = 4242 Pa Volumetric flow rate (V ) = 370LPH = 1.03 × 10−4 m 3/s

Figure 10. Effect of emulsifying agent volume fraction on droplet size at different times of emulsification with circular venturi at 20 bar pressure and γ = 0.1.

Diameter of the throat of the venturi (d) = 0.002 m

⎛ π ⎞ ⎜ ⎟ = 3.14 × 10−6 m 2 ⎝ 4d 2 ⎠

Flow area (a) =

small droplets are lower. It has been reported that an increase in the emulsifier concentration decreases the chances of coalescence and/or aggregation,14 which is also confirmed from the distribution curves of the emulsion droplets and PDI of the emulsion. In the present work, different emulsifying agent volume fractions used are 0.05, 0.09, and 0.11. All these fractions gave the stable emulsion for a fixed volume fraction of internal phase as used in the study. As the emulsifying agent concentration increases, the appearance of emulsion becomes translucent from white color, which indicates the formation of the nanoemulsion. For all the fractions of emulsifying agent used in this work, reduction in droplet size has been observed within 10 min of processing. At ϕ = 0.055, droplet size was 233 nm and it decreased to 193 and 175 nm at emulsifying agent fractions of 0.09 and 0.11, respectively. As the time of emulsification increases above 10 min with corresponding increase in the number of passes, droplet size decreased to 170 nm (from 175 nm at 10 min) after 20 min of emulsification at fraction of 0.11. The obtained droplet size was almost the minimum, and there was no further reduction with a further increase in the treatment time to 30, 40, and 50 min.

Velocity at the throat =

⎛V ⎞ ⎜ ⎟ = 32.73 m/s ⎝a⎠

⎛ ⎞ (P − P ) Cavitation number (Cv) = ⎜⎜ 21 2 v ⎟⎟ = 0.181 ⎝ 2 ρv ⎠

No. of passes = (Volumetric flow rate/Total volume of solution in the holding tank) × Time of operation No. of passes in 10 min =

(1.03 × 10−4) × 10 × 60 = 13 (6 × 10−3)

Power dissipated is P = ΔP × Volumetric flow rate = (3 × 105) × (1.03 × 10−4)

■

4. CONCLUSIONS Emulsification of coconut oil in water has been studied using hydrodynamic cavitation investigating the effect of different parameters on the droplet size and stability of emulsion. Hydrodynamic cavitation has been established to be effective at a pilot scale of operation and the formation of submicron size emulsion has been confirmed. Minimum droplet size of 170 nm has been observed at volume fraction of emulsifying agent as 0.11 and internal phase volume fraction of 0.1. It has been concluded from the results that the inlet pressure has beneficial effect on the droplet size of emulsion, and it was observed that there is a reduction in droplet size with an increase in the inlet pressure, attributed to the intensification in the cavitational activity. Slit venturi has more pronounced effect (possibly due to planar shear) on the droplet size reduction as compared to the circular venturi as established in the present work and lower number of passes were required to form a stable emulsion in the case of slit venturi as compared with circular venturi. Appearance of emulsion changed from opaque white color to translucent as the number passes increased confirming typical nanoemulsion behavior. Stability studies with extended time periods also confirmed the formation of stable emulsion.

= 30.8 W

AUTHOR INFORMATION

Corresponding Author

*Phone: 022 33612024. Fax: 022 33611020. E-mail: pr. [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Kiran A. Ramisetty acknowledges the University Grant Commission for funding to complete this project. Parag Gogate acknowledges the funding of UGC under the Major Research Project Scheme F. No. 39-852/2010 (SR) dt. 6th January 2011

■

REFERENCES

(1) Werner, D. Developments in the Continuous Mechanical Production of Oil-in-Water Macro-Emulsions. Chem. Eng. Process. 1995, 34, 205. (2) Parthasarathy, S.; Ying, T. S.; Manickam, S. Generation and Optimization of Palm Oil-Based Oil-in-Water (O/W) SubmicronEmulsions and Encapsulation of Curcumin Using a Liquid Whistle

16514



Article

Hydrodynamic Cavitation Reactor (LWHCR). Ind. Eng. Chem. Res. 2013, 52, 11829. (3) Abismaïl, B.; Canselier, J. P.; Wilhelm, a M.; Delmas, H.; Gourdon, C. Emulsification by Ultrasound: Drop Size Distribution and Stability. Ultrason. Sonochem. 1999, 6, 75. (4) Wang, X.; Zhang, Y. Degradation of Alachlor in Aqueous Solution by Using Hydrodynamic Cavitation. J. Hazardous Mater. 2009, 161 (1), 202. (5) Arrojo, S.; Benito, Y.; Martínez Tarifa, A. A Parametrical Study of Disinfection with Hydrodynamic Cavitation. Ultrason. Sonochem. 2008, 15 (5), 903−908. (6) Tang, S. Y.; Sivakumar, M. A Novel and Facile Liquid Whistle Hydrodynamic Cavitation Reactor to Produce Submicron Multiple Emulsions. AIChE J. 2013, 59, 155. (7) Ashokkumar, M.; Sonawane, S. H.; Gumfekar, S. P.; Kate, K. H.; Meshram, S. P.; Kunte, K. J.; Ramjee, L.; Mahajan, C. M.; Parande, M. G. Hydrodynamic Cavitation-Assisted Synthesis of Nanocalcite. Int. J. Chem. Eng. 2010, DOI: 10.1155/2010/242963. (8) Zupanc, M.; Kosjek, T.; Petkovšek, M.; Dular, M.; Kompare, B.; Širok, B.; Stražar, M.; Heath, E. Shear-Induced Hydrodynamic Cavitation As a Tool for Pharmaceutical Micropollutants Removal from Urban Wastewater. Ultrason. Sonochem. 2014, 21 (3), 1213. (9) Saharan, V. K.; Rizwani, M. A.; Malani, A. A.; Pandit, A. B. Ultrasonics Sonochemistry Effect of Geometry of Hydrodynamically Cavitating Device on Degradation of Orange-G. Ultrason. Sonochemistry 2013, 20, 345. (10) Griffin, W. C. Classification of Surface-Active Agents by HLB. J. Soc. Cosmet. Chem. 1949, 1, 311. (11) Tang, S. Y.; Shridharan, P.; Sivakumar, M. Impact of Process Parameters in the Generation of Novel Aspirin Nanoemulsions Comparative Studies between Ultrasound Cavitation and Microfluidizer. Ultrason. Sonochem. 2013, 20, 485. (12) Save, S. S.; Pandit, A. B.; Joshi, J. B. Microbial Cell Disruption. Trans. IChemE 1997, 75, 4. (13) Gaikwad, S. G.; Pandit, A. B. Ultrasound Emulsification: Effect of Ultrasonic and Physicochemical Properties on Dispersed Phase Volume and Droplet Size. Ultrason. Sonochem. 2008, 15, 554. (14) Leong, T. S. H.; Wooster, T. J.; Kentish, S. E.; Ashokkumar, M. Minimising Oil Droplet Size Using Ultrasonic Emulsification. Ultrason. Sonochem. 2009, 16, 721.

16515


Novel Approach of Producing Oil in Water Emulsion Using

Recommend Documents