ARTICLE pubs.acs.org/IECR
Intensification of Synthesis of Cumene Hydroperoxide Using Sonochemical Reactors Vivek P. Chavan† and Parag R. Gogate*,† †
Department of Chemical Engineering, Institute of Chemical Technology, Matunga, Mumbai 400019, India ABSTRACT: Intensification of chemical synthesis is a key research area due to the current constraints before the chemical industry due to competition as well as economics and demand for greener routes of processing. The present work illustrates the use of sonochemical reactors for the intensification of synthesis of cumene hydroperoxide from cumene. Air oxidation of cumene in the presence of cupric oxide powder as a catalyst has been investigated using a conventional approach and different sonochemical reactors such as an ultrasonic bath and a probe sonicator. Optimization of different operating parameters such as stirrer speed, temperature, catalyst quantity, air flow rate, and cumene hydroperoxide as an initiator have been investigated using conventional stirring method. The optimum conditions for the air oxidation of the cumene process have been obtained as stirrer speed of 300 rpm, temperature as 110 °C, catalyst quantity of 3 g, and air flow rate as 500 mL/min, and cumene hydroperoxide as an initiator had a very marginal effect. In the case of ultrasound assisted synthesis approach, various parameters studied were pulse of ultrasound, power of ultrasound, and frequency of ultrasound. Enhancement in conversion of cumene and reduction in the reaction time was observed in the presence of ultrasound as compared to silent conditions. The selectivity toward cumene hydroperoxide was marginally affected by the use of ultrasonic conditions. The maximum conversion obtained using ultrasound was 67.1% when 40 kHz frequency of ultrasound horn was used in 4 h, while 50.4% conversion was obtained in 8 h of reaction under otherwise similar operating conditions. The obtained selectivity was always greater than 95% for all conditions considered in the work. The present work has clearly revealed that substantial intensification is obtained for the synthesis of cumene hydroperoxide using ultrasound as compared to the conventional approach.
1. INTRODUCTION Process intensification has played a very vital role in organic synthesis to provide cutting edge technology in terms of improvement in the operation with an objective of enhancing the overall productivity. Process intensification has been looked upon as a novel approach for enhancing the efficacy of the chemical processing with substantial reduction in the operating costs. Use of process intensification principals can give enhanced reaction rates, conversion, yield, selectivity, and also use of mild reaction conditions. Sonochemical reactors have been revealed to give significant process intensification over a wide range of applications such as in the area of electrochemistry, food technology, chemical synthesis, materials extraction, nanotechnology, phase separation, surface cleaning, and water and sewage treatment.1 In last few decades, sonochemical reactors have been also explored to intensify the chemical synthesis process.2 Cavitation is the generation, subsequent growth, and collapse of cavities in the liquid medium releasing large magnitudes of energy over a very small location resulting in very high energy densities of the order of 1018 kW/m3.3 Cavitation results in physical effects of local turbulence and liquid microcirculation, which can enhance the rates of transport process and hence intensify the applications limited by transport processes. Cavitation also results in chemical effects such as the generation of hot spots and reactive free radicals, which can intensify the chemical processing applications limited by intrinsic chemical kinetics.2 It is expected that at lower frequencies of irradiation (typically in the range of 20 to 50 kHz), physical effects will be dominant, whereas at higher frequencies of irradiation (in the range of 100 to 500 kHz) chemical effects will be dominant. In actual processing, the net intensification will be due to a r 2011 American Chemical Society
combination of the physical and chemical effects of cavitation. Specifically, in the case of heterogeneous reactions involving the use of catalysts or multiphase reactants, in addition to the increase in the intrinsic rates of chemical reactions and/or initiation of the free radical reactions, turbulence created in the reactor also results in enhanced effectiveness of the catalyst either by cleaning action or by increasing the surface area of the catalyst due to the particle size reduction or deagglomeration.4 Also the turbulence generated due to the collapse of cavities helps in better contact of the reactants with the catalyst resulting in intensification of the rates.5 The present work has concentrated on exploring the use of sonochemical reactors for intensification of synthesis of cumene hydroperoxide. Conventional method for cumene hydroperoxide synthesis is based on the oxidation of cumene with air as an oxidant and sometimes cumene hydroperoxide has been used as an initiator.6 The conventional technique based on the use of stirring typically utilizes temperatures in the range of 45130 °C and reaction times of up to 12 h for achieving conversions in the range of 4050% based on the quantity of cumene used, type and quantity of the catalyst, air flow rate, and possibility of cumene hydroperoxide as an initiator.611 The present work has initially concentrated on investigating the effect of different process parameters for conventional approach followed by the use of these optimized parameters in Received: May 26, 2011 Accepted: October 10, 2011 Revised: October 7, 2011 Published: October 10, 2011 12433
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Scheme 1. Reaction Scheme for Cumene Oxidation to Cumene Hydroperoxide
cavitational approach of autoxidation of cumene in the presence of cupric oxide (CuO) as a catalyst. In the present work, cupric oxide (CuO) has been used as a catalyst as the rate of autoxidation been reported to be in the order as Mn(II) > Cu(II) > Co(II) > Ni(II) > Fe (II),11 but selectivity of Mn(II) was less as compared to Cu(II). The aim has also been to investigate the effect of different operating conditions like pulse, power, and frequency of ultrasound so as to maximize the extent of intensification using cavitation.
2. MATERIALS AND METHODS 2.1. Reaction Scheme. The reaction considered for the
present study is the oxidation of cumene with air in the presence of cupric oxide (CuO) powder as a catalyst. The reaction scheme can be schematically depicted as shown in Scheme 1. 2.2. Materials. Cumene (98%, AR grade) was purchased from M/s Sigma Aldrich Ltd. Cupric oxide (CuO) powder, silicone oil used as a heating media, acetonitrile, and methanol (HPLC grade) used as solvent for HPLC analysis were purchased from SD. Fine-Chem. Ltd., Mumbai, India. Cumene hydroperoxide (70%) solution was purchased from M/s HiMedia Laboratories Pvt. Ltd., Mumbai, India. All the chemicals were used as received from the supplier. 2.3. Method of Analysis. The samples were analyzed using high performance liquid chromatography (HPLC) with UV8010 detector set at a wavelength of 210 nm for determining the concentrations of cumene and cumene hydroperoxide. A C18 (JT Baker) octadecyl 5 μm, length 4.6 250 mm column was used. Samples were prepared by using 2 μL of the reaction mixture diluted with 40 mL of acetonitrile. In each run, 20 μL of the sample mixture was injected via an automatic injection system. The samples were analyzed isocratically using acetonitrile: DI water (80:20 v/v) at a flow rate of 0.55 mL/minute. The analog signal was recorded by an integrator, which calculated concentrations of cumene and cumene hydroperoxide. 2.4. Experimental Methodology. 2.4.1. Experimental Setup for Conventional Method. In order to quantify the efficacy of a conventional method, the reaction was carried out in a glass reactor of capacity 500 mL, equipped with six-bladed turbine impeller, a condenser, and thermocouple well. The entire reactor assembly was immersed in a thermostatic oil bath, which was maintained at the desired temperature with an accuracy of (5 °C. The reaction temperature was monitored with the help of a temperature controller. Agitation was provided by means of an electric motor having provision for speed control. A known quantity of cumene and cupric oxide powder as a catalyst were initially fed to the reactor. As soon as the desired temperature was reached in the reactor, air was introduced in the reactor using an air compressor and controlled using rotameter. Samples from the reaction mixture
Figure 1. Effect of stirrer speed on the extent of conversion at temperature 110 °C, catalyst quantity 3 g, reaction volume 200 mL, air flow rate 500 mL/min.
were withdrawn at regular intervals of time and analyzed using HPLC to monitor the progress of the reaction. 2.4.2. Experimental Setup for Acoustic Cavitation. The sonochemical reactors used in the present work were an ultrasonic bath and an ultrasonic horn, which were procured from Dakshin India Ltd. Mumbai. An ultrasonic bath operates at a frequency of 25 ( 2 kHz or 40 ( 2 kHz and rated power of 200 W. The unit consists of 6.5 L stainless steel tank of size 300 mm 1500 mm 150 mm (L B H) provided with piezoelectric transducers at the bottom. A 500 mL flat glass reactor equipped with a gas inlet tube, condenser, and thermocouple well was suspended into the ultrasound cleaner. Liquid in the tank can be heated to a maximum temperature of 70 °C using a heater and temperature controller. The other configurations of sonochemical reactors used in the work were an ultrasonic horn type reactor operating at a frequency of 40 kHz and 20 kHz with the same rated power of 120 W. An ultrasonic horn was fitted with a PZT transducer with a tip diameter of 2 cm. The horn was immersed into a 300 mL capacity glass vessel, which was also provided with a condenser and thermocouple well. A hot plate and thermostatic oil bath was used to maintain the temperature of the reaction mixture. The experimental setup configurations were very similar to that used for conventional operation except for the fact that the stirrer is replaced by an ultrasonic horn in the case of horn reactor and the glass reactor is immersed in the cleaning tank at the center position in the case of the ultrasound bath. The different operating parameters as used in the present work, to optimize the extent of conversion of cumene, include stirrer speed (200 rpm, 300 rpm, 400 rpm, 500 rpm and 600 rpm), temperature (50 °C, 70 °C, 90 and 110 °C), catalyst amount (0 g, 1 g, 3 g and 5 g), air flow rate (300 mL/min, 500 mL/min, and 1000 mL/min), and cumene hydroperoxide as an initiator (1 wt %, 3 wt %, and 5 wt % of cumene). Ultrasound parameters used for probe sonicator were duration of the pulse (5 s ON and 5 s OFF, 10 s ON and 5 s OFF, and 15 s ON and 5 s OFF), power (65 to 110 W), and frequency 20 kHz and 40 kHz. Also, an ultrasound bath of 25 and 40 kHz frequency was used to investigate the dependency of direct and indirect modes of irradiations. 12434
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Figure 2. Effect of temperature on the extent of conversion at reaction volume 200 mL, catalyst quantity g, air flow rate 500 mL/min.
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Figure 3. Effect of catalyst quantity on the extent of conversion at temperature 110 °C, reaction volume 200 mL, air flow rate 500 mL/min.
3. RESULTS AND DISCUSSION 3.1. Effect of Stirrer Speed. Initially, it was thought necessary to study the effect of speed of agitation to ascertain the importance of mass transfer resistances. Experiments were conducted with different speeds of agitation in the range from 200 to 600 rpm under otherwise similar conditions. The obtained results have been shown in Figure 1. It can be seen from the figure, that the conversion increased with time of reaction and around 40% conversion was obtained after 8 h. The selectivity toward the desired product (cumene hydroperoxide) was greater than 95% with negligible variation with the speed of rotation. Also the speed of rotation had no effect on the conversion beyond 300 rpm, and hence it can be concluded that there were no dominant external mass transfer resistances for transfer of cumene from bulk liquid phase to the outer surface of the catalyst beyond this speed. The initial increase in the extent of conversion can be attributed to the increased interfacial area for the reaction and enhanced contact of reactants with cupric oxide catalyst.12 Based on these results, all further experiments were conducted at 300 rpm which ensured the elimination of mass transfer resistance. 3.2. Effect of Temperature. To determine the effect of reaction temperature on cumene hydroperoxide formation, the reaction was carried out at different temperatures (50 °C, 70 °C, 90 °C, and 110 °C). Reaction was carried out for 8 h, and sampling was done at regular intervals of time. The obtained results have been shown in Figure 2. It has been observed that the conversion increases substantially with increasing temperature, which suggested that reaction was intrinsically kinetically controlled. Quantitatively, with an increase in the temperature from 50 to 110 °C, the extent of conversion increased from an initial value of 30.2% to 57.6%. Experimental results also revealed that at higher temperatures the conversion increased until a reaction time of 8 h beyond which a marginal decrease in conversion was observed for 90 and 110 °C. It has been also observed that the selectivity toward the desired product decreased with an increase in the operating temperature. The observed decreased in the conversion at higher temperatures beyond 8 h of reaction time can be attributed to possible decomposition of CHP.13 High temperature can increase cumene oxidation as well as CHP
Figure 4. Effect of air flow rate on the extent of conversion at temperature 110 °C, reaction volume 200 mL, catalyst quantity 3 g.
decomposition. Thus, reaction temperature is an important reaction parameter to maintain a high CHP selectivity and a high cumene conversion. 3.3. Effect of Catalyst Quantity. The rate of a catalytic reaction is also proportional to the number of active sites, when the mass transfer resistance is completely eliminated. Thus, the rate of reaction should be dependent on the catalyst quantity. The catalyst quantity was varied over a range of 0 g to 5 g, and the obtained results have been shown in Figure 3. It was observed that without catalyst conversion was 3.2% indicating the necessity of catalyst.14 When the amount of catalyst was increased from 1 g to 3 g, the cumene conversion after 8 h increased linearly from 29.9% to 43.9%. Further increase in the amount of catalyst to 5 g however decreased the conversion to 35.3%. Therefore, a 3 g amount of catalyst was the optimum catalyst amount which was selected for the subsequent studies. 3.4. Effect of Air Flow Rate. Effect of air flow rate was studied to investigate the amount of air required to get maximum conversion. Air flow rate was varied in the range from 300 mL/min to 1000 mL/min, and the obtained results have been given in Figure 4. It can be seen from the figure that the conversion of cumene increased with air flow rates when the air flow rate was less than 500 mL/min. It was mainly due to the fact 12435
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Table 1. Effect of Ultrasound Power Dissipation on the Extent of Conversion ultrasonic horn at 110 °C
Figure 5. Effect of cumene hydroperoxide as an initiator on the extent of conversion at temperature 110 °C, reaction volume 200 mL, catalyst quantity 3 g, air flow rate 500 mL/min.
that with an increase in the air flow rate, there is a substantial increase in the gas holdup which results in a larger gas liquid interfacial area and gas liquid volumetric mass transfer coefficient.15 It was found that conversion was 43.9% for 500 mL/min after 8 h, but a further increase in flow rate to 1000 mL/min resulted in a decrease in the conversion to 40.6%. This possibly can be attributed to the fact that increased air flow rate increased gas bubble quantity in the reaction mixture, and this may lead further to a decrease in the transfer of gas to the catalyst surface due to segregation of gas molecules in the form of pockets. 3.5. Effect of Cumene Hydroperoxide as an Initiator. It was intended to study the effect of addition of cumene hydroperoxide as an initiator. Cumene hydroperoxide concentration was varied as 1 wt %, 3 wt %, and 5 wt % of cumene, and the obtained results have been depicted in Figure 5. The figure also shows the obtained data under otherwise similar conditions of temperature, catalyst, and air flow rate but without any externally added CHP. It was observed that for 1 wt % CHP concentration, conversion was 42% which is marginally lower as compared to that obtained without the presence of initiator. Also for 3 wt % and 5 wt % CHP concentration, conversion was observed to be 39.9% and 34.7% respectively. It was observed from the chromatogram of the reaction mixture that with an increase in the loading of cumene hydroperoxide added as an initiator, the formation of byproduct due to side reactions increased and the main reaction of cumene oxidation is hampered. Therefore all further experiments were carried out without cumene hydroperoxide as an initiator. 3.6. Studies in an Ultrasonic Horn. 3.6.1. Effect of Pulse of Ultrasound. To study the effect of the pulse of ultrasound, the reaction was carried out in a round-bottom flask with direct immersion of ultrasound horn of 20 kHz frequency into the reaction mixture. Experimental parameters used were a temperature of 110 °C, cumene as 100 mL, catalyst cupric oxide (CuO) as 3 g, and air flow rate of 500 mL/min. Air flow rate and ultrasound irradiation were started as soon as the reaction
power (W)
65
91
110
time (h) conversion (%)
4 55.5
4 63
4 59
mixture reached the desired temperature. Total time for continuous ultrasound irradiation was 10 min, and after every 10 min ultrasound was stopped for 3 min in order to get sufficient time for transducer cooling. The oxidation reaction was studied for an ultrasound pulse of 5 s ON and 5 s OFF, 10 s ON and 5 s OFF, and 15 s ON and 5 s OFF. It has been observed that a higher extent of conversion was obtained for the case where ultrasound duration in the pulse was higher. To give a quantitative idea, for the pulse 5 s ON and 5 s OFF, the extent of conversion was 55.52%, whereas for 10 s ON and 5 s OFF, the conversion was 59.07%. For a pulse duration as 15 s ON and 5 s OFF, conversion of 63.18% was obtained. Hingu et al.16 reported a similar effect and showed that at lower pulse a macro stirring effect of the ultrasonic was too mild to mix the immiscible reactants well. Thus, depending on the stability of the reactor in terms of how efficient is the transducer cooling, an enhanced duration of continuous ultrasound usage can be decided to maximize the extent of intensification. 3.6.2. Effect of Power of Ultrasound. For investigations related to the effect of ultrasonic power dissipation, the reaction was carried out using direct immersion ultrasound horn operating at 20 kHz frequency into the reaction mixture, with all other parameters remaining the same. Ultrasound power was varied at three different levels viz. 65 W, 90.75 W, and 110 W, and the obtained results have been given in Table 1. It has been observed from the obtained results that with an initial increase in the power dissipation, conversion increases until an optimum power dissipation of 90.75 W but for 110W power conversion decreased marginally to 59%. The initial increase in the extent of conversion can be attributed to the enhanced mixing and circulation currents with an increase in the ultrasound power.13,16 The observed decrease beyond the optimum power dissipation is attributed to the cushioning effect of large pockets of cavities which results in decreased transfer of energy into the system. 3.6.3. Effect of Frequency of Irradiation. Effect of frequency of irradiation was also investigated using two ultrasonic generators operating at 20 and 40 kHz. Under otherwise similar operation conditions, it has been observed that the extent of conversion is marginally lower at higher operating frequency (40 kHz) attributed to the fact that the extent of physical effects which control the intensification will be lower at 40 kHz frequency as compared to the 20 kHz frequency of irradiation. To give a quantitative idea, the extent of conversion obtained in 4 h of reaction time was 63% at 20 kHz frequency (power dissipation of 91 W), whereas the use of an ultrasonic generator operating at 40 kHz resulted in a conversion of 58.5% at similar power dissipation levels. Thus it can be said that it is better to use low frequency irradiations (20 kHz generators are easily available) for intensification of oxidation of cumene. 3.6.4. Effect of Temperature. It is a well established fact that the use of ultrasonic irradiations generates cavitation events which can yield local hot spots (conditions of very high temperature and pressures) for very small time periods, but importantly the 12436
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Figure 6. Effect of operating temperature on the extent of conversion using an ultrasonic horn at catalyst quantity 3 g, air flow rate 500 mL/min, ultrasonic power dissipation of 91 W.
physical effects can dominate the progress of the heterogeneous catalytic reactions. It was thought desirable to check the dependency of the operating temperature in the case of an ultrasonic horn and establish whether lower operating temperatures give similar extents of conversion with an objective of possible reduction in the processing costs and improved selectivity of the desired product. The effect of operating temperature on the conversion in the case of an ultrasonic horn was investigated at two different temperatures of 70 and 110 °C. The obtained results have been shown in Figure 6, and it can be seen that the extent of conversions differed marginally at the two operating temperatures. The extent of conversion at the end of 4 h of reaction time was 59% at 70 °C which is marginally lower than that obtained at 110 °C (63%). Also the selectivity of CHP was lower at an operating temperature of 110 °C (95%) as compared to that obtained at 70 °C (98%). The observed difference for the variation in the conversion in the case of a conventional approach was significant over a similar range of operating temperatures. Quantitatively speaking, the extent of conversion was 30% at 70 °C, and it increased to 57% at 110 °C over the same reaction time of 8 h. Thus it can be said that the use of ultrasonic irradiations not only lowers the reaction time but also eliminates the strong dependency of the extent of conversion of cumene on the operating temperatures allowing possible use of lower operating temperatures which can give safe and economically favorable operation as well as higher selectivity. 3.7. Studies with an Ultrasound Bath. An ultrasound bath has also been used as a source of indirect irradiations as sometimes direct irradiation may not be allowed due to the possibility of contamination in the final product from the metal traces that can be eroded with continuous use. In the case of an ultrasonic bath, reactions were carried out for 8 h, and sampling was done at regular time intervals. Three different operating modes viz. only stirring, only ultrasound, and simultaneous application of ultrasound and stirring was investigated. It was observed that the extent of conversion was 29.8% using only mechanical agitation at 300 rpm, while only sonication resulted in 36.9% conversion after 8 h. When both mechanical agitation at 300 rpm along with
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sonication was used, the conversion further increased to 39.2%. Comparison of the obtained data with earlier results with an ultrasonic horn indicates that the use of indirect irradiations in the form of an ultrasonic bath does not yield a significant degree of intensification possibly attributed to dampened cavitational effects due to the use of a glass reactor. As ultrasonic power dissipation is an important parameter directly related to the processing costs, it was thought desirable to also compare the efficacies of the ultrasonic reactor configurations in terms of cavitational yields (sample calculation for an ultrasonic bath has been explained in Appendix I), defined as the quantity of product formed per unit amount of energy consumed for generation of cavitation effects. Under optimized conditions to yield maximum conversion, cavitational yield obtained for the ultrasonic bath was 6.33 1010 mol/kJ, whereas for the case of an ultrasonic horn the cavitational yield was observed to be 9.27 109 mol/kJ. Thus it can be said that the process intensification achieved using an ultrasonic horn is about 15 times more energy efficient as compared to the indirect irradiations using an ultrasonic bath. 3.8. Comparison of Acoustic Cavitation with Conventional Approach. It is worthwhile to compare the optimized operation of ultrasonic reactors with the conventional approach so that the distinct advantages of using sonochemical reactors can be highlighted. The investigation related to the effect of different operating parameters under conventional approach revealed that the optimized parameters obtained were stirrer speed of 300 rpm, temperature of 110 °C, catalyst quantity of 3 g, and air flow rate of 500 mL/min. In the case of sonochemical reactors, operation with an ultrasonic horn at 20 kHz, power dissipation of 91 W, and 15 s ON and 5 s OFF pulse duration was found to give maximum conversion among all the operating protocols using two types of an ultrasonic horn and bath. It has been observed that the maximum conversion obtained using the conventional approach was 43.9% in 8 h of reaction time, while the maximum conversion using an ultrasonic reactor under an optimized set of operating parameters was around 63% in only 4 h of treatment. It should be also noted here that not only conversion of cumene is important but also the selectivity toward the desired product CHP would be equally important considering the overall production. Within the set of operating conditions as used in the work, it has been observed that the change in selectivity due to the use of sonochemical reactors was marginal as compared to the conventional approach indicating that a very less amount of side products were formed additionally by possible decomposition of the cumene hydroperoxide due to ultrasound effects. This can also be confirmed by a better understanding of the cavitation process occurring at low frequency ultrasound. At low frequency operation (20 kHz or 40 kHz as used in the present work), the physical effects of the cavitation phenomena are dominant, and generally the hot spots generated in the system are for a very short duration and it is unlikely that the cumene hydroperoxide decomposition can occur in such a short period of microseconds. The main physical effects of cavitation i.e. enhanced turbulence along with liquid circulation currents dominate the observed enhancement of the cumene reaction to hydroperoxide. Perhaps at conditions of higher operating frequency (>100 kHz) where the chemical effects are expected to be more dominant, stability of the generated cumene hydroperoxide will be a factor of concern. Credence to this hypothesis can be given by the controlled application of low frequency sonochemical reactors for release of intracellular enzymes from the cell without any loss in the activity 12437
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of the enzyme.17 Overall it can be said that the use of sonochemical reactor significantly enhances the extent of conversion and also reduces the time required for achieving the desired conversion levels. It has been also observed that the high temperature requirements are not stringent in the use of sonochemical reactors, and substantial reduction in the operating temperature results only in marginal decrease in the extents of conversion over similar duration of reaction time. Overall, it can be said here that direct irradiation of reaction mixture with an ultrasound horn reactor can be used more efficiently to intensify the chemical synthesis of cumene hydroperoxide.
4. CONCLUSIONS The present work has clearly established the use of acoustic cavitation as an effective tool for intensification of organic synthesis and the approach to be used for synthesis of chemicals with an aim of maximizing the extent of conversion. The effect of different operating parameters in the conventional approach has enabled to decide the optimum operating conditions as stirrer speed of 300 rpm, temperature of 110 °C, catalyst quantity of 3 g, and air flow rate of 500 mL/min. The use of ultrasonic irradiations has been shown to improve the synthesis process for cumene hydroperoxide without any significant effect on the selectivity, and it has been established that direct irradiation of the reaction mixture with an ultrasound probe sonicator gives significant process intensification as compared to an ultrasonic bath. The work has also revealed that it might be possible to carry out the synthesis process at lower temperature in the case of sonochemical reactors without any significant decrease in the extent of conversion which is not possible using the conventional approach. ’ APPENDIX I: CAVITATIONAL YIELD CALCULATIONS Cavitational yields were obtained to know the quantity of product formed per amount of energy consumed in the operation. Ultrasonic bath operating at 40 kHz Reaction volume: 200 mL supplied energy dissipation ¼ 200 W For 8 h operation: total power input ¼ power rating time ¼ 200 ð8 3600Þ ¼ 5:76 106 J grams of product obtained total energy used 0:0005548 ¼ 5760000 ¼ 9:63 1011 g=J 1000 ¼ 9:63 1011 158 ¼ 6:33 1010 mol=kJ
ð1Þ
cavitational yield ¼
ð2Þ
’ REFERENCES (1) Mason, T. J. Sonochemistry and Sonoprocessing: the Link, the Trends and (probably) the Future. Ultrason. Sonochem. 2003, 10, 175–179. (2) Gogate., P. R. Cavitational Reactors for Process Intensification of Chemical Processing Applications: A Critical Review. Chem. Eng. Process. 2008, 47, 515–527. (3) Gogate, P. R.; Tayal, R. K.; Pandit, A. B. Cavitation: A Technology on the Horizon. Curr. Sci. 2006, 91, 35–46. (4) Mikkola, J. P.; Toukoniitty, B.; Toukoniitty, E.; Aump, J.; Salmi, T. Utilisation of On-Line Acoustic Irradiation as a Means to Countereffect Catalyst Deactivation in Heterogeneous Catalysis. Ultrason. Sonochem. 2004, 11, 233–239. (5) Kelkar, M. A.; Gogate, P. R.; Pandit, A. B. Process Intensification using Cavitation: Optimization of Oxidation Conditions for Synthesis of Sulfone. Ultrason. Sonochem. 2006, 13, 523–528. (6) Zhang, M.; Wang, L.; Ji, H.; Wu, B.; Zeng, X. Cumene Liquid Oxidation to Cumene Hydroperoxide over CuO Nanoparticle with Molecular Oxygen under Mild Condition. J. Nat. Gas Chem. 2007, 16, 393–398. (7) Fortuin, J. P.; Waterman, H. I. Production of Phenol from Cumene. Chem. Eng. Sci. 1953, 2, 182–192. (8) Matsui, S.; Fujita, T. New Cumene-Oxidation Systems O2 Activator Effects and Radical Stabilizer Effects. Catal. Today 2001, 71, 145–152. (9) He, Y. F.; Wang, R. M.; Liu, Y. Y.; Chang, Y.; Wang, Y. P.; Xia, C. G.; Suo, J. S. Study on Oxidation Mechanism of Cumene Based on GC-MS Analysis. J. Mol. Catal. A: Chem. 2000, 159, 109–113. (10) Hsu, Y. F.; Cheng, C. P. Mechanistic Investigation of the Autooxidation of Cumene Catalyzed by Transition Metal Salts Supported on Polymer. J. Mol. Catal. A: Chem. 1998, 136, 1–11. (11) Hsu, Y. F.; Yen, M. U.; Cheng, C. P. Autooxidation of Cumene Catalyzed by Transition Metal Compounds on Polymeric Supports. J. Mol. Catal. A: Chem. 1996, 105, 137–144. (12) Mills, A.; Holland, C. Effect of Ultrasound on the Kinetics of Oxidation of Octan-2-ol and other Secondary Alcohols with Sodium Bromate, Mediated by Ruthenium Tetraoxide in a Biphasic System. Ultrason. Sonochem. 1995, 2 (1), 33–38. (13) Toukoniitty, B.; Toukoniitty, E.; Maki-Arvela, P.; Mikkola, J. P.; Salmi, T.; Murzin, D.Yu.; Kooyman, P. J. Effect of Ultrasound in Enantioselective Hydrogenation of 1-phenyl-1,2-propanedione: Comparison of Catalyst Activation, Solvents and Supports. Ultrason. Sonochem. 2006, 13, 68–75. (14) Disselkamp, R. S.; Denslow, K. M.; Hart, T. R.; White, J. F.; Peden, C. H. F. The effect of Cavitating Ultrasound on the Aqueous Phase Hydrogenation of cis-2-buten-1-ol and cis-2-penten-1-ol on Pdblack. Appl. Catal., A 2005, 288, 62–66. (15) Ping, Z.; Mei, Y.; Xiaoping, L. Epoxidation of Cyclohexene with Oxygen in Ultrasound Airlift Loop Reactor. Chin. J. Chem. Eng. 2007, 15 (2), 196–199. (16) Hingu, S. M.; Gogate, P. R.; Rathod, V. K. Synthesis of Biodiesel from Waste Cooking Oil using Sonochemical Reactors. Ultrason. Sonochem. 2010, 17, 827–832. (17) Gogate, P. R.; Pandit, A. B. Application of Cavitational reactors for cell disruption for recovery of intracellular enzymes. J. Chem. Technol. Biotechnol. 2008, 83 (8), 1083–1093.
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