Microwave-Assisted Noncatalytic Destruction of Volatile Organic

Ind. Eng. Chem. Res. 2010, 49, 8461–8469

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Microwave-Assisted Noncatalytic Destruction of Volatile Organic Compounds Using Ceramic-Based Microwave Absorbing Media Sameer Pallavkar,† Tae-Hoon Kim,‡ Jerry Lin,§ Jack Hopper,† Thomas Ho,*,† Hye-Jin Jo,| and Jin-Hui Lee| Departments of Chemical Engineering, Industrial Engineering, and CiVil Engineering, Lamar UniVersity, Beaumont, Texas 77710, and Department of Chemical Engineering, Seoul National UniVersity of Technology, Seoul, Korea

Volatile organic compound (VOC) emissions from various sources such as chemical process industry, manufacturing industry, and automobiles have been an environmental and health concern. With the emerging emphasis on using green technologies to minimize greenhouse gas emissions, the use of microwave energy to achieve VOC emissions control with its electric power coming from nongreenhouse-related energy sources, such as wind, geothermal, solar, or even nuclear energy, becomes an attractive option. In this study, an experimental investigation involving the use of microwave energy to accomplish high temperature destruction of p-xylene in a packed bed reactor was performed using a SiC (silicon carbide) foam as the microwave absorbing media with air or nitrogen being the carrier gas. The experimental facilities consisted of a gas cylinder, a mass flow controller, a p-xylene vaporizer, a packed bed reactor packed with a SiC foam, a microwave applicator, and a gas chromatograph/mass spectrometer (GC/MS) for gas analysis. The SiC was found to be an excellent microwave absorber, which efficiently converts the microwave energy into heat energy. It was observed that the SiC temperature rises rapidly upon microwave irradiation and reaches a steady state temperature of higher than 800 °C within 2-3 min depending on the experimental conditions. A semiempirical energy balance model was formulated to describe the dynamic temperature profiles of the SiC in the reactor, and the model was found to simulate the observed profiles reasonably well. The destruction and removal efficiencies (DREs) for p-xylene were observed to reach 100% for all the experiments conducted with air being the carrier gas; however, the DREs never reached 100% with nitrogen being the carrier gas and the major destruction byproducts were observed to be benzene, toluene, styrene, biphenyl, and the unreacted p-xylene. The study has demonstrated that the microwave technology can be effectively developed to control the emissions of low concentrations of VOCs, especially in air. 1. Introduction Volatile organic compounds (VOCs) emitting from various industrial operations and automobiles are organic chemical species that readily volatilize in ambient air with many of them having great potential to pose serious long-term health and environmental impacts. Studies in the past have shown that prolonged exposure to VOCs such as toluene and p-xylene may affect central nervous functions and induce reproductive and developmental toxicity.1,2 Toluene in particular is recognized for its neurotoxicity effect on liver, heart, and kidney as well.2 Additionally, apart from being potential health hazards, many of these VOCs are photochemically active and, along with oxides of nitrogen and in the presence of sunlight, they have the potential to form ground level ozone which is a well-known secondary air pollutant.3 An urgent need, therefore, is to develop effective VOC treatment technologies to control VOC emissions to reduce potential health and environmental problems caused by these VOCs.3,4 Control of VOC emissions from various industrial operations at an acceptable level and with minimum energy usage constitutes a challenging task for the industry.5 Various VOC control devices, such as chilled water/refrigerated brine con* To whom correspondence should be addressed. Tel.: 409-880-8790. Fax: 409-880-2397. E-mail: [email protected]. † Department of Chemical Engineering, Lamar University. ‡ Department of Industrial Engineering, Lamar University. § Department of Civil Engineering, Lamar University. | Seoul National University of Technology.

densers, carbon/zeolite/polymer adsorbers, and membrane separation systems, are employed in many industrial applications to recover VOCs and achieve low VOC emissions.6-8 Other available VOC control devices also include thermal oxidizers, catalytic oxidizers, flares, and plasma/electron beam devices, where the first three involve the use of thermal energy generated from fossil fuel to destroy VOCs.9-14 Among them, thermal oxidizers are designed to treat waste streams with VOC concentrations ranging from 100 to 2000 ppm and are considered to have the broadest VOC control applicability with a high destruction and removal efficiency (DRE) ranging from 95 to 99%.15 The catalytic oxidizers are generally more energy efficient than the thermal oxidizers. However, they are more restricted in the application ranges and require additional maintenance for reliable operations. With the emerging emphasis on using green technologies to minimize greenhouse gas emissions,16 the employment of thermal oxidizers and catalytic oxidizers for VOC destruction with thermal energy generated from fossil fuels is becoming undesirable due to its potential generation of additional greenhouse gas, e.g., carbon dioxide. Instead, the use of microwave energy to achieve the control with its electric power coming from nongreenhouse-related energy sources, such as wind, geothermal, solar, or even nuclear energy, becomes an attractive option.5,17-26 Recent studies pertaining to VOC control technologies using activated carbon fiber cloths17,18 have shown desirable results in promoting microwave-assisted regeneration of these spent VOC adsorbents. These studies have indicated that microwave

10.1021/ie1009734  2010 American Chemical Society Published on Web 08/03/2010

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heating has an advantage over conventional heating as it allows selective heating depending on the dielectric properties of the substrate. It is worth pointing out that microwave heating is volumetric heating,17 with all of the infinitesimal volume elements within the object getting heated simultaneously, which is in contrast to surface heating such as from a hot gas stream where the direction of the heat flux was from the substrate surface inward. However, because of the absorption of microwave energy at the outer surfaces of the absorbing medium, the microwave field strength may be substantially reduced in the interior depending on the physical properties of the medium. Note that the use of microwave heating for VOC destruction had not been systematically investigated and was the objective of this study. 2. Objective The objective of the study was to conduct experiments to characterize the destruction of VOCs using microwave energy with silicon carbide (SiC) being the microwave absorbing media and p-xylene being the tested VOC. In the experiments, a specific concentration of p-xylene vapor in air or nitrogen was sent through a microwave-assisted packed-bed reactor containing a SiC foam and was destroyed in the reactor by the elevated temperatures generated by microwave irradiation. A gas chromatograph/mass spectrometer (GC/MS) was used to measure the DRE of p-xylene and to identify the destruction byproduct. The experimental parameters also included the carrier gas flow rate and the power level of the microwave energy. A model was developed to describe the energy balances in the system and simulate the temperature profiles of the silicon carbide foams during microwave heating. 3. Microwave Heating Technology The existence of electromagnetic waves was first predicted by Maxwell’s equation in 1864, and their rapid technological developments were realized during the Second World War era because of the development of radar.19,27 Microwaves are electromagnetic waves with frequencies ranging from 0.3 to 300 GHz in the vicinity of the high-frequency range of these radio waves. In order to avoid interference with telecommunication devices, particular frequencies have been allocated for purely industrial and domestic microwave systems. The standard frequency used in various microwave heating applications is 915 and 2450 MHz.19 The common equation relating the frequency (f) of the microwave and its wavelength (λ) is λ ) c/f

(1)

where “c” in this equation is the speed of light, i.e., 3 × 1010 cm/s. According to the above equation, the corresponding wavelengths for the above two frequencies, i.e., 915 and 2450 MHz, are 32.77 and 12.24 cm, respectively. It is worth pointing out that some materials are capable of absorbing microwave and getting heated up mainly through dielectric heating. The dielectric heating for a potential microwave absorber depends on its dipolar polarization, which is briefly described below.19,20,27 3.1. Dipolar Polarization. Dipolar polarization refers to materials which exhibit dipole moments, e.g., water, methanol, and ethanol. Under low-frequency irradiation, the dipoles of these materials are able to align themselves at these low frequencies and are able to keep in phase with the alternating electric field. However, at the higher microwave frequencies, these dipole moments lag behind the rapid changing electric fields resulting in increased molecular friction and collisions

Table 1. Dielectric Properties of Selected Materials28 material

ε′

ε′′

fused quartz silicon carbide

3.78 30.0

0.001 11.0

and the heating of the irradiated material. The extent to which these polar materials can convert the irradiated microwave energy into heat energy depends on their dielectric properties, namely, the relative dielectric constant (ε′) and the relative dielectric loss factor (ε′′). The relative dielectric constant represents the ability of the material to get polarized and the relative dielectric loss factor is the measure of the extent to which a dielectric material can convert the absorbed microwave energy to heat energy. Typical dielectric values for some of the materials are shown in Table 1 where silicon carbide is seen to have high values on both the two properties, i.e., 30 for ε′ and 11 for ε′′, respectively. It is, therefore, expected to be an excellent microwave absorbing media as well as an excellent material to convert the absorbed microwave energy to heat energy. On the contrary, quartz glass, with its ε′ value being at 3.78, is not considered a good microwave absorbing material. In addition, since its ε′′ value is very low, i.e., 0.001, it is not expected to be heated up at all by microwave irradiation. 3.2. Conversion of Microwave Energy to Heat Energy. The conversion of microwave energy to heat energy depends on the dielectric properties of the material (ε′ and ε′′), frequency of the microwave (ω), and the electric field intensity (Erms)17,20,21,27 given by the following equation: Qavg ) (ω)(ε0)(ε″)(Erms)2

(2)

where Qavg is the average heating potential, ω is the angular frequency, ε0 is the permittivity of free space () 8.85 × 10-12 F/m), and Erms is the electric field intensity. It should be noted that the electric field intensity (Erms) is a complex function of the microwave intensity and the physical properties of the material including ε′. 4. Experimental Section 4.1. Experimental Setup. A schematic diagram of the experimental setup is shown in Figure 1. It consists of a gas cylinder, a mass flow controller, a p-xylene vaporizer, a packed bed reactor, a microwave applicator, and a GC/MS (Varian model CP-3800 GC coupled with Varian Saturn 2200 MS) for gas analysis. The GC/MS was equipped with a built-in highperformance sample concentrator for parts-per-billion level detection capability designed by Lotus Consulting. The packed bed reactor was a 10.5 mm inside diameter (i.d.) and 304.8 mm long quartz tube from Technical Glass Products, Inc. It was packed with microwave absorbing material of silicon carbide foam supported on glass wool. The dimensions of the silicon carbide foam, supplied from Hi-Tech Ceramics, were 10 mm in outside diameter (o.d.) and 50 mm in height, and the reactor was placed inside a microwave applicator as shown in Figure 1. The applicator was a microwave application system shown in Figure 2 made up of a power supply, a microwave generator, a dummy load, a detector, a monitor, a three-stub turner, and a terminator. The system was safe-guarded and thoroughly examined using a microwave survey meter (ETS.Lindgren, Holaday EMF Measurement, model 1501) to ensure that no leaking of microwaves occurred during the experiments. 4.2. Experimental Procedure. The experimental procedure for each set of experiment involved the following sequential steps. The first was to assemble the packed bed with the


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Figure 1. Schematic diagram of the experimental setup.

designed bed material, i.e., silicon carbide, to the designated bed height. The next was to purge the assembled system with ultrahigh purity nitrogen (ultra high purity from Airgas) for about 15 min at a specific flow rate for purging by means of a mass flow controller (Brooks Instrument 5850-e series). The gas flow rate was then adjusted to a designated flow rate for experiments with nitrogen or switched to air for experiments with air (zero grade purity from Airgas). The procedure was followed by turning on the cooling water supply for the magnetron head and the short dummy load (Gerling Applied Engineering model GA1204). The data acquisition system (LabVIEW) was then turned on to record the temperature of the exit gas stream using a J type thermocouple (Omega Engineering Inc.) and the bulk surface temperature of the SiC foam using an infrared temperature (IR) measuring unit (Mikron model M90 with a temperature range of 700-2000 °C) through holes drilled through the applicator (see Figure 3). It is worth pointing out that the measured temperature based on the described IR system might not represent the true SiC temperature in the reactor because the SiC foam was enclosed in a quartz reactor. However, since quartz glass is considered IR transparent with a transparency index of 0.93 and since the quartz glass used in the experiment was thin (1.2 mm in thickness) and was in close contact with the SiC foam, the measured temperatures were interpreted as the SiC temperatures. The procedure was then followed by turning on the microwave generator and setting up the microwave power to the desired power level. Once the microwave power was turned on, both the forward power and the reverse power were monitored by two respective crystal detectors (Gerling Applied Engineering model GA3104/0015) and recorded on a dual microwave power meter (Gerling Applied Engineering model GA3004-2). The

forward microwave power was then fine-tuned to the designed level by adjusting a three-stub tuner. This setting of the threestub tuner was left undisturbed for the entire duration of a particular experimental run. With the microwave power being on, the temperatures of both the SiC foam and the exit gas were observed to rise rapidly. Once a steady temperature of the SiC foam in the reactor was achieved, the carrier gas (either nitrogen or air) was switched to the p-xylene vaporizer by a three-way control valve. The gas carried the vaporized p-xylene to the packed bed reactor containing the microwave-heated high temperature SiC foam. Upon contact with the high temperature SiC foam, the majority of the inlet p-xylene vapor was destructed. The effluent stream containing the potentially undestructed p-xylene and the destruction products was sampled and analyzed online using a GC/ MS. This allowed the DRE to be calculated based on the results from the GC/MS, which provided the mole concentration of p-xylene in the gas stream. The remaining effluent gas was directed to a water bubbler to ensure that positive pressure was maintained throughout the experiment, and it was then sent to the exhaust vent. Once the experiment was completed, the system was switched back to the purge mode with high-purity nitrogen gas flowing through the system to clean up the p-xylene residue and bring the system back to the starting conditions. A series of experiments was performed with the experimental parameters being the flow rate of the carrier gas and the power level of the microwave energy. In this study, three carrier gas flow rates were used, i.e., 200, 350, and 500 mL/min and the corresponding gas residence times in the SiC reactor were 1.30, 0.74, and 0.52 s, respectively.

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Figure 2. Block diagram and the corresponding setup of the microwave application system.

Figure 3. Holes drilled through the applicator for infrared temperature measurements.

5. Results and Discussion 5.1. Net Spent Microwave Power and Steady State Temperature. It was described in the Experimental Section that the designed microwave system was capable of measuring both the forward power and the reverse power with the net spent

microwave power being the difference between the two. While the forward power was a set value and was constant throughout an experiment, the reverse power was observed to increase steadily and reached a steady value once the system reached its steady state temperature. The relationships among the forward


Figure 4. Plot of forward power, net power, and the corresponding steady state temperature of SiC under different gas flow rates (carrier gas, nitrogen).

power, the net power, and the SiC temperature at the steady state under various operating conditions are plotted in Figure 4. The results in the figure indicate that the percentages of the net spent microwave power at a steady state are approximately 84%, 75%, and 68% of the forward power for the three gas flow rates studied, i.e., 200, 350, and 500 mL/min, respectively. The results also indicate that the steady state temperature is higher at a lower gas flow rate for all the power levels studied. The observed results are expected since the net power input is higher at a lower gas flow rate, which results in a higher steady state temperature. 5.2. Dynamic Temperature Profiles during Microwave Heating. Besides the steady state temperatures, the dynamic nature of the SiC temperature during microwave heating was also investigated in this study. Since SiC is an excellent microwave absorber and has an excellent dielectric loss factor to convert the microwave energy to heat energy, the temperature of the SiC foam was expected to rise rapidly and reach steady state values within a short period of time. Typical dynamic SiC temperature profiles during selected experiments are shown in Figure 5 where the results indicate that the steady state temperatures of higher than 800 °C are reached within about 2-3 min and that higher steady state temperatures were observed with higher microwave powers. In addition, the results also indicate that the introduction of p-xylene in the stream raises the steady state temperature slightly due to the exothermic nature of the reaction related to p-xylene combustion or decomposition. Table 2 summarizes the observed steady state temperatures with or without p-xylene under different experimental conditions. As expected, higher steady state temperatures are associated with higher microwave powers and lower gas flow rates. An attempt was made to simulate the observed dynamic temperature profiles by using the following energy balance equation, i.e., [(m)(Cp)(dT/dt)] ) Ps(1 - eβt) - [(h)(Ac)(T - To)/2 + (σ)(Ar)(T4 - Ts4)]

(3)

where m is the mass of the absorbing media, Cp is the specific heat of the absorbing media, (h)(Ac) is the convective heat transfer, (σ)(Ar) is the radiative heat transfer, Ps is the net

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microwave power consumed, and To and Ts are the gas inlet temperature and the surrounding temperature, respectively. In the above equation, the term on the left-hand-side represents the rate of increase of SiC temperature and the terms on the right-hand-side represent the net microwave energy contributed to the increase in SiC temperature with the first term representing the net microwave power being converted to heat energy, the second term representing the loss of heat energy to the gas through convective heat loss, and the third term representing the loss of heat energy to the surroundings through radiation heat loss. It should be noted that the term eβt appearing in eq 3 is an empirical expression representing the amount of net microwave energy not contributing to the heat energy balance of SiC, e.g., the energy absorbed by SiC but not converted to heat energy and/or the energy absorbed by other components of the system, e.g., the quartz glass or reactor walls. It is worth pointing out that the term Ps(1 - eβt) is theoretically a function of the dielectric properties of SiC, which in turn, are a complex function of temperature and other physical properties such as density, mass, and specific heat.17,19 However, since its correlation with temperature is not available at this time, the term is treated as a constant, i.e., independent of T, in the equation. In the simulation, the constant β was determined through trial and error to best-fit the simulation results to the experimentally observed values. It was assumed to be a constant for experiments with different microwave power levels but with the same gas and the same gas flow rate. Typical simulation results based on eq 3 are also plotted in Figure 5 (without considering the effect of p-xylene), and good agreement between the simulated and observed results is observed. It should be noted that, in Figure 5, measurement temperatures below 700 °C were not available due to the limitations of our infrared temperature unit which was designed for measuring temperatures between 700 and 2000 °C. The proposed equation for energy balance calculations, i.e., eq 3, was also used to provide insights into the distribution of the net spent microwave energy in various energy terms. A typical set of such simulation results is shown in Figure 6 where the results indicate that, at the beginning of the heating process, the majority of the net spent microwave energy is wasted with less than 25% being used to raise the temperature of the SiC. As the process is progressed, the wasted energy gradually diminishes and the majority of the microwave energy is converted to heat energy and lost to the surrounding via radiation loss. The convective heat loss to the carrier gas remains to be low throughout the entire VOC destruction process. It is worth pointing out that the proposed semiempirical model serves to describe the observed temperature profiles well. However, a more theoretical approach should be used for a more serious analysis. Although it was not involved in the current study, it should be pointed out that the microwave VOC destruction process can be improved in its energy efficiency through the use of reflective materials to reduce the radiative heat losses. Further study will be conducted to demonstrate the practice. 5.3. Destruction and Removal Efficiency of VOC. The DRE of a VOC is defined to be the amount of the VOC destroyed, i.e., the difference between VOCin and VOCout, over the input amount of the VOC with the equation given below: DRE ) [(VOCin - VOCout)/VOCin] × 100%

(4)

In this study, the VOC tested was p-xylene, the VOCin was the p-xylene mole concentration in the inlet stream, and the VOCout

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Figure 5. Temperature profiles of SiC during experiments with different levels of microwave irradiation (carrier gas, nitrogen; carrier gas flow-rate, 500 mL/min).

Figure 6. Distribution of net microwave power during the heating up of SiC (carrier gas, nitrogen; gas flow rate, 500 mL/min). Table 2. Steady State SiC Surface Temperatures under Different Experimental Conditions flow rate of nitrogen gas (mL/min)

microwave forward power (watt)

net microwave power (watt)

T (no p-xylene) (°C)

T (with p-xylene) (°C)

200 350 500 200 350 500 200 350 500

350 350 350 450 450 450 550 550 550

318 271 238 380 355 306 458 440 374

967.8 815.0 808.6 1065.8 910.0 880.0 1087.0 996.0 993.4

971.0 849.6 810.0 1067.0 931.9 882.9 1127.0 1010.6 995.0

was the p-xylene mole concentration in the outlet stream. Both the VOCin and VOCout were measured by the GC/MS after the system reached the steady state during an experiment.

It was generally observed that the destruction of p-xylene was always complete during our experiments when air was the carrier gas, i.e., the p-xylene concentration was undetectable in the outlet stream; and the DREs were always greater than 90% depending on the operating conditions when nitrogen was the carrier gas. It should be pointed out that, when nitrogen gas was the carrier gas, the main products were methane and ethane with trace amounts of destruction byproducts including benzene, toluene, styrene, biphenyl, and the unreacted p-xylene, which are to be discussed in the next subsection. However, when air was the carrier gas, the main products from this destruction process were carbon dioxide and water with a trace amount of carbon monoxide. Results from equilibrium calculations have indicated that, although the equilibrium trend favors CO over CO2 at high temperatures, the equilibrium ratios of CO/CO2 remain to be extremely low in the temperature range of our


Figure 7. DRE for p-xylene destruction (carrier gas, nitrogen; gas flow rate, 200 mL/min).

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experiments, i.e., approximately 2.0 × 10-8 at 900 °C to 4.0 × 10-5 at 1300 °C. Figures 7-9 plot DREs against the net microwave power with nitrogen being the carrier gas under different nitrogen flow rates, i.e., 200, 350, and 500 mL/min. Also plotted on the figures are the corresponding steady state temperatures. The results strongly indicate that the DREs are greater than 99.9% when the reactor temperatures are higher than 900 °C. However, the DRE can only be 90% when the reactor temperature is low at around 800 °C as indicated in Figure 9. It is worth pointing out that the DREs for the corresponding experiments with air being the carrier gas were all 100%, i.e., no destruction byproducts were detected. 5.4. Destruction Byproducts with Nitrogen being the Carrier Gas. As discussed previously, when nitrogen was the carrier gas, the destruction of p-xylene was greater than 99.9% at high temperatures with trace amounts of less than 0.1% of destruction byproducts including benzene, toluene, styrene, biphenyl, and the unreacted p-xylene. Typical GC/MS mass spectrum results showing the existence of these destruction byproducts are displayed in Figures 10 and 11. The results

Figure 10. GC/MS mass spectrum data for p-xylene destruction (carrier gas, nitrogen; gas flow rate, 200 mL/min; net power level, (A) 318 W, (B) 380 W, (C) 458 W; temperature, TA, 971 °C; TB, 1067 °C; TC, 1127 °C).

shown in Figure 10 indicate that, under the nitrogen flow rate of 200 mL/min, five major destruction byproducts, namely, benzene, toluene, styrene, biphenyl, and p-xylene, were detected at a lower microwave power level. The detected byproducts were reduced to two, i.e., p-xylene and biphenyl, at higher microwave power levels. The same two destruction byproducts were also

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Ind. Eng. Chem. Res., Vol. 49, No. 18, 2010 σ ) Stefan-Boltzmann constant, W/m2 K4 β ) empirical coefficient appearing in eq 3, 1/s ε0 ) permittivity of free space () 8.85 × 10-12), F/m ε′ ) relative dielectric constant of the absorbing media, ε′′ ) relative dielectric loss factor of the absorbing media, λ ) wavelength of the irradiated microwave, cm ω ) angular frequency of microwave energy, rad/s

Acknowledgment

Figure 11. GC/MS mass spectrum data for p-xylene destruction (carrier gas, nitrogen; gas flow rate, 500 mL/min; net power level, 374 W; temperature, 995 °C).

The authors are grateful for the financial support of this study from U.S. EPA through the University of Houston (EPA Project Number X833306). We specially acknowledge the National Science Foundation for a 2004 MRI (Major Research Instrumentation) award (NSF Award No. 0320818) for providing the GC/MS system for the project. The support from TCEQ (Texas Commission on Environmental Quality) for the microwave experimental facilities through a 2005 NTRD (New Technology and Research Development) project is also acknowledged.

detected at a higher nitrogen flow rate (500 mL/min) and a high microwave power level as indicated in Figure 11.

Literature Cited

6. Conclusions An experimental study involving the use of microwave energy to accomplish high-temperature destruction of p-xylene in a packed bed reactor has been performed using a SiC foam as the microwave absorbing media with air and nitrogen being the carrier gas. The SiC has been found to be an excellent microwave absorber which efficiently converts the microwave energy into heat energy. It has been observed that the SiC temperature rises rapidly upon microwave irradiation and reaches a steady state temperature of higher than 800 °C within 2-3 min depending on the experimental conditions. A semiempirical energy balance model has been formulated to describe the dynamic temperature profiles of the SiC in the reactor, and the model has been found to simulate the observed profiles reasonably well. The DREs for p-xylene have been observed to reach 100% for all the experiments conducted with air being the carrier gas; however, the DREs have never been observed to reach 100% with nitrogen being the carrier gas and destruction byproducts being benzene, toluene, styrene, biphenyl, and the unreacted p-xylene. The study has indicated that the microwave technology can be effectively developed to control the emissions of low concentration of VOCs especially in air. The use of microwave energy to achieve the control with its electric power coming from nongreenhouse-related energy sources, such as wind, geothermal, solar, or even nuclear energy, becomes an attractive option. Notations Ac ) convective heat transfer area, m2 Ar ) radiative heat transfer area, m2 Cp ) heat capacity of the absorbing media, J/kg K c ) speed of light, cm/s Erms ) electric field intensity, V/m f ) frequency of irradiated microwave energy, Hz h ) convective heat transfer coefficient, W/m2 K m ) mass of the absorbing media, kg Ps ) steady state microwave power, W Qavg ) average heat potential of the absorbing media, W/m3 T ) temperature of the absorbing media, K or °C To ) gas inlet temperature, K Ts ) surrounding temperature, K

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ReceiVed for reView April 27, 2010 ReVised manuscript receiVed July 7, 2010 Accepted July 21, 2010 IE1009734

Microwave-Assisted Noncatalytic Destruction of Volatile Organic

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