Paper

This article was downloaded by:[Indarto, Antonius] [Indarto, Antonius] On: 2 May 2007 Access Details: [subscription number 777799255] Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Chemical Engineering Communications

Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t713454788

CCL4 DECOMPOSITION BY GLIDING ARC PLASMA: ROLE OF C2 COMPOUNDS ON PRODUCTS DISTRIBUTION To cite this Article: , 'CCL4 DECOMPOSITION BY GLIDING ARC PLASMA: ROLE OF C2 COMPOUNDS ON PRODUCTS DISTRIBUTION', Chemical Engineering Communications, 194:8, 1111 - 1125 To link to this article: DOI: 10.1080/00986440701293363 URL: http://dx.doi.org/10.1080/00986440701293363

PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article maybe used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. © Taylor and Francis 2007

Downloaded By: [Indarto, Antonius] At: 18:28 2 May 2007

Chem. Eng. Comm., 194:1111–1125, 2007 Copyright # Taylor & Francis Group, LLC ISSN: 0098-6445 print/1563-5201 online DOI: 10.1080/00986440701293363

CCl4 Decomposition by Gliding Arc Plasma: Role of C2 Compounds on Products Distribution ANTONIUS INDARTO1, DAE RYOOK YANG2, JAE-WOOK CHOI1, HWAUNG LEE1, AND HYUNG KEUN SONG1 1

Plasma-Catalyst Chemical Process, Korea Institute of Science and Technology, Seoul, Korea 2 Department of Chemical and Biological Engineering, Korea University, Seoul, Korea The goal of this work is to investigate the role of existing C2 compounds in the plasma reactions of carbon tetrachloride (CCl4) decomposition. The experiment of CCl4 decomposition was carried out by gliding arc plasma. The decomposition products were dominated by CO, CO2, and Cl2. The conversion of CCl4 into Cl2 and (CO þ CO2) reaches
50% and
40%, respectively. Other chlorinated compounds were suspected to be produced, such as COCl, COCl2, and C2 compounds. In order to prove the existence of those compounds, for example, chlorinated C2 compounds, a kinetic simulation was performed and cross-checked with the experimental results to clarify the reactions mechanism. Keywords CCl4 decomposition; Gliding arc; Plasma; Reaction mechanism

Introduction Emissions from various industries of chlorinated volatile organic compounds (CVOCs), such as carbon tetrachloride (CCl4), create environmental problems (Butler, 2000; WMO, 2002). Chemical degradation of CVOCs in our atmosphere will produce another toxic chloride compound, HCl, which is classified as the main component of acid rain (Sanhueza, 2001). Some studies report that CCl4 will produce very active chlorine radicals by solar radiation reactions. These species will react and destroy ozone molecules in the stratosphere (Butler, 2000; U.S. EPA, 2002). Moreover, the most severe problem of the emission of CCl4 is due to its toxic and carcinogenic damage to human health (IARC, 1987). Thus there are reasons to find effective methods to reduce the emission of CVOCs. The most widely adopted technique for the treatment of CVOCs is thermal combustion or incineration (Cheremisinoff, 2000). The decomposition process is done by direct thermal reaction with oxidant, e.g., air and oxygen. Although this method is simple, it requires high burning temperature (between 800 and 1,100C) to achieve the optimum decomposition rate. Taylor and Dellinger reported that incomplete Address correspondence to Antonius Indarto, Plasma-Catalyst Chemical Process, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130–650, Korea. E-mail: [email protected]

1111

Downloaded By: [Indarto, Antonius] At: 18:28 2 May 2007

1112

A. Indarto et al.

combustion conditions could produce a large amount of complex chlorinated products (Taylor and Dellinger, 1988). To overcome these problems, many studies were carried out on the application of new technologies. Plasma-assisted technology is one of the promising ways to decompose CVOCs. Low thermal plasma processes, such as RF plasma (Lee et al., 1996), surface discharge reactor (Oda et al., 2002), dielectric barrier discharge reactor (Tonkyn et al., 1996), pulsed discharge reactor (Yamamoto et al., 1992), and capillary-tube type discharge reactor (Kohno et al., 1998), have been investigated and developed. In this study, gliding arc plasma was used to decompose carbon tetrachloride. Previously, we successfully conducted experiments with gliding arc plasma to treat CH2Cl2 (Indarto et al., 2006a, b), CHCl3 (Indarto et al., 2005b, 2006b), CO2 (Indarto et al., 2006c), and methane (Indarto et al., 2005b, 2006d). Compared with the above plasma methods, there is a greater chance that gliding arc plasma can be applied in the chemical industry (Fridman et al., 1999; Fanmoe et al., 2003). This method allows the higher flame temperature and energy that are necessary to destroy the chemical bond of toxic compounds in contrast to other plasmas, such as corona and DBD. In addition, gliding arc is applicable for high input flow rate conditions. Kinetic reaction models of CCl4 decomposition using electron beam in dry air (Penetrante et al., 1995; Koch et al., 1995; Nichipor et al., 2000) and liquid (Mak et al., 1997) have been investigated. The models suggested that the main products were dominated by chlorinated C1 compounds, such as COCl2, CO, CO2, ClNO3, ClO3, and Cl2. Fragmentation of CCl4 occurred by two reaction mechanisms (Penetrante et al., 1995). In the oxygen-rich condition, the atomic oxygen species, such as ground state of atomic oxygen O(3P) and excited atomic oxygen O(1D), have enough energy to destroy the bonds of CCl4. Oð3 PÞ þ CCl4 ¼ ClO þ CCl3

ð1Þ

Oð1 DÞ þ CCl4 ¼ CCl3 þ ClO2

ð2Þ

The second mechanism occurred via reaction with secondary electron. Secondary electrons will dissociate CCl4 into CCl3 and negative chlorine ion (Cl ): e þ CCl4 ¼ CCl3 þ Cl 

ð3Þ

Radical ClO and CCl3 were suspected to be the most important intermediate species to determine the final products of CCl4 decomposition. The concentration of O and Cl could also be influenced by the radical reactions, both initiation and termination reactions. Nichipor’s (2000) investigation showed that CO, Cl2, and CO2 were formed by dissociation process between electron and COCl2: e þ COCl2 ¼ CO þ Cl2

k ¼ 107 cm3 =mol

ð4Þ

Then, CO was oxidized by ClO and produced CO2: CO þ ClO ¼ CO2 þ Cl

ð5Þ

However, there has been less research on the importance of chlorinated C2 in the decomposition reaction of CCl4. In this study, we investigate the role of chlorinated C2 compounds on the reactions mechanism and product selectivity, especially CO, CO2, and Cl2. Two different schemes of reaction mechanism are proposed and compared with experimental results. Some reaction mechanisms, obtained from

Downloaded By: [Indarto, Antonius] At: 18:28 2 May 2007

CCl4 Decomposition by Gliding Arc

1113

microwave plasma and the combustion process, were used to approach the real system of gliding arc plasma. The simulation results were compared to the experimental ones to satisfy the kinetic models.

Experimental Setup The schematic diagram of experimental setup is shown in Figure 1. Carbon tetrachloride and dry atmospheric air were used as the source gases. Each part of the system is described in detail in the following section. The reactor was made from a quartz tube with an inner diameter of 45 mm and length of 300 mm. The upper and bottom part of the reactor were supplied with polytetrafluoroethylene (PTFE) seals, the lower one holding two electrodes. The electrode, made of stainless steel, has a triangular form with a height of 100 mm. The shortest gap between two electrodes was only 1.5 mm. The gas was injected between these electrodes through a capillary of inner diameter of 0.8 mm. A thermocouple, located 10 cm above the electrode, was installed to measure the outlet gas temperature. A high-frequency alternating current (AC) power supply (Auto Electric A1831, Korea) was connected to the electrodes of gliding arc to generate plasmas. Figure 2 shows the typical wave form of voltage and current obtained in this experiment. Liquid carbon tetrachloride (CCl4) was purchased from Kanto Chemical Co., with purity of more than 99.5%. The concentrations of CCl4 in the input gas were varied by 1, 3, 5, and 8 vol% of total flow rate. Dry atmospheric pressure air was used as the carrier gas and controlled by a mass flow controller (Tylan FC-280S, USA). The flow rates of air were 180, 240, and 300 L=h. CCl4 was introduced to the reactor by passing a portion of dry air through a bubbling tube of liquid CCl4, which was immersed in a water bath. Concentration of CCl4 was adjusted by controlling both the temperature of the water bath and injected gas flow rate

Figure 1. Schematic diagram of experimental setup.

A. Indarto et al.

Downloaded By: [Indarto, Antonius] At: 18:28 2 May 2007

1114

Figure 2. Voltage and current profile.

to the bubbling tube. The feed line stream was covered by a heating band to avoid the condensation of CCl4. Mass spectroscopy and two gas chromatographers (GCs) were used for the qualitative and quantitative analysis of the reactants and products. The concentrations of CCl4 in the gas mixture before and after the reaction were determined by a GC flame ionized detector (YoungLin M600D, column: Bentone, Korea), and the concentrations of CO and CO2 were measured by a GC thermal conductivity detector (YoungLin M600D, column: SK Carbon, Korea). Species analysis of the decomposition products was done by quadruple mass spectroscopy (Balzers QMS 200, USA) with Quadstar 421 software. Chlorine gas (Cl2) was determined by bubbling the output gas through 0.05 M of aqueous KI during measured-experiment time, followed by iodometric titration 0.05 M of Na2SO3 (Skoog et al., 2000). Selectivity of products and conversion of CCl4 were defined as: Selectivity of Cl2 ¼

moles of Cl2 formed  100% 2  moles of CCl4 converted

ð6Þ

moles of CO formed  100% moles of CCl4 converted

ð7Þ

Selectivity of CO ¼

Downloaded By: [Indarto, Antonius] At: 18:28 2 May 2007

CCl4 Decomposition by Gliding Arc

1115

Selectivity of CO2 ¼

moles of CO2 formed  100% moles of CCl4 converted

ð8Þ

Conversion of CCl4 ¼

moles of CCl4 consumed  100% moles of CCl4 introduced

ð9Þ

Cl2 =ðCO þ CO2 Þratio ¼

moles of Cl2 formed moles of CO formed þ moles of CO2 formed

ð10Þ

The consumed power for the process was calculated as the products of voltage and current wave form captured by an oscilloscope (Agilent 54641A, USA). In this experiment, we limited the power from 286 to 304 watts. Sample data were obtained after 30 min operation, referring to the stable temperature condition of the output line measured by the thermocouple.

Kinetics Study and Model To investigate the reaction mechanism, a chemical kinetic reaction model of CCl4 decomposition was constructed. The gas-phase reaction model consists of the 21 elementary reactions that are proposed by literatures as the most significant pathway of reactions (Lou and Chang, 1997; Chang and Senkan, 1989; NASA, 1994; Penetrante et al., 1995, Koch et al., 1995, Nichipor et al., 2000). The rate constant of each reaction is expressed in a modified Arrhenius form:
 Ej kj ¼ Aj T bj exp  ð11Þ RT The simulation was focused on the reactions of Cl2, CO, CO2, and chlorinated C1 production. Other products, such as chlorinated C2, were considered only as intermediate species because the concentrations of those components in the product line were small. Table I is a list of elementary chemical reactions of CCl4 decomposition. The model was coded in the MATLAB program (MathWorks, USA) and numerically solved using the shooting method (Walas, 1991; Chapra and Canale, 1990). The algorithm of the program is shown in Figure 3(a). MATLAB modules of ode23s and fmins were utilized to solve simultaneously the 15 sets (15 species) of differential equations (shown in Equations (12) and (13)) and minimize the absolute error. m   dxi X ¼ fj kj ; xi ðtÞ; . . . ; xn ðtÞ dt j¼1

ð12Þ

; xi ðtÞ ¼ xproduct xi ðt0 Þ ¼ xinput i i

ð13Þ

The concentration of Cl2 in the products was used as the basis (boundary condition) to calculate the Cl2 to (CO þ CO2) ratio and converted CCl4. To verify the validity of the model, the simulation and experimental results were compared for each point. The absolute error was calculated as: n     product product De ¼ abs xsim þ abs xsim Cl2  xCl2 ðCOþCO2 Þ  xðCOþCO2 Þ  o2 product þabs xsim ð14Þ CCl4  xCCl4

Downloaded By: [Indarto, Antonius] At: 18:28 2 May 2007

1116

A. Indarto et al.

Table I. Chemical kinetics for decomposition of CCl4 Reactiona 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

CCl2 þ Cl2 ¼ CCl3 þ Cl CCl2 þ O2 ¼ ClO þ COCl CCl3 þ O ¼ COCl2 þ Cl ðÞ CCl3 þ O2 ¼ COCl2 þ ClOðÞ CCl3 þ Cl2 ¼ CCl4 þ Cl CCl3 þ CCl3 ¼ C2 Cl6 CCl3 þ CCl3 ¼ C2 Cl4 þ Cl2 CCl4 ¼ CCl3 þ Cl ðÞ CCl4 þ O ¼ CCl3 þ ClOðÞ CO þ ClO ¼ CO2 þ Cl ðÞ COCl þ Cl ¼ CO þ Cl2 COCl þ M ¼ CO þ Cl þ M ðÞ COCl þ O ¼ CO þ ClO ðÞ COCl2 þ Cl ¼ COCl þ Cl2 C2 Cl4 þ O ¼ COCl2 þ CCl2 C2 Cl4 þ Cl ¼ C2 Cl5 C2 Cl5 þ Cl ¼ CCl3 þ CCl3 C2 þ Cl5 Cl ¼ C2 Cl4 þ Cl2 C2 Cl6 ¼ Cl2 þ C2 Cl4 C2 Cl6 ¼ Cl þ C2 Cl5 C2 Cl6 þ Cl ¼ Cl2 þ C2 cl5

log A

n

E

DHr(298 K) Ref.

12.70 13.00 14.00 13.00 12.40 36.15 26.35 35.87 10.40 11.78 13.10 14.30 14.00 13.50 13.00 35.42 27.23 27.10 35.21 36.13 13.80

0 0 0 0 0 7.48 4.43 6.52 0 0 0.5 0 0 0.5 0 7.71 4.01 4.73 6.53 6.48 0

3.0 1.0 0 28.0 6.0 6.7 9.0 75.4 2.3 7.4 0.5 6.5 0 20 5.0 5.3 12.1 8.9 63.2 74.4 18.3

7.8b 37.1b 102.8b 47.7b 11.4b 67.5b 40.7b 70.8b 5.0b 62.2b 52.4b 7.1b 58.7b 18.5b 54.3b 17.8c 1.0 41.7c 26.8c 68.5c 9.0c

a

k ¼ AT n expðE=RTÞ, in cm, kcal, s, and mole units. Lou and Chang, 1997. c Chang and Senkan, 1989.  Most significant reactions in this experiment. b

The model stiffness was checked by varying input guesses. Figure 3(b) shows that the model produces an almost similar absolute error although the input guess is varied from 3.9 to 6.5.

Results and Discussion CCl4 Conversion Figure 5(a) shows the effect of initial concentration of CCl4 on the conversion at a frequency of 20 kHz. Conversion decreases gradually when the initial concentration of CCl4 is increased. The maximum conversion reaches 80% at the concentration of 1 vol% and flow rate of 180 L=h. Increasing concentration of CCl4 will decrease the ratio of high-energy energetic species (e.g., electron and radical atoms=molecules) to CCl4. This is because at the same flow rate and supplied energy, the amount of highenergy energetic species, both quality and quantity, can be assumed to be same. This condition will decrease the relative probability of a single CCl4 molecule colliding with energetic species that are able to destroy the CCl molecule bonds. However, although the collision probabilities are lower, the effectiveness of absolute collision at higher initial concentration of CCl4 is higher that that at lower concentration of

1117

Downloaded By: [Indarto, Antonius] At: 18:28 2 May 2007

CCl4 Decomposition by Gliding Arc

Figure 3. (a) The algorithm of simulation; (b) error sensitivity of model as a function of input guess variation.

CCl4. For example, at 1% and 3 % CCl4 concentration, it can be calculated as 1 (% of input concentration)  80 (% of conversion) and 3  73, respectively. This will lead to the ratio of 80:219, which shows that the process at 3% CCl4 concentration produces 219=80 times more effectively than that at 1% of CCl4 concentration. Analysis of QMS spectrum (Figure 8) shows that the main gaseous products are CO, CO2, and Cl2. In addition to those products, other chlorinated compounds are also detected but the concentrations are small.

A. Indarto et al.

Downloaded By: [Indarto, Antonius] At: 18:28 2 May 2007

1118

Figure 4. Model scenario of CCl4 decomposition; (a) first scenario, (b) second scenario.

CO þ CO2 Selectivity Increasing initial concentration of CCl4 will affect lowering the selectivity of CO þ CO2. As shown in Figure 5(b), the selectivity of CO þ CO2 decreases around 2% when the concentration of CCl4 is increased from 1% to 8%. Our kinetic simulation calculates that higher initial concentration of CCl4 produces higher concentration of single chlorine species (Cl) in the reactor. The reactions will follow (Chang and Senkan, 1989): CCl4 ¼ CCl3 þ Cl

ð15Þ

CCl3 þ O ¼ COCl2 þ Cl

ð16Þ

Cl atom will compete with carbon atom (C) to react with oxygen (O). Higher concentration of Cl makes the probability of C and O reaction to produce CO smaller. Kinetic reaction studies of CO, CO2, and Cl2 formation in thermal oxidation show similar reaction mechanisms to those proposed by the literature (Chang and Senkan, 1989; Lou and Chang, 1997). The major pathways responsible for the formation of CO2 are: COCl þ Cl ¼ CO þ Cl2

ð17Þ

COCl þ M ¼ CO þ Cl þ M

ð18Þ

CO2 is mainly generated from the reaction of CO and ClO: CO þ ClO ¼ CO2 þ Cl

ð19Þ

1119

Downloaded By: [Indarto, Antonius] At: 18:28 2 May 2007

CCl4 Decomposition by Gliding Arc

Figure 5. Effects of initial CCl4 concentration on (a) CCl4 conversion, (b) (CO þ CO2) selectivity, and (c) Cl2 selectivity.

and ClO is formed via: CCl4 þ O ¼ CCl3 þ ClO

ð20Þ

CCl3 þ O2 ¼ COCl2 þ ClO

ð21Þ

Koch et al. (1995) reported a similar radical mechanism, as mentioned above, using an electron beam process for CCl4 decomposition in the presence of O2. However, Equation (19) is not counted as the main mechanism for Cl production because the concentration of CO2, measured in the output stream, was relatively low. The concentration of CO2 was five to ten times lower than CO in all of the experimental ranges. An interesting phenomenon was found in the case of nitrogen. The concentration of nitrogen in the air was around 80%. Analysis of the QMS spectrum shows no significant different of the concentration before and after plasma reaction. It means that although it has a lower excitation level, N2 acted as an inert gas in the gliding arc plasma. Products analysis by QMS also shows that there were no significant N-containing compounds detected, except a small concentration of N2O. In gliding arc plasma, oxygen tends to have an influence more than nitrogen. Our previous research on oxygen showed that atomic oxygen, both ground-state and excited form, could be more active than nitrogen (Indarto et al., 2005a; 2006c).

Downloaded By: [Indarto, Antonius] At: 18:28 2 May 2007

1120

A. Indarto et al.

The importance of ground-state atomic oxygen O(3P) and metastable atomic oxygen O(1D) in the reaction kinetics has been rigorously investigated (Davidson et al., 1978). Both O(3P) and O(1D) can be produced from dissociation reactions (Penetrante et al., 1995): e þ O2 ¼ e þ Oð3 PÞ þ Oð3 PÞ

ð22Þ

e þ O2 ¼ e þ Oð3 PÞ þ Oð1 DÞ

ð23Þ

In this experiment, the initial concentration of oxygen was around
20%, as we used atmospheric air as the dilution gas for CCl4. QMS spectrum analysis shows that in the output stream, the peak intensity of O2 in the product stream was slightly lower than that in the feed stream. Moreover, the magnitude of decreasing peak intensity of oxygen was not changed significantly when the initial concentration of CCl4 was varied. Based on this result, it can be assumed that the concentrations of oxygen atoms are similar for each process at the same power and flow rate. On the other hand, increasing concentration of CCl4 in the feed stream will increase the concentration of intermediate Cl atoms. It will effect a smaller probability of C and O reaction as the probability of Cl and O reaction is increasing. This analogy can be the reason why the selectivity of (CO þ CO2) decreases when the initial concentration of CCl4 is increased. Cl2 Selectivity Different from previous phenomena of CO and CO2 production, the selectivity of Cl2 increases when the initial concentration of CCl4 is also increased (Figure 5(c)). The existence of Cl atom will affect the termination reactions of intermediate chlorine molecules that produce Cl2. The major pathways of Cl2 formation can be: COCl2 þ Cl ¼ COCl þ Cl2

ð24Þ

COCl þ Cl ¼ CO þ Cl2

ð25Þ

The existence of COCl2 and COCl were detected by our QMS (Figure 8) and it gives a greater possibility for the above reaction to occur. In the higher initial concentrations of CCl4, the concentration of Cl will increase and produce more Cl2, following Equations (24) and (25). Simulation of Cl2, CO, and CO2 In the above reaction mechanisms, only chlorinated C1 compounds are counted as the intermediate species in the production of CO, CO2, and Cl2. In order to investigate the role of chlorinated C2 compounds in the decomposition reaction of CCl4, especially for CO, CO2, and Cl2 production, we constructed two types of reaction mechanisms based on the elementary reactions listed in Table I. The first scenario considers Equations (17)–(19) and (24)–(25) as the main reaction pathways to produce CO, CO2, and Cl2 and neglects the production of those compounds from the chlorinated C2 compounds, such as C2H4, C2H5, and C2H6 (Figure 4(a)). This reaction pathway is chosen to examine the dependence of Cl2, CO, and CO2 production from the proposed Equations (17)–(19) and (24)–(25). The second scenario will consider the existence of higher carbon-chloride and calculate its effects on the decomposition reactions (Figure 4(b)).

Downloaded By: [Indarto, Antonius] At: 18:28 2 May 2007

CCl4 Decomposition by Gliding Arc

1121

Figure 6 shows the party comparison plot of those two models. The horizontal axis shows the experimental results, and the vertical axis shows the simulation calculation. The second model shows that the results of simulation are closer to the experimental results than those of the first model. The first scenario of the model gives 8–50% error value, much higher than the second model, which produces error values of only 2–10%. Based on these two models, neglecting the existence of chlorinated C2 compounds in the reactions mechanism of CO, CO2, and Cl2 production will produce lower selectivity of chlorine gas (Cl2) and higher selectivity of CO and CO2 than the experimental results. Direct conversion of chlorinated C2 compounds to Cl2 could be counted as a significant pathway of Cl2 production. Lou and Chang (1997) also identified the production of Cl2 from chlorinated C2 compounds, e.g., C2Cl5: C2 Cl5 þ Cl ¼ CCl3 þ CCl3

ð26Þ

On the other hand, the existence of chlorinated C2 compounds will reduce the selectivity of CO and CO2. Instead of oxidation reactions, couple reactions of CCl3 can produce chlorinated C2 compounds: CCl3 þ CCl3 ¼ C2 Cl6

ð27Þ

CCl3 þ CCl3 ¼ C2 Cl4 þ Cl2

ð28Þ

Although the results of the first model are not matched exactly with experimental results, it can still be concluded that Equations (17)–(19) have an important role in

Figure 6. Parity plot of products selectivity comparison between experimental and simulation results.

Downloaded By: [Indarto, Antonius] At: 18:28 2 May 2007

1122

A. Indarto et al.

Figure 7. Main routes of CO, CO2, and Cl2 production from CCl4 decomposition.

the production of CO and CO2 and Equations (24)–(25) likewise in Cl2 production. Calculation of the first model shows that Equations (17)–(19) and (24)–(25) can enhance more than 50% of the production of CO, CO2, and Cl2. The existence of COCl2, which is obtained using our QMS, shown in Figure 8(b), can be good evidence for this case. COCl2 is one of the most important intermediate species in Cl2 production (Equation (24)). Figure 7 shows the main routes of Cl2, CO, and CO2 formation from CCl4 decomposition by gliding arc plasma. QMS Spectra QMS spectra of CCl4 decomposition diluted in atmospheric arc by gliding arc plasma are shown in Figure 8. Figure 8(a) shows the compounds spectra of 1 vol% of CCl4 diluted in 180 L=h of atmospheric air. The main spectra of CCl4 are m=z 83=85 ðCCl2þ Þ and m=z 117 ðCCl3þ Þ. CO2 has its molecular ion at m=z 44 ðCOþ 2 Þ. CO molecular ion spectrum is colliding with minor N2 at m=z 29 ðCOþ =N2þ Þ. The main N2 is at m=z 28 ðN2þ Þ. However, due to the small concentration of CO in the atmospheric air, CO compound can be neglected in this spectrum line. The spectra of the products of CCl4 decomposition are shown in Figure 8(b). The peak intensity of m=z 83=85 is decreased as well as the intensity of m=z 117, and a new spectrum of Cl2 appeared at m=z 71 ðCl2þ Þ. Intensity of CO2 increases but the difference between before and after plasma condition is small. High magnification of spectrum intensity occurred at m=z 29 of N2 and CO. Because N2 is classified as a stable compound and there is no available source of nitrogen (N) in this system to produce N2, it must be that the increment intensity of m=z 29 is caused by production of CO. At high initial concentration of CCl4, the spectrogram of products produces a new spectrum at m=z 63 ðCClOþ Þ. Based on the QMS library, it can be suspected to be COCl or COCl2. There is good evidence

1123

Downloaded By: [Indarto, Antonius] At: 18:28 2 May 2007

CCl4 Decomposition by Gliding Arc

Figure 8. QMS spectra of CCl4 decomposition; (a) input stream, (b) products stream. Note: obtained at 1 vol% of CCl4 and total gas flow rate of 180 L=h.

that COCl and COCl2, which have a significant role, especially in the production of CO, CO2, and Cl2, existed in the reaction mechanisms. Another intermediate species that possibly exists is CCl2 at m=z 84 (CCl þ ).

Conclusion The decomposition of CCl4 in gliding arc plasma as well as the kinetic study was investigated. The maximum conversion of CCl4 was 80% at 1 vol% of CCl4 and total flow rate of 180 L=h. CO, CO2, and Cl2 were identified as the main products of the decomposition process. CCl3, COCl2, and COCl were the important intermediate species in CO, CO2, and Cl2 production. The existence of chlorinated C2 compounds has to be also counted as the source of Cl2 production in the final products. However, formation of chlorinated C2 compounds can reduce the selectivity of CO and CO2 due to coupling reactions of intermediate species, e.g., CCl3.

Downloaded By: [Indarto, Antonius] At: 18:28 2 May 2007

1124

A. Indarto et al.

Acknowledgments This study was supported by the National Research Laboratory Program of the Korea Ministry of Science and Technology.

References Butler, J. H. (2000). Better budgets for methyl halides?, Nature, 403, 260–261. Chang, W.-D. and Senkan, S. (1989). Detailed chemical kinetic modeling of fuel-rich trichloroethane=oxygen=argon flames, Environ. Sci. Technol., 23, 442–450. Chapra, S. C. and Canale, R. P. (1990). Numerical Methods for Engineers, 2nd ed., McGraw-Hill, Singapore. Cheremisinoff, N. P. (2000). Handbook of Hazardous Chemical Properties, ButterworthHeinemann, Boston. Davidson, T. J., Schiff, H. I., Brown, T. J., and Howard, C. J. (1978). Temperature dependence of the rate constants for reactions of O(1D) atoms with a number of halocarbons, J. Chem. Phys., 69, 4277–4279. Fanmoe, J., Kamgang, J. O., Moussa, D., and Brisset, J. L. (2003). Application de l’arc glissant d’air humide au traitement des solvants industriels: Cas du 1,1,1-trichloroe´thane, Phys. Chem. News, 14, 1–4. Fridman, A., Nester, S., Kennedy, L. A., Saveliev, A., and Mustaf-Yardimci, O. (1999). Gliding arc gas discharge, Prog. Energy Combust. Sci., 25, 211–231. Indarto, A., Choi, J. W., Lee, H., and Song, H. K. (2005a). Gliding arc processing for decomposition of chloroform, Toxicol. Environ. Chem., 87(1–4), 509–519. Indarto, A., Choi, J. W., Lee, H., Song, H. K. (2005b). Kinetic modeling of plasma methane conversion using gliding arc plasma, J. Natur. Gas Chem., 14, 13–21. Indarto, A., Choi, J. W., Lee, H., and Song, H. K. (2006a). Treatment of dichloromethane using gliding arc plasma, Int. J. Green. Energy, 3(3), 309–321. Indarto, A., Choi, J. W., Lee, H., and Song, H .K. (2006b). Discharge characteristics of a gliding-arc plasma in chlorinated methanes diluted in atmospheric air, Plasma Devices Oper., 14(1), 15–26. Indarto, A., Choi, J. W., Lee, H., and Song, H. K. (2006c). Conversion of CO2 by gliding arc plasma, Environ. Eng. Sci., 23(6), 1033–1043. Indarto, A., Choi, J. W., Lee, H., and Song, H. K. (2006d). Effect of additive gases on methane conversion using gliding arc discharge, Energy, 31, 2650–2659. Koch, M., Cohn, D. R., Patrick, R. M., Schuetze, M. P., Bromberg, L., Reilly, D., Hadidi, K., Thomas, P., and Falkos, P. (1995). Electron beam atmospheric pressure cold plasma decomposition of carbon tetrachloride and trichloroethylene, Environ. Sci. Technol., 29, 2946–2952. Kohno, H., Berezin, A. A., Chang, J. S., Tamura, M., Yamamoto, T., Shibuya, A., and Honda, S. (1998). Destruction of volatile organic compounds used in a semiconductor industry by a capillary tube discharge reactor, IEEE Trans. Ind. Appl., 34(5), 953–966. Lee, W. J., Chen, C. Y., Lin, W. C., Wang, Y. T., and Chin, C. J. (1996). Phosgene formation from the decomposition of 1,1-C2H2Cl2 contained gas in an RF plasma reactor, J. Hazard. Mater., 48, 51–67. Lou, J. C. and Chang, Y. S. (1997). Thermal oxidation of chloroform, Combust. Flame, 109, 188–197. Mak, F. T., Zele, S. R., Cooper, W. J., Kurucz, C. N., Waite, T. D., and Nickelsen, M. G. (1997). Kinetic modeling of carbon tetrachloride, chloroform and methylene chloride removal from aqueous solution using the electron beam process, Water Res., 31(2), 219–228. NASA Panel for Data Evaluation. (December 15, 1994). Chemical Kinetics and Photochemical Data for Use in Stratospheric Modeling, Evaluation Number 11.

Downloaded By: [Indarto, Antonius] At: 18:28 2 May 2007

CCl4 Decomposition by Gliding Arc

1125

Nichipor, H., Dashouk, E., Chmielewski, A. G., Zimek, Z., and Bulka, S. (2000). A theoretical study on decomposition of carbon tetrachloride, trichloroethylene and ethyl chloride in dry air under the influence of an electron beam, Radiat. Phys. Chem., 57, 519–525. Oda, T., Takahahshi T., and Yaaji, K. (2002). Nonthermal plasma processing for dilute VOCs decomposition, IEEE Trans. Ind. Appl., 38(3), 873–878. Penetrante, B. M., Hsiao, M. C., Bardsley J. N., Merritt, B. T., Vogtlin, G. E., Wallman, P. H., Kuthi, A., Burkhart, C. P., and Bayless, J. R. (1995). Electron beam and pulsed corona processing of carbon tetrachloride in atmospheric pressure gas streams, Phys. Lett. A, 209, 69–77. Sanhueza, E. (2001). Hydrochloric acid from chlorocarbons: A significant global source of background rain acidity, Tellus, 53B, 122–132. Skoog, D. A., West, D. M., Holler, F. J., and Crouch, S. R. (2000). Analytical Chemistry: An introduction, 7th ed., Saunders College Publishing, Ft. Worth, Tex. Taylor, P. H. and Dellinger, B. (1988). Thermal degradation characteristics of chloromethane mixtures, Environ. Sci. Technol., 22, 438–447. Tonkyn, R. G., Barlow, S. E., and Orlando, T. M. (1996). Destruction of carbon tetrachloride in a dielectric barrier=packed-bed corona reactor, J. Appl. Phys., 80(9), 4877–4886. U.S. Environmental Protection Agency (EPA), Office of Atmospheric Programs. (April 2002). Greenhouse Gases and Global Warming Potential Values, EPA 430-R-02-003, U.S. Environmental Protection Agency, Office of Atmospheric Programs, Washington, D.C. Walas, S. M. (1991). Modeling with Differential Equations in Chemical Engineering, Butterworth-Heinemann, Boston. World Meteorological Organization (WMO). (2002). Scientific Assessment of Ozone Depletion, 2002. Report no. 47. Yamamoto, T., Ramanathan, K., Lawness, P. A., Ensor, D. S., Newsome, J. R., Plaks, N., and Ramsey, G. H. (1992). Control of volatile organic compounds by an AC energized ferroelectric pellet reactor and a pulsed corona reactor, IEEE Trans. Ind. Appl., 28(3), 528–534.