Response 1

CCl4 decomposition by gliding arc plasma: role of C2 compounds on products distribution Manuscript id: 130-06 Author response of the 1st reviewer General questions: Question: The author use a discharge in air (dry air or wet air is not specified). They then consider that the main active species responsible for the oxidation of chlorine from Cl(-I) to zero or higher oxidation state is the oxygen radical O°, which is reasonable due to the high oxidizing character of the species. Surprisingly no occurrence of any nitrogen compound is considered, although N+ forms at the minimum electrode gap and molecular species N2+ and N2* in the plasma plume additionally to NO. The formation of nitrogen oxohalides such as NOCl or others might then be expected. This point must be seriously examined. Answer: Thank you very much. In this experiment we used dry air (water or liquid-free). We put this information in the revised manuscript. Regarding the question on the role of nitrogen (N) in the plasma process, we did not neglect the existence of this species because we used air as the dilution gas which is contained around 80% of nitrogen, the most dominant molecule in this experiment. N2 has lower excitation energy compared to other molecules for example oxygen (O). Surprisingly, the concentration of nitrogen before and after plasma reaction, measured by our quadruple mass spectrometer (QMS), was not changed so much. It means that the nitrogen was inert in this experiment or it has a role similar like catalyst. The analysis behavior of N2 has been studied previously in our laboratory (Savinov, S.Y., et al. 2003. The effect of vibrational of molecules of plasmachemical reaction involving methane and nitrogen. Plasma Chem. Plasma Process. 23 (1), 159-173). Although the plasma type was different but the characteristic of nitrogen would be similar as in gliding arc. The lower excitation energy of nitrogen gives the higher probability of nitrogen to react in the reactions. However, based on our finding and that paper, the role of N 2 looks like only as a destruction agent (in this case we agree with the reviewer opinion) but it will not product any nitrogen compounds. Small amount of N2O was detected in our QMS. We put this explanation in the revised manuscript.

Question: The hypothetical formation of ozone is not considered at all, although it might also be a suitable oxidizing agent.

Answer: Thank you. Regarding the possibility of ozone (O3) as the active oxidizing agent, we already did some experiments using gliding arc before. Previously, we have a similar opinion with the reviewer that O3 can be very useful and active species for the decomposition reaction. However, our previous experiments show the phenomena of O3 production from O2 was not occurred (QMS products spectrum of plasma process of pure oxygen injection). We have also published 2 papers on the effects of O2 on the plasma reaction with methane (Indarto et al., Effect of additive gases on methane conversion using gliding arc discharge, Energy, 31: 2650) and CO2 (Indarto, et al., Conversion of CO2 by Gliding Arc Plasma, Environ Engineering Science, accepted) as the object material. Ozone was easily produced using non-thermal plasmas, for example dielectric barrier discharge (DBD). Using gliding arc which is classified as transition plasma (cold-arc plasma), the production of ozone was not significant. In order to make it clear, we put this additional information in our revised manuscript. Thank you for the author question on this matter.

Question: The oxidizing power of O° is known (E°[Ogas/OH-] = 1.6 V/NHE and E°[Ogas/ H2O] = 2.42 V/NHE) but these potential values are reported in aqueous medium only. Particular information in CCl4 medium are welcome, since changing from the potential scale in water to the potential scale in any other medium requires some extra-thermodynamic assumption that must be explicated. Answer: Thank you very much. We collected the kinetic data of the oxidation process from the references which have the same or similar environmental system. As written in the introduction section, the kinetics was obtained from non-thermal plasmas (microwave) and combustion process. And the value of the kinetic constants of each reaction can be assumed same in the case of gliding arc.

Question: The considered reactions involve only neutral species, i.e., molecules, atoms and neutral radicals, and no charged species (except eqn (3)), although anions and radical anions are probably also formed in the discharge. Have the authors specific arguments in favor of disregarding these charged species and the relevant reactions in the proposed mechanisms? Answer: Thank you very much. We really appreciate with the question. Yes, it is correct that in the plasma, the excited species of molecules or atoms can form charged species or radical. In this case, we constructed a general type of kinetics model which combine all of charged and ion

form in single neutral molecules or atoms. There are two reasons why we chose this type of simulation: 1. First, following the goal of this study, we want to study the importance of C 2 compounds which were neglected on the production of Cl2, CO, and CO2 in the previous papers. So, we do not really concern on the specific form of atoms and molecules and actually, we want to create a simple system (without neglecting the scientific meaning) and simply shows to the readers about our finding clearly and understandable. 2. Second, we do not want to construct very detail model, for example including charged ion form of species, in which we can not prove the existence of those particles, because we think it will be meaningless. Those are the reason, why we chose rather general form of species (neutral particle), which actually also represents the average activity of particle in different forms, to prove that C2 has to be counted also in the formation of Cl2, CO and CO2.

Additional questions:

Question: P3 Using C1 and C2 symbols may be confusing in the present case where chlorine in involved. I suggest changing C1 into (and similarly C2 into ) for organic compounds, which let Cl unambiguously refer to chlorine. Answer: thank you very much for suggesting the symbol to avoid the ambiguous between C1 and Cl. For this case, in the revised manuscript, we changed the symbol of C1 chlorinated compounds from C1 into C1 (C <subscribe>1) and kept chlorine as Cl. This was applied also for C2 compounds which is changed from C2 into C2 (C <subscribe> 2). We hope this new writing symbol will not give any ambiguous. Question: P3;L28. The authors state that a gliding discharge "can achieve higher flame temperature and power…. ". What reference temperature do the authors consider? A development of this assertion is welcome: the macroscopic temperature strongly depends on the position where it is measured (and on the working conditions). For example measurements performed at long distance show no thermal effect although the discharge remains efficient for bacteria inactivation and for the usual (D. Moussa et al., Europ. Phys J.- AP (2005) 189) chemical effects.

Answer: Thank you for the question related the temperature of gliding plasma. The temperature of gliding plasma is higher than non-thermal plasma. In the non-thermal plasmas, the gas temperature was only room temperature. However, in gliding plasma, the temperature is hotter. Higher temperature will give some advantages, for example: increasing decomposition rate and reaction rate. We took this information from two papers. First is written by Fridman et al. (Fridman, A., et al. (1999). “Gliding arc gas discharge.” Prog. Energy Combust. Sci., 25, 211231) and second by Question: P5; LL25,27. Although the meaning of the acronyms are known (i.e., FID or TCD), they must be explicated for their first use in a text. Answer: thank you very much. We corrected it in the revised manuscript. Question: P8. The chemical reactions (1) to (5) (Page 4) are considered as complete reactions (a single arrow, i.e., ? , is more explicit). The symbol is modified later, i.e., = , for eqns (15-21 and 24-28). Do this means that equilibriums are involved in the latter case and in Table 1 ? Answer: Thank you very much for the correction. All of the reactions written in the manuscript are in the equilibrium form. Question: P9; L9. Should we read : "…when O2 existed" or, better, "…in the presence of O2" ? P9; L14. The difference between O atom and O° is puzzling for me since both species have 6 electrons on the L level: 2s22p4. It might be clearer to identify the species as O(3P) and O(1D). It should enlighten eqs (22) and (23) are not clearly illustrative of the above sentence. P9; L 25 Should we read: "….to collide with " ? P10; L16. Examples of formed chlorinated compounds are C2H4 also, and illustrated in Fig4a. Fig 4 involves no hydrogenated compound; only C2Cl4, C2Cl5 and C2Cl5 are present and can be considered as species (Fig 4b). P12; L21 Read " CO2" Answer: Thank you very much. We corrected it in the revised manuscript with also other improvements especially in English sentences. Question: P.13 The literature is scanty on using gliding arc discharges. The following references might be added: T. Opalinska et al. on CFC decomposition by gliding arc in ISPC-16 Proc. (Taormina, It, 2003) J. Fanmoe et al. on the treatment of 111-trichloroethane (Phys Chem. News, 2003 14, 1) Also :

K.A. Fogkein et al. on the products of CCl2XY decomposition in thermal plasma [ISPC-17th Proc. Toronto, Can.2005] and eventually: F.T. Mak et al. (Wat Res. 1997, 31 ,219) on the e-beam degradation modeling of CCl4 Answer: Thank you for the literature suggestion from the reviewer. We take the last reference as the additional reference because it is close to our experiment.