Destruction of Toluene, Naphthalene and Phenanthrene as Model Tar Compounds in a Modified Rotating Gliding Arc Discharge Reactor
, Xiaodong Li 1,*, Ruiyang Xu 1, Ishrat Mubeen 2, Li Li 1 and Jianhua Yan 1Round 1
Reviewer 1 Report
Well written paper.
Author Response
Thank the reviewer very much for the review of our manuscript
Reviewer 2 Report
Report on article: Destruction of toluene, naphthalene and phenanthrene as model tar compounds in a modified rotating gliding arc discharge reactor
This article describes the decomposition of aromatic compounds (toluene, naphthalene, and phenathrene) by gliding arc discharge (GAD) The article is interesting, especially concerning the application of description of Ni/γ- Al2O3 catalyst. Additionally, this paper seems to be interested of readers for this journal. However, the article contains some inconsistencies.
Detailed Comments:
1. Introduction, the other reference concerning the decomposition of benzene as a model tar compound by microwave plasma (M.Wnukowski, P. Jamroz, Fuel Processing Technology 173 (2018) 229-242) should be cited
2. Was the moisture content in nitrogen (12%) optimized? The 8% moisture content seems to be better. Please comment.
3. Line 234. Should be kV instead V
4. The English should be improved
Author Response
Dear Editors and Reviewers,
We would like to pay our sincere regards to the reviewer’s careful comments on our manuscript entitled “Destruction of toluene, naphthalene and phenanthrene as model tar compounds in a modified rotating gliding arc discharge reactor”. These comments are very helpful for revising and improving our manuscript, as well as a significant guide to our researches. We have considered all the comments carefully and made corrections which are indicated in the text with yellow highlight in the revised manuscript. The responses to reviewers’ comments are as follows
Comment 1) Introduction, the other reference concerning the decomposition of benzene as a model tar compound by microwave plasma (M.Wnukowski, P. Jamroz, Fuel Processing Technology 173 (2018) 229-242) should be cited.
Reply: Thank you for your suggestion. The reference has been cited in the revised manuscript (reference 2).
Comment 2) Was the moisture content in nitrogen (12%) optimized? The 8% moisture content seems to be better. Please comment.
Reply: Indeed 8% moisture content is a better choice, as indicated by the results. But a moisture content of 12% is typical condition in a practical gasifier, so we choose the situation of 12% moisture to mimic more realistic condition. In addition, a moisture content of 12% also showed a relatively good performance, as shown in Fig. 5.
Comment 3) Line 234. Should be kV instead V
Reply: Sorry for the mistake. It has been corrected (Line 171)
Comment 4) The English should be improved
Reply: Thank you for the suggestion. The English of the revised manuscript has been checked and improved by a native English speaker.
Author Response File: 
Author Response.pdf
Reviewer 3 Report
The paper is interesting and very well written.
Just few amendments are request and in the following listed:
a) add some lines of text to explain how you made sampling, conditioning and analyses of gas and liquids.
b) rewrite the sentence in rows 172-173 because it is not clear what you consider "weaken the stability"
c) refer to water-gas shift and reforming reactions to explain the behavior of CO2, CO, C2H2 and hydrocarbons in general (e.g. rows 186-191)
d) it should be interesting to known if the partial cracking of PAHs (phenanthrene) leads to an increase of BTX and how the residence tie affect the composition of off gas other than the destruction efficiency.
e) the threshold values obtained for CO2 etc., are dependent by lab-scale size of the apparatus?
f) please pay attention to sense 243-244: ... because of oxidation of the CO2" is not correct. CO2 reforming and shift reactions should be considered in the results evaluation.
g) x-axis (249) is CO2
h) is carbon deposit present on the catalyst after the test? (row 299-301)
i) during liquid sampling the composition can vary due to cyclization and aromatic condensation. Be aware about the possible unreliability of liquid composition.
j) is the effect of catalyst at high flow rate linked to the scale effect of the apparatus used for the test?
Author Response
Dear Editors and Reviewers,
We would like to pay our sincere regards to the reviewer’s careful comments on our manuscript entitled “Destruction of toluene, naphthalene and phenanthrene as model tar compounds in a modified rotating gliding arc discharge reactor”. These comments are very helpful for revising and improving our manuscript, as well as a significant guide to our researches. We have considered all the comments carefully and made corrections which are indicated in the text with yellow highlight in the revised manuscript. The responses to reviewers’ comments are as follows.
Comment a): Add some lines of text to explain how you made sampling, conditioning and analyses of gas and liquids.
Reply: Thanks to the reviewer for this suggestion. Based on this comment, we made the following additions in the revised manuscript.
(Line 320-325) Each experiment operated 10 minutes for stabilization before the remaining tar was collected. A three-way valve was used to control flow of the exhaust gas into the absorption bottles. After 10 minutes’ collection, the liquid in all three absorption bottles was collected and diluted with n-hexane to a final volume of 100 ml. The gas products were collected by using sampling bags after the absorption bottles.
(Line 328) The column temperature of the GC was set as 80°C.
Comment b): Rewrite the sentence in rows 172-173 because it is not clear what you consider "weaken the stability"
Reply: Sorry about the confusing words which explain the reason why the destruction efficiency drops down sharply with the increase of tar concentration. We changed the sentence:
(Line 106-108) This is because, as the experiment shows, phenanthrene addition tendsto cause frequent breaking of the gliding arc, especially when both tar and moisture concentrations are high. Although the arc can be regenerated, the breaking decreases the destruction efficiency.
Comment c): Refer to water-gas shift and reforming reactions to explain the behavior of CO2, CO, C2H2 and hydrocarbons in general (e.g. rows 186-191)
Reply: Thank you very much for this suggestion. As proposed by the reviewer, water gas shift and reforming reactions are very likely related to the behavior of the major gas production (CO2, CO, C2H2, H2). Therefore, we revised the following sentences in the revised manuscript.
(Line 122-128) The reason can be explained by water-gas shift reaction (equation 1) and reforming reaction of C2H2 (equation 2). The increase of tar concentration leads to the increase of CO and C2H2. The increase of CO and C2H2 promote the positive reaction of water-gas shift and reforming reaction respectively, which increases the production of all the gas products. Although, the concentration of H2O is constant, but this limits the conversion rate of CO and C2H2 in the case of high tar concentration, leading to a high selectivity of CO and C2H2 while lowering the selectivity of CO2
(equation 1,2)
CO+H2O→CO2+H2 | (1) |
C2H2+2H2O→2CO+3H2 | (2) |
Comment d): It should be interesting to known if the partial cracking of PAHs (phenanthrene) leads to an increase of BTX and how the residence tie affect the composition of off gas other than the destruction efficiency.
Reply: Thank you for the suggestion. As proposed by the reviewer, partial cracking of phenanthrene can probably also lead to the formation of BTX. Our previous study of single naphthalene destruction has indicated that the destruction of naphthalene can produce phenylethyne. But the amount of is very small (less than 0.1% of input naphthalene). Further study of single phenanthrene destruction process will be conducted to confirm this hypothesis.
Based on this comment, we added the following discussion points in the revised manuscript.
(Line 280-282) Previous study indicates that the destruction of naphthalene in this reactor can produce phenylethyne. Therefore, it is expected that the partial cracking of phenanthrene can also lead to the formation of bicyclic or even monocyclic products.
As to the effect of residence time, our previous study has indicated that the residence time (total flow rate) can largely affect the composition of off gas, but is negligible when it comes to the selectivity of gas products.
Comment e): The threshold values obtained for CO2 etc., are dependent by lab-scale size of the apparatus?
Reply: Thank you for this valuable comment. According to our opinion, the size of the apparatus will definitely influence the performance of this process, but the effect of different factors on the reaction should be quite similar. We will study the effect of the size of the apparatus in our future work.
Comment f): Please pay attention to sense 243-244: ... because of oxidation of the CO2" is not correct. CO2 reforming and shift reactions should be considered in the results evaluation.
Reply: Sorry to mislead you. What we want to express in this sentence is that CO2 can oxidize C2H2 or H2. According to your suggestion, we have rewritten the sentence and explain the behavior of gas products using CO2 reforming.
(line 180-182) When the concentration of CO2 increases, the amount of CO in the product increases and the amount of H2 and C2H2 decreases because of the reverse reaction of water-gas shift (equation 1) and the dry reforming reaction of C2H2 (equation 3).
(equation 3)
C2H2+2CO2→4CO+2H2 | (3) |
Comment g): X-axis (249) is CO2
Reply: Sorry about that. The figure has been corrected.
Comment h): Is carbon deposit present on the catalyst after the test? (row 299-301)
Reply: After an operation of 1.5 hours, the carbon deposition was observed on the catalyst, but only a small production. No decrease in catalyst activity was observed after the 1.5 hours’ operation in our study. We made the following revisions in the revised manuscript.
(line 238-240) It should be noted that, a slight carbon deposition was observed on the catalyst after an operation of 1.5 hours, which should be considered in the application of plasma catalysis.
Comment i): During liquid sampling the composition can vary due to cyclization and aromatic condensation. Be aware about the possible unreliability of liquid composition.
Reply: Thank you for your comment. This is an important point which should be concerned about. In this study, repeated experiments have been conducted and the liquid composition showed similar results. In addition, the liquid products were analyzed immediately after the sampling, which ensured the liquid composition results are much reliable.
Comment j): Is the effect of catalyst at high flow rate linked to the scale effect of the apparatus used for the test?
Reply: Thanks for this great comment. As proposed by the reviewer, the effect of catalyst at different flow rates is probably related to the scale effect of the apparatus in this study. However, it is expected that a high flow rate will also show a better performance when the catalyst is combined with plasma. We will investigate the effect of the size of the apparatus on the plasma catalysis performance in our further study.
Author Response File: Author Response.pdf
