Review Reports - Char from Pyrolysis of Waste Tires to Increase Bitumen Performances

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript entitled " Char from pyrolysis of waste tires to increase bitumen performances " is devoted to modify bitumens through addition of fine particles char coming from the pyrolysis of waste tires. The obtained results may open possibilities for using residue coming from the pyrolysis of a waste to increase the mechanical characteristics of a bitumen, fulfilling the recent circular- based needs for environmental protection. However, the discussion part needs more illustration, And The manuscript should be improved before being accepted for publications process. My comments and recommendations are below.

- The highlights needs to be provded.

- Keywords should be arranged in alphabetical order.

- Introduction is written in more general way. It should include the focus of the present topic. Hence, whole introduction must be written again emphasizing novelty.

- Line #98-99, Authors need to provide the sample (char) collection and preparation from the pyrolysed mixture.

- Scale bar in Fig 1 (CO₂-char and N₂-char) should be clearer for reader.

- Image and particle size distributions for N₂ + CO₂-char should e provided.

- Line #185-186, CO2-char particles are generally smaller than N2-char ones. But what leads to smaller particle size of CO2-char, please explaine.

- All figures shoud be presented in good quality.

- In most part of result and discussion section, authors only have introduced the results and I was not able to find any discussion about the results. I highly recommend the authors to compare their results with previous studies.

Author Response

Q.the highlights needs to be provided.

A. highlights have been provided in the revised version

Q. Keywords should be arranged in alphabetical order.

A. done

Q. Introduction is written in more general way. It should include the focus of the present topic. Hence, whole introduction must be written again emphasizing novelty.

A. The introduction has been revised, we removed too general and/or unnecessary parts and we added the following part to emphasize, as suggested by the reviewer, the novelty of the work.

“Although these parameters have been explored in the literature, to the best of our knowledge the effect of the gas flowing on the material under pyrolysis process has not yet deeply studied. This is a serious lack of knowledge, since the type of the flowing gas can affect the chemical reactions taking place at the material under pyrolysis, especially at the surface.”

Q. Line #98-99, Authors need to provide the sample (char) collection and preparation from the pyrolysed mixture.

A. We thank Reviewer for pointing this out. As reported in the manuscript, all samples (char) were obtained through pyrolysis/activation of waste tires under nitrogen and carbon dioxide constant flow rate. Different samples were obtained by changing synthesis parameters as reported in Table 1 in the main text. All of them were collected at the end of the procedure when the reactor reached room temperature In the light of the referee comment, we added these information in the revised version for clarity sake.

Q. Scale bar in Fig 1 (CO₂-char and N₂-char) should be clearer for reader.

A. We improved the scale bar for better readability.

Q. Image and particle size distributions for N₂+ CO₂-char should be provided.

A. The particle size distributions for N₂+ CO₂-char is in between that of the N₂–char and CO₂-char. So, for clarity sake we showed the two extremes and put them in the same plot (histograms) for immediate comparison. We added this information in the revised manuscript and we thank the referee for his suggestion.

Please note that further comparison with other methods for dispersing char particles has been carried out, obtaining the same result. This reinforced the clues we obtained (CO2-char particles are generally smaller than N2-char ones). Supporting information has been provided together with the revised manuscript.

Q. Line #185-186, CO2-char particles are generally smaller than N2-char ones. But what leads to smaller particle size of CO2-char, please explain.

A. We would like to Thank the Reviewer for this useful comment. As pointed out, the particles size for char obtained after CO₂ treatment look smaller than those subjected to N₂ environment do. The observed differences can be attributed to the oxidizing environment (CO₂) that is more aggressive and reactive in the synthesis phase compared to an inert environment (N₂). This information has been added in the revised manuscript

Q. All figures shoud be presented in good quality.

A. Figures related to N2 adsorption and PSD look already of good and adequate quality. In case just let us know and we will save them with higher quality.

Q. In most part of result and discussion section, authors only have introduced the results and I was not able to find any discussion about the results. I highly recommend the authors to compare their results with previous studies.

A. According to the referee’s comment, but also in response to the other referees’ suggestions, more comments have been added in the revised manuscript, see for example lines 414-420 in the last part of section 3, lines 330-338 of the same section, lines 243-248.

Reviewer 2 Report

Comments and Suggestions for Authors

I have reviewed the manuscript entitled “Char from Pyrolysis of Waste Tires to Increase 2 Bitumen Performances”. I recommend major revision and have the following comments:

1- Abs, please put numerical values and your important findings, in addition to the general statements.

2- English needs to be revised carefully. I detected mistakes.

3- Please avoid long sentences.

4- The introduction is written weakly. Please rewrite.

5- Please revise the structure of the manuscript. For instance, the introduction has a different font size. The last paragraph is only one sentence, and so on.

6- “The characteristics of the 87 bitumen have been determined in previous investigations” it is better to list them.

7- Did you come up with the pyrolysis conditions or they are based on others’ works?

8- Please clarify the Nl in Table 1.

9- “a lot of care was taken to ensure that temperature….” Please identify your procedure.

10- “These samples are labelled as “…RTFOT75”” What are these dots?

11- You need to put the article name and authors in the Supplementary file.

12- There are two Figure S2 in the supplementary file!!

13- "The N2-char size distribution is therefore shifted to slightly larger sizes compared to that of CO2-char" Please explain why.

14- What is the difference between Fig 1 and Fig S2? Why you put one in the manuscript and the other in the SI?

15- Again, The explanation of data has many typo and structural errors, please revise.

Comments on the Quality of English Language

Must be improved.

Author Response

Abs, please put numerical values and your important findings, in addition to the general statements.
According to the referee’s comment we added:

1) the numerical values (“increase in transition (gel to sol) temperature of up to 4 °C and an increase in rigidity under working conditions (50 °C) of up to about one order of magnitude”)

2) the important findings (More marked effects using char from pyrolysis under CO2; smaller char coming from pyrolysis under CO2 and with higher surface-to-volume ratio; interpretation)

English needs to be revised carefully. I detected mistakes.
We thank the Reviewer for his/her suggestion. According to this comment we carefully revised the entire manuscript.

Please avoid long sentences.
as for the previous comment, we carefully revised the entire manuscript.

The introduction is written weakly. Please rewrite.
As for the similar comment from referee #1, we revised the introduction removing too general and/or unnecessary parts and emphasizing the novelty of the work.

Please revise the structure of the manuscript. For instance, the introduction has a different font size. The last paragraph is only one sentence, and so on.
Division in paragraph has been revised, use of different fonts has been already corrected by the editorial team. We thank the referee for this observation

“The characteristics of the bitumen have been determined in previous investigations” it is better to list them.
Done. Crossover temperature, i.e. the temperature at which the bitumen passes from a glassy elastic solid (G’>G’’) to a viscoelastic liquid (G’<G’’), AND penetration grade has been briefly reported.

Did you come up with the pyrolysis conditions or they are based on others’ works?
These conditions were chosen after preliminary thermogravimetric tests and follows the general trend of pyrolysis of different raw materials (see for example Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2023, 672, 131727; International Journal of Hydrogen Energy, 2022, 47(42), pp. 18384–18395; Journal of Analytical and Applied Pyrolysis, 2020, 152, 104974; Energies, 2020, 13(9), 2237.). According to the referee’s comment, this information has been added to the revised manuscript (see experimental section).

Please clarify the Nl in Table 1.
We Thank the Reviewer for pointing this out. “Nl” in the table indicates the “Normal liter”. In response to the referee’s comment, this information has been reported in the table caption.

“a lot of care was taken to ensure that temperature….” Please identify your procedure.
The procedure has been described in details (lines 139-141 revised version). As for the thermal conditions, they are reported immediately after, at lines 142-143, which report the cooling rate (5°C min^-1) and the annealing time (15min). We realize that “a lot of” is unnecessary, so it has been removed from the revised version, thanking the reviewer for his/her observation.

“These samples are labelled as “…RTFOT75”” What are these dots?
labels were supposed to end with “RTFOT75” so the dots indicated the previous part of the label. However, we have realized that this labelling has not been used in the manuscript so, according to the reviewer’s comment and to avoid confusion this labelling has been removed from the manuscript. We thank the referee for his/her observation.

You need to put the article name and authors in the Supplementary file.
Done

There are two Figure S2 in the supplementary file!!
We Thank the Reviewer for his/her comment. Following it we modify the numbering of the figures in the supplementary materials.

"The N2-char size distribution is therefore shifted to slightly larger sizes compared to that of CO2-char"Please explain why.
Similar comment has been made by referee #1. As for that comment, our hypothesis lies on the higher oxidizing environment in CO₂ due to the presence of oxygen atom. This environment should be more aggressive and reactive in the synthesis phase compared to an inert environment (N₂) giving in general smaller particles. As for the reply to referee #1 comment, this hypothesis has been added in the revised manuscript

What is the difference between Fig 1 and Fig S2? Why you put one in the manuscript and the other in the SI?
The two figures reported in the main text and in the supplementary information are similar but not the same. In particular, Figure 1 it is related to char materials dispersed into silicon oil while Figure S2 refers to dispersion into water/AOT solutions. Proper discussion is present in the manuscript. Since S2 (and also S3) reinforces the clues shown by S1 we decided to use supporting information to keep only essential parts in the manuscript for better readability of for conciseness purposes

Again, The explanation of data has many typo and structural errors, please revise.
As for the similar comment from referee #2, we carefully revised the entire manuscript and typos/errors have been expunged.

Reviewer 3 Report

Comments and Suggestions for Authors

In the present study a 50/70 bitumen has been modified by addition of char obtained by the pyrolysis of waste tyres. The effect of the gas type flowing under pyrolysis process (CO2, N2 and CO2+N2) on the mechanical characteristics of the bitumen has been investigated. The current study is important in terms of improving the performance of modified bitumen and recycling waste tires. However, to further improve the quality of the manuscript and ensure readability, experimental parameters should be further improved. It is appropriate to publish it in Applied Science after considering the comments given below;

1. The authors have previously performed a study on improving the bitumen properties by char obtained from waste pyrolysis (https://doi.org/10.1016/j.colsurfa.2023.132199). Many of the methods applied in the current manuscript (e.g. bitumen preparation) are also available in previous work. The bitumen used is also the same. However, the authors did not mention or cite this study. This previously published study should be mentioned and compared with the present research.

2. The composition, physical and chemical properties (C, H, O, S percentages, humidity, volatiles, ash, etc.) of the waste tire used in char production should be specified. In particular, the chemical composition that may be harmful to the environment should be determined.

3. Char characterization is inadequate. TGA, FTIR and XRD should also be evaluated. The elemental composition of the char should also be given.

4. The effect of the modification with char on the physical properties of bitumen such as penetration, softening point and viscosity should be interpreted. The temperature sensitivity of char-modified bitumen should also be determined. Penetration index can be used for this purpose.

5. In 2. Experimental in line 88, the characteristics of the bitumen should be given briefly at this part by citing the related references.

6. In line 104, “………….. char was added in three varying proportions (1, 3, 6% wt/wt) to bitumen” Which of these do the characterization results belong to?

Comments for author File: Comments.pdf

Author Response

Q. The authors have previously performed a study on improving the bitumen properties by char obtained from waste pyrolysis (https://doi.org/10.1016/j.colsurfa.2023.132199). Many of the methods applied in the current manuscript (e.g. bitumen preparation) are also available in previous work. The bitumen used is also the same. However, the authors did not mention or cite this study. This previously published study should be mentioned and compared with the present research.

A. That article was a study to show the effect of waste chosen for pyrolysis on the bitumen performances. The current manuscript, explore the effect of flowing gas during pyrolysis. This said, that article was still under revision process when we submitted the current one. Now that it is published we can certainly cite that paper. We therefore thank the referee for this suggestion. Basic clues from that paper are reported at the end of the results and discussion section for comparative purposes suggesting future directions.

The following part has been added:

“It must be underlined that a recent study [46] highlighted that pyrolysis of materials rich in carbon, like waste tires, can give carbon-rich char which can be well accommodated within the bituminous matrix. In this regard, the clues of the present work well integrate that study, by suggesting the use of CO2 as the flowing gas to be used during pyrolysis for even more marked effects. The chemical explanation for this effect, i.e. the higher reactivity of CO2 with respect to N2, allows to suggest that other reactive gases could be explored for future experiments in the piloted design of char for bitumen modification.”

Q. The composition, physical and chemical properties (C, H, O, S percentages, humidity, volatiles, ash, etc.) of the waste tire used in char production should be specified. In particular, the chemical composition that may be harmful to the environment should be determined.

A. According to the referee’s comment we added, in the revised version, the results of proximate and ultimate analysis on waste tires. They have been reported in a new table (table 1 in revised manuscript) in the experimental section as well as some pertinent comments about their treatment for environmental attention.

Q. Char characterization is inadequate. TGA, FTIR and XRD should also be evaluated. The elemental composition of the char should also be given.

A. Apart from XRD, which cannot be carried out at the moment in our laboratories for technical problems, as requested by the reviewer we carried out Thermogramimetry (TGA) and FT-IR and SEM-Wavelength Dispersive Spectroscopy (WDS) for elemental analysis on selected areas. This widened a lot the characterization of the char. The results have been concisely described and commented (lines 243-271, with figures and reports reported in supporting information to avoid excessively long section, within the manuscript, dedicated to the char characterization.). The clues were found to be consistent with the other clues coming from the other techniques (carbonaceous materials, presence of sulphur, more reactive particles in CO2-char… ) so we thank the referee for his/her suggestion.

Q. The effect of the modification with char on the physical properties of bitumen such as penetration, softening point and viscosity should be interpreted. The temperature sensitivity of char-modified bitumen should also be determined. Penetration index can be used for this purpose.

A. The effect of modification with char on the physical properties of bitumen is well-known, as already written in the unrevised version of the manuscript. However, in the light of the reviewer’s comment, a brief explanation has been given in the revised version. The following part has been therefore added:

“This is basically due to interactions between the bituminous molecules and the particles surface. In this way, a network formed by alternate …bitumen-particle-bitumen-particle… is made with an overall effect to reinforce the overall structure. In this sense, and this is the scientific idea at the basis of the present work, organic-based particles like those of char can offer an organic-based surface for effective interactions with bituminous molecules. This chemical compatibility is expected to allow (i) better accommodation of the car-bon-based particles within the bituminous matrix and (ii) effective interactions with the molecules of bitumen and a more marked effect of the hosted char.”

The temperature sensitivity, intended as the resistance of bitumen upon temperature increase, is already reported considering T*. It is reported in Fig. 4A. Also, the change of T* and G’@50°C as a function of aging time is reported and discussed (see Fig. 5).

As for the penetration index, values have been reported in the revised version. This actually contributes to better show the modification of the physical properties of bitumen by char addition, so we sincerely thank the referee for his/her suggestion

Q. In 2. Experimental in line 88, the characteristics of the bitumen should be given briefly at this part by citing the related references.

A. characteristics have been briefly given in revised manuscript

Q. In line 104, “………….. char was added in three varying proportions (1, 3, 6% wt/wt) to bitumen” Which of these do the characterization results belong to?

A. Characterization was carried out for all of them. The results are in fact reported as a function of char added (see Fig. 4B and Fig.5) and comments are given about the dependence on the content

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript is organized well in all the aspects. However some minor issues are found as listed below.

The Char from Pyrolysis of Waste Tires is a nice approach and recognized across globe. Explain the novelty here.

During the process, is there any pollution issue? How can you resolve?

What is the effect of pressure on this?

What is the motivation of this work?

Conclusions need to be rewritten.

Comments on the Quality of English Language

minor

Author Response

Comment: The manuscript is organized well in all the aspects. However some minor issues are found as listed below.

Reply: we thank the referee for his/her comment

Comment: The Char from Pyrolysis of Waste Tires is a nice approach and recognized across globe. Explain the novelty here.

Reply: similar comment has been made by referee #1. The novelty of the work has been better emphasized in the introduction section.

Comment: During the process, is there any pollution issue? How can you resolve?

Reply: Although environmental aspects of the process are already present in the unrevised manuscript (see for example: Pyrolysis is a fundamental act in the reduction of urban waste at lines 50-51), in the light of the referee’s comment other comments have been added: “It must be also noted that the absence of oxygen prevents combustion and therefore CO2 emission.” At lines 54-55.

Overall, these aspects have been emphasized by adding the following sentence at the end of the introduction: “Apart from the comparison of all the data, which will give important information for future char production and its application, [15] the environmental benefit of this work needs to be emphasized….”

So, environmentally speaking, pyrolysis reduces pollution. The only problematics to pay attention to is the treatment of the waste tires, which are wastes with CER 16 01 03, so they need to be treated according to the specific legislation. This aspect has been added in the revised manuscript at lines 88-89.

Comment: What is the effect of pressure on this?

Reply: pressure in pyrolysis is generally the ambient pressure: due to the high temperature and the high number of chemical reactions occurring during pyrolysis hermetically closed reactors would not be safe. In any case pressure control would require more expensive and complex apparata. Consequently, pressure effects have not been object of our study.

Comment: What is the motivation of this work?

Reply: the motivation of the work has been better pointed out in the introduction section at lines 64-68 by adding the following part “Although these parameters have been explored in the literature, to the best of our knowledge the effect of the gas flowing on the material under pyrolysis process has not yet deeply studied. This is a serious lack of knowledge, since the type of the flowing gas can affect the chemical reactions taking place at the material under pyrolysis, especially at the surface.”

Comment: Conclusions need to be rewritten.

Reply: Conclusions have been rewritten

WE THANK THE REFEREE FOR HIS/HER PRECIOUS COMMENTS

Reviewer 5 Report

Comments and Suggestions for Authors

The article examines a quite special segment, which clearly fits the magazine's profile. Since the research hypothesis/goal is not formulated precisely and clearly, it is difficult to measure whether the set goal has been achieved. The residue from the pyrolysis of tires has been used to improve the properties of bitumen used in road construction, and this material is referred to as a green additive. I'm not sure does pyrolysis deserve the label "green" in any way, i.e. energy consumption, gases produced, etc.

The conclusion is a real conclusion, it succinctly summarizes the results achieved, but I miss the explanation of the practical significance of the results for readers less experienced in the field. Why is it beneficial to increase or not significantly decrease certain values?

In Table 1, such data and why were highlighted in green?

Author Response

Comment: The article examines a quite special segment, which clearly fits the magazine's profile. Since the research hypothesis/goal is not formulated precisely and clearly, it is difficult to measure whether the set goal has been achieved. The residue from the pyrolysis of tires has been used to improve the properties of bitumen used in road construction, and this material is referred to as a green additive. I'm not sure does pyrolysis deserve the label "green" in any way, i.e. energy consumption, gases produced, etc.

Reply: Actually, this criticism has been made by the other referee: we have realized that the motivation, the hypothesis beyond it, the novelty, and the goal were not formulated successfully. These aspects, in response also to the criticisms raised by the other referees, have been clarified in the revised version, see as just mere examples lines 64-68, 73-75, 416-422.

Also, the environmental benefits in using pyrolysis have been made clearer, see for example 54-55 and again 73-75.

All the added comments have been also added, as clues in the rewritten conclusion section.

In this context, and this is the philosophy our study, we used a residue (char) coming from a process reducing urban wastes (pyrolysis) to improve bitumens prolonging their life-time and reducing the related maintenance, with further benefits towards environment. For this reason, and to reinforce our scientific take-home message, we considered the use of the term “green”. However, if the referee believes it is not the case, we can remove the word “green” from the manuscript in a further revision or, we hope, in the proof correction stage.

Comment: The conclusion is a real conclusion, it succinctly summarizes the results achieved, but I miss the explanation of the practical significance of the results for readers less experienced in the field. Why is it beneficial to increase or not significantly decrease certain values?

Reply: the conclusion section has been rewritten, also in response to the comment to reviewer #4. In the light of the referee’s criticism, the following specific comments have been added:

(line 439-440): “This means that the modified bitumen has a stronger resistance against temperature, which may be advantageous for uses in certain (hot) conditions.” It explains why the obtained values are an advantage.
(lines 445-446) “The anti aging effect of the char is important because it prolongs the life-time of a bitumen and reduces maintenance costs “. It explains why the anti-aging effect is important.

Comment: In Table 1, such data and why were highlighted in green?

Reply: because we wanted to evidence the finale step, involving static temperature condition. In the light of the referee comment, the use of green text in table 1 has been explained in the table caption.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for your revised version. Most of my concerned issues are addressed. It can be accepted now.

Author Response

We thank the referee for his/her kind attention to our work.

Reviewer 2 Report

Comments and Suggestions for Authors

1- As I mentioned earlier, please put numerical values in the abs. such as the section you mentioned the surface area difference under CO2 and N2, please mention them. Also, please show your numerical key findings.

2- In the introduction, the last paragraph of in the present work, please put it separately.

3- In the introduction, please mention some other similar studies’ findings.

4- The last paragraph in the introduction should be mostly about your work, you can’t put general sentences from other references in the last part.

5- I still see language problems, please revise it with the aid of a professional of native speaker editor.

6- Line 145, annealing time is 15 min, do you mean after reaching 900 C, you left the sample to pyrolyze for only 15 min? isn’t it a short time? Please clarify.

Comments on the Quality of English Language

should be revised

Author Response

COMMENT 1: As I mentioned earlier, please put numerical values in the abs. such as the section you mentioned the surface area difference under CO2 and N2, please mention them. Also, please show your numerical key findings.

REPLY: As suggested by the referee in the abstract we added also the BET specific surface values and the micropore volume fractions (V_MIC/V_T ratios) of the two chars. We also added the numerical values of the transition temperature increases for the char-containing bitumens. Also, short comments have been added in the discussion section.

COMMENT 2: In the introduction, the last paragraph of in the present work, please put it separately.

REPLY: Also in accordance to the referee’s comments #3 and 4, as suggested by the referee, findings from similar studies were mentioned, the last paragraph of introduction has been put separately and is mostly about our work. Actually the second-half part of the introduction has been rewritten

COMMENT 3: In the introduction, please mention some other similar studies’ findings.

REPLY: lso in accordance to the referee’s comments #2 and 4, as suggested by the referee, findings from similar studies were mentioned, the last paragraph of introduction has been put separately and is mostly about our work. Actually the second-half part of the introduction has been rewritten

COMMENT 4: The last paragraph in the introduction should be mostly about your work, you can’t put general sentences from other references in the last part.

REPLY: Also in accordance to the referee’s comments #2 and 3, as suggested by the referee, findings from similar studies were mentioned, the last paragraph of introduction has been put separately and is mostly about our work. Actually the second-half part of the introduction has been rewritten

COMMENT 5: I still see language problems, please revise it with the aid of a professional of native speaker editor.

REPLY: We checked the text for language problems expunging typos and errors. A mother tongue author (Dr. A. Abe) also did his best in this. Also, some sentences have been rephrased for better readability. We need to point out that we cannot affort the MDPI language correction service, due to its cost. We hope that our checks will be enough.

COMMENT 6: Line 145, annealing time is 15 min, do you mean after reaching 900 C, you left the sample to pyrolyze for only 15 min? isn’t it a short time? Please clarify.

REPLY: We apologize for not being clear in this. The annealing time is the time required for the bitumen to return to room temperature after being mixed with char at 150 °C. The text if fact begins with:

“After miìxing…” ( mind: at 150 °C) “…the modified bitumen was poured …” “…a temperature of 25 °C”

So, in the light of the referee’s comment we have made clearer this aspect by rephrasing this part

The revised part is therefore: “After mixing the bitumen with char at the aforementioned temperature of 150 ± 10 °C, the modified bitumen was poured into a sealed can, stored in a dark chamber at allowed to cool down to temperature of 25 °C. Due to the sensitivity of the samples to the annealing time [24], i.e. the time required for cooling down to room temperature, care was taken to ensure that the temperature cooling rate (5°C min^-1) and annealing time (25 min) of all the investigated samples were the same.”

Incidentally, we recognized that a typo was present: the time was not 15 min but 25 min. We corrected the text and we thank the referee for his attention to this aspect.

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors