Catalytic Pyrolysis of Waste Plastics over Industrial Organic Solid-Waste-Derived Activated Carbon: Impacts of Activation Agents

Round 1

Reviewer 1 Report

This manuscript describes the pyrolysis of some fossil plastics employing carbonized industrial waste, activated through different methodologies. The topic is interesting and adequate for the journal, but the manuscript lacks some very important details that are necessary for the experiments to be reproducible. I cannot recommend the paper for publication unless these are added. Please find a detailed list of points to address below.

1) Although the English of the manuscript is largely understandable, there are some errors and a revision is recommended.

2) The Introduction contains many statements that are not supported by cited references, especially in the first paragraph.

3) The Introduction should be revised to present facts in a more logic way (at first the introduction of the scenario, then the state of the art, then the knowledge gaps and finally the aim of the work) and presenting the situation in a general sense, rather than citing the results of few specific articles.

4) It is not true that there is "limited published work" on "valorizing organic waste into valuable chemicals", there actually is a wealth of existing articles.

5) The information on the employed feedstock is insufficient. It should be described in detail in terms of products that comprise it and characterised (proximate and ultimate analysis). The same applies for the employed plastics: are they pure? Where were they obtained from?

6) The manuscript should include the mass yields of the obtained activated materials with reference to the starting waste.

7) Section 2.3: A picture may describe the setup/operating procedure in a clearer way.

8) Section 3.1: If a material has a surface area of 6.68 m2/g, it cannot be called "activated carbon": a requirement for ACs is a surface area of at least 500 m2/g.

9) Page 5: There are two "Section 3.1".

10) Fig. 2: It would be valuable to also include the TG behaviour of the activated materials alone.

11) Table 2: This may be clearer as a figure.

12) Section 3.3: If some results are important to understand the achievements of the manuscript and are commented in it, they cannot be put in the supporting information (Fig. S2 and S3).

13) There is an extensive discussion on the pyrolysis reaction mechanisms. Are these innovative or similar to other schemes provided in the literature for these plastics? Do the employed activated catalysts significantly alter the reaction pathway? This should be addressed in the text.

14) Scheme 1a's quality should be enhanced.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript contains a significant and valuable scientific information on the catalytic pyrolysis of waste plastics with use of activated carbons as catalysts. The influence of activation method (physical and/or chemical) of these carboneous materials on the catalytic pyrolysis performance (in fact only on the product yield and composition) was investigated and discussed.  

The carried out experiments are described clearly with significant details. The adequate and contemporary experimental methods and devices– such as thermogravimetry, BET, FTIR, Raman spectroscopy and GC - were employed. The obtained results were discussed in terms of product yields and composition depending on the used catalyst. Also the reaction mechanism – i.e. possible reaction pathways - were indicated.

Despite of my very high evaluation of the manuscript content I have serious doubts if it can be published in the Processes journal. However, it for sure is worth publication but in a journal of different scope. From my point of view, manuscripts published in Processes should give more detailed information on the process performance.

In this case, the manuscript should contain some indications on the process kinetics, which should make possible an estimation of the catalytic pyrolysis rate and it dependence on operating conditions as well as on kind and amount of the catalyst.  

However, of course, I leave a decision to the Editor.  Therefore I marked "Consider after major revisions" recommendation.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have provided replies to my comments and accordingly enhanced the quality of the manuscript. I only have a few minor observations. If these are implemented, the paper can be published.

1) At the beginning of page 3, there seems to be a part that was pasted from the template and not deleted.

2) The authors explained in their replies to me that the employed plastics are pure. However, this should also be stated in the manuscript (possibly together with an indication of where they were purchased from).

3) Line 344 should be changed to "should not be considered activated carbon".

Author Response

1) At the beginning of page 3, there seems to be a part that was pasted from the template and not deleted.

Reply: Thanks for comments. We have corrected this mistake.

2) The authors explained in their replies to me that the employed plastics are pure. However, this should also be stated in the manuscript (possibly together with an indication of where they were purchased from).

Reply: Thanks for comments. We have added the plastic source in the manuscript.

3) Line 344 should be changed to "should not be considered activated carbon."

Reply: Thanks for comments. We have changed "should not be considered carbon" to "should not be considered activated carbon."

Reviewer 2 Report

I highly estimated the work presented in the manuscript. However, in my opinion it is rather a report on the performed studies (carried out on a high scientific level) than an article for publication in the Processes journal.  My main critical comment is that the presented conclusions are only qualitative, not quantitative – no any equation is given. It's a pity because from the TGA results a lot of useful quantitative information can be extracted. The authors did not do it.

However due to mentioned important (qualitative) information I recommend this manuscript for publication.

Author Response

Reply: Thanks for comments. In the article, we have supplemented the activated energy obtained from plastic pyrolysis reaction kinetic calculations.