Review of Carbon Capture and Methane Production from Carbon Dioxide
Ismail Alkhatib
Round 1
Reviewer 1 Report
The authors provided a comprehensive overview of different CO2 separation and capture technologies. I think this manuscript can be published in Sustainability with suitable revisions.
1. Currently, few cited papers are published in the last five years, which can not reveal the recent research progress on the topic of CO2 conversion. Please include important works in the revised manuscript.
2. Both CO2 and CH4 are greenhouse gas. Is the methanation of CO2 the preferable solution to lower preferable concentration.
Author Response
Response to Reviewer 1 Comments
Point 1: The authors provided a comprehensive overview of different CO2 separation and capture technologies. I think this manuscript can be published in Sustainability with suitable revisions.
Currently, few cited papers are published in the last five years, which can not reveal the recent research progress on the topic of CO2 conversion. Please include important works in the revised manuscript.
Response 1: This has been addressed. Please refer to page 22, section 7
Point 2: Both CO2 and CH4 are greenhouse gas. Is the methanation of CO2 the preferable solution to lower preferable concentration?
Response 2: Today, there is a great deal of interest in the methanation of CO2 because it provides a method for recycling carbon by converting significant amounts of CO2, as shown in the equation. Hydrogen and carbon oxide combine to form methane and water using a nickel catalyst. The fact that methane is a cleaner fuel than coal and oil is increasing interest in this type of chemistry while increasing the use of methane in transportation. To reduce the ideal concentration, methanation of CO2 becomes the preferred solution. Therefore, the most practical and accessible method of storing significant volumes of intermittent energy generated from renewable sources for extended periods is the generation of synthetic natural gas or liquid fuels.
This has also been indicated in the manuscript. Please refer to section 9.2.1, page 29, lines 853 - 859
Author Response File: 
Author Response.docx
Reviewer 2 Report
The authors propose an overview/review of carbon capture technologies, besides some final perspectives on CO2 conversion into methane. Although the topic is interesting and truly worthy of investigation, there are many points both in the structure and in the contents that are not clear. Among others:
· As a general remark, I find the paper structure more similar to a book chapter than to a research paper. A thorough review has to comprise all the research papers on the investigated topics in the chosen years (2000-2022), which in this case are much more than the 187 references the authors included in the review. In this regard, I suggest a more appropriate choice of the keywords (i.e.: CO2 capture, amine scrubbing, chemical looping etc, rather than very specific chemical compound names such as zeolites, that are indeed used for many applications other than carbon capture).
· Process description for the technologies are not clear or described thoroughly. The plant components and their operating conditions (together with the required catalysts/sorbents etc.) should be reported and described. In the tables reporting comparisons (i.e.: tables 1, 2) some parameters useful for the comparison must be reported, such as efficiency, CO2 concentration (in/out), CO2 purity, costs (e.g.: euro/kg CO2 separated).
· A proper review of methane production from CO2 should be added, if included in the title. Section 7 is definitely too synthetic to be considered a focus of the paper.
Minor comments regarding style and language:
- Use of tenses must be revised. Past simple and present perfect are mixed. I recommend using one of the two tenses (preferably past simple). The English language is overall good, but a revision is required.
- Please use the same English type throughout all the text (either US or UK)
- The reference style in the text is not standard.
I find the research topic interesting. Though, the manuscript must be drastically improved before final publication. I therefore recommend rejection at this stage.
Author Response
Response to Reviewer 2 Comments
The authors propose an overview/review of carbon capture technologies, besides some final perspectives on CO2 conversion into methane. Although the topic is interesting and truly worthy of investigation, there are many points both in the structure and in the contents that are not clear. Among others:
Point 1: As a general remark, I find the paper structure more similar to a book chapter than to a research paper. A thorough review has to comprise all the research papers on the investigated topics in the chosen years (2000-2022), which in this case are much more than the 187 references the authors included in the review. In this regard, I suggest a more appropriate choice of the keywords (i.e.: CO2 capture, amine scrubbing, chemical looping etc, rather than very specific chemical compound names such as zeolites, that are indeed used for many applications other than carbon capture).
Response 1: This has duly been addressed. Please refer to the abstract section, Page 1, lines 25 & 26.
Point 2: Process description for the technologies are not clear or described thoroughly. The plant components and their operating conditions (together with the required catalysts/sorbents etc.) should be reported and described. In the tables reporting comparisons (i.e.: tables 1, 2) some parameters useful for the comparison must be reported, such as efficiency, CO2 concentration (in/out), CO2 purity, costs (e.g.: euro/kg CO2 separated).
Response 2: This has been addressed. Please refer to the following Tables:
Table 1, Page 7
Table 2, page 7
Table 3, page 8
Table 4, page 9
Table 5, page 11
Table 6, page 14
Table 7, page 15
Point 3: A proper review of methane production from CO2 should be added, if included in the title. Section 7 is definitely too synthetic to be considered a focus of the paper.
Response 3: This has been addressed. Please refer to section 9 all through to section 9.2.3
Point 4: Minor comments regarding style and language:
Use of tenses must be revised. Past simple and present perfect are mixed. I recommend using one of the two tenses (preferably past simple). The English language is overall good, but a revision is required.
Please use the same English type throughout all the text (either US or UK)
The reference style in the text is not standard.
I find the research topic interesting. Though, the manuscript must be drastically improved before final publication. I therefore recommend rejection at this stage.
Response 4: This has been addressed throughout the manuscript.
Author Response File: Author Response.docx
Reviewer 3 Report
Dear authors
Your article summarizes all knowledge about CCS and CCU technologies and about these processes. The summarized is very important for next work. But I have two small comments.
I would like to see more detail information about these technologies. In absorption technologies is possible to use amine with enzyme and other possible technologies. Please could you add more detail?
I am missing a chapter about technical maturity and possible application in industry. Which technologies are the closest to the application, especially technologies dealing with the production of methane?
Thank you for your work and I would like to if you will continue with this work.
Best regards
Author Response
Response to Reviewer 3 Comments
Dear authors
Your article summarizes all knowledge about CCS and CCU technologies and about these processes. The summarized is very important for next work. But I have two small comments.
Point 1: I would like to see more detail information about these technologies. In absorption technologies is possible to use amine with enzyme and other possible technologies. Please could you add more detail?
Response 1: This has been revised. Please refer to section 5.1, page 7, line 214 - 226
Point 2: I am missing a chapter about technical maturity and possible application in industry. Which technologies are the closest to the application, especially technologies dealing with the production of methane?
Thank you for your work and I would like to if you will continue with this work
Response 2: This has been duly addressed. Please refer to section 8, page 25, line 661 – 698.
However, as far as methane production technologies are concerned, CO2 methanation is the most studied, being mostly conventional thermal-catalytic conversion.
Author Response File: Author Response.docx
Reviewer 4 Report
According to the title of the manuscript, it summarizes results related to CO2 capture and CO2 methanation. The absorption, adsorption, and chemical binding of CO2 were discussed in detail, but the reaction of CO2 with hydrogen was only briefly described by mentioning only some catalysts. If both processes are mentioned in the title, I think that methanation should also be written in more detail. For example, it is not even mentioned that CO can also be produced in the CO2 + H2 reaction, although the selectivity of CH4 formation is important from the point of view of the usability of the products
I couldn't decide whether the authors wanted to write a general or a scientific review. In the first case, I miss the more detailed cost analysis, in the latter case, the concrete results. In some cases, such data were given, e.g. in line 155, where the increase in costs is mentioned, or in table 3, where the adsorption capacity of some adsorbents is summarized.
Specifying the authors is completely confused. In the references, if there are more than 3 authors, only the name of the first author is given. I think the other authors also deserve to have their names listed. In the text, if the authors are referred to by name, the form chosen is random. Please unify the references.
It is written in line 559 “Energy carriers such as CO2 can be used to transform renewable energy.” Sorry CO2 is not energy carrier.
The introduction of chapter 6 and section 6.4 have many similarities. Please modify these paragraphs.
Author Response
Response to Reviewer 4 Comments
Point 1: According to the title of the manuscript, it summarizes results related to CO2 capture and CO2 methanation. The absorption, adsorption, and chemical binding of CO2 were discussed in detail, but the reaction of CO2 with hydrogen was only briefly described by mentioning only some catalysts. If both processes are mentioned in the title, I think that methanation should also be written in more detail. For example, it is not even mentioned that CO can also be produced in the CO2 + H2 reaction, although the selectivity of CH4 formation is important from the point of view of the usability of the products
Response 1: This has been addressed. Please refer to section 9 all through to section 9.2.3
Point 2: I couldn't decide whether the authors wanted to write a general or a scientific review. In the first case, I miss the more detailed cost analysis, in the latter case, the concrete results. In some cases, such data were given, e.g., in line 155, where the increase in costs is mentioned, or in table 3, where the adsorption capacity of some adsorbents is summarized.
Response 2: This has been revised.
Please refer to the following Tables:
Table 1, Page 7
Table 2, page 7
Table 3, page 8
Table 4, page 9
Table 5, page 11
Table 6, page 14
Table 7, page 15
Point 3: Specifying the authors is completely confused. In the references, if there are more than 3 authors, only the name of the first author is given. I think the other authors also deserve to have their names listed. In the text, if the authors are referred to by name, the form chosen is random. Please unify the references.
Response 3: This has been revised.
Please refer to the reference section
Point 4: It is written in line 559 “Energy carriers such as CO2 can be used to transform renewable energy.” Sorry CO2 is not energy carrier.
Response 4: This has been addressed. “CO2 is a chemical feedstock”
Please refer to section 9.2.1, line 848, Page 29
Point 5: The introduction of chapter 6 and section 6.4 have many similarities. Please modify these paragraphs.
Response 5: This has been revised
Kindly refer to section 6, pages 365 – 400.
Author Response File: Author Response.docx
Reviewer 5 Report
In this work, the authors provide a review of current state of the art on carbon capture and methane production from CO2. The work is very detailed and well organized, with excellent writing. But the novelty of the work is limited. The literature has been saturated with reviews on CO2 capture (the largest portion of the current manuscript), with similar level of detail, analysis and comparisons, essentially, offering nothing relatively new in this area. Particularly, with the standard scope looking at the types of capture systems, and traditional solvents and solid materials.
The second portion of the manuscript on CO2 conversion to methane, though appearing in the title of the manuscript, is very limited and basic.
The review offers simply an account of known state of the art without any critical evaluation or analysis on the gaps and expected or proposed future direction of research in this area.
I appreciate the effort of the authors in this work, however, it would be better to take a step back and re-evaluate the novelty of the work, focusing on a specific niech that has not been previously explored.
Author Response
Response to Reviewer 5 Comments
Point 1: In this work, the authors provide a review of current state of the art on carbon capture and methane production from CO2. The work is very detailed and well organized, with excellent writing. But the novelty of the work is limited. The literature has been saturated with reviews on CO2 capture (the largest portion of the current manuscript), with similar level of detail, analysis and comparisons, essentially, offering nothing relatively new in this area. Particularly, with the standard scope looking at the types of capture systems, and traditional solvents and solid materials.
Response 1: This has been revised
Please refer to section 7.
Point 2: The second portion of the manuscript on CO2 conversion to methane, though appearing in the title of the manuscript, is very limited and basic.
Response 2: This has been revised.
Please refer to section 9 all through to section 9.2.3
Point 3: The review offers simply an account of known state of the art without any critical evaluation or analysis on the gaps and expected or proposed future direction of research in this area.
I appreciate the effort of the authors in this work, however, it would be better to take a step back and re-evaluate the novelty of the work, focusing on a specific niech that has not been previously explored.
Response 3: This has been revised, thank you
Author Response File: Author Response.docx
Round 2
Reviewer 4 Report
The authors significantly modified the manuscript according to the reviewer's advice and suggestions. Thus, in my opinion, the manuscript is acceptable.
I would like to suggest that in some cases, especially when a technology or procedure is, it should refer to reviews rather than to paper that examines the efficiency of a catalyst system.
Author Response
Thank you very much for your insightful comment. This has duly been noted.
Author Response File: Author Response.docx
Reviewer 5 Report
I appreciate the effort of the authors in enhancing the current manuscript. The modifications added by the authors have uplifted the novelty of the work significantly and added depth to the review. Small adjustments are needed given the current state of literature, specifically in the area of solvents for CO2 capture via absorption. It is worth it for the authors to add the following references and highlight the area of water-free and water-lean solvents, and novel process configurations:
- https://doi.org/10.1016/j.seppur.2021.120093
- https://doi.org/10.1016/j.seppur.2021.119516
- https://doi.org/10.1039/C3EE41016A
- https://doi.org/10.1021/acssuschemeng.0c03800
Author Response
Thank you for your insightful comments.
This has been duly attended to.
In the area of solvents for CO2 capture via absorption. Water-free, water lean-solvents and novel process configurations have been highlighted.
Please refer to section 5.1, Page 7, lines 231 – 285.
