A Comprehensive Review on Biofuels from Oil Palm Empty Bunch (EFB): Current Status, Potential, Barriers and Way Forward

Round 1

Reviewer 1 Report

Dear Authors

Manuscrip ID: Sustainability-1326330 is an excellent review on the application of empty bunches of dende as a raw material in the production of bio-oil covering fundamental issues such as proximate and elemental characterization (C, N, H, S), thermal transformation processes, in particular pyrolysis, influence of process variables in the yield and quality of bio-oil, physicochemical and compositional characterization of bio-oil, comparison of the characteristics of bio-oil with those of fossil biofuels, application as biofuels in transport, as well as environmental impacts. In order to receive the maximum grade, all that is needed is to describe the yield graph using a software such as origin 8.0, since excell is not specific to produce graphs.

Author Response

Thank you very much for your comments and insights. I appreciate that very much.  I have installed Origin 8.0 and revised the graph in Figure 5 using Origin 8.0.

Author Response File: Author Response.pdf

Reviewer 2 Report

This work presented a comprehensive review of oil palm empty fruit bunch (EFB) as a biomass resource, which systematically studied the principles and processes for conversion of EFB into bio-oil. The method to upgrade the bio-oil was also summarized in this manuscript. Besides, the environmental impact and the way forward by using EFB as a promising renewable energy resource were discussed. However, there are still some problems with the manuscript. The specific suggestion could be seen as follow:

1. Please correct the title “1.1” and the title ”ⅱ” at line 31 and line 465, respectively.
2. The information from line 92 to 93 can’t be found in Table 2.
3. There are some grammatic errors in the manuscript, such as line 114-115, line 210-211 and line 283-284. Please proofread thoroughly.
4. Please improve the quality of the Figure 3.
5. It is suggested to improve the background of study on catalyst in section 2.2.1.
6. It is recommended to supplement the content about the slow pyrolysis process. Some closely related studies should be added as references, e.g., Fuel 291 (2021) 120128; Chemical Engineering Journal 425 (2021) 130649.
7. Please modify the format of “Most critical to Least critical Property” in Table 8 and 9 to make it consistent.
8. Please improve the quality of the Table 9, such as the position of tick should be aligned. Besides, the “Description” of “Molecular distillation” in Table 9 has a mistake.
9. The units in Table 10 should be uniform.

Author Response

Thank you very much for a very constructive comments. Here are my replies:

1. Please correct the title “1.1” and the title ”ⅱ” at line 31 and line 465, respectively. - Ok done correction
2. The information from line 92 to 93 can’t be found in Table 2. - Latest statistics has been replaced by reference, not Table 2 (mistake)
3. There are some grammatic errors in the manuscript, such as line 114-115, line 210-211 and line 283-284. Please proofread thoroughly. - Corrections done. line 114-115 (line 166-168), line 210-211 (line 260-263) and line 283-284 (line 390-392).
4. Please improve the quality of the Figure 3. - Figure 3 improved.
5. It is suggested to improve the background of study on catalyst in section 2.2.1. - Catalyst and noncatalytic part has been edited and added from line 298 till 316, and line 318 till 326.
6. It is recommended to supplement the content about the slow pyrolysis process. Some closely related studies should be added as references, e.g., Fuel 291 (2021) 120128; Chemical Engineering Journal 425 (2021) 130649. - I have added the slow pyrolysis content in section 2.3 Slow Pyrolysis Reactor from line 353 till 367.
7. Please modify the format of “Most critical to Least critical Property” in Table 8 and 9 to make it consistent. - I have modified Table 8 and 9 to more consistent.
8. Please improve the quality of the Table 9, such as the position of tick should be aligned. Besides, the “Description” of “Molecular distillation” in Table 9 has a mistake. - I have aligned the tick position. The description of "Molecular distillation" has been corrected.
9. The units in Table 10 should be uniform. - Energy consumption per ton unit has been standardized into GJ.

Reviewer 3 Report

The review article entitled ‘A Comprehensive Review on Biofuels from Oil Palm Empty  Bunch (EFB): Current State, Potential, Barriers and Way Forward’. The concept of the review article is interesting and suitable to publish in the Sustainability. However, in the present form it can not be accepted and it required substantial major revision.

The major comments as follows:

• Title should be modifying in the precise way instead ‘Current State’ Write ‘Current Status’. 
• Abstract section should be rewritten and look very general and not informative. In abstract authors should mention the importance of research work briefly at the end.
• Provide a nice graphical abstract representing the overview of the MS with key highlights. For review articles it should be mandatory and don’t use the figures used in the manuscript.
• Introduction looks very general. In the introduction section, write the novelty of the work and the problem statement clearly. The detailed discussion about the novelty, significance of your research work and research gap relative to the literature is essential.
• For Table 1 which literature they have used give details.  For Table 3 give details in the text as well.
• Some researchers used rice bran for biodiesel production and add the details somewhere Fuel 253, 975-987, 2019; Fuel 239, 153-161, 2019. Give more details about the pretreatment of EFB.
• Techno Economic challenges of the developed system using EFB need to be addressed
• Write the practical applications and future research perspectives and challenges by adding a new section before conclusions.
• What are the limitations of pyrolysis for commercial application?
• Authors should discuss some integrated approaches to enhance the process efficiency  and practical applicability.
• The conclusion of the study is not discussed with the specific output obtained from the study, it could be modified with precise outcomes with a take home message.
• English and grammar mistakes are present. The author should check the manuscript by native English Speaker to improve the quality of the manuscript.

Author Response

Thank you for a very constructive comments to improve this manuscript. Here are my reply:

• Title should be modifying in the precise way instead ‘Current State’ Write ‘Current Status’. - Title changed to Current Status (line 3).
• Abstract section should be rewritten and look very general and not informative. In abstract authors should mention the importance of research work briefly at the end. - Abstract has been revised (line 26-30).
• Provide a nice graphical abstract representing the overview of the MS with key highlights. For review articles it should be mandatory and don’t use the figures used in the manuscript. - I have provided the graphical abstract, below the abstract. 
• Introduction looks very general. In the introduction section, write the novelty of the work and the problem statement clearly. The detailed discussion about the novelty, significance of your research work and research gap relative to the literature is essential. - I have revised the introduction (line 62-70).
• For Table 1 which literature they have used give details.  For Table 3 give details in the text as well. - I have added some descriptions for Table 3 (line 238-241).
• Some researchers used rice bran for biodiesel production and add the details somewhere Fuel 253, 975-987, 2019; Fuel 239, 153-161, 2019. Give more details about the pretreatment of EFB. - I have added Fuel 253, 975-987, 2019; Fuel 239, 153-161, 2019 at line 121. And I have added more details in the pretreatment section 2.2.2.
• Write the practical applications and future research perspectives and challenges by adding a new section before conclusions. - I have revised the section 5.0 Limitations and Way Forward (line 735-742, 745-759).
• What are the limitations of pyrolysis for commercial application? - I have added the limitations at section 5.0.
• The conclusion of the study is not discussed with the specific output obtained from the study, it could be modified with precise outcomes with a take home message. - I have added the section 6.0 Conclusions (line 707-803).
• English and grammar mistakes are present. The author should check the manuscript by native English Speaker to improve the quality of the manuscript. - Corrections have been checked grammatically.

Round 2

Reviewer 2 Report

Moderate English changes required

Author Response

Thank you very much for your comments.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors have substantially revised the manuscript according to the comments.

The present form of the manuscript can be accepted for publication.

Author Response

Thank you very much for your comments.

Author Response File: Author Response.pdf