A Short Review on Catalyst, Feedstock, Modernised Process, Current State and Challenges on Biodiesel Production

Round 1

Reviewer 1 Report

The manuscript submitted by Abdulkareem-Alsultan et al. is presented by the interesting review on biodiesel (FAME) production. Many reviews were published in this field recently. As the Journal scope is the catalysis and catalysts, I recommend the authors focus mainly on the description of catalysts used in biodiesel production (i.e. catalyst design and nature, etc.). I suppose that Section 3.2. Heterogeneous catalysts can be extended because there are many types of research devoted to the development of heterogeneous catalysts for transesterification. Also, I recommend reviewing the biocatalysts used for the production of biodiesel. The manuscript requires to be revised in the terms of structure. Moreover, the paper is too hard to read and the revision of the style is needed. Thus, I recommend the major revision.

Author Response

Thank you very much for your comment 

Author Response File: Author Response.pdf

Reviewer 2 Report

The present paper entitled ”A Short Review on Catalyst, Feedstock, Modernised Process, Current State and Challenges on Biodiesel Production” by the authors G. Abdulkareem-Alsultan, N. Asikin-Mijan, Zueriani Ibrahim, Robiah Yunus, Siti Zulaika Razali, N  Mansir, Aminul Islam and Yun Hin Taufiq-Yap makes a review about biodiesel production using catalytic and non-catalytic routes. The manuscript also discusses about different biodiesel feedstocks and the most common biodiesel production techniques employed. The review concludes comparing the physical properties of biodiesel with those of petroleum-derived and examines the current status and future perspectives of biodiesel production in the world.   

The manuscript is well-written, clearly presented, and easy to read. However, I have several comments and suggestions that should be addressed by authors before the article could be finally accepted.   

• Although authors define their contribution as “A short review” there are some aspects which should not be forgotten in the manuscript. For example, the use of biomass-based catalysts has gained a great attention in recent years, and they have not been discussed. There are several contributions in the literature describing the use of waste biomass as catalysts for both low and high FFA oil which I consider relevant for the reader. Likewise, physical properties of biodiesel are discussed but analytical techniques employed for characterizing FAME produced are absent. I consider really helpful to describe some of the most relevant techniques employed in the characterization of biodiesel.
• In section 1, It would be highly recommendable to include a scheme showing both transesterification and esterification reactions. This is really useful for the reader for visualizing the production of biodiesel by the sequential transformation of triglycerides on the one hand, and the conversion of free fatty acids on the other one.
• It would be very useful to include some tables summarizing the different catalysts discussed in the biodiesel production. A table for each type of catalytic system could help the reader to identify easily the examples examined in the text. Some data as feedstock, conditions, yield and reference could appear in these tables allowing an easy comparison between all different contributions discussed.
• At the end of section 4, authors discussed a reduction in the activity displayed by the system WO3/ZrO2 provoked by a redox reaction with FFA. In addition to being a confusing sentence in the way it is written, this does not appear to be the real cause. In reference 29, provided by authors, which actually is a review, there is not an explanation for the low activity. However, in the original work, cited in reference 29, Prasad et al (Applied Catalysis A: General 276(1): 163-168) explain that the formation of monoclinic phases of zirconia and crystalline oxide have detrimental effects on the esterification of FFA. Therefore, I would recommend rewrite the sentence or provide the correct reference which can justify the argument given in the text.
• Data of production given in section 7 should be updated.

Author Response

Thank you very much for your comments.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The quality of the manuscript seems to be better. The authors revised all the issues and answered all the questions.  I recommend the paper to be published in the current form. 

Reviewer 2 Report

It seems that most of the suggestions and comments for the original manuscript have been adequately addressed.  In my opinion current version of the manuscript seems to be much clearer for readers, and it can be considered for publication in Catalysts as it is.