Production of Biodiesel from Waste Cooking Oil via Deoxygenation Using Ni-Mo/Ac Catalyst

Round 1

Reviewer 1 Report

This is a re-submitted draft that I reviewed before.
However, I didn't find significant improvement compared with the previous version. Therefore, I still suggest a major revision before accepting it.

My previous comments still apply here:

1. The name of the catalyst is not consistent throughout the manuscript. In the title, the catalyst was named Ni-Mo/Ac, while in the manuscript, the catalyst was named NiO-MoO/AC. The authors should unify the name of the catalysts.
2. Also, “AC” represent activated carbon in this manuscript, but the term “activated carbon” didn’t appear until Line 4 in Page4. The authors should provide more detailed description of the catalysts in both the abstract and the introduction part to avoid confusion.
3. The authors analyzed the composition of the biodiesel produced from the 3 types of waste cooking oil by GC-MS and GC-FID, which showed different selectivity and yield. However, the author should also provide the original composition of the 3 types of waste cooking oil. Without these information, it is meaningless to make comparison between the biodiesel products..
4. Finally, I'm curious why the figures in the new version are simplified compared to the original version. For example, all the error bars in Fig. 7 and Fig. 8 are gone, which were presented in the previous version.

Author Response

Please find the file attachment for author response. 

Author Response File: Author Response.docx

Reviewer 2 Report

Review of the article: "Production of Biodiesel from Waste Cooking Oil via Deoxygenation using Ni-Mo/Ac Catalyst".

Points for consideration:
1. The whole article has to be corrected by a native speaker - there are many linguistic mistakes.
2. The Abstract should be rewritten - far too much information is given in parentheses. Moreover, on the basis of the Abstract, it is impossible to understand what the aim of the article is. The Abstract should clearly state what the aim of this work is.
3. The quality of the figures (Figure 2, Figure 3, Figure 4, Figure 5, Figure 6) should be improved.
4. The Conclusions section has to be extended - at present, from the Conclusions section, it is impossible to understand what the aim of the work was.
   Moreover, in the Conclusions section should be added more general, important, scientific conclusions that can be drawn from the work, i.e. presentation of simple evaluation of three samples is not enough. Generally, this work looks like technical report, without clear aim and clear, scientific conclusions.
5. References should be written in one way.

Author Response

Please find attachment for author response review.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I agree to accept the revised manuscript for publication.

Reviewer 2 Report

Thank you for these corrections.
The Authors addressed correctly to all my comments and concerns. Now the article is much better and in my opinion it can be published in Processes.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

This study aims to present the production of biodiesel from waste cooking oils via deoxygenation. Indeed, the exploration of biofuels production processes via residual biomass utilization is an interesting research area that is being systematically studied the last years. More specifically, there are plenty research studies available in the literature in this field utilizing waste cooking oils for biodiesel production. However, my major problem with this paper is its low quality of presentation and significance of content. Therefore, I do not consider this paper appropriate for publication.

The abstract is incomplete and does not clarify the nature of the research, whereas the introduction clearly fails to provide sufficient background and to include all the relevant literature data in the specific field. The study’s goal and novelty are not evidently reported in the introduction section. In the experimentation section several points are missing, for instance a figure of the reactor that the experiments were performed while also the experimental conditions are not thoroughly described. Furthermore, the products are not qualitative characterized even though the authors report them as biodiesel (a qualitative analysis of the utilized feedstocks is also missing). Moreover, the results are not clearly presented and elucidated, as well. For instance, commonly the product of the deoxygenation process has lower acidity compared to its feedstock , but the authors report in Table 1 line 151 that the liquid product oil has higher acidity than the WCO. Another unexplained point is the coke formation after the deoxygenation process, the authors do not explain under which experimental conditions coke is formed and why is formed. The catalyst analyses are not fully explained and not compared with other results. In addition, the composition of the hydrocarbons of the products is not analyzed in detail, while their classification in groups, like paraffins, iso-paraffins, etc. would be more informative. Throughout the manuscript there are grammatical errors, and editing of the English language and style are required. The conclusions are not fully supported by the results.

Therefore, I do not consider this paper appropriate for publication.

Reviewer 2 Report

This manuscript reported the synthesis of Ni-Mo/AC catalysts for the production of biodiesel from waste cooking oil through the deoxygenation process. The authors employed a series of materials characterization methods to study the properties of the catalysts and tried to elucidate the effects of fed waste cooking oil on the quality of the final biodiesel product. Overall, this is an interesting work, however, I found insufficient analysis of the experimental data in the manuscript, which leads to some groundless conclusions. Therefore, I would suggest a major revision and my comments are as follows:

1. The name of the catalyst is not consistent throughout the manuscript. In the title, the catalyst was named Ni-Mo/Ac, while in the manuscript, the catalyst was named NiO-MoO/AC. The authors should unify the name of the catalysts.
2. Also, “AC” represent activated carbon in this manuscript, but the term “activated carbon” didn’t appear until Line 82 in Page2. The authors should provide more detailed description of the catalysts in both the abstract and the introduction part to avoid confusion.
3. The section 2.0 Materials and Methods should be reorganized.

• Line 57, it should be “2. Materials and Methods” instead of “2.0 Materials and Methods”;
• Section 2.2 catalyst synthesis, a schematic is needed to illustrate the sample preparation process;
• Section 2.3.5, 2.3.6 and 2.3.7 should be combined to make an independent section 2.4 Catalyst Performance Evaluation.

4. According to Line 84, the authors prepared totally 3 types of catalysts: bimetallic catalysts NiO-MoO/AC, and single metallic catalysts NiO/AC and MoO/AC. However, I didn’t find any description of the two single metallic catalysts in the manuscript. The authors should provide at least the materials characterization data and catalytic performance results of the two single metallic catalysts as control groups, and try to explain why the NiO-MoO/AC outperformed the other two catalysts.
5. The authors analyzed the composition of the biodiesel produced from the 3 types of waste cooking oil by GC-MS and GC-FID, which showed different selectivity and yield. However, the author should also provide the original composition of the 3 types of waste cooking oil. Without this information, it is meaningless to make a comparison between the biodiesel products.

Reviewer 3 Report

The presented manuscript reports deoxygenation of waste cooking oil using Ni-Mo/Ac catalyst. Authors Analyze three types of used cooking 1) used only once, 2) used for 3-5 times, and 3) used undetermined times which possibly means more than 5 but are not specified. Authors used Ni oxide and Mo oxide based catalyst that was deposited on Activated carbon before use.

The topic is certainly very interesting, and but the approach, experimental details, and reporting leave a lot to be desired. Firstly, the manuscript is written in poor English leaving the impression that it was neither polished nor proofread making numerous sentences and statements hard or impossible to understand. From the science point of view, the manuscript is not well composed. It lacks key explanations, reasons, and experimental details. Furthermore, almost no explanations are provided why this system was tested and what is the rationale behind the catalyst selection.

Unfortunately, the manuscript does not meet novelty or condition requirements and cannot be recommended for publication. Below are some of the questions and points that the reviewer thinks will be helpful for authors if they wish to improve upon it.

• Why was Palm oil specifically chosen for study? Can this be a model system for other oil systems?
• What is the rationale behind catalyst selection? Why Ni or Mo oxides? Can one of the metals be sufficient? Do authors have control experiments with either of these metals alone?
• NiO: MoO: AC ratio is reported as 10%: 10%: 80%. Is this an optimal ratio? No experiments or explanation is provided to explain why this specific ration is tested and no other.
• Lines 97-98 have two sentences both of which seem to convey the same message.
• In part 2.3.5. lines 106-110. The presence of the sentence and the citation “Alsultan et al. [10] stated that the reactor must be purged with N2 ……” is confusing.
• The lines 122 and 136 contain equations but they lack explanations. There are no descriptions of the terms or methods used.
• More explanations of the data such as FTIR is needed. For example, the reduction of carbonyl pear at 1740-5 is somewhat evident in Figure 2 top left and bottom spectra but is not evident at all in the top right spectra. Have this sample did not undergo a significant reduction?
• In part 3.3, line 188, we read “The formation of coke that exists on the external surface of the catalyst during reaction degraded the DO activity instead of metal leaching” which is not clear. How do authors know that there is no leaching? What control experiments were done? What are the findings?
• In lines 191-193 we read about “Superior resistance towards coke formation”, “tremendous catalyst stability”, and “prospects for further application in pilot-scale due to its long-life and reuse”. None of these claims seem to have any foundation. The authors don’t even mention that the catalyst was recycled and used. So, how do they know it's stable or reusable? More research needs to be done to show these.
• Figure 3 left the TGA graph. The weight of the sample “after calcine” starts at 100% and around 1000 °C drops below -20%. How can this happen? All solids have evaporated at that temperature. Even this cannot explain the negative number.
• In line 213, authors refer Figure 4b and state the presence of “irregular spherical shapes with particle size > 1 μm.” But TEM image shows no sign of particle. This needs to be addressed.