Investigation of Novel Transition Metal Loaded Hydrochar Catalyst Synthesized from Waste Biomass (Rice Husk) and Its Application in Biodiesel Production Using Waste Cooking Oil (WCO)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1.      The innovation in the introduction part is not attractive enough for readers. Wish to see some more sparkling aspects in this article. Besides, the characterization method of the material should not be reflected in the Abstract.

2.      Experimental design，Line 199, Line 206, Please supplement relevant literature supporting the calculation of Eq 1 and Eq 2.

3.      It is customary to plot FTIR spectra with the binding energy increasing from bottom to top. Please modify the binding energy axis accordingly.

4.      Results, Fig. 4: The XRD data in the graph should be smoothed and clear scale lines added. The font format in figures should be consistent throughout, and careful revision of the main figure and table is necessary.

5.      Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS): Is there any evidence proving that cobalt particles completely cover the pores of RHAC? Can you provide an EDS plot for RHAC-Co?

6.      Thermo-gravimetric analysis (TGA), Line 314: What exactly are the volatile matter released by degradation of celluloses and hemicelluloses present inside the precursor (75% mass loss)? It would be helpful if more information about these volatile matters can be provided for better understanding.

7.      Optimization studies for Biodiesel yield by RSM, Line 437: The author claims that RSM's prediction was checked by conducting trials twice under ideal conditions where both times resulted in an average value of 96.3%. However, further details are needed for a more convincing argument.

8.      The results section should include subheadings for important findings or significant research methods, rather than focusing on material characterizations. It is essential to emphasize the logical progression of the research process. Additionally, please ensure that the title number in your manuscript is corrected.

Comments on the Quality of English Language

Minor editing of English language required

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The presented paper examines a novel transition metal-loaded hydrochar catalyst synthesized from waste biomass (rice husk) and its application in biodiesel production using waste cooking oil (WCO). The article falls within the scope of the journal and addresses an important area of study; I congratulate you on your research. The manuscript has potential for publication but requires minor revisions and clarifications, as stated below:

1.     Page 3 : Line 105: Can you provide the rationale for choosing this particular cobalt-loaded activated carbon 110 (RHAC-Co) catalysts.

2.     Page 3: Line 138-139: HC was rinsed with deionized water and filtered by grade 41 of Whatman filter paper. After filtration, did you oven-dry the sample again? If so, at what temperature?

3.     How does the use of rice husk as a biomass precursor for the hydrochar affect the catalyst's properties and performance compared to other potential waste biomass sources?

4.     During the hydrochar production by hydrothermal carbonization, what temperature and pressure did you adopt?

5.     The loaded catalyst was effectively used in the transesterification of waste cooking oil (WCO) and methanol, achieving a maximum biodiesel yield of 96.3%, in line with ASTM standards. What is the pH value of this biodiesel yield of 96.3%? The pH of biodiesel is a crucial indicator for the corrosion of engine parts, reduced oxidative stability, shelf life, and performance in engines

Comments for author File: Comments.pdf

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

The focus of this study is to find a new way to convert used WCO into biodiesel by developing novel heterogeneous rice husk-derived cobalt-loaded activated carbon catalysts. The catalyst is then characterized using Fourier Transform Infrared Spectroscopy, X-ray diffraction, Brunauer Emmett and Teller, Thermogravimetric Analysis, Scanning Electron Microscopy and Energy Dispersive Spectroscopy characterizations. Complete characterization of the produced biodiesel using catalysts was carried out to prove its feasibility as fuel. Furthermore, the relationship between independent process parameters and optimum conditions of biodiesel yield was studied via RSM. The percentage yield of biodiesel is affected by input variables and that effect was studied using the central composite design.

Please check the order of affiliation two, I think you should number as affiliation 2 instead of 3. Kindly check

Page 1, line 40, “….Paris Agreement that aims to keep 40 the global temperature as minimum as 2 °C,”, kindly mention the year of the agreement. In addition, do you mean the global temperature raise annually? The sentence is not informative.

The authors have performed the biodiesel production using two step esterification transesterification reaction. In the first step of esterification, the authors used sulfuric acid to react free fatty acids with methanol, then they used their synthesized catalyst. I invite the authors to consider performing the same way, however using lipases. Lipases can do the two processes, esterification and transesterification in one step without the doubt of soap formation.

I couldn’t find the specifications of the used cooking oil, it will be useful to include them in the supplementary, especially the starting free fatty acids content.

Page 10, line 333 – 335. I suggest to remove this information to materials and methods section.

Page 10, section 3.2.1., “The optimal conditions for reducing the FFA content in WCO were determined to be a mixture of 60 ml of ethanol and 3% sulfuric acid, agitated at 55 °C for 3 hours at 300 rpm” I couldn’t find the optimization of this process in the manuscript, if you have optimized this process in another paper, then please include a reference. Otherwise, details should be mentioned in the results and discussion section.

I suggest to move fig. 9 to supplementary.

The title of Fig. 10 is confusing, I suggest to remove (A), (B), (C),..etc, as ready already can understand from the name of the parameter.

 

No 2023 and 2024 papers were cited, kindly update your refence list, I suggest to cite the following https://doi.org/10.1016/j.seta.2023.103200

https://doi.org/10.1016/j.biotechadv.2023.108275

Conclusion should be more informative by adding the optimum parameters values.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

 The manuscript can be accepted in present form

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have considered all comments raised by the reviewer. I suggest publication.