Carbon-Based Solid Acid Catalyzed Esterification of Soybean Saponin-Acidified Oil with Methanol Vapor for Biodiesel Synthesis

Round 1

Reviewer 1 Report

The following paper discusses the carbon-based solid acid catalyzed esterification of soybean saponin acidified oil with methanol vapor for biodiesel synthesis. This paper is interesting; however, it has many issues that need to be solved before considering the paper for publication. I list my comments below:

1.      Page 1, line 30, 31, “As one of the non-petroleum-based fuels, biodiesel has gained wide attention because it is regarded as an excellent alternative to fossil fuels”  the sentence should be ended at the word “attention”, otherwise, start the sentence with the word “biodiesel has…”

2.      Page 1, line 34, and page 2, line 73. The reason of adding each reference should be clearly known. Therefore, please eliminate multiple references. This should be done by characterizing each reference individually and by mentioning 1 or 2 phrases per reference to show how it is different from the others and why it deserves mentioning.  Example for this are references [3,4] and [21,22

3.      Page 2, line 46, “….consists of 30% to 48% soap, 8% to 45 27% neutral oil, 40% to 60% fatty acid salts,….”, it is enough that you write soap or fatty acid salts, chose one of them. Because actually soap here is sodium salt of fatty acids.

4.      You can add the following related article to the reference list when you write about the Common heterogeneous acid catalysts page 2, line 56. “Synthesis and characterization of new bifunctional SnZrSi oxide catalysts for biodiesel production”

5.      In introduction, the authors need to explain what is the new of this study compared to what they did in their previous published work, references (24,25,36,37)

6.      Page 3, line 112,113 “………also been fully investigated in previous studies by various characterization methods”. A reference should be placed at the end of this sentence.

7.      Page 3, line 98, please mention the name of the plant.

8.      Section 2.4, I highly recommend that the authors provide a schematic diagram for experimental set up.

9.      Page 3, line 134, “…….a methanol-oleic acid molar ratio 134 of 30:1 to 70:1, a reaction temperature………” why molar ratio was considered based on oleic acid and not on soybean saponin acidified oil?

10.  Page 3, line 133-135, why the minimum and maximum limits of the studied conditions were selected as molar ratio of 30:1 to 70:1, a reaction temperature of 72 to 80 °C and a reaction time of 2 to 5 h?  the authors need to explain in the manuscript why they chosen those limits specifically.

11.  Page 4, lines 146-149, I suggest to add a separate section about catalyst reusability. More explanation is required in the reusability study. Why you wash with hexane and ethanol?

12.  Results and discussion, the authors need to compare their results with similar published related papers.  Please cite the related works in this section and critically discusses your finings with the results of others.

13.  Why authors didn’t analyze their trans esterified samples using GC? Such way can determine the biodiesel yield, as the acid value calculations overlooks the trans esterified triglycerides into biodiesel.  

14.  The authors have not discussed the byproduct “glycerin”, SSAO has many triglycerides, then considerable amount of glycerin will be generated, authors should discuss this. Also, the generated glycerin can be considered as a credit for the process profitability, therefore its price can be also added to the economic study of this paper. Please justify.

There are many grammatical errors, please improve the quality of writing.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper "Carbon-based Solid Acid-Catalyzed Esterification of Soybean 2 Saponin Acidified Oil with Methanol Vapor for Biodiesel Synthesis" is nicely organized. The work is adequately planned and adds value to the literature. 

There are a few queries that need to be addressed prior to moving forward

1. The author needs to explain why the work is also required some similar works has been done in recent time how is it different from them?

2. At many places several claims are made that need references. Please add relevant references 

3. The authors need to improve discussions for a few sections. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Editor-in-Chief,
Thank you for inviting me to evaluate the article entitled “Carbon-based Solid Acid Catalyzed Esterification of Soybean Saponin Acidified Oil with Methanol Vapor for Biodiesel Synthesis”. The authors focused on the preparation of carbon-based solid acid catalyst from waste bamboo by in situ sulfonation and using to catalyze the esterification reaction of SSAO and methanol vapor.

This manuscript contains acceptable results and can be accepted for publication in the Sustainability after some moderate revisions.
I have some comments as follows to strengthen the manuscript should be authors consider them to get the work better:
1- The “Title” of the article is appropriate; there is no need for any change.
2- The abstract must be revised with the brief methods (one sentence).
3- Modify the keywords; Sort keywords alphabetically.
4- Arrange the numbers of Eqs. 4, 5 and 6 in the column below No. 3.
5- “To allow the reaction to proceed completely, the effect of reaction time on conversion was investigated at a catalyst loading of 6 wt%, a reaction temperature of 76°C, and a methanol/oil molar ratio of 50:1.” explain more! (Lines 237 to 239).
6- Correct the sentence, which has begun with “AND” in line 378!; Remove “AND” from the beginning of the sentence. (And Table 2 shows that the metal ion content of C150-4 after the sixth batch reaction is 3.72 mmol, which is 0.76 mmol more than that of fresh C150-4, accounting for 23.1% of the total loss of sulfonic acid.)
7- It is suggested to add the “Nomenclatures” section after the conclusions.

The manuscript is readable. I understand what the authors mean, but the Quality of the English language needs minor revision. Check the punctuation, and typographical & spelling errors in the manuscript thoroughly.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have addressed all the reviewer's comments. I suggest publication.