Sodium Methoxide/Zeolite-Supported Catalyst for Transesterification of Soybean Waste Cooking Oil for Biodiesel Production
Round 1
Reviewer 1 Report
The authors synthesized the zeolite/NaOMe catalysts, characterized their partial physicochemical properties, and evaluated their catalytic activities for the transesterification of waste cooking oil (WCO). This work contains some new results and could be considered for publication. However, the authors should revise their manuscript before acceptance for publication according to the following comments:
1. The abstract is too long, and it should be shortened.
2. The zeolite/NaOMe catalyst seems to be denoted as NaOMe/zeolite, rather than zeolite/NaOMe.
3. Is the drop in surface area of zeolite/NaOMe (compared with that of zeolite Y) due to the presence of sodium methoxide inside the pores of the zeolite Y? NaOMe located outside the pores of zeolite Y could block the pores of zeolite Y.
4. Usually, turnover frequency (TOF) is calculated for the supported noble metal catalysts. In the present work, however, the catalyst is zeolite/NaOMe, how do the authors calculate the TOFs?
5. What are the active sites or active species for the addressed reaction?
6. What are the roles of NaOMe and zeolite in catalyzing the addressed reaction?
7. How about the catalytic stability of the typical sample?
8. What are the catalytic mechanisms?
9. A comparison on catalytic activity of the as-obtained typical sample should be made with those of the related samples reported in the literature.
10. There are some inappropriate English words or expressions in the manuscript. The authors should carefully polish the English of the whole manuscript.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript "Zeolite/NaOMe Heterogeneous Catalyst for Transesterification of Soybean Waste Cooking Oil for Biodiesel Production", in the reviewer opinion, could have had potential to inform readers about technological aspects of production of fatty acid methyl esters form waste cooking oils. The manuscript covers topical aspects of re-fabrication of waste products and production of sustainable bio-fuels. However, the manuscript suffers from the lack of rigorous methodology and, presumably, correct English. The reviewer is a non-native English speaker and understands how uncomfortable it is to communicate scientific information to non-native English speakers; however, the authors should consider revising most parts of the manuscript. The main obstacle arises from the methodology of testing of “heterogeneous” catalysts. The minor obstacles, although still significant, are listed below. The reviewer was unsure whether to suggest major revisions or rejection. At the end, major revisions were suggested in order to give the opportunity to the authors to improve their manuscript.
Comments and considerations:
(1) Is the sodium methoxide on zeolite really the heterogeneous catalyst? One can expect that some water moistures can cause hydrolysis. Transesterification of triglycerides then proceeds as a quantitative reaction in surpluses of methanol or the reaction proceeds under kind of homogeneous catalysis. This issue is normally solved by repeated catalytic runs. The contact catalyst is separated from the reaction mixture and reuse in another catalytic run. This is repeated several times. 10 times for example. At the end, the spent catalyst is analyzed for the content of sodium methoxide. Was it done ? Other possibility is to place extrudates or spheres or kid of shaped catalysts into stirrer (into sieve holder, for example) and just the reaction mixtures are replaced several times. At the end, the shaped catalyst is removed from the holder and analyzed for the content of the sodium methoxide. Was it done?
(2) Please unify the nomenclature. Use “biodiesel” or “fatty acid methyl esters” )”FAME” uniformly trough the entire body of the manuscript.
(3) Introduction or discussion of problematic aspects of FAME, i.e. content of reactive carboxylic and olefinic groups, should be provided with the relation to hydrotreating of waste cooking oil (hydro-deoxygenation) that simply provide saturated hydrocarbons; sure, on the expense of hydrogen.
(4) Please re-phrase the introduction section. “In conclusion” seems strange on line 85.
(5) Lines 92-95: Please specify all catalysts you use in the study. Their surface area and particle-size fraction should be provided. These are the fundamental parameters of heterogenous catalysts.
(6) Figure 2: Please specify, which line belongs to which catalyst.
(7) L160 and elsewhere in the manuscript: The term “tabulated in Figure x” is hardly find in scientific literature, the reviewer is afraid. Please use Tables in the way how it is recommended in the instructions for authors. Use templates if available.
(8) Figure 3: Differential curves are mostly used for the pore-size distribution.
(9) How many catalysts “zeolite/NaOMe” were actually prepared? Why they are not listed in Table “Figure 5”?
(10) Figure 10: NaOMe and zeolite/NaOMe exhibit practically the same activity. So; where the effect of “zeolite” is? Better recycling? How easy is to filter out the zeolite? What is the particle-size distribution of zeolite/NaOMe?
(11) Figure 11: Where the solid catalyst is? Is it any emulsion?
(12) L231: Please define conversions of oils and yields of FAMEs in the manuscript.
(13) Figure 14 is about FAME degradation, probably.
(14) Please explain, why sections 3.4.1 and 3.4.2 are present. Why not to determine the concentration of each individual FAME? This is a routine in triglyceride analysis. FTIR and NMR does not say much about the content of FA. Why to analyze glycerol?
(15) Line 304-305: Sure, FAME were formed. One would expect quantitative analysis.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The authors present the study of the transesterification of soybean waste cooking oil for biodiesel production with Zeolite/Sodium methoxide heterogeneous catalyst.
The topic is of relevant scientific interest, however, making a very general review of the manuscript, aspects can be observed, which it is necessary to be corrected.
Title
It is necessary to change because NaOMe is an abbreviation
Abstract
It is necessary to correct and complement, because some data is wrong, for example:
Line 1-2. It is necessary to correct …This study aims to prepare a heterogeneous catalyst based on zeolite, nanoclay and titanium dioxide doped with NaOMe (sodium methoxide) or transition metal (Mo, W), because in this manuscrite only describe Zeolite/Sodium methoxide catalyst preparation.
Line 10. It is necessary to eliminate …. and viscosity analysis… because the catalysts cannot be characterized by this technique.
Line 10-11. It is necessary to correct, because the surface area values do not correspond to those reported in the results section 3.1.3
Line 15. It is necessary to complement …. 1H-NMR… with and viscosity analysis
Introduction
It is necessary to improve.
Materials and Methods
Line 90. It is suggested to eliminate … and Measurements…. because in this manuscript there are not measurements.
Line 91-92. It is necessary to eliminate … The anhydrous methanol, molybdenum (V) chloride, TiO2, NaOMe, ammonium metatungstate hydrate, nanoclay, and zeolite Y… and only CH3NaO and zeolite Y, should appear, but it is necessary to describe characteristics of both materials, for example, the purity and in the case of zeolite: The Si/Al ratio, the pore size, the specific surface area, whether it is in an ammonium or acid form, etc.
Line 94-95. It is suggested to eliminate the description of ball-milling in this section and move this information to the beginning of section 2.3.
Line 95-96. It is suggested to eliminate the description of analysis of the WCO and transesterification product in this section and move this information to the end of section 2.4.
Line 97-104. It is suggested to eliminate the description of characterization techniques in this section and move this information to the end of section 2.3.
Line 105. It is suggested to eliminate 2.2. Waste cooking oil sample preparation and integrate in section 2.1
Line 116. It is necessary to improve the description of characterization techniques
Results and Discussion
Line 139. It is necessary to change: cm-1 for cm-1
Line 141. It is necessary to change: MO4 for MO4
Line 151-153. It is suggested to eliminate the description of characterization by XRD in this section and move this information to the end of section 2.3.
It is necessary to improve all the figures
3.1.3. BET Surface Area. It is necessary to change cc/g by cm3/g
It is necessary to improve the text.
It is necessary to carry out a deep review of the manuscript because there are too many inconsistencies.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
After carefully checked the responses and modifications of the revised manuscript, I think that the authors have basically modified their manuscript according to the Reviewers' comments, and it may be now acceptable for publication.
Reviewer 2 Report
The authors have addressed each of the reviewer's points. In the reviewer opinion, the manuscript could be published in its present form.
