Rendering of Beef Tallow for Biodiesel Production: Microwave versus Boiling Water and Acetone Fat Extraction

Round 1

Reviewer 1 Report

Manuscript Title: Rendering of Beef Tallow for Biodiesel Production. Microwave versus Boiling Water and Acetone Fat Extraction

1. The presentation covers much too much previous research, and some details are missing. For example: Details on the preparation and characterization of the catalyst are given in a previous publication [34]. Could it be presented in detail and cited [34] in this paper?

2. Too old reference (year 2020) for fats raw materials prices in Table 1 (…accessed August 2020).

3. There is no description on the particle size, figure, percent purity CaO, or pore size of the filter used to remove the catalyst after the reaction process.

4. In the introduction, discuss the fundamental explanation of the extraction. Authors need to explain deeply for some literature review. Theory of microwave for rendering oil from animal fat, and effects of microwave rendering on the yield and characteristics from other research papers.

5. A pressure cooker for 40 min, how much pressure in process that pressure value was designed to boil water under lower atmospheric pressure? Moreover, 40 min was fixed, it was not varied to study oil yields. In addition, the author claimed that the cooking duration was optimized to extract the maximum fat. There is only text; there is no data or graph. Data should be added with details to explain pressure, temperature, and cooking times.

6. This paper need to study two objective of research (rendering, and biodiesel production)? The authors need to sharpen and improve the writing about the aim of this study in the last paragraph of the introduction. 

7. The microwave-assisted was the most performant methodology in the extraction procedure since it presents the lowest power consumption per gram of extracted fat. Why? To compare energy consumption, 100 g of fat was fixed and extracted using different techniques. The maximum fat content was determined by the extraction reactor's capacity, however the highest content of beef tallow was not yet examined for each technique. This statement could be clearer.

8. In the result and discussion session, the author mentioned the energy consumption in Table 2, but there were very few explanations in the paragraph. The result and discussion session should be written more clearly and concisely by separating the sub-heading, e.g., 3.1 Thermal stability, 3.2 FAME Yield analysis, 3.3 Energy Consumption, and 3.4 Glycerin analysis. Each session should be further explained and discussed.

9. In table 2, % fatty acidity was obtained 0.81, 1.96, and 2.39 when MW, BW, AE were used to extract beef tallow. For what reason do the free fatty acid levels differ? More explanation is required by the theories of MW, BW, and AE, which influence free fatty acid levels. The FFA content of fat is an important parameter to consider in order to continue the biodiesel production process.

10. At note listed in Table 2, 15% moisture in BW. More explanation is required for the 15% that is 30 fat yield including moisture content of 15%? If yes, must show percent fat after completed oven processing to eliminate water in fat.

11. Final FAME yield should be confirmed with GC method which was standard analysis method to check purity of ester.

12. Authors need to put a table to describe the composition of raw materials, final products and residues after the methanolysis process with different extraction conditions such as triglyceride, diglyceride, monoglyceride, FFA, ester. 

13. Should discuss the analysis of the fat extraction condition with varying approaches as mentioned as shown in Figure 4 (for example, 50%boiling tallow+ acetone and 50% MW tallow+acetone) before methanolysis to match the main title of this study. (…MW versus BW and AE). Need more discussion for comparison of various extraction methods.

14. The condition of methanolysis (methanol/oil=12 molar ratio; Wcat/Woil=5%; 2.5h reaction time) is fixed. This condition is obtained from some reference, or how come? 

15. The author compared the FAME yield results with the methanolysis of soybean oil. The results of this study did not meet the standard (over 96.5% STD for purity of methyl ester). Can you explain some reason or excuse for this issue?

16. A few recommendations must be given for further studies beyond the microwave-assisted approach in the concluding session.

Author Response

Reviewer #1

Manuscript Title: Rendering of Beef Tallow for Biodiesel Production. Microwave versus Boiling Water and Acetone Fat Extraction

1. The presentation covers much too much previous research, and some details are missing. For example: Details on the preparation and characterization of the catalyst are given in a previous publication [34]. Could it be presented in detail and cited [34] in this paper?

Details on the catalyst preparation and characterization are available in the introduction section of the revised manuscript.

2. 
   Too old reference (year 2020) for fats raw materials prices in Table 1 (…accessed August 2020).

As suggested by the Reviewer the references were updated and new sentences were included in the Introduction section.

3. 
   There is no description on the particle size, figure, percent purity CaO, or pore size of the filter used to remove the catalyst after the reaction process.

New data on the catalyst characterization (XRD, FTIR and SEM) were included in the revised manuscript. The filter paper characterization was also included in the experimental section.

4. In the introduction, discuss the fundamental explanation of the extraction. Authors need to explain deeply for some literature review. Theory of microwave for rendering oil from animal fat, and effects of microwave rendering on the yield and characteristics from other research papers.

The literature on the extraction of animal fat with microwaves is not abundant and the existing literature does not explain how MW act in the solvent-free extraction of fat. Taking into account the mechanism described for the extraction of microalgae oils, it is assumed that the MW heat the water molecules found in the adipose tissue, which promotes localized heating and increased pressure, which causes the breakdown of adipocytes, releasing so triglycerides. A new sentence was included in the introduction section.

5. A pressure cooker for 40 min, how much pressure in process that pressure value was designed to boil water under lower atmospheric pressure? Moreover, 40 min was fixed, it was not varied to study oil yields. In addition, the author claimed that the cooking duration was optimized to extract the maximum fat. There is only text; there is no data or graph. Data should be added with details to explain pressure, temperature, and cooking times.

The boiling in the pressure cooker was carried out at 1.5 atm and 112 ºC (data is now included in the experimental section of the manuscript). No data for lower cooking periods is available since the main goal was to maximize the extracted fat.

6. This paper need to study two objective of research (rendering, and biodiesel production)? The authors need to sharpen and improve the writing about the aim of this study in the last paragraph of the introduction. 

As suggested the last paragraph of the introduction section was rewriteen.

7. The microwave-assisted was the most performant methodology in the extraction procedure since it presents the lowest power consumption per gram of extracted fat. Why? To compare energy consumption, 100 g of fat was fixed and extracted using different techniques. The maximum fat content was determined by the extraction reactor's capacity, however the highest content of beef tallow was not yet examined for each technique. This statement could be clearer.

The capacity of the extraction reactors in the different methods was not evaluated because such an evaluation was not possible. The microwave equipment, the pressure cooker and the round acetone extraction flask had very different volumes.

8. In the result and discussion session, the author mentioned the energy consumption in Table 2, but there were very few explanations in the paragraph. The result and discussion session should be written more clearly and concisely by separating the sub-heading, e.g., 3.1 Thermal stability, 3.2 FAME Yield analysis, 3.3 Energy Consumption, and 3.4 Glycerin analysis. Each session should be further explained and discussed.

In the authors' opinion, the volume of data presented is not sufficient to justify the subdivision of section 3 into several subsections. The authors prefer to keep the organization of section 3 as it is presented without the subdivisions suggested by the Referee.

9. In table 2, % fatty acidity was obtained 0.81, 1.96, and 2.39 when MW, BW, AE were used to extract beef tallow. For what reason do the free fatty acid levels differ? More explanation is required by the theories of MW, BW, and AE, which influence free fatty acid levels. The FFA content of fat is an important parameter to consider in order to continue the biodiesel production process.

The authors recognize that the acidity of the extracted fat is an important characteristic of the extracted fat as the free fatty acids will partially neutralize the basic catalyst. The acidity of the fats extracted by the various processes is different which is a result of the different extent of the hydrolysis reactions of the triglycerides that take place during the extraction. Acetone extraction being the longest process provides more time for the hydrolysis of the extracted fat leached to a higher free fatty acid content. The immiscibility of glycerin formed with acetone also contributes to a greater extent of fat hydrolysis. A new sentence, below Table 2, was added regarding the explanation of the different acidities of the extracted fats.

10. At note listed in Table 2, 15% moisture in BW. More explanation is required for the 15% that is 30 fat yield including moisture content of 15%? If yes, must show percent fat after completed oven processing to eliminate water in fat.

The fat was used in the methanolysis reaction without removing the moisture.

11. Final FAME yield should be confirmed with GC method which was standard analysis method to check purity of ester.

Quantification of FAME using FTIR is a widely used technique and is already available to determine FAME levels in an industrial environment. In any case, the biodiesel produced was not purified and therefore it makes no sense to use the standardized technique (EN14214) as the objective of the work is to compare FAME yields obtained by transesterification of beef tallow submitted to different extraction processes. The calibration curve used for the determination of FAME allows us to have confidence in the values determined.

12. Authors need to put a table to describe the composition of raw materials, final products and residues after the methanolysis process with different extraction conditions such as triglyceride, diglyceride, monoglyceride, FFA, ester. 

The authors do not consider that the exhaustive characterization of the extracted fats contributes positively to the evaluation of the viability of the different fat extraction processes. The objective of the work is to evaluate the energy consumption of the different rendering processes used, taking into account that the extracted fat must have good behavior in the methanolysis reaction. Thus, only the fat acidity and water content are relevant properties. Furthermore, the laboratory budget is too short to pay for analysis to fill tables.

13. Should discuss the analysis of the fat extraction condition with varying approaches as mentioned as shown in Figure 4 (for example, 50%boiling tallow+ acetone and 50% MW tallow+acetone) before methanolysis to match the main title of this study. (…MW versus BW and AE). Need more discussion for comparison of various extraction methods.

The authors consider that the discussion presented is adequate to the data presented. We're sorry but we don't have any more data.

14. The condition of methanolysis (methanol/oil=12 molar ratio; Wcat/Woil=5%; 2.5h reaction time) is fixed. This condition is obtained from some reference, or how come? 

The reaction conditions used are the standard ones used in the methanolysis of oils using calcium catalysts. A bibliographic reference was added in the experimental section.

15. The author compared the FAME yield results with the methanolysis of soybean oil. The results of this study did not meet the standard (over 96.5% STD for purity of methyl ester). Can you explain some reason or excuse for this issue?

The characterized biodiesel samples were not purified so they do not meet the standard for FAME content (96.5% by mass, EN14214). Even so, a longer reaction time could have been used to obtain a higher yield of FAME.

16. A few recommendations must be given for further studies beyond the microwave-assisted approach in the concluding session.

As suggested by the Reviewer, recommendations on future work have been included at the end of the results and discussion section.

 

 

Author Response File: Author Response.docx

Reviewer 2 Report

Manuscript ID processes-1647736 entitled “Rendering of Beef Tallow for Biodiesel Production. Microwave versus Boiling Water and Acetone Fat Extraction” presents an valuable topic that may be of interest to readers. However, in its current form, the manuscript does not meet the standards of scientific work. In my opinion, it can be accepted after deep corrections. Some of my remarks below:

1. Abstract: no enough result can be found in abstract, and the description of research background occupy large portion of this part. Graphical abstract will be very useful for readers to understand Authors intentions.
2. The authors must underline the major findings of their work and explain novelty of this study comparatively with their published papers or other similar studies.
3. Please take into account the research hypotheses that were formulated and that were verified.
4. Due to the fact that the heating method is one of the most important elements studied and analyzed in the manuscript, in my opinion, more information on the characteristics of microwave radiation and its application in renewable energy technologies should be provided. Devoting one sentence is definitely not enough and does not allow the reader to judge the legitimacy of using microwave radiation. It is imperative to expand this paragraph: Until now, microwave radiation has been used for the depolymerization of biomass before the methane fermentation process [https://doi.org/10.3390/app11157067, 1016/j.biombioe.2019.105324], lipid recovery from microalgae biomass [https://doi.org/10.3390/pr9020369] and other organic substrates, including waste [https://doi.org/10.3390/bioengineering4020057]. The research conducted so far has proven that microwave radiation can be a justified method of ensuring appropriate thermal conditions in fermentation bioreactors [https://doi.org/10.3390/pr10010045]. This is in many cases economically justified and allows for higher, final technological effects [https://doi.org/10.3390/fermentation7010012].
5. The methodology is unclear. There is no clear division of experiments into stages, variants and series. The analytical procedures are very briefly described. There is no exact physical and chemical characteristics of the biomass used: beef tallow and soybean. Needs to be completed.
6. An organizational chart of the research conducted would be very helpful in understanding the Authors' intentions.
7. There is no indication of the type of devices, analytical equipment, models, producers and countries of origin used. It needs to be completed.
8. The greatest weakness of the manuscript is the lack of a properly conducted statistical analysis of the research results. Without a comparative analysis, the results and conclusions are unreliable, with no scientific value. What statistical tests were used to assess the significance of differences between the variables, what level of probability or significance was used, what post-hoc tests were used. This has to be completed and the results of the static analysis are given in the tables.
9. The Authors do not even provide standard deviations, and the results are based on averages, which gives no information about the scatter of the results. This also needs to be completed.
10. Lack of information on the number of replicates of the study.
11. The data was presented in a too simple way in the text. Depth discussion is necessary. The discussion of the results is very poor, it can be said that it does not exist at all. This has to be extended significantly. Please compare the obtained results with the works of other authors.
12. Economic analysis of the process and perform energy balance is absolutely necessary.
13. The Conclusion must be revised. The main results must be presented in this section.
14. The paper was written in standard, but correction English is necessary. The size of the article is to short to the contents.
15. The manuscript adheres to the journal's standards after major revision.

Author Response

Comments and Suggestions for Authors

Manuscript ID processes-1647736 entitled “Rendering of Beef Tallow for Biodiesel Production. Microwave versus Boiling Water and Acetone Fat Extraction” presents an valuable topic that may be of interest to readers. However, in its current form, the manuscript does not meet the standards of scientific work. In my opinion, it can be accepted after deep corrections. Some of my remarks below:

1. Abstract: no enough result can be found in abstract, and the description of research background occupy large portion of this part. Graphical abstract will be very useful for readers to understand Authors intentions.

 

In the authors' opinion, the most important results are already in the abstract when it is said that the fats extracted by different methods behave similarly in the production of biodiesel. Considering the Reviewer's comment, data on FAME yields were included in the abstract.A graphical abstract is now provided.

 

2. The authors must underline the major findings of their work and explain novelty of this study comparatively with their published papers or other similar studies.

 

3. Please take into account the research hypotheses that were formulated and that were verified.

The goal that the authors set themselves was the production of biodiesel by methanolysis of tallow with heterogeneous basic calcium catalysts. The results show that this objective was met.

 

4. Due to the fact that the heating method is one of the most important elements studied and analyzed in the manuscript, in my opinion, more information on the characteristics of microwave radiation and its application in renewable energy technologies should be provided. Devoting one sentence is definitely not enough and does not allow the reader to judge the legitimacy of using microwave radiation. It is imperative to expand this paragraph: Until now, microwave radiation has been used for the depolymerization of biomass before the methane fermentation process [https://doi.org/10.3390/app11157067, 1016/j.biombioe.2019.105324], lipid recovery from microalgae biomass [https://doi.org/10.3390/pr9020369] and other organic substrates, including waste [https://doi.org/10.3390/bioengineering4020057]. The research conducted so far has proven that microwave radiation can be a justified method of ensuring appropriate thermal conditions in fermentation bioreactors [https://doi.org/10.3390/pr10010045]. This is in many cases economically justified and allows for higher, final technological effects [https://doi.org/10.3390/fermentation7010012].

 

The suggested papers were included in the introduction section by referring them in a new sentence.

5. The methodology is unclear. There is no clear division of experiments into stages, variants and series. The analytical procedures are very briefly described. There is no exact physical and chemical characteristics of the biomass used: beef tallow and soybean. Needs to be completed.

The structure of the manuscript always reflects the authors' choices. The authors chose not to describe in detail the analytical techniques used because they are widely described in other publications and because a manuscript that is too long is not attractive for other researchers to read. Bibliographic references are provided so that the reader interested in the details of the techniques can consult the publication where those details are described.

6. An organizational chart of the research conducted would be very helpful in understanding the Authors' intentions.

As suggested a flowchart for the experimental procedures was included in the experimental section.

7. There is no indication of the type of devices, analytical equipment, models, producers and countries of origin used. It needs to be completed.

 

For fair market reasons, the data included in the manuscript regarding the equipment used are strictly necessary.

 

8. The greatest weakness of the manuscript is the lack of a properly conducted statistical analysis of the research results. Without a comparative analysis, the results and conclusions are unreliable, with no scientific value. What statistical tests were used to assess the significance of differences between the variables, what level of probability or significance was used, what post-hoc tests were used. This has to be completed and the results of the static analysis are given in the tables.

The catalytic tests reproducibility was evaluated and error bars were included in Fig. 8. For fat extraction tests the reproducibility was evaluated by replicating 3 times each extraction batch.

 

9. The Authors do not even provide standard deviations, and the results are based on averages, which gives no information about the scatter of the results. This also needs to be completed.

 

As suggested error bars were included in the FAME yield graphic and the experimental section was amended to include the description of the reproducibility tests.

 

10. Lack of information on the number of replicates of the study.

As suggested data on the reproducibility of catalytic tests were included in the revised manuscript.

11. The data was presented in a too simple way in the text. Depth discussion is necessary. The discussion of the results is very poor, it can be said that it does not exist at all. This has to be extended significantly. Please compare the obtained results with the works of other authors.
12. The data obtained were already compared with data from the literature, but as suggested by the Reviewer, more data from the literature were included for comparison (Table 3, new). Economic analysis of the process and perform energy balance is absolutely necessary.

The authors are working on a life cycle analysis (LCA) study for the production of biodiesel from low-value materials including animal fat extracted by different methods. This study together with the economic evaluation cannot be included in this manuscript.

13. The Conclusion must be revised. The main results must be presented in this section.

Taking into account the Reviewer comment the conclusion section was rewritten and data on FAME yields were included.

 

14. The paper was written in standard, but correction English is necessary. The size of the article is to short to the contents.

As suggested the manuscript language was revised

 

15. The manuscript adheres to the journal's standards after major revision.

 

Round 2

Reviewer 1 Report

Author have revised the manuscript satisfactorily and the quality has improved. 

Reviewer 2 Report

Thanks a lot for improving manuscript. In my opinion in can be publish in current form.