Catalytic Biolubricant Production from Canola Oil Through Double Transesterification with Methanol and Neopentyl Glycol

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Manuscript ID: catalysts-3256101

Title: Catalytic Biolubricant Production from Canola Oil through Double Transesterification with Methanol and Neopentyl Glycol

 

The authors firstly studied the trans-esterification reaction of canola oil to give fatty acids methyl esters (FAMEs), namely biodiesel, and, after that, the second trans-esterification reaction of FAMEs in the presence of neopentyl glycol (NPG) to give a bio-based lubricant.

In the first trans-esterification reaction, sodium methoxide was used as a homogeneous catalyst while in the second trans-esterification reaction three different catalysts were used and compared: sodium methoxide, p-toluensulfonic acid and titanium isopropoxide. After the selection of the most efficient catalyst, namely sodium methoxide, the authors investigated the effect of the temperature, catalyst amount and FAMEs/NPG molar ratio on the conversion of biodiesel.

The paper is clearly readable, the results are quite interesting, and the topic fits well into the journal Catalysts. However, the manuscript needs a major revision before it can be accepted for publication. As follows:

 

Major comments:

1.     The authors should better emphasise the innovative aspects of the present work in the manuscript (in particular in the Introduction and Conclusion sections) because both the raw material, the selected homogeneous catalysts and the synthesised biolubricant are not new.

2.     In the Introduction section (in particular, in Paragraph 1.2), the authors must also mention the new generation and promising source of oil and biodiesel represented by microbial oil obtained from oleaginous microorganisms through fermentation of biomass-derived sugars as recently reported in the following literature studies: https://doi.org/10.1016/j.cattod.2024.114941, https://doi.org/10.3390/catal11111291.

3.     In the Introduction section, the authors should mention and discuss the alternative catalytic approach for obtaining the same lubricant based on the first hydrolysis reaction of canola oil to give free fatty acids and their following catalytic esterification in the presence of NPG. The authors should emphasise the main advantages and disadvantages of this last approach with respect to the double trans-esterification approach proposed in the present work.

4.     Line 123: the authors should reformulate Table 2 by removing the column relating to the authors' names and inserting several columns relating to the type of product obtained, the reagents used (and their molar ratio), the temperature adopted, the reaction time, the type and quantity of catalyst, the oil conversion, the lubricant yield, and finally reference to the different literature studies.

5.     Lines 248-250: the authors should explain why they chose this alcohol (NPG). Is it fossil-based or can it be derived from organic sources? What are the main advantages of NPG with respect to other commercial glycols for the production of biolubricants?

6.     Lines 248-253: the three selected homogeneous catalysts are not innovative...the authors should better explain the reasons for the choice of these catalysts and their main advantages.

7.     In Figure 6 the conversion of FAMEs is reported. Is the conversion value the same for each type of FAME? The authors should better discuss this aspect.

8.     The comparison of the results achieved in the present study with respect to those reported in the literature for the valorisation of canola oil to give biolubricants should be better discussed by the authors.

9.     For the catalytic tests shown in Figure 6, the temperature was 100 °C and the catalyst loading was 1.0 %wt/wt. After the preliminary screening of the three selected catalysts, sodium methoxide was selected for further investigation of the effect of the NPG/FAME molar ratio. However, for the tests shown in Figure 7, i.e. those carried out at different molar ratios, the temperature and the catalyst loading were also modified to 120 °C and 0.25 %wt/wt, respectively. Why did the authors change 3 different reaction parameters at the same time if they decided to use an OVAT (one-variable-at-a-time) approach?

10.  What is the fate of the homogeneous catalyst? How is possible to separate it from the product?

11.  The authors should estimate the cost of the biolubricant produced from canola oil and compare it with the cost of other bio-based and fossil-based commercial lubricants.

Minor comments:

1.     Line 42: revise “food w”.

2.     Lines 57-59: revise “…react with methanol (also, methanol can be used for this purpose) to…” because it is not clear.

3.     Lines 66-67: the authors should place Figures 2 and 3 immediately after mentioning them in the text in order to facilitate understanding of the concepts described.

4.     Line 112: replace “lipases” with “immobilised lipases” because the authors mentioned the heterogeneous catalysis. Free lipases represent a homogeneous catalytic approach.

5.     Line 117: add the full name of the neopentyl glycol before the acronym (NPG).

6.     Line 117: avoid the use of a table for the description of only 2 patents. The information described in Table 1 can be discussed in the text.

7.     Table 1: Thermomyces lanuginosus must be written in italics as it is the name of a fungus species.

8.     Line 149: the authors should add the coordinates of the plantation.

9.     In line 151, the authors refer to the acidity test but the latter is not described in the Materials and Methods section. The authors should add a description of the method used.

10.  Lines 160-166: the amount of oil used in the first trans-esterification reaction should be added.

11.  Section 2.3: the authors should include a description of the quantities of reagents used, the temperature and time ranges, and the type and quantity of catalysts investigated.

12.  Lines 196-199: the authors should describe in detail the work-up procedure to recover and purify the synthesised biolubricant.

13.  In the Materials and Methods section the authors should include all equations used in their study, such as the formula for calculating the conversion of each reaction.

14.  Lines 203-204: include a brief description of each method used in the study. Avoid using Table 3 to describe experimental methods.

 

15.  Line 224: add a column to Table 4 showing the minimum levels required by the EU and US quality standards for biodiesel.

Comments for author File: Comments.pdf

Author Response

Dear reviewer,

First of all, thank you so much for your thorough and complete review, which has helped us (without a doubt) to improve the quality of this work. Our answers to your questions and concerns are the following: 

The authors firstly studied the trans-esterification reaction of canola oil to give fatty acids methyl esters (FAMEs), namely biodiesel, and, after that, the second trans-esterification reaction of FAMEs in the presence of neopentyl glycol (NPG) to give a bio-based lubricant.

In the first trans-esterification reaction, sodium methoxide was used as a homogeneous catalyst while in the second trans-esterification reaction three different catalysts were used and compared: sodium methoxide, p-toluensulfonic acid and titanium isopropoxide. After the selection of the most efficient catalyst, namely sodium methoxide, the authors investigated the effect of the temperature, catalyst amount and FAMEs/NPG molar ratio on the conversion of biodiesel.

The paper is clearly readable, the results are quite interesting, and the topic fits well into the journal Catalysts. However, the manuscript needs a major revision before it can be accepted for publication. As follows:

Thank you for your encouraging remarks.

 

Major comments:

1. The authors should better emphasise the innovative aspects of the present work in the manuscript (in particular in the Introduction and Conclusion sections) because both the raw material, the selected homogeneous catalysts and the synthesised biolubricant are not new.

You are right about the point that the separate use of these concepts are not innovative. Nevertheless, their combination is new, adding a new product that can widen the knowledge in biolubricant field. It should be noted that the selection of a certain vegetable oil, along with a specific alcohol in second transesterification, provides a unique product with specific viscosity and oxidation stability values, which is essential to understand its specific use in industry. We have pointed out these aspects in the introduction (Subsection 1.3.) and conclusion sections.

2. In the Introduction section (in particular, in Paragraph 1.2), the authors must also mention the new generation and promising source of oil and biodiesel represented by microbial oil obtained from oleaginous microorganisms through fermentation of biomass-derived sugars as recently reported in the following literature studies: https://doi.org/10.1016/j.cattod.2024.114941, https://doi.org/10.3390/catal11111291.

We have commented these issues, including the corresponding references.

 

3. In the Introduction section, the authors should mention and discuss the alternative catalytic approach for obtaining the same lubricant based on the first hydrolysis reaction of canola oil to give free fatty acids and their following catalytic esterification in the presence of NPG. The authors should emphasise the main advantages and disadvantages of this last approach with respect to the double trans-esterification approach proposed in the present work.

We have added this point in the introduction section. Thank you for your suggestion. There are plenty of methods to produce biolubricants, and double transesterification presents the advantage of being suitable as the basis of a biorefinery based on vegetable oils.

 

4. Line 123: the authors should reformulate Table 2 by removing the column relating to the authors' names and inserting several columns relating to the type of product obtained, the reagents used (and their molar ratio), the temperature adopted, the reaction time, the type and quantity of catalyst, the oil conversion, the lubricant yield, and finally reference to the different literature studies.

We have reformulated Table 2, adding most of the columns.

 

5. Lines 248-250: the authors should explain why they chose this alcohol (NPG). Is it fossil-based or can it be derived from organic sources? What are the main advantages of NPG with respect to other commercial glycols for the production of biolubricants?

NPG is a typical alcohol used in biolubricant production through transesterification of FAMEs, as observed in the literature. Its main advantage is that, as in the case of other alcohols, a biolubricant with a certain and specific viscosity value is obtained. These issues were explained in the final text (materials and methods section).

 

6. Lines 248-253: the three selected homogeneous catalysts are not innovative...the authors should better explain the reasons for the choice of these catalysts and their main advantages.

The reasons are their high efficiency according to the literature, along with their availability and price. As explained in the introduction section, heterogeneous catalysts would be a better option in the future, once their reusability and the conversion of the process is improved. We have explained these details in the Materials and Methods section.

 

7. In Figure 6 the conversion of FAMEs is reported. Is the conversion value the same for each type of FAME? The authors should better discuss this aspect.

Conversion of FAMEs is obtained by assessing the decrease in FAME content in the final product (compared to the original biodiesel). In general, it can be assumed that the conversion of each FAME in the mixture is similar, as the percentages of FAME profiles does not vary during the reaction (there are changes in few % units). This fact was explained in the final text.

 

8. The comparison of the results achieved in the present study with respect to those reported in the literature for the valorisation of canola oil to give biolubricants should be better discussed by the authors.

 

Further comparisons with other canola-based biolubricants has been carried out in the results and discussion section (after Table 4, changes in red).

9. For the catalytic tests shown in Figure 6, the temperature was 100 °C and the catalyst loading was 1.0 %wt/wt. After the preliminary screening of the three selected catalysts, sodium methoxide was selected for further investigation of the effect of the NPG/FAME molar ratio. However, for the tests shown in Figure 7, i.e. those carried out at different molar ratios, the temperature and the catalyst loading were also modified to 120 °C and 0.25 %wt/wt, respectively. Why did the authors change 3 different reaction parameters at the same time if they decided to use an OVAT (one-variable-at-a-time) approach?

You are right about this point. The changes were mainly due to the operating conditions in our laboratory. We chose 1 % for this first experiment due to the typical addition found in the literature. However, for MeONa, the reaction was relatively violent (provoking the collapse of the reactor, as methanol generated during second transesterification “dragged” other reagents and products from the reactor). That is the reason why we reduced catalyst addition in further experiments. We consider the catalyst selection and the rest of optimization parameters as “isolated” experiments. We have pointed out this issue in the final text.

 

10. What is the fate of the homogeneous catalyst? How is possible to separate it from the product?

The homogeneous catalyst is partially removed from the final biolubricant during the filtering process, but some traces can be retained. In this sense, other alternatives could be the use of ionic exchange columns to remove Na, as it could act as a catalyst in oxidation processes. This fact was explained in the final text.

 

11. The authors should estimate the cost of the biolubricant produced from canola oil and compare it with the cost of other bio-based and fossil-based commercial lubricants.

This is a very interesting point. However, at laboratory scale, the estimation of biolubricant production under our circumstances require further studies, including reactor design in a biorefinery context. Nevertheless, we have pointed out this fact as “further studies” in the conclusion section.

 

Minor comments:

1. Line 42: revise “food w”.

It was a typo. Sorry for the inconvenience, we have removed it from the text.

 

2. Lines 57-59: revise “…react with methanol (also, methanol can be used for this purpose) to…” because it is not clear.

We meant “ethanol” in the second case. Thank you for your observation!

 

3. Lines 66-67: the authors should place Figures 2 and 3 immediately after mentioning them in the text in order to facilitate understanding of the concepts described.

We have placed these figures according to your criteria.

 

4. Line 112: replace “lipases” with “immobilised lipases” because the authors mentioned the heterogeneous catalysis. Free lipases represent a homogeneous catalytic approach.

You are right, we have specified the term throughout the text. Thank you!

 

5. Line 117: add the full name of the neopentyl glycol before the acronym (NPG).

In this part of the text, the full name is included, maybe you mean to add the acronym, which we have done.

 

6. Line 117: avoid the use of a table for the description of only 2 patents. The information described in Table 1 can be discussed in the text.

We have removed Table 1, adding the information in the text.

 

7. Table 1: Thermomyces lanuginosusmust be written in italics as it is the name of a fungus species.

You are right, thank you! We have made the change.

 

8. Line 149: the authors should add the coordinates of the plantation.

The coordinates of the plantation were the following:

38°51'10.0"N 6°40'15.1"W

We have added this information in the final text.

 

9. In line 151, the authors refer to the acidity test but the latter is not described in the Materials and Methods section. The authors should add a description of the method used.

In reality, it was the acid number test, explained in the materials and methods. We have clarified this point, referring to this procedure.

 

10. Lines 160-166: the amount of oil used in the first trans-esterification reaction should be added.

The amount of oil was added (150 g for each specific experiment).

 

11. Section 2.3: the authors should include a description of the quantities of reagents used, the temperature and time ranges, and the type and quantity of catalysts investigated.

These details have been added to the final text.

 

12. Lines 196-199: the authors should describe in detail the work-up procedure to recover and purify the synthesised biolubricant.

We have added more details about this aspect (changes in red).

 

13. In the Materials and Methods section the authors should include all equations used in their study, such as the formula for calculating the conversion of each reaction.

We have added the conversion formula in Equation 1.

 

14. Lines 203-204: include a brief description of each method used in the study. Avoid using Table 3 to describe experimental methods.

More details about the methods included in Table 2 have been added to the final text (after this table).

 

15. Line 224: add a column to Table 4 showing the minimum levels required by the EU and US quality standards for biodiesel.

Two columns were added: for lower and upper limits of the UNE-EN 14214 standard.

 

Again, thank you so much for your help and sincerely,

Dr. Sergio Nogales Delgado.

Reviewer 2 Report

Comments and Suggestions for Authors

The current work reports an interesting process for catalytic biolubricant production from canola oil through double transesterification with methanol and neopentyl Glycol. To enhance the clarity of this work, I propose to consider the following items:

 

1.       Page 1, line 43, check typo “food w”.

2.       I suggest to add the expression “double transesterification” to the keywords of this manuscript

3.       Page 4, line 316, when writing about the advantages and disadvantages of using lipases, kindly place a reference. I suggest the following references to be added “Has the time finally come for green oleochemicals and biodiesel production using large-scale enzyme technologies? Current status and new developments”, “Lipase catalyzed reactions: a promising approach for clean synthesis of oleochemicals”.

4.       Section 2.1., please mention the address of the oil provider. Also please mention the purity of the used alcohols, the provider, and its address.

5.       Sections 2.2 and 2.3: It would be very nice to the reader if you include a schematic diagram that illustrates the entire process of double transesterification.

6.       Please explain the developed the authors done in this study compared to their previous publications in the same area, REF 25, and 26.

7.       Materials and methods, the authors should write the details of GC analysis like GC specifications, derivatization method, oven, FID,…etc.

8.       Conclusion should be fed by the results obtained in this study.

9.       Please add 2024 references to your reference list.

Author Response

Dear reviewer,

Firstly, thank you for your review, which has clearly contributed to the improvement of the quality of this work. Our replies to your comments are the following:

The current work reports an interesting process for catalytic biolubricant production from canola oil through double transesterification with methanol and neopentyl Glycol. To enhance the clarity of this work, I propose to consider the following items:

 

1. Page 1, line 43, check typo “food w”.

It was corrected and removed, thank you!

 

2. I suggest to add the expression “double transesterification” to the keywords of this manuscript.

The term was added to the keywords.

 

3. Page 4, line 316, when writing about the advantages and disadvantages of using lipases, kindly place a reference. I suggest the following references to be added “Has the time finally come for green oleochemicals and biodiesel production using large-scale enzyme technologies? Current status and new developments”, “Lipase catalyzed reactions: a promising approach for clean synthesis of oleochemicals”.

The references were added. Thank you for the suggestion.

 

4. Section 2.1., please mention the address of the oil provider. Also please mention the purity of the used alcohols, the provider, and its address.

The location of the oil provider was given (Guadajira, Badajoz, Spain).

 

5. Sections 2.2 and 2.3: It would be very nice to the reader if you include a schematic diagram that illustrates the entire process of double transesterification.

A schematic diagram about the process was added, pointing out the biorefinery context.

 

6. Please explain the developed the authors done in this study compared to their previous publications in the same area, REF 25, and 26.

Compared to these studies, this work provides further information about a new biolubricant, which is obtrained through double transesterification with methanol and NPG. In this sense, the possibilities of combinations are practically endless, as different vegetable oils can be used with different alcohols to obtain biolubricants with variable viscosity and oxidation stability values. We have specified this point in the final text (Section 2).

 

7. Materials and methods, the authors should write the details of GC analysis like GC specifications, derivatization method, oven, FID,…etc.

GC details were added in the corresponding table. No derivatization methods were used once FAMEs were produced.

 

8. Conclusion should be fed by the results obtained in this study.

We have added specific results to the conclusion section.

 

9. Please add 2024 references to your reference list.

We have added recent references (2024) throughout the text.

 

Again, thank you for your review and attention. Sincerely,

Dr. Sergio Nogales Delgado.

Reviewer 3 Report

Comments and Suggestions for Authors

In the presented manuscript, the authors describe biolubricant production from canola oil by using double-transesterification homogeneous catalytic processes. The reaction conditions were optimized in the second stage of transesterification by changing various parameters, e.g., the catalyst concentration, the type of catalyst used, temperature, and reactant ratios. Both the Biodiesel and the biolubricant were characterized. As explained in the introduction part, there are economic and environmental interests in developing efficient methods for biodiesel and biolubricant production; therefore, the study is of importance. However, before acceptance of this paper, some issues need to be considered. Please see the comments below.

1)      The information in Tables 1 and 2,  does not explain the motivation for the specific research with the specific catalyst and alcohols used. The choice of the specific system is not explained enough. The authors describe in the introduction the advantages of heterogeneous catalysis – and the challenges that still exist in these systems, mainly in the low reusability and low reaction time. Why did they choose to use a homogeneous catalyst?  In section 1.3 they write “ showing innovative approach that could expand...” What is the innovative approach? Also, they mention in the same paragraph that the specific study of lubricant production from canola oil by using double transesterification with methanol and neopentylglycol has not been widely studied in the literature- were they able to obtain better results in their system? 

2)      Some specific comments:

Line 17-  the words: “As a result”  should be erased.

Lines 41-42 – or food w – should be erased.

Please correct the sentence in line 58: “react with methanol (also, methanol  can be used for this purpose)  

Lines 106-107 – “conversion values and reaction times are normally longer compared to the use of homogeneous catalysts” should be changed to “conversion values are low and reaction times are normally longer compared to the use of homogeneous catalysts”,

Line 108: “these homogeneous catalysts” - should be changed to heterogeneous catalysts

In lines 313-314, the sentence “ Thus, once the lubricant was purified through filtration, the main characteristics of the final product were included in Table 5” should be rephrased.

3)      In different places in the text, the authors used the word experience instead of experiment.

4) In line 312 – the authors summarize the optimal reaction condition. Based on Figures 9 and 10. It is not clear why they concluded that 120^oC is the optimal temperature

Comments on the Quality of English Language

English editing is recommended for this manuscript

Author Response

Dear reviewer,

Thank you for your time and attention to accomplish this review. Your comments and prospects have helped us to improve the quality of this work. Our replies to your requirements are the following:

In the presented manuscript, the authors describe biolubricant production from canola oil by using double-transesterification homogeneous catalytic processes. The reaction conditions were optimized in the second stage of transesterification by changing various parameters, e.g., the catalyst concentration, the type of catalyst used, temperature, and reactant ratios. Both the Biodiesel and the biolubricant were characterized. As explained in the introduction part, there are economic and environmental interests in developing efficient methods for biodiesel and biolubricant production; therefore, the study is of importance. However, before acceptance of this paper, some issues need to be considered. Please see the comments below.

Thank you for the encouraging words and analysis of our article.

 

• The information in Tables 1 and 2,  does not explain the motivation for the specific research with the specific catalyst and alcohols used. The choice of the specific system is not explained enough. The authors describe in the introduction the advantages of heterogeneous catalysis – and the challenges that still exist in these systems, mainly in the low reusability and low reaction time. Why did they choose to use a homogeneous catalyst?  In section 1.3 they write “ showing innovative approach that could expand...” What is the innovative approach? Also, they mention in the same paragraph that the specific study of lubricant production from canola oil by using double transesterification with methanol and neopentylglycol has not been widely studied in the literature- were they able to obtain better results in their system? 

Interesting questions and remarks. Tables 1 and 2 are presented as a support of the use of NPG in biolubricant synthesis. The motivation of this work was to apply canola oil to produce biolubricants through double transesterification with methanol and NPG, in order to provide a product based on a new feedstock (or, at least, not widely covered in the literature). We have chosen homogeneous catalysts due to the high conversion that can be obtained compared to heterogeneous ones. In any case, further studies could include the use of innovative and improved heterogeneous catalysts (we have added this point in the conclusion section). To the best of our knowledge, there are not specific works about the specific product obtained in this work, after a new search in our search engines.

 

2)      Some specific comments:

Line 17-  the words: “As a result”  should be erased.

We have removed this expression in the abstract.

 

Lines 41-42 – or food w – should be erased.

We have removed this typo. Sorry for the inconvenience.

 

Please correct the sentence in line 58: “react with methanol (also, methanol  can be used for this purpose)  

We have corrected this sentence. We meant “ethanol” in the second case.

 

Lines 106-107 – “conversion values and reaction times are normally longer compared to the use of homogeneous catalysts” should be changed to “conversion values are low and reaction times are normally longer compared to the use of homogeneous catalysts”,

The change has been made. Thank you, as the sentence is clear now.

 

Line 108: “these homogeneous catalysts” - should be changed to heterogeneous catalysts

You are right, thank you for the suggestion!

 

In lines 313-314, the sentence “ Thus, once the lubricant was purified through filtration, the main characteristics of the final product were included in Table 5” should be rephrased.

This sentence has been rephrased to clarify the main idea.

 

3) In different places in the text, the authors used the word experience instead of experiment.

We have changed the term experience for experiment or work, depending on the context.

 

4) In line 312 – the authors summarize the optimal reaction condition. Based on Figures 9 and 10. It is not clear why they concluded that 120^oC is the optimal temperature

In this case, we decided to follow efficiency factors, using intermediate conditions to avoid the degradation of the sample (highly affected by temperature and Na concentration, especially regarding oxidation stability). In this sense, we wanted to assure a high conversion (exceeding 90%) without compromising quality parameters in the final product such as oxidation stability. This fact is explained in the final text.

 

Again, thank you so much for your attention and sincerely,

Dr. Sergio Nogales Delgado.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors significantly improved the quality of their paper and properly implemented the required revisions. In the present form, the manuscript can be accepted for publication.