Optimization of the Production of Enzymatic Biodiesel from Residual Babassu Oil (Orbignya sp.) via RSM

Round 1

Reviewer 1 Report

This manuscript describes the biodiesel production from residual babassu oil through enzymatic esterification catalyzed by Novozyme®435. A highest yield of 96.84% was obtained under optimal conditions. The biodiesel properties were analyzed and showed reasonable agreement with the specifications of the European standard 498 EN 14214 and ASTM D6751. As the authors claim, this implies that the free fatty acids of the residual babassu oil can be a promising raw material for the production of biodiesel. Therefore, I recommend the publication of this manuscript. However, the following point should be clarified before publication.

The ratio between the bands at 1732 cm-1 and 1654 cm-1 in the IR spectrum after reaction significantly decreased than that of Novozyme®435 (2.678 and 3.663, Figure 5). However, the SEM and elemental analyses (Figure 6 and Table 8) did not show any significant change after reaction. The authors should discuss why such different results were obtained, depending on the analytical characterization.

Author Response

We would like to thank the reviewers for their important and constructive critics that allowed us to greatly improve the scientific quality of our work. Here are the answers to their questioning. The language has been carefully revised and corrected; however, due to a large number of corrections, they have not been highlighted to make it easier for the editor and reviewers to read. The figure's quality has been improved, and the title of the paper has been changed to suit the work proposal. All modifications were marked in yellow in the revised manuscript version.

1. The ratio between the bands at 1732 cm-1 and 1654 cm-1 in the IR spectrum after reaction significantly decreased than that of Novozyme®435 (2.678 and 3.663, Figure 5). However, the SEM and elemental analyses (Figure 6 and Table 8) did not show any significant change after the reaction. The authors should discuss why such different results were obtained, depending on the analytical characterization.

Answer: Thank you for your comments and contributions. The following paragraph was added to the results and discussions.

FTIR is one of the most powerful techniques of molecular analyses for material characterization. This technique has high-sensibility and allows the identification of many functional groups. Thus, since Novozyme® 435 is formed by immobilization of the Candida Antarctica lipase B adsorbed on a macroporous resin composed by poly(methyl methacrylate acid) (PMMA) crosslinked with divinylbenzene (DVB), it is possible to use the FTIR as a tool to the identification of subtle change in this materials. Besides, this technique is based on the analysis of a certain amount of materials, usually in the milligram range. SEM and elementary analysis from the EDS spectrum are usually obtained through the upper few micrometers of the sample. That is, it is not a bulk analysis technique. However, these techniques provide information on a small area of the sample, since the measurement is being carried on the surface of a single particle, or in a small set of particles.

Reviewer 2 Report

1. The thesis contained in the title ("...as a lo-cost raw material for biodiesel production.....") has not been proved in the text. Please add information about the cost of this process (the cost of biomass, the cost of the catalyst, the cost of the process).
2. Table 1 should be improved - some columns should be rejected because contained the same information in all rows (Lipase - Novozyme 435; Reaction - transesterification; Application - Biodiesel synthesis); maybe it would be better to put this information in the table title.
3. Combine Tables 3 and 4 in the one Table
4. Line 131, line 146 - Table 4 (not 3)?
5. Table 5 is illegible as well as the text describing the results it contains
6. The manuscript contains a huge amount of results that are not described successively, which is why it is difficult to analyze them. It would definitely make it easier to place a schematic and more accurately write conclusions.
7. The present version of this manuscript is written carelessly and need linguistic and editorial correction. English of this manuscript is very poor and because of this, it is very hard to read it. Please look once again through the manuscript and correct all editorial errors (misprints, mistakes, and format).

Author Response

We would like to thank the reviewers for their important and constructive critics that allowed us to greatly improve the scientific quality of our work. Here are the answers to their questioning. The language has been carefully revised and corrected; however, due to a large number of corrections, they have not been highlighted to make it easier for the editor and reviewers to read. The figure's quality has been improved, and the title of the paper has been changed to suit the work proposal. All modifications were marked in yellow in the revised manuscript version.

1. The thesis contained in the title ("...as a low-cost raw material for biodiesel production.,.") has not been proved in the text. Please add information about the cost of this process (the cost of biomass, the cost of the catalyst, the cost of the process).

Answer: Thank you for your comments and contributions. The paragraph below was added to the introduction of the paper, seeking to include the economic aspects. However, the focus of the work is on the production of biodiesel using a residual raw material used for enzymatic catalysis.

Cost reduction in biodiesel production has been a major challenge for more than 20 years. With this, efforts have been made to enable the use of a wide range of raw materials, to optimize processes, and to investigate more efficient catalysts. This caused a search for low-cost alternatives, raw materials from a non-edible resource. Some factors that directly affect the economic viability of biodiesel production are the cost of the raw material and the sales value of the biodiesel produced. Raw material cost is one of the most important parameters in biodiesel production, it corresponds to 80% of the total production cost. According to Baskar and Aiswarya (2016), raw material and the type of biocatalyst are the most important factors for the efficient production of biodiesel. Heterogeneous catalysts have been used as an effective substitute for reactions using homogeneous catalysts. Heterogeneous catalysts such as enzymes are used as a new method in the purification and production of biodiesel, to obtain greater conversions, to reuse the catalyst in consecutive cycles, to produce products with high added value and to achieve higher yields in relation to the processes catalyzed by chemicals.

2. Table 1 should be improved - some columns should be rejected because contained the same information in all rows (Lipase - Novozyme 435; Reaction - transesterification; Application - Biodiesel synthesis); maybe it would be better to put this information in the table title.

Answer: Thank you for your comments and contributions. The table was redone following the recommendations indicated, the changes are highlighted in yellow in the revised manuscript.

3. Combine Tables 3 and 4 in the one Table.

Answer: Thank you for your comments and contributions. The tables were combined following the recommendations, the changes are highlighted in yellow in the revised manuscript.

4. Line 131, line 146 - Table 4 (not 3)?

Answer: Thank you for your comments and contributions. The error has been fixed, the changes are highlighted in yellow in the revised manuscript.

5. Table 5 is illegible as well as the text describing the results it contains

Answer: Thank you for your comments and contributions. The table was edited following the recommendations and the text describing it was rewritten, the changes are highlighted in yellow in the revised manuscript.

6. The manuscript contains a huge amount of results that are not described successively, which is why it is difficult to analyze them. It would definitely make it easier to place a schematic and more accurately write conclusions.

Answer: Thank you for your comments and contributions. The outline was attached before the results and discussions. And the results and discussions were reviewed, organized and rewritten, following the recommendations, the changes are highlighted in yellow in the revised manuscript.

7. The present version of this manuscript is written carelessly and need linguistic and editorial correction. English of this manuscript is very poor and because of this, it is very hard to read it. Please look once again through the manuscript and correct all editorial errors (misprints, mistakes, and format).

Answer: Thank you for your comments and contributions. The language was carefully revised and corrected, however, due to a large number of corrections, these corrections were not highlighted to facilitate the reading of the editor and reviewers.