Evaluation of Babassu Cake Generated in the Extraction of the Oil as Feedstock for Biofuel Production
, Luciana Bertini 1,3, Maria Maciel 4 and Maria Rios 1,5,*Round 1
Reviewer 1 Report
The manuscript proposed by the authors have aimed increase knowledge about new feedstock for the production of briquettes. This topic is still relatively new, so every new study potentialy makes a major contribution to this area.
According to the authors, in their study, babassu cake generated in the oil extraction was evaluated as feedstock for the production of briquettes in blends with cashew nutshell, sugarcane bagasse, carnauba straw, and carnauba stalk. Authors evaluated the basic parameters of the basic raw material and its mixtures with other types of biomass (HHV, FC, A, VM and M). However, these are parameters that do not change during the briquetting process. Even the mixing process is not necessary here to obtain the values of the studied parameters. In this case, an analysis of the individual components of the mixtures would be sufficient. Having these data, the value of the studied parameters of the presented biomass mixtures can be obtained by calculation.
The briquetting process carried out by the authors is unnecessary in this case because the authors did not carry out any evaluation of the parameters of the briquettes obtained which depend on the pressure agglomeration process (especially the specific density and mechanical durability of the obtained briquettes). Only after obtaining such results and comparing them to the requirements of quality standards for briquettes can it be said that the studied biomass and biomass mixtures are suitable or not for briquette production. Based on the results presented in the paper, we can only say that the analyzed biomass, in terms of Energy, has the potential to be a fuel. Conversely, we cannot say anything about how it will behave during briquetting.
Returning to the results obtained, they should be given in the dry state so that they can be compared. In my opinion, the results will be more accurate if done on the components of the mixtures and not on the mixtures. The paper does not state how the material for analysis was prepared (how was the briquette homogenized before HHV and other measurements?). Błąd na tym etapie może doprowadzić do błędnych wyników. An error at this stage can lead to incorrect results. This can be indicated by the results in Table 1 and Table 2 - how to explain the differences in Ash and Fixed Carbon with unchanged HHV values between Fresh and Aged samples? In addition, how do the authors explain the decrease in HHV of the material carbonized at 350, and 400 °C with an increase in Fixed Carbon?
Summarizing, the article contains the results of a basic analysis of the studied raw materials. These results do not determine the briquette production process in any way. Thus, the goal of the research set by the authors has not been achieved. Due to that facts, article requires significant extension and thorough editing. Article is addressed to a journal of high status, so I am forced to reject the article. At the same time I encourage you to resubmit after making the necessary changes.
Author Response
We would like to thank the reviewer for the thoughtful review of the manuscript. The reviewer raises important issues, and your inputs are helpful for improving the manuscript. We respond below to each of the reviewer’s comments. Our point-by-point detailed responses are in blue and italics. Changes in the Ms text are highlighted in yellow.
We thank the reviewer for your comments and suggestions. According to the recommendation, the manuscript was rewritten to approach the fuel potential of the babassu cake and other biomasses. All words and comments about the briquetting process were substituted by solid fuel and mechanical densification. As for the results of ash, fixed carbon, and HHV for the fresh and aged samples, the differences occur probably by changes in the maturation stages, as included in the Discussion section. About the decrease in HHV in the material carbonized at 350 and 400 °C, despite the increase in Fixed Carbon, the ash content also increase, and this parameter decreases the calorific value and damages the apparent heat obtained from burning biomass once the energy needed by ash forming inorganics, thermal breakdown, and phase transition is taken from the burning of biomass, and it leads to a reduction of the calorific value. The explanation was revised in the new version of the manuscript. Thus, considering all revisions realized in the manuscript, I would like to request reconsideration of the revised manuscript.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The article "Evaluation of babassu cake generated in the extraction of the oil as feedstock for biofuel production" provides relevant material on the use of agricultural waste for biofuel production. Studies carried out to investigate the energy properties of biofuel and to solve environmental problems are detailed.
Observations:
1. Many parameters have been determined by scientific research, however some tests are done with two repetitions only. Are two experiment repetitions sufficient for reliable results?
2. The article does not provide the additional costs of storing the biomass for 90 additional days, nor the required conditions to prevent storage losses.
3. The increase of oil yield from matured (90 days) kernels compared to fresh kernels should be explained in more detail.
4. It is not clear whether the data presented in the sixth figure is statistically reliable as the error values of the obtained results are not presented.
5. Is it appropriate to use all waste to produce biofuel? Maybe it would be appropriate to use some of it as biological fertilizer for growing biomass?
Author Response
We would like to thank the reviewer for the thoughtful review of the manuscript. The reviewer raises important issues, and your inputs are helpful for improving the manuscript. We respond below to each of the reviewer’s comments. Our point-by-point detailed responses are in blue and italics. Changes in the Ms text are highlighted in yellow.
- Many parameters have been determined by scientific research, however some tests are done with two repetitions only. Are two experiment repetitions sufficient for reliable results?
R.: We thank the reviewer for this question. In our study, only the results shown in Table 4 were executed in duplicate. Everyone else experiments were carried out in quadruplicate. As they are the same samples, we did only this characterization (Table 4) in duplicate.
- The article does not provide the additional costs of storing the biomass for 90 additional days, nor the required conditions to prevent storage losses.
R.: We thank the reviewer for this question. The biomasses were ground, sieved, and stored in plastic bags to prevent storage losses. They were stored at room temperature in a covered storage shed next to the laboratory. The additional costs would be only for the plastic bags.
- The increase of oil yield from matured (90 days) kernels compared to fresh kernels should be explained in more detail.
R.: We thank the reviewer for this suggestion. The increase in oil yield from matured kernels was explained in more detail.
- It is not clear whether the data presented in the sixth figure is statistically reliable as the error values of the obtained results are not presented.
R.: We thank the reviewer for this suggestion. The error values of the results were included.
- Is it appropriate to use all waste to produce biofuel? Maybe it would be appropriate to use some of it as biological fertilizer for growing biomass?
R.: We agree with the reviewer. Indeed, waste biomass can be applied in other areas, for example, as fertilizers for growing biomass.
Author Response File: Author Response.docx
Reviewer 3 Report
Comments to Rios et al
Summary
The proposed article deals with the prospects of employing babassu cake obtained during the extraction of babassu oil for biofuel production. The authors conducted proximate analysis and determined the Higher Heating Value for babassu before and after the oil extraction as well as after carbonization. Furthermore, the authors manufactured briquettes mixing babassu cake with various other agricultural residues and repeated the proximate analysis and the Higher Heating Value assessment. According to the results, the babassu biomass is at least compatible with other biomasses.
General comments
The study, in considering a bioprocess byproduct as source of energy, is relevant for the scope of the processes journal. Moreover, the manuscript contains the customary sections of a scientific article. In addition, the scientific contribution, while perhaps not revolutionary, appears to be novel and solid. As for English language, it is generally at an acceptable level, but the manuscript would improve from an additional language check to eliminate occasional unidiomatic syntax. A bigger problem is however the structure of the text with some repetitiveness and lack of story line. The focus should be more on transmitting the message to the readers in a coherent comprehensible manner than on prolonging the text.
Finally, the tables and figures are of good quality, even though the former will probably require som modification to match the recommended format of the journal.
Specific comments
Line 25: Something missing in the sentence.
Line 58: …sugarcane biomass being…
Lines 60-62: Rather long and unnecessary complicated sentence.
Line 70: If the intention in this sentence really is to employ two contrastive tenses, then better combine the simple present with the present perfect: …facilitates transportation and has solved the inconvenience…
Line 82: …can yet be regarded…
Lines 86-87: Here you would need a transition. The entire paragraph discusses general aspects of burning biomass, except for the last sentence, which suddenly goes into experimental detail. You could also save the information in the last sentence for next paragraph or next section.
Lines 92, 109, 148; Figure 2: …carbonized babassu cake.
Line 106 and elsewhere: The conjugation of grind is grind (present), ground (past), ground (past participle). Grounded, on the other hand is the past of ground – to lay on the ground, to establish.
Lines 175-176: word order.
Line 308: This use of the word once here but also elsewhere in the manuscript is a bit confusing, like if the process not yet had resulted in compounds rich in carbon, but we are hopeful that once this happens, the energy potential will increase. It is clearer to suggest that the main aim … is to increase … as solid compounds …
Lines 475-478: I struggle with the understanding of this sentence; if the oil content depends on the maturation of the fruits, the region and species, why can you then attribute different yields to the long storage period?
Line 483: What do you mean by inert effect? The expression almost sounds like an oxymoron. Perhaps the intention is to say there is a diminishing effect.
Line 556: Figure 6 presented the correlation…
Line 558: The sentence needs reformulation. Comparative (better) is for comparison of two cases. Of course, you cannot use superlative (best) either, because based on a few measurement points, you cannot conclude that the optimum would be at exactly 300°C. Try to find a subtler phrasing, telling us that the HHV increases with temperature until it reaches a maximum at approximately 300 after which it starts decreasing with temperature.
Line 565: …various proportions were used.
Line 577: …did not show significant differences…
Conclusions section: It is unnecessary to repeat details about the scope and methods in this section; it should rather focus on what were the main findings of the study. One option would be a list of bullet points comprising those findings.
References: Reference 9 lacks author and journal information.
Comments for author File: 
Comments.pdf
Author Response
We would like to thank the reviewer for the thoughtful review of the manuscript. The reviewer raises important issues, and your inputs are helpful for improving the manuscript. We respond below to each of the reviewer’s comments. Our point-by-point detailed responses are in blue and italics. Changes in the Ms text are highlighted in yellow.
General comments
The study, in considering a bioprocess byproduct as source of energy, is relevant for the scope of the processes journal. Moreover, the manuscript contains the customary sections of a scientific article. In addition, the scientific contribution, while perhaps not revolutionary, appears to be novel and solid. As for English language, it is generally at an acceptable level, but the manuscript would improve from an additional language check to eliminate occasional unidiomatic syntax. A bigger problem is however the structure of the text with some repetitiveness and lack of story line. The focus should be more on transmitting the message to the readers in a coherent comprehensible manner than on prolonging the text.
Finally, the tables and figures are of good quality, even though the former will probably require some modification to match the recommended format of the journal.
R.: We thank the reviewer for this suggestion. The text was revised according to your considerations.
Specific comments
Line 25: Something missing in the sentence.
R.: The text was rewritten.
Line 58: …sugarcane biomass being…
R.: The text was rewritten.
Lines 60-62: Rather long and unnecessary complicated sentence.
R.: The text was rewritten.
Line 70: If the intention in this sentence really is to employ two contrastive tenses, then better combine the simple present with the present perfect: …facilitates transportation and has solved the inconvenience…
R.: The text was rewritten.
Line 82: …can yet be regarded…
R.: The text was rewritten.
Lines 86-87: Here you would need a transition. The entire paragraph discusses general aspects of burning biomass, except for the last sentence, which suddenly goes into experimental detail. You could also save the information in the last sentence for next paragraph or next section.
R.: The information was included in the next paragraph.
Lines 92, 109, 148; Figure 2: …carbonized babassu cake.
R.: The word was rewritten in all text.
Line 106 and elsewhere: The conjugation of grind is grind (present), ground (past), ground (past participle). Grounded, on the other hand is the past of ground – to lay on the ground, to establish.
R.: The word was rewritten in all text.
Lines 175-176: word order.
R.: The text was rewritten.
Line 308: This use of the word once here but also elsewhere in the manuscript is a bit confusing, like if the process not yet had resulted in compounds rich in carbon, but we are hopeful that once this happens, the energy potential will increase. It is clearer to suggest that the main aim … is to increase … as solid compounds …
R.: The text was rewritten.
Lines 475-478: I struggle with the understanding of this sentence; if the oil content depends on the maturation of the fruits, the region and species, why can you then attribute different yields to the long storage period?
R.: The different yields to the long storage period were attributed to the maturation of the fruits (90 days).
Line 483: What do you mean by inert effect? The expression almost sounds like an oxymoron. Perhaps the intention is to say there is a diminishing effect.
R.: The text was rewritten.
Line 556: Figure 6 presented the correlation…
R.: The text was rewritten.
Line 558: The sentence needs reformulation. Comparative (better) is for comparison of two cases. Of course, you cannot use superlative (best) either, because based on a few measurement points, you cannot conclude that the optimum would be at exactly 300°C. Try to find a subtler phrasing, telling us that the HHV increases with temperature until it reaches a maximum at approximately 300 after which it starts decreasing with temperature.
R.: The sentence was rewritten.
Line 565: …various proportions were used.
R.: The text was rewritten.
Line 577: …did not show significant differences…
R.: The text was rewritten.
Conclusions section: It is unnecessary to repeat details about the scope and methods in this section; it should rather focus on what were the main findings of the study. One option would be a list of bullet points comprising those findings.
R.: The conclusion section was rewritten.
References: Reference 9 lacks author and journal information.
R.: The information was included.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors, as they themselves stated, replaced the „All words and comments about the briquetting process were substituted by solid fuel and mechanical densification”. However, such a substitution adds nothing to the article. The problem is that the authors performed the process of compacting the tested mixtures without any evaluation of the resulting briquettes (I am talking about the evaluation of parameters that depend on the compacting process - specific density and durability). Only after such an assessment can it be said that the tested material is suitable or not for the production of compacted solid biofuels. Thus, the part of the paper on the compaction process is redundant and does not provide anything.
As I wrote previously, Authors evaluated the basic parameters of the basic raw material and its mixtures with other types of biomass (HHV, FC, A, VM and M). However, these are parameters that do not change during the briquetting proces and even during the mixing proces. So mixing proces is also here not necessary to obtain the values of the studied parameters.
In this case, an analysis of the individual components of the mixtures would be sufficient. Having these data, the value of the studied parameters of the presented biomass mixtures can be obtained by calculation. In my opinion, the results will be more accurate if done on the components of the mixtures and not on the mixtures.
Returning to the results obtained, they should be given in the dry state so that they can be compared. The authors did not follow this suggestion.
Summarizing, the article contains the same results of a basic analysis of the studied raw materials. These results do not determine the biomass comperssion process in any way. Due to that facts, I am still forced to reject the article.
Author Response
Response to reviewer 1:
We would like to thank the reviewer for the thoughtful review of the manuscript. The reviewer raises important issues, and your inputs are helpful for improving the manuscript. We respond below to each of the reviewer’s comments. Our point-by-point detailed responses are in blue and italics. Changes in the Ms text are highlighted in turquoise.
The authors, as they themselves stated, replaced the „All words and comments about the briquetting process were substituted by solid fuel and mechanical densification”. However, such a substitution adds nothing to the article. The problem is that the authors performed the process of compacting the tested mixtures without any evaluation of the resulting briquettes (I am talking about the evaluation of parameters that depend on the compacting process - specific density and durability). Only after such an assessment can it be said that the tested material is suitable or not for the production of compacted solid biofuels. Thus, the part of the paper on the compaction process is redundant and does not provide anything.”
R.: We thank the reviewer for your comments. However, in this manuscript, we aimed to evaluate the cake generated in the extraction of the babassu oil as a possible feedstock for biofuel production. This residue has been studied for the first time. In other papers of my team residual biomasses have been characterized by specific density, energy density, and performance: "Cashew nut husk and babassu coconut husk residues: evaluation of their energetic properties”, https://doi.org/10.1080/15567036.2019.1692976; “Investigation of the potential of the carnauba stalk and of the carnauba's straw to use as biofuel”, https://doi.org/10.1590/S1517-707620190002.0690; “Blends of sugarcane bagasse with the mango tree and cashew tree's pruning: properties characterization and investigation of their energy potentials”, https://doi.org/10.1590/S1517-707620190002.0687. So, according to our previous experience and the results presented in the manuscript, we believe that the babassu cake has potential for the production of solid fuels. For this reason, we substituted all terms for solid fuel and mechanical densification. However, the suggestion of the reviewer about briquettes characterization will be used to direct our next work with babassu cake.
As I wrote previously, Authors evaluated the basic parameters of the basic raw material and its mixtures with other types of biomass (HHV, FC, A, VM and M). However, these are parameters that do not change during the briquetting proces and even during the mixing proces. So mixing proces is also here not necessary to obtain the values of the studied parameters. In this case, an analysis of the individual components of the mixtures would be sufficient. Having these data, the value of the studied parameters of the presented biomass mixtures can be obtained by calculation. In my opinion, the results will be more accurate if done on the components of the mixtures and not on the mixtures.
R.: We thank the reviewer for your suggestion and apologize for not including the information about components in the first revised version of the manuscript. In the new version, the authors included Supplementary material with six tables. Tables S5 and S6 present proximate analysis values for the cashew nutshell, sugarcane bagasse, carnauba straw, and carnauba stalk on a wet and dry basis.
Returning to the results obtained, they should be given in the dry state so that they can be compared. The authors did not follow this suggestion.
R.: We apologize for not including the results on a dry basis in the first revised version of the manuscript. In the new version, the authors substituted all results on a dry basis and presented the results on a wet basis in the Supplementary material (see Tables S1, S2, S3, and S4).
Summarizing, the article contains the same results of a basic analysis of the studied raw materials. These results do not determine the biomass comperssion process in any way. Due to that facts, I am still forced to reject the article.
R.: We greatly appreciate the reviewer for the thoughtful review of the manuscript. The raised issues and your inputs helped improve the work considerably. Given the new modifications realized in the manuscript, we ask for your reconsideration.
Author Response File: Author Response.docx
Round 3
Reviewer 1 Report
Still the article has not been significantly improved according to suggestions from previous reviews. The submitted text differs from the previous one only in the added references to Supplementary material and the adding to the tables of values converted from the analytical state ( probably) to the dry state. At the same time, the tables also contain information about the conversion of moisture content to the dry state, which is a clear error - according to the authors the moisture content of the material in the dry state is higher than the analytical moisture content. How is this possible? The moisture content of the material in the dry state is 0 and so we can compare the results of other parameters to each other. Why did the authors not convert to dry state HHV? In addition, the authors have placed in Supplementary material those results which should be in the article.
The article still includes the methodology for compacting samples and photos of the obtained agglomerates (because they are not briquettes nor pellets) and does not include the results of the parameters of these agglomerates that depend on the compaction process (specific density, mechanical durability). The part of the article about compaction should be removed because it does not contribute anything to the work.
In addition, the tables contain errors, for example, table 4 - babassu cake has 3.86% of Ash in the dry state, according to table S5 carnauba stalk has 5.87% of Ash in the wet state. After converting this result to the dry state, carnauba stalk has 6.47% of Ash therefore a 50:50 mixture of babassu cake + carnauba stalk should have 5.2% of Ash in the dry state according to calculations. In Table 4, the results for this mixture is 6.22%. If this is the result obtained from the combustion of the prepared mixture, it means that the preparation of the sample was incorrect, more than 50% of carnauba stalk was deposited in the sample.
In addition, the results are given with a very large spread, for example, according to EN-ISO 18122 maximum acceptable differences between results is 10% relative. Table S5 carnauba straw - Ash 9.77% plus or minus 3.44%? Such a result is completely untrustworthy.
Summarizing, article still requires significant corrections. So I am forced to reject the article
Author Response
Please see the attachment.
