Exploring the Potential of Biomass Pyrolysis for Renewable and Sustainable Energy Production: A Comparative Study of Corn Cob, Vine Rod, and Sunflower

Round 1

Reviewer 1 Report

This is an interesting study as we move towards renewable energy and aim to reach zero carbon emission in the upcoming future.

 

However, the number of references used (26) in this article is insufficient for a research article.

 

The author should consider increasing the number of references in the section 3 result and discussion to support their claim. The evidence is very weak at the current form.  

 

I think it is a common understanding and many research papers already showed that plant materials such as corn cob, vine rod and sunflower, and even algae can be used as a biofuel.

 

What are the innovative findings of this research? The authors must justify their innovations before the paper maybe published. This maybe a good technical report but not reaching the level required by a scientific article.

The citation format is incorrect. Please follow the MDPI journal format. Some spelling and grammar mistakes were noticed which requires the author’s attention.

Author Response

This is an interesting study as we move towards renewable energy and aim to reach zero carbon emission in the upcoming future.

However, the number of references used (26) in this article is insufficient for a research article. The author should consider increasing the number of references in the section 3 result and discussion to support their claim. The evidence is very weak at the current form.  

Response: We note reviewer’s comments and agree that presenting wider range of results from biomass used for pyrolysis and comparison is needed. We have added references in all parts of the paper, including section 3, leading to a total number of 48 references.

 

I think it is a common understanding and many research papers already showed that plant materials such as corn cob, vine rod and sunflower, and even algae can be used as a biofuel.

What are the innovative findings of this research? The authors must justify their innovations before the paper may be published. This may be a good technical report but not reaching the level required by a scientific article.

Response: In response to the inquiry about the innovative findings of our research, we would like to emphasize that our study presents specific aspects that have not been thoroughly explored before. The study for the first time applies multicriteria assessment approach to compare quality of different biomass materials based on 3 criteria for the char, bio-gas and bio-oil, leading to total multicriteria score that shows the suitability of the biomass types for pyrolysis. Also, the literature typically presents analysis of 1 biomass source only, considering the scale of the experimental work required for one sample analysis, hence presenting differences of 3 biomass sources, in our view, gives an optimal number of biomass sources to demonstrate the methods for assessment of their quality. In addition, the following sentence in the Introduction section highlights the innovation of the work:

“There have been multiple analytical techniques applied for evaluation of biofuel pro-duction distribution, including hyphenated thermo-analytical techniques, such as TG-MS, TG-FTIR and other methods [32]. However, the use of the analytical techniques to de-termine the feedstock quality and evaluate biomass’ most effective use have not been sufficiently evaluated in the past.”

 

 

Comments on the Quality of English Language

The citation format is incorrect. Please follow the MDPI journal format. Some spelling and grammar mistakes were noticed which requires the author’s attention.

Response: Thank you for bringing these issues to our attention. We apologize for any inconvenience caused by the incorrect citation format. We rechecked the MDPI journal format for citations and used it in the paper revision. We carefully reviewed and revised the document to ensure its quality and accuracy for spelling and grammar mistakes.

Reviewer 2 Report

The research on renewable energy sources is one of the hot topics today as human beings struggle with the growing energy demand and climate change problems caused by traditional fossil fuels. The authors used corn cobs, vine poles and sunflowers as research materials and systematically evaluated the differences between the three biomass feedstocks by methods such as pyrolysis experiments and modeling studies, and emphasized their suitability as candidate feedstocks for pyrolytic conversion into high value-added fuels. In my opinion, this work is adequate, but the manuscript still requires substantial revisions to be accepted by Sustainability, and the following are specific comments:

1. Several Keywords in the Abstract should be capitalized in the first letter.

2. In the Abstract of the manuscript, the authors list the three plants in this experiment, but lack a comparison of the three plants in different tests. I noticed that the author actually mentioned these in the content section of the article, but did not show them in the abstract section. In addition, the Abstract is more confusingly logical and somewhat similar to a listing of conclusions.

3. Does the use of renewable energy produce the same greenhouse gases as fossil fuels? If the same, are there only quantitative savings between sustainable and conventional energy sources? Please re-contextualize the research within the manuscript.

4. The authors mentioned that "Three biomass feedstock materials were selected for this study, which comprised of corn cob, vine rod and waste from sunflower. The selection of these agricultural residues was conducted because of their availability and abundance." However, I do not seem to have read an explanation of this in the preamble.

5. "In contrast, the corn cob exhibited three troughs within the temperature range of 200°C and 400°C, indicating a different decomposition behavior associated with hemicellulose." The description in this paragraph is excessively vague, please explain in detail why.

6. The quality of the images in this manuscript needs to be strengthened, placing the letter sequences at the bottom of the figure detracts from the overall aesthetics of the figure.

7. Figure 1 lacks a legend, please add one to enhance the visualization of the picture.

8. In the legend of Figure 2, the chemical substances are written in the wrong way, such as CO2 and CH4.

9. The detected functional groups should be labeled in Figure 3, otherwise it is difficult to see the peak shifts.

10. Line 120, formatting errors in units of degrees Celsius.

11. The first letter of the name of the substance should be capitalized consistently in all tables.

12. Please double-check the font of the words in Table 6.

13. In the Results and discussions, the authors do a terrible job of explaining what practical significance their conclusions have. What is the significance and what are the advantages of the three plants as biomass fuels, such as biogas content, functional groups and organic compounds in the pyrolysis oil?

14. The multi-criteria assessment section of the biomass samples should be supplemented with a comparison of the three plants with traditional materials to show their great potential for sustainable energy product

The quality of the English language requires some modifications.

Author Response

1. Several Keywords in the Abstract should be capitalized in the first letter.

Response: The keywords in the abstract are now capitalized in the first letter.

 

2. In the Abstract of the manuscript, the authors list the three plants in this experiment, but lack a comparison of the three plants in different tests. I noticed that the author actually mentioned these in the content section of the article, but did not show them in the abstract section. In addition, the Abstract is more confusingly logical and somewhat similar to a listing of conclusions.

Reply: The abstract now has comparison between the different biomass samples. The following sentences were added to the abstract:

“The corn cob showed the smallest final residual mass of 20.4%, while the vine rod exhibited the largest mass loss of 33.5%.”

“Sunflower presented the largest calorific value of the produced bio-gas, while corn cob the lowest.”

 

3. Does the use of renewable energy produce the same greenhouse gases as fossil fuels? If the same, are there only quantitative savings between sustainable and conventional energy sources? Please re-contextualize the research within the manuscript.

Response: Emissions of CO₂ to the atmosphere do not account towards global warming, because these emissions are biogenic. The following sentence is added in the Introduction:

 

“Another benefit of biomass is when CO₂ is released from its use, it is of biogenic origin, which does not account in GHG emission estimates because it releases the same amount of CO₂ that has been originally fixed from the atmosphere during the life cycle of the biomass.”

 

4. The authors mentioned that "Three biomass feedstock materials were selected for this study, which comprised of corn cob, vine rod and waste from sunflower. The selection of these agricultural residues was conducted because of their availability and abundance." However, I do not seem to have read an explanation of this in the preamble.

Response: The authors have added reference [34] in this section. Also, in the Introduction section, while explaining the objectives of the research, the authors have added the following part:

“These agricultural residues hold significance due to their widespread availability, based on the global production of crops, namely corn cob as waste from cereal crops with one-third of the total crop production, sunflower from oil crops with 12% production and vine rod from the fruits with 10% production [33]. These residues are by-products of agricultural food production, hence can complement the food production industry to improve the overall sustainability of the agricultural industry.”

 

5. "In contrast, the corn cob exhibited three troughs within the temperature range of 200°C and 400°C, indicating a different decomposition behavior associated with hemicellulose." The description in this paragraph is excessively vague, please explain in detail why.

Response: This paragraph has been expanded as shown in the following section:

“In contrast, the corn cob exhibited three troughs within the temperature range of 200°C and 400°C, indicating a different decomposition behavior associated with hemicellulose, as it is one of the major components of the plant cell walls of corn cobs, composed of various sugars. The presence of three distinct troughs within the specified temperature range suggests that the decomposition behavior of the corn cob is not uniform throughout the whole process, showing the complex interaction of several components. The first trough occurs at lower temperature, corresponding to the removal of moisture and other volatile compounds, causing a reduction in mass. The second trough shows degradation of hemicellulose, where it undergoes depolymerization and breaks down into smaller sugar units. This results in the release of volatile organic compounds and a further reduction in mass. The third trough occurring at higher temperature range shows the degradation of other complex compounds, lignin and cellulose, contributing to the final mass loss ob-served in the TGA curve.”

 

6. The quality of the images in this manuscript needs to be strengthened, placing the letter sequences at the bottom of the figure detracts from the overall aesthetics of the figure.

Response: We revised the images and the letters are now positioned within the image.

 

7. Figure 1 lacks a legend, please add one to enhance the visualization of the picture.

Response: Legend is added to Figure 1, explaining the curves.

 

8. In the legend of Figure 2, the chemical substances are written in the wrong way, such as CO2 and CH4.

Response: The authors have reviewed and updated the legend in figure 2.

 

9. The detected functional groups should be labeled in Figure 3, otherwise it is difficult to see the peak shifts.

Response: The wavelength of the identified functional groups are now presented in Figure 3.

 

10. Line 120, formatting errors in units of degrees Celsius.

Response: The unit of degrees Celsius has been formatted.

 

11. The first letter of the name of the substance should be capitalized consistently in all tables.

Response: The first letter of the name of the compound in Tables 2,3 and 4, for the composition of the bio-oils from the three samples have been capitalized.

 

12. Please double-check the font of the words in Table 6.

Response: Table 6 font has been re-checked and adjusted with the necessary font for the journal’s requirements.

13. In the Results and discussions, the authors do a terrible job of explaining what practical significance their conclusions have. What is the significance and what are the advantages of the three plants as biomass fuels, such as biogas content, functional groups and organic compounds in the pyrolysis oil?

Response: We have expanded the Results and Discussions Section, making comparisons with previously published data and with the three biomass samples. We have compared the results with previously published data shown in the following sections:

“Examining the work of Adilaih et al [35], a comparison was drawn among multiple studies regarding proximate analysis. The results of the corn cob in this investigation displayed similarities, albeit with a slightly higher moisture content of around 7%. In a similar vein, the research conducted by Putun et al. [36] explored the yields and compositions of products from sunflower pyrolysis. These findings closely resembled the results obtained from the proximate analysis carried out on the sunflower samples in the current study.”

“The mass loss curves can be correlated with the findings from the proximate analysis, as depicted in Table 1. When examining the results of the proximate analysis for the three biomass samples, it becomes evident that the vine rod exhibits the highest concentration of fixed carbon at 22.71% and the lowest amount of volatile matter with 69.33%. This correlation can be drawn from the mass loss curves illustrated in Figure 1, which indicate the most substantial mass loss at 33.5%. Similarly, the sunflower displays fixed carbon and ash percentages of 16.71% and 8.3% respectively, resulting in a final residual mass of 24.3%. Finally, the corn cob showcases the lowest fixed carbon content along with highest amount of volatile matter, culminating in the smallest final residual mass of 20.4%. The differential thermogravimetric curves of vine rod and sunflower displayed similar behavior, characterized by two troughs in the rate of weight loss. In contrast, the corn cob exhibited three troughs within the temperature range of 200°C and 400°C, indicating a different decomposition behavior associated with hemicellulose.”

“Among the samples, vine rod exhibited the highest quantity of bio-gas at 21.2%, followed by sunflower with 18.8%, while corn cob yielded the lowest amount of bio-gas at 12.3%. The observed higher mass loss in the vine rod samples correlates positively with a greater amount of biogas production. This connection implies that the pyrolysis process for vine rod generates a higher quantity of gas products, likely due to the breakdown of organic compounds. This result underscores the potential of vine rod as a feedstock for bioenergy production.”

“The results confirm similar chemical composition of the bio-oils from the selected biomass types compared to other studies [41, 42], indicating high concentrations of acids. The higher catechol content in the vine rod samples could be indicative of its chemical composition, as certain compounds tend to yield specific by-products during pyrolysis. The presence of catechol might contribute to the observed trends in biogas production and mass loss, linking chemical properties to pyrolysis outcomes.”

14. The multi-criteria assessment section of the biomass samples should be supplemented with a comparison of the three plants with traditional materials to show their great potential for sustainable energy product

Response: It is difficult to compare the three samples with any other analysis in the literature because of differences in pyrolysis conditions and instruments used. In any case, we used the general discussion to discuss the opportunity of the energy and fuel generation from pyrolysis of biomass in the Conclusion section:

“The obtained data provide important reference information on the opportunities for energy and fuel generation from pyrolysis of the analysed biomass. Although biofuel production through pyrolysis is still hindered by high production costs and lower competitiveness when compared to fossil based fuels [44], improving the techno-economic viability of the technology can be achieved through production of higher value petrochemical products, including hydrogen, and integrating pyrolysis with solar power systems [45]. The market growth for energy consumption of biofuels is projected to grow from 4 EJ in 2021 to 11 EJ by 2050, while for solid bioenergy from 11 to 16 EJ [12]. Changes in government policies, such as targeted feed-in tariff policies, carbon accounting [46] and mandatory renewable energy targets [47] can accelerate the energy transformation, especially considering the 8% projected decline in world energy demand by 2050 due to increased energy efficiency and behavioural change [48].”

Reviewer 3 Report

Authors have carried out a comparative study to explore the potential for renewable energy production of 3 different biomasses: corn cob, vine rod and sunflower. This is a currently very relevant topic so, first of all, I would like to congratulate the authors for their work and encourage them to keep on working on this research line.

I also would like to say that, in general, the idea seems good for me and the manuscript is obviously the result of a hard work carried out by the authors. However, I am trying to provide some comments and suggestions in order to help the authors to improve the quality of the manuscript prior to be published:

1.     First of all, I would like to highlight what for me is the main shortcoming of this work, i.e., the lack of discussion found in this manuscript. There is no comparison of the results obtained in this work with others found in the literature, nor comments about whether the values found here are in a usual range for this type of biomass, etc. The literature on this topic is extensive, including many different types of biomasses used for pyrolysis, so, in my opinion, an extense contextualization and comparison of the results with previously published data is highly necessary to get a greater scientific contribution.

2.     Also related to the previous issue, there are some important paragraphs which require any reference in all the sections: Introduction, Materials and Methods (no references are included in the Materials and Methods section), Results and Discussion. Please, revise the references in the whole document and try to relate existing literature with your results and with the main statements included in the Introduction section. As an example, in lines from 58 to 61, authors mention that “according to an official report, …”, but no reference of this report is indicated.

3.     The Introduction section is very good, problem statement and solution from an abstract point of view to more concrete issues have been defined to focus this manuscript. Just revise the references.

4.     I strongly suggest to review and homogenize the use of acronyms, for example, define GHG or TGA the first time that “greenhouse gas” or “thermogravimetric analysis” appear in the text, and use the acronym later, every time it appears in the text. Evaluate other examples which can be found in the text.

5.     Every time authors make an statement such as “these agricultural residues hold significance due to their widespread availability” ( lines 108-109) or “the selection of these agricultural residues was conducted because of their availability and abundance” (lines 117-118), it must be referenced with published data about their availability in the world or in the evaluated area.

6.     Not only relationships between the results of this manuscript and published works need to be stablished, also relationships between data showed in different sections of the manuscript may be stablished, for example, in section 2, it is shown the high fixed carbon content of the biomasses or moisture and ashes contents, could you explain the relationship with the mass loss curves obtained in section 3.1.?

7.     Try to connect your results and make discussion about that, for example, vine rod showed: 1. The higher mass loss, the higher amount of biogas production, the lower residual mass, the higher Catechol content, etc. ¿Is there any relation among all these results?, Could the authors conclude something about vine rod behavior during the pyrolysis experiments?

8.     Please, avoid the use of conditional sentences, for example, in line 175, “bio-oils are not suitable for direct use but MAY be suitable for production of chemicals”. Try to find references of their use for chemicals production and modify it to say that “they are suitable for …”.

9.     Also avoid the use of information resources which are not scientific resources, for example, “general internet search was conducted” (line 180-181), add a base reference or the resource used in this case.

10.  In the Materials and Methods section, it would be clarifying for readers to explain in a more extensive way the calculation of the income derived from the oils obtained or the methodology of proximate analysis.

11. Finally, a question arised for me when I was reviewing the manuscript. Showed values are average values or they comes just for 1 unique experiment with every biomass? I guess that they are not coming just from 1 experiment, so, please, if they are average values, include the standard deviation values in tables and text.

Hope these suggestions are taken into consideration and help to improve the quality of this manuscript.

Thank you.

Author Response

1. First of all, I would like to highlight what for me is the main shortcoming of this work, i.e., the lack of discussion found in this manuscript. There is no comparison of the results obtained in this work with others found in the literature, nor comments about whether the values found here are in a usual range for this type of biomass, etc. The literature on this topic is extensive, including many different types of biomasses used for pyrolysis, so, in my opinion, an extense contextualization and comparison of the results with previously published data is highly necessary to get a greater scientific contribution.

Response: We note reviewer’s comments and agree that presenting wider range of results from biomass used for pyrolysis and comparison is needed. We have compared the results with previously published data shown in the following sections:

“Examining the work of Adilaih et al [35], a comparison was drawn among multiple studies regarding proximate analysis. The results of the corn cob in this investigation displayed similarities, albeit with a slightly higher moisture content of around 7%. In a similar vein, the research conducted by Putun et al. [36] explored the yields and compositions of products from sunflower pyrolysis. These findings closely resembled the results obtained from the proximate analysis carried out on the sunflower samples in the current study.”

“The results confirm similar chemical composition of the bio-oils from the selected biomass types compared to other studies [41, 42], indicating high concentrations of acids.”

2. Also related to the previous issue, there are some important paragraphs which require any reference in all the sections: Introduction, Materials and Methods (no references are included in the Materials and Methods section), Results and Discussion. Please, revise the references in the whole document and try to relate existing literature with your results and with the main statements included in the Introduction section. As an example, in lines from 58 to 61, authors mention that “according to an official report, …”, but no reference of this report is indicated.

Response: The references were added and revised throughout the whole document and were included in all sections. We have added 22 additional references, which leads to total number of 48 references that relate the existing literature with the results.

According to the comment about adding a reference for the sentence starting with “according to an official report, …”, reference [9] has been added.

3. The Introduction section is very good, problem statement and solution from an abstract point of view to more concrete issues have been defined to focus this manuscript. Just revise the references.

Response: We are thankful for this comment. We revised and added new references, leading to total number of 33 references in the Introduction part.

4. I strongly suggest to review and homogenize the use of acronyms, for example, define GHG or TGA the first time that “greenhouse gas” or “thermogravimetric analysis” appear in the text, and use the acronym later, every time it appears in the text. Evaluate other examples which can be found in the text.

Response: We agree with the reviewer’s comment. The frequently utilized terms (e.g., greenhouse gas (GHG), thermogravimetric analysis (TGA), Gas Chromatography (GC), Gas Chromatography–mass spectrometry (GC-MS), Fourier transform-infrared (FTIR) spectroscopy) were reviewed and were given acronyms, that were subsequently employed throughout the text.

5. Every time authors make an statement such as “these agricultural residues hold significance due to their widespread availability” ( lines 108-109) or “the selection of these agricultural residues was conducted because of their availability and abundance” (lines 117-118), it must be referenced with published data about their availability in the world or in the evaluated area.

Response: The mentioned statements were revised and were referenced. The following section in the manuscript justifies the availability of these samples:

“These agricultural residues hold significance due to their widespread availability, based on the global production of crops, namely corn cob as waste from cereal crops with one-third of the total crop production, sunflower from oil crops with 12% production and vine rod from the fruits with 10% production [33]. These residues are by-products of agricultural food production, hence can complement the food production industry to improve the overall sustainability of the agricultural industry.”

“Three biomass feedstock materials were selected for this study, which comprised of corn cob, vine rod and waste from sunflower. The selection of these agricultural residues was conducted because of their availability and abundance [34].”

6. Not only relationships between the results of this manuscript and published works need to be stablished, also relationships between data showed in different sections of the manuscript may be stablished, for example, in section 2, it is shown the high fixed carbon content of the biomasses or moisture and ashes contents, could you explain the relationship with the mass loss curves obtained in section 3.1.?

Response: Relationship between the data shown in section 2 and section 3.1 is established. The following section in the manuscript in section 3.1. explains the relationship:

“The mass loss curves can be correlated with the findings from the proximate analysis, as depicted in Table 1. When examining the results of the proximate analysis for the three biomass samples, it becomes evident that the vine rod exhibits the highest concentration of fixed carbon at 22.71% and the lowest amount of volatile matter with 69.33%. This correlation can be drawn from the mass loss curves illustrated in Figure 1, which indicate the most substantial mass loss at 33.5%. Similarly, the sunflower displays fixed carbon and ash percentages of 16.71% and 8.3% respectively, resulting in a final residual mass of 24.3%. Finally, the corn cob showcases the lowest fixed carbon content along with highest amount of volatile matter, culminating in the smallest final residual mass of 20.4%.”

7. Try to connect your results and make discussion about that, for example, vine rod showed: 1. The higher mass loss, the higher amount of biogas production, the lower residual mass, the higher Catechol content, etc. ¿Is there any relation among all these results? Could the authors conclude something about vine rod behavior during the pyrolysis experiments?

Response: The authors added correlations between the results from the vine rod samples, as shown in the following section:

“The observed higher mass loss in the vine rod samples correlates positively with a greater amount of biogas production. This connection implies that the pyrolysis process for vine rod generates a higher quantity of gas products, likely due to the breakdown of organic compounds. This result underscores the potential of vine rod as a feedstock for bioenergy production.”

“The higher catechol content in the vine rod samples could be indicative of its chemical composition, as certain compounds tend to yield specific by-products during pyrolysis. The presence of catechol might contribute to the observed trends in biogas production and mass loss, linking chemical properties to pyrolysis outcomes.”

8. Please, avoid the use of conditional sentences, for example, in line 175, “bio-oils are not suitable for direct use but MAY be suitable for production of chemicals”. Try to find references of their use for chemicals production and modify it to say that “they are suitable for …”.

Response: The sentence has been revised and reference was added, as shown in the following section:

“Considering the bio-oils are composed of a wide range of compounds, they are not suitable for direct use, but are suitable for production of biofuels, phenols, carboxylic acids, furfural and aromatic hydrocarbons, depending on their composition and processing methods [38].”

9. Also avoid the use of information resources which are not scientific resources, for example, “general internet search was conducted” (line 180-181), add a base reference or the resource used in this case.

      Response: Base reference has been added:

“The cost of each compound was assessed based on the cheapest value of the lowest purity available in the software for all compounds, except for 2-hydroxycyclohexane-1-carboxylic acid and hexanoic acid, 3-hydroxyl-, which were not available in this system and the values for these two compounds were found in [39].”

10. In the Materials and Methods section, it would be clarifying for readers to explain in a more extensive way the calculation of the income derived from the oils obtained or the methodology of proximate analysis.

      Response: The methodology for the proximate analysis is explained in a more extensive way, as shown in the Materials and methods section:

      “Before starting with the experimental analysis, the samples underwent a 2-hour vacuum drying process at 80°C. The proximate analysis of each sample was conducted following the ASTM D7582 test methods with results shown in Table 1. Consequently, the proximate analysis revealed the composition of moisture, volatile matter, ash, and fixed carbon for each biomass sample. The measurement procedure was organized into a sequence of three stages. Initially, the sample underwent heating from 25°C to 110°C, facilitated by a heating rate of 10°C/min. Subsequently, the sample was maintained at 110°C for a span of 5 minutes. Throughout the experimentation, nitrogen was employed as the carrier gas, flowing at a rate of 50 ml/min. The temperature was then progressively raised from 110°C to 900°C, with a heating rate of 50°C/min. The sample was held at this temperature for 15 minutes. Finally, the nitrogen atmosphere was exchanged with air, with a flow rate of 50 ml/min. During this phase, the sample was held at a temperature of 900°C for a duration of 10 minutes.

11. Finally, a question arised for me when I was reviewing the manuscript. Showed values are average values or they comes just for 1 unique experiment with every biomass? I guess that they are not coming just from 1 experiment, so, please, if they are average values, include the standard deviation values in tables and text.

Response: We note reviewer’s comment and state out that one experiment per method was done with each biomass sample according to the cost and size of the project, which is also a common practice for the pyrolysis experiments across the literature.

Reviewer 4 Report

1.         The comparative study only examines three specific biomass sources (cabbage stalk, grapevine rod, and sunflower). Why does the study not extend to other biomass sources to ensure a more robust analysis of their suitability for renewable energy production ?

2.         Does renewable energy meet future energy needs, adapt to environmental and climate changes, and respond to market dynamics? Does it have the potential to completely replace fossil fuels with renewable energy sources by 2050 ?

3.         Although the research explores the potential of biomass pyrolysis to generate energy, when pyrolysis produces CO2, C0 and CH4, it has the potential to release these substances which cause greenhouse gas pollution, air pollution. and how to treat the by-products of pyrolysis affecting the soil and water environment ?

4.         The study's failure to incorporate recent technological advancements in the biomass pyrolysis process leads to a limited understanding of the potential of biomass pyrolysis as a sustainable energy solution ?

5.         The study fails to address the competition between utilizing biomass for energy production versus other purposes, such as food production or animal feed. If biomass sources are diverted for alternative purposes, it could have adverse impacts on food security and ecological balance ?

6.         Although the study explores the potential, it may not delve into the economics of deploying biomass pyrolysis on a commercial scale. Economic factors such as technology costs, availability of raw materials, market demand and without government support, will the project be implemented ?

7.         How does the study address future market projections and potential challenges that could impact the widespread adoption of biomass pyrolysis for energy production?

8.         A comprehensive analysis should consider factors such as policy changes, global energy demand, and technological breakthroughs that could influence the energy landscape ?

 Moderate editing of English language required.

Author Response

1. The comparative study only examines three specific biomass sources (cabbage stalk, grapevine rod, and sunflower). Why does the study not extend to other biomass sources to ensure a more robust analysis of their suitability for renewable energy production ?

 

Response: We note reviewer’s comments and agree that presenting wider range of biomass sources would give more robust analysis, however, we had to draw a line between demonstration of the presented methods, cost and size of the project. The literature typically presents analysis of 1 biomass source only, considering the scale of the experimental work required for one sample analysis, hence presenting differences of 3 biomass sources, in our view, gives an optimal number of biomass sources to demonstrate the methods for assessment of their quality. The following section in the manuscript justifies the selection of these samples:

 

“The objectives of this research are to study the thermal behavior and characterize the pyrolysis products of three commonly available biomass materials, namely corn cob, vine rod and sunflower, under slow pyrolysis conditions and to determine the relative quality of each biomass for the type of biofuel production. These agricultural residues hold sig-nificance due to their widespread availability, based on the global production of crops, namely corn cob as waste from cereal crops with one-third of the total crop production, sunflower from oil crops with 12% production and vine rod from the fruits with 10% production [33].”

 

2. Does renewable energy meet future energy needs, adapt to environmental and climate changes, and respond to market dynamics? Does it have the potential to completely replace fossil fuels with renewable energy sources by 2050 ?

 

Response: To address this comment, we added the following section in the Introduction section:

 

“Currently, bioenergy supplies approximately 24 EJ of energy, making it the largest renewable energy source today supplying approximately 10% of the world energy [12]. Bioenergy is expected to have a substantial role in transitioning the world to carbon net zero economy by 2050, with projections for the bioenergy supply of up to 313 EJ by 2050, or 37% of the world energy demand [13].”

 

 

3. Although the research explores the potential of biomass pyrolysis to generate energy, when pyrolysis produces CO2, C0 and CH4, it has the potential to release these substances which cause greenhouse gas pollution, air pollution. and how to treat the by-products of pyrolysis affecting the soil and water environment ?

 

Response: Emissions of CO₂ to the atmosphere do not account towards global warming, because these emissions are biogenic. The following sentence is added in the Introduction:

 

“Another benefit of biomass is when CO₂ is released from its use, it is of biogenic origin, which does not account in GHG emission estimates because it releases the same amount of CO₂ that has been originally fixed from the atmosphere during the life cycle of the biomass.”

 

Also, the following sentence is inserted in the Conclusions section:

 

“Efficient collection of the bio-gas is essential to ensure high energy production at minimized release and pollution to the environment.”

 

4. The study's failure to incorporate recent technological advancements in the biomass pyrolysis process leads to a limited understanding of the potential of biomass pyrolysis as a sustainable energy solution ?

 

Response: The revised manuscript now includes 22 additional references outlining the recent advancements in biomass pyrolysis.

 

 

5. The study fails to address the competition between utilizing biomass for energy production versus other purposes, such as food production or animal feed. If biomass sources are diverted for alternative purposes, it could have adverse impacts on food security and ecological balance ?

 

Response: The reviewer implies to the first generation of biofuels which competes with food production. The biomass resources used in this study are agricultural wastes and the proposed conversion to biofuels would be classified as second generation biofuels. The use of agricultural waste to produce value added products, as presented, can improve sustainability of the agricultural industry. The following is inserted at the end of the Introduction section to clarify the benefits of using the proposed biomass:

 

“These residues are by-products of agricultural food production, hence can complement the food production industry to improve the overall sustainability of the agricultural industry.”

 

6. Although the study explores the potential, it may not delve into the economics of deploying biomass pyrolysis on a commercial scale. Economic factors such as technology costs, availability of raw materials, market demand and without government support, will the project be implemented ?

 

Response: Reviewer is correct when discussing the importance of techno-economics in the assessment. Although this is not a focus of our work, as the work is focused on evaluation of the suitability of the three biomass feedstocks for biofuel production, we agree that the importance of the viability of the biomass pyrolysis should be mentioned. For this reason, the following is added in the Conclusions section:

 

“Although biofuel production through pyrolysis is still hindered by high production costs and lower competitiveness when compared to fossil based fuels [44], improving the techno-economic viability of the technology can be achieved through production of higher value petrochemical products, including hydrogen, and integrating pyrolysis with solar power systems [45].”

 

7. How does the study address future market projections and potential challenges that could impact the widespread adoption of biomass pyrolysis for energy production?

 

Response: The following sentence about the market growth is added in the Conclusions section:

 

“The market growth for energy consumption of biofuels is projected to grow from 4 EJ in 2021 to 11 EJ by 2050, while for solid bioenergy from 11 to 16 EJ [12].”

 

8. A comprehensive analysis should consider factors such as policy changes, global energy demand, and technological breakthroughs that could influence the energy landscape ?

Response: The following sentence is added in the Conclusions section to address the comments about the importance of policy changes and global market demand:

 

“Changes in government policies, such as targeted feed-in tariff policies, carbon accounting [46] and mandatory renewable energy targets [47] can accelerate the energy transformation, especially considering the 8% projected decline in world energy demand by 2050 due to increased energy efficiency and behavioural change [48].”

Round 2

Reviewer 1 Report

There is a major flaw in this article in which the authors did not compare their results with the other literatures in the result and discussion section. It is very important to compare the results with other works to ensure the quality of this work. Also, it is very important to calibrate the GC/MS before conducting an experiment, which is not shown in the material and methods section. Was the GC/MS calibrated before the experiment? The authors must show the GC/MS equipment is calibrated with a QA/QC process, which ensure the robustness of the result. Therefore, I do not recommend this article to be published at the present form. 

There is room for improvement in the English writing. Please check the spelling and the grammar.

Author Response

There is a major flaw in this article in which the authors did not compare their results with the other literatures in the result and discussion section. It is very important to compare the results with other works to ensure the quality of this work.

 

Response: We added two new sections with comparison of the results with literature values. In the section 3.1, the following sentences with comparison are added:

“The corn cob char yield at 500°C determined in this study was in the similar range to 22.1%-22.5% reported by Ceranic et al. [41], who revealed that the char yield of corn cob depends on the biomass particle size, with the larger particle sizes producing larger fraction of biochar. The sunflower in the current work produced higher biochar yield and lower pyrolysis conversion rate compared to sunflower bagasse [42] and sunflower stalks [43], which were reported at 28% char yield at 520°C, and 25% char yield at 540°C, respectively. Vine rod in the current work showed higher char production rates at 500°C comparing to the work by Suárez et al. [44] who produced 35% biochar rates at the same temperature, which significantly reduced to 20% when the biomass was leached with distilled water prior to pyrolysis”

 

In the section 3.5, the following sentences were with comparison were added:

“When comparing other biomass sources to the selected three using the proposed multicriteria approach, mallee tree and wheat straw produced comparable biochar yields of 35.6% and 32.2% at 500°C, respectively [49], to the sunflower biomass in the current work. However, the calorific value of the bio-gas produced from pyrolysis of mallee tree and what straw at 500°C under similar pyrolysis conditions were estimated at 5.5 MJ/kg and 5.1 MJ/kg, respectively, which are significantly larger than the selected three biomass samples. The selected biomass samples are comparable to paper sludge biomass which produced 36% of solid char and bio-gas with a calorific value of 1.2 MJ/kg [50].”

 

Also, it is very important to calibrate the GC/MS before conducting an experiment, which is not shown in the material and methods section. Was the GC/MS calibrated before the experiment? The authors must show the GC/MS equipment is calibrated with a QA/QC process, which ensure the robustness of the result. Therefore, I do not recommend this article to be published at the present form.

 

Response: The bio-oil analysis was conducted using the recommended quantitative approach for analysis of the complex pyrolysis oils. The following sentence is added in the Methods section 2.3:

“The quantification of the bio-oil compounds was conducted based on the calculated peak areas from the total ion current. As recommended by Staš et al. [38], this type of quantification is acceptable when the bio-oils are produced under the same pyrolysis process and analyzed under the same analytical conditions.”

Reviewer 2 Report

1.Specific functional groups can also be represented in Figure 3 in the diagrams.

2.The multi-criteria assessment of biomass samples section should be supplemented with a comparison of the three plants with conventional materials, and this section may be limited by conditions that prevent it from showing specific detailed comparisons, but in a macro sense, what are the advantages of biomass fuels? Environmentally friendly? Theoretically higher calorific value?

Minor editing of English language required.

Author Response

1.Specific functional groups can also be represented in Figure 3 in the diagrams.

 

Response: The specific functional groups are now represented in Figure 3.

 

 

2.The multi-criteria assessment of biomass samples section should be supplemented with a comparison of the three plants with conventional materials, and this section may be limited by conditions that prevent it from showing specific detailed comparisons, but in a macro sense, what are the advantages of biomass fuels? Environmentally friendly? Theoretically higher calorific value?

 

Response: We added the following comparison of the multicriteria assessment:

“When comparing other biomass sources to the selected three using the proposed multicriteria approach, mallee tree and wheat straw produced comparable biochar yields of 35.6% and 32.2% at 500°C, respectively [49], to the sunflower biomass in the current work. However, the calorific value of the bio-gas produced from pyrolysis of mallee tree and what straw at 500°C under similar pyrolysis conditions were estimated at 5.5 MJ/kg and 5.1 MJ/kg, respectively, which are significantly larger than the selected three biomass samples. The selected biomass samples are comparable to paper sludge biomass which produced 36% of solid char and bio-gas with a calorific value of 1.2 MJ/kg [50].”

Reviewer 3 Report

Manuscript quality has been significantly improved according to the comments and suggestions made by the reviewers. Obviously, discussion section has been extended and a higher number of references have been included and I feel glad for that. 

In my opinion, the manuscript acquired enough quality for publishing, just try to deeply revise the english language.

Thanks, 

English language has been highly improved. Some minor mistakes can be found.

Author Response

Manuscript quality has been significantly improved according to the comments and suggestions made by the reviewers. Obviously, discussion section has been extended and a higher number of references have been included and I feel glad for that.

 

In my opinion, the manuscript acquired enough quality for publishing, just try to deeply revise the english language.

 

Response: We are thankful for the comment. The English language was further reviewed and corrected.

Reviewer 4 Report

Literature review should be extended:

Yuan Kang Wu et al., A Short-Term Wind Power Forecasting Tool for Vietnamese Wind Farms and Electricity Market, 2018 4th International Conference on Green Technology and Sustainable Development.

Neural Comput & Applic. An improved equilibrium optimizer for optimal placement of photovoltaic systems in radial distribution power networks, 2022.

Minor editing of English language required

Author Response

Literature review should be extended:

 

Yuan Kang Wu et al., A Short-Term Wind Power Forecasting Tool for Vietnamese Wind Farms and Electricity Market, 2018 4th International Conference on Green Technology and Sustainable Development.

 

Neural Comput & Applic. An improved equilibrium optimizer for optimal placement of photovoltaic systems in radial distribution power networks, 2022.

 

Response: The literature review is extended with 7 new articles with now a total of 55 references. We reviewed the recommended articles by the reviewer but found them outside of the scope of the current work as they are related to wind and solar power.

Round 3

Reviewer 1 Report

Although the authors did not gave their best effort to improve their paper, I have no objection for this paper to be published in current form.

Please double check the grammar and spelling throughout the paper

Author Response

Please double check the grammar and spelling throughout the paper.

 

Response: We double checked the grammar and spelling and revised accordingly.