Composition and Textural Characteristics of Char Powders Produced by Thermomechanical Processing of Sunflower Seed Husks

Round 1

Reviewer 1 Report

1. The manuscript is too long and more than 22 figures are added inside. I suggest the authors could shorten the manuscript and make it concise. 

2. The conclusions are too long and should be shortened. 

3. wt%.

4. Please reorganize the manuscript. 

Author Response

We are grateful to the reviewer for valuable comments. We have made our best to follow all the comments. All changes in the revised manuscript are marked in yellow.

1. The manuscript is too long and more than 22 figures are added inside. I suggest the authors could shorten the manuscript and make it concise.

We have considerably shortened the manuscript by presenting results for only one of three samples as they look about similar.

2. The conclusions are too long and should be shortened.

We have shortened the Conclusions.

3. wt%.

We have changed %wt. to wt% everywhere.

4. Please reorganize the manuscript. 

We have reorganized the manuscript by removing an unnecessary material and reducing the number of sections.

Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript deals with the sunflower husk ash powder production by using thermomechanical method. Composition and textural characteristics were analyzed. While I have many comments for improving readability and emphasizing key results, the manuscript is worth consideration for publication after extensive editing of English language and style as well as addressing these first major comments and revising the manuscript:

1.     As feedstock for the experiments sunflower seed husks was used, which further treated by thermomechanical treatment with pulsed shock waves and jets to obtain the sunflower husk ash. One of my initial concerns was whether it would be possible to accurately identify and pinpoint a potential of sunflower seed husks in gasification in comparison with other bio-waste based “powders”. Please focus on powder due to the journal research focus. This will make the motivation for this experiment easier to understand in my opinion and introduce the reader better into the topic.

2.     Please go through following papers to improve your manuscript:

https://doi.org/10.1016/j.egyr.2023.03.085

https://doi.org/10.3390/ma14102484

Detailed review of this paper can be provided just after clearing of these important points.

Author Response

We are grateful to the reviewer for valuable comments. We have made our best to follow all the comments. All changes in the revised manuscript are marked in green.

This manuscript deals with the sunflower husk ash powder production by using thermomechanical method. Composition and textural characteristics were analyzed. While I have many comments for improving readability and emphasizing key results, the manuscript is worth consideration for publication after extensive editing of English language and style as well as addressing these first major comments and revising the manuscript:

Our native English-speaking colleague has kindly checked the manuscript, thank you.

1. As feedstock for the experiments sunflower seed husks was used, which further treated by thermomechanical treatment with pulsed shock waves and jets to obtain the sunflower husk ash. One of my initial concerns was whether it would be possible to accurately identify and pinpoint a potential of sunflower seed husks in gasification in comparison with other bio-waste based “powders”. Please focus on powder due to the journal research focus. This will make the motivation for this experiment easier to understand in my opinion and introduce the reader better into the topic.

The goal of this study was to obtain a highly dispersed char powder which could be used as a sorption-active material for organic substances. We have achieved this goal and obtained a char powder with particles of tens nanometer in size. Unfortunately, these particles were agglomerated after the thermomechanical treatment due to the presence of condensed moisture. Our future work will be aimed at drying and fragmenting the obtained char powder agglomerates by pulsed shock waves and jets of incondensable gas (e.g., nitrogen). To address this comment, we have added the following sentences to the Introduction (with adding some new relevant references), Results and Discussion, and to the Conclusions:

Introduction:

“The most promising solution to the problem is the thermal treatment of waste, accompanied by a partial recovery of energy and material resources. The environmental impact of the thermal treatment technologies is relatively small and is caused by gas and flying ash emissions as well as generation of liquid tar and solid residues. The available thermal treatment technologies include direct combustion, pyrolysis, gasification, and their combinations [7-11]. The solid residues (ash powders) generated during combustion, pyrolysis and gasification processes of sunflower seed husks are used as adsorbents for remediation of water or industrial liquid effluents [12,13], in the ceramic industry [14], in the iron ore sintering process [15], and as a filler for epoxy-based composites [16]. The smallest impact on the environment is produced by high-temperature gasification technologies based on the use of superheated water or superheated steam [17–19] and/or CO2 [20],…”

“This powder is intended as a sorption-active material for organic substances.”

Results and Discussion

“It is also worth noting that the char powder thus obtained can be subject to wetting and agglomeration after the termination of thermomechanical treatment in the FG due to steam condensation. The latter implies the possible need in additional drying and fragmentation operations for the char powder.”

“…and the presence of condensed moisture after the thermomechanical treatment. The SPM data and the data on particle size distribution imply that the samples are mainly composed of agglomerates of fine char particles that are 20–30 nm in average size. This means that further drying and fragmentation of the obtained char powder could significantly increase the specific surface thus contributing to high sorption properties of the resultant char powder.”

Conclusions:

“Thus, we have achieved the objective of the study and obtained a very fine char powder with particles of tens nanometers in average size. Unfortunately, these particles were agglomerated after the thermomechanical treatment due to the presence of condensed moisture. The future work will be aimed at fragmenting and drying the obtained char powder agglomerates by pulsed shock waves and jets of incondensable gas, e.g., nitrogen.”

2. Please go through following papers to improve your manuscript:

https://doi.org/10.1016/j.egyr.2023.03.085

https://doi.org/10.3390/ma14102484

We have included these references to the List of References, thank you.

Detailed review of this paper can be provided just after clearing of these important points.

Author Response File: Author Response.pdf

Reviewer 3 Report

Thank you for submitting the manuscript "Composition and textural characteristics of char powders produced by thermomechanical processing of sunflower seed husks" to Powders.

Line#28-38: this information is too broad and therefore inadequate. Replace with data on waste generation in the world and how these impacts on the environmental concern of the industry and the consumer.

There are already many studies with sunflower husks and I believe that it would be important to report the physical-chemical, technological and chemical characteristics. See: https://doi.org/10.1111/1750-3841.15719 and https://doi.org/10.1007/978-3-030-91381-6_4

What will this powder be applied to? Human or animal food? It would be good if this was justified in the introduction item as well.

Line#89-115: This sounds like more study results to me. The authors could consider changing these results to the beginning of the results item and in the Material and Methods item describe how these analyzes were performed.

The set of figures and tables is very numerous, which makes it difficult to understand the text.

Author Response

We are grateful to the reviewer for valuable comments. We have made our best to follow all the comments. All changes in the revised manuscript are marked in blue.

Thank you for submitting the manuscript "Composition and textural characteristics of char powders produced by thermomechanical processing of sunflower seed husks" to Powders.

Line#28-38: this information is too broad and therefore inadequate. Replace with data on waste generation in the world and how these impacts on the environmental concern of the industry and the consumer.

We have changed the beginning of Introduction and added two more references to the review articles:

Giusti, L. A review of waste management practices and their impact on human health. Waste Management 2009, 29(8), 2227–2239. doi:10.1016/j.wasman.2009.03.028.

Goutam Mukherjee, A.; Ramesh Wanjari, U.; Chakraborty, R.; Renu, K.; Vellingiri, B.; George, A.; Valsala Gopalakrishnan, A. A review on modern and smart technologies for efficient waste disposal and management. J. Environm. Manag. 2021, 297, 113347. doi:10.1016/j.jenvman.2021.113347.

There are already many studies with sunflower husks and I believe that it would be important to report the physical-chemical, technological and chemical characteristics. See: https://doi.org/10.1111/1750-3841.15719 and https://doi.org/10.1007/978-3-030-91381-6_4

We have added these two references (Refs. 5 and 6) to the List of References, thank you. In addition, we have added some more references (Refs. 12 to 16) discussing the possible applications of sunflower seed husks ashes and byproducts.

What will this powder be applied to? Human or animal food? It would be good if this was justified in the introduction item as well.

To address this comment, we have added the following sentence to the Introduction:

“This powder is intended as a sorption-active material for organic substances.”

Line#89-115: This sounds like more study results to me. The authors could consider changing these results to the beginning of the results item and in the Material and Methods item describe how these analyzes were performed.

We have reorganized the Sections as recommended by the reviewer. We have left the material on the original feedstock in Material and Methods and moved the photo of char powder to Results and Discussion.

The set of figures and tables is very numerous, which makes it difficult to understand the text.

We have considerably shortened the manuscript by presenting results for only one of three samples as they looked about similar.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript has been revised correspondingly. 

Author Response

Thank you very much for valuable comments!

Reviewer 2 Report

1.     Section 2. Line 91. The authors stated: The sunflower seed husks consist of approximately 48.4% cellulose, 34.6% hemicellulose and 17% lignin [38]. For which sunflower variety? Is it the same for all varieties? I’m not sure. Please clarify. What moisture content of the sunflower husk was used for PDG?

2.     Fig 1b: Is it cross-section of the sunflower husk? In which part of sunflower husk. Furthermore, what is the different between zone 1 and zone 2? Is it the same material?

3.     Figure 2: Any description of the methodology for the Energy-dispersive spectrum? Sample preparations? Which equipment was used?

4.     Line 204-221: the historical information should be transferred to the introduction section or avoid.

5.     R&D: Energy-dispersive spectrum of char powder (fig 5) should be combined with SEM microscopy (fig 7). And the zone or point for Energy-dispersive spectrum analysis should be highlighted.

6.     Figure 6 and table 5 duplicate the same information. I recommend to add the formula to the fig 6.

7.     Line 288: This part should be add in to the M&M section.

8.     R&D. What is the different between samples 1-3? IS it just replicate? If yes, then data should be shown as an average.

9.     Table 4. What does proximate analysis means?

General question:

The authors should reorganize the M&M and R&D sections due the readability. Fig 2-3 and table 1 should be transferred in to the R&D section.            R&D section should start from SEM images (highlight the EDS point)→ EDS elemental mapping→ elemental composition → SPM analysis → Size distribution of char powder particles.

The sunflower husk might contain a huge amount of residual oil. How does it affect on the PDG technology? The authors did not addressed this crucial point in the M&M (table 1) and R&D sections.

The overall English of the text can be improved further. In particular, the usage of articles (a, an, the) is very commonly omitted. The authors are invited to make further re-reads and improve the structure of the manuscript.

Based on the above points, I would propose a major revision of the manuscript.

Author Response

We are grateful to the reviewer for valuable comments. We have made our best to follow all the comments. All changes in the revised manuscript are marked in green.

1. Section 2. Line 91. The authors stated: The sunflower seed husks consist of approximately 48.4% cellulose, 34.6% hemicellulose and 17% lignin [38]. For which sunflower variety? Is it the same for all varieties? I’m not sure. Please clarify. What moisture content of the sunflower husk was used for PDG?

This composition corresponds to the sunflower variety Belgorodsky 94 used in the study. The moisture of the sunflower seed husks was 9.95-10.00 wt%. We have added this information to the manuscript.

2. Fig 1b: Is it cross-section of the sunflower husk? In which part of sunflower husk. Furthermore, what is the different between zone 1 and zone 2? Is it the same material?

Figure 1b shows a section of sunflower seed husks in its original form. Scanning electron microscopy was carried out in conjunction with energy dispersive analysis, which made it possible to determine the content of elements at various points of the sample. This is one material in which the content of the elements was established at two different points. We have added this information to the text.

3. Figure 2: Any description of the methodology for the Energy-dispersive spectrum? Sample preparations? Which equipment was used?

The description of the device is given in section 2.3. Nevertheless, we have added some more information to the text:

“Nova NanoSEM has an intralens secondary electron detector that provides high detail of the near-surface region of a sample. No special preparation of a sample before analysis is required.”

4. Line 204-221: the historical information should be transferred to the introduction section or avoid.

We have replaced the historical information by the references to the most noteworthy publications dealing with the scanning probe microscopy.

5. R&D: Energy-dispersive spectrum of char powder (fig 5) should be combined with SEM microscopy (fig 7). And the zone or point for Energy-dispersive spectrum analysis should be highlighted.

To follow this comment, we have extended Figure 5 with a microphotograph showing the zone where the energy dispersive analysis was made.

6. Figure 6 and table 5 duplicate the same information. I recommend to add the formula to the fig 6.

To follow this comment, we have replotted Figure 6 by adding the information from Table 5 and removed Table 5 from the manuscript. In view of it, all subsequent tables were reordered.

7. Line 288: This part should be add in to the M&M section.

This sentence is moved to Section 2.5 in the M&M section.

8. R&D. What is the different between samples 1-3? IS it just replicate? If yes, then data should be shown as an average.

We mention at the beginning of R&D section that “three samples of char powder are obtained from sunflower seed husks in three experiments under approximately the same experimental conditions (average temperature of the walls of the flow reactor of 400–450 °C; atmospheric pressure; a feedstock batch of 2 kg).” The differences in the reactor wall temperature indicate that the experimental conditions were not exactly the same. Therefore, in the original manuscript, we have discussed the data for each sample separately despite the similarity of all examined properties except for particle size distribution and specific surface area. In the first revised version of the manuscript, following the reviewers’ comments, we have shortened the manuscript and consider only one sample as an example and do not discriminate between samples 1, 2, and 3. Nevertheless, for particle size distribution and specific surface area we do discriminate between these three samples in Tables 6 and 7 as the differences are essential. Since these differences could be caused by different experimental conditions in terms of the reactor wall temperature, we do not provide the average values.

To address this comment, we have added several sentences when discussing Tables 6 and 7.

9. Table 4. What does proximate analysis means?

We have replaced “proximate analysis” by “chemical composition.” Sorry for the misleading table caption.

General question:

The authors should reorganize the M&M and R&D sections due the readability. Fig 2-3 and table 1 should be transferred in to the R&D section.            R&D section should start from SEM images (highlight the EDS point)→ EDS elemental mapping→ elemental composition → SPM analysis → Size distribution of char powder particles.

A somewhat similar comment was made by Reviewer #3. In the revised version of Round 1, we made some rearrangements which seemed to satisfy the reviewer. In the current manuscript, the properties of feedstock (husks) and the research methods are included in the M&M section, whereas all the obtained results for char powder are included in the R&D section.

The sunflower husk might contain a huge amount of residual oil. How does it affect on the PDG technology? The authors did not addressed this crucial point in the M&M (table 1) and R&D sections.

As mentioned in the Introduction and in Section 2.2, the PDG technology is originally aimed at the high-temperature (above 2000 C) complete (without organic solid residue) gasification of different organic wastes to obtain a high-quality syngas composed solely of H2 and CO. In the present manuscript, we apply the PDG technology to obtain a solid residue - char powder. For this purpose, we decrease the PDG fill and the operation frequency, thus decreasing the average temperature of the gasifying agent (H2O+CO2) in the flow reactor. The latter worsens the gasification process leading to the decrease in the yields of H2 and CO and increase in the yields of CH4, higher hydrocarbons including tar, and CO2 in the produced syngas, as well as the appearance of solid residue (fine char). The oil, if present, is also subject to gasification like husks. The experimental conditions for obtaining the char powder of desired properties (using the PDG technology) may obviously depend on the oil content. In our case, the feedstock was not oily and the effect of oil content was beyond the scope of our study.

The overall English of the text can be improved further. In particular, the usage of articles (a, an, the) is very commonly omitted. The authors are invited to make further re-reads and improve the structure of the manuscript.

We have double-checked the text in terms of English.

Based on the above points, I would propose a major revision of the manuscript.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

The authors answered my questions in current manner. The manuscript now can be accepted.