Influence of Miscanthus Rhizome Pyrolysis Operating Conditions on Products Properties

Round 1

Reviewer 1 Report

The work of Klemencova, Grycova and Lestinsky is interesting, but it has some flaws that must be addressed. My main point is the generation of wastes from Miscanthus. Authors say in the Introduction "Miscanthus is typically harvested during winter or early spring". I do not see a relation between harvesting and rhizomes. Are the whole plants extracted during harvesting? If yes, it is not a harvesting. This part must be clarify since authors claims valorizing a waste by pyrolysis, so the waste must be clearly identified.

 

Other points:

The tittle should clearly indicate the word “rhizomes”, i.e. change “Miscanthus” by “Miscanthus rhizomes”.

Line 25. Miscanthus giganteus must be in italic.

Line 27. Miscanthus Sinensis and Miscanthus Sacchariflorus must be changed by M. sinensis and M. sacchariflorus.

Line 37. Please specify what kind of thermochemical method is going to be used in the paper, i.e. pyrolysis. If authors do not want to talk about the pyrolysis process and its products in the introduction section, please refer to a review paper on pyrolysis (for example: Biodiesel and other value-added products from bio-oil obtained from agrifood waste, Processes, 2021, 9(5), 797).

Line 51. The reviewer does not understand the sentence “A type of biochar mainly determines the possible effect”.

Line 67. “a source of food”. I would say “a carbon source”.

Lines 81-91. The objectives of the paper are no clear enough. Please specify the aim of the work and how you are going to do it.

Lines 11-113. “Based on the initial results of experiments with selected temperatures, for a temperature of 600 °C, two other residence times were chosen (15 minutes and 1 hour).”. Well, in the Results and discussion section there is not a real discussion for why authors have selected 600 °C as pyrolysis temperature. Furthermore, there is not discussion on the effect of the residence time at that temperature.

Line 113. “The heating rate 5 °C/min was used the same for all experiments”. In the Conclusions section, authors claim that the heating rate of the imput material also had the great influence on the quality of the biochar.

Line 118. “prepared retort”?

In Material and Methods, the conditions for GC and GC-MS are not well described.

Line 130. Are authors calling “condensate” to “biooil”?

Lines 173. “Samples of rhizomes contained large amounts of volatile combustibles”. Which are they?

Line 180. “The first peak is connected with water evaporation”. And the volatile combustibles? They have much lower boiling point.

Figure 1 and so on. Please change “,” by “.” for decimals.

Tables y Figures in general. “Biochar 600/2”, etc., should be defined for a better understanding.

Line 207. Change “Error! Reference source not found” by “Table”.

Line 210, Figure 3. “the third sampling had the highest higher heating value”. Why? An explanation should be given in the text.

Table 1. Why the percentage of carbon dioxide decrease with the temperature? It does not make sense, does it not? And there is no relationship with the percentages of CO.

Line 226. “The water content was determined by Karl-Fischer titration on TitroLine 226 7500 KF”. This belongs to the Material and Methods section.

Line 230. “The condensate samples were analysed by gas chromatography using Agilent 7890b 230 with mass spectrometer“. This belongs to the Material and Methods section.

Figure 4 shows important compound such as furfural in the biooil. Authors should highlight the compound in great concentration and with the highest economic, pharmaceutic, etc., potential. Several papers published in 2022 in MDPI journals deals with pyrolysis of agricultural wastes. Authors should compare and discuss their results with those found by other authors and highlight the potential applications of the compounds found after the pyrolysis of Miscanthus rhizomes.

Lines 255-258. The reviewer does not understand what the authors mean.

Table 2. “W” (water?) and “VM” (volatile matter?) should be defined. Do biochar contain metals? Table 5 shows the heavy metals in the raw material, but not in the biochars. As many of the organic matter is not in the biochar (is in the biooil and syngas), the concentration of metals in biochars should be higher than in the raw material.

Line 266. Change “Error! Reference source not found” by “Figure”.

Figure 7. The figure caption must be rewritten and must describe properly the samples.

The section Conclusions is too generic. Furthermore, sentences such as “temperature in the pyrolysis zone of the reactor, the heating rate of the input material and the residence time in the reaction space also had the great influence on the quality of the biochar” (lines 376-378), “A temperature of 600 °C and a residence time of 2 hours were found appropriate for the preparation of biochar with looked for chemical and physical properties” (lines 383-385), and “ can be considered as a source of nutrients, and in addition to its properties can be used to adjust the soil pH” (lines 387-388) have been not proved by the research.

Author Response

Dear Reviewer, the responses to your valuable comments are attached.

Author Response File: Author Response.pdf

Reviewer 2 Report

This study has investigated the pyrolysis of Miscanthus and the effect of conditions on the properties of products. Pyrolysis of Miscanthus has been previously reported, thus the authors should emphasize the novelty and new findings in the present study. Besides, further revisions are required.

1. The scientific writing of this manuscript should be significantly improved. The English should also be carefully checked throughout this manuscript.
2. The abstract did not quantitatively present the results and findings of this study. Moreover, the contributions should be highlighted. The keywords should carefully selected.
3. The research gap was not properly identified in the introduction, thus the authors failed to clearly state the objectives of this study and novelty and contribution of this study.
4. The quality of figures and tables should be improved. For example, the caption of Figure 3 is not clear. The font of words in Figures 4 and 6 are not clearly readable. The caption of table 2 should be more detailed. Table 6 is not properly organized. Samples in Figure 7 are not clearly indicated.
5. Authors claimed that they applied the biochar in the field for application. However, in the results and discussion, only adsorption analysis was presented, which is not sufficient for the application as soil conditioner.
6. To be qualified as superior soil conditioner, multiple criteria should be evaluated. Thus, the selection of pyrolysis condition should be comprehensively considered. For example, the Table 6 only presented the concentration of nutrients and metallic elements in biochar 600/2, which is not convincing.
7. The conclusion did not elucidate the main findings and contributions in terms of scientific and industrial perspectives.

Author Response

Dear Reviewer, 

Thank you for your valuable comments. Please find attached the answers.

Author Response File: Author Response.pdf

Reviewer 3 Report

Poor novelty, insignificant contribution to the research progress in this field. 

Author Response

Dear Reviewer,

Thank you for your valuable comments. Please find attached the answers.

Author Response File: Author Response.pdf

Reviewer 4 Report

1. Line 1. Please select the type of paper.
2. In the abstract, some relevant and quantitative results should be presented (e.g. specify the heating rate/temperatures/ residence times of the experiments and pyrolysis products). Instead of PAHs please use Polycyclic aromatic hydrocarbons.
3. What type of apparatus (e.g. thermogravimetric analyzer, mill) was used. Please state manufacturer/company, city and country from where equipment has been sourced.
4. How the obtained results in g can prove the operation of large-scale industrial systems?
5. What about the heat and mass transfer constraints of TGA experiments, can that reliable compared with real scale systems?
6. Why a fixed bed reactor was used?
7. Define better conclusions, it should vary vague and support better what the innovation is, the unique finding of this work as compared to similar works in international literature done through the years. The conclusion should better reflect the content of the paper and the main results.
8. The reference list is deficient. There are several recent topical references concerning the TGA, pyrolysis study not included, e.g. https://doi.org/10.3390/en13174472, https://doi.org/10.3390/en13092318
9. The titles of references have a different formats. The title of the article is written in capital letters at the beginning of words, others only in lower case. Also, the standardized format of presentation in the journal's name. Because names have been written in a different format, one is not abbreviated, and others are not.

Author Response

Dear Reviewer,

 

Tjank you for your valuable comments. Please find attached the answers.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have largely improved their manuscript and, in most cases, properly replied my criticisms and queries. 

Still, authors should work in the English language of the text (including the new added sentences), and correct some minor format mistakes such as citing the new Table 1 in the text, separation of Table 3 from Figure 4, etc.

Besides, I think that the word rhizomes should be always with Miscanthus. Thus, Figure 1 caption should be "Figure 1.  Thermogravimetric curve of Miscanthus rhizomes". The same goes for other Tables and Figures, when it is pertinent.

Author Response

Dear Reviewer, 

please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

The authors had addressed to my previous concern properly. 

Author Response

Dear Reviewer, 

please see the attachment.

Author Response File: Author Response.docx