Investigation of Thermochemical Properties and Pyrolysis of Barley Waste as a Source for Renewable Energy
, Juntakan Taweekun 2,*, Shammya Afroze 3, Shohel Ahmed Siddique 4, Md. Shahinoor Islam 5,6,*, Chongqing Wang 7,* and Abul K. Azad 3
Round 1
Reviewer 1 Report
Reviewer Comments
The study entitled “Investigation of Thermochemical Properties and Pyrolysis of Barley Waste for Renewable Energy Source” aims to characterize and pyrolyze barley waste to evaluate the potentiality of producing biofuels as a substitute for renewable energy sources. By different kinds of analysis, it is concluded that barley waste can be a valuable source of renewable energy due to its good qualities and pyrolysis yields. But the article needs to resolve the following Major Revisions before publication.
- The Abstract needs to be revised as it is not following the basic guidelines to write an abstract i.e. problem statement, scope of the study in the literature, objective of the study, methodology used in the article, results, conclusions, limitations, and future directions.
- The article is lacking in the connection between the paragraphs. Please revise the whole article and try to create a story for a clear understanding of the process. For example,
● There is no introduction given about the ASTM method. What is this method? Why it is important to follow this study?
● Heading 2.3 has no background that why these parameters are required to find out.
● Table 1: The background for Elephant grass, Imperata cylindrical, and Switchgrass are missing. Same for Table 2.
- Figure 1: The sample preparation process can define in one sentence in the text. It would be better to add pictures of the samples instead of writing just the processes' names. The study will be better supported by pictures.
- Proximate Analysis and Ultimate Analysis are repeated in headings names i.e Heading 2.3 and 3.1. Isn’t it better to choose different terms for the same headings in the results section or manage the data in the same paragraph?
- It is mentioned in the article that different sample analyses (Ultimate analysis, Morphology and elemental analysis (SEM/EDX), etc, ) took place at different laboratories (Japan, Thailand, etc). Please explain how this whole process is managed with the same samples.
- Figure 3: It is suggested to add the real picture of the pyrolysis setup as well. Also, make the caption of the figure technical.
- Please describe, what is the significance of figure 4 to this study.
- Figure 6: It is better to zoom in on the required part of the figure instead of pasting the full window as it would be clear to understand.
- Figure 7: Please revise the figure and it would be better to highlight the values of the wavenumber on the line graph.
- It is suggested to revise the grammar of the article as well.
Author Response
Reviewer Comments
The study entitled “Investigation of Thermochemical Properties and Pyrolysis of Barley Waste for Renewable Energy Source” aims to characterize and pyrolyze barley waste to evaluate the potentiality of producing biofuels as a substitute for renewable energy sources. By different kinds of analysis, it is concluded that barley waste can be a valuable source of renewable energy due to its good qualities and pyrolysis yields. But the article needs to resolve the following Major Revisions before publication.
Response: Thanks for the comments. We responded to all the specific comments accordingly.
Comment 1. The Abstract needs to be revised as it is not following the basic guidelines to write an abstract i.e. problem statement, scope of the study in the literature, objective of the study, methodology used in the article, results, conclusions, limitations, and future directions.
Response: According to the suggestion of the reviewer we have updated the abstract (Line 22,23,37~39).
Comment 2. The article is lacking in the connection between the paragraphs. Please revise the whole article and try to create a story for a clear understanding of the process. For example,
- There is no introduction given about the ASTM method. What is this method? Why it is important to follow this study?
- Heading 2.3 has no background that why these parameters are required to find out.
- Table 1: The background for Elephant grass, Imperata cylindrical, and Switchgrass are missing. Same for Table 2.
Response: According to the suggestion of the reviewer we have updated the manuscript (Line 52, 53, 64, 69,70, 81~84, 207, 216, 229, 338).
Comment 3. Figure 1: The sample preparation process can define in one sentence in the text. It would be better to add pictures of the samples instead of writing just the processes' names. The study will be better supported by pictures.
Response: We have mentioned and explained the process as a diagram. For the privacy issue of the lab, we have avoided the pictures.
Comment 4. Proximate Analysis and Ultimate Analysis are repeated in headings names i.e Heading 2.3 and 3.1. Isn’t it better to choose different terms for the same headings in the results section or manage the data in the same paragraph?
Response: Section 2 is for the experiment and section 3 is for the analysis and discussion. For homogeneity, we mentioned the same heading for two different sectors.
Comment 5. It is mentioned in the article that different sample analyses (Ultimate analysis, Morphology and elemental analysis (SEM/EDX), etc,) took place at different laboratories (Japan, Thailand, etc). Please explain how this whole process is managed with the same samples.
Response: The raw sample we collected, prepared and stored at one time in different sealed bags. We used sealed samples for different experiments in different laboratories.
Comment 6. Figure 3: It is suggested to add the real picture of the pyrolysis setup as well. Also, make the caption of the figure technical.
Response: We have mentioned and explained the process as a diagram. For the privacy issue of the lab we have avoided the pictures.
Comment 7. Please describe, what is the significance of figure 4 to this study.
Response: According to the suggestion, we have explained the significance (Line 302, 303).
Comment 8. Figure 6: It is better to zoom in on the required part of the figure instead of pasting the full window as it would be clear to understand.
Response: According to the suggestion of the reviewer we have shown the bigger picture (Line 352).
Comment 9. Figure 7: Please revise the figure and it would be better to highlight the values of the wavenumber on the line graph.
Response: According to the suggestion of the reviewer we have updated the figure (Line 371).
Comment 10. It is suggested to revise the grammar of the article as well.
Response: According to the suggestion of the reviewer we have revised the manuscript.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
I consider that the present manuscript is acceptable to be published in Sustainability with major revisions and with the addition of new results. The subject matter is adequate for the Journal and I find the contributions are interesting. The work presented is framed within a current topic of biomass valorization. The present paper of Reza and col. reports the optimization of pyrolytic conditions for processing Barley waste, which is a crucial by-product in agricultural production. I consider that the main problems of the article include the scarce characterization of biomass material and the insufficient analysis of pyrolysis products. For example, neither our own results nor bibliographical references that provide information related to the cellulose, hemicellulose and lignin content of the original biomass are shown. The proportion of these polymers, together with the content of proteins, volatiles and others, characterize the biomass. The relative content of the biopolymers determines the quality of the pyrolytic bioliquid. Please review the following points:
1-In figure 2 the text “ash content” is repeated
2-Experimental Section: Please indicate clearly how the yields are calculated for each fraction (solid, liquid and gas). Add the necessary equations.
3-Experimental Section: Condensable gases only have contact with a refrigerant? What temperature was it? Was any other condensation system used?
4-Experimental Section: In the text (line 163) it is mentioned: “the bio-oil was taken from the Erlenmeyer flask.”. However, usually a fraction of the bioliquid can be retained as waxes in the reactors/condensation system. Were waxes observed? These compounds, that present low fluidity, were taken into account to determine the yield to the liquid fraction?
5- Experimental Section: With the heating ramp used for this work (25°C/min) it can be considered that a slow pyrolysis is carried out. For how long was the biomass left at the desired temperature?
6- In order to maximize the yield towards the liquid fraction, was an attempt made to heat the reactor to the desired temperature in a very short time?
7- Experimental Section: Details related to thermogravimetric measurements are missing. For example cell used, substrate mass, gas phase flow rate, etc..
8- The TGA in an oxidizing atmosphere was carried out with pure O2(g)? Please clarify in the text. Usually during thermogravimetric measurements a gas stream is used that also contains inert.
9-Could the authors provide information related to the cellulose, hemicellulose and lignin content of the original sample? If they do not have their own results, they could add bibliographical references.
10-Please carefully review the following paragraph (line 183): “ The volatile matter is the part in the sample that is driven off as the gases, including moisture at high temperatures [26]. Combustible substances (tars, light hydrocarbons, CH4, CO, H2, C2H2, H2S,, and other similar substances) and certain non-combustible substances make up the majority of volatile matter (CO2, HCl, H2O, N2, NO, NO2, N2O, NH3, SO2, KCl, NaCl, SO3, NaOH, and KOH) [27]. If the VM is high in biomass, the reactivity will be increased for the thermochemical process. Generally, it varies from 60-85% for the biomass [26]….
The percentage called VM (~73 wt.%), shown in Table 1, is the fraction that generates gases during the combustion process. If incomplete combustion occurs (most likely at low temperature) remaining hydrocarbon molecules and CO2, CO, H2O, etc. may be generated. Please clarify that the discussion is approached considering an oxidizing atmosphere. Please, expand this discussion and indicate which biomass compounds are those that generate the MV. In addition, indicate at what temperature the combustion of the so-called volatiles occurs and that corresponding to the combustion of biochar. How would the values of MV, FC and ashes affect the performance and quality of the pyrolytic bioliquid?
11-What do the authors mean when they mention "reactivity"? During the pyrolysis process, non-condensable gases and condensable gases are formed. The latter give rise to the formation of the bioliquid. The reactivity of the molecules that are formed during pyrolysis and the probability of secondary reactions will strongly depend on the original composition of the initial biomass and the reactive functional groups.
12-Although it is mentioned that the atomic ratios of (N+O)/C (0.760), O/C (0.690), H/C (1.770), and the percentages of carbon (46.04%), hydrogen (6.84%), and other elements are very competitive to other biomass for the generation of bioenergy, the authors do not show any property of the bioliquid that allows deducing or obtaining “a priori” an indication of its quality. For example, authors should add the pH and the elemental composition (CHONS) of the obtained bioliquid and, also should calculate the effective hydrogen ratio (H/C eff). H/Cef is understood as the relative abundance of hydrogen in the bioliquid and it is calculated with the following equation: H/Cef=(H − 2O)/C where H, C and O are the number of moles of each element in the bioliquid. [X. Li, Appl. Catal. A, 455 (2013) 114–121]. On the other hand, it is recommended to carry out a GC-MS analysis of the bioliquid, these data would provide valuable information for a subsequent upgrading process.
Author Response
Comments and Suggestions for Authors
General Comments: I consider that the present manuscript is acceptable to be published in Sustainability with major revisions and with the addition of new results. The subject matter is adequate for the Journal and I find the contributions are interesting. The work presented is framed within a current topic of biomass valorization. The present paper of Reza and col. reports the optimization of pyrolytic conditions for processing Barley waste, which is a crucial by-product in agricultural production. I consider that the main problems of the article include the scarce characterization of biomass material and the insufficient analysis of pyrolysis products. For example, neither our own results nor bibliographical references that provide information related to the cellulose, hemicellulose and lignin content of the original biomass are shown. The proportion of these polymers, together with the content of proteins, volatiles and others, characterize the biomass. The relative content of the biopolymers determines the quality of the pyrolytic bioliquid. Please review the following points:
Response: Thanks for the above general comments. We addressed all the specific comments.
Comment 1-In figure 2 the text “ash content” is repeated
Response: According to the suggestion of reviewer we have revised the figure 2 (Line 116).
Comment 2-Experimental Section: Please indicate clearly how the yields are calculated for each fraction (solid, liquid and gas). Add the necessary equations.
Response: According to the suggestion of reviewer we have mentioned the equations (Line 186~192).
Comment 3-Experimental Section: Condensable gases only have contact with a refrigerant? What temperature was it? Was any other condensation system used?
Response: According to the suggestion of reviewer we have updated this section (Line 180, 181).
Comment 4-Experimental Section: In the text (line 163) it is mentioned: “the bio-oil was taken from the Erlenmeyer flask.”. However, usually a fraction of the bioliquid can be retained as waxes in the reactors/condensation system. Were waxes observed? These compounds, that present low fluidity, were taken into account to determine the yield to the liquid fraction?
Response: For the calculation of bio-oil yield, we considered everything inside the Erlenmeyer flask as bio-oil. For future studies, we will distillate the products to determine different composition.
Comment 5- Experimental Section: With the heating ramp used for this work (25°C/min) it can be considered that a slow pyrolysis is carried out. For how long was the biomass left at the desired temperature?
Response: According to the suggestion of reviewer we have mentioned the period (Line 179,180)
Comment 6- In order to maximize the yield towards the liquid fraction, was an attempt made to heat the reactor to the desired temperature in a very short time?
Response: According to the suggestion of reviewer we have mentioned the process (Line 176).
Comment 7- Experimental Section: Details related to thermogravimetric measurements are missing. For example cell used, substrate mass, gas phase flow rate, etc.
Response: As the TGA was done form PSU, Thailand the available information which we have was mentioned here.
Comment 8- The TGA in an oxidizing atmosphere was carried out with pure O2(g)? Please clarify in the text. Usually during thermogravimetric measurements a gas stream is used that also contains.
Response: According to the suggestion of reviewer we have clarified this inert (Line 169, 170).
Comment 9-Could the authors provide information related to the cellulose, hemicellulose and lignin content of the original sample? If they do not have their own results, they could add bibliographical references.
Response: Sorry, we didn’t perform the lignocellulosic compositional analysis. In our future studies, we will perform these analyses.
Comment 10-Please carefully review the following paragraph (line 183): “ The volatile matter is the part in the sample that is driven off as the gases, including moisture at high temperatures [26]. Combustible substances (tars, light hydrocarbons, CH4, CO, H2, C2H2, H2S,, and other similar substances) and certain non-combustible substances make up the majority of volatile matter (CO2, HCl, H2O, N2, NO, NO2, N2O, NH3, SO2, KCl, NaCl, SO3, NaOH, and KOH) [27]. If the VM is high in biomass, the reactivity will be increased for the thermochemical process. Generally, it varies from 60-85% for the biomass [26]….
The percentage called VM (~73 wt.%), shown in Table 1, is the fraction that generates gases during the combustion process. If incomplete combustion occurs (most likely at low temperature) remaining hydrocarbon molecules and CO2, CO, H2O, etc. may be generated. Please clarify that the discussion is approached considering an oxidizing atmosphere. Please, expand this discussion and indicate which biomass compounds are those that generate the MV. In addition, indicate at what temperature the combustion of the so-called volatiles occurs and that corresponding to the combustion of biochar. How would the values of MV, FC and ashes affect the performance and quality of the pyrolytic bioliquid?
Response: According to the suggestion of reviewer we have updated this section (Line 210~212, 218~222).
Comment 11-What do the authors mean when they mention "reactivity"? During the pyrolysis process, non-condensable gases and condensable gases are formed. The latter give rise to the formation of the bioliquid. The reactivity of the molecules that are formed during pyrolysis and the probability of secondary reactions will strongly depend on the original composition of the initial biomass and the reactive functional groups.
Response: According to the suggestion of reviewer we have explained this section (Line 218~220).
Comment 12-Although it is mentioned that the atomic ratios of (N+O)/C (0.760), O/C (0.690), H/C (1.770), and the percentages of carbon (46.04%), hydrogen (6.84%), and other elements are very competitive to other biomass for the generation of bioenergy, the authors do not show any property of the bioliquid that allows deducing or obtaining “a priori” an indication of its quality. For example, authors should add the pH and the elemental composition (CHONS) of the obtained bioliquid and, also should calculate the effective hydrogen ratio (H/C eff). H/Cef is understood as the relative abundance of hydrogen in the bioliquid and it is calculated with the following equation: H/Cef=(H − 2O)/C where H, C and O are the number of moles of each element in the bioliquid. [X. Li, Appl. Catal. A, 455 (2013) 114–121]. On the other hand, it is recommended to carry out a GC-MS analysis of the bioliquid, these data would provide valuable information for a subsequent upgrading process.
Response: For the basic characterization we have mentioned the results from the ultimate analysis. The individual characterization of the pyrolytic products and GC-MS analysis will be done in future work.
Author Response File: Author Response.pdf
Reviewer 3 Report
I have some minor requests for the manuscript. Please check the file for more information.
Comments for author File: Comments.pdf
Author Response
Comments and Suggestions for Authors
I have some minor requests for the manuscript. Please check the file for more information.
Comment to the authors :
The author presented the interested topic on investigating the barley waste for future application as the feedstock for the source of renewable sources. The studied results might be promising for the future sustainable biofuel. I have some minor comments on this manuscript.
Comment 1. Figure 5, the scale bar should be added with bigger size on SEM images
Response: According to the suggestion to the reviewer we have included the bigger SEM images with a scale bar (Line 340).
Comment 2. Figure 7, the important and representative wavelength number (fingerprint region) should be added with their bondage name for better description on the visual aids.
Response: According to the suggestion to the reviewer we have included the bondage name for the related wavelength (Line 371).
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The paper has been revised accordingly.
Author Response
We appreciate the reviewer's time and comments.
Reviewer 2 Report
In this short time, part of the suggested changes were made. Mainly, some aspects related to the experimental details were improved. However, some suggested experiences, which could give a greater value to the work, have not been carried out. Results of characterizations of the starting material and results of the yields to biochar, biogas and bioliquid fractions are presented. Characteristics of the pyrolysis products are not shown, which could be very interesting, and , also, it would give an accurate idea of the potential use of pyrolysis products. Could the authors re-evaluate the possibility of carrying out some characterization of the products? For example, elemental analysis of the bioliquid or SEM-EDX of the biochar
As minor points, the following points could be improved:
1- Line 237: In the pyrolysis process, ash could show catalytic activity for biofuel generation [31]. Could the authors resume this discussion taking into account the SEM-EDX results? What ions could catalytically influence pyrolysis?
2- If only the bioliquid collected in the Erlenmeyer flask is taken into account, the real yield to bioliquid could be a bit higher.
Author Response
Comments and Suggestions for Authors
Comment : In this short time, part of the suggested changes were made. Mainly, some aspects related to the experimental details were improved. However, some suggested experiences, which could give a greater value to the work, have not been carried out. Results of characterizations of the starting material and results of the yields to biochar, biogas and bioliquid fractions are presented. Characteristics of the pyrolysis products are not shown, which could be very interesting, and, also, it would give an accurate idea of the potential use of pyrolysis products. Could the authors re-evaluate the possibility of carrying out some characterization of the products? For example, elemental analysis of the bioliquid or SEM-EDX of the biochar.
Response: We highly appreciate the above comments. However, in the current stage, we are unable to perform a full set of experiment. We will consider these suggestions for our future experimental plan. We have revised the paper from literature value as yellow mark in the manuscript (Line 452~457, 467~471, 484~489, 497~499).
As minor points, the following points could be improved:
Comment: 1- Line 237: In the pyrolysis process, ash could show catalytic activity for biofuel generation [31]. Could the authors resume this discussion taking into account the SEM-EDX results? What ions could catalytically influence pyrolysis?
Response: According to the suggestion of the reviewer we have revised this part (Line 242~245).
Comment: 2- If only the bioliquid collected in the Erlenmeyer flask is taken into account, the real yield to bioliquid could be a bit higher.
Response: According to the suggestion of the reviewer we have updated this portion (Line 192, 193).
Author Response File: Author Response.pdf
Round 3
Reviewer 2 Report
Although no new results have been added, the manuscript has been improved. New references and discussions have been added. It is suggested that the work be accepted.
