Catalytic Co-Pyrolysis of Mesua ferrea L. De-Oiled Cake and Garlic Husk in the Presence of Red-Mud-Based Catalysts

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors studied the catalytic pyrolysis of two waste streams. First of all, using red mud as a catalyst for pyrolysis has been widely studied. In addition, personally speaking, the rationale of co-pyrolysis is weak if researchers randomly select any two or more feedstock just for paper publication. Unless the final product quality can be greatly improved due to some specific mutual reactions compared to individual pyrolysis, then, co-pyrolysis is worth studying. Moreover, half of the results are focused on the characterization of experimental materials, which is boring to me. Most of these analyses can be put in the supplemental information. Readers care more about the final product.

Comments on the Quality of English Language

above average and acceptable

Author Response

Reviewer-1

 

Minor Comments

 

1. The authors studied the catalytic pyrolysis of two waste streams. First of all, using red mud as a catalyst for pyrolysis has been widely studied. In addition, personally speaking, the rationale of co-pyrolysis is weak if researchers randomly select any two or more feedstock just for paper publication. Unless the final product quality can be greatly improved due to some specific mutual reactions compared to individual pyrolysis, then, co-pyrolysis is worth studying. Moreover, half of the results are focused on the characterization of experimental materials, which is boring to me. Most of these analyses can be put in the supplemental information. Readers care more about the final product.

Ans. The authors have included a detailed literature explaining the reason behind considering these types of wastes and the potential application of conversion of these wastes to value-added products. The results are explained more clearly aiming the end application of the final product.

Reviewer 2 Report

Comments and Suggestions for Authors

Do the authors anticipate separating the catalyst from the char after the pyrolysis process?

Can the catalyst be used multiple times, and if so, are there any regeneration processes required?

The use of a catalyst in a 1:1 ratio with the material subjected to pyrolysis is highly energy-intensive. Heating such a large amount of catalyst significantly reduces the economic justification for the pyrolysis process.

Considering the cost of the catalyst, the potential reactor scale-up costs in the case of catalyst use, and the expense of its regeneration, is using the catalyst cost-effective? Given all the costs, does using the catalyst remain worthwhile? The reviewer sees limited potential for industrial application of the presented research.

 

In Figure 3, the "MDC + GH" graph should represent the combination of the graphs for MDC and GH. However, the graph currently depicts something entirely different. I kindly request a comment or explanation regarding this inconsistency.

 

I kindly request the authors to provide an explanation for the rationale behind conducting catalytic pyrolysis on this waste material. The paper addresses the aspect of enhancing the Higher Heating Value (HHV) of the oils, but would it not have been more beneficial to incinerate these wastes without undergoing catalytic pyrolysis? Furthermore, do the resultant oils have any applications beyond their use as fuels?

Obtaining Bis(2-ethylhexyl) phthalate as the main component of the pyrolytic oil seems rather unlikely. This is a complex compound, and during biomass pyrolysis, a wide range of substances is typically produced, without this specific compound being the predominant one.

The quantity of Bis(2-ethylhexyl) phthalate obtained in the catalytic process is not provided, and the GC-MS analysis appears to be somewhat unclear. Would the authors be able to present all results of GC-MS in a table for better clarity?

 

In Figure 8, only the results for co-pyrolysis are presented. Do the authors have similar results for the individual feedstocks as well?

 

 

 

Author Response

Reviewer-2

 

Minor Comments

1. Do the authors anticipate separating the catalyst from the char after the pyrolysis process?

Ans. In our current study, we did not specifically discuss how to separate the catalyst from the char. The primary focus of our research was to demonstrate the catalytic effects of the red-mud based catalyst during pyrolysis. However, we acknowledge that in real-world industrial applications, the catalyst must be separated from the char to be used continuously and effectively.

2. Can the catalyst be used multiple times, and if so, are there any regeneration processes required?

Ans. This study does not include the regenerability and recyclability studies of the catalyst. 

3. The use of a catalyst in a 1:1 ratio with the material subjected to pyrolysis is highly energy-intensive. Heating such a large amount of catalyst significantly reduces the economic justification for the pyrolysis process.

Ans. The selection of a (1:1) feedstock ratio in our study was made after conducting preliminary characterization and optimization studies. Whereas the catalyst to feedstock ratio is selected as (1:5). This ratio was chosen to maximise the catalytic impact of the Red-mud based catalyst.

4. Considering the cost of the catalyst, the potential reactor scale-up costs in the case of catalyst use, and the expense of its regeneration, is using the catalyst cost-effective? Given all the costs, does using the catalyst remain worthwhile? The reviewer sees limited potential for industrial application of the presented research.

Ans. The economic viability of using the catalyst may differ based on certain industrial  applications, even if cost considerations are essential for industrial approval. The primary goal of our research is to demonstrate the catalytic capability of using red mud. To establish a firm opinion of its cost-effectiveness, additional economic analyses and feasibility studies suited to industrial scenarios would be required. We note the reviewer's concerns and value their input, but we also acknowledge that practical implementation might require additional economic analysis.

5. The quantity of Bis(2-ethylhexyl) phthalate obtained in the catalytic process is not provided, and the GC-MS analysis appears to be somewhat unclear. Would the authors be able to present all results of GC-MS in a table for better clarity?

Ans. Thank you for your comments. The quantity of Bis(2-ethylhexyl) phthalate have been highlighted in section 3.6.

 

Major Comments

1. In Figure 3, the "MDC + GH" graph should represent the combination of the graphs for MDC and GH. However, the graph currently depicts something entirely different. I kindly request a comment or explanation regarding this inconsistency.

Ans. The co-pyrolysis of different biomass, such MDC and GH can result in a synergistic effect, which enhances specific reaction pathways. When using two or more biomass as pyrolysis feedstocks, such as MDC And GH, their combined effect leads to complex interactions that affect the overall pyrolysis behavior. These interactions can alter the thermal degradation behavior, leading to unexpected deviations from the individual pyrolysis behavior of biomass.

2. I kindly request the authors to provide an explanation for the rationale behind conducting catalytic pyrolysis on this waste material. The paper addresses the aspect of enhancing the Higher Heating Value (HHV) of the oils, but would it not have been more beneficial to incinerate these wastes without undergoing catalytic pyrolysis? Furthermore, do the resultant oils have any applications beyond their use as fuels?

Ans. Enhancing the Higher Heating Value (HHV) of the oils made from these waste biomass was the primary objective of our research. We sought to improve the quality of the bio-oils through catalytic pyrolysis, making them suitable to being utilised as fuels. Catalytic co-pyrolysis of these waste biomass facilitates the synthesis of high value bio-oil fractions with future applications beyond conventional thermochemical conversion technology. While our research has focused on utilizing bio-oil as fuels, it is crucial to remember that these oils can also be used in various other applications. Bio-oils can be used as feedstocks to produce chemicals and other bio-based materials. They can also be blended with traditional fuels to reduce their environmental footprint.

3. Obtaining Bis(2-ethylhexyl) phthalate as the main component of the pyrolytic oil seems rather unlikely. This is a complex compound, and during biomass pyrolysis, a wide range of substances is typically produced, without this specific compound being the predominant one

Ans. Yes, the authors agree with the Reviewer’s comment. Necessary Modifications have been made and a part of section 3.5 is rewritten.

4. In Figure 8, only the results for co-pyrolysis are presented. Do the authors have similar results for the individual feedstocks as well?

Ans. Thank you for your comment. The figure is modified.

Reviewer 3 Report

Comments and Suggestions for Authors

Comments to the Author:

This manuscript titled “Catalytic co-pyrolysis of Nahar de-oiled cake and Garlic husk in the presence of Red-mud based catalysts” by Abhishek and co-authors studied the catalytic co-catalysis of de-oiled cake and Garlic husk over red mud based catalysts. This catalysts worked to reduce oxygen, but increase carbon yield remained in bio-oil. This study has good strong results analysis, and data support. Overall, I can recommend the publication after following revisions.

 

Introduction section: why did author use garlic husk? Is this a kind of biomass waste? Can authors give more brief introduction to garlic husk?

For the red mud, what is the most widely used disposal ways for it?

For metal loaded catalysts, they are usually used for catalysis in hydrogen gas environment, so why did the author use Ni loading, especially in nitrogen environment? How did the Ni metal work to de-oxygen in nitrogen?

Please provide a higher resolution one for Figure 2b.

In Figure 2c, why did the peak at wavenumber 1000cm^-1 become weaker after Ni loading?

For Figure 3, the first initial mass loss should be at around 100 ºC because of the evaporation of free moisture, in Figure 3 DTG plot, it is around 70-75 ºC and please see the first trough. At 150 ºC, there is a very small peak in DTG, this is should be due to release of bound water, or maybe some dehydration, and light volatiles. Please double check and revise.

What is the reuse performance of red mud catalyst?

Author Response

Reviewer-3

 

Minor Comments

 

1. Introduction section: why did author use garlic husk? Is this a kind of biomass waste? Can authors give more brief introduction to garlic husk?

Ans. Thank you for your comment. Necessary Modifications have been made in Introduction section.

2. For the red mud, what is the most widely used disposal ways for it?

Ans. Since red-mud is an industrial waste during the extraction of alumina (aluminium oxide) from bauxite ore in the Bayer process. The most widely used methods for disposal of red mud includes pond storage, dry stacking, and exploring potential beneficial uses such as in construction materials.

3. For metal loaded catalysts, they are usually used for catalysis in hydrogen gas environment, so why did the author use Ni loading, especially in nitrogen environment? How did the Ni metal work to de-oxygen in nitrogen?

 Ans. Although it is true that many catalytic reactions, particularly those involving hydrogenation, take place in hydrogen-rich environments, the objective of our study was to examine the distinct function of the Ni catalyst in nitrogen-rich environments. In pyrolysis studies, nitrogen is frequently used as an inert atmosphere to prevent undesired oxidation reactions and ensure the analysis of deoxygenation explicitly.

4. What is the reuse performance of red mud catalyst?

Ans. Though this study does not include reusability of red-mud catalyst, there is literature available on reusability of red-mud catalysts for various other applications (An et al., 2023; Chen et al., 2022).

 

Major Comments

 

1. Please provide a higher resolution one for Figure 2b.

Ans. Thank you for your comment. The figure is modified.

2. In Figure 2c, why did the peak at wavenumber 1000cm^-1become weaker after Ni loading?

Ans. The addition of Ni to Red mud catalyst can result in chemical transformation within the catalyst surface. Ni may interact with components of red mud and alter its chemical structure. Since Red mud contains various functional groups or substances that can absorb at about 1000 cm^-1, these groups or substances would experience chemical changes in the presence of Ni, changing the FTIR spectra.

3. For Figure 3, the first initial mass loss should be at around 100 ºC because of the evaporation of free moisture, in Figure 3 DTG plot, it is around 70-75 ºC and please see the first trough. At 150 ºC, there is a very small peak in DTG, this is should be due to release of bound water, or maybe some dehydration, and light volatiles. Please double check and revise.

Ans.  The Authors agree with the Reviewer’s comments. Necessary Modifications have been made.

 

References

1. An, Q., Tang, M., Deng, S., Jiao, Y., Liu, C., Yang, M., Ye, Z., & Zhao, B. (2023). Methyl Orange Degradation with Peroxydisulfate Activated with the Synergistic Effect of the Acid-Modified Red Mud and Biochar Catalyst. Arabian Journal for Science and Engineering, 48(7), 8819–8834. https://doi.org/10.1007/s13369-022-07398-w
2. Chen, J., Wang, D., Luo, F., Yang, X., Li, X., Li, S., Ye, Y., Wang, D., & Zheng, Z. (2022). Selective production of alkanes and fatty alcohol via hydrodeoxygenation of palmitic acid over red mud-supported nickel catalysts. Fuel, 314. https://doi.org/10.1016/j.fuel.2021.122780

 

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

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