Catalytic Transformation of Biomass-Derived Hemicellulose Sugars by the One-Pot Method into Oxalic, Lactic, and Levulinic Acids Using a Homogeneous H2SO4 Catalyst
Round 1
Reviewer 1 Report
The authors made an effort to directly converting the hemicellulose to fine chemicals which are significantly important. Although the use of corrosive sulfuric acid is problematic and the process is against the environmental, but I can recommend the paper if the authors made the several changes as per my direction. I would like to see a revised version of this paper after they made all the comments.
1. There is a gradual increase in the products from hemicellulose as going from 0.1 M to 0.5 M sulfuric acid, while the yield was decreased beyond the concentration of 0.5 M, why? What are the by-products that are expected to be formed simultaneously?
2. The authors are encouraged to show their results diagrammatically / in a couple of figures.
3. Did the reactions are performed under autogenic pressure? or it requires an externally pressurized reactor?
4. The authors should highlight any pre-treatment of hemicellulose, if they have done.
5. I would like to see the NMR spectra or any other characterization methods to justify the products are formed at all, also the HPLC chromatogram is encouraged to provide.
Biomass conversion to platform chemicals is the topmost scientific priority that is required currently. Authors can cite several important papers on biomass conversions: Nanoscale 2022, 14 (42), 15875-15888; Chemical Engineering Journal, 2022, 450, Part 2, 138032; DOI: 10.1016/j.cej.2022.138032
6. Also, the organocatalytic approach for biomass valorization is growing interest in the academia and industry since this is more environmentally appealing. Authors are required to cite the important papers in the respective section: ACS Sustainable Chemistry & Engineering 2021, 9 (37), 12431-12460.
7. Authors should correct line no 90. Hydrolysis/dehydration follows the conversion of aldohexoses to HMF and then rehydration to levulinic acid, formic acid and so on.
8. In figure 2, the structures of rhamnose and glucuronic acid were poorly executed. Redraw
9. The comparative study based on previous literature survey is encouraged to show by the authors during the discussion of their results.
10. Conclusion is significantly erroneous and therefore a high quality and more correction is required in this section.
11. Why not the authors show the mechanism of their product formations in a stepwise manner?
Author Response
Dear Reviewer,
We are appreciate for all comments and suggestions, which we followed accordingly.
In the file you can find our answers and detailed explanations.
With kind regards,
Izabela Czekaj
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This article is devoted to the study of catalytic transformations of hemicellulose sugars into oxalic, lactic and levulinic acids using the H2SO4 catalyst. The article is written in a clear and accessible language. The main ideas of this article do not raise questions. However, there are some points that it is desirable to finalize:
1. Abstract needs to be expanded and reworked.
2. Sulfuric acid is one of the traditional reagents in biomass processing. Recently, there has been a trend towards the transition from sulfuric acid to solid acid catalysts. Sulfuric acid is increasingly being abandoned in science and industry. Why did the authors choose this particular reagent for the study?
3. It is desirable to justify why the authors take these ratios of hemicellulose sugars.
4. It is desirable to add more comparison with literary sources. There are many results in the literature for both solid catalysts and H2SO4 in this (and similar) process.
5. Please cite: 10.1007/s00226-022-01363-4.
6. Part "Discussion" should be significantly expanded. A significant part of the article is a table. The authors need to describe them in more detail.
Author Response
Dear Reviewer,
We are appreciate for all comments and suggestions, which we followed accordingly.
In the file you can find our answers and detailed explanations.
With kind regards,
Izabela Czekaj
Author Response File: Author Response.pdf
Reviewer 3 Report
In this manuscript, one-pot method was used to convert biomass-derived hemicellulose carbohydrates to oxalic acid (OA), lactic acid (LA), and levulinic acid (LA) using H2SO4 as a catalyst at various molar concentrations (0.1-1 M) in the temperature range of 100 to 250 °C. Both the work's content and writing are good. The manuscript will be considered after a minor revision.
1. There is a two notations for levulinic acid in 87 and 92 lines. Please correct it.
2. Please add the comparison table of your work with literature.
3. I have found all the references are old. Please add recent literature
4.In line 12, the lactic acid and levulinic notations are the same. Please correct it.
5. In line 125, the xylose composition is 550%. Please correct the right value.
6. The total compositions of mixtures (M1, M2 and M3) should be 100%. But the values are not 100%. M3 value is exceeded. Please check the values.
7 I have found many publications on dilute sulfuric acid-catalyzed hemicellulose hydrolysis. What is the novelty of your work? Please add the necessary discussion in the introduction.
8. In Table.1 When the reaction temperature is increased from 100 to 200°C, the conversion drops from 87% to 16% for 0.1 M H2SO4. Why this drastic fall in the conversion?
9. The discussion of the results is very brief. The authors improve the discussion of how the reaction temperature and Sulphuric acid concentration influence the product distribution.
Author Response
Dear Reviewer,
We are appreciate for all comments and suggestions, which we followed accordingly.
In the file you can find our answers and detailed explanations.
With kind regards,
Izabela Czekaj
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Although the authors made an effort, however question 6 was not answered as well as English writing needs to be improved. Also, conclusion is not fully justified. Authors should re-consider this in their next version.
Reviewer 2 Report
Accepted
