Effective Depolymerization of Sodium Lignosulfonate over SO42−/TiO2 Catalyst
Round 1
Reviewer 1 Report
The manuscript entitled “Effective depolymerization of sodium lignosulfonate over SO42-/TiO2 catalyst” from Gu and coworkers explores the optimization of reaction conditions for depolymerization of sodium lignosulfonate in methanol/glycerol using SO42-/TiO2 the catalyst to obtain bio-oil and high-value chemicals. The authors studied the effect of temperature, catalyst loading, reaction time, etc. over the yield of oil and liquefaction. Furthermore, authors have analyzed the liquefaction products using analytical tools such as GC-MS, FT-IR, etc. However, the following description details my concerns about this manuscript; I would like to reconsider the detailed review after resubmission of the article after addressing the below major concerns. Without addressing the below mentioned methodological errors, it is hard to consider the manuscript for the publication in the journal Catalysts.
- I have the biggest concern about the experimental design/procedure, Authors have used 70 °C bath temperature to remove reaction solvent methanol using a rotary evaporator under reduced pressure (I assume). I believe at this bath temperature under reduced pressure authors might have distilled out the majority of liquids, which are below 150 °C boiling point e.g. acetic acid. To remove methanol under reduced pressure on the rotary evaporator authors should use around 40 °C bath temperature to avoid distillation of low boiling liquids along with methanol. Hence, I believe the characterization and reported composition of bio-oil is definitely inconsistent. Moreover, the authors used ethyl acetate (10 mL) to extract bio-oil from the aqueous phase, which I believe is not sufficient. Authors might not have succeeded in extracting complete bio-oil from the aqueous phase. Authors need to extract the aqueous phase, at least three times with around 30 mL of ethyl acetate each time (3 × 30 mL). Moreover, the aqueous phase also needs to analyze to assess any water-soluble material in it. Hence, authors need to repeat the entire study with a new protocol as suggested above.
- Please reorganize the introduction section. It is very short and needs to improve a lot. For example, define briefly the important terms, which have been used throughout the manuscript such as biomass, liquefaction, G-type, S-type, H-type products, etc. Please define the processes depolymerization, repolymerization, what are key differences in it? What are the key products of these processes? The introduction should be started with the background and descriptions of general challenges or problems or gaps in current research. The efforts of others to tackle those challenges/problems should be explored. Finally, the introduction ends with your proposed solutions and explain why your methods are better.
- Briefly describe the significance of these findings towards the catalysts community in the section conclusions of the manuscript.
- Could the authors better express if each experiment, especially while studying reducibility of the catalysts, was performed in duplicate?
- Line 45: Please add references
- Line 52: Authors demonstrated that 150-160 °C is the optimum reaction temperature, then what about 130 °C, 140 °C, these key data points are missing.
- Line 52: What is oil yield? What is liquefaction yield?
- Line 65: Optimum reaction time is 1 h, then the authors need to check the yields at 15 min, 30 min, and 45 min. Need to introduce these key data points.
- Figure 3: What is scale % on Y-axis, in other figures it is mentioned as % yield.
- Line 89: Add data point at 1.25% catalyst loading.
- The English and the presentation of the manuscript is very low, making it difficult to find some spots of significance. The manuscript as not presented in the scientific and concise language. Avoid phrases like ‘generally speaking”, ‘as can be seen from the figure’, avoid the use of words such as ‘meanwhile’ multiple times.
- There are many typos throughout the manuscripts.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper "Effective depolymerization of sodium lignosulfonate over SO42-/TiO2 catalyst" (Manuscript Number: catalysts-904806) is devoted to the catalytic depolymerization of sodium lignosulfonate. Optimization of the reaction conditions has been carried out. The prepared bio-oil was analyzed by elemental analysis, FT-IR and GC-MS. I recommend this manuscript for publication in Catalysts.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The manuscript authored by Xiaoli Gu et al investigated sodium lignosulfonate depolymerization over SO42-/TiO2 catalyst. Lignin depolymerization is important for lignin utilization. Although good liquefaction and oil yields were reported in this study, the significance of the work is not clearly explained. The following questions and comments should be addressed:
- In the abstract, what is the "concerning effect"?
- Provide abbreviation for G and S in the abstract
- Line 44, the statement ending “references about solid super acid catalyst were reported” is missing references.
- Line 46, the authors mentioned that SO42-/TiO2 is a super acid. Is there any reference to support this?
- Figure 1, how is the yield calculated? Move the equations 1, 2 and 3 from page 8 (experimental) to results and discussion, so that the readers can easily follow.
- Equation 2, Page 8, Is the glycerol missing in the oil yield? Only methanol is included in the equation.
- How do the authors know that there is no glycerol in the final bio-oil formed?
- Line 75, the statement “active site of catalyst was gradually blocked by SL fragments, and the activity of which was gradually reduced” needs references.
- Figure 2 and 3, what is the reaction temperature? I recommend the authors to include the reaction conditions (time, temperature etc) for all the figures.
- Irrespective of reaction time, temperature and methanol/glycerol ratio, the liquefaction and bio oil yield are not changing significantly. The differences appear to look more within experimental error. How many times where these experiments repeated? Are those average of multiple runs?
- Line 105, “showed that the structure of solid residue was more abundant than before” rephrase this sentence. It is not very clear.
- Line 113, replace “the spectrum of” with “the bands at”?
- Tabe 3, what is high vanillic acid?
- grammatical errors/typos in few places eg. Line 177, missing close bracket for glycerol.
- Line 195, did the authors perform reactions without hydroquinone to compare the yield?
- Did the authors try reactions without methanol or glycerol? Just with one neat solvent. The need for two solvents should be explained.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Most of the concerns have been addressed by the authors. I agree to accept this article for publication.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The revised manuscript is not technically sound yet. There are so many issues with the paper.
The following questions needs to be addressed :
Did the authors perform a reaction without any catalyst? Control experiments are required to confirm the bio oil or liquefaction yields.
As mentioned earlier, there is not much difference in the bio oil or liquefaction yields with respect to change in reaction time, temperature and methanol/glycerol ratio. A discussion must be added to the manuscript explaining this. If the reaction were run at say, 120 C or time (<1h), would it change the yields? The author should perform the experiments and report the difference in yields in order to confirm that there is no error in their yield calculations.
Table 3, the molecular formula for sterol is wrong. Is it really sterol or some other alcohol?
Table 3, octadecanoic acid or Ctadecanoic acid? What is RT? The authors should check Table 3 data carefully.
Line 227, the liquefaction yield also includes the mass of glycerol? The yield calculation is not clear.
Line 229, the bio-oil yield calculation does not seem right!
The mass of Aq. Phase – mass of glycerol input will just provide the mass of water?
Some discussion on the reaction mechanism will be useful for the readership of “catalysts” journal
The authors should try the reaction with just one solvent ( methanol or glycerol) and report the results.
The reference 18 that the authors cited for mixed solvents is not correct. It talks about plasma electrolysis under acidic conditions. The authors should carefully check all the references.
Author Response
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Author Response File: Author Response.pdf
Round 3
Reviewer 3 Report
The authors revised the manuscript, answering questions and addressing clarifications.
Manuscript's language could be further improved. Eg. removing words such as, "actually" from the manuscript.
