Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Fig. 3. Actually, there is no need to use catalyst for the isomerisation of fructose (linear form) to fructofuranose cyclic form. These forms are in equilibrium in solutions. Please, correct the scheme. 

The main problem of 5-HMF synthesis is it's isolation and purification. It is highly desirable to add an additional section on the ways of 5-HMF isolation  used nowadays according to the papers and patents.      Comments on the Quality of English Language

Please, check the capitals in the beginning of the sentences. 

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

Lines 65-96, Xuebin Lu, Jian Xiong et al. wrote, “A variety of synthetic routes for HMF have been reported in recent years[7-10]. Relevant review studies have mainly focused on catalysts, catalytic systems and solvent effects, and few reports have comprehensively reviewed the conversion of HMF from the perspective of different biomass-derived feedstocks, especially non-food biomass, inulin and watermelon rind.”

References 7 to 10 deal with new biomass that could be used to produce HMF (i.e., chitosan, agarose, galactose). It should be noticed that more than half of the review discusses classic feedstocks (fructose, glucose but HFCS is missing). However, citations of reviews of HMF production from unconventional feedstocks are absent (See Biotechnology Advances,37 (2019) 107422, DOI: 10.1016/j.biotechadv.2019.107422, Molecules 2018, 23(9), 2201, DOI: 10.3390/molecules23092201 among others). The authors should emphasize in their introduction the aim of this short review and the added value of their review.

 

In section 2, the authors review the catalytic system for synthesizing HMF from different raw materials. Among the latter, the authors listed fructose (2.1.1) and glucose (2.1.2) but forgot the High Fructose Corn Syrup (HFCS), which is industrially made corn starch. Since HFCS is widely available in the food industry and is a good source of fructose and glucose, it could be considered a competitive feedstock for 5-HMF production (see an example of recent work Catalysis Today 407 (2023) 274-280, DOI: 10.1016/j.cattod.2021.07.032).

One of the key points in the production of 5-HMF is the separation from the reaction mixture. This point is barely addressed in the review and deserves further development. The authors should cite and discuss the review of J. Slak et al. on intensification, separations, and purifications of hydroxymethylfurfural (HMF) (Chemical Engineering Journal 429 (2022) 132325, DOI: 10.1016/j.cej.2021.132325).

Lines 158-160: The production of 5-HMF from fructose using IL systems could not be considered green. The authors should mitigate this point by considering the synthesis of IL, back extraction of HMF from IL, and reuse of IL.

The sentence lines 358-360, “Therefore, there is a need to continue to explore efficient and inexpensive reaction solvent systems to improve the conversion of the target product HMF in aqueous solvents.” is meaningless. Did the authors want to emphasize biphasic systems?

 

 

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript of Tao et al., reviews different catalytic systems and different feedstocks for the production of 5-hydroxymethylfurfural (HMF). Furanic production is currently hot topic and is excessively studied/reviewed already (with numerous types of homogeneous/heterogeneous catalysts & feedstocks). It is not clear to the reviewer what the novelty is or what new information is brought to the readers in this review? It seems that new information is very limited compared to other review articles in the field. The authors refer to the use of inulin as the feedstock being the novelty in this review article, however, there are already review articles (besides the research articles) present that show the use case of inulin as a feedstock (i.e., https://doi.org/10.1016/j.jiec.2018.10.002, https://doi.org/10.3390/molecules23092201, https://doi.org/10.1016/j.biotechadv.2019.107422, among others). There are also several statements in the introduction section that require references. There are numerous typos to be found in the manuscript. For these reasons the reviewer thinks that this manuscript does not merit publication in Catalysts.

Comments on the Quality of English Language

See comments above.

Author Response

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Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have introduced references suggested in my review. Some other modifications have been made, In particular, new figures. 

I never saw the top pathway drawn in the new Figure 2. In particular, the dehydration leading to an exocyclic double bond looks strange to me. Can the authors provide data or ref that justify the formation of such an intermediate.

In Figure 3, most dehydrations are isomerizations, and it would be interesting to explain how the molecule in the vertical center right could be transformed into HMF.

1/ molecule must be numbered

2/Pathways are important and could not just be considered as an illustration. Why did the authors want to differentiate a “cyclic dehydration pathway” and a “non-cyclic dehydration pathway”. Linear and cyclic sugars are in equilibrium (the cyclic form is favor). Why did the authors want to emphasize the difference between the pathways?

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

The authors performed a spelling and grammar check provided by MDPI services, which is highly appreciated by the reviewer. The authors also added a new section to the manuscript based on the comments of the other reviewers. However, the major issue (novelty) is still not addressed sufficiently and the answer of the authors regarding this issue is not satisfying. The question is what *new* information or *new* insights this manuscript brings to the readership of Catalysts. "An extended discussion on the one pot conversion of non-food biomass to HMF" is a rather vague description. The reviewer also suggested some review manuscripts that already described the use of inulin as a feedstock for HMF production (however, the authors decided not to include these in this manuscript). Therefore again, what *new* information is presented in this manuscript that could be of use to the readers of catalysts (and is not already present in other review manuscripts considering the synthesis of non-food feedstocks to HMF)? New reaction mechanism insights, new research papers describing new catalytic systems and/or higher HMF yields, ... This is still not sufficiently clear. 

Author Response

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