High Cellulose Purity by Acid Hydrolysis Pretreatment on Kenaf Outer Bast
, Ji Yeon Jeong 1,2, Yang Mo Gu 2,3, Jin Hyung Lee 2,* and Soo-Jeong Shin 1,*Round 1
Reviewer 1 Report
Acid hydrolysis pretreatment using H2SO4 under different reaction conditions was conducted on kenaf outer-bast fiber. Then analyses of compositional carbohydrates and lignin were conducted on the obtained residues.
If my understanding is correct, the authors have conducted experiments under 27 different conditions, each with 3 repetitions. It must have taken great amounts of time and effort. However, the writing and presentation need extensive improvement.
English proofreading is a MUST, before we proceed further reviewing process. I cannot understand exactly what the authors want to say, so I could evaluate the logical soundness of this manuscript only to a certain extent.
There are also two major issues that must be pointed out.
Firstly, I don’t think presenting the data in table-form (only) is appropriate. It makes it very difficult to understand the changes and trends of the results, especially since comprehensive reactions were conducted under three different parameters, namely reaction temperature, concentration of H2SO4 used, and reaction time.
The second issue is the discussion and conclusion of this manuscript. I understood that the authors’ direct aim is obtaining highly pure cellulose as possible from kenaf outer-base fiber. However, the examined elements and evaluation methods seem to me insufficient and difficult to accept. Especially, I felt uncomfortable by the fact that the authors do not mention anything about lignin, although it is also an influential component for obtaining pure cellulose. Moreover, the final goal of this type of study is practical implementation and good commercialization of the obtained cellulose, just as the authors have mentioned in the Introduction section. So, I have felt uncomfortable by the fact that the authors have determined the optimum conditions of the pretreatment ONLY by cellulose purity. How much purity the authors think is necessary for utilization? Are the characteristics (such as degree of crystallinity, degree of polymerization etc.) of the obtained cellulose good enough for utilization? I think such details should also be included in the Discussion, then the optimum conditions (namely, conclusion) would become more easily accepted.
Additional minor comments:
1 (l.74) First of all, “CH3COOH” is acetic acid. Chemical compounds do not need to be capitalized.
2 I am unfamiliar with the analytical method conducted in 2.5. Is this method well accepted for the quantification of compositional sugars in the biomass? How did you differentiate glucose monomers obtained from hemicellulose and cellulose? (I am asking this because this is essential data for this study.) Additionally, please mention about the secondary hydrolysis under 3% H2SO4. (I assume that the authors must have done this.) This last comment refers to 2.6 as well.
3 How did you obtain the figures presented in the “Result and Discussion”? Are those figures in the Tables 2-6 the averages of the three repetitions? If so, how about the data variability?
4 I think that the figures for “Extractives Hydrophilic” and “Extractives Hydrophobic” should be reversed. Please DO be careful with the data presentation. In 3.2, the authors confuse the description (meaning) of the figure as the amount of removal, where they are that of the residual. The description of the figures mentioned in text as those related to Table 4 cannot be seen in the Table. I think they are the figures for Table 5.
Author Response
Dear Mr/Ms. Reviewer
Thank you for your review. I and my research team tried to improve our paper.
Here are the responses:
Firstly, I don’t think presenting the data in table-form (only) is appropriate. It makes it very difficult to understand the changes and trends of the results, especially since comprehensive reactions were conducted under three different parameters, namely reaction temperature, concentration of H2SO4 used, and reaction time.
- I tried to present the data more simply by reading. Thus, previous in effect of time is table now as figure 4.. Meanwhile, tables 3 and 4 represent the effect of acid concentration and temperature more making it easier to see "only" trends between different concentrations (table 3) and temperatures (table 4) in overall our experiment.
The second issue is the discussion and conclusion of this manuscript. I understood that the authors’ direct aim is obtaining highly pure cellulose as possible from kenaf outer-base fiber. However, the examined elements and evaluation methods seem to me insufficient and difficult to accept. Especially, I felt uncomfortable by the fact that the authors do not mention anything about lignin, although it is also an influential component for obtaining pure cellulose. Moreover, the final goal of this type of study is practical implementation and good commercialization of the obtained cellulose, just as the authors have mentioned in the Introduction section. So, I have felt uncomfortable by the fact that the authors have determined the optimum conditions of the pretreatment ONLY by cellulose purity. How much purity the authors think is necessary for utilization? Are the characteristics (such as degree of crystallinity, degree of polymerization etc.) of the obtained cellulose good enough for utilization? I think such details should also be included in the Discussion, then the optimum conditions (namely, conclusion) would become more easily accepted.
àIn result 3.1 I already mentioning lignin, where bleaching pretreatment for delignification prior to acid hydrolysis as the main treatment. Thus, I focus to obtain pure cellulose by removing hemicellulose after semi-bleaching treatment. Regarding the purity of cellulose, I tried to conduct more than 95% and save the yield. I can say our work was the first step to obtaining high cellulose content by selectively removing hemicellulose. Your suggestion was great, perhaps analysis such as degree of crystallinity, degree of polymerization could be nice when I focus on the fiber characteristic of cellulose
Additional minor comments:
1 (l.74) First of all, “CH3COOH” is acetic acid. Chemical compounds do not need to be capitalized. (Thank you, I already changed it)
2 I am unfamiliar with the analytical method conducted in 2.5. Is this method well accepted for the quantification of compositional sugars in the biomass? How did you differentiate glucose monomers obtained from hemicellulose and cellulose? (I am asking this because this is essential data for this study.) Additionally, please mention about the secondary hydrolysis under 3% H2SO4. (I assume that the authors must have done this.) This last comment refers to 2.6 as well.
à 2.3.2. Determination of polysaccharide composition (previous 2.5) have been existed since 1992 here is one of the articles “Vliegenthart, J. F., Dorland, L., & van Halbeek, H. (1983). High-resolution, 1H-nuclear magnetic resonance spectroscopy as a tool in the structural analysis of carbohydrates related to glycoproteins. In Advances in carbohydrate chemistry and biochemistry (Vol. 41, pp. 209-374). Academic Press”. Glucose from cellulose consider the α and β-glucose peak, meanwhile, the glucose from hemicellulose existed by the mannose peak. Where glucose in hemicellulose come from glucomannan in hardwood/annual plant/ grass etc. I found mannose peak around 2% from total carbohydrates, for 2.6 (now 2.3.3) I already changed it to, Thank you.
3 How did you obtain the figures presented in the “Result and Discussion”? Are those figures in the Tables 2-6 the averages of the three repetitions? If so, how about the data variability?
- Right, those from the average of at least three repetitions with a low standard deviation, hence I put standard deviation in tables.
4 I think that the figures for “Extractives Hydrophilic” and “Extractives Hydrophobic” should be reversed. Please DO be careful with the data presentation. In 3.2, the authors confuse the description (meaning) of the figure as the amount of removal, where they are that of the residual. The description of the figures mentioned in text as those related to Table 4 cannot be seen in the Table. I think they are the figures for Table 5.
- Thank you, I already changed it to flip the extraction name and the residual of hemicellulose from removal into the amount of remaining. The description value I already changed according to table 4.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Manuscript ID: applsci-2037258
Title
High Cellulose Purity by Acid Hydrolysis Pretreatment on Kenaf Outer Bast
Review
General comments
The article reports experimental investigation of biomass pretreatment for cellulose separation. The tests demonstrated here are done with sulfuric acid at different conditions. In my opinion this work is of interest for the scientific community and the topic is well in line with the most recent trends in this field. However, there are some parts that need more attention and for example, the biomass samples characterization.
More detailed comments
- As a general recommendation, in the introduction section, you can mention what was done in this regards in the recent literature underlying where this article gives an added value. In other words, what was done before on this topic and what instead was not tried and what is the added value of this article.
- The acid processing of biomass to separate the cellulose can be done with different kind of acids, underline here with a more extensive description what are the diverse acids used and use some references for these studies. As an example of biomass pre-treatment using alternative methods, we have acetic acid: Kildegaard et al. Processes 2022, 10(5), 943; https://doi.org/10.3390/pr10050943
- Introduce the characterization done and why these methods were used
- For the acid pretreatment you can illustrate the process steps with a diagram, drawings and photos of the setup used.
- Remember to include the instrumentation output for all the characterization done (spectra etc. )
- Revise and illustrate accurately the justification of why you have those compounds in fig. 1
- Biomass and composition analysis. Please provide a sufficient amount of information for the biomass feedstock: proximate/ultimate analysis etc.
Author Response
Reviewer 2
Dear Mr/Ms. Reviewer
Thank you for your review. I and my research team tried to improve our paper.
Here are the responses:
- As a general recommendation, in the introduction section, you can mention what was done in this regards in the recent literature underlying where this article gives an added value. In other words, what was done before on this topic and what instead was not tried and what is the added value of this article.
à I tried to solve your suggestion in the last paragraph of the introduction. It is maybe not perfect, overall, I tried to say acid hydrolysis was exist for removing hemicellulose and obtaining cellulose, thus to use kenaf outer bast fiber with high cellulose content to obtain the purity of cellulose
- The acid processing of biomass to separate the cellulose can be done with different kind of acids, underline here with a more extensive description what are the diverse acids used and use some references for these studies. As an example of biomass pre-treatment using alternative methods, we have acetic acid: Kildegaard et al. Processes 2022, 10(5), 943; https://doi.org/10.3390/pr10050943
à Thank you. I input your article as one of our references to mention others acid catalysts in introduction reference no. 18
- Introduce the characterization done and why these methods were used
à done, I mention in 2.3.2 and 3.1, Thank you
- For the acid pretreatment you can illustrate the process steps with a diagram, drawings and photos of the setup used.
àdone, I put in 2.3.2 part
- Remember to include the instrumentation output for all the characterization done (spectra etc. )
à I hope what I improve is according to what you want. That in figure 2 and 3
- Revise and illustrate accurately the justification of why you have those compounds in fig. 1
à done, in 3.1
- Biomass and composition analysis. Please provide a sufficient amount of information for the biomass feedstock: proximate/ultimate analysis etc.
à sorry, I did not do that. Like ultimate analysis was analyzed the CHO and NC. This analysis is good for lignin analysis with the different atoms C with carbohydrates. Meanwhile, our result analyzed the cellulose and hemicellulose which have almost similar CHO.
Author Response File: Author Response.pdf
Reviewer 3 Report
1) Verify the identities and affiliations of the authors. Author affiliations are given beside the author's name using alphabets, however the affiliation section uses numbers
2) Can include a graphical abstract to make the paper more attractive.
3) In page2, line 82 include the specifications of the milling machines used in this study.
4)In page 2, line 92 check the unit of 80 0 c
5) include the structural characterization of the fibers
6) Conduct a statistical analysis on this optimization procedure
7) The raw sample has 57.2% cellulose. Usually, treatments enhance the cellulose content. Why it decreases on applied treatment?
8) What is the reason for decreased cellulose percentage on increased concentration of acid?
9) Do the authors conduct a study to assess the variation in cellulose percentage and yield at a temperature lower than110 0c
10) Is the cellulose percentage in the sample only determines its purity?
11) Include an environmental risk analysis and cost analysis of the study.
Author Response
Reviewer 3
Dear Mr/Ms. Reviewer
Thank you for your review. I and my research team tried to improve our paper.
Here are the responses:
1) Verify the identities and affiliations of the authors. Author affiliations are given beside the author's name using alphabets, however the affiliation section uses numbers
àdone, thank you
2) Can include a graphical abstract to make the paper more attractive.
àsure, I hope you like that.
3) In page2, line 82 include the specifications of the milling machines used in this study.
à Done.
4)In page 2, line 92 check the unit of 80 0 c
àdone thank you
5) include the structural characterization of the fibers
à done, I tried to explain in the last paragraph of 3.1
6) Conduct a statistical analysis on this optimization procedure
àMy team only re-organized and select by the trend considered by high temperature with various of acid concentration
7) The raw sample has 57.2% cellulose. Usually, treatments enhance the cellulose content. Why it decreases on applied treatment?
à I show remaining value after treatment where cellulose can be decrease during treatment, however cellulose content in mass balance was highly increase consider from hemicellulose already hydrolyze
8) What is the reason for decreased cellulose percentage on increased concentration of acid?
à Refers to kinetic reaction of acid hydrolysis treatment, hemicellulose hydrolyzed into monosaccharide is k1 (kinetic reaction 1) and k2 from xylose into decomposition. During those reaction, cellulose can be hydrolyses into glucose (k3).
9) Do the authors conduct a study to assess the variation in cellulose percentage and yield at a temperature lower than110 0c
àSure, my team already tried. But with low temperatures, the treatment needs high acid concentration and long reaction time. Here, we try to save chemical solutions and energy us much we can.
10) Is the cellulose percentage in the sample only determines its purity?
àOf course not, fiber length, depolymerization, crystallinity, etc. we can conduct. Honestly, we limited our research in this paper to determined the chemical composition of kenaf outer bast
11) Include an environmental risk analysis and cost analysis of the study.
à done, in the last paragraph of the optimal condition part in result.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
I had made the previous decision since I thought "revision" cannot improve the manuscript to warrant for publication. So basically, I am not thinking of changing the decision. (Otherwise, I didn’t reject in the first place.)
However, I did briefly check the answers to my previous comments and some of the revised manuscript. (My apology for not checking them deeply, since the Editorial urge me to reply within very little time.) And I will make additional comment.
Regarding my previous minor comment No.2, the authors seem to be not understanding the essential point of my question.
I was aware that the method is accepted for quantification of monomeric sugars. What I was asking is that "Is the method is accepted for quantification of COMPOSITIONAL SUGARS in the (herbaceous plant) BIOMASS”? The reference which the authors have mentioned seems it was for glycoproteins and it will not be an answer to my question.
Additionally, the amount of glucose determined with this method is substantially the sum of glucose obtained from cellulose and that from hemicellulose. We (researchers working in pulp and paper) use this result for SPECULATING the amount of cellulose, but NOT MORE THAN THAT. Since the main topic of this manuscript is on cellulose purity, the authors should pay extra attention to this point when discussing the results. So far I read the manuscript, I couldn't believe the authors are aware of this important point
Therefore, I still think this (revised) manuscript is not suitable for the publication.
Since I am not an expert on kenaf, I couldn’t come up with the best example. However, at least, the authors should check the article by Neto, C.P. et al: Industrial Crops Products 5(3), 189 (1996), for a start. Basically, kenaf and its utilization is not a new topic. Probably, there are other appropriate articles that the authors should be checking.
Comments for author File: Comments.pdf
Author Response
Dear Mr/Ms. Reviewer.
Regarding my previous minor comment No.2, the authors seem to be not understanding the essential point of my question.
I was aware that the method is accepted for quantification of monomeric sugars. What I was asking is that "Is the method is accepted for quantification of COMPOSITIONAL SUGARS in the (herbaceous plant) BIOMASS”? The reference which the authors have mentioned seems it was for glycoproteins and it will not be an answer to my question.
- To the best of our knowledge, 1H NMR spectra are a good method for quantifying sugar content in biomass hydrolysates. The advantages are rapid determination and the ability to predict concentrations of major sugar components (glucose and xylose) and minor sugars by the anomeric proton region, with two signals existing for each sugar (α and β anomers). This method already exists and is adaptable. Reviewers can check these articles:
- Co˜pu¨r Y, Kiemle D, Stipanovic A, Koskinen J, Makkonen M (2003) 1H-NMR spectroscopic determination of carbohydrates and yield in pine and maple pulps. Pap Puu-Pap Tim 3:158–162
- Kiemle DJ, Stipanovic AJ, Mayo KE (2004). Proton NMR methods in the compositional characterization of polysaccharides. In: Gatenholm P and Tenkanen M (eds) Hemicelluloses: science and technology, American chemical society, pp 122–139
- Shin, SJ., Cho, NS. Conversion factors for carbohydrate analysis by hydrolysis and 1H-NMR spectroscopy. Cellulose15, 255–260 (2008).
- Gjersing, E., Happs, R. M., Sykes, R. W., Doeppke, C., & Davis, M. F. (2013). Rapid determination of sugar content in biomass hydrolysates using nuclear magnetic resonance spectroscopy. Biotechnology and Bioengineering, 110(3), 721-728.
Several papers have already been cited by more than 50 articles, which means this method could be accepted.
Additionally, the amount of glucose determined with this method is substantially the sum of glucose obtained from cellulose and that from hemicellulose. We (researchers working in pulp and paper) use this result for SPECULATING the amount of cellulose, but NOT MORE THAN THAT. Since the main topic of this manuscript is on cellulose purity, the authors should pay extra attention to this point when discussing the results. So far I read the manuscript, I couldn't believe the authors are aware of this important point
- I am sorry if my previous response was unclear to your comment. The most component type of hemicellulose in hardwood or herbaceous plants is xylan, and only a few are glucomannans. Where in the glucomannan glucose: mannose ratio is around 1:1 or 1:2. I found a mannose peak around 2% in the kenaf outer bast. Thus, glucose in hemicellulose is around 1-2%. So, for simplicity of the calculations, we considered the α and β-glucose peaks by glucose from cellulose. I am aware that high-purity cellulose is an important point. Hence, in optimum condition, discussion in table 6. I explain that considering high-purity cellulose must affect the yield content. Meanwhile, I give alternative conditions if readers want to consider high yield too.
Therefore, I still think this (revised) manuscript is not suitable for the publication.
- I appreciate your comments and suggestion to improve the quality of my manuscript. Thank you
Since I am not an expert on kenaf, I couldn’t come up with the best example. However, at least, the authors should check the article by Neto, C.P. et al: Industrial Crops Products 5(3), 189 (1996), for a start. Basically, kenaf and its utilization is not a new topic. Probably, there are other appropriate articles that the authors should be checking.
You are right. Kenaf and its utilization are not a new topic like cellulose derivatives modified production. Here I tried to optimize the high purity of cellulose content as raw materials from kenaf biomass, for example, nanomaterial production. I notice this sentence in line 47. We cannot deny that cellulose fiber is the promoting biorefinery source that supports sustainability. Moreover, I changed my introduction; I hope that with this new story, you can understand it easier to re
Reviewer 2 Report
The authors have addressed this reviewer's comments.
The article can be accepted in my opinion
