Analytical Pyrolysis as a Tool to Assess Residual Lignin Content and Structure in Maritime Pine High-Yield Pulp
Round 1
Reviewer 1 Report
This article evaluates the analytical pyrolysis as a tool to assess residual lignin content and structure in maritime pine pulp, which I consider of interest to the journal.
Remove from the introductory part lines 68-84.
2 Materials and methods
The pyrolysis products were identified by using the NIST library and literature. Do authors think that the use of standards is necessary or not? Please clarify.
2.3. Lignin content determination:
Please add more details about the NIR model mentioned (even if it was published, some details about that model should be added in the section)
3 RESULTS AND DISCUSSION
3.1. Klason lignin in pulp can be estimated from Py-lignin
3.2. Pulp residual lignin and wood have different H/G ratios
3.3. Pulp residual lignin and wood have different patterns of pyrolysis products
3.4. The PCA of pyrolysis products separates samples by their lignin content
I am not familiar with these types of subtitles; they are more like bullet points than titles…
3.1. Klason lignin in pulp can be estimated from Py-lignin:
In my opinion, Figure 1 is not clear, maybe a table showing the differences/data/deviations could help readers to follow the explanation written in the text.
It could be better if the authors add a general closure paragraph in section 3.1, in order to obtain a clear conclusion of this part of the results.
3.2. Pulp residual lignin and wood have different H/G ratios:
I believe that to discuss the H/G ratios it is better to first present the results of table 1 (where are defined the 22 compounds that are H-type or G-type) or to add an extra table with H/G values and details.
3.4. The PCA of pyrolysis products separates samples by their lignin content:
Please add more details about the PCA model (Data preprocessing, RMSEC, RMSECV, cumulative variance) for more accurate reliability of your model.
Did the authors use a validation set of samples to test the potential of the Pyrolysis -PCA to discriminate samples according to lignin content? Or all samples were included in the calibration set?
Author Response
Please see the attachment
Author Response File: 
Author Response.docx
Reviewer 2 Report
1. The content of lines 70-84 seems irrelevant to this article. Please proofread carefully.
2. Is it feasible to determine residual lignin content by Py-GCMS? It is generally accepted in the literature that Py-GC/MS cannot be used in quantitative detected.
3. Can the increase of H/G ratio prove that G-type lignin is preferentially removed than H-type lignin? It is also possible that G-type lignin forms H-type lignin by shedding the methoxyl group.
4. The pyrolysis products in Table 1 cannot represent all lignin products, there are a lot of lignin pyrolysis products that are not completely pyrolyzed and condensed during pyrolysis. Please refer to: Sequential fractionation of lignin-derived pyrolysis Oil via extraction with acombination of Water and Organic Solvents. BioResources, 2019,14(1):2144-2159.
5. Maritime pine is a conifer of the pinaceae family,the lignin is mainly G- lignin, it it hardly to say Py-GC/MS analysis(H/G ratio etc.) can provide information regarding how lignin is degraded during the pulping process.
Author Response
Please see the attachment
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The experimental design and presentation of the results of this study still could be improved, however, the authors tried to resolve all doubts and issues in the initial review.
Author Response
"Please see the attachment."
Author Response File: Author Response.docx
Reviewer 2 Report
As shown in Fig1 and Fig2, the relationship is based on the lignin content in pulp ranging from 8.2% to 15.1%. If the residual lignin content in pulp is lower than 3% (with the application of modern advanced delignification technology, the residual lignin content in most unbleached sulfate pulp is relatively low), Does the relationship between py-lignin and Klason lignin content follow this linear relationship? Could the title of the paper be revised to "Analytical Pyrolysis as a tool to assess residual lignin content in high-yield pulp"?
Author Response
"Please see the attachment."
Author Response File: Author Response.docx
