Qualitative and Quantitative Analysis of Heavy Crude Oil Samples and Their SARA Fractions with ¹³C Nuclear Magnetic Resonance

Round 1

Reviewer 1 Report

Solution state NMR is used to characterise four crude oil samples of widely varying viscosities. The key parameter investigated is the chemical composition as revealed by four components, namely saturates, aromatics, resins and asphaltenes (termed SARA fractionation). The paper sets the scene well and indicates how this fundamental chemical analysis via quantitative 13C NMR works. The data is carefully presented using integration of the quantitative spectra to examine the chemical make up of the four SARA fractions in terms of four different carbon local bondings. The data is collected at high magnetic field (16.5 T) and from the description, with experimental parameters that should allow the quantitative analysis. There is then compositional variation between the four crude oil samples in two distinct dimensions; the variation in the SARA fraction and the variation in the individual compositions between the four carbon types, which this paper investigates. Overall the writing is adequate, with a good use of figures and tables and referencing that is for the most part also OK. It is good to see that there are no typographic errors that could be detected. Overall the paper can be published, but before this can happen several matters need further consideration and probably amendment.

Significant points for consideration

1. It is slightly odd in a paper of this level of sophistication to have the points 1-7 made on page 2. These are somewhat textbook points. I guess it is dependent on the likely target readership, since if it is a standard chemistry audience this should not be necessary. If it is for oil specialists of widely varying backgrounds then it can stay.
2. Also on page 2 the references given to illustrate the utility of NMR for ‘laboratory and industrial analysis’ are all but one from the authors of this paper. There is no objection to including papers from the authors, but there should be more balance in this list.
3. Throughout experimental data is reported. This will be subject to proper experimental errors, but there are no errors quoted. For example in Table 2 (p3) it is unlikely that the % fractions are accurate to two decimal places. Also in Tables 4-8 all will have associated errors which need to be added.
4. In the experimental description, p2, Sec 2.2, overall it is very good to see this level of information, such as the line broadening used, spectral width, etc. However the probe used is not stated nor are the actual pulse lengths used. So these should be added.
5. The analysis of NMR spectra by these authors for such materials is presented in previous references [32,34]. However it would be helpful to add as supporting information this methodology and also some of the equations that derive the aromaticity factor and the mean chain length. Also is it not clear how in for example Table 7 the Csq in the crude oil is related to the Csq values in the four component parts. More explanation needs to be added around this.

Minor corrections

6. p2, line 49, peculiarities should be characteristics
7. p2, line 70, it is difficult to see how the start of the sentence then means it is ‘fully justified’. Perhaps one should say ‘valid or highly appropriate’
8. p9, line 206, increasing should be increase
9. p12, line 218, analyse should be analyzingv

Author Response

Dear Reviewer,

Thank you very much for the valuable critical comments concerning our manuscript. We have tried to take into account all of them and submit a corrected version of the paper. To fulfill them we have introduced Supplementary Materials. All changes in the revised version of the manuscript are color-marked.

Below you can find the replies on your queries.

On behalf of all co-authors,

Dr. Ilfat Rakhamatullin

It is slightly odd in a paper of this level of sophistication to have the points 1-7 made on page 2. These are somewhat textbook points. I guess it is dependent on the likely target readership, since if it is a standard chemistry audience this should not be necessary. If it is for oil specialists of widely varying backgrounds then it can stay.

Reply:

The points 1-7 on page 2 are deleted.

Also on page 2 the references given to illustrate the utility of NMR for ‘laboratory and industrial analysis’ are all but one from the authors of this paper. There is no objection to including papers from the authors, but there should be more balance in this list.

Reply:

Thank you for the opportunity to expand the list of the petroleum related NMR references. We have introduced more references, namely ([19-23], [25-27]) in the revised version and deleted 5 items of self-references.

Throughout experimental data is reported. This will be subject to proper experimental errors, but there are no errors quoted. For example in Table 2 (p.3) it is unlikely that the % fractions are accurate to two decimal places. Also in Tables 4-8 all will have associated errors which need to be added.

Reply:

The SARA data accuracy in Tables 2, 5-8 has been corrected. The evaluation of the data in Tables 4-8 was carried out according to the formulas presented in Supplementary Materials.

In the experimental description, p2, Sec 2.2, overall it is very good to see this level of information, such as the line broadening used, spectral width, etc. However the probe used is not stated nor are the actual pulse lengths used. So these should be added.

Reply:

The required information was added in Sec 2.2 on page 2.

The analysis of NMR spectra by these authors for such materials is presented in previous references [32,34]. However it would be helpful to add as supporting information this methodology and also some of the equations that derive the aromaticity factor and the mean chain length. Also is it not clear how in for example Table 7 the Csq in the crude oil is related to the Csq values in the four component parts. More explanation needs to be added around this.

Reply:

Thank you for the opportunity to present Equations which we were forced to delete in initial submission to avoid self-plagiarism. All required equations were added in Supplementary Materials.

Concerning the relation between parameters C_sq in the crude oil and in fraction, unfortunately it is hard to compare fractions between each other. Each fraction was analyzed as a separate sample with subsequent spectrum integration and calculation of parameters for comparison with crude oil and other fractions. We tried to avoid such complications in the presented research.

Minor corrections

p2, line 49, peculiarities should be characteristics

Reply:

The sentence (p.2, lines 47-49) was rewritten.

p2, line 70, it is difficult to see how the start of the sentence then means it is ‘fully justified’. Perhaps one should say ‘valid or highly appropriate’

Reply:

The sentence was deleted.

p9, line 206, increasing should be increase

Reply:

The sentence (new position: p.8, lines 184-187) was edited.

p12, line 218, analyse should be analyzing

Reply:

The sentence (new position: p.9, lines 198-201) was edited.

Reviewer 2 Report

Please clarify the importance of this work?

Very similar research wroks from same or other groups have been published and actually more than 1 times

Similar published papers from same or different groups are listed below

https://www.sciencedirect.com/science/article/abs/pii/S0920410519303626

https://www.sciencedirect.com/science/article/pii/S0016236112008241?via%3Dihub

https://pdfs.semanticscholar.org/17bb/2ec6350160b795c69b9ec6e3df847a1e3a39.pdf

https://www.sciencedirect.com/science/article/abs/pii/S0920410518304005

https://www.sciencedirect.com/science/article/pii/S0016236109003512?via%3Dihub

https://pubs.acs.org/doi/abs/10.1021/ef401476j

Author Response

Dear Reviewer,

Thank you very much for the valuable critical comments concerning our manuscript. We have tried to take into account all of them and submit a corrected version of the paper. To fulfill them we have introduced Supplementary Materials. All changes in the revised version of the manuscript are color-marked.

Below you can find the replies on your queries.

On behalf of all co-authors,

Dr. Ilfat Rakhamatullin

Please clarify the importance of this work?

Reply:

In this work a full ¹³C NMR analysis was carried out for each of the SARA fractions of the four different crude oils and the obtained parameters were compared with each other. Such data were never before presented in literature at least for 15 samples from 20 studied. Information on content of general functional groups obtained by ¹³C NMR spectroscopy can be useful for fast prediction of oil product properties changing upon different type of treatment and also to develop a fingerprinting approach. We also added additional sentence (p.2, lines 74-78) in Sec. Introduction that emphasized the importance of the work.

Author Response File: Author Response.docx

Reviewer 3 Report

Qualitative and quantitative analysis of heavy crude oil samples and their SARA-fractions with 13С nuclear magnetic resonance

By Ilfat Rakhmatullin et al


This paper is related to the uses of NMR for heavy crude oil characterization. The paper is interesting and the introduction didactic on the NMR analysis. All the steps a well describe. This study could be publish after minor revision as follow:

Introduction :

-The uses of paramagnetism of Vanadium that is present in crude oil have been used. This can be added in the introduction with some references.

Material and methods:

Line 125 “chloroform (CDCl3) “ add “deutered” chloroform (CDCL3)

Results:

-it seems that there is not CDCL₃ peak on figure 1-1 and 1-3 spectrum?

-Why the CDCl3 peak is larger for some samples?

-A figure presenting all the aromatic area (one of the main part of the NMR Spectra) for all the samples would be nice to be added in order to compare all the samples/fractions on the same figures

Conclusion:

-Mine 242 : “describe …  supramolecular” : could you precise more where you give supramolecular information with NMR? This should be more explain in the discussion.

Others:

-Line 100 : “Samples” instead of “Species”

Author Response

Dear Reviewer,

Thank you very much for the valuable critical comments concerning our manuscript. We have tried to take into account all of them and submit a corrected version of the paper. To fulfill them we have introduced Supplementary Materials. All changes in the revised version of the manuscript are color-marked.

Below you can find the replies on your queries.

 On behalf of all co-authors,

Dr. Ilfat Rakhamatullin

Introduction :

The uses of paramagnetism of Vanadium that is present in crude oil have been used. This can be added in the introduction with some references.

Reply:

Thank you very much for the idea for our next research! In this paper, we did not take into account, use and discuss the influence of paramagnetic centers on NMR. We just mention it in the literature survey for dynamic nuclear polarization. Moreover, according to the comments of Reviewer 1 we have deleted any mentioning of some peculiarities (advantages) of NMR in general including mentioning of influence of the paramagnetic centers.

Influence of paramagnetic vanadium on nuclear properties (but only on protons) is quite comprehensively reviewed in work (ref. 34) in reference list of the revised version. We also inserted additional references into this Section Introduction [36,37] to give a reader more points for information.

Material and methods:

Line 125 “chloroform (CDCl3) “ add “deutered” chloroform (CDCL3)

Reply:

The sentence (new position: p.3, lines 102-103) was edited.

Results: it seems that there is not CDCL₃ peak on figure 1-1 and 1-3 spectrum?

Reply:

The Figure 1 (in p. 4) was edited.

Why the CDCl3 peak is larger for some samples?

Reply:

The ¹³C NMR spectrums of asphaltene fractions have the worst resolution. Therefore, in order to show the presence of signals, these spectra are shown in Figures 2-5 on an enlarged scale.

A figure presenting all the aromatic area (one of the main part of the NMR Spectra) for all the samples would be nice to be added in order to compare all the samples/fractions on the same figures

Reply:

We thought that such Figure would be too overloaded due to the large number of studied samples. The required information presented by diagrams of C_ar parameters in Figure 6.

Conclusion:

Mine 242 : “describe …  supramolecular” : could you precise more where you give supramolecular information with NMR? This should be more explain in the discussion.

Reply:

The sentence (new position: p.10, lines 220-223) was edited: «¹³C NMR spectroscopy can significantly expand the repertoire of research methods to study structural-group composition of oil and oil fractions, adequately describe qualitatively and quantitatively not only the elemental composition but also the molecular structures of natural organic material, its fractions, intermediate and target products».

Others:

-Line 100 : “Samples” instead of “Species”

Reply:

The sentence (new position: p.2, lines 83-84) was edited.

Round 2

Reviewer 2 Report

Major comments

1. I think the introduction part of this manuscript needs to be revised to follow a decent logical flow. My feeling is that this introduction part has multiple places with repeating pieces of information. For example, lines 40 to 42, lines 47 to 49, line50 to 53, and lines 60 to 63 tell the same information.

The authors may follow below:

• Importance of knowing information about the structure and properties of the obtained fractions and its characterization
• Background and history for characterization using radio spectroscopic techniques +definition and mechanism of NMR
• The advantages of the authors’ method ( starting with NMR, then move to 13C or 1H NMR method) compared with other approaches or conventional methods concerning the oil components characterization.
• Importance of the research（in other words, what is new and novel of this research?）
  
  
  

2. I have a hard time to distinct the spectra illustrated in Figures 1, 2, 3, 4, and 5 due to their overlaying to one another. I would suggest to use different colors or give a larger space among each spectrum.

Minor comments

1. Line 34: change “analysis in-depth” to “in-depth analysis” .
2. Line 35: change “is” to “are” .
3. Line 56: add “the” in front of “characterization”.
4. Line 61: change “this” to “these.”
5. Line 56: add “the” in front of “rapid development”.
6. Line 74: insert “a” in front of “correlation”.
7. Line 77: remove “of”.
8. Line 84: add “a” in front of “list”.
9. Table 3. “precipitation” should be “precipitation”?
10. Line 107: what is the full name of LB?
11. Line 108 “were made”. “were conducted” maybe better wording.
12. Line 106 add “the” before “number”.
13. Line 226 add “the” before “contribution”.

Author Response

Dear Editors,

Dear Reviewer,

Thank you again for the valuable critical comments concerning our manuscript. We have tried to take into account all of them and submit a corrected version of the paper. All changes in the revised version of the manuscript are color-marked.

Below you can find the replies on the Reviewer queries.

On behalf of all co-authors,

Dr. Ilfat Rakhamatullin

Reviewer 2

Major comments

1. I think the introduction part of this manuscript needs to be revised to follow a decent logical flow. My feeling is that this introduction part has multiple places with repeating pieces of information. For example, lines 40 to 42, lines 47 to 49, line50 to 53, and lines 60 to 63 tell the same information.

The authors may follow below:

• Importance of knowing information about the structure and properties of the obtained fractions and its characterization
• Background and history for characterization using radio spectroscopic techniques +definition and mechanism of NMR
• The advantages of the authors’ method (starting with NMR, then move to 13C or 1H NMR method) compared with other approaches or conventional methods concerning the oil components characterization.
• Importance of the research（in other words, what is new and novel of this research?）

Reply:

The introduction part of the manuscript was edited.

2. I have a hard time to distinct the spectra illustrated in Figures 1, 2, 3, 4, and 5 due to their overlaying to one another. I would suggest to use different colors or give a larger space among each spectrum.

Reply:

The Figures 1-5 were edited.

Minor comments

1. Line 34: change “analysis in-depth” to “in-depth analysis” .
2. Line 35: change “is” to “are” .
3. Line 56: add “the” in front of “characterization”.
4. Line 61: change “this” to “these.”
5. Line 56: add “the” in front of “rapid development”.
6. Line 74: insert “a” in front of “correlation”.
7. Line 77: remove “of”.
8. Line 84: add “a” in front of “list”.
9. Table 3. “precipitation” should be “precipitation”?
10. Line 107: what is the full name of LB?
11. Line 108 “were made”. “were conducted” maybe better wording.
12. Line 106 add “the” before “number”.
13. Line 226 add “the” before “contribution”.

Reply:

All minor comments were taken into account and highlighted in color.