Extractive desulfurization of liquid fuel using diamine-terminated polyethylene glycol as a very low vapour pressure and green molecular solvent

Removal of sulfur compounds from liquid fuel is one of the important issues in the field of energy and environment. Among the available methods, extractive desulfurization (EDS) is of great interest due to its convenient operating conditions. In this study, EDS performance of 4,7,10-trioxatridecane-1,13-diamine (TTD), a very low vapour pressure diamine-terminated oligomeric polyethylene glycol (PEG), was studied. Effect of the influencing factors, as well as multiple extraction, mutual solubility, reusability and regeneration of TTD were investigated. Results showed that the TTD/fuel volume ratio of 0.5 could extract benzothiophene, dibenzothiophene and dimethyl dibenzothiophene with the efficiencies 67%, 74% and 53%, respectively, in less than 1 min at ambient temperature. The distribution coefficient (KN) value for removal of dibenzothiophene by TTD was 3.66 higher than that of PEG, and it is similar to KN values (approx. 4) for polyethylene glycol dimethyl ether (as a modified PEG) and Lewis acid-containing ionic liquids. It was observed that spent TTD after five cycles could be regenerated using the back-extraction method. Also, deep EDS was achievable after three times extraction using fresh TTD. Finally, the extraction mechanism was studied using 1H-NMR. These observations, as well as very low vapour pressure and insignificant dependency of TTD on the initial S-concentration of fuel and temperature, make this extractant to be introduced as a valuable option for green and effective EDS.


2)
The experiments are not presented in sufficient details. For example, the initial Scompound concentrations are not listed clearly and as a consequence, the experiments cannot be reproduced by the interested reader. 3) The overall amount of experiments is rather low and does not approve the publication. The full paper should make a greater contribution to the development of green technologies in the purification of liquid fuels. I propose to include the results of investigations on the extraction mechanism and clarification of the role of amine and ether functional groups in the extraction of benzothiophene compounds by TTD, which the authors suggest themselves in section 3.5, for future submission of the article.
The necessary corrections are listed below: 1.
Although the authors used a word template file to prepare their article, the recommended sections were not followed. Results and Discussion sections should be written separately.

2.
Summary section contains a reference which is not in accordance with the journal's recommendations.

3.
Briefly explain what a molecular solvent is. 4.
In the Introduction, the authors state a specific value of the vapor pressure of TTD (0.001 mmHg) and compare it as 'less than the PEG value'. This fact is confusing because they previously stated that the PEG value was 'less than 0.01 mmHg', which can generally mean that it is also less than the value of TTD. It is necessary to specifically define the value of PEG, as precisely as possible. 5.
The experimental part (Section 2.2) is written too generally, and therefore is not entirely clear to understand. Modification of experimental description is necessary so that each reader can repeat the experiment from the description. It is necessary to clearly write the investigated Scompounds concentrations, the used quantities of chemicals and operating conditionstemperature, experiment time, volume ratio of TTD / fuel… 6.
From the above mentioned, it is necessary to define why, how and for what purpose these experimental conditions were chosen. 7.
From the text it is not clear that heptane is a model fuel -it has to be explicitly stated. Please explain why heptane was chosen as the model fuel. Moreover, BT, DBT and DM-DBT are typical S-components of diesel, and heptane is unfortunately far from being the best choice for one-component model diesel fuel. The boiling point of heptane is 98.42 °C, and boiling points of BT, DBT and DM-DBT are 221, 332.6 and 364.9 °C, respectively. Therefore, those compounds are unlikely to be present in the same refinery fraction. For instance, n-hexadecane with boiling point of 286.9 °C (similar to investigated S-compounds) would be a better choice. 8.
In Section 3.3., a reference should be given to compare the results with PEG. (line 28-29) 9.
In Figure 2, 4 i 5, the space is missing between 'of' and 'DBT' on y-axis. 10.
In Figure 5 it is not clear which y-data refer to which x-data -the x-axis label needs to be adjusted.

11.
The results quoted as Figure 5 are discussed as extraction efficiency (EE) within the text. However, the figure shows the dependence of DBT concentration on the number of extraction degrees. Although the quantities are mutually related, this way of presenting and discussing the results makes no sense.
Decision letter (RSOS-200803.R0) We hope you are keeping well at this difficult and unusual time. We continue to value your support of the journal in these challenging circumstances. If Royal Society Open Science can assist you at all, please don't hesitate to let us know at the email address below.
Dear Dr Kianpour: Title: Extractive desulfurization of liquid fuel using diamine-terminated polyethylene glycol as a very low vapor pressure and green molecular solvent Manuscript ID: RSOS-200803 Thank you for your submission to Royal Society Open Science. The chemistry content of Royal Society Open Science is published in collaboration with the Royal Society of Chemistry.
The editor assigned to your manuscript has now received comments from reviewers. We would like you to revise your paper in accordance with the referee and Subject Editor suggestions which can be found below (not including confidential reports to the Editor). Please note this decision does not guarantee eventual acceptance.
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RSC Subject Editor:
Comments to the Author: (There are no comments.) ********************************************** Reviewers' Comments to Author: Reviewer: 1 Comments to the Author(s) Extractive desulfurization is a feasible technology in gasoline or diesel refining. The results from manuscript suggests that extractive desulfurization using TTD is feasible. However, the manuscript still needs major revisions. Some experiments should be supplmented to clarify what I am concerned about. 1. Regeneration of TTD is very important. So the authors should provide data about the regeneration. 2. Selectivity of sulfurs to aromatics is also important. The author should give the corrsponding data regarding the selectivity. 3. How about the mutual solubility for TTD and model oil? TDD is N-containing extarctant. So its dissolution in oil will cause second contamination besides the extractant loss. Besides, the oil, especially the aromatic-containing oil, will be dissolved in TTD. This results in the oil loss. I do not think that TTD and the oil are immiscible completely.

Compared with PEGs and NHD, what are advantages of TTD?
Reviewer: 2 Comments to the Author(s) Fatemeh Rafiei Moghadam et al. studied extraction of benzothiophene, dibenzothiophene and dimethyl dibenzothiophene using diamine-terminated polyethylene glycol as potential green molecular solvent in desulfurization of liquid fuel. For that purpose they investigated the effects of extractant/fuel volume ratio, process time, temperature, initial S-compound concentration, Scompound type, multiple extraction and the recyclability of extractant on EDS.
Here are the main objections: 1) In Results and Discussion section, the authors claim to have investigated the recyclability of the extractant. Nevertheless, only the reuse has been investigated. The full potential of the recyclability can be achieved with the regeneration of the extractant only, and the authors did not investigate or at least offer such a possibility. I propose to examine all the regeneration possibilities, experimentally if possible.
2) The experiments are not presented in sufficient details. For example, the initial S-compound concentrations are not listed clearly and as a consequence, the experiments cannot be reproduced by the interested reader.
3) The overall amount of experiments is rather low and does not approve the publication. The full paper should make a greater contribution to the development of green technologies in the purification of liquid fuels. I propose to include the results of investigations on the extraction mechanism and clarification of the role of amine and ether functional groups in the extraction of benzothiophene compounds by TTD, which the authors suggest themselves in section 3.5, for future submission of the article.
The necessary corrections are listed below: 1. Although the authors used a word template file to prepare their article, the recommended sections were not followed. Results and Discussion sections should be written separately. 2. Summary section contains a reference which is not in accordance with the journal's recommendations. 3. Briefly explain what a molecular solvent is. 4. In the Introduction, the authors state a specific value of the vapor pressure of TTD (0.001 mmHg) and compare it as 'less than the PEG value'. This fact is confusing because they previously stated that the PEG value was 'less than 0.01 mmHg', which can generally mean that it is also less than the value of TTD. It is necessary to specifically define the value of PEG, as precisely as possible. 5. The experimental part (Section 2.2) is written too generally, and therefore is not entirely clear to understand. Modification of experimental description is necessary so that each reader can repeat the experiment from the description. It is necessary to clearly write the investigated S-compounds concentrations, the used quantities of chemicals and operating conditions -temperature, experiment time, volume ratio of TTD / fuel… 6. From the above mentioned, it is necessary to define why, how and for what purpose these experimental conditions were chosen. 7. From the text it is not clear that heptane is a model fuel -it has to be explicitly stated. Please explain why heptane was chosen as the model fuel. Moreover, BT, DBT and DM-DBT are typical S-components of diesel, and heptane is unfortunately far from being the best choice for onecomponent model diesel fuel. The boiling point of heptane is 98.42 °C, and boiling points of BT, DBT and DM-DBT are 221, 332.6 and 364.9 °C, respectively. Therefore, those compounds are unlikely to be present in the same refinery fraction. For instance, n-hexadecane with boiling point of 286.9 °C (similar to investigated S-compounds) would be a better choice. 8. In Section 3.3., a reference should be given to compare the results with PEG. (line 28-29) 9. In Figure 2, 4 i 5, the space is missing between 'of' and 'DBT' on y-axis. 10. In Figure 5 it is not clear which y-data refer to which x-data -the x-axis label needs to be adjusted. 11. The results quoted as Figure 5 are discussed as extraction efficiency (EE) within the text. However, the figure shows the dependence of DBT concentration on the number of extraction degrees. Although the quantities are mutually related, this way of presenting and discussing the results makes no sense.

Author's Response to Decision Letter for (RSOS-200803.R0)
See Appendix A.

Recommendation? Accept with minor revision (please list in comments)
Comments to the Author(s) 1. As shown in Fig. 5, extraction efficiency of TTD greatly reduces after solvent washing. So, the authors should further explain what causes this siginificant reduction. 2. Fig. 6 provides UV spectrum for TTD in heptane. However, there's no specific data of the solubility of TTD in heptane. As far as I know, UV can give this data.

Comments to the Author(s)
Comments to the Author(s) after revision Most of the suggestions have been corrected, but the manuscript still needs minor revisions. • The authors need to complete investigations on the extraction mechanism and include them in this manuscript. The mutual solubility and regeneration of TTD are basic experiments in this research area, and they can not significantly improve the quality of the work for publication. • The author's answer(3) about molecular solvent should be included in the manuscript. • The author's answer(6) about experimental conditions choice should be included in the manuscript.

Decision letter (RSOS-200803.R1)
We hope you are keeping well at this difficult and unusual time. We continue to value your support of the journal in these challenging circumstances. If Royal Society Open Science can assist you at all, please don't hesitate to let us know at the email address below.

Dear Dr Kianpour:
Title: Extractive desulfurization of liquid fuel using diamine-terminated polyethylene glycol as a very low vapor pressure and green molecular solvent Manuscript ID: RSOS-200803.R1 Thank you for submitting the above manuscript to Royal Society Open Science. On behalf of the Editors and the Royal Society of Chemistry, I am pleased to inform you that your manuscript will be accepted for publication in Royal Society Open Science subject to minor revision in accordance with the referee suggestions. Please find the reviewers' comments at the end of this email.
The reviewers and handling editors have recommended publication, but also suggest some minor revisions to your manuscript. Therefore, I invite you to respond to the comments and revise your manuscript.
Because the schedule for publication is very tight, it is a condition of publication that you submit the revised version of your manuscript before 01-Oct-2020. Please note that the revision deadline will expire at 00.00am on this date. If you do not think you will be able to meet this date please let me know immediately.
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Supplementary files will be published alongside the paper on the journal website and posted on the online figshare repository (https://figshare.com). The heading and legend provided for each supplementary file during the submission process will be used to create the figshare page, so please ensure these are accurate and informative so that your files can be found in searches. Files on figshare will be made available approximately one week before the accompanying article so that the supplementary material can be attributed a unique DOI. ************************************* RSC Associate Editor: Comments to the Author: (There are no comments.) RSC Subject Editor: Comments to the Author: (There are no comments.) ************************************** Reviewer comments to Author: Reviewer: 1 Comments to the Author(s) 1. As shown in Fig. 5, extraction efficiency of TTD greatly reduces after solvent washing. So, the authors should further explain what causes this siginificant reduction. 2. Fig. 6 provides UV spectrum for TTD in heptane. However, there's no specific data of the solubility of TTD in heptane. As far as I know, UV can give this data.

Reviewer: 2
Comments to the Author(s) Comments to the Author(s) after revision Most of the suggestions have been corrected, but the manuscript still needs minor revisions. • The authors need to complete investigations on the extraction mechanism and include them in this manuscript. The mutual solubility and regeneration of TTD are basic experiments in this research area, and they can not significantly improve the quality of the work for publication.

Decision letter (RSOS-200803.R2)
We hope you are keeping well at this difficult and unusual time. We continue to value your support of the journal in these challenging circumstances. If Royal Society Open Science can assist you at all, please don't hesitate to let us know at the email address below.
Dear Dr Kianpour: Title: Extractive desulfurization of liquid fuel using diamine-terminated polyethylene glycol as a very low vapor pressure and green molecular solvent Manuscript ID: RSOS-200803.R2 It is a pleasure to accept your manuscript in its current form for publication in Royal Society Open Science. The chemistry content of Royal Society Open Science is published in collaboration with the Royal Society of Chemistry.
The comments of the reviewer(s) who reviewed your manuscript are included at the end of this email.
Thank you for your fine contribution. On behalf of the Editors of Royal Society Open Science and the Royal Society of Chemistry, I look forward to your continued contributions to the Journal. extracted 75% of DBT with the average value of 2.2 for KN. [8]. Moreover, TTD, with vapor pressure <0.001 hPa, has lower pressure than PEGs (<0.01 hPa) as well as NHD (<0.01 hPa). In the case of extractive desulfurization performance, almost the same results were obtained for TTD and NHD.

Reviewer: 2
Comments to the Author(s) Fatemeh Rafiei Moghadam et al. studied extraction of benzothiophene, dibenzothiophene and dimethyl dibenzothiophene using diamine-terminated polyethylene glycol as potential green molecular solvent in desulfurization of liquid fuel. For that purpose they investigated the effects of extractant/fuel volume ratio, process time, temperature, initial S-compound concentration, S-compound type, multiple extraction and the recyclability of extractant on EDS.
Here are the main objections: 1) In Results and Discussion section, the authors claim to have investigated the recyclability of the extractant. Nevertheless, only the reuse has been investigated. The full potential of the recyclability can be achieved with the regeneration of the extractant only, and the authors did not investigate or at least offer such a possibility. I propose to examine all the regeneration possibilities, experimentally if possible.
Authors reply: Based on your suggestion, regeneration of extractant was studied. Results are discussed and highlighted in the manuscript and obtained data are presented in Figure 5.
2) The experiments are not presented in sufficient details. For example, the initial Scompound concentrations are not listed clearly and as a consequence, the experiments cannot be reproduced by the interested reader.