Demulsification of Heavy Oil-in-Water Emulsion by a Novel Janus Graphene Oxide Nanosheet: Experiments and Molecular Dynamic Simulations

Round 1

Reviewer 1 Report

Review Xu et al.

 

The authors carried out a study on demulsification of oil-water mixtures. The authors carry out both experiments and molecular dynamics simulations. The study provides novel insights and fits the scope of Molecules. Yet, there are some language and technical problems that have to be addressed before the manuscript can be published. The reviewer is no native English speaker and refrains of making individual suggestions for improvements. It starts with the second sentence of the abstract which is very long and hard to digest. There are many similar language problems in the manuscript. This needs to be revised thoroughly.

 

Moreover, the authors should address the following points:

 

1. In the introduction, the authors provide a reasonable overview of the technological aspects of the topic. Yet, no overview and state-of-the-art is presented regarding the employed methods (experiments and MD simulations). How were these methods applied before in the literature for addressing similar questions? There is for example a wealth of literature on fluid interfaces of mixtures molecular simulations – also with oil and gas sector motivations/ backgrounds. See [Fuels & Energy 32 (2018) 2095 DOI 1021/acs.energyfuels.7b03863] [Fluid Phase Equilib. 518 (2020) 112583 DOI: 10.1016/j.fluid.2020.112583] [Fluid Phase Equilib. 476 (2018) 9 DOI: 10.1016/j.fluid.2017.06.016] for examples and [Int. Rev. Phys. Chem. 39, 3, 319-349 (2020) 10.1080/0144235X.2020.1777705] for a review.
2. Analogue, the experimental methods used by the authors should be introduced in the introduction such as the reader gets an idea how these methods were used for similar problems before and which outcomes were thereby obtained.
3. The authors state “Asphaltene could fabricate a protective film at the oil/water interface to prevent the coalescence of the emulsion droplets”. This is in line with the fact that the authors find an enrichment of components at the fluid interface. Yet, this is an extensively studied phenomenon on the atomistic scale in recent years, which is not addressed yet in the manuscript. In many mixtures, a light boiling component will usually accumulate at the interface [Int. Rev. Phys. Chem. 39, 3, 319-349 (2020) 10.1080/0144235X.2020.1777705] [J. Phys. Chem. B 125, 25, 6968 (2021) 10.1021/acs.jpcb.1c03037]. It is intensely discussed in recent years that this accumulation probably influences mass transfer [J. Chem. Phys. 144, 044703 (2016) 10.1063/1.4940137] [Mol. Phys. 119, 3, e1810798 (2021) 10.1080/00268976.2020.1810798] [Colloid J. 81, 491 (2019) 10.1134/S1061933X19040021] [Chem. Eng. Proc. 171 (2022) 108501 DOI: 10.1016/j.cep.2021.108501]. This is possibly also closely related to the separation of “crude oil-in-water emulsion”, which the authors study. All this should be discussed by the authors in their manuscript.
4. Moreover, it has been shown that the enrichment/ accumulation of components at fluid interfaces can be considered as the precursor of the formation of a new phase from a thermodynamics point of view [Phys. Chem. Chem. Phys. 22, 12544-12564 (2020) 10.1039/D0CP01411G] [J. Chem. Phys. 78, 7300 (1983) 10.1063/1.444720]. This is in line to the picture and mechanism proposed by the authors in Fig. 6. The authors should discuss their findings and understandings in the light of previously published results such as the mentioned references.
5. It is very unusual to first present the results and then afterwards introduce the methods. I strongly recommend to change the order of chapter 3 and 2.

 

Author Response

Comments to the author：

The authors carried out a study on demulsification of oil-water mixtures. The authors carry out both experiments and molecular dynamics simulations. The study provides novel insights and fits the scope of Molecules. Yet, there are some language and technical problems that have to be addressed before the manuscript can be published. The reviewer is no native English speaker and refrains of making individual suggestions for improvements. It starts with the second sentence of the abstract which is very long and hard to digest. There are many similar language problems in the manuscript. This needs to be revised thoroughly.

1. In the introduction, the authors provide a reasonable overview of the technological aspects of the topic. Yet, no overview and state-of-the-art is presented regarding the employed methods (experiments and MD simulations). How were these methods applied before in the literature for addressing similar questions? There is for example a wealth of literature on fluid interfaces of mixtures molecular simulations – also with oil and gas sector motivations/ backgrounds. See [Fuels & Energy 32 (2018) 2095 DOI 1021/acs.energyfuels.7b03863] [Fluid Phase Equilib. 518 (2020) 112583 DOI: 10.1016/j.fluid.2020.112583] [Fluid Phase Equilib. 476 (2018) 9 DOI: 10.1016/j.fluid.2017.06.016] for examples and [Int. Rev. Phys. Chem. 39, 3, 319-349 (2020) 10.1080/0144235X.2020.1777705] for a review.

Answer: Thanks for the reviewer’s suggestion and useful references. In the valuable literatures, the methods about molecular dynamics simulations for the investigation on the interfacial fluid mixtures are closely related to our present system, which propose the novel insight for us. We have added the literatures of reviewer’s suggestions in the introduction part (Ref. 39, 40, 41, 47).

2. Analogue, the experimental methods used by the authors should be introduced in the introduction such as the reader gets an idea how these methods were used for similar problems before and which outcomes were thereby obtained.

Answer: Thanks for the reviewer’s advice. We have added some literatures related to molecular dynamics simulations to support our view. These articles mainly employed molecular dynamics methods to explore interfacial molecular interactions on atomistic scale and are of great relevance to our research. [1, 2] We have added the literatures in the introduction part (Ref. 44, 45).

3. The authors state “Asphaltene could fabricate a protective film at the oil/water interface to prevent the coalescence of the emulsion droplets”. This is in line with the fact that the authors find an enrichment of components at the fluid interface. Yet, this is an extensively studied phenomenon on the atomistic scale in recent years, which is not addressed yet in the manuscript. In many mixtures, a light boiling component will usually accumulate at the interface [Int. Rev. Phys. Chem. 39, 3, 319-349 (2020) 10.1080/0144235X.2020.1777705] [J. Phys. Chem. B 125, 25, 6968 (2021) 10.1021/acs.jpcb.1c03037]. It is intensely discussed in recent years that this accumulation probably influences mass transfer [J. Chem. Phys. 144, 044703 (2016) 10.1063/1.4940137] [Mol. Phys. 119, 3, e1810798 (2021) 10.1080/00268976.2020.1810798] [Colloid J. 81, 491 (2019) 10.1134/S1061933X19040021] [Chem. Eng. Proc. 171 (2022) 108501 DOI: 10.1016/j.cep.2021.108501]. This is possibly also closely related to the separation of “crude oil-in-water emulsion”, which the authors study. All this should be discussed by the authors in their manuscript.

Answer: Thanks for the reviewer's suggestion. In recent years, the fact that lighter components can accumulate at interfaces and influence the distribution of substances is indeed a hot research topic. We have reviewed the literatures about the separation of "crude oil-water emulsions" and cited these papers. We have added the literatures in the introduction part and discussed correspondingly (Ref. 42, 43, 44, 45, 46, 48).

4. Moreover, it has been shown that the enrichment/ accumulation of components at fluid interfaces can be considered as the precursor of the formation of a new phase from a thermodynamics point of view [Phys. Chem. Chem. Phys. 22, 12544-12564 (2020) 10.1039/D0CP01411G] [J. Chem. Phys. 78, 7300 (1983) 10.1063/1.444720]. This is in line to the picture and mechanism proposed by the authors in Fig. 6. The authors should discuss their findings and understandings in the light of previously published results such as the mentioned references.

Answer: Thanks for the reviewer’s suggestion. We have read the two articles mentioned carefully and found them of great interest. In our study, the adsorbed asphaltene molecules construct the protective film at the oil/water interface, generating the new phase to stabilize the heavy oil-in-water emulsion from the thermodynamic aspect (Figure 6). We have cited the above two articles to further confirm our findings in the results and discussion part (Ref. 41, 52).

5. It is very unusual to first present the results and then afterwards introduce the methods. I strongly recommend to change the order of chapter 3 and 2.

Answer: Thanks for the reviewer’s suggestion to change the sequence of part 2 and 3. According to the format requirement of the journal Molecules, the results and discussion section usually come first and the experiments and methods section to follow.

References

1. Lian, P.; Jia, H.; Wei, X.; Han, Y.; Wang, Q.; Dai, J.; Wang, D.; Wang, S.; Tian, Z.; Yan, H., Effects of zwitterionic surfactant adsorption on the component distribution in the crude oil droplet: A molecular simulation study. Fuel 2021, 283.
2. Liu, X.; Li, Y.; Tian, S.; Yan, H., Molecular Dynamics Simulation of Emulsification/Demulsification with a Gas Switchable Surfactant. The Journal of Physical Chemistry C 2019, 123, (41), 25246-25254.

Reviewer 2 Report

The manuscript “Demulsification of Heavy Oil-in-Water Emulsion by a Novel Janus Graphene Oxide Nanosheet: Experiments and Molecular Dynamic Simulations ” by Yingbiao Xu et al. reports a study on the demulsification of oil-water emulsion by Janus Graphene Oxide. They show a higher demulsification efficiency of JGO than GO. It is an interesting study and makes sense. This reviewer suggests publication after some minor revision.

 

-. The scientific impact looks a little bit low because of the high efficiency of GO 92.5%. Can authors tailor and elaborate more on the necessity of JGO? It is not clear that we really need this JGO to increase only 6%, in terms of cost, effort, time, etc.

 

-. Why does GO still show a high demulsification? It seems contracting with the mechanisms the authors provided.

 

-. Can the sheets be reusable?

 

-. How can they know that only one side of GO is functionalized? It is not clear through the synthesis method. Did they confirm it through characterization? Or just assumption.  

Author Response

Comments to the author：

The manuscript “Demulsification of Heavy Oil-in-Water Emulsion by a Novel Janus Graphene Oxide Nanosheet: Experiments and Molecular Dynamic Simulations” by Yingbiao Xu et al. reports a study on the demulsification of oil-water emulsion by Janus Graphene Oxide. They show a higher demulsification efficiency of JGO than GO. It is an interesting study and makes sense. This reviewer suggests publication after some minor revision.

1. The scientific impact looks a little bit low because of the high efficiency of GO 92.5%. Can authors tailor and elaborate more on the necessity of JGO? It is not clear that we really need this JGO to increase only 6%, in terms of cost, effort, time, etc.

Answer: Thanks for the reviewer’s question. Although the demulsification efficiency of GO has reached 92.5%, the residual water can cause serious downstream production problems of fouling and corrosion in heat exchangers, pipelines, and upgrading equipment. [1, 2] Then we think it is still necessary to investigate the novel demulsifier with higher efficiency, which is a current research hotspot. As the reviewer pointed out, the fabrication of JGO requires higher cost, effort, and time. Thereby, it is highly necessary to explore the simpler synthesis methods and higher yields to reduce additional costs in our future investigation.

2. Why does GO still show a high demulsification? It seems contracting with the mechanisms the authors provided.

Answer: Thanks for the reviewer to remind us to further interpret the proposed mechanism clearly. The amphiphilic GO/JGO can spontaneously migrate the oil-water interface and interact with asphaltene molecules. At the same time, due to the strong interaction between GO/JGO and asphaltene, the protective film formed by the asphaltene will be destroyed by the collision of oil droplets. The partial destruction of the protective film provides a place for small oil droplets to agglomerate into larger droplets. [3-5] The amphiphilicity of JGO is improved by the asymmetric modification with n-octylamine. At the oil-water interface, the overlapped parts of JGO nanosheets may not be as rigid as those of GO nanosheets due to the hinderance of n-octylamine. Therefore, the emulsion with JGO adsorbed at interfaces would be much easier to deform and merge into larger droplets. Therefore, the GO’s demulsification ability does not conflict with our proposed mechanism.

3. Can the sheets be reusable?

Answer: Thanks to the reviewer for the important consideration about the cyclic utilization of the nanosheets. A series of preliminary experiments were attempted to explore the reusability of JGO nanosheets after the demulsification, such as extraction, centrifugation, and heating experiments. However, the above methods hardly separated the sheets from the aggregates. We are planning to further employ some complicated methods with a view to achieving reusability, which can highly reduce the cost.

4. How can they know that only one side of GO is functionalized? It is not clear through the synthesis method. Did they confirm it through characterization? Or just assumption.

Answer: Thanks for the reviewer’s reminder. The successful modification of JGO is based on the results in our previous report. [6, 7] In our previous report, we have carried out many experiments (FT-IR, UV-vis, XPS, contact angle and zeta potential measurements) to confirm the successful unilateral modification of JGO. [6] In the present study, we have focused on the demulsification behavior of JGO, so we briefly use the contact angle measurements to confirm the JGO structure.

References

1. Kralova, I.; Sjoblom, J.; Oye, G.; Simon, S.; Grimes, B. A.; Paso, K., Heavy Crude Oils/Particle Stabilized Emulsions. Advances in Colloid and Interface Science 2011, 169, (2), 106-127.
2. Wang, D.; Yang, D.; Huang, C.; Huang, Y.; Yang, D.; Zhang, H.; Liu, Q.; Tang, T.; El-Din, M. G.; Kemppi, T.; Perdicakis, B.; Zeng, H., Stabilization mechanism and chemical demulsification of water-in-oil and oil-in-water emulsions in petroleum industry: A review. Fuel 2021, 286.
3. Liu, J.; Li, X. C.; Jia, W. H.; Li, Z. Y.; Zhao, Y. P.; Ren, S. L., Demulsification of Crude Oil-in-Water Emulsions Driven by Graphene Oxide Nanosheets. Energy & Fuels 2015, 29, (7), 4644-4653.
4. Falls, A. H.; Scriven, L. E.; Davis, H. T., Adsorption, structure, and stress in binary interfaces. The Journal of Chemical Physics 1983, 78, (12), 7300-7317.
5. Stephan, S.; Hasse, H., Interfacial properties of binary mixtures of simple fluids and their relation to the phase diagram. Phys Chem Chem Phys 2020, 22, (22), 12544-12564.
6. Huang, P.; Jia, H.; Wang, T. Y.; Xu, Y. B.; Zhang, L. Y.; Wei, X.; Jia, H. D.; Wen, S. J.; Lv, K. H.; Liu, D. X., Effects of Modification Degrees on the Colloidal Stability of Amphiphilic Janus Graphene Oxide in Aqueous Solution with and without Electrolytes. Langmuir 2021, 37, (33), 10061-10070.
7. Jia, H.; Huang, P.; Han, Y.; Wang, Q.; Wei, X.; Huang, W.; Dai, J.; Song, J.; Yan, H.; Liu, D., Synergistic effects of Janus graphene oxide and surfactants on the heavy oil/water interfacial tension and their application to enhance heavy oil recovery. J. Mol. Liq. 2020, 314.

Reviewer 3 Report

In this work, graphene oxide Janus-like modified particles were obtained by using graphene oxide sheets and octylamine

The paper is well written and shows promising results, although a point should be addressed before approval:

1. There is literature that shows a similar mechanism of graphene oxide modification and use to demulsify crude oil-in-water emulsions, in this case with octylamine. The authors should summarize and cite this paper Ortiz et al. https://doi.org/10.1016/j.fuel.2018.11.151
2. On the one hand, there are works that show asphaltene containing O/W interfacial measurements without definitive proof of the role of asphaltenes stabilizing oil in water emulsion https://doi.org/10.1016/j.fuel.2016.10.066 https://doi.org/10.1016/j.colsurfa.2019.04.017 There is literature indicating water-in-crude oil asphaltenes’ emulsification role, nevertheless without definitive proof of asphaltenes acting like a hydrophilic surfactant that can stabilize O/W emulsions according to R Winsor theory
3. On the other hand, there is definitive proof that polymeric molecules or surfactants that come from demulsifier or EOR processes https://doi.org/10.1021/acsami.0c15387
4. Therefore, looking into the contradictions, particularly the following paragraphs of known researchers, there should be included in the introduction of the paper a review of the works that indicate the mechanisms of crude oil in water emulsion stabilization. Furthermore, there should be a discussion with several references, that should indicate how asphaltenes are responsible for the stabilization of the emulsion. Thus, allowing to make the discussion and MD simulations shown in the research.

4.1 Contradiction with the assertion that asphaltenes stabilize crude oil in water emulsions:

On the contrary, the coalescence dynamics of oil droplets are much faster and are largely insensitive to asphaltene concentration and aging time. In addition, the contact of water against asphaltene-laden oil solutions induces spontaneous emulsification where micron-sized water droplets, stabilized by asphaltenes, appear. Oil droplets, on the other hand, are observed to coalesce very quickly and in a manner that is insensitive to asphaltene concentration and aging time. We believe that this difference in behavior between the two types of droplets is related to the arrangement of asphaltene molecules at the oil/water interface (32) and the resulting interface–interface interactions (Figure 6). In the water droplet case, hydrophobic repulsion occurs because of the interaction between aliphatic tails. (3) In the oil droplet case, the aromatic portion of the asphaltenes interacts, producing attractive forces. https://doi.org/10.1021/acs.langmuir.7b02638

4.2 Works indicating that hydrophilic surfactants that stabilize O/W emulsions according to Winsor and HLD theories is necessary to stabilize this crude oil in water emulsions:

When the previous treatments have involved an O/W formulation (in particular because of an excess of demulsifier used in the petroleum production), the formulation change is performed in this case from HLDN < 0 to HLDN = 0, by adding a somewhat lipophilic surfactant with an SCPN > 0, generally block copolymers, i.e., very big surfactant-like molecules that play complex synergies, and allows to flocculate small oil droplets and to concentrate them and favor their separation https://doi.org/10.20944/preprints202203.0011.v2 https://doi.org/10.1016/j.colsurfa.2019.04.017

Additionally, the following corrections should be addressed (the paragraphs do not have line numbers because the manuscript for review does not have them. It should be advisable that authors include line numbers):

most oilfield-s has-ve reached the high water cut stage

to readily adsorb on the oil/water interface and dramatically enhance the emulsion stability Comment: are the authors implying that asphaltenes stabilize oil-in-water emulsions. I thought asphaltenes were oil-soluble, and does not go to the water phase. Please revisit the following works: https://doi.org/10.3390/cosmetics7030057 https://doi.org/10.1021/acs.energyfuels.1c03349

The extremely stable emulsion can cause serious problems to the downstream process, such as fouling and corrosion in heat exchangers, pipelines, and upgrading equipment [13, 14]. Comment: are you talking about W/O emulsions?? Because in your work, the center of research is a O/W emulsion (from what I know, these are stabilized by hydrophilic surfactants from EOR, or even more by polymeric surfactants (or polymers) from EOR that go to the interface and form a high mechanical resistance high elasticity interface

The proposed strategies for oil-water separation mainly include adsorption. Comment: then the following reference is added Frising, T.; Noik, C.; Dalmazzone, C., The liquid/liquid sedimentation process: From droplet coalescence to technologically enhanced water/oil emulsion gravity separators: A review. JOURNAL OF DISPERSION SCIENCE AND TECHNOLOGY 2006, 27, (7), 1035-1057. I would recommend the authors to make a very clear distinction between water-in-crude oil (emulsions in produced crude oil) and crude oil-in-water emulsions (produced water emulsions). Thus, all the introduction to this paragraph should include that distinction and then you start with just crude oil-in-water emulsions (that is the subject of your research)

Asphaltene could fabricate a protective film at the oil/water interface to prevent the coalescence of the emulsion droplets [37]. Comment: This is for water-in-crude oil emulsions. Again, the authors center their work on the stabilization of O/W emulsions but present reference (37) on water-in-oil emulsions. There continues to be confusion.

The adsorbed asphaltene molecules construct the protective film at the oil/water interface, generating the stable heavy oil-in-water emulsion (Fig. 6a). Comment: you have in this system large water to oil ratio (WOR), that is, a large quantity of water in relation to oil. Therefore, when you emulsify, the external phase would be water. That does not mean that the asphaltene effect on the measurement of interfacial rheology would be reflected in that O/W emulsion stability because asphaltenes actually stabilize W/O emulsions

Best regards

 

Author Response

Comments to the author：

In this work, graphene oxide Janus-like modified particles were obtained by using graphene oxide sheets and octylamine. The paper is well written and shows promising results, although a point should be addressed before approval: There is literature that shows a similar mechanism of graphene oxide modification and use to demulsify crude oil-in-water emulsions, in this case with octylamine. The authors should summarize and cite this paper Ortiz et al. https://doi.org/10.1016/j.fuel.2018.11.151 On the one hand, there are works that show asphaltene containing O/W interfacial measurements without definitive proof of the role of asphaltenes stabilizing oil in water emulsion https://doi.org/10.1016/j.fuel.2016.10.066

https://doi.org/10.1016/j.colsurfa.2019.04.017

There is literature indicating water-in-crude oil asphaltenes’ emulsification role, nevertheless without definitive proof of asphaltenes acting like a hydrophilic surfactant that can stabilize O/W emulsions according to R Winsor theory. On the other hand, there is definitive proof that polymeric molecules or surfactants that come from demulsifier or EOR processes https://doi.org/10.1021/acsami.0c15387

Therefore, looking into the contradictions, particularly the following paragraphs of known researchers, there should be included in the introduction of the paper a review of the works that indicate the mechanisms of crude oil in water emulsion stabilization. Furthermore, there should be a discussion with several references, that should indicate how asphaltenes are responsible for the stabilization of the emulsion. Thus, allowing to make the discussion and MD simulations shown in the research.

1. Contradiction with the assertion that asphaltenes stabilize crude oil in water emulsions: On the contrary, the coalescence dynamics of oil droplets are much faster and are largely insensitive to asphaltene concentration and aging time. In addition, the contact of water against asphaltene-laden oil solutions induces spontaneous emulsification where micron-sized water droplets, stabilized by asphaltenes, appear. Oil droplets, on the other hand, are observed to coalesce very quickly and in a manner that is insensitive to asphaltene concentration and aging time. We believe that this difference in behavior between the two types of droplets is related to the arrangement of asphaltene molecules at the oil/water interface (32) and the resulting interface–interface interactions (Figure 6). In the water droplet case, hydrophobic repulsion occurs because of the interaction between aliphatic tails. (3) In the oil droplet case, the aromatic portion of the asphaltenes interacts, producing attractive forces. https://doi.org/10.1021/acs.langmuir.7b02638

Answer: Thanks to the reviewer for pointing out our oversight.

Firstly, the above literature is closely related to our study and is of great reference value. Amine-modified graphene oxide mentioned in the literature is a novel demulsifier that can effectively destabilize water-in-oil emulsions. We have cited the literature in the introduction part. (Ref. 37)

  Secondly, as mentioned by the reviewer, although the articles by Liu et al. [1] and Tian et al. [2] suggest that asphaltenes are present at the interface of O/W emulsions, there is no conclusive experimental evidence that asphaltenes act as hydrophilic surfactant to form an interfacial layer of limited thickness in the interfacial region when the system consisting of aqueous solution and crude oil. In this study we mainly referred to the experiment method in Liu’s literature. [3] As they illustrated, the stability of O/W emulsions is due to the repulsive force of the double electric layer between the oil droplets and the protective film, which is mainly consist of asphaltenes and resins. Furthermore, it seems that there are no other substances with typical amphiphilicity in the crude oil/water system.

  Frankly speaking, as mentioned by the reviewer, asphaltenes are hydrophobic and generally form W/O emulsions. Nevertheless, the water/oil ratio and the asphaltene concentration are also key factors for the formation of different types of emulsions. In the present study, the water/oil ratio was relatively high and the asphaltene concentration was lower than 1.5wt%, in which case the O/W emulsions usually generated [4]. Furthermore, the complicated molecular structures of the asphaltenes and resins may be another uncertain factor. Therefore, it is speculated that the formation of O/W emulsions maybe reasonable. In the introduction, we included a systematical review on the works that indicate the formation of crude oil in water emulsion stabilized by asphaltene. It is concluded based on thermodynamic aspect that the adsorbed asphaltene molecules could construct the protective film at the oil/water interface, generating the new phase to stabilize the heavy oil-in-water emulsion (Figure 6) [5, 6].

2. Works indicating that hydrophilic surfactants that stabilize O/W emulsions according to Winsor and HLD theories is necessary to stabilize this crude oil in water emulsions: When the previous treatments have involved an O/W formulation (in particular because of an excess of demulsifier used in the petroleum production), the formulation change is performed in this case from HLDN < 0 to HLDN = 0, by adding a somewhat lipophilic surfactant with an SCPN > 0, generally block copolymers, i.e., very big surfactant-like molecules that play complex synergies, and allows to flocculate small oil droplets and to concentrate them and favor their separation https://doi.org/10.20944/preprints202203.0011.v2 https://doi.org/10.1016/j.colsurfa.2019.04.017

Answer: Thanks to the reviewer to remind us to pay more attention to the reasons for the generation of O/W emulsions, which has been fully discussed in the answer to Q1.

3. Additionally, the following corrections should be addressed (the paragraphs do not have line numbers because the manuscript for review does not have them. It should be advisable that authors include line numbers):“most oilfield-s has-ve reached the high water cut stage”to readily adsorb on the oil/water interface and dramatically enhance the emulsion stability Comment: are the authors implying that asphaltenes stabilize oil-in-water emulsions. I thought asphaltenes were oil-soluble, and does not go to the water phase. Please revisit the following works: https://doi.org/10.3390/cosmetics7030057 https://doi.org/10.1021/acs.energyfuels.1c03349

The extremely stable emulsion can cause serious problems to the downstream process, such as fouling and corrosion in heat exchangers, pipelines, and upgrading equipment [13, 14]. Comment: are you talking about W/O emulsions?? Because in your work, the center of research is an O/W emulsion (from what I know, these are stabilized by hydrophilic surfactants from EOR, or even more by polymeric surfactants (or polymers) from EOR that go to the interface and form a high mechanical resistance high elasticity interface.

Answer: Thanks to the reviewer for correcting our mistakes. We have corrected the inaccurate statement “With the excessive exploitation, most oilfields have reached the high water cut stage”. “the hazards of fouling and corrosion in heat exchangers, pipelines, and upgrading equipment are mainly influenced by W/O emulsion, which is not match the O/W emulsion” was changed to “The extremely stable emulsion can cause serious problems to the downstream process, such as the generation of large amounts of polluting oily wastewater.” [7, 8]

4. The proposed strategies for oil-water separation mainly include adsorption. Comment: then the following reference is added Frising, T.; Noik, C.; Dalmazzone, C., The liquid/liquid sedimentation process: From droplet coalescence to technologically enhanced water/oil emulsion gravity separators: A review. JOURNAL OF DISPERSION SCIENCE AND TECHNOLOGY 2006, 27, (7), 1035-1057. I would recommend the authors to make a very clear distinction between water-in-crude oil (emulsions in produced crude oil) and crude oil-in-water emulsions (produced water emulsions). Thus, all the introduction to this paragraph should include that distinction and then you start with just crude oil-in-water emulsions (that is the subject of your research)

Answer: Thanks to the reviewer’s suggestion. We have reorganized W/O emulsions and O/W emulsions and subsequently introduced the focus of our research (O/W emulsions). Some mistakes are corrected in the introduction section.

5. Asphaltene could fabricate a protective film at the oil/water interface to prevent the coalescence of the emulsion droplets [37]. Comment: This is for water-in-crude oil emulsions. Again, the authors center their work on the stabilization of O/W emulsions but present reference (37) on water-in-oil emulsions. There continues to be confusion.

Answer: Thanks to reviewer for pointing out our error. The paper studied the water-in-oil (W/O) emulsion via molecular dynamics simulation. We have replaced it with a reasonable reference to support the proposed mechanism.

6. The adsorbed asphaltene molecules construct the protective film at the oil/water interface, generating the stable heavy oil-in-water emulsion (Fig. 6a). Comment: you have in this system large water to oil ratio (WOR), that is, a large quantity of water in relation to oil. Therefore, when you emulsify, the external phase would be water. That does not mean that the asphaltene effect on the measurement of interfacial rheology would be reflected in that O/W emulsion stability because asphaltenes actually stabilize W/O emulsions.

Answer: Thanks to reviewer’s question. As reviewer mentioned, our system contains large water to oil ratio (WOR), which directly determines the oil-in-water emulsion. According to many previous work [3,9], we believe that the formation of uncommon oil-in-water type emulsions is reasonable based on three reasons: 1) The amount of water is much greater than the amount of oil; 2) The low asphaltene concentration; 3) The structure of asphaltenes is inherently complex and it is difficult to clarify the formation of oil-in-water emulsion as a result of changes in asphaltene structure. Previous reports also shown that the stability of oil-in-water emulsions is due to the repulsion of the asphaltene protective film on the surface of the oil droplets. Besides, this statement is consistent with the reviewer’s reference to hydrophobic repulsion occurring between asphaltene aliphatic tails. [10] Therefore, it is believed that the asphaltenes can affect the rheological property and stability of oil-in-water emulsions in the present study.

 

 

References

1. Liu, J.; Wang, H.; Li, X.; Jia, W.; Zhao, Y.; Ren, S., Recyclable magnetic graphene oxide for rapid and efficient demulsification of crude oil-in-water emulsion. Fuel 2017, 189, 79-87.
2. Tian, S.; Gao, W.; Liu, Y.; Kang, W., Study on the stability of heavy crude oil-in-water emulsions stabilized by two different hydrophobic amphiphilic polymers. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2019, 572, 299-306.
3. Liu, J.; Li, X. C.; Jia, W. H.; Li, Z. Y.; Zhao, Y. P.; Ren, S. L., Demulsification of Crude Oil-in-Water Emulsions Driven by Graphene Oxide Nanosheets. Energy & Fuels 2015, 29, (7), 4644-4653.
4. Radnia, H.; Solaimany Nazar, A. R.; Rashidi, A., Effect of asphaltene on the emulsions stabilized by graphene oxide: A potential application of graphene oxide in enhanced oil recovery. Journal of Petroleum Science and Engineering 2019, 175, 868-880.
5. Falls, A. H.; Scriven, L. E.; Davis, H. T., Adsorption, structure, and stress in binary interfaces. The Journal of Chemical Physics 1983, 78, (12), 7300-7317.
6. Stephan, S.; Hasse, H., Interfacial properties of binary mixtures of simple fluids and their relation to the phase diagram. Phys Chem Chem Phys 2020, 22, (22), 12544-12564.
7. Dai, Q.; Chung, K. H., Hot water extraction process mechanism using model oil sands. Fuel 1996, 75, (2), 220-226.
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Round 2

Reviewer 1 Report

The authors have reasonably responded to the reviewers points

Reviewer 3 Report

The authors responded to all the requests in a reasonable way. Although in the manuscript there is just certain parts that are highlighted (are those the only corrections?, did the authors upload the correct manuscript?)

Best regards