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by
  • Sandugash Tanirbergenova 1,
  • Yerdos Ongarbayev 1,2 and
  • Zulkhair Mansurov 1,2
  • et al.

Reviewer 1: Yanxiao Ma Reviewer 2: William Zimmerman

Round 1

Reviewer 1 Report

This manuscript described an experimental selection of the solvents to remove the asphaltene-resin-paraffin deposits which would affect the condition of the oil fields from oil fields samples. The basic idea looks OK, however, the whole manuscript needs to be improved significantly from experimental design and characterization scientifically. Here are my suggestions:

  1. Design more scientific experiments to fully understand the dissolve mechanism of the asphaltene-resin-paraffin deposits.
  2. Design detailed control experiments in different conditions.
  3. A complete characterization process is needed in this manuscript to confirm the composition and dissolve of the compound. For example, HPLC, NMR, TGA, DSC.
  4. Some language and scientific explanation need to be improved. For example, Table 4 doesn't have units, etc.

Author Response

First of all, I would like to thank the reviewer for systematic and accurate comments to the article.

I completely agree with the reviewer's all comments on this article and reedited it according to comments.

  1. In this regard, I made different scientific experiments to fully understand the dissolve mechanism of the Also some synonym terms are uniformed.
  2. I added the results in different conditions to the new content of the article. In the same time, added new references regarding to these concepts.
  3. For the completing characterization process the results of Infrared spectrum and chromatographic analyses were added.
  4. I agree with the last comment, too. So I changed the table 3 and scientific and grammatical improvement of article language quality provided by MDPI English editing service.

Author Response File: Author Response.docx

Reviewer 2 Report

This paper is novel and original by construction.   Asphaltenes and parafin deposits are a well known issue for degrading performance, with many approaches to remove them, which are reviewed in the introduction of the paper.  The approach here is to a specific type of mixture matching the composition appropriate to a specific field, and a wide array of solvent mixtures proposed.  I believe that the paper should be published, as it is in scope, and the results will be leading for a wider set of applications that just the targeted field.   However, there are some clarity issues that should be addressed, particularly around the mechanism controlling the dissolving power of the solvent:

1.  Gasoline and petrol are synonyms in much of the world, but one or the other is used exclusively.  Both are used here, so if there is a distinction, it should be defined -- particular formulations perhaps?  

2.  There are typically two concepts in solubility --  saturation and dissolved concentration, which can both be temperature dependent.  Saturation occurs at equilibrium, typically after a long contacting time.   Dissolved concentration should be time dependent in a dissolution experiment.

There are two different scenarios depending on the initial mass of dissolvable material:

Solute limited is when initial solute mass divided by initial solvent volume is less than the solubility limit (concentration at saturation), in which case it is possible to completely dissolve the solute.  

Solvent limited is the opposite case, where it is only possible to dissolve the solute to the saturation level -- some solute will remain undissolved.

These scenarios do not apply if there is no solubility limit -- some materials are miscible in all proportions.

Quite separate from these endpoint solubilities are the rate of dissolution, which depends on the contacting of the two phases -- interfacial surface area -- and the manner in which they contact (free or forced convective stirring or just molecular diffusion).

Commonly, the average concentration C(t) in solution of a dissolving species satisfies an ordinary differential equation if well mixed:

dC/dt =  kLa  (S(T)-C)

with C(t=0)=0

which has solution C(t) =  S(T) (1-Exp[-t/kLa])

where the solution is defined for all time with solvent limited scenarios, and up to the final concentration of initial mass divided by solvent volume for solute limited scenarios.

a  in this case is the surface area per unit volume, so has units of inverse length.   kL is the mass transfer coefficient.  kLa is typically phenomenologically fitted to the time profile of concentration.

The experiments here have focussed on the removal of mass from geometrically similar configurations, rather than the liquid side study as above.   In the context of the liquid side analysis, the mixing is typically controlling.  In this set of experiments, there is no forced convection, so the active mechanisms are diffusion and free convection.  Those with high kL are likely to be free convection dominated, i.e. the solute when dissolved in the liquid creates a density difference that drives motion, moving solute away from the mass more rapidly.  Those with low kL are likely to be diffusion-limited, i.e. dissolved solute is closer to neutral buoyancy with the solution.

Seen in the light of the controlling transport phenomena, it should be clear that the driving force for dissolution in these cases is the density change upon dissolution, which controls kL by inducing free convection.

Where the data has three different concentration values for three different contacting times, then kLa should be estimated by nonlinear regression (built into Matlab and Mathematica).   Where there are only two different measurements (where the last two are the same out of three, for example), only a lower bound on kLa can be estimated.  

Were I leading the research, I would insist on grinding the masses to small particulates and dissolving to determine the volume change on dissolution, so as to quantify the driving force for free convection.  But since I am not, then the authors should at least include the liquid-side analysis as above and acknowledge that the solubilities at saturation are very similar for the solute/solvent mixtures, so do not determine the dissolution rate to any great extent.   The dominate feature is the mechanism for liquid-side mass transfer, which due to the variation in kLa is diffusion limited in slow cases but free convection dominated due to volume change on dissolution in the faster cases.  In general, there are two types of solutions classes -- ideal solutions with no volume change on solvation and non-ideal where the density changes (due to chemical affinity for decrease in volume and due to chemical disparity in volume increase on mixing).   

Although the journal frowns on self citations by referees, I should point out that many of these issues are discussed quite some time ago in a wholly different context in my analysis of the formation of stable stratifications:

W.B. Zimmerman, ``The effect of chemical equilibrium on the formation of stable stratification.’’     Appl. Sci. Res., 59:298-298 (1998).

There is an analogy to thermal free convection for the solutal free convection that is apparently controlling in this paper, and that is shown to be dependent on the geometry of the configuration / contacting scenario in a paper just in press, forming convection cells that are good at mixing but potentially stable stratifications that are poor in mixing with non-monotonic density dependences on temperature (or by analogy solute concentration):

https://www.sciencedirect.com/science/article/pii/S1359431122006640

Author Response

First of all, I would like to thank the reviewer for systematic and accurate comments to the article.

I completely agree with the reviewer's comments on this article. In this regard, I made a different analysis and added the results to the new content of the article. Scientific and grammatical improvement of article language quality provided by MDPI English editing service.

  1. Gasoline and petrol are synonyms in much of the world, so I used only term of “Gasoline”
  2. I agree with the second comment, too. So I designed some experimental analyses and added new references regarding to these concepts.

Round 2

Reviewer 1 Report

After review the revised version, I feel the manuscript is significantly improved and I think it is publishable.