Integrated a Fused Silica Capillary Cell and In Situ Raman Spectroscopy for Determining the Solubility of CO2 in n-Decane and n-Decane + n-Hexane System
Round 1
Reviewer 1 Report
The authors represent experimental data on the solubility of CO2 in n-decane and in a liquid phase containing hexane as third compound. The CO2 concentrations are derived from Raman measurements of the mixtures.
For several reasons I recommend rejection of this manuscript:
Firstly, the authors do not compare their measured CO2 concentrations with the CO2 concentrations measured my others for the same binary system (CO2 + n-decane) for the same experimental conditions. https://doi.org/10.1021/je60085a012
Secondly, the authors do not use any other data to prove that their evaluation method works properly. It is “good scientific practice” to demonstrate that the measurements can at least replicate data that are known for sure. This is missing here.
Thirdly, there are several other shortcomings:
· The authors completely ignored the work on CO2-oil systems, that have been carried out at the Ruhr Universität Bochum (Profs M. Petermann and S. Pollak)
· The authors completely ignored the work of Prof A. Braeuer (also Germany) about the measurement of vapor liquid equilibria and solubilities of CO2 containing mixtures (also in FS-capillaries) in this p&T range.
· The authors are using the PREoS for the computation of the amount of substance of CO2 fed into the chamber, instead of having used the much more precise Span and Wagner EoS, which has especially been developed for CO2, an which is available here
https://webbook.nist.gov/chemistry/fluid/
· The authors claim that their calibration curve for CO2/decane is also true for CO2/decane/hexane. During calibration they kept the ratio of hexane/decane constant with only a very small hexane fraction. Of course, 3wt% hexane do not alter the CH stretch vibration signal relative to the CO2 Fermi dyad significantly. If the authors want to evaluate the binary and the ternary system with the same calibration line, they would have to show that the calibration lines for the binary system CO2/decane is identical to the one for CO2/hexane, just because the wt % of hexane in the CO2 saturated solution will vary significantly from the 3wt% regarded during calibration.
· The authors explain their findings on the solubility as a function of pressure in the light of a distance between the molecules. I do not think that this is state of the art. Solubility behaviours of CO2 in alkanes have been measured and discussed for many years and have been described on a much more solid physical ground (in combination with volume expansion and interfacial tension).
· No information is provided how the intensities are computed from the spectra (peak height, or peak area) and how the spectra were processed. The CO2 Fermi dyad usually is interfered from signal peaks of the alkane.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The article “Integrated a fused silica capillary cell and in situ Raman spec- 2 troscopy for determining the solubility of CO2 in n-decane and n-decane + n-hexane system” describes investigations about the solubility of CO2 in n-decane and n-decane + n-hexane system. The authors measured the CO2 solubility using a fused silica capillary cell with in situ Raman spectroscopy.
This study is pertinent but the reviewer would like to make some comments:
- The manuscript needs an English revision performed by an English-spoken revisor.
To illustrate this recommendation the following sentence (extracted from the abstract) needs to be revised:
The sentence in the abstract:
“It was found that under low pressure conditions, the addition of co-solvent n-hexane did not enhanced the solubility of CO2, while it had a certain enhancement effected on the dissolution of CO2 under high-pressure conditions.
Should be
“It was found that under low-pressure conditions, the addition of co-solvent n-hexane did not enhance the solubility of CO2, while it had a certain enhancement effect on the dissolution of CO2 under high-pressure conditions.”
- INTRODUCTION.
At the end of the introduction, please justify shortly the study with co-solvent (nature and content)
- CONCLUSION
Mentioning that when the temperature was constant, the solubility of CO2 increased with the pressure increase or that, under constant pressure, the solubility of CO2 decreased with the temperature increase, is a predicted result. These results could be mentioned if the values are different from those predicted (much higher for example, in this case, the authors should mention values).
The reviewer suggests, for example, completing this information by comparing the obtained data with simulated data, or mentioning when differences occur between simulated and experimental data giving your interpretation.
The authors could mention the innovative grade of this study and emphasize the vantages related to this methodology compared to the present situation. The authors could describe the impact of these results on current situations.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
This is a well-written manuscript that presents some novel results on the solubility of carbon dioxide at high pressure in n-decane and decane/hexane mixtures. The temperature dependence of the carbon dioxide solubility is also explored. The authors use Raman spectroscopy to determine the solubility which is a novel application. The experiments are clearly described and the results are also clearly presented. The discussion of the results is good and the conclusions drawn are reasonable.
Author Response
please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors modified their submission only marginally. The main concerns of the reviewers have not been addressed in the revised version, neither in the manuscript nor in the answer letter. According to the reviewer’s opinion, the quality of the manuscript is still far from what the reviewer expects from a manuscript that can be recommended for publication. The reasons for the recommendation “reject” are to a large extend still the same which have been mentioned in the first review.
· No comparison of experiments against known solubility data
· Poor description of observed phenomena
· Poor physical explanation of the observations
· Calibration carried out in a very limited range of hexane fractions, but is then transferred to liquid phases of the VLE in which the hexane fraction can exceed 3wt%.
Author Response
please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
The reviewer appreciates the extensive work done by the authors. The manuscript quality (content and syntax) has significantly increased following the recommendations sent. However, some minor syntax (or typos) remain. Therefore, the reviewer emphasizes that an English-spoken should review the manuscript, as the reviewer him/herself is not English-spoken. The following are examples of corrections done in the last version.
Abstract:
Understanding the solubility of CO2 is critical to for the implementation of CO2-enhanced oil recovery (CO2-EOR).
Please write:
Understanding the solubility of CO2 is critical for implementing CO2-enhanced oil recovery (CO2-EOR).
Line 188: “Figure 2. Show...” Please write “Figure 2. shows ….”
Line 328: “Table 9 show….” Please write “Table 9 shows….”
Author Response
please see the attechment
Author Response File: Author Response.pdf
