Effects of Alkanolamine Absorbents in Integrated Absorption–Mineralization
Round 1
Reviewer 1 Report
In this work, several alkanolamine-based aqueous solutions were used for integrated absorption–mineralization (IAM) process. Alkanolamines used includes monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), and aminomethyl propanol (AMP). The CO2 capacity, CO2 absorption rate, and the percentage of CO2 conversion to carbonates in each solution are investigated and compared. The effect of precipitation steps and concentration of solution are also studied. The results indicate that AMP is the best candidate for multicycle IAM regarding CO2 capacity, conversion rate and time efficiency. I think this work can be published after addressing following concerns.
1. In the precipitation process, the volume increase (150 ml) is abandoned. If so, a certain amount of alkanolamine would be abandoned simultaneously, which may affect the CO2 capacity and percentage of CO2 conversion.
2. In the section 3.4, the authors mentioned the absorbent pores. As liquid absorbents are used in this work, can authors explain what is the absorbent pore for liquid absorbents?
Author Response
General comments:
In this work, several alkanolamine-based aqueous solutions were used for integrated absorption–mineralization (IAM) process. Alkanolamines used includes monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), and aminomethyl propanol (AMP). The CO2 capacity, CO2 absorption rate, and the percentage of CO2 conversion to carbonates in each solution are investigated and compared. The effect of precipitation steps and concentration of solution are also studied. The results indicate that AMP is the best candidate for multicycle IAM regarding CO2 capacity, conversion rate and time efficiency. I think this work can be published after addressing following concerns.
Response:
We sincerely appreciate the reviewers' comments and suggestions. We can evaluate our manuscript and continue to improve it. Revisions in the manuscript are shown in blue color. In accordance with the reviewers’ comments and suggestions, the adjusted contexts are marked with text highlight yellow color. We hope that the revisions in the manuscript and accompanying responses are adequately acceptable and sufficient to make our manuscript suitable for publication. Thank you for your consideration.
Detailed comments:
Q1: In the precipitation process, the volume increase (150 ml) is abandoned. If so, a certain amount of alkanolamine would be abandoned simultaneously, which may affect the CO2 capacity and percentage of CO2 conversion.
A1: Thank you for your insightful comment. After the precipitation process, the disposal of alkanolamine and brine mixtures seemed to have a small effect on CO2 capacity and conversion in the repeated IAM cycles. High-concentration absorbents are dramatically affected when the mixtures are removed. In this experiment, we used absorbents at low concentrations of 5, 10, and 15 wt.% in 300 ml of the solution in order to avoid this impact. The low concentration of absorbent while adding brine was lower than before. As a result, there was an insignificant difference in the results obtained whether using all mixtures or volume-restricted mixtures.
The volume of the remaining mixtures was controlled throughout each cycle of iteration. Thus, it was just to compare the amount of CO2 absorbed and transformed with identical conditions. In addition, the size limitation of the absorption tower (700 ml) disallowed the holding of enough mixtures over cycle 2.
Q2: In the section 3.4, the authors mentioned the absorbent pores. As liquid absorbents are used in this work, can authors explain what is the absorbent pore for liquid absorbents?
A2: We felt sorry for the inaccurate description. Because the absorption process occurs in the gas-liquid stage, CO2 binds to N-H bonds in the absorbent. The statement was revised in the manuscript [Line 378-381].
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript: “Effects of alkanolamine absorbents in integrated absorption-mineralization” that was submitted in the Journal Minerals is interesting and describes the use of alkano-amine based absorbents for CO2-mineralization purposes. The authors have used a scientifically sound research methodology and their outcomes can contribute to the scientific topic of developing absorbents with high CO2-sorption capacity and the formation of carbonated materials. In general, the manuscript is interesting but it needs some improvements. The Conclusions section is short and it must be updated including some details of the conducted research. Some Figures should also be amended regarding their design. In addition, minor English modifications are also suggested, whereas in the Results section some parts that provide interpretation of the results should be moved to the Discussion section. Therefore, I suggest Minor Revisions.
1. Line 24: Maybe you should merge the key-phrase Integrated Adsorption Mineralization (IAM) with the keyword multicycle into one phrase: multicycle Integrated Adsorption Mineralization (IAM).
2. Line 41-42: “Utilization and storage….tons per year”: Please give a citation
3. Line 44: “low energy intensive” maybe it should be replaced with “low energy intensity”
4. Line 48: “There are two representative approaches to converting….” Replace “converting” with “convert”
5. Line 56: “….to form carbonates… and pressure [16]” This part is a little confusing, please rephrase.
6. Line 75 and 76: I think USD should go after the million
7. Line 80-83: “Alkano-amine based….aqueous solution”: Enlgish should be improved: You can rephrase as follows: Alka-nolamine-based absorbents contain two functional groups: (a) the amino group (RNH2, RNH, and RN; R is the alkyl group), which is involved in CO2 capture and (b) the hydroxyl group (OH) that offers solubility in an aqueous solution.
8. Line 85-87: “Monoethanolamine (MEA)….low cost [27,28]”: Please rephrase the sentence using better English.
9. Table 1: Why the Table caption is in red color?
10. Line 190: I think equation-6 is missing. Please clarify
11. Line 197 and 199: Why are the numbers in red color?
12. Figure 2: a) Why red colors in the Figure caption?, b) The pink triangle symbol is missing from the figure legend, c) If the pink symbol corresponds to the average capacity as it is described in line 197-198, it should be as follows: MEA 5wt% --> 574 gr CO2, MEA 10 wt% --> 528 gr CO2 and MEA 15 wt% --> 503 gr CO2. However, the value of MEA 5wt% in the diagram of Figure 2 is lower than 574 gr. The same is observed for the MEA 15 wt% which is higher than 503 gr in the diagram. Please clarify.
13. Figure 3: Increase the font size of the image (including the legend) because it is difficult to read.
14. Figure 4: The legend includes 2 colors (blue and gray); however, the bars of the diagram exhibit 4 different colors. Maybe it is better to illustrate the legend only with the symbols without colors.
15. Line 265: MEA>>AMP>DEA>TEA. In 10% and 15% the capacities are relatively equal or slightly higher for DEA than AMP. Please check once again.
16. Line 300-304: “Although Equations…CO2 [32]”. In the results section you should only provide a description of the results without interpretation. The interpretation should be in the discussion section. I think you should move these sentences in this section.
17. Line 332-333: “The recycled…structure [32]”. It is interpretation. I think it should be moved to the discussion section.
18. Line 367: Please correct the CO2
19. Discussion section: Line 488-494: This can be moved as an introduction of the Conclusions section. In addition, the discussion section should not only present a summary of the key findings, but it should also include the interpretation of the major outcomes using the appropriate references. As mentioned above some parts of the Results section should be moved in this section.
20. Conclusions section: The Conclusion section is too short. Please reorganize it. Include some details of your study describing the major aspects of your research. It would be also suggested to provide a brief interpretation of the key findings.
Author Response
General comments:
The manuscript: “Effects of alkanolamine absorbents in integrated absorption-mineralization” that was submitted in the Journal Minerals is interesting and describes the use of alkanolamine-based absorbents for CO2 mineralization purposes. The authors have used a scientifically sound research methodology and their outcomes can contribute to the scientific topic of developing absorbents with high CO2 absorption capacity and the formation of carbonated materials. In general, the manuscript is interesting but it needs some improvements. The Conclusions section is short and it must be updated including some details of the conducted research. Some Figures should also be amended regarding their design. In addition, minor English modifications are also suggested, whereas in the Results section some parts that provide interpretation of the results should be moved to the Discussion section. Therefore, I suggest Minor Revisions.
Response:
We highly appreciate your comments and suggestions, which will assist us to improve our manuscript. We organized the sections of the result, discussion, and conclusion for this revised manuscript. In addition, we modified the experimental graphs' text size and color to make them clearer and more discussion-friendly. Revisions in the manuscript are shown in blue color. In accordance with the reviewers’ comments and suggestions, the adjusted contexts are marked with text highlight yellow color. We hope that the revisions in the manuscript and accompanying responses are adequately acceptable and sufficient to make our manuscript suitable for publication. Thank you for your consideration.
Detailed comments:
Q1: Please give a citation [Line 41-42].
A1: We added the reference for the report on utilization of CO2 in the revised manuscript [Line 43].
Q2: Equation 6 is missing. Please clarify [Line 190].
A2: We were sorry for the missing information; thus, we revised the contents of the manuscript [Line 163-171].
Q3: The average capacity as it is described in line 197-198, it should be as follows: 5 wt.% MEA --> 574 g. CO2, 10 wt.% MEA --> 528 g. CO2 and 15 wt.% MEA --> 503 g. CO2. However, the value of 5 wt.% MEA in the diagram of Figure 2 is lower than 574 g. The same is observed for the 15 wt.% MEA which is higher than 503 g in the diagram. Please clarify [Figure2].
A3: We were sorry for the unclear explanation; thus, we added the information on curve fitting in the revised manuscript [Line 222-223].
The curve of CO2 absorption capacity was fixed to Allometric1 function in OriginPro 8.5 [Line 222-223]. As shown in Figure 2, the average CO2 absorption capacity from the literature is represented by the pink dot. Additionally, the curve fitting of the average CO2 absorption capacity is represented by the pink line. 574.33, 528.86, and 503.9 g. CO2/ kg. Absorbent of 5, 10, and 15 wt.% MEA were calculated using the following formula derived from a curve fitting.
Ac = 695.57α(-0.119)
Where Ac is CO2 absorption capacity [g. CO2/ kg. Absorbent] and α is MEA concentration [wt.%]
Q4: MEA>>AMP>DEA>TEA. In 10 and 15 wt.% the capacities are relatively equal or slightly higher for DEA than AMP. Please check once again [Line 265].
A4: We apologized for the inaccurate information. The CO2 absorption capacity of DEA was slightly higher AMP in each concentration, the order was MEA>>DEA>AMP>TEA. The statement was revised in the manuscript [Line 269, 526].
Q5: Revised writing.
A5: We felt sorry for the unclear use of words or sentences, we have reworded and sequenced the content for easier understanding in this revised manuscript, including cutting off the unnecessary phrase or sentence. The parts of discussion and conclusion were reorganized.
- Merging “Integrated absorption-mineralization (IAM)” and “Multicycle” into “Multicycle integrated absorption-mineralization (IAM)” [Line 24].
- “low energy intensive” to “low energy intensity” [Line 44].
- “converting” with “convert” [Line 47].
- “USD … million” to “… million USD” [Line 28, 76-77].
- As your suggestion, we edited as: “(a) the amino group (RNH2, RNH, and RN; R is the alkyl group), …. and (b) the hydroxyl group (OH) …” [Line 81-84].
- We rechecked the subscript numbers of chemical composition.
Author Response File: Author Response.pdf
