Direct Synthesis of Dimethyl Carbonate from Methanol and CO2 over ZrO2 Catalysts Combined with a Dehydrating Agent and a Cocatalyst
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors reported the synthesis of dimethyl carbonate from methanol and CO2 using ZrO2 catalysts. The submission is unacceptable for several reasons including the following points:-
1. The title should be revised to be informative, reflecting the author’s main findings. Remove redundant words such as ‘Direct synthesis of’; and ‘catalysts combined with a dehydrating agent and a cocatalyst’.
2. The novelty of the study is low and should be improved. ZrO2 has been reported for the same application e.g., Wang, X.; Zhao, J.; Sun, W.; Pei, Y.; An, J.; Li, Z.; Ren, J. A DFT Study of Dimethyl Carbonate Synthesis from Methanol and CO2 on Zirconia: Effect of Crystalline Phases. Comput. Mater. Sci. 2019, 159, 210–221, doi:10.1016/j.commatsci.2018.12.011; Tomishige, K.; Ikeda, Y.; Sakaihori, T.; Fujimoto, K. Catalytic Properties and Structure of Zirconia Catalysts for Direct Synthesis of Dimethyl Carbonate from Methanol and Carbon Dioxide. J. Catal. 2000, 192, 355–362, doi:10.1006/jcat.2000.2854; Tomishige, K.; Sakaihori, T.; Ikeda, Y.; Fujimoto, K. A Novel Method of Direct Synthesis of Dimethyl Carbonate from Methanol and Carbon Dioxide Catalyzed by Zirconia. Catal. Letters 1999, 58, 225–229, doi:10.1023/A:1019098405444……….
3. Selectivity should be included.
4. Recyclability should be investigated.
5. The catalyst after reaction should be fully characterized.
6. Mass spectrometry should be including showing the molecular structure and species present in the reaction solution.
7. A comparison with previously published catalysts should be discussed ad summarized in a Table.
8. CO2 conversion has been reviewed in Ref. 10.1016/j.jece.2023.110467; 10.1016/j.mcat.2023.113608; 10.1002/aoc.6753. These examples should be included showing the advantages of the current method.
9. The language should be revised and typos should be corrected.
Comments on the Quality of English LanguageThe language should be revised and typos should be corrected.
Author Response
First of all, the authors would like to thank the reviewer for his/her comments that will help us to improve our article. Please find our detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.
Comments 1: The title should be revised to be informative, reflecting the author’s main findings. Remove redundant words such as ‘Direct synthesis of’; and ‘catalysts combined with a dehydrating agent and a cocatalyst.
Response 1: There are different routes to synthesize DMC, but the direct synthesis from MeOH and CO2 is a green way, so we wanted to insist on that. The innovation of this study is the addition of a co-catalyst, therefore, it is also important for us to indicate this in the title of the paper.
Comments 2: The novelty of the study is low and should be improved. ZrO2 has been reported for the same application e.g., Wang, X.; Zhao, J.; Sun, W.; Pei, Y.; An, J.; Li, Z.; Ren, J. A DFT Study of Dimethyl Carbonate Synthesis from Methanol and CO2 on Zirconia: Effect of Crystalline Phases. Comput. Mater. Sci. 2019, 159, 210–221, doi:10.1016/j.commatsci.2018.12.011; Tomishige, K.; Ikeda, Y.; Sakaihori, T.; Fujimoto, K. Catalytic Properties and Structure of Zirconia Catalysts for Direct Synthesis of Dimethyl Carbonate from Methanol and Carbon Dioxide. J. Catal. 2000, 192, 355–362, doi:10.1006/jcat.2000.2854; Tomishige, K.; Sakaihori, T.; Ikeda, Y.; Fujimoto, K. A Novel Method of Direct Synthesis of Dimethyl Carbonate from Methanol and Carbon Dioxide Catalyzed by Zirconia. Catal. Letters 1999, 58, 225–229, doi:10.1023/A:1019098405444……
Response 2: We do agree that many studies have already focused on synthesizing DMC using ZrO2 catalysts, but a major issue in these papers is the low production of DMC, which does not meet industrial needs. Therefore, the primary goal of this research is to enhance DMC production. To the best of our knowledge this is the first time that a co-catalyst is added to enhace the hydration of TMM used as dehydrating agent. This is to our point of view a novelty which is worth to be communicated tot he scientific community.
Comments 3: Selectivity should be included.
Response 3: In our case it is unfortunately not possible to calculate selectivity as supplementary MeOH is formed by the hydration of TMM making impossible the calculation of a real conversion. For this reason we decided to represent the performances of the process by DMC production in mmol per g of catalyst.
Comments 4: Recyclability should be investigated.
Response 4: We do agree that stability of the performances is important in view of a potential industrial application. However, the main purpose of this paper is to show a way to increase DMC production. To achieve this, we focused on finding a suitable co-catalyst to accelerate the hydration rate of the dehydrating agent, thereby enhancing DMC production. In our subsequent research, we will examine the recyclability of our catalysts.
Comments 5: The catalyst after reaction should be fully characterized.
Response 5: As said in the previous answer, the main purpose of this research is to show the possibility to increase DMC production. We do agree that stability of the performances is a crucial point that must be further studied but it will be included in a future paper. In our subsequent research, we will characterize the catalysts after reaction.
Comments 6: Mass spectrometry should be including showing the molecular structure and species present in the reaction solution.
Response 6: The main product of the reaction is DMC, which has been analyzed by GC-FID which was accurately calibrated. We did not detect any unidentified byproducts by this tecchnique so we found unnecessary to conduct GC-MS in this case.
Comments 7: A comparison with previously published catalysts should be discussed ad summarized in a Table.
Response 7: We do agree with the comment and thank the revieweer for this nice suggestion. We have added in Table 3 a comparison of the DMC production per g of catalysts of our work with those of previous studies. It shows very clearly the improvement that our work brings (factor of 2 to 3).
Comments 8: CO2 conversion has been reviewed in Ref. 10.1016/j.jece.2023.110467; 10.1016/j.mcat.2023.113608; 10.1002/aoc.6753. These examples should be included showing the advantages of the current method
Response 8: Thank you for your comment. Three references have been cited in the article, and highlighted in red in the Reference list.
Comments 9: The language should be revised and typos should be corrected.
Response 9: We have carefully reviewed the manuscript and polished it as much as we can.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript entitled “Direct synthesis of dimethyl carbonate from methanol and CO2 over ZrO2 catalysts combined with a dehydrating agent and a 3 cocatalyst” was well written by authors. In the manuscript, the authors utilized the global gas for the synthesis of dimethyl carbonate. Therefore, I recommend this article can be published after addressing the following comments.
1. In TPD, the authors need to correlate with reported literature because on basis of crystalline phase.
2. In page 3, line 130, the word “heterogeneous” should be replaced with “mesoporous”.
3. In page 5, line, the word “They” should be replaced with “We”.
4. In page 7, line 211, the word but” should be replaced by “and”.
5. The authors discussed about the DMC and neglected the by-products.
6. The conversion of methanol and CO2 is not reported anywhere.
7. I suggest the authors to study the catalytic performance of 13X only and a combination 13X and TMM. Compare the results with ZrO2 then only one can get complete picture of catalytic system.
Comments on the Quality of English LanguageQuality of English should be improved.
Author Response
First of all, the authors would like to thank the reviewer for his/her comments that will help us to improve our article. Please find our detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.
Comments 1: In TPD, the authors need to correlate with reported literature because on basis of crystalline phase
Response 1: Thank you for your comment. We have correlated the TPD results with those reported in the literature previously and added a reference in our paper (page 6, lines 178-179).
Comments 2: In page 3, line 130, the word “heterogeneous” should be replaced with “mesoporous”.
Response 2: The word has been replaced as suggested. This modification is highlighted in red in the resubmitted manuscript.
Comments 3: In page 5, line, the word “They” should be replaced with “We”.
Response 3: We did not understand clearly this comment but we modified a bit the sentence line 165, page 5. This modification is highlighted in red in the resubmitted manuscript .
Comments 4: In page 7, line 211, the word but” should be replaced by “and”.
Response 4: The sentence page 7 lines 210-213 was rephrased. This modification is highlighted in red in the resubmitted manuscript.
Comments 5: The authors discussed about the DMC and neglected the by-products.
Response 5: The products in the liquid phase were analyzed by GC-FID and we did not detect any unidentified species. The gas phase products were not analyzed.
Comments 6: The conversion of methanol and CO2 is not reported anywhere
Response 6: Since methanol is both a reactant and a product of the hydration of the dehydration agent TMM, calculating the conversion of methanol becomes challenging. Additionally, because the reaction is conducted in a batch reactor, the amount of CO2 purged into the reactor cannot be measured, making it impossible to determine the CO2 conversion.
Comments 7: I suggest the authors to study the catalytic performance of 13X only and a combination 13X and TMM. Compare the results with ZrO2 then only one can get complete picture of catalytic system
Response 7: Thank you for your comment. The catalytic performances of 13X only and in combination with TMM were measured, but no DMC was detected. This information has now been included in the paper (page 7, lines 210-212).
Reviewer 3 Report
Comments and Suggestions for Authors1. Figure 4, have repeated tests been done? Please show the error bars for tests under each temperature
2. Similar to Point 1, all figures from 6-9 requires repeated test and error bars
3. Figure 6: This is a batch reaction, so indicating the equilibrium amount of DMC is feasible in the graph. Please indicate this in figure 6 for reader to compare how far this is from the equilibrium, especially after 50 hours.
4. Figure 7, what is the blue line and what is the red line? Please indicate clearly in the figure with legend
5. Figure 8, the addition of TMM seems to be counterintuitive, especially with 2:1 ratio of MeOH:TMM because further distillation is needed to purify DMC from TMM. This could incur higher capital cost and process energy from a process standpoint. As has been mentioned, the carbonation of methanol is energy intensive, adding another separation seems to make more challenges.
6. Figure 6 and 8, it seems interesting to observe that as the time lengthen, the reaction become faster (6-24 h production rate is slower that 24-48 h). Please explain
Overall, the paper could be published with the edits above
Author Response
First of all, the authors would like to thank the reviewer for his/her comments which will help us to improve our paper. Detailled answers are given below.
Comments 1: Figure 4, have repeated tests been done? Please show the error bars for tests under each temperature.
Response 1: Thank you for your comment. Repeated tests have been done 3 times and error bars have now been added to Figure 4.
Comments 2: Similar to Point 1, all figures from 6-9 requires repeated test and error bars.
Response 2: Repeated tests have been done and error bars have been added to Figures 6-9.
Comments 3: Figure 6: This is a batch reaction, so indicating the equilibrium amount of DMC is feasible in the graph. Please indicate this in figure 6 for reader to compare how far this is from the equilibrium, especially after 50 hours
Response 3: The equilibrium of the reaction is displaced by TMM used as dehydrating agent. As TMM and CO2 are used in large excess we could in theory get a total conversion of methanol to DMC but the calculation is made complicated by the fect that Methanol is also produced by TMM hydration. So this maximum is not indicated in Figure 6.
Comments 4: Figure 7, what is the blue line and what is the red line? Please indicate clearly in the figure with legend.
Response 4: We have now indicated clearly what are the blue and red lines in the legend of Figure 7.
Comments 5: Figure 8, the addition of TMM seems to be counterintuitive, especially with 2:1 ratio of MeOH:TMM because further distillation is needed to purify DMC from TMM. This could incur higher capital cost and process energy from a process standpoint. As has been mentioned, the carbonation of methanol is energy intensive, adding another separation seems to make more challenges.
Response 5: Distillation is admittedly a challenge from an economical point of view, but the main purpose of adding TMM is to remove the water formed, and then the amount of TMM remaining in the reactive medium at the end of the reaction is reduced.
Comments 6: Figure 6 and 8, it seems interesting to observe that as the time lengthen, the reaction become faster (6-24 h production rate is slower that 24-48 h). Please explain
Response 6: We think that the rate of DMC formation increases with reaction time because of the role of TMM which reacts with water formed but a detailled kinetic study would be necessary to better undertand this.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors addressed most of the comments and the revised version can be accepted.
Comments on the Quality of English LanguageThe language should be revised and typos should be corrected.
Author Response
Comment 1: The authors addressed most of the comments and the revised version can be accepted.
Reply 1: The authors would like to thank the reviewer for his/her help in improving their manuscript.
Comment 2: The language should be revised and typos should be corrected.
Reply 2: The paper has been revised carefully and polished.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors answered all queries. Now the manuscript can be accepted in its original form.
Author Response
Comment 1: The authors answered all queries. Now the manuscript can be accepted in its original form.
Reply 1: The authors would like to thank the reviewer for his/her help in improving their manuscript.
Reviewer 3 Report
Comments and Suggestions for AuthorsI recommend authors to add the response 5 into the paper where the drawback and future challenges is discussed.
Response 6 does not make sense. The authors need to think about a more plausible reason for this anomaly and discuss this in the paper
After these the paper is recommeneded for publishing
Author Response
Comment 1 : I recommend authors to add the response 5 into the paper where the drawback and future challenges is discussed.
Reply 1: One sentence was added in the paper (lines 278-280) to underline the fact that improvement must still be made to the proposed process for totally converting TMM to avoid high separation costs related to the purifcation of DMC by distillation.
Comment 2 : Response 6 does not make sense. The authors need to think about a more plausible reason for this anomaly and discuss this in the paper
Reply 2: Comments 6 was as follows: " Figure 6 and 8, it seems interesting to observe that as the time lengthen, the reaction become faster (6-24 h production rate is slower that 24-48 h). Please explain". We think the reviewer intended to refer to Figures 6 and 9 showing the evolution of the production of DMC vs. reaction time. Indeed, the rate of DMC production seems to increase with reaction time which is an interesting observation. Several reactions are in competition and their rates may change with the evolution of the composition in the reactive medium. Water is principally concerned, as it is co-produced with DMC and then consummed by the reaction with TMM which released methanol when hydrated. A complete detailed kinetic study would be necessary to answer properly the question of the reviewer.
Comment 3: After these the paper is recommeneded for publishing
Reply 3: The authors thank the reviewer for his/her help in improving their paper.
