A Novel Process of H₂/CO₂ Membrane Separation of Shifted Syngas Coupled with Gasoil Hydrogenation

Round 1

Reviewer 1 Report

The manuscript entitled “A novel process of H2/CO2 membrane separation of shifted syngas coupled with wax-oil hydrogenation” describes the process modelling, economic and comparative assessment of a wax oil hydrogenation system that utilizes membranes in substitution to PSA units.

The topic of this manuscript is relevant to process engineering; nonetheless, the reviewer has concerns regarding the scientific contribution of this work. At the moment, this is a nice technical report, but has not enough merit for scientific publication, unless the following is clearly outlined:

• Integrating membranes in H2/CO2 containing systems is not new. This has been done extensively (see technical reports from US Department of Energy, etc).
  1. What is the novelty of this work?
  2. What is the new knowledge that this paper intends to give to the readers?
  3. What is the value of this study?
  4. How can the community use the results obtained here to develop better processes?
• The major issue with membrane technology is aging. This manuscript assumes that membranes have the same lifetime as PSA. Membranes are more prone to polymer plasticization, poisoning and defects. A single pinhole would require changing the whole membrane unit. The results of this paper are meaningless, unless a reasonable membrane lifetime is considered.
• The process in itself integrates the membranes in substitution of PSA but does not show any new physical effects (e.g. process intensification in membrane reactors).

Author Response

Dear Reviewers and Editors,

We would like to thank the respected reviewers and the editor for the rigorous and constructive comments and suggestions.

The manuscript (Processes 778832) has been revised taking into account all of the helpful comments and suggestion. The details of the comments and their responses are also presented in the following. We hope meet with your approval. And we hope this revision can make our manuscript more acceptable.

The point to point responses to the reviewer’s comments are as follows.

Response to Reviewer 1 Comments

The manuscript entitled “A novel process of H2/CO2 membrane separation of shifted syngas coupled with gasoil hydrogenation” describes the process modelling, economic and comparative assessment of a wax oil hydrogenation system that utilizes membranes in substitution to PSA units.

The topic of this manuscript is relevant to process engineering; nonetheless, the reviewer has concerns regarding the scientific contribution of this work. At the moment, this is a nice technical report, but has not enough merit for scientific publication, unless the following is clearly outlined:

Point 1: Integrating membranes in H2/CO2 containing systems is not new. This has been done extensively (see technical reports from US Department of Energy, etc.).

• What is the novelty of this work?

Response 1(1): Thank you for your comments. We are sorry that the writing of our manuscript is not clear, which leads to unclear innovation points.

Although membrane separation technology for H₂ / CO₂ separation has been proposed, compared with the traditional process, the work in this manuscript has the following innovations:

(a) A novel process of membrane separation for H₂/CO₂ of syngas coupled with gasoil hydrogenation (NMGH) is proposed.

(b) A new process, with two-stage CO₂-selective and one-stage H₂-selective membranes, was developed to remove CO₂ and purify H2 in coal gasification refineries. Moreover, high purity and recovery of H₂ and CO₂ are achieved.

(c) The H₂ concentration of the hydrogenation reactor inlet was increased by about 11 mol % compared with the conventional direct recycling process, and the total system pressure of reactor was reduced by about 2470 kPa. Which will improve the regulation capacity of hydrogen partial pressure in the reactor.

(d) The NMGH process utilizes H₂-selective membranes to further purify and decarbonize the recycle H₂, thus reducing carbon accumulation and ensuring the smooth operation of the devices over a long period of time.

These innovations can be found in the abstract and conclusion. Please review it again, and we hope to get your approval for innovation.

(2) What is the new knowledge that this paper intends to give to the readers?

 Response 1(2): Thank you for your comments. Your questions help us to think more about the significance of manuscript work. We believe that readers can learn the following new knowledge:

(a) In the process of CO₂ capture of shifted syngas, the two-stage CO₂-selective membranes coupling process can achieve high purity and yield of CO₂, thus membranes coupling process is a potential process alternative to traditional VPSA process.

(b) The intensification of separation to the reaction process can be realized by integrating the hydrogen purification process and hydrogenation process. For example, recycle hydrogen is introduced into H₂-selective membrane HM-101 for purification. On the one hand, the concentration of hydrogen at the reactor R-101 inlet is increased, which can reduce the reactor inlet pressure from 13 MPa to 11.57 MPa, which will lead to a reduction of investment and operation costs in compressor K-104 in front of the reactor. On the other hand, H₂-selective membrane was used to decarbonize the recycle hydrogen, thus reducing carbon accumulation and improving the service life of catalyst, and ensuring the smooth operation of the devices over a long period of time.

(c) The economic comparison between traditional process and new membrane separation process enables readers to understand the potential and advantages of new technology.

(3) What is the value of this study?

Response 1(3): Thank you for your comments. Your questions help us to think more about the value of study. We believe that the value of this study is as follows.

(a) The new process of membrane separation will be a valuable alternative for the H₂/CO₂ separation of shifted syngas.

(b) The membrane performance data used in this study are all from commercial membranes used in industrial production, and the optimized process parameters can directly provide basis and references for industrial process design.

(c) The integrated study of membrane separation and hydrogenation reaction will promote the further study of the effect of inlet hydrogen concentration on the hydrogenation reactor, thus promoting the research of hydrogenation catalyst.

(4) How can the community use the results obtained here to develop better processes?

Response 1(4): Thank you for your comments. Your questions help us to think more.

We think the community can further consider from the following aspects to get a better process.

(a) When membrane separation is used to increase the inlet concentration of the reactor, for the existing modification process, on the premise of ensuring the partial pressure of hydrogen in the reactor, it can be considered to reduce the use of recycle hydrogen of reactor to obtain the better process.

(b) Coupling process of membrane and PSA is usually a feasible strategy to make better use of the advantages of different separation units. Therefore, membrane separation and PSA coupling process can be considered in H₂/CO₂ separation of shifted syngas to get a better process.

The authors will continue to work on new and better processes in the future.

Point 2: The major issue with membrane technology is aging. This manuscript assumes that membranes have the same lifetime as PSA. Membranes are more prone to polymer plasticization, poisoning and defects. A single pinhole would require changing the whole membrane unit. The results of this paper are meaningless, unless a reasonable membrane lifetime is considered.

Response 2: Thank you for your comments.

We agree with the reviewer comment that the membranes are more easily damaged. However, we would like to explain the selection basis of depreciation life of membrane and PSA in this manuscript.

The authors have been engaged in the research of gas membrane separation process for a long time, and have designed and applied many sets of gas membrane separation devices for Chinese factories. According to the feedback data from the factory, as long as the gas pretreatment is done well, the service life of the gas membrane separator can reach 5 years or more. Therefore, in this study, the depreciation life of membrane separator is set as 5 years.

Because the investment of adsorbent accounts for a large proportion of the total investment of PSA, generally accounting for 60-70%. Moreover, due to the damage caused by many factors such as water in the feed, too fast speed of pressure rise and fall, overload of impurities and so on, it is necessary to replace the adsorbent in PSA after a period of time. Therefore, according to the characteristics of water content in shifted syngas and replacement period of adsorbents, the depreciation life of PSA in this study is set as 5 years. In this regard, the authors added a description of depreciation life to the manuscript. See Table 3.

Point 3: The process in itself integrates the membranes in substitution of PSA but does not show any new physical effects (e.g. process intensification in membrane reactors).

Response 3: Thank you for your comments. In the new process of this study, the strengthening effect of membrane separation on the reaction process is mainly reflected. The specific analysis is as follows:

The intensification of separation to the reaction process can be realized by integrating the hydrogen purification process and hydrogenation process. For example, recycle hydrogen is introduced into H₂-selective membrane HM-101 for purification. On the one hand, the concentration of hydrogen at the reactor R-101 inlet is increased, which can reduce the reactor inlet pressure from 13 MPa to 11.57 MPa, which will lead to a reduction of investment and operation costs in compressor K-104 in front of the reactor. On the other hand, H₂-selective membrane was used to decarbonize the recycle hydrogen, thus reducing carbon accumulation and improving the service life of catalyst, and ensuring the smooth operation of the devices over a long period of time.

Point 4: Does the introduction provide sufficient background and include all relevant references?  Must be improved

Response 4: Thank you for your comments. In the introduction, authors added the literatures review of the technology of membrane separation and reaction integration. The details are as follows:

Arias et al. [10] proposed a two-stage membrane system for hydrogen separation in refining processes, a H² product purity of 0.90 and H2 recovery of 90% are achieved.

Membrane separation can remove the reaction products, which will improve the reaction rate and conversion rate, at the same time, a more complete reaction will reduce the separation energy consumption and material consumption of the reaction products. Finally, the integration of membrane separation and reaction can increase the overall efficiency of the system [19]. For example, a polymer membrane reactor system was developed in place of a water-gas shift reaction and a Selexol process for carbon dioxide removal in production of electricity from coal. Three kinds of polymer membrane reactor processes (2-stage PSMR, 3-stage PSMR, MR) were presented and optimized [20]. However, the H₂ / CO₂ selectivity range of the membrane used in this work is 25-75, which is higher than the separation performance of the polymer membrane in the industry. Moreover, a membrane reactor was proposed to produce propylene and ultra-pure hydrogen in the propane dehydrogenation process. The propylene production increased by 3.12% by dehydrogenation reactors coupled with membrane modules. The higher propane conversion and ultra-pure hydrogen production were achieved simultaneously [21].

References：

10. Arias, A.M.; Mores, P.L.; Scenna, N.J.; Caballero, J.A.; Mussati, S.F.; Mussati, M.C. Optimal Design of a Two-Stage Membrane System for Hydrogen Separation in Refining Processes. Processes 2018, 6, 208, doi:10.3390/pr6110208
11. Cruellas, A.; Heezius, J.; Spallina, V.; van Sint Annaland, M.; Medrano, J.A.; Gallucci, F. Oxidative Coupling of Methane in Membrane Reactors; A Techno-Economic Assessment. Processes 2020, 8, 274, doi:10.3390/pr8030274.
12. Radcliffe, Andrew J.; Singh, Rajinder P.; Berchtold, Kathryn A. Modeling and optimization of high-performance polymer membrane reactor systems for water-gas shift reaction applications. Processes 2016, 4(2), 8. doi:10.3390/pr4020008
13. Jowkary, H.; Farsi, M.; Rahimpour, M. R. Supporting the propane dehydrogenation reactors by hydrogen permselective membrane modules to produce ultra-pure hydrogen and increasing propane conversion: Process modeling and optimization. International Journal of Hydrogen Energy 2020, 45(12), 7364-7373, doi:10.1016/j.ijhydene.2019.04.286.

Thank you very much for your time and considerations.

I look forward to hearing from you soon.

Yours sincerely

Wu Xiao and coauthors

Reviewer 2 Report

The paper has a limited interest because the technique is new but very limited, in the reviewer's opinion. Nevertheless, we have no comments on the soundness of the result and on the written paper.

I suggest updating the literature with some recent papers on related topics. 

Author Response

Dear Reviewers and Editors,

We would like to thank the respected reviewers and the editor for the rigorous and constructive comments and suggestions.

The manuscript (Processes 778832) has been revised taking into account all of the helpful comments and suggestion. The details of the comments and their responses are also presented in the following. We hope meet with your approval. And we hope this revision can make our manuscript more acceptable.

The point to point responses to the reviewer’s comments are listed below.

Response to Reviewer 2 Comments

The paper has a limited interest because the technique is new but very limited, in the reviewer's opinion. Nevertheless, we have no comments on the soundness of the result and on the written paper.

Point 1: I suggest updating the literature with some recent papers on related topics. 

Response 1: Thank you for your comments. In the introduction, authors added the literatures review of the technology of membrane separation and reaction integration. The details are as follows:

Membrane separation can remove the reaction products, which will improve the reaction rate and conversion rate, at the same time, a more complete reaction will reduce the separation energy consumption and material consumption of the reaction products. Finally, the integration of membrane separation and reaction can increase the overall efficiency of the system [19]. For example, a polymer membrane reactor system was developed in place of a water-gas shift reaction and a Selexol process for carbon dioxide removal in production of electricity from coal. Three kinds of polymer membrane reactor processes (2-stage PSMR, 3-stage PSMR, MR) were presented and optimized [20]. However, the H2 / CO2 selectivity range of the membrane used in this work is 25-75, which is higher than the separation performance of the polymer membrane in the industry. Moreover, a membrane reactor was proposed to produce propylene and ultra-pure hydrogen in the propane dehydrogenation process. The propylene production increased by 3.12% by dehydrogenation reactors coupled with membrane modules. The higher propane conversion and ultra-pure hydrogen production were achieved simultaneously [21].

References：

19. Cruellas, A.; Heezius, J.; Spallina, V.; van Sint Annaland, M.; Medrano, J.A.; Gallucci, F. Oxidative Coupling of Methane in Membrane Reactors; A Techno-Economic Assessment. Processes 2020, 8, 274, doi:10.3390/pr8030274.
20. Radcliffe, Andrew J.; Singh, Rajinder P.; Berchtold, Kathryn A. Modeling and optimization of high-performance polymer membrane reactor systems for water-gas shift reaction applications. Processes 2016, 4(2), 8. doi:10.3390/pr4020008
21. Jowkary, H.; Farsi, M.; Rahimpour, M. R. Supporting the propane dehydrogenation reactors by hydrogen permselective membrane modules to produce ultra-pure hydrogen and increasing propane conversion: Process modeling and optimization. International Journal of Hydrogen Energy 2020, 45(12), 7364-7373, doi:10.1016/j.ijhydene.2019.04.286.
22.  

Thank you very much for your time and considerations.

I look forward to hearing from you soon.

Yours sincerely

Wu Xiao and coauthors

Reviewer 3 Report

The manuscript describes the membrane separation process for H₂/CO₂ separation of shifted syngas integrated with wax-oil hydrogenation by a simulation study. Sufficient economic analysis of traditional and membrane process was carried out. Besides, pressure ratio, compressor power and membrane area were optimized. The manuscript is well organized, and the study is sufficiently performed. I would recommend publication of the manuscript after some edits. The remarks are provided as follows:

• Pag. 2, line 46, put the space between “CO₂ [4]” and “More”
• In Figures, add the space between the title and unit
• Pag. 5, table 1, the authors reported the permeance of gas,  change “permeability” to “permeance” in the title of the table.
• Pag. 7, line 229, I suggest changing “were” to “was” in the following sentence “CO₂ concentration were too small”
• I suggest changing the terms “carbon membrane and the hydrogen membrane area”, they can be confused with the membrane material
• Pages 8 and 9, specify the units for CO₂ and H₂ concentration in the figures 6 and 7
• Regarding the separation of the gas pair H₂ and CO₂, In some cases, it is written as H₂/CO₂ (In the title “A novel process of H₂/CO₂ membrane separation of shifted syngas coupled with wax-oil hydrogenation”) or CO₂/H₂ (lines 105-106, “this work proposed a novel membrane separation process for CO₂/H₂ separation of shifted syngas and developed a new coupling process with wax-oil hydrogenation”). Check in the text
• Pag. 6, line 211, in the sentence “the membrane area of CM-101 increased due to the increasing CM-101 area” there is a repetition, Check it
• Pag. 6 lines 213-216, The part of the text “…due to the increase in the pressure ratio under the same membrane area, which resulted in a decrease in the pressure on the permeate side of CM-101; that is, the pressure before the compressor was lowered, but in order to ensure the inlet pressure of CM-102, a larger K-101 power was required” is difficult to follow. The author should rewrite it
• What does “$ per” mean? What does apex indicate in “other equipment”? 

Author Response

Dear Reviewers and Editors,

We would like to thank the respected reviewers and the editor for the rigorous and constructive comments and suggestions.

The manuscript (Processes 778832) has been revised taking into account all of the helpful comments and suggestion. The details of the comments and their responses are also presented in the following. We hope meet with your approval. And we hope this revision can make our manuscript more acceptable.

The point to point responses to the reviewer’s comments are listed below.

Response to Reviewer 3 Comments

The manuscript describes the membrane separation process for H₂/CO₂ separation of shifted syngas integrated with gasoil hydrogenation by a simulation study. Sufficient economic analysis of traditional and membrane process was carried out. Besides, pressure ratio, compressor power and membrane area were optimized. The manuscript is well organized, and the study is sufficiently performed. I would recommend publication of the manuscript after some edits. The remarks are provided as follows:

Point 1: Pag. 2, line 46, put the space between “CO₂ [4]” and “More”

Response 1: Thank you for your comments and suggestion. The space between “CO₂ [4]” and “More” has been added.

Point 2: In Figures, add the space between the title and unit

 Response 1: Thank you for your comments and suggestion. The space between the title and unit in all figures has been added.

Point 3: Pag. 5, table 1, the authors reported the permeance of gas, change “permeability” to “permeance” in the title of the table.

 Response 1: Thank you for your comments and suggestion. “permeability” of the title of table 1 has been revised to “permeance”.

Point 4: Pag. 7, line 229, I suggest changing “were” to “was” in the following sentence “CO₂ concentration were too small”

 Response 1: Thank you for your comments and suggestion. “were” has been revised to “was” in the following sentence “CO₂ concentration were too small”.

Point 5: I suggest changing the terms “carbon membrane and the hydrogen membrane area”, they can be confused with the membrane material

Response 1: Thank you for your comments. The materials of the carbon membrane and the hydrogen membrane have been clearly described in Table 1.

Table 1. Membrane permeance [28].

¹ 1 GPU = 10^-6 cm³(STP)/(cm²•s•cmHg)  ² Data from industrial production

Point 6: Pages 8 and 9, specify the units for CO₂ and H₂ concentration in the figures 6 and 7.

Response 1: Thank you for your comments. The units for CO₂ and H₂ concentration in the figures 6 and 7 have been revised to molar concentration.

Point 7: Regarding the separation of the gas pair H₂ and CO₂, In some cases, it is written as H₂/CO₂ (In the title “A novel process of H₂/CO₂ membrane separation of shifted syngas coupled with gasoil hydrogenation”) or CO₂/H₂ (lines 105-106, “this work proposed a novel membrane separation process for CO₂/H₂ separation of shifted syngas and developed a new coupling process with gasoil hydrogenation”). Check in the text

 Response 1: Thank you for your comments. (lines 105-106, “this work proposed a novel membrane separation process for CO₂/H₂ separation of shifted syngas and developed a new coupling process with gasoil hydrogenation”) has been revised to (lines 105-106, “this work proposed a novel membrane separation process for H₂/CO₂ separation of shifted syngas and developed a new coupling process with gasoil hydrogenation”). At the same time, the authors checked and revised the full manuscript.

However, for carbon membranes (CO₂-selective membranes), CO₂ is preferentially permeated, so its selectivity is expressed in the form of CO₂ / H₂. For example, in line 6 of the first paragraph of section 3. Basic parameters of process design and simulation, “and membrane materials such as PEO can achieve CO₂/H₂ selectivity of 8–15 or more”. And the title of Figure 9, “Figure 9. Impact of CO₂/H₂ selectivity of the CO₂-selective membrane on total investment cost under different pressure ratios.”

Thanks again for the reviewer’s comments.

Point 8: Pag. 6, line 211, in the sentence “the membrane area of CM-101 increased due to the increasing CM-101 area” there is a repetition, Check it

 Response 1: Thank you for your comments. The mistake has been revised. “the membrane area of CM-101 increased due to the increasing CM-101 area” has been modified as “the membrane area of CM-101 increased”.

Point 9: Pag. 6 lines 213-216, The part of the text “…due to the increase in the pressure ratio under the same membrane area, which resulted in a decrease in the pressure on the permeate side of CM-101; that is, the pressure before the compressor was lowered, but in order to ensure the inlet pressure of CM-102, a larger K-101 power was required” is difficult to follow. The author should rewrite it.

 Response 1: Thank you for your comments. This paragraph has been rewritten. The revised expression is as follows.

Under the same membrane area, the pressure on the permeate side of CM-101 decreases with the increase of pressure ratio, that is, the inlet pressure of compressor K-101 decreases. When the outlet pressure is constant, the power of compressor K-101 will increase.

Point 10: What does “$ per” mean? What does apex indicate in “other equipment”? 

Response 1: Thank you for your comments. “$ per” mean “$ per year”. And “$ per” has been revised to “$/year”.

The explanation of apex indicate in “other equipment” has been added at the bottom of Table 3.

Other equipment includes heat exchangers, vessels, alkaline washing towers and mixers in process.

Other amendments:

• “Wax-oil” has been revised to “gasoil” according to the literature.
• “CPWH and NMWH” have been revised to “CPGH and NMGH”.

Thank you very much for your time and considerations.

I look forward to hearing from you soon.

Yours sincerely

Wu Xiao and coauthors

Round 2

Reviewer 1 Report

The authors have satisfactorily answer all the reviewer's concerns and modified the manuscript accordingly. I happy to accept the manuscript for its publication in Processes.