High-Power Closed-Loop Pilot System for Nitric Acid Production Using Inductively Coupled Microwave Plasma
, Qi Rao 1, Elizaveta Grushnikova 1, Kenshin Ushiroda 1, Tommy Kesler 2, Stephen Dvorak 2 and Jovan Jevtic 1,3Round 1
Reviewer 1 Report
Comments and Suggestions for Authorsplease check attechment..
Comments for author File: 
Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe paper by Ian McKinney et al. presents a detailed characterization of a large-scale pilot plant for nitric acid production utilizing atmospheric-pressure plasma in a closed-loop configuration. The study aims to assess the scientific and practical feasibility of applying high-power Cerawave™ microwave plasma torch technology to enhance nitric acid production rates via plasma-assisted nitrogen fixation.
The paper by Ian McKinney et al. presents a detailed characterization of a large-scale pilot plant for nitric acid production utilizing atmospheric-pressure plasma in a closed-loop configuration. The study aims to assess the scientific and practical feasibility of applying high-power Cerawave™ microwave plasma torch technology to enhance nitric acid production rates via plasma-assisted nitrogen fixation.
The primary objective is to achieve a specific energy consumption (SEC) comparable to smaller-scale systems previously reported in the literature. The authors provide a comprehensive description of the pilot plant’s components, operational strategy, and modeling used to interpret its performance. Preliminary system optimization results are presented, including a batch run in which 198.9 liters of nitric acid at 28.6% concentration by weight were produced over 30.9 hours at 50 kW plasma power, corresponding to an SEC of approximately 5.3 MJ/mol.
The manuscript makes a substantial contribution by demonstrating the first successful batch operation of a high-power, modular plasma-based system for nitric acid synthesis. Operating at up to 100 kW, the plant integrates a closed-loop configuration that enables precise control over pressure and gas composition with minimal losses. The system effectively scales up NO generation and absorption to industrially relevant throughputs and positions the Cerawave™ torch as a viable high-throughput oxidizer.
Furthermore, the implementation of a dynamic mass-balance model for the closed-loop gas system enaibles the determination of time-dependent gas concentrations across the process components. However, despite the strengths of this model, several critical aspects require further elaboration and clarification, as outlined below.
While the study is thoughtfully conceived and effectively executed, there are several points that need clarification:
The manuscript does not account relevant nitrogen species such as NO₃ and N₂O₅, which may play significant roles in the formation of nitric acid. Moreover, the pathways leading to the formation of HNO₂ and HNO₃ are not explained.
The inclusion of a reaction scheme with the mechanisms leading to the formation of these species, supported by kinetic modeling, would greatly improve this work.
In conclusion, this manuscript addresses a significant technological challenge by demonstrating the feasibility of plasma-assisted nitric acid production using high-power Cerawave™ microwave plasma torches.
However, this work would be significantly enhanced by a more rigorous discription of the process involved, including the identification of the reaction pathways that lead to the formation of nitric acid.
This work is suitable for publication, provided that the authors implement minor revisions to address the points outlined above.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThis manuscript focuses on presenting a high-power closed-loop pilot system for nitric acid production using inductively coupled microwave plasma. This article is interesting but has some concerning points.
In Introduction
Page 3, Figure 1: The figure should be labeled with the location of each piece of equipment.
In Materials and Methods
The author should provide details of the device, such as the model, manufacturer, and specific settings used.
The author should present the experimental methods, number of replicates, and measurement methods with references used in the experiment.
Page 13: The symbols used in the equations should be explained.
In Results and discussion
Lines 531-532, line 544: The author should present the experimental methods, number of replicates, and measurement methods with references used in Materials and Methods.
In Conclusion
Page 17, lines 614-633: This part should be in the discussion section with reference.
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThank you for addressing all the comments. As this is a pilot system for nitric acid production, it is important to know the efficiency of the plasma system. If possible, please add both plug-in power and absorbed power together so that the reader can understand power efficiency. After this modification, the article should be acceptable.
Author Response
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Author Response File: Author Response.pdf
Round 3
Reviewer 1 Report
Comments and Suggestions for AuthorsThe author has addressed all the reviewers' comments. If no further remarks are raised by the other reviewers, the paper may be considered acceptable for publication.
