Hydroprocessed Ester and Fatty Acids to Jet: Are We Heading in the Right Direction for Sustainable Aviation Fuel Production?

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This article is a comparative study on sustainable aviation fuel production pathways.

At present, the hydrolysis of esters and fatty acids to jet (HEFA tJ) is considered the most promising and economically attractive sustainable approach for the production of aviation fuel (SAF). This topic fits the scope of journal Energies well.

This is a report style article. Economic analysis are performed.

And this present report is like a R&D and investment advice report or forecast report.

The scientific background or research review are missing.

The greenhouse gas emission reduction potential of the HEFA tJ pathway is significantly lower.

Life cycle analysis and carbon footprint evaluation are recommended.

And lot of data are coming from references. The author are required to critically review or analyze the data.

A model developed by the authors or a calculation model from literature should be performed.

The reference numbers are astonishing. Too many references but not well addressed with respect to the scientific values.

Author Response

See the answers to all reviewers' comments in the attached Word file.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In the present work, Pominville-Racette et al. presented a comprehensive techno-economic and environmental analysis of the HEFA-tJ pathway, especially in comparison with road biofuels. The authors provided an extensive literature review, introducing several original calculations, and highlighting important aspects often under-discussed in the SAF debate. In the following my comments are listed:

• Chapter 2: some assumptions (e.g. in economic models, resource availability, yield definitions) are highly system-specific and may not generalize to all regions or future scenarios. Please comment on possible limitations of this approach
• Paragraph 3.4.1: the authors should briefly emphasize the need for ongoing model refinement rather than simply highlighting current inconsistencies
• Row 415: estimates of global availability remain uncertain and highly dependent on regional collection efficiencies and policy support. Please comment on the importance of harmonized data collection efforts for more robust assessments
• Row 455: a brief mention of ongoing projects could help frame the potential, albeit limited, role of the mentioned resources (camelina, etc.)
• Row 620: with regards to the hydrogen need, I suggest to add further references which recently evaluated the role of alternative sources of hydrogen and comment the possible role (see for example 1016/j.jclepro.2023.138141 and 10.1016/j.renene.2020.06.077)

Author Response

Please see the attached Word file.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

The manuscript offers a relevant and timely contribution to the ongoing debate on aviation sustainability by critically and comprehensively analyzing the technical, economic, and environmental viability of the HEFA-to-Jet (HEFA-tJ) pathway compared to alternatives such as renewable diesel (RD). Its main strength lies in questioning the actual effectiveness of HEFA-tJ in reducing greenhouse gas (GHG) emissions, considering not only yield and carbon intensity (CI), but also regulatory, logistical, and market-related impacts—factors often overlooked in standard assessments. However, despite its relevance, the article would benefit from some adjustments prior to publication, as outlined below:

1. Although the manuscript provides a critique of the HEFA-tJ pathway, it does not present explicit research objectives. I recommend add a paragraph at the end of the introduction clearly stating the main aims, such as: “to comparatively evaluate the economic and environmental impacts of HEFA-tJ versus RD.”
2. The methodology would benefit from a more detailed description of data sources and analytical tools. Although the approach is inspired by frameworks such as Deloitte’s, the manuscript does not specify which mathematical models, computational tools, or assumptions were used to estimate key variables like yield, CI, and GHG reduction. This limits the transparency and reproducibility of the analysis.
3. In section 3.6, data on used cooking oil availability are presented as “global” but are applied to inferences concerning the U.S. market. It is important to clarify the geographic scope of the data used or to distinguish clearly between regional and global contexts.
4. Figures 6 and 8 must be improved graphical quality and a more professional presentation, with clearer labeling, consistent formatting, and enhanced resolution. Presenting the results using more scientifically-oriented visualization standards will improve clarity and strengthen the overall impact of the analysis.
5. The final section would benefit from a more applied synthesis of the findings. For example, after showing that HEFA-tJ substitution may be environmentally inferior in certain contexts, it would be helpful to provide alternative policy suggestions or mitigation strategies for decision-makers.
6. The division into subsections such as 3.4.1, 3.4.2, 3.6.1, and 3.6.2 results in some redundancy and affects the flow of the text. The discussion on the environmental impacts of tallow, PFAD, and POME could be consolidated into a single, more concise section.
7. While the manuscript critically examines the HEFA-tJ route, it offers limited discussion of alternative SAF pathways such as ATJ or GFT. Including a brief comparison with other promising SAF routes would strengthen the strategic dimension of the analysis.

Author Response

Please see the attached Word file.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript (energies-3693963) entitled “HEFA-to-Jet: are we heading in the right direction for sustainable aviation fuel production?” by Nicolas Abatzoglou et. al. provides critical data to enhance understanding of the opportunities and challenges associated with the HEFA-tJ pathway. The manuscript emphasizes the need for more transparent data and effort in this regard before envisaging rising drastically HEFA-tJ

production. The authors suggested that overall, reducing road diesel carbon intensity appears to be less capital intensive, risky, and several times more efficient in reducing GHG emissions.

The manuscript is interesting, however, there are some issues need to be addressed.

 

Specific comments for improving the manuscript are as following:

(1) The information for authors affiliation is not complete.

(2) The abstract part is quite confusing and misleading. It is not acceptable in its current form. The abstract should contain only limited background, while summarize major data and emphasize on major conclusions.

(3) In abstract part, what is “GHG”? Full name should be shown when the first time an abbreviation is shown.

(4) Figure 5 is too blurry and hard to see.

(5) Equation 6 is not shown correctly.

 

Author Response

Please see tha attached Word file.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

This revision can be accepted.