Effect of Carboxylic Acids on Corrosion of Type 410 Stainless Steel in Pyrolysis Bio-Oil

Round 1

Reviewer 1 Report

In my opinion the Manuscript sustainability-1903637 entitled "Effect of Carboxylic Acids on Corrosion of Type 410 Stainless-Steel 2 in Pyrolysis Bio-Oil”  is not suitable in present form for publication in the Sustainability journal after major revision.

The manuscript includes important issues that may be of interest  to a broad chemical engineering and/or applied electrochemistry audience. The applied techniques are not quate adequate to the undertaken considerations. Conclusions are related to the obtained results but are partly trivial and predictable.

Remarks:

1)    Formic acid is an aggressive corrosive medium, it was obvious and trivial that concentrated acid causes more corrosion damage than diluted acid.

2)    Line 71 - I suppose the sample was placed in methanol to purge it of bio-oil. In my opinion, it would be more appropriate to use an ultrasonic bath for this purpose, because holding steel samples in methanol can lead to surface methoxylation (J. Banaś at all., Corrosion and passivity of metals in methanol solutions of electrolytes, Journal of Solid State Electrochemistry, 13, 2009, 1669, U. Lelek-Borkowska at all., The e ff ect of the methanol-water interaction on the surface layer on titanium in CH3OH-H2O-LiClO4 solutions, Electrochem 1 (2) 2020, 87)

3)    Fig. 5 and 6 - Not much can be seen at this SEM magnification. A higher magnification would be especially useful in Fig. 6, as it would highlight the differences in the surface image of the steel exposed to formic and acetic acid. There can not be seen anything interesting on the elements distribution maps. A SEM photo at higher magnification with EDS analysis of a selected part of the surface would be much more readable.

4)    The weight loss method gives an overall picture of the corrosion rate, but does not say much about what is happening on the surface. Much more information can provided by polarization and impedance techniques. A technique that, in my opinion, would work here is electrochemical impedance spectroscopy.

5)    Line 190  - trivial statement, this is commonly known that higher content of Cr is connected with higher corrosion resistance.

6)    Line 213 – could the method of introducing of formic acid into solution affects the properies of the acid???

7)    Line 216, 217 - it is trivial that dilution of formic acid dimishes its concentration and corrosive properies.

8)    Line 221-222 “The increase in mass change of SS410 specimens compared to those exposed in the baseline oil  suggests inhibition effect of diluted acetic acid on corrosion” Does the oxidation products were carefully removed from the surface? They can affect the mass loss.

9)    Conclusions: It is trivial that acetic acid is less aggressive than formic acid. Do propionic and hexanoic acid have inhibition effect?

10) Line 246 – “cross-sectional electron microscopy??? There was made a cross section of the sample?

11) Line 249 “formic acid is the most aggressive among the four  acids tested.” This is a truism that has been known for a long time.

Author Response

Thanks for your comments, please see attached.

Author Response File: Author Response.docx

Reviewer 2 Report

General Comments

The work done is interesting and of technological importance.

However, the authors need to effect a few corrections/enhancements which would improve the quality of their interesting work.

In addition to mass loss plots, authors should calculate the corrosion rates from the mass loss data for each acid and add them to the manuscript possibly in one Figure plate (.e.g. Fig Xa, b, c and d). Presenting data in terms of corrosion rate makes it easier for readers to compare the corrosion data from this work with already available data on the steel used.

Secondly, solvent volume-corrected plots of the acid additions with highly concentrated acids are necessary to strengthen the conclusion that the difference is due to dilutive effects.

Thirdly, for context, the authors should highlight published corrosion rate data for the steel used in this work in a variety of environments, particularly those related to the subject of this work in the introduction section.

Specific Comments

LINE 21: Write “acid contents” instead of “acids”.

LINE 77: The photo of the Teflon should be taken on a light but not white background so that the Teflon is easily discernible.

LINE 113: What is the diluent/solvent in the 10% formic acid solution added? The lower mass loss at a similar concentration of formic acid by using the low concentration of formic acid might be linked to the moderation of its corrosion effect by the solvent in the system. This should be discussed and preferably clarified by solvent volume-corrected plots of the additions with highly concentrated formic acid. This might not need further experiments, just some calculations on the “blue data points”

The same applies to the other acids.

Author Response

Thanks for your comments, please see attached.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors responded positively to the vast majority of the reviewer's comments. After taking into account the corrections and comments, the corrected manuscript sustainability-1903637 entitled "Effect of Carboxylic Acids on Corrosion of Type 410 Stainless-Steel 2 in Pyrolysis Bio-Oil”  may be approved in present form for publication in the Sustainability journal.