Hydrogen Storage: Thermodynamic Analysis of Alkyl-Quinolines and Alkyl-Pyridines as Potential Liquid Organic Hydrogen Carriers (LOHC)

Round 1

Reviewer 1 Report

Thermodynamic properties of the hydrogenation/dehydrogenation reactions of substituted quinolines and pyridines have been studied by experimental and theoretical methods to evaluate their potential application as LOHC. Transpiration method was used to obtain the vapor pressure of methyl-quinolines and standard molar vaporization enthalpies were obtained from the vapor pressure and temperature correlation. The liquid phase enthalpies of hydrogenation/dehydrogenation reaction for substituted quinolines and pyridines were calculated and compared with other potential LOHC that showed the potential of these molecules for hydrogen storage applications.  

Comments-

1. Line 558- the sentence is incomplete. 
2. Lines 573 and 574- N should be italicized. 

Author Response

We are grateful to the reviewer for the attentive reading of the paper.

Comments:

1)    Line 558- the sentence is incomplete.

Author´s reply: thank you for your careful work with the manuscript. The sentence was completed as follows:

However, it seems unlikely that the enthalpies of hydrogenation in the gaseous state differ from the enthalpies in the liquid phase, since the enthalpies of vaporization of the reactants do not differ significantly.

2)    Lines 573 and 574- N should be italicized.

Author´s reply: corrected

Reviewer 2 Report

This paper is relevant to the field of hydrogen storage and is well written. It could be published in Applied Sciences after the following corrections have been made:

• You have to clearly indicate in the introduction the gravimetric hydrogen storage capacities for each reaction, labelled 1, 2 and 3.
• You should also give the melting points for pyridine, quinoline and other compounds. Discuss about their viscosity at room temperature.
• 2 phenyl-quinoline is proposed as a possible LOHC, but its melting point is actually 85°C…This must be indicated in the introduction.
• Table 4: please write correctly “methyl”
• Line 511: replace “dehydrated” by “hydrogenated”
• About Figure 4, I am not convinced about the accuracy of the “centrepiece” approach for the calculation of the enthalpy of formation in the case of the cyclo-hexyl addition. Has this approach previously been demonstrated as reliable in this particular case?
• Line 558: the end of the sentence is missing. “from ??”.

As a conclusion, this study is interesting and well conducted, even if the molecules proposed are not very promising as LOHCs. Their hydrogenation/dehydrogenation enthalpies are not favourable for reversible storage at room temperature and, actually, more promising compounds have been reported (e.g. carbazoles).

Author Response

thank you for your careful work with the manuscript. The step by step replies are given in the separate document

Author Response File: Author Response.docx