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

Sergey P Verevkin,Sergey V Vostrikov,Sergey P Safronov,Artemiy A Samarov

doi:10.3390/app112411758

Abstract

The liquid organic hydrogen carriers (LOHC) are aromatic molecules, which can be considered as an attractive option for the storage and transport of hydrogen. A considerable amount of hydrogen up to 7–8% wt. can be loaded and unloaded with a reversible chemical reaction. Substituted quinolines and pyridines are available from petroleum, coal processing, and wood preservation, or they can be synthesized from aniline. Quinolines and pyridines can be considered as potential LOHC systems, provided they have favorable thermodynamic properties, which were the focus of this current study. The absolute vapor pressures of methyl-quinolines were measured using the transpiration method. The standard molar enthalpies of vaporization of alkyl-substituted quinolines and pyridines were derived from the vapor pressure temperature dependencies. Thermodynamic data on vaporization and formation enthalpies available in the literature were collected, evaluated, and combined with our own experimental results. The theoretical standard molar gas-phase enthalpies of formation of quinolines and pyridines, calculated using the quantum-chemical G4 methods, agreed well with the evaluated experimental data. Reliable standard molar enthalpies of formation in the liquid phase were derived by combining high-level quantum chemistry values of gas-phase enthalpies of formation with experimentally determined enthalpies of vaporization. The liquid-phase hydrogenation/dehydrogenation reaction enthalpies of alkyl-substituted pyridines and quinolines were calculated and compared with the data for other potential liquid organic hydrogen carriers. The comparatively low enthalpies of reaction make these heteroaromatics a seminal LOHC system.

Highlights

Introduction published maps and institutional affilThe liquid organic hydrogen carriers (LOHC) systems are considered as an attractive option for the storage and transport of hydrogen and enable the gradual transition from fossil fuels to a CO2 emission-free energy supply for both mobile and stationary applications
The reversible hydrogenation/dehydrogenation reactions of substituted pyridines or quinolines according to Figure 1 could be interesting, since the main sources of pyridines and quinolines include petroleum, coal processing, wood preservation and shale oil, or they can be synthesized from anilines [2]
Vapor pressures of methylquinolines at different temperatures were measured by using the transpiration method [3,4]

Summary

Materials and Methods

Available samples of methyl-quinolines have been used in this work (see Table S1). They were purified by the fractional distillation. Purities were determined using a gas chromatograph equipped with a capillary column HP-5 and a flame ionization detector. No impurities (greater than 0.0004 mass fraction) were detected in samples used for vapor pressure measurements. Vapor pressures of methylquinolines at different temperatures were measured by using the transpiration method [3,4]. Were derived from the temperature dependences of vapor pressures. The quantum-chemical composite method G4 [5]. Short descriptions of experimental were converted to the ∆f Hm and theoretical techniques applied in this work are given in ESI

Absolute Vapor Pressures and Thermodynamics of Vaporization

Vaporization Thermodynamics of Alkyl-Quinolines and Alkyl-Pyridines

Validation Using Normal Boiling Temperatures Tb

Validation Using the Group-Additivity Principles: “Centerpiece Approach”

Liquid-Phase Standard Molar Enthalpies of Formation of the “Hydrogen Lean”

Liquid-Phase Standard Molar Enthalpies of Formation of the “Hydrogen Reach”