Systematic evaluation of physicochemical properties for the selection of alternative liquid organic hydrogen carriers

Abstract

Chemical hydrogen storage is a key step for establishing hydrogen as a main energy vector. For this purpose, liquid organic hydrogen carriers (LOHCs) present the outstanding advantage of allowing a safe, efficient, and high-density hydrogen storage, being also highly compatible with existing transport infrastructures. Typical LOHCs are organic compounds able to be hydrogenated and dehydrogenated at mild conditions, enabling the hydrogen storage and release, respectively. In addition, the physical properties of these chemicals are also critical for practical implementation.In this work, key properties of potential LOHCs of three different chemical families (homoaromatics, and N- and O-heteroaromatics) are estimated using molecular simulations. Thus, density, viscosity, vapour pressure, octanol-water coefficient, melting point, flash point dehydrogenation enthalpy and hydrogen content are estimated using the programs COSMO-RS and HYSYS. In addition, we have also evaluated the performance of several binary mixtures as LOHCs using these methodologies.Considering the hydrogen content, characteristic temperatures, and previous experimental results of the cyclic process; our simulation results suggest that 1-methylnaphthalene/1-methyldecahydronaftalene and methylbenzylpyridine/perhydromethylbenzylpyridine pairs are appropriate candidates for chemical hydrogen storage. Binary mixtures of LOHCs are also relevant alternatives since substances with a great potential can be used as LOHCS when dissolved. That is the case of naphthalene and 1-methyl-naphthalene mixtures or indoles dissolved in benzene or benzylbenzene. Concerning O-compounds, although several pairs could be used as LOHCs, thermodynamic and kinetic feasibility of the hydrogenation/dehydrogenation cycles must be better studied.