Dehydrogenation and Hydrogenation Cycle of Methylcyclohexane–Toluene System for Liquid Phase Hydrogen Storage: Thermodynamic Reaction Equilibrium Investigation

Despite H2 being a clean and high-energy carrier, it poses storage and transportation problems, due to high liquefaction pressure, low volumetric density, as well as low boiling point. Consequently, research efforts are focused on the search for sustainable alternative H2 storage technology. In this study, the thermodynamic analyses of liquid organic hydrogen carriers (LOHCs), which utilize the reversible methylcyclohexane–toluene system (MTS) for H2 storage, are investigated. The study employs the Gibbs free energy minimization procedure by treating the non-ideal behavior of the participating species using the Soave–Redlich–Kwong https://www.e-education.psu.edu/png520/m10_p5.html (SRK) equation of states. The “fmincon” optimization algorithm in MATLAB (R2016 version) was employed to find the Gibbs free energy minima. The study reveals close to 100% equilibrium conversion of methylcyclohexane (MCH), with about 99% yield of H2at325oC and 1 bar. In the literature report, PtSn/Mg–Al and Pt/Ce1.4-Mg–Al catalysts showed operability close to the equilibrium conversion. On the other hand, toluene hydrogenation is favored by low temperature and high pressure. The thermodynamic calculation reveals close to 100% equilibrium conversion at 100 °C and 1 bar, which is not achievable by existing catalytic systems due to kinetic limitations. Much improvement is desirable in catalyst design for this process operating at atmospheric pressure, suggested by this thermodynamic study and clearly, a high-pressure–low-temperature system is desirable for the hydrogenation reaction.