Liquid Organic Hydrogen Carriers: An Upcoming Alternative to Conventional Technologies. Thermochemical Studies.

A system based on the catalytic hydrogenation/dehydrogenation reactions of N-ethylcarbazole is one of the most promising as the new class of the liquid organic hydrogen carrier (LOHC) compounds. Enthalpy of formation of the liquid dodecahydro-N-ethylcarbazole (fully hydrogenated N-ethylcarbazole) was measured using combustion calorimetry. Vaporization enthalpy for this compound was derived from vapor pressure-temperature dependence measured by transpiration. The enthalpy of formation of the gaseous dodecahydro-N-ethylcarbazole was derived and validated with the high-level quantum chemical calculation. Vapor pressures of the liquid N-ethylcarbazole (0.0008 bar) and dodecahydro-N-ethylcarbazole (0.01 bar) at a practical and relevant temperature (400 K) were assessed from the new experimental data. It has turned out that these vapor pressures were low enough to fulfill the basic requirement for an LOHC.