Hydrogenation of N-ethylcarbazole with Hydrogen-Methane mixtures for hydrogen storage

Abstract

Hydrogen is a clean secondary energy as well as an efficient energy carrier, but the low density and small molecular hydrogen result in high economic and energetic efforts to store and transport hydrogen. In addition, the hydrogen produced by the current industry is usually impure and requires gas separation, which consequently increases the cost of hydrogen. A promising hydrogen storage technology using liquid organic hydrogen carrier (LOHC) can permit the safe storage of hydrogen for long time through the reversible chemical reaction in the presence of catalyst. The selective hydrogenation reaction of N-ethylcarbazole (NEC), an attractive LOHC compound due to the low dehydrogenation temperature of perhydro-N-ethylcarbazole (12H-NEC), with hydrogen was conducted in this study to achieve both separation and hydrogen storage for hydrogen-rich raw gas from natural gas steam reforming. First, hydrogenation experiments of molten NEC under a pure hydrogen atmosphere were carried out to determine the suitable hydrogenation conditions and reaction pathways. Then, the effect of methane addition on NEC hydrogenation was analyzed. Results indicate that there are multiple parallel pathways in the hydrogenation of NEC. The reaction rate from 8H-NEC to 12H-NEC step is extremely slow and this step is unstable at 453 K. The optimal hydrogenation temperature of NEC is 443 K and the apparent activation energy is 67.6 kJ·mol−1. The addition of methane reduces the initial reaction rate from 0.877 gH2·(gRu·min)−1 to 0.640 gH2·(gRu·min)−1 but increases the maximum degree of hydrogenation (DoH) from 0.870 to 0.909.