Study On A Novel Organic Liquid Hydrogen Storage System

As a new hydrogen storage material, N-ethylcarbazole has potentially interesting prospects in hydrogen storage area because of its reversible hydrogen sorption properties in low temperature.In this present thesis, the hydrogenation kinetics of N-ethylcarbazole over Raney-Ni catalyst was studied firstly by investigating the finences of the reaction temperature, pressure and catalyst concentration on the mass transfer-reaction processes. The results show that the kinetics of reaction is controlled by the chemical process on the catalyst surfaces, the mass transfer resistance at gas-liquid interface and that from the bulk liquid phase to the surface of the catalyst particles can be ignored; a storage capacity of 5.0 wt% H2 is achieved at the optimum reaction temperature 180℃-200℃; the hydrogenation reaction followefirst-order kinetics with an apparent activation energy of 65.17 KJ/mol in the temperature range of 120-200℃at 2.0-6.0 MPa on 1-10 wt% catalyst concentration; the apparent kinetics model of the hydrogenation can be written as:Because of the multi-production of hydrogenation of N-ethylcarbazole, such as tetrahydro-N-ethylcarbazole,octahydro-N-ethylcarbazole,dodecahydro-N-ethylcarbaz-ole etc, the pathway of reaction was discussed. Using Gaussian, the optimized geometric configuration of N-ethylcarbazole and the intermediate compounds were obtained. The thermal energy was calculated using density functional theory (DFT). Based on experimental results, the relative thermodynamically stabilities of different candidate intermediate compounds and products were predicted reasonably.Then the dehydrogenation of dodecahydro-N-ethylcarbazole was studied. The dehydrogenation reaction conversion accelerates with increased temperature, proceeding a maximum 76.1% recovery of the stored H2 at 218℃. However, when the temperature further increases to 232℃, the hydrogen uptake decreased to 73.6%. The main dehydrogenated products are tetrahydro-N-ethylcarbazole, octahydro-N-ethylcarbazole, dodecahydro-N-ethylcarbazole. Finally, hydrogenation-dehydrogenation integration process was studied, and the cyclic of this integrated process was followed, which were taken in a batch reactor. It is founded that within 6 hours the hydrogenation-dehydrogenation can successfully be carried out at180℃-200℃, but the cyclic stability is not ideal.