Study On The Hydrogenation And Dehydrogenation Reaction Of N-ethylcarbazole Over Ni-based Catalysts

As a new type of organic liquid hydrogen storage material, N-ethylcarbazole has good development space and interesting application prospects in the field of hydrogen storage.In the present work, the preparation process of Ni/Al2O3 was studied by investigating the influences of hydrazine hydrate dosage, temperature and Ni loading contents on the N-ethylcarbazole hydrogenation reaction. The experimental results show that Ni/Al2O3 has a good catalytic hydrogenation performance when uesd γ-Al2O3 as the carrier and hydrazine hydrate as reductant in glycol solution. The best load of Ni was 20%. On this basis, Ni-Cu/Al2O3 catalysts were prepared.Then the N-ethylcarbazole hydrogenation over 20%Ni/Al2O3 catalyst was investigated. The effect of temperature, pressure and catalyst dosage on the hydrogenation rate and absorption capacity was also discussed. The results show that an appropriate increasing of temperature, pressure and catalyst dosage is contributed to hydrogenation behavior. The optimum hydrogenation condition is 200℃,6MPa and 1.5g 20%Ni/Al2O3. Under this condition, lOg N-ethylcarbazole can achieve an optimum value of 0.28mol and the conversion rate reaches 91.2%.The kinetics analysis of N-ethylcarbazole over 20%Ni/Al2O3 catalyst find that initial hydrogenation reaction is controlled by the chemical reactions on the surface of catalyst, the mass transfer resistance of the gas-liquid and liquid-solid interface are negligible. The hydrogenation reaction followed first-order kinetics with an apparent activation energy of 61.36 kJ/mol under the temperature range of 180～220℃, at 3.0 ～7.0 MPa on 0.5-2.0 g catalyst dosage, and the apparent kinetics equation is: robs=29.67·e-6.136×104/RT·6m/ρpdp Finally, dehydrogenation of dodecahydro-N-ethylcarbazole on the Ni-Cu/Al2O3catalyst was studied. The results reveals that Ni-Cu/Al2O3 catalyst has good catalytic dehydrogenation performance, with the increase of Cu load, dehydrogenation rate and conversion rate are improved obviously, at the same time, raising the temperature and catalyst dosage can also be beneficail to dehydrogenation reaction. At the condition of 230℃,1.25 g 20%Ni-0.5%Cu/Al2O3, an appropriate 80.8%recovery of the stored H2 can be obtained with 2mL dodecahydro-N-ethylcarbazole. The main dehydrogenated products are tetrahydro-N-ethylcarbazole and N-ethylcarbazole.