Ultra-deep Hydrodesulfurization of Kerosene for Fuel Cell System. (Part 3). Development and Evaluation of Ni/ZnO Catalyst.

Abstract

Adequate regeneration of NiS in simple Ni/ZnO model catalysts was certified by highly accelerated long runs of the adsorptive ultra-deep hydrodesulfurization (UD-HDS) reaction of kerosene in the laboratory. Then, model Ni/ZnO catalysts containing 5wt% and 12wt% Ni were developed and evaluated in bench plant long life tests. From the results, a practical Ni/ZnO catalyst estimated to have a one-year life was selected. Preparations of catalysts were carried out checking the surface ratio of Ni by chemisorption of NO on a reduced Ni form. In kinetic studies, the apparent reaction order, activation energy, reaction order of H2 and reaction order of CO2 were 1.9-2.2, 31kJ/mol, 0.18, and -2.0, respectively. 200l of 12wt% Ni/ZnO catalyst was certified by long life evaluations as an auto-regenerative adsorptive UD-HDS catalyst for the 200kW kerosene-fed phosphoric acid fuel cell (PAFC) system, which was estimated to produce kerosene containing 0.025-0.040wtppm sulfur for at least 5900h of operation. Because of the small influence of H2 partial pressure, the long run was attained under near atmospheric pressure of 25% CO2 containing H2. By the end of the catalyst life, 36mol% of ZnO was consumed as the acceptor of H2S. The activity of Ni/ZnO catalyst is controlled by the balance of poisoning rate and regeneration rate of surface Ni. The life of the Ni/ZnO catalyst was theoretically interpreted as functions of the regeneration rate of NiS, the rate of sulfur charge, the content of ZnO, and the diffusion resistance of H2S.