Fabrication Of Metal/carbon Composites And Application In Catalytic Conversion Of Carbonyl Sulfides

The removal of sulfur specises is crucial in Integrated Gasification Combined Cycle (IGCC) technology which is regarded to be the most promising technology due to the high efficiency and low pollution features. The sulfur-containing compounds in the coal gas include mainly hydrogen sulfide and organic sulfur, such as carbonyl sulfides, carbon bisulfide and neglectable thiol, thiophene. Hydrogen sulfide can be removed successfully using metal oxide. However, organic sulfur removal is not so easy, which is difficult to reach the requirements of fine desulfurization. Therefore, the removal of organic sulfur (COS) in hot coal gas become an important topic today. Hydrodesulfurization is thought of the most appropriate method on removal of carbonyl sulfide because it not only has high desulfurization precision, simple operation, but also H₂ in the gas can be used directly without additional gas source.Transition metal nickel and molybdenum are both effective active components for carbonyl sulfide hydrodesulfurization reaction andγ-Al₂O₃ exclusively act as carrier. Because there is strong intercation betweenγ-Al₂O₃ and metal oxides, it is easy to form Al-O-Mo phase which is not propitious to presulfurize and. reduces the conversion of COS. This problem can be solved using activated carbon as carrier. However, the reports on research for catalytic conversion of carbonyl sulfides using (Ni)Mo/AC catalysts are few. Furthermore, traditional catalysts are prepared by incipient-wetness impregnation, dryness, calcined and presulfuration treatment using metal salts solution as modifiers. The catalysts using impregnation method have two aspects weakness. On one hand, the metal active component in the catalysts cannot be highly dispersed. On the other hand, presulfuration process is complicated to operate due to harsh conditions and energy-consuming. Moreover, the active components may not become entirely metal sulfide. The present work has been conducted focusing on three aspect problems refered.(1) Phenolic resin-based activated carbon desulfurized (M/PAC) containing the different kinds of metal and Mo with different loading are prepared using the mixture of low-cost water-soluble phenolic resin and metal salts as precursors and applied to the COS hydrogenation catalytic reaction to solve the problems of carrier and metal dispersing; (2) MAC desulfurizers are prepared by incipient-wetness impregnation method using ammonium tetrathiomolybdate (ATTM) as modifiers and commercial coconut shell activated carbon as catalyst carrier and applied to hydro-conversion behaviors study of carbonyl sulfide (COS) in hot coal gas to figure out the problems of carriers and presulfuration.The results show that M0S2 is the main active component. Ni sulfide specises are mainly responsible for better dispersion of Mo specises on actived carbon surface, as a result, more active centres can be formed. The catalysts with Mo and Ni-Mo both have high removal ability to COS under the experiment conditions. During reaction process, the optimal reaction temperature for M/AC and M/PAC is in the range of 200°C-300°C and 240°C-300°C, respectively. The removal of the COS includes both absorption and hydro-conversion courses using M/AC catalysts, whereas the catalytic conversion of COS is exclusively responsible for the removal of COS in M/PAC. Metal sulfide serves as active components in these catalysts, therefore both of them suffer from sulfur loss with low sulfur species in the gas system during reaction process. However, the sulfur loss time of M/AC catalysts is longer than that of M/PAC. The results also show COS conversion rate of M/AC is higher than that of M/PAC when the reaction approaches the state of equilibrium.