A Novel Method of Removal of Nitrogen and Sulfur by Use of Nanoparticles Containing Composites Produced from Inexpensive Raw Materials

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This project has been performed to develop a novel method of removing nitrogen and sulfur by using nanoparticles containing composites, which are produced from inexpensive raw materials, from a viewpoint of hot gas cleanup for an integrated gasification combined cycle process. The main achievements are summarized as follows :(1) Nanoscale Fe particles on coal chars, prepared by carbonizing brown coals with externally added Fe ions, show higher activity in the catalytic decomposition of NH_3 to N_2 than Fe catalyst loaded on a commercial activated carbon, when 2000 ppm NH_3 diluted with He is fed at a high space velocity of 45000 1/h.(2) The TEM, XRD and TPD measurements strongly suggest that the highly dispersed Fe particles play the crucial role in NH_3 decomposition and catalyze this reaction through a cycle mechanism involving α-Fe and the nitride species(3) Some chars, prepared by simply pyrolyzing low rank coals with significant amounts of Fe and Ca cations naturally present as minerals, also work efficiently as the catalysts, and there is a strong correlation between NH_3 conversion and Fe content in char.(4) The char with the largest content (2 wt%) of inherent Fe provides the stable conversion of 80% during 25 h reaction at 750℃ and achieves complete decomposition of NH_3 at 850℃.(5) When NH_3 decomposition is carried out in the presence of 2000 ppm H_2S, CaO in the char is completely deactivated to form CaS, but Fe particles in it are still active, showing that the char can realize the removal of sulfur compounds and the catalytic decomposition of NH_3 simultaneously.(6) The coexistence of syngas, a mixture of CO and H_2 with the molar ratio of 2 : 1, lowers the activity of the Fe catalyst, whereas the addition of C0_2 to syngas restores the performance to the original state without syngas, which suggests that some chars can be utilized in an actual hot gas cleanup process.