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

本项目从整体气化联合循环过程的热气净化角度出发，开发了一种利用含纳米颗粒的复合材料脱除氮和硫的新方法，这些复合材料是由廉价的原材料制成的。(1)在以45000 1/h的高空速进料2000ppm的NH_3时，添加外加铁离子的褐煤炭化制备的纳米Fe粒子对NH_3分解为N_2的催化活性高于工业活性炭负载的Fe催化剂。(2)透射电子显微镜、X射线衍射仪和程序升温脱附测试表明，高度分散的Fe粒子在NH_3分解中起关键作用，并通过α-Fe和氮化物物种的循环机理催化这一反应。用天然存在的大量Fe、Ca阳离子的低变质煤简单热解得到的焦炭，同样具有很好的催化作用，NH_3转化率与焦炭中铁含量有很强的相关性。(4)固有铁含量最高(2wt%)的焦炭在750℃下25h的稳定转化率可达80%，在850℃时NH_3完全分解。(5)在2000ppm H_2S存在下进行NH_3分解时，焦炭中的CaO完全失活生成CaS，但其中的Fe颗粒仍具有活性。(6)CO和H_2的摩尔比为2：1的合成气的存在降低了Fe催化剂的活性，而在合成气中加入CO_2使催化剂的性能恢复到没有合成气的原始状态，这表明部分焦炭可以用于实际的热气净化过程。

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.