:Thermal Decomposition of Benzene on Active Carbon in the Presence of Iron and Hydrogen Sulfide
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In part 1, we reported that carbon beads containing >3wt% of sulfur were readily whiskerized with a number of short carbon fibers by catalysis of sulfur during thermal decomposition of propylene at 1, 000°C. In the present work, whiskerization of sulfur-free carbonaceous materials has been examined by using cooperative promotion of fine iron particles and hydrogen sulfide.Active carbon of 500-1, 200μm granules was used as a substrate for whiskerization. The active carbon granules were impregnated with a Fe (NO3)3 solution, followed by reduction at 1, 100°C in hydrogen. The amount of iron was 0.82wt%. A mixture of benzene (12.1%) and hydrogen was used as a reactant gas for carbon fiber preparation. When catalysis of sulfur was employed, hydrogen sulfide (2.5%) was also mixed in the feed gas. Thermal decomposition was performed at 1, 100°C for 10-120min in a flow system.When benzene was decomposed on the iron-containing active carbon (no hydrogen sulfide was added), long carbon fibers of 10-20μm diameters were obtained (Fig. 2(a)). The formation density (50-150 fibers/mm2), however, was too small from the point of view of whiskerization. Carbon fibers were also grown on iron-free active carbon when hydrogen sulfide was mixed in the feed gas (Fig. 2(b)). However, the formation density was even smaller, and most of the fibers were thin, short, and meandering compared with the iron-catalyzed fibers. The simultaneous employment of iron and hydrogen sulfide catalysts drastically increased the formation density to 5-10×104 fibers/mm2 (Fig. 3), which was 3-5 times the whiskerization results of the sulfur-containincga rbon beads reported before. The fiber diameter ranged 0.1-2μm, and the length 20-100μm. The fiber yield was 5-8% on the basis of carbon atoms fed as benzene. Structure and crystallinity of the fibers were similar to those of the usual, iron-catalyzed carbon fibers. Therefore, the well-whiskerized active carbon particles are of interest as a new type of strengthening agent in composite materials.As seen from Fig. 3(c), every fiber grown on the active carbon surface carried a certain particle on its tip, which was about the same size as the fiber diameter itself. This particle was identified as FeS by electron diffraction (Fig. 5). In addition, the shape of the fiber tip after treatment with hydrochloric acid (Fig. 6) suggested that the FeS particles melted under the reaction conditions. Cooperative promotion of iron and hydrogen sulfide, therefore, may be ascribed to the formation of the fine FeS droplets which act as active centers for carbon fiber growth.
- 公益社団法人 石油学会の論文
公益社団法人 石油学会 | 論文
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