No abstract

No abstract

On the other hand, in HzO, the reaction profiles for both catalysts were different: two stages with nickel and a single stage with iron. This may be explained by the difference in the chemical form of the catalyst during the reaction. The nickel catalyst existed in a form of metallic nickel, whereas the chemical form of the iron catalyst was magnetite in H20. The minimum H2/H20 ratios required to convert the lowest metallic oxide to the metal at 923 K are approximately 3 for Fe and 0.005 for Ni. Thus, only nickel can be in the metallic state in the presence of small amounts of reducing gases such as volatile matter and/or gasification products.The first-stage gasification in H2 terminated at a coal conversion around 75 wt% with the iron catalyst and 85 wt% with the nickel catalyst, and the rate became very small thereafter ( Figure 1). As the reaction proceeded, the particle size of iron metal increased from 29 nm on devolatilization to 54 nm at the ultimate conversion of 76 w t % ( Table 111). The size of the nickel particles also increased from 8 nm at the initial stage to 32 nm at the termination point. This sintering is due to the consumption of char around the metal particles. The termination of the first-stage gasification may be related to the deactivation of the catalyst owing to sintering. The disappearance of the first stage at a high temperature of 1273 K (Figure 2) may also be due to the sintering of iron catalysts. Similar results were obtained for the nickel-catalyzed hydrogasification. At 1273 K nickel particles of about 0.1 pm in size were observed even at the initial stage.26 It is emphasized again that the presence of fine metallic particles is necessary for the occurrence of the two-stage gasification. Acknowledgment. Y.Ohuchi and E. Sat0 are thanked for their assistance in carrying out experiments. . (26) Higashiyama, K.; Tomita, A.; Tamai, Y. Fuel 1985,64,1525-1530.The high-performance liquid chromatographic (HPLC) separated fractions of pyridine/water extracts of selected crude petroleums were analyzed by electron paramagnetic resonance (EPR) spectroscopy to determine the first coordination sphere around the vanadium. The extracts were separated by polarity on an octadecylsilane column (ODS) into three fractions-low, moderate, and high polarity. As determined by EPR, the Boscan moderate-polar and Prudhoe Bay moderate-and low-polar fractions exhibited NzS2 coordination. Cerro Negro and Wilmington moderate-polar fractions showed S4 coordination, and the Boscan low-polar fraction showed N4 coordination. The coordination of the Cerro Negro low-polar fraction had distinctly different parameters, showing a NOS2 coordination. These results are important in the identification of non-porphyrin metal-containing compounds in heavy crude petroleums and residua.