Effects of heavy metals on activity and selectivity of zeolite cracking catalysts. Part 3. Effects of metal oxide addition on vanadium tolerance of zeolite.:Effects of Metal Oxide Addition on Vanadium Tolerance of Zeolite
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As was previously reported1), the vanadium migrate to the zeolite at regenerator conditions of FCC catalysts and destroy the crystalline zeolite structure. In order to develop a vanadium tolerant catalyst, the effects of metal oxides addition on V-tolerance of zeolite were examined.The affinity of metal oxides for V2O5 were evaluated by the amount of adsorbed V on metal oxide in NH4VO3 solution at 100°C (Table 2). The affinities of MgO and La2O3 for V were considerably higher compared with those of other metal oxides or zeolites. REHY showed higher affinity than ZrO2, TiO2 and SiO2. This suggested that these oxides possess low capability for mitigating the migration of V to REHY. The affinities of alumina with different structures were dependent on their surface areas.In the system of metal oxide-V2O5 mixture, the reactivity of metal oxide for V2O5 was measured by using high temperature X-ray diffraction at 650°C. As shown in Fig. 1, the reactivity, i.e., the crystallinity retention of V2O5 mixed with metal oxide depended on electronegativity (χi) of metal ion except for θ, α-Al2O3 and α-Fe2O3. The low reactivities of θ, α-Al2O3 are probably due to a lattice stabilization or an increase of crystal size.The effectiveness of metal oxide as a V trapping agent was further considered by a system of V2O5-metal oxide-HY mixture at 800°C. In Fig. 2, the time-course of crystallinity of HY mixed with V2O5 and metal oxide is shown. The crystallinity of HY was obtained by using the peak intensity of (533) planes of the zeolite. In the systems of MgO or La2O3 mixtures, the destruction of HY by V was deminished markedly. SiO2 and TiO2 did not show any effects on the crystallinity retention of HY. The crystallinity retention of HY after heat treatment at 800°C for 2hr showed linear correlation with χi (Fig. 3). These results suggests that the acidic-basic property of metal oxide is one of the most important factor for the usefullness as a V trapping agent.As an example examined in the FCC catalyst system, the effect of γ-Al2O3 addition on V tolerance is shown in Fig. 4. Catalyst-B consist of HY, SiO2 and kaolin was prepared by the same way as commercial catalyst. Catalyst-A was prepared by the same way as Catalyst-B except kaolin was substituted with γ-Al2O3. Catalyst-A maintained higher activity even after 12, 000ppm V deposition, suggesting that γ-Al2O3 acts as a V trapping agent.Based on the above results, the effects of V on activity can be deminished by adding the V trapping agents, such as MgO, La2O3 or γ-Al2O3, but further work on improvements of selectivity and hydrothermal stability will be necessary.
- 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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