JJpnPetrolInst_29_267.pdf 3.9 MB
Synthesis of Light Olefins from Synthesis Gas Utilizing Zeolite
Alkaline earth metal
ゼオライトを用いて種々の複合触媒を調製し, 合成ガスからのエチレン, プロピレンなどの低級オレフィン合成を検討した。鉄とゼオライトを組み合わせたFe-Ti-V-およびFe-Ti-Mn-ゼオライト触媒では比較的高い(C2=+C3=)選択率が得られた。また, メタン生成の抑制という点から, メタノール合成触媒とゼオライトを組み合わせた複合触媒を用いて反応を行った。アルカリ土類金属で修飾したH-ZSM-5型触媒を用いた複合触媒では, (C2=+C3=)選択率が増加することがわかった。さらにゼオライト触媒の水素化能をも明らかにした。
Selective synthesis of light olefins (ethylene, propylene) from synthesis gas was studied utilizing various zeolitebased catalysts. (1) New metal/zeolite catalyst: The catalyst was synthesized hydrothermally from zeolite and Fe(II or III) compounds such as Fe3O4, Fe2O3, FeOOH. Figure 1 shows scanning electron micrographs of Fe3O4 and the Fe3O4/ZSM-5 catalyst. No Fe3O4 particle was observed in the latter. Figure 2(b) shows an X-ray diffraction diagram of this catalyst. The reflections of ZSM-5 and Fe2O3 were observed. Appearance of the diffraction peaks in Fe2O3 are attributed to oxidation of Fe3O4 in this catalyst by calcination in air. Figure 3 illustrates X-ray photoelectron spectra of the catalyst before and after grinding. The catalyst before grinding had very weak peaks of iron. By grinding the catalyst, these peaks became very strong, while the silicon peaks did not substantially change. From these results, it is concluded that the Fe3O4/ZSM-5 catalyst thus obtained has a unique texture in which Fe3O4 particles are enveloped with ZSM-5 zeolite. The results of conversion of synthesis gas over various metal/zeolite catalysts are given in Table 1. (2) Zeolite-based iron catalyst: The catalyst was prepared using FeSO4 and Fe(NO3)3 as a source of iron in the same method described above. The synthetic zeolite-based iron catalyst had a well defined crystalline ZSM-5 structure (Fig. 4). Figure 5 shows the results of conversion of synthesis gas over the catalysts. The catalysts prepared from an Fe(II) compound were more active than those prepared from an Fe(III) compound. The (C2H4+C3H6) selectivity of the former was lower than that of the latter. In order to elucidate these differences involving the activity and the selectivity, X-ray diffraction patterns of various catalysts were measured (Fig. 6). In the case of the catalysts prepared from the Fe(III) compound, the d(084)-spacing sharply increased with the Fe/Si atomic ratio.
On the other hand, in the case of the catalysts prepared from the Fe(II) compound, the spacing remained unchanged. This suggests that only Fe(III) can replace a portion of the silicon atoms in the crystal lattice and that Fe(II) is present in enveloped form with the zeolite. The differences of both the catalytic activity and the product selectivity may be attributed to the amount of iron which does not replace a portion of silicon atoms. (3) Zeolitebased iron catalyst promoted with various transition metals: Figure 8 shows the results of conversion of synthesis gas over variously promoted zeolite-based iron catalysts (Fe-M-zeolite catalyst, M: promoter). The (C2H4+C3H6) selectivity increased over the catalyst promoted with Ti, Mn and Zr, with Ti being the most effective. Figure 9 illustrates the influence of the second promoter on CO conversion and the selectivity. Addition of V, Mn and Zr to the Fe-Ti-zeolite catalyst increased the (C2H4+C3H6) selectivity. The high (C2H4+C3H6) selectivity was obtained on the catalyst of Fe:Ti:V(Mn)=1:1:1 (Tables 3 and 4). (4) Composite catalyst composed of methanol synthesis catalyst and zeolite catalyst: Conversion of synthesis gas to light olefins was carried out in a two-stage system (Fig. 12). The C2 and C3 hydrocarbons produced over H-ZSM-5 catalyst were mainly paraffins.
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Graduate School of Engineering