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Hydrocracking of Benzene over Various Zeolite Catalysts
ZSM-5, モルデナイトなどの強酸点を有するゼオライト触媒上でベンゼンの水素化分解が進行することを明らかにした。水素化分解活性は用いたゼオライト触媒の種類およびSiO2/Al2O3比に大きく依存し, H-ZSM-5およびH-モルデナイト触媒は高い活性を示したが, H-Y, H-ZSM-34および無定形シリカ•アルミナ触媒は低い活性であった。生成物としては, 分解生成物であるメタン, エタン, プロパン以外にベンゼンのアルキル化されたトルエン, キシレンも比較的高い選択率で得られた。また, ベンゼンの水素化生成物であるシクロヘキサンの水素化分解をも行い反応スキームを検討した。
Hydrocracking of benzene was investigated over various zeolites. The reaction was carried out at 300-600°C under 40kg/cm2, using a high pressure fixed bed system. As shown in Fig. 1, the catalytic activity was dependent on both the kind of zeolite and SiO2/Al2O3 ratio in the used zeolite. H-mordenite(H-M) and H-ZSM-5 showed high activity. In case of HZSM-5, the catalytic activity decreased with increase in SiO2/Al2O3 ratio. However, H-Y, H-ZSM-34 and silicaalumina showed very low activity. In order to investigate the effect of impurities contained in the zeolite, the zeolites were carefully analyzed by X-ray fluoresence spectrometry and inductively coupled argon plasma emission spectrometry. Only a trace amount of Fe was detected in the zeolite (Table 1). The other metals were far below the detection limit of the inductively coupled argon plasma emission spectroscope (Shimadzu ICPS-50). From these results, it was concluded that the hydrocracking of benzene takes place on the acidic sites of the zeolite. Figure 2 shows the product distribution resulting from the hydrocracking of benzene over various H-ZSM-5 plotted against SiO2/Al2O3 ratio. Figures 3 and 4 show the relationship between conversion and selectivity for the hydrocracking products over H-ZSM-5 (SiO2/Al2O3=40) and H-M. These results suggest that the product distribution is dependent not on SiO2/Al2O3 ratio but on conversion. Figure 5 shows the results of the hydrocracking of benzene over various H-ZSM-5 type catalysts modified with alkaline earth metals. The catalytic activity decreased in the following order: H-ZSM-5>Mg-H-ZSM-5>Ca-HZSM-5>Sr-H-ZSM-5>Ba-H-ZSM-5. The product distribution on these catalysts was similar to that over H-ZSM-5 at the same conversion. Moreover, cyclohexane and methylcyclopentane were detected in the effluent gas when the reaction temperature was about 300°C. In order to clarify the reaction scheme, the hydrocracking of cyclohexane was carried out by using H-ZSM-5 and Ba-H-ZSM-5 (Fig. 6 and Table 2).
The product distribution on these catalysts was similar to that resulting from the hydrocracking of benzene over H-ZSM-5. Based on the results obtained, the plausible reaction scheme was proposed.
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Graduate School of Engineering