Kozo Imura

Conversion of Light Naphtha to Aromatic Hydrocarbons. Part 5. Evaluation of Catalytic Performance of Pt/KL for the Aromatization of Hexane in Pilot-scale Reactors.

Catalytic conversion of light naphtha to aromatics over platinum supported on zeolite L (Pt/KL) was studied using pilot scale units of an externally heated tubular reactor and an adiabatic reactor under operating conditions close to those used for commercial reactors, and simulated using data from laboratory experiments. Product distributions and temperature profiles in the catalyst bed of the adiabatic reactor and the externally heated tubular reactor agreed fairly well with the simulated values. The simulated performances of the adiabatic reactor and the externally heated tubular reactor were compared, suggesting that the externally heated tubular reactor is more advantageous than the adiabatic reactor, since the operating temperature at the catalyst bed can be lowered, resulting in a slower reaction rate of hydrocracking and a consequent increase in the benzene yield.

Conversion of light naphtha into aromatic hydrocarbons (part 3) ; Effects of pre-sulfiding of ZnH-ZSM-5 on catalytic performance and stability of zinc

The effects of steaming and hydrogen reduction of ZnH-ZSM-5, concerning catalytic activity in aromatization of n-hexane were examined to evaluate the stability of ZnH-ZSM-5 in commercial operating conditions, in comparison with H-ZSM-5. Steaming at high temperature resulted in greater drop in the yield of aromatics over H-ZSM-5 than that over ZnH-ZSM-5. Hydrogen reduction had little effect on the yield of aromatics over H-ZSM-5, while a remarkable drop in the yield of aromatics was observed over ZnH-ZSM-5. It was found that zinc oxide in ZnH-ZSM-5 was reduced with hydrogen to give metallic zinc, which was then vaporized from the catalyst. This vaporization led to an irreversible decline in the activity for aromatization. Pre-sulfiding of ZnH-ZSM-5 was found to be effective in preventing the vaporization of zinc, by conducting thermogravimetric measurement of vaporized zinc from the catalyst. ZnH-ZSM-5 was pre-sulfided, using thiophene, dimethylsulfide, and disulfidecarbonate, as sulfiding agents, which reduced not only the vaporization of zinc, but also the cracking activity to yield light gases, such as CH 4 and C 2 H 6 .

Conversion of Light Naphtha into Aromatic Hydrocarbons (Part 1) Kinetic Studies on Hexane Conversion on Zn/H-ZSM-5.

Conversion of light naphtha into aromatic compounds was studied on series of ZSM-5 catalysts loaded with various metal species. Among the catalysts, Zn-, Cd- and Ga-loaded ZSM-5 exhibited. high performances for aromatization of n-hexane. The mechanism of conversion of n-hexane into aromatic compounds over Zn/H-ZSM-5 catalyst was investigated. It is found that aromatization of n-hexane involves dehydrocracking of n-hexane into lower olefins, oligomerization of lower olefins, and dehydrogenation of higher olefins to aromatic compounds. In order to investigate the reaction pathway for aromatization of higher olefins, a series of conversion of n-hexane, 1-hexene, hexadiene, hexatriene, and cyclohexane over Zn/H-ZSM-5, H-ZSM-5, and Pt/H-ZSM-5 were conducted. It is suggested that aromatization proceeds in successive dehydrogenation of higher olefins, and that Zn species play a role to promote formation of hydrogen molecule. On the basis of experimental results, a general reaction model in transformation of light naphtha over Zn/H-ZSM-5 was developed. From results of the kinetic analysis, it is found that promoting the activities for dehydrocracking of n-hexane, dehydrogenation of lower paraffins, and formation of hydrogen molecules may make the catalyst more selective in aromatization of light naphtha.