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 .