Aromatization of pentane catalyzed over various metallosilicates

Abstract

Various metallosilicates were synthesized using a hydrothermal method and characterized by SEM, XRD, Si-29 MAS NMR, chemical analysis and surface area measurements. These results showed that they had a MFI structure. The pentane aromatization reaction was carried out over these metallosilicates in a continuous now reactor at 550 degrees C, He/pentane=3, WHSV=1.5 h(-1) and 1 atm. Among the various metallosilicates, [Ga]ZSM-5(20) (52.3 %) and [Zn]ZSM-5(40) (37.6 %) showed higher aromatic selectivities for pentane aromatization. When [Al] ZSM-5(40) was ion-exchanged with gallium nitrate and zinc chloride, the selectivities for aromatics increased from 23.0 % to 35.5 % and to 32.7 %, respectively. The Si/metal mole ratios of [Ga]ZSM-5 and [AI]ZSM-5 were changed from 20 to 250 and NH3 temperature programmed desorption (TPD) was carried out. As the Si/metal ratio was changed from 250 to 20, the selectivities for aromatics were increased from 5.3 % to 52.3 % over [Ga]ZSM-5 and from 10.1% to 25.7% over [Al]ZSM-5. NH3 TPD of [Ga]ZSM-5 indicated that the sites of medium acidity play an important role in the formation of aromatics. When H-2 and CO were added to the reactant of pentane, the production of methane and ethane increased and that of aromatics decreased.