The crucial role of reaction pressure in the reaction paths for i-butane conversion over Zn/HZSM-5

Catalytic conversion of i-butane over Zn-modified HZSM-5 catalyst was systematically investigated at different reaction pressures. A special fixed-bed reactor involving a vacuum unit which could modulate reaction pressure from subatmospheric to positive pressure was used. Results show that reaction pressure can change the initial activation and subsequent reaction paths of i-butane over Zn/HZSM-5 catalyst. At subatmospheric pressure, the decrease in reaction pressure favors the dehydrogenation of i-butane, meanwhile inhibits both the cracking of i-butane and the secondary reactions such as the oligomerization, cracking and aromatization. Consequently, the selectivities to the undesired by-products (methane and ethane) are notably abated, and the selectivities to the desired products (ethylene, propylene and aromatics) significantly increase. Although space velocity affects the reaction paths for i-butane conversion, the change in reaction pressure has a more profound effect on the reaction paths.

Reaction pressure is a key factor for i-butane conversion paths over Zn/HZSM-5. At subatmospheric pressure, it effectively inhibits the cracking of i-butane to by-products (methane and ethane), but promotes the dehydrogenation of i-butane to desired products (ethylene, propylene, butenes and BTX). At subatmospheric pressures, the reaction is controlled by kinetic, however at positive pressures it is controlled by thermodynamic.Figure optionsDownload as PowerPoint slideHighlights
• Special fixed-bed reactor adjusts reaction pressure from vacuum to positive pressure.
• A decrease in reaction pressure changes i-butane conversion paths on Zn/HZSM-5.
• The cracking activation of i-butane decreases with reaction pressure.
• The dehydrogenation of i-butane increases with the decrease of reaction pressure.
• The selectivity to desired products increases with the decrease of reaction pressure.