Regenerable Light Olefin Production via Steam-Enhanced Catalytic Cracking of n-Dodecane on P-ZSM-5 Extrudate

To address the growing demand for light olefins and the declining use of middle-distillate transportation fuels, this study investigated steam catalytic cracking (SCC) of n-dodecane (n-C12) over ZSM-5-based catalysts as a model system for heavier hydrocarbon feeds. Commercial H-ZSM-5 zeolites with different SiO2/Al2O3 molar ratios (SAR) were first evaluated under dry catalytic cracking (DCC) and SCC conditions. In DCC, high-SAR ZSM-5 provided the highest light olefin yield, whereas in SCC, the low-SAR ZSM-5 achieved the highest light olefin yield with strongly suppressed coke deposition. On the optimal zeolite ZSM-5, an intermediate P loading (1–2.5 wt %) increased the n-C12 conversion without sacrificing olefin selectivity, owing to suppression of the strong acidity, decreased concentrations of Bro̷nsted and Lewis acid sites, and improved hydrothermal stability. The optimal 1.5P-ZSM-5 (30) was shaped into cylindrical extrudates by using colloidal silica as an Al-free binder, giving sufficient mechanical strength while preserving the catalytic performance of the powder catalyst. Under optimized SCC conditions, the optimal catalyst extrudate retained a light olefin yield of >60% after 100 h on stream and showed excellent regenerability with minimal loss of acidity. These results demonstrate that phosphorus-modified ZSM-5 extrudates are promising industrial catalysts for the SCC of long-chain hydrocarbons.