Optimization study of light olefins production in gasoil cracking over HZSM-5 catalyst: temperature and catalyst loading as key parameters
摘要
The catalytic cracking of atmospheric gasoil over protonic HZSM-5 zeolite (SiO₂/Al₂O₃ = 33.3) was studied in a fixed-bed reactor. The effects of temperature (500, 550, and 600 °C) and catalyst loading (0.1, 0.3, and 0.5 g) on conversion of gasoil and selectivity of ethylene and propylene were thoroughly investigated. Both ethylene and propylene selectivities increased with rising temperature at all catalyst loadings, whereas the propylene-to-ethylene (P/E) ratio declined. The highest total light olefins selectivity (60.0 wt%) was achieved at 600 °C with 0.5 g of catalyst. Gasoil conversion exhibited a non-monotonic trend at low-to-moderate catalyst loadings, reaching a minimum at 550 °C, attributed to rapid coke deposition and pore blockage; where it recovered at 600 °C due to the decomposition of these reaction intermediates or volatilization. Conversion increased steadily with temperature at 0.5 g catalyst loading owing to greater availability of active sites and improved coke tolerance. Stability tests at 500 °C and 0.3 g revealed stable light olefin selectivity over 6 h time on stream, despite progressive deactivation (conversion dropped from ~ 87% to ~ 35%). The results highlight that there is an optimal catalyst loading-temperature point and further demonstrates the need for consideration of the balance between light olefins yield and catalyst stability.