High catalyst to oil ratio mainly leads to carbenium ion catalytic reaction, which LPG and coke yields were remarkably increased but dry gas yield was basically unchanged.

The impact of dry gas on FCC reaction becomes increasingly pronounced with lower reactor temperature and lower hourly space velocity, greater catalyst to oil ratio and longer reaction time.

The result showed proper reaction temperature, catalyst to oil ratio and short reaction time may detriment thermal cracking reaction, hydrogen transfer reactions, and get high propylene selectivity.