Reasons for inadequate conversion of light gasoline in two-stage maximizing propylene experiment

Recycling the olefin-rich light gasoline can further increase the yield of propylene in the two-stage riser catalytic cracking of heavy oil for maximizing propylene(TMP) process which is a new technology of producing propylene with heavy oil as the feed.The experimental results show that if the recycled light gasoline accounting for 19% of the fresh heavy oil feed,the yields of propylene can increase by more than 5%,while the dry gas less than 1%.But in the commercial tests,if the recycled light gasoline accounting for 21.88% of the fresh feed,the propylene yield can only increase by 1.51%,while the dry gas 1.37%.The main reasons are that the dilute domain of the catalyst created by the recycled light gasoline and heavy oil injected at a high velocity leads to inadequate contact,adsorption and catalytic conversion between the light gasoline and the catalyst;and low fluid density of the catalyst can not promptly terminate the thermal cracking caused by the light gasoline unadsorbed,thus causing a lower yield of propylene but higher yield of dry gas.