EFFECTS OF HIGH-LEVEL ADDITIONS OF ZSM-5 TO A FLUID CATALYTIC CRACKING (FCC) RE-USY CATALYST

The effect of the addition of high levels of ZSM-5 to steamed rare ear th ultra-stabilized fluid catalytic cracking (FCC) catalyst has been s tudied in an isothermal, bench scale, once-through riser pilot plant. Catalyst mixtures consisting of RE-USY blended with ZSM-5 at additive levels of 12.5, 25, 50, and 75 wt.-% were examined. Results indicate y ields of fight alkenes could be maximized by operating with large amou nts of ZSM-5. For the particular gas oil used in this study, a maximum of light alkenes yield occurs at an additive level of about 25 wt.-%; other feeds can show a different response, At the 25 wt.-% additive l evel we observed maximum yield increases of about 150% in propene and isobutene, and 120% in n-butenes. At lower additive levels (<25 wt.-%) , conversion of reactive gasoline-range species (mainly alkenes) is no t complete. Above 25 wt.-%, conversion of these species is essentially complete, and the major effect of ZSM-5 is dilution of the base crack ing catalyst with concomitant loss in overall conversion. The FCC naph tha octane (both RON and MON) also increased with additive level up to 25 wt.-%. We also observed an increase in ethylene yield, along with suppression of some undesirable products such as methane. In the prese nce of 25 wt.-% ZSM-5 additive, there were no significant shifts in bo ttoms (or HCO, heavy cycle oil) and light cycle oil (LCO) at constant conversion and only a slight decrease in coke yield at constant cat/oi l ratio.