EFFECTS OF HIGH-TEMPERATURE AND HIGH ZSM-5 ADDITIVE LEVEL ON FCC OLEFINS YIELDS AND GASOLINE COMPOSITION

FCC yields were quantified for operation under conditions that maximiz e the production of light olefins. These conditions include high react ion temperatures, use of low unit cell size base catalysts (USY and RE -USY), and addition of large amounts of ZSM-5. Adding 25% ZSM-5 additi ve nearly tripled propene yields, and increased butenes by about 60%. The fraction of isobutene in the butenes rose from 32-35 wt.-% to its equilibrium value of about 40%. For the base catalysts alone, increasi ng the reaction temperature from 811 K to 852 K gave a modest increase in C-3-C-4 olefins, but this effect was largely absent for the ZSM-5/ base catalyst mixture. This suggests that raising temperature loses ef fectiveness as a means of increasing light olefins yield, in the prese nce of large amounts of ZSM-5. Addition of 25% ZSM-5 additive had effe cts on C-2- species and butadiene which have not generally been observ ed with lower levels of ZSM-5. Ethylene yields increased, and methane and ethane yields decreased, while butadiene yields were halved. Incre asing temperature gave significant increases in the yields of butadien e, all C-2- species, and a decrease in butanes; these trends are the o pposite of those seen with ZSM-5 addition. PIONA analysis of selected gasoline samples showed that raising temperature gave a more olefinic gasoline. ZSM-5 addition increased olefin branching and shifted olefin s and paraffins to lower carbon numbers. Most yield shifts could be un derstood in terms of how changing temperature and adding ZSM-5 affect the relative rates of cracking versus hydrogen transfer for the gasoli ne-range olefins.