HEXADECANE CONVERSION IN THE EVALUATION OF COMMERCIAL FLUID CATALYTICCRACKING CATALYSTS

The conversion of n-hexadecane over fluid catalytic cracking (FCC) cat alysts was studied at 788 K and compared with the conversion of n-hexa ne over these FCC catalysts and the conversion of a vacuum gas oil fro m the micro activity test (MAT). The product distribution could be ful ly explained by reaction pathways identical with those in n-hexane con version (i.e., protolytic cracking, dehydrogenation and hydrogen trans fer). The rates via all three reaction pathways decreased at long time on stream. As with n-hexane, two reaction pathways to dehydrogenate n -hexadecane were identified; one that is affiliated with the protolyti c activation over strong Bronsted acid sites, and the other that is ca talyzed by Lewis acid sites and rapidly deactivates with time on strea m. With time on stream, the rate of aromatic formation in parallel wit h coking markedly decreased within the first 2500 s. n-Hexadecane conv ersion varied in parallel with the MAT activity. The octane numbers ob served in the MAT test were directly proportional to the iso/n-paraffi n ratio and the paraffin/olefin ratio of n-hexadecane cracking. The ra te of conversion to isoalkanes (characteristic of hydride transfer) is directly correlated to the amount of coke formed in the MAT experimen ts.