Hexadecane Conversion in the Evaluation of Commercial Fluid Catalytic Cracking Catalysts

The conversion of n-hexadecane over fluid catalytic cracking (FCC) catalysts was studied at 788 K and compared with the conversion of n-hexane over these FCC catalysts and the conversion of a vacuum gas oil from the micro activity test (MAT). The product distribution could be fully explained by reaction pathways identical with those in n-hexane conversion (i.e., protolytic cracking, dehydrogenation and hydrogen transfer). 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 protolytic activation over strong Brønsted acid sites, and the other that is catalyzed by Lewis acid sites and rapidly deactivates with time on stream. With time on stream, the rate of aromatic formation in parallel with coking markedly decreased within the first 2500 s. n-Hexadecane conversion varied in parallel with the MAT activity. The octane numbers observed in the MAT test were directly proportional to the iso/n-paraffin ratio and the paraffin/olefin ratio of n-hexadecane cracking. The rate of conversion to isoalkanes (characteristic of hydride transfer) is directly correlated to the amount of coke formed in the MAT experiments.