Catalytic cracking of n-dodecane and alkyl benzenes over FCC zeolite catalysts: Time on stream and reactant converted models

Catalytic cracking of three hydrocarbon model compounds (n-dodecane, 1,3,5-tri-iso-propylbenzene, and 1,4-diisopropylbenzene) has been investigated over two FCC zeolite catalysts in a novel riser simulator that resembles closely the operating conditions of large scale FCC units. The catalytic cracking experiments were carried out at different reaction times and temperatures using the two FCC zeolite catalysts, FCC-B based on USY-zeolite and FCC-GKF based on ZSM-5. The experimental results were modeled using quasi-steady state approximation with the catalyst activity decay function based on both time on stream (TOS) and reactant conversion model (RC). The kinetics for the n-dodecane cracking as well as for the two alkyl benzenes has been modeled as a first order process. The higher apparent activation energies of cracking observed over the USY-based catalyst (FCC-B) for n-dodecane, coupled with the lowest value observed for the same molecule over the ZSM-5 based catalyst (FCC-GKF), seems to suggest that stronger acid sites are more important for n-dodecane cracking as compared to alkyl benzenes where weaker acids are sufficient for dealkylation.