Effects of Feedstock and Catalyst and Oil Contact Time on ZSM-5 Cracking Chemistry in FCC Process

Considering the rapidly increasing demand for light olefins in the emerging markets, especially propylene, as petrochemical feedstocks, apart from steam cracking a number of processes such as catalytic cracking and metathesis are being modified and/or developed to enhance the propylene production. The current study focuses on fluid catalytic cracking (FCC) process using catalyst with ZSM-5 functionality to enhance propylene selectivity. Due to its smaller pore dimensions compared to standard Y-zeolite catalyst, the ZSM-5 mainly facilitates cracking of gasoline range olefins to LPG (C3-C4) olefins. Most of the studies on ZSM-5 chemistry were conducted in fixed-bed reactors which have very different hydrodynamics and much longer catalyst and oil contact time than that in a plug flow riser reactor used in commercial FCC process. The primary objective of this work is to understand the effect of contact time and feedstock on the ZSM-5 cracking chemistry especially on propylene production. The study was performed in a lab scale microriser reactor, whose riser length can be easily varied to simulate different catalyst and oil contact times and has similar hydrodynamics of a commercial riser reactor. Two commercial gas oil feedstocks with large difference in their aromatics content were used for the study. The catalytic cracking experiments were carried out with different contact times up to 5.4 s using both the base and ZSM-5 containing FCC catalysts in order to understand the effect of ZSM-5 in a quantitative way. This presentation will discuss our findings on the effects of contact time and feed on the overall cracking activity and product distribution, especially their impact on light gaseous hydrocarbon yields. Since ZSM-5 only reacts with gasoline olefins, the impact of contact time on gasoline composition and gasoline octane number will also be addressed for both the feeds studied.