Short Contact Time Catalytic Cracking

Short contact time cracking in fluid catalytic cracker units (FCCU) at times on the order of 2 s in the riser demonstrated benefits of lower dry gas yields, lower delta coke on catalyst and more selective cracking to gasoline and light olefins. The capabilities of short contact time cracking were extended to ultra short times of less than 1 s by designing reactor systems that either eliminated or greatly changed the hydrodynamics of the riser and catalyst separation from the cracked hydrocarbon vapor. The hotter cracking temperatures with more active catalyst employed promoted desirable, fast catalytic reactions, while the shorter contact time reduced undesired secondary reactions. As a result, more selective product distributions were obtained, especially for the production of light olefins. Gasoline olefinicity also increased, raising the octane rating. Potential benefits of shorter oil-catalyst contacting times include better metals resistance, reduced catalyst deactivation and finer control of the reactor system.

We first briefly review process technology starting with two short contact time cracking devices: fluid catalytic cracking riser termination devices that shorten the residence time in the riser and downflow reactors that can reduce the backmixing found in upflow riser reactors. Catalyst considerations encountered in short contact cracking are discussed before briefly reviewing three ultra short processes. We then develop the process economics for a conceptual ultra short contact time catalytic cracker using the NExCC™ reactor-regenerator cracking vacuum gas oil.