Many parts of the world have imbalanced fuel markets, short on diesel and long on gasoline, degrading FCC profitability. Current technology for FCC mid distillate maximization is unsatisfactory because of the high aromatic content and low yield of the LCO fraction. A new technology is proposed which replaces carbocation (carbenium or carbonium ions) mediated cracking with free radical cracking, as in thermal cracking, by using a proprietary catalyst and by injecting 1 to 2% of oxygen (or the equivalent amount of air) in the riser as a free radical initiator. The technology was demonstrated with simple changes to the ACE unit test and later confirmed in a circulating pilot riser with VGO (vacuum gas oil) and ATB (atmospheric bottoms) feeds. The heat released in the limited combustion was safely absorbed by the catalyst and the products, resulting in a 5°C increase in the ACE unit cracking temperature profile. Mid distillate yield and quality were close to those obtained in delayed coking when processing ATB feed, with lower coke yield and better bottoms conversion. The amount of aromatics in the LCO fraction showed a 25% reduction resulting in a 15 point improvement in cetane index. The lower aromatic content of the new LCO makes it far easier to meet the ULS diesel specifications after hydrotreating and blending with other components. The technology enables the FCC to switch from gasoline to diesel production by changing the catalyst and oxygen supply to the riser, thus becoming a truly flexible conversion process.
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