U.S. Pat. No. 3,193,480 describes a process whereby a hydrocarbon stream having a high metal content is subjected to mild cat cracking in a first cracking zone and a hydrocarbon stream of low metal content is subjected to severe cat cracking in a second cracking zone, cracked products are recovered from both cracking zones and the cycle oil fractions produced are subjected to solvent extraction resulting in the production of an aromatics rich extract and a non-aromatics rich raffinate, this raffinate then being recycled to the severe cracking zone. The aromatic hydrocarbons are recovered from the extract and recycled to the mild cat cracking zone. See also U.S. Pat. Nos. 3,164,542 and 3,303,123.
U.S. Pat. No. 3,281,351 teaches a process wherein a hydrocarbon stream is cracked and the effluent is fractionated. The gasoline and fuel oil fractions are hydrotreated and then solvent extracted to produce an aromatics extract and a paraffinic/olefinic raffinate which is recycled to the cracking zone.
U.S. Pat. No. 3,714,022 teaches a process wherein a naphtha is subjected to low severity reforming and the reformate is subjected to an aromatics removal process whereby a saturates rich fraction is subsequently recovered, the saturates rich fraction being then sent to a cracking zone to give light hydrocarbons and a heavy cracked material. The heavy cracked material is sent to the aromatics separation zone resulting in an increased in the amount of saturates recovered in said zone and consequently recycled to the cracking zone.
U.S. Pat. No. 3,758,410 teaches a process wherein a low octane light straight run gasoline is cracked in a first cracking zone and a cracked product is recovered, a gas oil is cracked in a second cracking zone and light cracked gasoline and heavy cracked gasoline fractions are recovered; the heavy cracked gasoline is subjected to reforming to produce a reformate which is solvent extracted to produce an aromatics rich extract and a saturates rich raffinate. This raffinate stream is recycled to the first cracking zone. The cracked product from the first cracking zone is combined with the light cracked gasoline from the second cracking zone to produce a combined gasoline product. A C.sub.2 and C.sub.3 olefin stream is also recovered from the first cracking zone while a C.sub.3 and C.sub.4 olefin stream is recovered from the second cracking zone. See also U.S. Pat. No. 3,763,034.