Download Rclimdex R . . . It is known that the catalytic cracking of a gasoline-containing feedstock, such as petroleum crudes, naphthas or hydrocracks, using a catalytic "fluid bed" process provides a gasoline product which is rich in aliphatic hydrocarbons, particularly those with 6 to 12 carbon atoms, and a cracked distillate fraction rich in aromatic hydrocarbons. The catalytic cracking process generally requires temperatures on the order of 600.degree. to 800.degree. F., and the cracking activity is expressed by the contact time of the feedstock with the catalyst. The catalytic cracking of a feedstock which contains significant quantities of nitrogen tends to favor aromatics production at the expense of aliphatics. In order to avoid such loss, it is known to pretreat the feedstock by admixture with liquid comprising a Fischer-Tropsch (hereinafter F-T) product. The purpose of the F-T treatment is to reduce or eliminate the quantities of nitrogen in the feedstock which tends to favor the production of aromatic hydrocarbons. The F-T product is liquid and its admixture with the feedstock imparts a stability to the stream of hydrocarbons which is subject to the catalytic cracking operation. The F-T reaction is generally an exothermic reaction, and the feedstock containing F-T product tends to be subjected to autogenous heat evolution. Aromatic hydrocarbons generally tend to be more difficult to crack than aliphatic hydrocarbons, and it is known that there is a hydrocracking-aromatics selectivity relationship. It has been found that cracking of the paraffins which make up the aliphatics of a hydrocarbon stream to light olefins (generally C.sub.2 to C.sub.4) tends to increase the relative amount of aromatic hydrocarbons obtained when the paraffins are cracked to gasoline products. Thus, the relative proportion of aromatic hydrocarbons obtained tends to decrease with increasing conversion of the feedstock to gasoline. It is known to extract the propane and other paraffin components from the F-T product which is used as the admixture with the feedstock. f30f4ceada
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