Conversion, Liquid Yield, Coke Content

The chemical character of liquid products usually coincides with that of gaseous ones. The gaseous products over clay catalysts are predominantly alkenes compared with alkanes over US-Y [16, 17]. Similarly over ZSM-5 gaseous products are predominantly alkenes, although more aromatics are formed too [8]. 

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In vacuum residue, the metals content can be very high - sometimes more than 200 wppm nickel-plus-vanadium. In an FCC unit, these metals are bad news. Nickel increases coke formation and decreases liquid yields. Vanadium reduces conversion, decreases liquid yields, and destroys the catalyst. For these reasons, refiners pretreat the residue in a hydrotreater before sending it on to the FCC. 

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