Page 104 - Fluid Catalytic Cracking Handbook

FCC Feed Characterization 81

can
index at any given temperature, the RI (2o) be calculated from the
following equation. Example 2-5 illustrates the use of the equation.

RI (2m = RI(t) + 6.25 x (t - 20) x 10" 4

t = temp, °C

Example 2-5

With the refractive index @ 78°C = 1.4810, determine the refrac-
tive index @ 20°C.

RI (2()) = 1.4810 + 6.25 x (67 - 20) x 10" 4

RI (20) = 1.5104

(Note that the calculated RI (20) closely matches that using the TOTAL
correlation.)

Pretreatment of FCC feedstock through hydroprocessing has a
number of benefits including:

• Hydrodesulfurization (HDS)
• Hydrodenitrogenation (HDN)
• Hydrodemetallization (HDM)
• Aromatic Reduction
• Conradson Carbon Removal

Desulfurization of FCC feedstocks reduces the sulfur content of FCC
products and SOX emissions. In the United States, road diesel sulfur
can be 500 ppm (0.05 wt%). In some European countries, for example
in Sweden, the sulfur of road diesel is 50 ppm or less. In California,
the gasoline sulfur is required to be less than 40 ppm. The EPA's
complex model uses sulfur as a controlling parameter to reduce toxic
emissions. With hydroprocessed FCC feeds, about 5% of feed sulfur
is in the FCC gasoline. For non-hydroprocessed feeds, the FCC
gasoline sulfur is typically 10% of the feed sulfur.