Page 231 - Fluid Catalytic Cracking Handbook

Products and Economics 199

DO is the lowest priced product and the goal is to reduce its yield,
The DO's yield largely depends on the quality of the feedstock and
the conversion level. Naphthenic and aromatic feedstocks tend to yield
more bottoms than paraffinic feedstocks. If the conversion is in the
low- to mid-70's, increasing catalyst-to-oil ratio or using a catalyst
with an active matrix can reduce slurry yield. Raising conversion
reduces bottoms yield. If the conversion is in the 80's, little more can
be done to reduce bottoms yields.

Decant Oil Quality

DO properties vary greatly depending on the feedstock quality and
operating conditions.
Selling the DO as CBFS yields a better return than selling it as
cutter stock. To meet the CBFS specification, DO must have a mini-
mum Bureau of Mines Correlation Index (BMCI) of 120 and a low
ash content (Table 6-2). Aromaticity and ash content are the two most
important properties of CBFS.

Table 6-2
Typical Carbon Black Feedstock Specifications

Property Specification
Gravity, °API 3.0, maximum
Asphaltenes, wt% 5.0, maximum
Viscosity, SUS @ 210°F (98.9°C) 80, maximum
Sulfur, wt% 4.0, maximum
Ash, wt% 0.05, maximum
Sodium, ppm 15, maximum
Potassium, ppm 2, maximum
Flash, °F 200, (93.3°C) minimum
BMCI* 120, minimum

*Bureau of Mines Correlation Index (BMCI)
BMCI = (87,552/T) + [473.7 x (141.5/131.6 + °AP1 Gravity)] - 456.8
Where:
T = Mid boiling point, °R
For Example:
T = 7!0°F (376.7°C) = 7JO°F + 460 = 1I70°R
"API = 1.0
BMCI = 23.9