Page 71 - Fluid Catalytic Cracking Handbook

FCC Feed Characterization 41

coke-making tendency of a given feed. Associated with this 900°F+
fraction is a higher level of contaminants such as metals and nitrogen.
As discussed later in this chapter, these contaminants deactivate the
catalyst and produce less liquid product and more coke and gas.
Distillation data is the backbone of FCC feed analyses. As will be
shown, published correlations use distillation data to determine the
chemical composition of FCC feed.

Aniline Point

Aniline is an aromatic amine (C 6H 5NH 2). When used as a solvent,
it is selective to aromatic molecules at low temperatures, and paraffins
and naphthenes at higher temperature. Aniline is used to determine
aromaticity of oil products, including FCC feedstocks. Aniline point
(AP) is the minimum temperature for complete solubility of an oil
sample in aniline.
ASTM D-611 involves heating a 50/50 mixture of the feed sample
and aniline until there is only one phase. The mixture is then cooled
and the temperature at which the mixture becomes suddenly cloudy
is the aniline point. The test senses solubility via a light source that
penetrates through the sample.
The aniline point increases with paraffinicity and decreases with
aromaticity. It also increases with molecular weight. Naphthenes and
olefins show values that lie between those for paraffins and aromatics.
Typically, an aniline point higher than 200°F (93°C) indicates paraffinicity
and an aniline point lower than 150°F (65°C) indicates aromaticity.
Aniline point is used in some correlations to estimate the aromaticity
of gas oil and light stocks. TOTAL'S [1] correlation uses aniline point
and refractive index. Others, such as n-d-M [2], employ refractive
index to characterize FCC feed.

Refractive Index

Similar to aniline point, refractive index (RI) shows how refractive
or aromatic a sample is. The higher the RI, the more the aromatics
and the less crackable the sample. A feed having an RI of 1.5105 is
more difficult to crack than a feed with an RI of 1.4990. The RI can
be measured in a lab (ASTM D-1218) or predicted using correlations
such as the one published by TOTAL.