The thermal cracking of a vacuum
residue from a Brazilian refinery
was studied in a continuous pilot plant. Reaction runs were carried
out at 440–520 °C, 446–1825 kPa, and space times
of 23–69 s. Reaction products were lumped into gas, naphtha,
light gas oil (LGO), and heavy gas oil (HGO). The increase of the
reaction pressure increased the residue conversion and the product
yields. A power law kinetic modeling of the experimental data was
performed, comprising first-order irreversible reactions. Two reaction
schemes were evaluated: the first scheme consisted of four parallel
reactions (one for each product lump), and the second scheme included
the consecutive conversion of HGO in LGO. Kinetic parameters were
estimated taking into account the experimental error. In the parallel-reaction
scheme, almost all estimated parameters were statistically significant
(except for the small gas formation at the highest pressure). The
LGO and HGO formation reactions presented lower activation energies
and higher rate constants. Inclusion of the consecutive reaction led
to parameters without statistical significance for all reaction conditions.
Furthermore, empirical correlations from the literature were fitted
to the product yield data as a function of the process severity. The
severity index was modified to include the effect of pressure explicitly,
providing a slight improvement of the correlations.
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