Kinetic Modeling of the Thermal Cracking of a Brazilian Vacuum Residue

Abstract

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.

Predictive correlations for thermal upgrading of petroleum residues

“…As pressure is increased, dry gas production is suppressed due likely to an effect of thermodynamic equilibrium and susceptibility of higher holdups of light species to undergo secondary reactions [8]. Recently, similar trends were observed [35] for a vacuum residue which underwent increased conversions and raised liquid productions when the reaction pressure was increased systematically. However, the exact role of pressure in the thermal upgrading of different heavy residues, including the reaction conversion itself, can somehow appear far from our intuitive expectation and still stands in need of further determination.…”

A Review of Thermal Cracking, Hydrocracking, and Slurry Phase Hydroconversion Kinetic Parameters in Lumped Models for Upgrading Heavy Oils

“…Specific gravity is a good measure of how heavy a petroleum liquid is, with a value of >1 defining an extra heavy oil. Figure concerns the residue feedstocks used in the kinetic models considered here. ,,− It gives the frequency distribution for feedstock specific gravity for the three types of process studied. The widest range of feedstocks has been used to research thermal cracking while the heaviest liquids were used in studies into slurry phase hydroconversion.…”

Experimental Evaluation and Kinetic Modeling of Thermal Upgrading of Iranian Heavy Crude Oil

“…The computed pre-exponential parameter and activation energies agree well with those reported in earlier publications. 17,18,20 To assess quality of the optimum found by the above-mentioned method, in Figure 7 variation of objective function versus deviation of each parameter from optimum is plotted. As shown, zero deviation from optimum yield the lowest amount of objective function.…”

“…Kinetic parameters for thermal cracking of selected compounds are already available in various publications. − In addition to that, upgrading experiments on some specific heavy oils have yielded useful information regarding their kinetic parameters. − In these studies the whole spectrum of feed and possible products is discretized into few pseudocomponents (lumps) based on boiling range or molecular structure of the involved components. The heavier pseudocomponents are then assumed to follow a set of serial/parallel reactions to form lighter pseudocomponents.…”