Petroleum is made of different compounds and its characterization is very difficult. In addition to being a complex mixture of hydrocarbons its composition also depndes on its origin. This research is part of a study that aims to develop a computational/experimental model for the characterization of petroleum and some of its fractions, such as fuel oil from the Fluid Catalytic Cracking (FCC) process.

This work presents a kinetic study for the catalytic cracking of three model molecules (1 octene, 2,2,4 trimethylpentane and n octane) on the surface of two types of commercial FCC catalysts made of USY zeolite supplied by PETROBRAS (without rare earth (STR) and with rare earth (CTR)) deactivated by steam. The main objectives are:

1. propose a reaction mechanism that takes into account the adsorbed species on the acid solid surface;

2. establish the kinetics parameters;

3. describe the catalytic behavior of the catalyst using model molecules that are present in a petroleum fraction, to validate a computational model under development.

The cracking experiments were carried out with a fixed bed tubular rector made of quartz, between 325 and 685 K for 1 octene, between 575 and 920 K for 2,2,4 trimethylpentane and between 725 and 975 K for n octane at a total pressure of 1 atm. The mass of catalysts was varied from 0.025 to 0.100 g. A flowrate of 150 ml min-1 of nitrogen (99,99 %) was injected in a reservoir at 305 K containing the model compound with the use of a sparger. The reactants are subsequently sent to a condenser maintained at 300 K. The saturated gas was then fed into the tubular reactor containing the solid catalyst.

The main products obtained from the cracking of 1 octene were 4 octene,(Z)-, 2 hexene 2,3 dimethyl, 3 octene,(Z)-, 4 octene,(E)-, cyclohexane,1,3 dimethyl-cis- and cyclopentane,1 ethyl 2 methyl cis-, corresponding to 99,2 % of the total stream of products. For the cracking of 2,2,4 trimethylpentane the main products were methylcyclopropane, toluene, 2 pentene,3 ethyl, 1 methyl,1 isopropylcyclopropane, 2 butene,2 methyl and 2 pentene,4,4 dimethyl-,(Z)-, corresponding to 98,1 % of the total stream of products. And for the cracking of n octane the main products were trans 1 ethyl 2 methyl cyclopentane, nonane, heptane, decane and 1 pentene,2 methyl, corresponding to 98,0 % of the total stream of products.

The data obtained for the above experimental conditions were: catalytic and thermal conversion, selectivity, rates of reaction, activation energies and the amount of coke deposited on the surface. The compound 1 octene was the most reactive chemical compared with the 2,2,4 trimethylpentane or n octane. The catalytic cracking of 1-octene took place on the lowest range of temperatures studied and no thermal cracking was observed.

To describe the mechanism of formation of the products of catalytic cracking on the catalyst surface, five families of reactions were considered. The families of reactions were: initiation steps, isomerization steps, adsorption/desorption steps, oligomerization/â scission processes and hydride transfer processes. The kinetic model developed was based on these families of reaction and the kinetics parameters were determined.

The model was efficient for the evaluation of the commercial catalysts for the catalytic cracking. It generated a reduced number of products which enabled the proposal of a reaction mechanism and the determination of the reaction that are most important in the formation of the products. In addition, reaction rates, conversion, selectivity and activation energies were also estimated.