ASSESSMENT OF HYDROCARBON ADSORPTION CONSTANTS UNDER REACTION CONDITIONS

AVILA, ADOLFO; BIDABEHERE, CLAUDIA; SEDRAN, ULISES

Rio de Janeiro, Brasil

Congreso; ENPROMER; 2005

Universidad Federal do Rio de Janeiro

The assessment of adsorption parameters in heterogeneous catalytic systems under realistic conditions is subjected to serious limitations due to the simultaneous existence of diffusion and reaction. The knowledge of these parameters is particularly important for design and simulation purposes in some processes like, for example, the stripping step in the catalytic cracking of hydrocarbons. The fluidized bed, stirred batch laboratory reactor called Riser Simulator is an useful tool for experiments where injections of pure compounds or mixtures are contacted with the catalyst for a short time, pressure evolutions are recorded, and system compositions are determined by GC analysis. Experiments were performed with pure hexane, decane and toluene, using different reactant concentrations on an equilibrium commercial catalytic cracking catalyst at temperatures between 250 and 350 ºC. The constants were assessed by calculating the masses of hydrocarbons that are adsorbed on the catalyst and that are present in the gas phase at equilibrium with the catalyst. Results showed that the order of adsorption was decane > toluene > hexane. At the highest temperature (350 ºC), some conversion was observed in the case of decane. Results were consistent, and they were explained based on a heterogeneous model that shows that apparent adsorption constants depend not only on well known parameters such as temperature, but also on the ratio between solid and gas volumes and the contact time. Also a link was established with a previous model of diffusive transport in zeolite solids.