Reaccoes de Misturas Binarias de Olefinas Leves com Parafinas sobre o Zeolito USHY

The aim of the present work is to contribute to the understanding of the influence of high concentrations of light olefins on the transformation of paraffins over USHY zeolite. The catalytic behaviour observed during transformation of binary mixtures (olefin + paraffin) of ethene, propene and 1-butene, with n-hexane, n-heptane and methylcyclohexane, is studied at 623 K using different partial pressures of each reactant in the mixtures. This study has revealed differences on the catalytic behaviour associated with the structure and the chain length of the molecules of each hydrocarbon. The relative reactivity over USHY zeolite obtained for the different pure hydrocarbons follows the sequence: n-hexane<ethene<n-heptane<methylcyclohexane<propene<1-butene. It was concluded that the magnitude of this relative reactivity determines the kind of interaction between the olefin and the paraffin molecules present in the mixture as what concerns the possible reaction processes at the surface of the zeolite. This study brought a significant evidence that the influence of light olefins on the transformation of paraffins over USHY zeolite depends on the following variables: structure and chain length of paraffin molecules, partial pressure of olefin and paraffin in the feed mixture, and chain length of olefin molecules. This work also presents a new semi-lumped dynamic molecular model for the simulation of the ensemble of reactions taking place during the global process of catalytic cracking of paraffins. The computer algorithm developed involves simulation of the reaction network that takes into account pure cracking, chain growth and chain transfer elementary reactions, between all the present gas phase and adsorbed species, and is detailed to the carbon atom number level. Despite the assumptions considered, this approach provides a good qualitative and semi-quantitative agreement between experimental results and simulated results predicted for the cracking of n-heptane, suggesting that the simplified structure of this version of the model is adequate and promisingAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga