Selective hydroconversion of a model mixture and hydrotreated FCC gasoline for octane enhancement

The present study analyzes the catalytic behavior of Metal/HZSM5–Al2O3 catalysts (Metal = Ni, Mo or Pt), in the hydroconversion of a model mixture of n-heptane–benzene–toluene. A systematic study was performed to understand the activity and selectivity properties of the catalysts, and to analyze the relationship between the acid/metal balance of the catalysts and the main reaction paths, with impact on octane enhancement and liquid yield. Finally, the results obtained with the model mixture are contrasted with those obtained using a real hydrotreated FCC gasoline with less than 1.0 wt.% olefins. The main reaction pathways for octane enhancement over monofunctional HZSM5(x)–Al2O3 catalysts are isomerization and cracking of n-heptane, dimerization–cracking of n-heptane, and aromatic alkylation reactions, being the last two routes the most important for producing high octane hydrocarbons. In the presence of a strong metallic function isomerization and cracking of n-heptane, and aromatics hydrogenation reactions are the main routes. In this case octane enhancement is achieved mainly through isomerization reactions. These results indicate that although there is an opposite trend between the RON and liquid yield of the product, it is possible to increase the barrel-octane with the catalysts used here. When a hydrotreated FCC gasoline was used as the feed, the observed changes in RON and liquid yield when the process variables were changed, followed similar trends to those of the synthetic feed, although less drastic. A detailed analysis (PIONA) of the product distribution indicates that for FCC gasoline RON enhancement comes mainly from cracking and isomerization of paraffins and naphthenes, and from the formation of alkylated aromatics. The main reaction pathways in the hydroconversion process leading to higher RON with the synthetic mixture and the real feed are similar.