Selective ring opening of naphthenes: From mechanistic studies with a model feed to the upgrading of a hydrotreated light cycle oil

The catalytic hydroconversion of desulfurized and dearomatized light cycle oil (DeAr-LCO) with a Cetane Index (CI) of 41.7 was investigated at 7.0 MPa and in the temperature range from 290 to 350 °C in a down-flow fixed bed reactor. Two catalysts made up, respectively, of 3 wt% iridium and 4 wt% platinum loaded on Y zeolite exchanged with Na were used. The hydroconversion of DeAr-LCO over the above-mentioned catalysts resulted in a remarkable change of chemical structure of the feed with a strong decrease of condensed naphthenic structures and a concomitant increase of alkyl substituted cyclohexanes and open-chain alkanes. In the case of tests carried out with the platinum-based catalyst the alkanes concentration passed from 21% in the feed to 44% in the product obtained at the highest conversion levels. GCxGC-MS analyses showed that the hydrocracking associated with the hydroconversion process was relatively modest and that the observed changes in chemical composition were mainly the consequence of the selective ring opening pathway of naphthenic structures. The results clearly show that along with the changes in chemical structure during hydroconversion the products are characterized by a higher CI. For the platinum- and iridium-based catalysts an increase of CI of 11 and 7 units, respectively, was observed at a gasoil yield of 80 wt%. The positive results indicate that the use of a metal function with a high hydrogenolytic activity and selectivity coupled with a properly tuned concentration and strength of the Brّnsted acidic sites can lead to remarkable improvements in the cetane properties of gasoil cuts. The practical consequence of this result is the possibility of upgrading aromatic-rich streams to products meeting the current Cetane Number specification of gasoil.