Hydroconversion of a model mixture and fluid catalytic cracking gasoline for octane enhancement. Main reaction pathways over monofunctional HZSM5(x)-alumina catalysts

The changes in RON and liquid yield during the hydroconversion of an n-hept ane-benzene-toluene mixture were evaluated in a continuous high-pressure fl ow reactor using HZSM5(x)-alumina catalysts with variable contents of zeoli te. The results from these experiments were compared with those obtained wi th a real fluid catalytic cracking (FCC) hydrotreated gasoline as the feeds tock. An increase in the zeolite concentration altered the acid properties of the catalysts that showed a gradual increase in the intensity of the 361 2 cm(-1) IR band, associated with the internal strong Bronsted acid sites o f the zeolite. The hydroconversion results;show that increasing the zeolite content in the catalyst leads to a gradual increase in both the RON number of the liquid product and the amount of light hydrocarbons (less than or e qual toC(4)), promoted mainly by secondary cracking and dealkylation reacti ons. Because of this opposite trend df RON and liquid yield, zeolite conten ts higher than 10 wt % led to an almost constant barrel-octane (RON x fract ional liquid yield). The catalytic experiments:with the synthetic mixture a s the feedstock show that the main reactivity is associated with the cracki ng of n-heptane and with alkylation bf the aromatics by olefins produced du ring n-heptane cracking. Additionally, other reaction pathways that lead to the production of small amounts of n-paraffins (other than n-heptane), iso paraffins, cycloparaffins, and, to a lesser extent, olefins are observed. T he main reaction pathways,leading to higher RON with the hydrotreated FCC g asoline as the feedstock seem to be similar to those observed with the synt hetic mixture.