MECHANISM OF AROMATIC HYDROCARBON FORMATION IN FCC NAPHTHA

A microactivity test study of the FCC naphtha composition at increasin g conversions was carried out. At low conversions (ca. 10-20%), the na phtha is rich in olefinic and aromatic hydrocarbons. As the conversion increases, the composition changes dramatically. The olefins initiall y increase and then decrease sharply. The paraffins increase continual ly, and the aromatics initially decrease and then increase slightly. T he naphthenics remain constant in the conversion range studied. These results indicate that, at low conversions, the aromatics in the gasoli ne are mainly formed by dealkylation of heavy aromatic molecules prese nt in the feed. At higher conversions, however, the aromatics in the n aphtha are mainly formed by cyclization followed by hydrogen transfer of the olefins formed during cracking. This reaction also increases th e relative concentration of paraffinic hydrocarbons. The distribution of C9 aromatics showed that, as the conversion increases, there occurs an isomerization of the alkyl chain, to increase the branching of the ring.