Synergism of Pt/.gamma.-Al2O3 and Pt/.beta. Zeolite in the Reforming of Naphthenes

Abstract

Composite catalysts of Pt supported on both zeolite [beta] and [gamma]-Al[sub 2]O[sub 3] are employed for the reforming of methylcyclopentane and methylcyclohexane. Due to its relatively high Pt dispersion, Pt/[gamma]-Al[sub 2]O[sub 3] is responsible for dehydrogenation reactions leading to methylcycloolefins. Pt/[beta] zeolite, which has a much higher Bronsted acidity than [gamma]-Al[sub 2]O[sub 3],is responsible for the bimolecular alkylation reactions leading to aromatics, the transalkylation reactions of aromatics, and the isomerization reactions of methylcycloolefins to C[sub 6] cycloolefins which further via dehydrogenation lead to benzene. The residence time plays an important role because the dehydroisomerization reactions are much slower than the bimolecular alkylation reactions. At a high residence time and with methylcyclopentane as feed, the composites generate a synergistic effect which leads to a maximum in the benzene yield at about 40 wt % Pt/[beta] zeolite. With methylcyclohexane as feed, high aromatic (mainly toluene) yields are obtained for zeolite contents below 30 wt %. Bimolecular alkylation reactions, which are stimulated by the zeolite pore structure and the high Bronsted acidity of zeolite [beta], also occur and lead to aromatics with a larger number of carbon atoms than the feed naphthene and to a better utilization Of C[sub <6] olefins and paraffinsmore » generated by cracking. Beneficial effects can be achieved by balancing the acidic with the dehydrogenation functions of a reforming catalyst through the incorporation of Pt/[beta] zeolite into Pt/[gamma]-Al[sub 2]O[sub 3].« less