(509aq) A Reaction Model for the Hydroconversion of 2-Methylnaphthalene Over Pt/mordenite Catalysts
Catalytic hydroconversion is an attractive secondary conversion process in the modern refinery to get more valuable products as well as clean atmosphere from heavier petroleum fractions. An example is the Light Cycle Oil (LCO) fraction, a by-product from catalytic cracking, which is normally high in sulfur, nitrogen and particularly in polyaromatics. This material usually in the same boiling range as diesel can be used as a diesel-blending component only after hydrotreating. LCO is rich in multi-ring aromatics, which will produce fuel with very low cetane number. Upgrading LCO to higher cetane number fuels or to hydrocarbons in the gasoline boiling range requires hydrogenation of multiring aromatics and then rings opening. Therefore, a bifunctional acid/metal catalyst is necessary in order to promote the hydroconversion reactions. Metal/acid zeolite catalysts are bifunctional catalysts widely used in petroleum refining, especially in hydrocracking and hydroisomerization processes. Highly active sulphur resistant catalysts have been recently developed, mainly based on Pt, Pd, or mixtures of both, supported on acidic carriers. On these catalysts, the transformation of hydrocarbons involves the hydrogenation and dehydrogenation steps on metal sites and rearrangement and/or cracking steps on acid sites, plus the step of migration of the reaction intermediates from metal to acid sites. Therefore, the number and characteristics of the metal and acid sites will determine the activity and selectivity of bifunctional catalysts. Indeed, it has been shown clearly that the balance between metal and acid sites influences remarkably the performance of bifunctional catalysts in the hydroconversion of different hydrocarbons such as n-paraffins, naphthenes and aromatics. However, the studies regarding the hydroconversion of polyaromatics and the effect of the acid/metal balance over the activity and selectivity are scarce. In this study, the effect of the acid/metal ratio of Pt/mordenite catalysts over the activity, selectivity and main reaction pathways, during the hydroconversion of 2-methylnaphthalene is analysed. In addition, a reaction model, based on the single-event concept, is also proposed in order to explain the product distribution of the main groups of hydrocarbons during the hydroconversion of 2-methylnaphthalene.
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