(476ai) Hydroconversion of 2-Methylnaphthalene on Pt/Mordenite Catalysts. Effect of the Acid/Metal Balance of the Catalyst over the Main Reaction Pathways
Nowadays there is a global shift toward higher quality fuels, along with an increasing necessity for upgrading the low-value fuel streams. An example is the Light cycle Oil (LCO) a by product from catalytic cracking, which is normally high in sulfur, nitrogen and particularly in polyaromatics. This material usually in the same boling 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 it is necessary to use a bifunctional acid/metal catalyst in order to promote the hydroconversion reactions. Metal/acid zeolite catalysts are bifunctional catalysts widely used in petroleum refining, especially in hydrocracking and hydroisomerization. On these catalysts the transformation of hydrocarbons involves the hydrogenation and dehydrogenation steps on metal sites and the rearrangement and/or cracking steps on acid sites, plus the step of migration of the reaction intermediates from metal sites to acid sites. Therefore the activity and selectivity of bifunctional catalysts will be determined by the characteristics of the metal sites and the acid sites. Indeed, it has been shown very 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. Therefore in this study we analyze the effect of the acid/metal balance of Pt/mordenite catalysts over the activity, selectivity and main reaction pathways, during the hydroconversion of 2-methylnaphthalene. The hydroconversion experiments were performed over pre-reduced Pt/mordenita catalysts. The acid/metal balance of the catalyst was modified by changing the metal content (0.05-1.0 wt% Pt) and the SiO2/Al2O3 molar ratio (12 and 20). The catalytic experiments were conducted in a well stirred 500 ml batch reactor (Parr instruments 4570/80) using a solution containing 3 wt % of 2-methylnaphthalene in n-decane. The reaction temperature was 523 K and the operating hydrogen pressure of 600 lb/in2. The reaction products were analyzed by gas chromatography and the identification performed by mass spectrometry. The catalysts were also characterized by XRD, 27Al-NMR, TEM and pyridine-FT-IR. The results of the hydroconversion experiments indicated the main reaction pathways during the hydroconversion of 2-methylnaphthalene were: one or two ring hydrogenation, isomerization of 2-methylnaphthalene, ring contraction, ring opening and cracking. A catalyst with a more acid character (higher acid/metal balance) diminishes the catalytic activity and shifts the selectivity to heavy C11+ products. Whereas a catalysts with a low acid/metal balance increases the catalytic activity and favors the selectivity to high value products, in fact a stronger hydrogenation function on the catalyst increases the rate of hydrogenation leading to methyltetralines, and methyldecalines followed by isomerization and ring opening to produce alkylindanes, alkylaromatics and alkyl-cycloalcanes.