Selective hydroconversion of naphthalenes into light alkyl-aromatic hydrocarbons

Abstract

2-Ring aromatics such as naphthalene and alkyl-naphthalenes constitute a high fraction in the diesel boiling point range by-products from oil refining and petrochemical plants. A two-step catalytic process, consisting of a selective hydrogenation of naphthalenes to tetralins and a subsequent hydrocracking of tetralins into light alkyl-aromatic hydrocarbons rich in BTX (benzene, toluene, xylenes), was postulated and studied in a fixed bed down-flow reactor under a moderate pressure of 3–4MPa. For the selective hydrogenation of naphthalenes to tetralins, it was found that the catalytic performances of Mo2C-supported catalysts were superior in terms of tetralins yield as well as selectivity to the conventional metal-supported catalysts such as Pt, Co, Ni and NiW supported catalysts. The hydrocracking of tetralin was demonstrated to produce light alkyl-aromatic hydrocarbons rich in BTX over a monofunctional H-Beta and a bifunctional Ni/H-Beta catalyst. For the high per pass yield of BTX in the hydrocracking of tetralin in which chemical equilibrium limits its conversion and product selectivity, the bifunctional Ni/H-Beta catalyst was found to be highly promising compared with the monofunctional H-Beta catalyst. The bifunctional Ni/H-Beta showed the BTX selectivity in liquid product and the total BTX yield as high as 69.5% and 40.7wt%, respectively, at the tetralin conversion of 99.5% at 450°C under 4MPa. The catalytic behavior of Ni/H-Beta suggests that BTX yield can be much improved by properly controlling the hydrogenation power of metallic sites (i.e., suppressing the hydrogenation activity), the acidity of H-Beta and their balance on the bifunctional hydrocracking catalysts.