Hydrogenolysis of methylethylbenzenes to xylenes : study of p-MEB over NiMo/Al₂O₃ catalyst

Abstract

Due to the recent specifications for gasoline requiring less aromatic content, a large quantity of C₉⁺ aromatics produced from pygas upgrading has become surplus and, therefore, available as a new source of benzene, toluene, and xylenes (BTX) production. One attractive route to convert C₉⁺ aromatics to high value-added products is the hydrogenolysis reaction. In this research, the study of methylethylbenzenes converted into xylenes via hydrogenolysis reaction was focused by using p-methylethylbenzene (p-MEB) as a model feed. The catalytic activity of NiMo/Al₂O₃ commercial catalyst was carried out in a continuous flow fixed bed reactor under various conditions: reaction temperature (350-500°C), pressure (50 psi), H₂/feed ratio (4-10), and an LHSV (2-4 h⁻¹). Moreover, the synthesized Mo/y-Al₂O₃, Ni/y-Al₂O₃ , and NiMo/y- Al₂O₃ were also studied. It was found that among four different types of catalyst, the commercial NiMo/ Al₂O₃ catalyst gave the highest toluene selectivity from hydrogenolysis of ethylbenzene. The optimum condition for hydrogenolysis of p-MEB over the commercial Ni- Mo/ Al₂O₃ was attained at 400°C, 50 psi, H₂/feed of 8 molar ratio, and LHSV of 2 h⁻¹. The results showed that p-MEB was hydrogenolyzed into p-xylene, toluene, and ethylbenzene, with the major product of p-xylene. It was observed that a primary hydrogenolysis of p(-MEB resulted in p-xylene as a major product while a secondary one yields toluene which is also produced via deethylation reaction. Ethylbenzene was also observed from dealkylation of methyl groups attached to the aromatic rings. It was apparent that the commercial NiMo/Al₂O₃ catalyst is suitable for the primary hydrogenolysis of p-MEB under the optimum condition.