Low temperature hydrocracking of 9, 10-dihydrophenanthrenes over Brønsted acidic Y zeolites

Facing the escalating challenge of processing heavier and lower-quality crude oils, the utilization of light cycle oil (LCO) derived from fluid catalytic cracking units is constrained by its high aromatic content. The transformation of LCO into lighter aromatic hydrocarbons through catalytic conversion emerges as a more advantageous and valuable strategy, addressing the surplus of diesel and the scarcity of light aromatics. Consequently, the hydroconversion of 9,10-dihydrophenanthrenes (9,10-DHP), serving as a representative molecule of polycyclic aromatic hydrocarbons (PAHs), over metal-free zeolite Y catalysts with varying acidity, has been investigated in a stirred batch reactor. The experiments were conducted at temperatures ranging from 250 to 350 ℃ under a pressure of 4.0 MPa. The study delved into the impact of reaction temperature and the Brønsted acidity of zeolite Y on the reaction pathway. Product analysis revealed the formation of a diverse array of products, including biphenyls, naphthalenes, tetralins, indanes, alkylbenzenes, benzene, and minor alkanes, during the hydrocracking of 9,10-DHP. The reaction pathway for the hydrocracking of 9,10-DHP to monocyclic aromatic hydrocarbons (MAHs) over acidic zeolite Y was proposed to follow two potential routes: one involving hydrogen transfer leading to the formation of phenanthrene and tetrahydrophenanthrene, followed by terminal ring opening; the other characterized by a direct central ring opening. The interplay between these two pathways is contingent upon the reaction temperature and the acidity of the employed zeolite. Promoting central ring opening and suppressing hydrogen transfer can be realized by manipulating the reaction temperature and enhancing the acid density of the zeolite. However, excessive hydrogenation and cracking are observed with further increases in reaction temperature. Additionally, augmenting the strength of acidic sites is beneficial for ring opening and isomerization of hydrogenated aromatics, as well as dealkylation to produce MAHs. The findings underscore a promising approach for the design of PAHs hydrocracking catalysts and reaction techniques.