Catalytic cracking of three-ring polycyclic aromatic hydrocarbons in the presence of hydrogen donors

Abstract

Catalytic cracking of three-ring polycyclic aromatic hydrocarbons (PAHs) in the residue fluid catalytic cracking (RFCC) process was investigated. Catalytic cracking of mixtures of three-ring PAHs and various model hydrocarbons was carried out using RFCC equilibrium catalysts. Most of the three-ring PAHs were converted to coke in the absence of hydrogen donors, whereas coke formation was suppressed and decomposition of three-ring PAHs was promoted in the presence of aliphatic hydrocarbons, saturated rings, and aromatic ring side chains. Three-ring PAHs were first converted to noncondensed two-ring PAHs and subsequently decomposed to monocyclic aromatic hydrocarbons and condensed two-ring PAHs. This reaction can be depicted by partial hydrogenation of three-ring PAHs by hydrogen transfer reaction with coexisting hydrogen donors and sequential cracking of saturated rings. When a hydrogen donor was sufficiently present, cracking of saturated rings was the rate-determining step, and the reaction can be accelerated by increasing the reaction temperature or using a catalyst with a high acid content. These results are expected to lead to the effective utilization of heavy oil by promoting PAH cracking in the RFCC process.