Selective dealkylation of alkyl polycyclic aromatic hydrocarbons towards innovative upgrading process of practical heavy oil

Abstract

The dealkylation of alkyl polycyclic aromatic hydrocarbons (APAHs) in vacuum gas oil (VGO) was studied as a novel upgrading process alternative to conventional processes. A silica-monolayer loaded on alumina (SMA) with weak Brønsted acid sites and large pore size exhibited higher activity than amorphous silica-alumina and zeolites (USY and ZSM-5). The SMA almost completely converted the APAHs into aromatics and alkanes, but a small amount of APAHs with methyl and ethyl groups (short-chain) were unreacted. The larger pore size of the SMA was proposed to be enough for bulky APAHs to diffuse. The dealkylation by the SMA formed large amounts of long-chain alkanes, which can be utilized as light oil and kerosene for fuel, lubricating oil, etc. The cracking of long-chain alkanes did not proceed, and thus scarcely formed lighter alkanes. The SMA in the reaction adsorbed alkanes but did not form coke, and therefore exhibited continuous dealkylation activity. Additionally, it was revealed that the pore size of the SMA slightly affected the composition of the formed alkanes.