Characterization of heteroatoms in residue fluid catalytic cracking (RFCC) diesel by gas chromatography and mass spectrometry

Quan Shi,^*,† Chunming Xu,^† Suoqi Zhao,^† and Keng H. Chung^‡

^†State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, People’s Republic of China, and^‡Department of Chemical and Petroleum Engineering, The University of Calgary, 2500 University Drive Northwest, Calgary, Alberta T2N 1N4, Canada

Corresponding Author: Email: sq@cup.edu.cn

DOI: 10.1021/ef900783z

Keywords: Aromatic compounds; Chromatography; Hydrocarbons; Ions; Nitrogen compounds

Abstract: Nitrogen-, sulfur-, and oxygen-containing hydrocarbons in a residue fluid catalytic cracking (RFCC)-derived diesel were characterized by a gas chromatograph equipped with a pulsed flame photometric detector and an electron impact, ammonia chemical ionization mass spectrometer. Caustic and acid extractions on RFCC diesel were performed to isolate the phenolic and basic nitrogen compounds, respectively. The fraction of RFCC diesel that contained the basic nitrogen compounds was reacted with acetic anhydride to allow for chromatographic separation of amino-aromatic compounds from the rest of the non-reactive basic nitrogen compounds. The majority of basic nitrogen compounds were anilines, as expected. Non-basic nitrogen compounds in RFCC diesel were alkyl indoles and alkyl carbazoles. Double-ring and poly-aromatic amines were identified in RFCC diesel by the acetylation reaction. The majority of sulfur compounds in RFCC diesel were alkyl benzothiophenes and dibenzothiophenes, after being isolated by Pd²⁺ ligand-exchange chromatography. Dihydrobenzohiophenes and dihydronaphthanthiophenes, despite a low concentration, were also identified in the subfractions. The majority of oxygen compounds in RFCC diesel were phenolic compounds. In addition to alkylphenols, bicyclic and polycyclic phenols were identified and characterized in the acidic fraction.