Characterization of Sulfur-Containing Compounds in Petroleum Using AgSbF₆ as a Methylation Reagent

Yafen Ge, Jianxun Wu, Yahe Zhang, Yongmei Liang, and Quan Shi*

State Key Laboratory of Heavy Oil Processing, Petroleum Molecular Engineering Center(PMEC), China University of Petroleum, Beijing 102249, PR China

^{*Corresponding Author: E-mail: sq@cup.edu.cn; Tel: +86 010 89739157}

DOI: 10.1021/acs.energyfuels.0c01987

Keywords: components; electrospray-ionization; identification; molecular characterization; oil; resonance mass-spectrometry; separation

Abstact: Molecular characterization of sulfur-containing compounds in petroleum is of great significance for not only the oil refining but also geochemical application. One practical approach for the characterization is to convert nonpolar sulfur compounds into methyl sulfonium with methyl iodide/AgBF₄ and to analyze them by electrospray ionization high-resolution mass spectrometry. However, the derivatization requires a very long reaction time, which limits the wide application of this method. In this study, we proposed a new derivatization reagent, silver hexafluoroantimonate (AgSbF₆), which can significantly reduce the reaction time. The method was validated by model sulfur compounds and successfully applied on the crude oil and diesel fraction. A comparison between AgBF₄ and AgSbF₆ was conducted to evaluate the advantages of this method. The new reagent provides a high conversion yield and low structural discrimination and, thus, can be used to characterize a trace amount of refractory sulfur compounds in deep hydrodesulfurization fuels. In addition, a quick methylation can be more useful for selective separations of thiophenes and sulfides from petroleum fractions than the methylation/demethylation method.