Characterization of Acidic Compounds in Heavy Petroleum Resid by Fractionation and Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Analysis

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• 作者：Litao Wang ; Chen He ; Yahe Zhang ; Suoqi Zhao ; Keng H. Chung ; Chunming Xu ; Chang Samuel Hsu ; Quan Shi
• 刊名：Energy & Fuels
• 出版年：2013
• 出版时间：August 15, 2013
• 年：2013
• 卷：27
• 期：8
• 页码：4555-4563
• 全文大小：618K
• 年卷期：v.27,no.8(August 15, 2013)
• ISSN：1520-5029

文摘

Negative-ion electrospray ionization (ESI) enabled the direct mass spectrographic analysis of phenols, naphthenic acids, and neutral nitrogen compounds in petroleum fractions without prefractionation; however, ESI results provide few quantitative and structural information about the analytes: the composition of acidic compounds in heavy oil, such as distillate resid, is still unclear. In this study, extrography was used to fractionate oilsands bitumen-derived vacuum-topped bitumen (VTB) and its maltene and asphaltene fractions into multiple subfractions. The molecular compositions of acidic functional compounds in the VTB and its subfractions were analyzed by negative-ion ESI Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Extrographic separation was a necessary step to isolate acidic compounds of various acidities and/or polarities in vacuum resid fractions to achieve a systematic analysis. The results showed that the O₂ class species in VTB were highly condensed phenols and carboxylic acids. The maltene fraction contained most of the less condensed naphthenic acids, whereas the asphaltene fraction contained highly condensed carboxylic acids and phenolic compounds with a bouble-bond equivalent (DBE) higher than 6. The presence of acids had no significant impact on the yield of asphaltenes in n-C₇ solvent precipitation. Acid-free asphaltene fractions, which account for more than 90 wt % of the asphaltenes, cannot be ionized by negative-ion ESI.