Characterization of Asphaltene Deposits by Using Mass Spectrometry and Raman Spectroscopy

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• 作者：James S. Riedeman ; Naveen Reddy Kadasala ; Alexander Wei ; Hilkka I. Kenttämaa
• 刊名：Energy & Fuels
• 出版年：2016
• 出版时间：February 18, 2016
• 年：2016
• 卷：30
• 期：2
• 页码：805-809
• 全文大小：262K
• ISSN：1520-5029

文摘

Crude oil deposition in oil transfer pipelines and bore wells afflicts many oil reservoirs. Asphaltenes play a major role in this process because of their tendency to precipitate in pipelines upon changes in temperature and/or pressure. Asphaltenes are defined by their lack of solubility in n-alkane solvents, which means that they likely contain many compounds that do not actively contribute to the deposition of crude oil in pipelines. The preponderance of studies in the literature have focused on asphaltenes derived from crude oil, whereas far fewer investigations have focused on asphaltenes derived from oil deposits. In this study, structural parameters of oil-deposit asphaltenes were examined using Raman spectroscopy and tandem mass spectrometry and compared to results reported previously for petroleum asphaltenes. On the basis of D1 and G band intensities in the Raman spectrum of oil-deposit asphaltenes, the average aromatic sheet size of these molecules was 21.0 Å, slightly larger than earlier values reported for petroleum asphaltenes (15.2–18.8 Å). Mass spectrometric experiments of oil-deposit asphaltenes ionized via atmospheric pressure chemical ionization (APCI) using CS₂ solvent were used to measure the molecular weight distribution (MWD), saturated carbon content, and the number of fused aromatic rings in the cores of the asphaltene molecules. The MWD was found to be 150–1050 Da with an average molecular weight (average M_W) of 497 Da, which are significantly lower than those reported previously for petroleum asphaltenes (200–1500 Da and 570–700 Da, respectively). Aromatic core sizes were estimated to contain 8 fused rings on average for the most abundant species in oil-deposit asphaltenes, with 5–15 carbons in their alkyl side chains, as compared to averages of 3–7 aromatic rings and 17–41 alkyl carbons for petroleum asphaltenes.