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

Abstract

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.

Physical and chemical aspects of “precursor films” spreading on water from natural bitumen

“…In the present work, electrospray ionization (ESI) mass spectrometry, in positive and negative modes (i.e., (+)ESI and (-)ESI), has been used to provide an indication of heteroatomic class species in the precursor film compared with the original bitumen. (-)ESI is able to detect phenols, naphthenic acids, and neutral nitrogen compounds without pre-fractionation [24,43], whereas (+)ESI is able to detect basic nitrogen (e.g., pyridine homologs) [24,44]. Fig.…”

“…Unsurprisingly, therefore, interfacial materials are enriched in polar species, and chemical analysis has identified numerous species classes, including carboxylic and hetero-acids [22]. Such species are associated with operational problems, including corrosion, catalyst poisoning, deposit formation and emulsion stabilization [22], which has led to research into their isolation and characterization [23,24]. Isolated acid fractions (generically referred to as "naphthenic acids") frequently contain phenols but are principally complex mixtures of carboxylic acids [1].…”

“…For example, Qian and Robbins reported the presence of a range of classes, including O2, O3, O4, and O2S1, O3S1 and O4S1, in a South American heavy crude oil[46]. Wang et al[24] separated a vacuum topped Canadian oil sands bitumen into maltenes and asphaltenes fractions and found similar relative abundances of O2 species in all fractions-, but the asphaltene fractions were enriched in O2S1, O2S2, N1O2 and some higher oxygenated classes. Stanford et al[23] and Muller et al[51] reported similar abundances of O2 class species in interfacial materials isolated from water-in-crude oil emulsions as found in the respective original oils, for several geographically distinct conventional and heavy crude oils.…”

Catalytic aquathermolysis of Shengli heavy crude oil with an amphiphilic cobalt catalyst

“…Combined with soft ionization methods, e.g., electrospray ionization (ESI), FT-ICR MS was applied to investigate catalytic aquathermolysis of heavy oil (Wu et al 2005;Smith et al 2008;Colati et al 2013;Wang et al 2013). 10 mg oil sample was firstly dissolved in 1 mL toluene, and then diluted with toluene/ methanol (1:3, v/v) to yield a 0.2-mg/mL solution.…”

Characterization of crude oil asphaltenes by coupling size‐exclusion chromatography directly to an ultrahigh‐resolution mass spectrometer

“…Additionally, separation of isomers remains a challenge as they are not detectable by direct infusion mass spectrometry. Thus, the future of crude oil analysis by mass spectrometry will involve couplings to different separation techniques …”