Asphaltenes are defined as the petroleum fraction insoluble in n-alkanes and soluble in aromatic solvents, such as toluene. Such definition implies that asphaltenes are not a homogeneous material but a mixture of fractions. Asphaltenes represent one of the major contributors to several problematic issues for the petroleum industry. Destabilized asphaltenes can cause arterial clogging within pipelines and wellbores, corrosion and fouling of production equipment, reduction of catalyst activity in refining processes, and other problems. This work describes an investigation of the separation of asphaltenes into three different fractions by adsorption onto silica particles. These fractions (two adsorbed and one non-adsorbed onto silica) were characterized by elemental analysis (C, H, and N), Fourier transform infrared spectroscopy coupled to attenuated total reflectance (ATR−FTIR), proton nuclear magnetic resonance ( 1 H NMR) spectroscopy, and atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry (APPI−FT-ICR MS). APPI−FT-ICR MS and ATR−FTIR accessed chemical information on a molecular level [molecular formula, carbon number (CN) and double bond equivalent (DBE) distributions, and organic groups], whereas 1 H NMR and elemental analysis provided the aromaticity degree and C/H atomic ratio of the samples, respectively. The C/H atomic ratio decreases in the following the order: non-adsorbed > whole asphaltene > adsorbed > irreversibly adsorbed. The irreversible fraction adsorbed had the lowest percentage of aromatic hydrogen compared to other fractions by 1 H NMR. There was a good correlation between the results of NMR and elemental analysis. The efficiency of fractionation on silica particles was proven to be successful by the low concentration of polyaromatic hydrocabons observed for two samples adsorbed onto silica and the increasing of the aromaticity degree and C/H ratio for the non-adsorbed fraction. N 2 , N 2 O, and NO compound classes were selectively separated from whole asphaltene and concentrated in polar fractions (adsorbed fractions onto silica), with their CN and DBE distributions reported. Therefore, this work demonstrated the selectivity of the fractionation method onto silica to retain highly polar compounds and, moreover, extends to the study of the adsorbent surface and how the molecules of the asphaltenes will behave against this change.
Naphthenic
acids (NAs), present in a typical Brazilian acid crude
oil and its thermal degradation products, were investigated using
two separation methodologies: solid-phase extraction (SPE) and liquid–liquid
extraction (LLE). Fractions produced were characterized by proton
nuclear magnetic resonance spectroscopy (1H NMR) and negative-ion-mode
electrospray ionization Fourier transform ion cyclotron resonance
mass spectrometry (ESI(−)-FT-ICR MS). Of the NAs extraction
methods studied, SPE was more efficient than LLE. Further, ESI(−)-FT-ICR
MS results showed that the SPE method with eluent phase variation
allowed for the detection of a larger amplitude of NAs compounds (m/z 200–1200), reducing the occurrence
of ion suppression on the NAs of higher average molecular weight (M
w) distribution. It was noted that the aromaticity
or double bond equivalent (DBE) of these produced collective fractions
as well as their M
w values increased as
a function of the polarity of the extraction system (DCM →
DCM:MeOH:FA). Also, 1H NMR analysis revealed the alkyl
predominance evidenced by the presence of high Hβ content in fractions, suggesting that the NAs compounds have long
and unbranched chains. The behavior of NAs species during the thermal
degradation process was also evaluated, and the results showed their
presence in only five SPE extracts out of six, containing different M
w values (M
w = 366,
417, 531, 662, and 836 Da). This suggests that, in the last SPE fraction
(named SF6: m/z 700–1150,
carbon number of C52–C72, and DBE = 0–15;
detected only in virgin crude oil), the NAs were selectively cracked
during the thermal degradation process.
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