Asphaltenes subfractions characterization and calculation of their solubility parameter using ESI(-) FT-ICR MS: Part II

Abstract

Negative ion-mode electrospray (ESI(-)) technique coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) provides ionization of polar constituents with ultra-high resolution and mass accuracy. This study aimed to characterize asphaltenes and subfractions obtained from precipitation with different n-hexane/asphaltenes ratios (3.5 V, 3.5–6 V, and 6–40 V), and three subfractions obtained from adsorption onto CaCO3 (non-adsorbed, adsorbed, and irreversibly adsorbed) by FT-ICR MS, and to estimate the solubility parameters (δ) of the molecules with the data generated from ESI(-) analysis. Mean values of solubility parameters between 16 and 24 MPa0.5 were found for whole asphaltenes and their subfractions. ESI(-) data showed that a higher number of polar species were found for the 6–40 V and irreversibly adsorbed subfraction. Besides, subfraction 6–40 V presented a more aromatic profile than of remaining subfractions. Moreover, 6–40 V and irreversibly adsorbed subfractions presented a shift to higher solubility parameters, indicating that the polarity and aromaticity have influenced the solubility of the subfractions. Species containing multiple heteroatoms showed higher solubility parameters, suggesting that these species appear to be responsible for the lower solubility of subfractions.