Investigation of structural parameters and self-aggregation of Algerian asphaltenes in organic solvents

Abstract

Elemental analysis, Fourier transform infrared (FTIR), 1 H-NMR, fluorescence spectroscopy, and surface tension methods have been used to characterize the molecular structure and the aggregation behaviors of two asphaltenic fractions derived, respectively, from an Algerian petroleum well and a corresponding storage tank deposit. Elemental analysis, FTIR, 1 H-NMR, and fluorescence spectroscopy were used to investigate the chemical composition and structural parameters of asphaltenes, while the surface tension method was used to measure the critical micelle concentration (CMC) in organic solvents with different solubility parameters and polarities in order to characterize the asphaltenes' aggregation behaviors. Results show that the unstable asphaltenes fraction extracted from the storage tank deposit possesses a higher polarity (higher heteroatoms content) and a lower aromaticity than stable asphaltenes from the petroleum well. The CMC results indicate that asphaltenes with high polarity and low aromaticity have a high solubility in polar solvents such as nitrobenzene, whereas asphaltenes with low polarity and high aromaticity are more soluble in solvents with weak polarity, like toluene. It is concluded that the difference of structure of asphaltene samples and polarity of solvents can lead to difference of aggregation behaviors.

Toward Separation and Characterization of Asphaltene Acid and Base Fractions

“…The infrared spectrum of the asphaltene sample shown in Figure is similar to those obtained by several authors (Daaou et al and Larbi et al). The spectrum shows a low intensity of a band appearing between 3500 and 3100 cm –1 , indicating the presence of a small amount of N–H group amines, alcohols, and O–H group phenols.…”

The Structure of Bitumen: Conceptual Models and Experimental Evidences

“…Using the same technique, Rogel et al [103] reported that the CMC values of unstable ASP in different solvents varied in the range of 1-30 g/L. Larbi et al [104] estimated the CMC of two Algerian ASPs dispersed in toluene, pyridine, and nitrobenzene solvents, and found values between 0.98 and 4.17 g/L. They concluded that the aggregation behavior was principally driven by the structure and polarity of the ASP, as well as by the solvent polarity.…”

Formation of Noncovalent Complexes between Complex Mixtures of Polycyclic Aromatic Hydrocarbons (Asphaltenes) and Substituted Aromatics Studied by Fluorescence Spectroscopy

“…These new insights into the asphaltene structure have aided in consolidation and revision of some of the previously postulated mechanisms, while they also imply new mechanisms for asphaltene aggregation, such as those based on radical interaction . The exact structure and molar mass of the asphaltene molecules vary depending on the geographical source of the crude oil. , The molar mass of individual asphaltene molecules is on the order of 500 g mol –1 on average. ,, Due to their complex chemical structures and compositions, asphaltenes are usually considered a chemical class that is soluble in aromatic solvents (benzene or toluene), but insoluble in alkanes ( n -pentane or n -heptane). ,,− The stepwise process of aggregation of asphaltenes (Figure ) has traditionally been studied by using light scattering from suspensions of their solid particles (dynamic light scattering). − Small-angle X-ray scattering has been used to determine the aggregate size based on the short-range order, ,, and surface tension can provide information on the critical micelle concentration. − Absorption electronic and near-IR (UV–vis–IR) spectroscopy has also been utilized. − However, each of these methods comes with advantages and limitations. For instance, the presence of nanoaggregates or larger particles in asphaltene solutions leads to strong scattering, which usually obscures the absorption signal and may provide inaccurate data.…”