Critical Variables for the Characterization of Asphaltenes Extracted from Vacuum Residues

Abstract

Asphaltenes represent a solubility class of petroleum constituents that has been associated with a number of problems that arise from the use of heavier crude oils. As they are defined by their solubility and not their chemical structure, there are often certain difficulties in distinguishing them from other solubility fractions. In a widely adopted separation procedure, saturates generally consist of naphthenes and paraffins while aromatics, resins, and asphaltenes are often quite similar polynuclear aromatic species which may vary in the number of heteroatoms and sizes of ring systems and side-chains that are present. In our attempts to characterize asphaltenes extracted from vacuum residues, we found that the procedures employed for separating asphaltenes in a certain sample have a significant effect on the analytical data that is generated from it. We have thus investigated the influence of different variables on vacuum residues obtained from two Brazilian and one Venezuelan crude and suggest that the most important factors are: the proportion of heptane to sample, treatment by ultra-sound and recovery of asphaltenes in residues by toluene. Combinations of these variables can be employed to hinder aggregation and afford a better separation of asphaltenes and resins. The analytical techniques that were used to confirm this are: NMR ( 1 H and 13 C), gel permeation chromatography (GPC), infrared spectroscopy (IR), and elemental analysis. Information on the types of aromatic ring substitution patterns and terminal methyl groups may be obtained from spectroscopic techniques particularly from NMR.

Impact of Thermal Treatment on Asphaltene Functional Groups

“…OPUS software (version 6.5) from Bruker was used to correct the base lines, determine the absorbance at specific wavenumbers, and integrate the areas between wavenumbers. The wavenumbers used in determining the functional groups in asphaltenes are reported in the literature. − The FTIR spectra were analyzed by comparing the ratios of intensities and/or the ratios of integrated areas within the same spectrum, and not between the spectra of different samples. Thus, our discussion is based on ratios and relative values, not on absolute quantitative values.…”

“…Many studies utilized the FTIR spectroscopic technique to study asphaltene molecules. − Coelho et al studied the linear relationship between the intensity ratios at 2927 and 2957 cm –1 and the ratios of n CH 2 / m CH 3 for carbon chains of alkyl-benzene to determine the aliphatic chains of asphaltenes and resins. They proposed a methodology for determining the functionality and calculating the percentage of single and paired hydrogen atoms attached to aromatic rings for asphaltene and resin .…”

Solvent Content Measurements of the Produced Stable Water-in-Oil Emulsions During Solvent-Aided Thermal Recovery Processes

“…On the other hand, GPC is an efficient characterization method for predicting the molecular weight distribution of high-boiling hydrocarbon mixtures. GPC is a form of liquid chromatography that principally focuses on the characterization of heavy components of crude oils, whereas GC is mainly used and reliable for light components. , Different studies combined the GPC with various methods such as VPO, HPLC, and different spectroscopy methods to characterize asphaltene and heavy oil components. − Moreover, GPC coupled with elemental analysis, nuclear magnetic resonance (NMR), and infrared (IR) spectroscopy were used for the investigation of the molecular structure of asphaltene and maltene fractions …”