Subfractionation and Characterization of Mayan Asphaltene

Abstract

Mayan crude, residuum, and hydrocracked asphaltenes have been separated into two fractions by extended Soxhlet extraction in n-heptane. Although the solubility, composition, and molecular structures differ slightly, the greatest difference between the two asphaltene fractions is the degree to which they associate in solution. The vapor-phase osmometry molecular weight, molecular size by size-exclusion chromatography, and small-angle neutron scattering indicate that approximately 25% of Mayan asphaltene is not highly associated in aromatic solvents and, thus, is noncolloidal. By contrast, the remaining asphaltene forms large, rodlike colloidal particles in solution and has a higher apparent molecular weight. Although laser desorption mass spectrometry indicates that the molecular weight of the individual molecules in maltenes and asphaltenes is not very different, high-resolution mass spectrometry indicates that the size of the aromatic core of asphaltenes is significantly larger than those in maltenes. Furthermore, the tendency of the residuum fractions to form coke during thermal cracking is likely related to the size of the largest polyaromatic rings.

Structural Study of Asphaltenes from Iranian Heavy Crude Oil

“…The higher capacity of n-pentane for the precipitation of asphaltenes compared with the yield obtained with n-heptane is a common finding reported in the literature [26]. Apparently, the use of higher carbon-number alkane solvents results in lower asphaltene yields and increased levels of resinous materials [26,32]. Similar behavior is observed for oils from different sources that have different API gravities using n-C 5 and n-C 7 for asphaltene precipitation [33], and the results of the present work showed the same behavior: 21.5% versus 15.5% for n-C 5 and n-C 7 asphaltenes, respectively (Fig.…”

Characterization of asphaltenes precipitated with three light alkanes under different experimental conditions

“…It has been found that the yield and properties of asphaltenes precipitated from a crude oil depend on various factors, such as the precipitant, liquid precipitant-to-oil volume ratio, contact time, pressure, and temperature [12][13][14]. Some standard precipitation methods have been developed in laboratory to obtain an accurate and consistent asphaltene content.…”

Dispersing of Petroleum Asphaltenes by Acidic Ionic Liquid and Determination by UV-Visible Spectroscopy

“…[2]. Asphaltenes are petroleum hydrocarbons with extremely complex molecular structure containing sulfur (0.3-10.3%), oxygen (0.3-4.8%), nitrogen (0.6-3.3%), and metal elements, such as Fe, Ni, and V in a small amount [3][4][5][6]. One of the most important problems in oil industries is the precipitation of heavy components of crude oil such as asphaltenes.…”