The proposition of the hypothesis-relating structure with properties of asphaltenes is a very important endeavor.
In view of their complexity, being an intricate mixture of high-molecular-mass compounds, experimental and
theoretical procedures must be designed to check whether the structures proposed are consistent with expected
and found behavior. During recent years, a structural characteristic of asphaltene, whereby the several polycyclic
systems present in them are joined by flexible aliphatic chains, has been proposed by several authors. For
simplicity, we will refer to this as the rosary-type structure. In this paper, using both reported as well as new
experimental and theoretical results, an attempt is made to show how asphaltene properties, such as molecular-mass distribution, molecular fragmentation, solubility, adsorption, trapping of molecules, solvent swelling,
and aging, could be accounted for in terms of the above rosary-type structures.
A method using liquid-liquid extractions has been developed for matrix simplification and evaluated by gel permeation chromatography hyphenated with inductively coupled plasma and mass spectrometry (GPC ICP MS). In this method, maltenes were dissolved in n-heptane (HEP), and extractions with methanol (MeOH), acetonitrile (ACN) and dimethylformamide (DMF) were performed. The extraction with ACN is more efficient than that of MeOH for the removal of
A method of sequential liquid-solid extraction (leaching) has been developed to extract the V, Ni and S compounds present in asphaltenes (n-C 7) according to their molecular weight distribution. For the high molecular weight (HMW) compounds, two new families of compounds were extracted, labeled HMW1 and HMW2, where the latter was smaller than HMW1, and together represented approximately 85% of the asphaltene mass according to the mass balance obtained after the extractions. The compounds associated with HMW1 were asphaltenes that were insoluble in hot dimethylformamide (DMF), while the compounds associated with HMW2 were soluble in DMF but insoluble in the second leaching step based on hot acetone. The third family of obtained compounds was the medium molecular weight (MMW) compounds, which were soluble in hot acetone but insoluble in acetonitrile (ACN). The last fraction to be obtained was the low molecular weight (LMW) compounds, which were soluble in ACN. The results reported here represent a new method that allows the extraction of different types of aggregated asphaltenes according to their molecular weights. With respect to the temperature and number of extraction steps, it was observed that an increase in both parameters increased the extraction efficiency.
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