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1. ASPHALTENES  (molecular properties) 
1.1  Molecules of molecular aggregates ???

     Currently, in most publications on asphaltenes (including textbooks) it is stated that asphaltenes, both in crude oils and in simple solvents, have a "critical micelle concentration" ("CMC") of several grams (or even tens of grams) per litre. Accordingly, a common belief is that experiments at concentrations somewhat lower than "CMC" provide information on the properties of individual molecules (monomers) of asphaltenes. One of the conclusions of such experiments has been that asphaltenes have an extremely high molecular weight (MW) - in excess of tens of thousands Dalton. In petroleum engineering, the knowledge of asphaltene MW is essential for development of effective technologies for removal/prevention of deposits, tertiary oil recovery, heavy oil processing, etc.
   Our studies (with an active contribution of EEE students - D.Yu. Eliseev, B.R. Akhmetov, S.A. Losev and others) for the first time provided direct experimental evidence of asphaltene aggregation  at concentrations three orders of magnitude lower that believed before. Namely, the simplest molecular aggregates (asphaltene dimers) are formed at asphaltene concentrations, not exceeding 3-5 MILLIGRAMS per litre.

    By analysis of the newly discovered aggregation stages we suggested that true MW of asphaltene molecules does not exceed 1000 Dalton. (More recent direct experiments by Mullins and others in USA provide MW <750 Dalton for asphaltenes).

  This new information on asphaltene agregation stages has been obtained in studies of  Russian crude oils from various georgaphical locations  (measurements of viscosity, density, UV/Vis absorption, refractive index, static and dynamic light scattering, NMR spin-spin relaxation, etc)



Stages of molecular aggregation into more and more complex entities with increasing asphaltene content in a crude oil solution (measurements of optical absorptivity)


Principally different UV/Vis absorption spectra for: 
(1) asphaltene monomers in a crude oil solution ( 3.7 mg/L asphaltenes) and
(2) asphaltene molecular nanoclusters in a crude oil solution ( > 300 mg/L asphaltenes)


Principally different correlations of NMR relaxation time and dynamic viscosity in dilute crude oil solutions, containing asphaltene monomers and simple oligomers (А-С) and in concentrated solutions, containing asphaltene molecular nanoclusters and more complex aggregates (D-E)

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      Last Update : 29.03.2005