Sans study of asphaltene aggregration
- Exxon Research and Engineering Co., Annandale, NJ (USA)
The colloidal properties of asphaltenes have long been recognized from peculiarities in their solubility and colligative properties. A layered micellar model for asphaltenes was proposed by Pfeiffer and Saal in 1940, in which a highly condensed alkyl aromatic formed the central part, and molecules of decreasingly aromatic character (resins) clustered around them. Numerous studies, based on a variety of techniques such as ultracentrifugation and electron microscopy indicated a particulate nature for asphaltenes with size 20-40 {angstrom} diameter. T.F. Yen and co-workers proposed a refined model based on x-ray diffraction and small angle scattering. In this model, interactions between flat sheets of condensed aromatic rings form the central crystallite part of a spherical particle with the outer part being comprised of the aliphatic positions of the same molecules. These particles are bunched together with some degree of entanglement into micelles. Concentration and solvent dependent radii of gyration, ranging from 30-50 {angstrom} were reported. The aggregation creates a good deal of uncertainty as to the true molecular size of weight of asphaltenes. Neutron scattering offers novel contrast relative to light scattering (refractive index) and x-ray scattering (electron density). This is because the scattering length of proton is negative, whereas that from deuterium and other nuclei such as C, S, O, and N are positive. Thus by replacing hydrogen with deuterium in either the solvent or the scatterer the contrast can be varied, and different parts of the molecule can be highlighted.
- OSTI ID:
- 5236053
- Report Number(s):
- CONF-8806304-; CODEN: ACPCA
- Journal Information:
- American Chemical Society, Division of Petroleum Chemistry, Preprints; (USA), Vol. 33:2; Conference: Symposium on characterization and chemistry of tar sand, Toronto (Canada), 5-10 Jun 1988; ISSN 0569-3799
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ASPHALTENES
STRUCTURAL CHEMICAL ANALYSIS
AGGLOMERATION
EXPERIMENTAL DATA
NEUTRONS
SMALL ANGLE SCATTERING
ASPHALTS
BARYONS
BITUMENS
DATA
ELEMENTARY PARTICLES
FERMIONS
HADRONS
INFORMATION
NUCLEONS
NUMERICAL DATA
ORGANIC COMPOUNDS
OTHER ORGANIC COMPOUNDS
SCATTERING
TAR
040500* - Oil Shales & Tar Sands- Properties & Composition