A comparison of the macrostructure of Ratawi asphaltenes in toluene and vacuum residue
- Texaco R&D, Beacon, NY (United States)
Asphaltenes are a mixture of molecules precipitated from vacuum residue by heptane. As such they are a solid, somewhat graphitic material. When dissolved in a good solvent such as toluene, small angle nuclear scattering (SANS) results show that asphaltenes from Ratawi vacuum residue are spherical, approximately 20-50 {angstrom} in radius. The question then arises as to whether asphaltenes exist in a similar state in vacuum residue. In other words, is toluene a model solvent which one can use to study asphaltenes, and have some confidence that the results obtained are relevant to asphaltenes in their natural state. This work compares small angle X-ray scattering (SAXS) results for asphaltenes in Ratawi vacuum residue to the SANS results for the same asphaltenes dissolved in toluene. Ratawi is a high sulfur asphaltenic crude oil from the middle east. The authors also compare the shear rheology for Ratawi asphaltenes/toluene solutions with that for ashaltenes in vacuum residue, and find that the Ratawi asphaltenes have essentially the same microstructure. In either environment that are spherical particles approximately 20-50 {angstrom} in radius. There is a polydispersity of sizes, and the degree of polydispersity is the same. The asphaltenes are solvated by the surrounding medium, either toluene, or the non-asphaltenic fraction of vacuum residue. The size of the solvation shell depends on the medium and the temperature. It is the same for Ratawi asphaltenes in toluene at room temperature as for these asphaltenes in vacuum residue at 93{degrees}C. Thus except for an offset in temperature, which is a measure of the strength of the asphaltene-medium interactions, toluene appears to be a good solvent to use for studying asphaltenes.
- OSTI ID:
- 141326
- Report Number(s):
- CONF-930304--
- Country of Publication:
- United States
- Language:
- English
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