Evidence for the Aging of Wax Deposits in Crude Oils by Ostwald Ripening

The ageing of wax deposits is known to occur in paraffinic waxes forming in pipelines and storage tanks. It is characterized by a hardening of the deposit and an increase in paraffin content. A mechanism for the ageing of deposits, based on diffusion caused by temperature-concentration gradients wit...

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Bibliographic Details
Published in:Petroleum science and technology 2003-02, Vol.21 (3-4), p.381-391
Main Authors: Coutinho, João A. P., Lopes da Silva, J. A., Ferreira, Artur, Rosário Soares, Maria, Daridon, Jean-Luc
Format: Article
Language:English
Subjects:
Aging
Applied sciences
Constitution and properties of crude oils, shale oils, natural gas and bitumens. Analysis and characteristics
Crude oil
Crude oil, natural gas and petroleum products
Deposition
Diffusion
Energy
Exact sciences and technology
Fuels
Hardening
Ostwald ripening
Paraffins
Recrystallization
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Summary:The ageing of wax deposits is known to occur in paraffinic waxes forming in pipelines and storage tanks. It is characterized by a hardening of the deposit and an increase in paraffin content. A mechanism for the ageing of deposits, based on diffusion caused by temperature-concentration gradients within the wax, has been previously proposed. This work presents evidence indicating Ostwald Ripening to be another ageing mechanism of wax deposits. Rheology of paraffinic crudes, kept isothermally at temperatures in the neighborhood of the pour point, shows a kinetic of hardening of the oil samples. The X-ray diffraction and Cross Polar Microscopy indicate this phenomenon to be caused by an increase of the crystallites size with time. The DSC measurements support the idea that recrystallization takes place in the wax sample. The evidence gathered shows another ageing mechanism based on the recryztallization of the paraffins, such as Ostwald Ripening, to be responsible for the ageing of wax deposits besides the diffusion mechanism previously proposed
ISSN:1091-6466
1532-2459
DOI:10.1081/LFT-120018527