EVIDENCE FOR THE AGING OF WAX DEPOSITS IN CRUDE OILS BY OSTWALD RIPENING

摘要

Gel aging is well known to occur in wax deposits forming in pipelines and storage tanks. It is characterized by a hardening of the deposit and an increase in paraffin content. It has been shown that counter diffusion caused by temperature-concentration gradients within the wax is one of the mechanisms for the aging. This work demonstrates the existence of another mechanism for the aging of wax deposits. Samples of paraffinic crudes were kept isothermally at temperatures below the Wax Appearance Temperature (WAT). In the absence of a temperature gradient, a slow kinetic of the hardening of the samples is observed in rehology. The X-ray diffraction and Cross Polar microscopy shows that this phenomenon to be caused by the increase of the average crystal size. The evidence indicates that Ostwald ripening may be another mechanism responsible for the gel hardening besides the counter diffusion mechanism previously reported.