Influence of Asphaltene polarity on wax deposition of waxy oils

Abstract

Asphaltenes are the most polar components of crude oils. The influences of asphaltene polarity on the wax deposition were studied in this investigation using model waxy oils. Asphaltenes contained by a Venezuelan crude oil were fractionated into four subfractions of different polarity utilizing a liquid/liquid extraction technique and used to prepare asphaltene-containing waxy model oils. The mass, composition, dielectric characteristics and mechanical characteristics of the waxy deposits formed in the presence of asphaltene fractions of different polarity were characterized. It was found that the less polar asphaltenes in waxy oils lower the deposit mass but cause the wax content of the deposits to increase. In addition, the inner diffusion of longer n-alkanes and the outer diffusion of shorter n-alkanes are accelerated by the less polar asphaltenes. Furthermore, the waxy deposits formed with waxy oils containing less polar asphaltenes are enriched with less amount of asphaltene and present reduced internal effective diffusion coefficient as was characterized by NMR. Besides, the presence of less polar asphaltenes causes the radius of Nyquist diagram of waxy deposits to increase, indicating higher resistance. Eventually, rheological characteristics, such as gelation temperature and yield stress, suggest increased structural strength of waxy deposits formed in the presence of less polar asphaltenes.