Asphaltene Stability in Crude Oils and Petroleum Materials by Solubility Profile Analysis

A new method to evaluate the colloidal stability of crude oils and related products was developed on the basis of the evaluation of the solubility profile or solubility distribution of asphaltenes in these materials. The new method uses an on-column precipitation coupled with an evaporative light scattering detector (ELSD). The new method requires a small amount of sample, takes only 35 min to perform, and can work for asphaltene concentrations as low as 500 ppm. Using this method, different patterns for asphaltene solubility profile distributions were found depending upon the origin and processing history of the samples. Extracted asphaltenes from virgin and processed materials exhibit uni- and bimodal distributions, respectively. On-column precipitated asphaltenes usually have bimodal distributions, where the separation between the peaks is related to the colloidal stability of the asphaltenes. In general, asphaltenes from unstable materials are characterized by wider solubility profile distributions than asphaltenes from stable materials. A characteristic parameter of the solubility profile distribution, ΔPS, can be obtained and correlated to the colloidal stability of the samples.