Asphaltene flocculation, precipitation, and Liesegang ring

Precipitations of Ratawi and Kuparuk asphaltene in toluene/heptane mixed solvents were investigated using a newly developed dripping test method. Precipitation of asphaltene solution at a critical heptane volume ratio can be readily identified. In addition, for the first time, a Liesegang-like phenomenon [Liesegang, R. E. Naturwiss. Wochenschr. 1896,11, 353] was observed for the Ratawi asphaltene system. Similar but less-profound Liesegang rings were observed for asphaltene derived from Kuparuk crude oils. Clear crossover and a diffusive hyperfine structure were observed in the Ratawi asphaltene precipitation pattern, whereas asphaltene derived from Kuparuk crude oil showed only marginal crossover phenomenon. The patterns of the rings from Ratawi asphaltene seem to fit the space law of the Liesegang pattern. Both the post-nucleation Ostwald-Prager process and the pre-nucleation spinonal decomposition phase separation process are possible precipitation mechanisms.