Microscopic study on the settling velocity of asphaltenes

Impens N., Van Laer J., Fonteyne A.

SCK•CEN, Boeretang 200, B-2400 Mol, Belgium.

In the past, blown bitumen (R85/40) has been used as a matrix for several types of radioactive waste salt. A weight ratio of 60/40 bitumen/waste was applied. In order to study the feasibility to recover the maltenes from the waste, it is first mixed with a 50 % aromatic solvent. Then the precipitation of asphaltenes is induced by adding a paraffinic so-called non-solvent. The settling velocity was investigated using turbidimetry as a function of sample height and as a function of time. As a function of the amount of added non-solvent, an optimum settling velocity of the asphaltenes was observed at a certain solvent:non-solvent ratio. These results were reported on the 5^th international conference on phase behaviour and fouling. In this paper, we study what happens on a microscopic scale and try to understand why an optimum in settling velocity is found at a certain solvent-non-solvent ratio.