(29g) Properties Controlling Aggregation and Precipitation Rates of Asphaltenes

Properties Controlling Aggregation and
Precipitation Rate of Asphaltenes

Nasim Haji Akbari
Balou¹ and H. Scott Fogler¹

¹The University of Michigan, Department of Chemical
Engineering, Ann Arbor, MI

Asphaltenes
are the heaviest and most polar fraction of crude oil and can precipitate due
to change in temperature, pressure and composition. Their precipitation and
deposition can lead to serious economical impacts in
the oil industry. For years it was believed that instability of asphaltenes can
be detected shortly after changing the operational conditions. However, recent
studies in our group demonstrated that asphaltene-precipitant mixtures can be
unstable even at very low precipitant concentrations and it can take weeks and
sometimes even months to detect such instabilities [1, 2]. We have observed
that this kinetic behavior is universal among different crude oils. However,
the precipitation rates strongly depend on the properties of the crude
oil.  Our goal in this study is to
identify the properties that are responsible for differing aggregation and
precipitation kinetics. Due to the complexity of crude oil, model mixtures are
used as alternatives to measure the precipitation rates for different solvents
and asphaltenes.

A
new analysis approach has been developed to estimate the precipitation rates by
accounting for the properties governing the aggregation kinetics such as
viscosity and solubility parameter.  The
results show that precipitation rates strongly depend on the solvent used for
asphaltenes stabilization. However, we show that under certain assumptions all
the differences for different types of asphaltenes and solvents can be well
explained, and their precipitation rates collapse onto a single curve. The
results also demonstrate that not only the solvent, but also the asphaltene
content of the solution can play an important role in controlling the
aggregation rate. We have observed that solutions with lower asphaltene content
show a higher tendency for destabilization and eventual precipitation.  These findings will lead to a better
understanding of the properties that govern the destabilization and growth
processes of asphaltenes.

[1] T.Maqbool,
A.T. Balgoa, and H. S. Fogler,
? Revisiting Asphaltene Precipitation from Crude Oils: A Case of Neglected
Kinetic Effects,? Energy & Fuels, vol. 23, no. 7 , pp. 3681-3686,
Jul. 2009.

[2] M.Hoepfner,
C.V.B Favero and H. S. Fogler,
? Understanding the Instability of Asphaltenes,? Oral at Petrophase
2011, London.