SOLVENT EFFECTS ON ASPHALTENE ISOLATION

Peter R. Seidl¹, Erika C.A.N. Chrisman¹. Carolina C.V. Carvalho¹, Katia Z.Leal² and Sonia M. C. de Cabral³

¹ Universidade Federal do Rio de Janeiro, Brazil; ²Universidade Federal Fluminense, Brazil; ³ PETROBRÁS – CENPES, Brazil

We have recently shown that certain factors have a significant influence on the type and amount of asphaltene that is extracted. Our simulations of the separation of aggregates in different solvents reveal the importance of structural factors on the dissociation process. In the present work we compare the results of extraction with selected solvents with those observed for different grades of n-heptane. Hydrogen NMR was used to monitor the types of structure that was obtained in each procedure.

Two different types of experiment were run. In the first, asphaltenes extracted from vacuum residues by the IP-143 method were re-extracted with methylisobutylketone, carbon tetrachloride and others while, in the second, 99% n-heptane was substituted for "95% n-heptane". This apparently small difference in solvent grade resulted in an almost threefold difference in the amount of asphaltene that is extracted, but hydrogen NMR did not indicate large variations in the type of functional group that is present. On the other hand,  the solvents carbon tetrachloride and methylisobutylketone provided the best discrimination among constituents. The former will favor the extraction of aromatic constituents and the latter, those made up mainly of aliphatic groups. These results are in agreement with our simulations of asphaltene dimers: disaggregation observed in an equimolar amount of n- and isobutane is considerably lower than that of either of these solvents separately and comparable to that observed for n-heptane while toluene affords the best separation between monomers and would probably compete with them in terms of affinity for aromatic constituents.