Studies on precipitation performance of n-heptane and n-pentane/n-heptane on C7 and C5/C7 asphaltenes and maltenes from 350 °C atmospheric residuum of three Nigerian light crudes

Asphaltenes behave like blood cholesterol in that they deposit on the walls of crude oil transportation pipes thereby narrowing the internal diameters, thus posing great dangers. This study was designed to remove asphaltenes from light crudes by solvent precipitation and to investigate the comparative performance of n-heptane (single solvent) and n-pentane/n-heptane (mixed solvent) in this regard. Each of three Nigerian crudes: Bonny Export, Bodo and Mogho crudes were first distilled at 350 °C to obtain the atmospheric residuum. Asphaltenes were precipitated from each residuum at different stirring times with single n-heptane and mixed n-pentane + n-heptane solvents. The precipitated asphaltenes were characterized with FTIR, UV–visible spectrophotometers while the maltenes were fractionated to obtain the various fractions. Results show that the asphaltenes were made up of saturated (cyclic aliphatic hydrocarbons) and unsaturated (substituted aromatic hydrocarbon). Also, aromatics to saturates ratio and resins to asphaltenes ratio was higher in Bonny Export and lower in Mogho crude, thus, indicating that Bonny Export has the lowest asphaltene precipitation risk while Mogho crude has the highest risk. The results also showed that resins stabilize asphaltenes in crude as addition of resins to the different crudes reduced the quantity of asphaltene precipitated.