Effect of Organic Additives on the Onset of Asphaltene Precipitation

Abstract

Onset of solid precipitation from oils was determined by identifying the minimum in near-infrared absorbance. Solvent-induced precipitation typically causes asphaltene precipitation, but is also known to cause high-molecular-weight waxes to come out of solution. The effects of the addition of solid saturated and unsaturated compounds on the onset of solvent-induced precipitation from a crude oil were examined. Crude oil from Rangely, an oil field in northwestern Colorado was used. The solvent-induced precipitation was brought about using pentane, hexane, and heptane. On the basis of limited solvent carbon number investigated (5−7), less solvent was required for precipitation onset as the carbon number of alkanes decreased. As the flow rate of the precipitant increased, the onset was delayed. Addition of solid n-alkanes, such as eicosane and tetracosane to the oil initially, accelerated the onset of precipitation. When solid polyaromatic compounds (naphthalene and phenanthrene) were dissolved in the oil, more solvent was required to initiate onset of precipitation. It was also shown that the crude oil was considerably undersaturated with respect to the asphaltenes and that initial dissolution of asphaltenes in the oil accelerated the precipitation. The data provided insight on solubility-related solids precipitation from oils.