Study on inhibition behaviors of asphaltene inhibitor to asphaltene aggregations

The changes in the stability of asphaltene in crude oil will give rise to its aggregation, coalescence and deposition from crude oil. The preferred method for improving asphaltene stability is the addition of asphaltene inhibitor (ASIN). The interactions between asphaltene and six inhibitors (S1-S6) were investigated from effects of the ASIN molecular properties such as the acidity, the relative positions of polar and non-polar groups on the benzene ring, and molecular size on the effectiveness of ASIN. The effectiveness, asphaltene aggregation number and degree of solvation for the asphaltene of Canadian oil sand bitumens (COSB) in heptol with or without ASIN were obtained by the solution viscosity and spectrophotometric measurements. The groups impacting the inhibitor effectiveness from high to low are sulfonic acid group, hydroxyl group and the amine group attached to the benzene ring. The interaction between the boric acid group in S5 and asphaltene is stronger than that between sulfonic acid group in S6 and asphaltene, indicating that the spatial protection to asphaltene by macromolecular chains of S5 relative to acidity is expected to prevail. Because of their suitable spatial structure, the inhibitor molecules with the polar and nonpolar groups located at the para-position of the benzene ring are more favorable to inducing dense arrangement of inhibitor molecules on asphaltene and thus provide a stronger protective effect for asphaltene. Viscosity measurements showed that the aggregation number of asphaltene in heptol with inhibitors decreased and the solvation constant increased, leading to improve the compatibility of asphaltene aggregates with solvents.