Irwin A. Wiehe

Design of Synthetic Dispersants for Asphaltenes

Abstract Synthetic dispersants can greatly increase the solubility of asphaltenes in crude oils at low concentrations. They have one or more head groups that complex with the polynuclear aromatic structures in asphaltenes and long paraffinic tails that promote solubility in the rest of the oil. As a result, synthetic dispersants can be much more effective than the natural dispersants in the oil, the resins. At high concentrations, synthetic dispersants can even make all the asphaltenes soluble in n-heptane and thereby convert asphaltenes to resins. Asphaltene dispersants were optimized according to their ability to reduce the toluene equivalence of 05a crude oil. By synthesizing families of prospective dispersants, one sulfonic acid group was determined to be the most effective head attached to a two ring aromatic structure. As previously reported, a straight chain paraffinic tail is not effective above 16 carbons. We discovered that this was because of decreased solubility in the oil caused by crystallization with other tails and with waxes in the oil. In addition, not previously reported, n-alkyl-aromatic sulfonic acids lose their ability to disperse asphaltenes with time. Both of these problems were solved by using two branched tails of varying length proportions between the two tails. As a result, the effectiveness of the dispersant increases with total tail length, well above 30 carbons and it remains effective with time.