Acid–base chemistry enables reversible colloid-to-solution transition of asphaltenes in non-polar systems

Abstract

The conjugated π-bonding in asphaltenes, a naturally occurring member of the polyaromatic hydrocarbon family, provides a unique platform for investigating electrostatics and electronics in non-polar systems, but at the same time causes asphaltenes to be insoluble in all except aromatic liquids. Asphaltenes precipitate from petroleum fluids under a variety of conditions, including depressurization and compositional changes, plaguing both recovery operations and remediation in the case of equipment failure. Aromatic solvents like toluene dissolve asphaltenes, but only at very high concentrations, nearly 50% by weight. Polymeric dispersants can stabilize asphaltene colloids, and in some cases can inhibit asphaltene precipitation entirely. Strong organic acids such as dodecyl benzene sulfonic acid (DBSA) can dissolve precipitated asphaltenes when introduced in concentrations as little as 1 percent by weight. Here we demonstrate for the first time that DBSA enables a reversible transition from unstable to stable colloidal-scale asphaltene suspensions to molecularly stable solutions. A continuum of acid–base reactions explains the apparent dual-action of DBSA. The suspension–solution transition occurs through the protonation of heteroatomic asphaltene components and subsequent strong ion pairing with DBSA sulfonate ions, effectively forming DBSA-doped asphaltene complexes with a solvation shell.