In Situ Monitoring of the Inhibition of Asphaltene Adsorption by a Surfactant on Carbon Steel Surface

Simple surfactants have proven to be some of the most effective agents to mitigate the deposition of asphaltenes on pipeline walls; however, the best practices for their application are often empirical, and the actual mechanisms of their action remain elusive. Here, inhibition of asphaltene adsorption as viscoelastic films on carbon steel by a surfactant, dodecylbenzenesulfonic acid (DBSA), was directly monitored using quartz crystal microbalance with dissipation. Different protocols for application of the inhibitor were assessed, including treatment of the clean surface before adhesion and application by premixing and postprecipitation. Asphaltenes were found to form a tightly bound viscoelastic layer on the carbon steel surface, and administering DBSA on preadsorbed asphaltenes removes most (86.5%) of this adsorbate. Premixing of DBSA and asphaltenes to simulate the commonly used application method results in a very short contact time (∼35 s) before most of asphaltenes (86.0%) are desorbed from the surface. Pretreatment of the metal surface with DBSA was found to be particularly effective, and it results in nearly complete (98.5%) removal. The efficacy of DBSA in organic scale removal, mainly asphaltenes, over prolonged time by repeated treatment was also investigated. The results indicate that alternating application of toluene and DBSA is the most effective protocol that prevents the loosely bound toluene-soluble fraction of asphaltenes to act as a nucleation layer that triggers the onset of growth of the asphaltene layers.