Investigation of adsorption behaviors of paraffin waxes on iron, iron oxide, and iron III oxide pipeline's internal surfaces using adsorption locator model

Abstract

Wax deposition in pipelines leads to pressure drop, reduced effective cross-sectional area, and blockages. Although mathematical models and experimental loops were used to model wax precipitation on pipeline surfaces, its prediction at molecular levels is not fully recognized. Molecular dynamics is another powerful approach that can predict wax precipitation at the molecular level. This paper uses molecular dynamics simulations with the adsorption locator model found in Material Studio Software to investigate the adsorption behaviors of Icosane-C20H42, Docosane-C22H46, and Tetracosane-C24H50 paraffin waxes on the Fe, FeO, and Fe2O3 pipeline internal surfaces. Modeling is performed by varying temperature values and validated with experimental data. It was found that as the temperature altered, the adsorption energies, probability energy distribution and adsorption density field on the surfaces also changed; on the other hand, the energetic analysis results showed adsorption energies increase with carbon numbers increase due to its larger surface contacting areas and lower aspect ratio, which resulted in stronger interaction with the surfaces. Further, paraffin waxes showed to adsorb easily on Fe surfaces than oxide surfaces. At temperatures below Wax Appearance Temperature (WAT) on both simulations and experiments showed wax deposition. The lower adsorption energy capacity observed on the Fe2O3 pipeline surface confirms it's vitality and suitability for crude oil transportation pipelines surface lining material.