Effect of Hydrophobic/Hydrophilic Groups of Surfactants on Wax Deposition Studied by Model Waxy Oil System

Abstract

Abstract It is well known that surfactants can be used as a wax dispersant, however, with properly adjusted ratios between the hydrophobic and hydrophilic groups of non-ionic surfactants, they can not only reduce the waxy oil pour point, but also reduce the detected wax appearance temperature (DWAT) and thus reduce wax deposition. Non-ionic surfactants with different numbers of hydrophobic/hydrophilic groups were studied as wax inhibitors using a model waxy oil system. Two model oils with different amounts and distribution of wax in dodecane were used in this study. High temperature gas chromatography (HTGC) was used to analyze the wax distributions. Surfactants with varying levels of ethoxylation and saturation were studied to find the most efficient structures for wax inhibition. A pour point tester was employed as an initial screening tool to determine the oil pour point and DWAT. A Turbiscan was used to evaluate the wax dispersing capabilities of the surfactants. Capillary flow through (CFT) wax deposition tests were then performed to verify the wax deposition reduction efficiency and to study the effect of the test parameters on wax deposition. The results showed that a surfactant with a moderate number of linear saturated alkane chains at an optimized dosage level can interact with the wax in dodecane, and thus reduce the pour point and DWAT. More alkane chains make the surfactants perform as a wax inhibitor (WI) but cause the solubility issues. Hydrophilic groups on the surfactants improve their solubility and interfere with the formation of wax crystals; however, having too many results in the surfactant self-assembling. The interaction between surfactants and wax changes with wax molecular weight (MW) and content. By optimizing the balance of hydrophobic and hydrophilic groups, the surfactant's wax inhibition performance can be improved. From this systematic study on the kinetic and dynamic behaviors of wax deposition, it was demonstrated that surfactants can be optimized to inhibit wax crystallization. By better understanding the relationship between their chemical structures and their performance, surfactant selection can be optimized with purpose-designed lab screening tests. Surfactants which are effective at wax inhibition could further mitigate wax deposition and keep the formulated WI package cost effective.