Modifying Commercial Poly(ethylene-vinyl acetate) to Improve Its Performance as a Pour Point Depressant: A Study in Waxy Model Oils at Different Concentrations.

Abstract

Poly-(ethylene-vinyl acetate) (EVA) is the most used pour point depressant (PPD) in crude oil. Because it does not exhibit a high performance in all kinds of oils, other structures have been studied. Both hydrolyzed EVA and EVA:clay minerals can exhibit a higher performance than unmodified ones, but their mechanisms of action have not yet been fully clarified. In this work, we evaluated for the first time a nanocomposite based on EVA joining the contribution of hydrolysis and clay minerals, besides the proposition of action mechanisms. For this purpose, two EVA commercial samples (EVA7 and EVA11 containing 7.0 and 11.0 mol % vinyl acetate, respectively) were hydrolyzed, and EVAOH:palygorskite nanocomposites were prepared. The products were characterized by nuclear magnetic resonance, energy-dispersive spectroscopy, and scanning and transmission electron microscopy. Their behavior was evaluated in terms of pour point and morphology by optical microscopy, using waxy model oils with different wax contents in toluene. Both unmodified EVA and hydrolyzed EVA7 exhibited the worst performance. In contrast, EVA11:PALY, EVA11OH, and EVA11OH:PALY outperformed EVA11. However, the combined effect of hydrolysis and nanoclay in the EVA11OH:PALY nanocomposite did not significantly improve its performance. This behavior suggests that the effect of the hydroxyl groups overlapped that of the clay mineral. Optical microscopy images revealed that the additives produced different wax crystal morphologies, which is directly related to the performance. Moreover, the spacing between crystals plays a more important role in oil fluidity than the reduction in the crystal size. A correlation between the polarity and solubility of the additives in the model system and their action mechanisms could be proposed.