Hydrophilic Nanoparticles Facilitate Wax Inhibition

Abstract

A new class of hybrid pour point depressants (PPDs) are developed on the basis of poly(octadecyl acrylate) (POA) functionality and POA/nanosilica hybrid particles. Activity performance is demonstrated using a model waxy oil system consisting of 10 wt % macrocrystalline wax dissolved in dodecane, effectively emulating the essential characteristics of waxy petroleum fluids. Differential scanning calorimetry (DSC) evidence confirms that POA molecules enhance the solubility of wax in the continuous oil phase, reducing the wax appearance temperature. The presence of POA also serves effectively to modulate the crystal morphology to a more regular spherical-like shape, instead of the disc-like morphologies common to pristine paraffin wax crystals, affecting reduced gelation temperatures in accordance with percolation theory predictions. In addition, rheometric yield stresses decrease with increasing dosage rates of POA. A solvent-blending protocol is followed to subsequently prepare POA/nanosilica hybrid particles. Optimal PPD performance of the hybrid particle system is attained at a dosage rate of 100 ppm. At dosages higher than the optimal dose, the gel strength increases in an analogous manner to the directionality of the Einstein equation for viscosity. The POA/nanosilica hybrid particle system provides spherical templates for wax precipitation, resulting in a compact precipitate structure, which suppresses gelation and improves the flowability of the model waxy oil by several orders of magnitude. DSC data confirm that a vast majority of the POA molecules become solubilized in the continuous oil phase upon dispersion of the hybrid nanoparticle system. As such, the free POA molecules enhance wax solubility in the continuous oil phase. Hydrophobic nanoparticles retain a more robust ability to modulate waxy oil rheology at low-dosage rates, as compared to purely polymeric functionality. The primary mechanism of hybrid particle PPDs involves heterogeneous nucleation activity. The hybrid particles effectively provide solid–liquid interface sites as wax precipitation templates, which result in spherical-like spherical wax morphologies. The compact morphologies hinder and suppress the percolation process necessary to form a volume-spanning network of wax crystals. As such, the hybrid nanoparticles constitute effective and economic PPD additives and may serve as the basis for next-generation environmentally friendly wax inhibition agents, by reducing the amount of additives needed.