PPD architecture development via polymer–crystal interaction assessment

Abstract

Abstract A novel filtration technique is used to investigate the physical nature of interactions between pour point depressant polymers and paraffin wax crystals, with the aim of furthering development of new PPD polymer architectures. Polymer–paraffin interactions are isolated using model waxy fluids containing commercial paraffin wax dissolved in an organic solvent. Initial physical property characterization comprising pour point, wax appearance temperature and carbon number distribution serves to identify a Fischer–Tropsch wax as suitable for the investigation, with properties similar to waxes naturally occurring in paraffinic crude oils. Five pour point depressant polymers with various active chemistries are selected for the investigation. The filtration technique reveals concomitant trends in quantitative phase partitioning and liquid depletion, showing two separate and distinct activity modes: (1) thermodynamic and (2) interfacial. Quantitative phase partitioning analysis shows that thermodynamically-active architectures induce a drastic reduction in mid-range paraffin solubility, and steady state fluorescence emission analysis reveals that thermodynamically-active polymers are depleted during paraffin precipitation, confirming co-crystallization of paraffin wax molecules together with PPD polymers. Gibbs free energy thermodynamic equilibria computations performed for untreated systems confirm deviatoric precipitation induced by thermodynamically-active PPD architectures. Interfacially-active polymer architectures, on the other hand, show a distinctly dissimilar activity mode. Interfacially-active polymer architectures are not heavily depleted during paraffin precipitation and do not induce an extraordinary reduction in mid-range paraffin solubility, but are instead preferentially active at the interface. Both polymer types may impart steric repulsion, entropic repulsion, and/or morphological modulation to afford overall fluid flowability and inhibit gel formation. Finally, concrete evidence is presented of paraffin solubilization comprising an important activity mode for certain PPD architecture types, based on DSC data, cross polarized microscopy, steady state fluorescence, as well as high temperature gas chromatography. In aggregate, the filtration technique establishes a useful R&D tool for assessment of PPD activity mechanisms, elegantly illustrating architecture-modulated activity modes on a compositional basis.