Abstract
Molecular weight fractionation via stepwise precipitation or chain scission is performed on four pour point depressant polymers to study the pour point reduction mechanism. An homologous series of model oils is prepared by dissolving 5 wt % of a single-component paraffin wax (n-C24, n-C28, n-C32, or n-C36) in n-C12. The polymers are dosed at 500 ppm in the model oils and moderately reduce crystallization temperatures by elevating the nucleation barrier. Polymers containing carboxylate or acrylate moieties also modestly enhance equilibrium wax solubility. Reduction in crystallization temperature is largely independent of polymer molecular weight, except for carboxylate polymers where low molecular weight fractions are largely ineffective. In general, model fluids containing shorter wax chains show a larger reduction in crystallization temperature than model fluids containing longer wax chains. However, yield stress reduction often shows a distinct dependence on polymer molar mass. Low molecular weight fractions of carboxylate and acrylate polymers provide smaller reductions in yield stress than the overall parent fraction. Cross-polarized microscopy reveals that polymers reduce the crystal size, alter the crystal morphology from platelet to needle-like, and induce branching. Crystal branching and formation of dendrite-like structures result from strong polymer binding at the wax crystal interfaces. Hence, single-component wax crystal branching occurs phenomenologically along with yield stress reduction.
Highlights
Flow assurance strategies for prevention, mitigation, and remediation of production problems caused by paraffin wax typically involve implementation of thermal, mechanical, or chemical management measures.[1]
pour point depressants (PPD) τ and PPD Ω are manufactured for general purposes, and HPLC chromatograms indicate that both PPDs have narrow molecular weight distributions.[25]
The PPDs and PPD fractions are doped into an homologous series of waxy model oils containing single-component waxes of varying carbon chain length
Summary
Flow assurance strategies for prevention, mitigation, and remediation of production problems caused by paraffin wax typically involve implementation of thermal, mechanical, or chemical management measures.[1]. Wang reported that among three polymethacrylate wax inhibitor polymers tested, the polymer with the longest alkyl side-chain (C18) exhibited the strongest effect in suppressing the WAT and elevating the WDT of a model fluid consisting of n-C24 dissolved in n-C10.21 Jung et al demonstrated that varying the vinyl acetate content of EVA influences the nucleation, structure, and morphology of treated n-C32 wax crystals.[22] Application of poly(ethylene−butylene) random copolymers of various ethyl side branching frequencies to model monodisperse n-paraffin solutions reveals that lower ethyl side branching frequencies (i.e., higher crystallinity) are more effective toward longer n-paraffin components, while higher ethyl side branching frequencies (i.e., lower crystallinity) are more effective toward shorter n-paraffin molecules.[23] Optimal pour point depression efficacy for systems containing 20 wt % wax has been shown to occur when the PPD polymer solubility threshold temperature is ∼15 °C lower than the WAT.[24]. The utilized series of paraffin carbon chain lengths facilitates elucidation of component-specific efficacies and interactions
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