Influence of Wax Inhibitor Molecular Weight on Solution Crystallization and Rheology of Monodisperse Waxes

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.

Effects of Structure and Asphaltenes on Paraffin Inhibitor Efficacy in a Light Crude Oil Model

“…Each PI is characterized as having a weight- average molecular weight of ∼5000 g mol −1 (GPC, THF, 1 mL m −1 , poly(propylene glycol) standards), and all contain similar mixtures of petroleum-derived heavy aromatic naphtha solvents (Table 1). Given that dependencies of efficacy on molecular weight are known and have been reported in the literature, 30 our selection of PIs of similar molecular weight seeks to remove this effect. 2.2.…”

Synthesis of crystallizable poly(behenyl methacrylate)-based block and statistical copolymers and their performance as wax crystal modifiers

“…This concentration is at the lower end of the typical wax content in crude oils (5–30% w/w) 12 , but such conditions produced sufficient wax crystals for characterization by optical and scanning electron microscopy (SEM). Moreover, Ashbaugh et al 19 and Kurniawan et al 46 used comparable wax concentrations in their studies. Macrocrystalline paraffin wax comprises mainly low molecular weight n -alkanes (C 16 –C 40 ) and generally crystallizes in the form of either needles or platelets.…”

Advances in and Perspectives on Strategies for Improving the Flowability of Waxy Oils

“…Paso et al 239 explored the mechanism of pour point depressant action from both thermodynamic and interfacial aspects, and concluded that the interaction mechanism between pour point depressant and wax molecules is not single, and pour point depression is generated by a combination of thermodynamic interaction between pour point depressant and wax and interfacial modification. Kurniawan et al 240 thought that the interaction between polymeric pour point depressants and wax crystal interfaces is stronger for high molecular weight polymeric pour point depressants, while ensuring the solubility of polymeric pour point depressants in the solution environment is also crucial for their efficacy. Madani et al 241 studied the viscosity of crude oil before and after dosing using data mining.…”