Wax Inhibition by Comb-like Polymers:  Support of the Incorporation−Perturbation Mechanism from Molecular Dynamics Simulations

Abstract

Deposition of wax on a cold surface is a serious problem in oil production. Progress in developing more effective wax inhibitors has been impeded by the lack of an established mechanism connecting the molecular structure to inhibitor efficiency. Some comb-like polymers having long alkyl side chains are known to decrease the rate of wax formation. Among several possible mechanisms, we investigate here the incorporationperturbation mechanism. According to this mechanism, the inhibitor molecules in oil are preferentially partitioned (incorporation) toward the wax-rich (amorphous) wax deposits (soft wax), which then serves as a perturbation to slow down the ordering transition of soft amorphous wax into more stable but problematic hard wax crystals. Indeed, molecular dynamics simulations on an effective inhibitor molecule in both the oil phase and in the amorphous wax phase support the idea that the oil-to-wax partition of the inhibitor is energetically favorable. With the inhibitor molecule embedded, the structure of wax crystal is disturbed, significantly decreasing the order and significantly lowering the cohesive energy density relative to that of the pure wax crystal, supporting the slower transition from soft wax to hard wax. Thus, in the presence of an effective wax inhibitor, crystallization (formation of hard wax) is slowed dramatically, so that there is time to flush out the soft wax with a high-pressure flow inside the pipeline. This suggests design principles for developing improved wax inhibitors.

Investigation of inhibitors efficacy in wax deposition mitigation using a laboratory scale flow loop

“…It has been reported that comb‐shaped inhibitors are known to be more effective compared to linear inhibitors . The comb‐shaped inhibitor (oligomer of poly [octadecyl acrylate]) reduces the cohesive energy density (driving force for ordering transformation) three times compared to no inhibitor . The linear inhibitor can self‐assemble into micelle‐like aggregates providing a crystalline form and soluble hairy platelet structures that surround the core, and these structures can reduce the super‐saturation, delay the growth rate of wax crystals, and form abundant smaller wax crystals .…”

“…Even though many studies were reported in the literature, the exact mechanism of wax inhibitors is still not completely understood. Several mechanisms including the incorporation‐perturbation theory, nucleation sequestering theory, and adsorption on pipe wall theory have been proposed. The nucleation sequestering theory suggested that the wax inhibitor can affect the nucleation process.…”

Targeting High Molecular Weight Wax

“…To help prevent the nucleation and formation of wax crystals, wax inhibitors are typically used during crude oil production. Wax inhibitors are generally comb polymers, ethylene polymers, and copolymers, and other branched polymers with long alkyl chains (Jang et al 2007;Kelland 2009). These polymers contain a segment capable of solubilizing wax molecules and a segment that interferes with the packing of wax molecules to form crystals.…”

Molecular Recognition of Wax Inhibitor Through Pour Point Depressant Type Inhibitor

“…Other work have successfully studied the interaction between crystal planes of wax and EVA in diesel fuels had been made by Wu et al and Zhang et [17], [18]. In addition, the mechanism of wax inhibition was successfully been studied by Jang et al (2007) where their focussing on incorporation-perturbation mechanism. This mechanism investigation included the enthalphic aspect of the molecular level interaction between a wax and inhibitor in crude oil [2].…”

“…In addition, the mechanism of wax inhibition was successfully been studied by Jang et al (2007) where their focussing on incorporation-perturbation mechanism. This mechanism investigation included the enthalphic aspect of the molecular level interaction between a wax and inhibitor in crude oil [2]. Behind to this mechanism, the inhibitor molecules in oil are preferentially partitioned (incorporation) toward the wax-rich (amorphous) wax deposits (soft wax), which then serves as a perturbation to slow down the ordering transition of soft amorphous wax into more stable but problematic hard wax crystals.…”