Wax-Inhibitor Interactions Studied by Isothermal Titration Calorimetry and Effect of Wax Inhibitor on Wax Crystallization

Abstract

Isothermal titration calorimetry (ITC) is applied to investigate the interactions of polymeric pour-point depressants (PPDs) or asphaltenes with macrocrystalline wax in a model oil system. This represents a novel approach to measure and compare the heat of interaction for solid wax crystals with different wax inhibitors (WIs). In addition, the PPDs were characterized via size-exclusion chromatography (SEC) and differential scanning calorimetry (DSC), and the effect of PPDs or asphaltenes onto the wax appearance temperature (WAT) and the formed wax-oil gel was investigated using DSC, cross-polarized microscopy (CPM), and rheometry. The results show that there is detectable interaction heat with wax crystals for all PPDs, and asphaltenes. DSC and viscometry show a decrease in observed WAT for all WIs as compared to the additive-free blank case. CPM imaging shows differences in structure, shape, and size of the wax crystals formed in presence of particular PPDs or asphaltenes, which is also seen as a decrease in gel-breakage strength. Overall, there is no direct correlation between interaction heat and WI performance characteristics, such as a high decrease in WAT or gel strength. Ethylene-vinyl acetate copolymer (EVA) with 25 % vinyl actetate accounts for the highest interaction heat measured, but shows effective decrease in wax crystals size for only part of the crystals while acting as a flocculate to others, which resulted in a low effect on gel strength.Commercial PPDs based on polycarboxylate have the best performance for the model oil system used, but show only overage interaction heat values. The interaction heat of asphaltenes with wax is measurable, but lower than for the PPDs tested. The presence of asphaltenes significantly lowered the gel strength and changed the wax crystal morphology to rounder and dendrite like shapes. These findings suggest that asphaltene compounds are incorporated into the wax crystals, changing the structure and shape of the crystals.

Effect of Polyethylene-Vinyl Acetate Pour Point Depressants on the Flow Behavior of Degassed Changqing Waxy Crude Oil before/after scCO2 Extraction

“…With further cooling, the liquid phase among the crystal branches gradually solidifies into the crystallization structure. The precipitated wax crystals gradually crosslink to form a 3D network structure and bind the light oil. , At this stage, G ′ is increasing much faster than G ″, resulting in the more and more obviously elastic response of the system. For oil sample A, G ′ equals to G ″ at the gel point of 23.8 °C, while the gel point is 25.7 °C for oil sample B.…”

“…In addition, the difference in polarity between the vinyl acetate (VA) segment of EVA and wax molecules inhibits the growth of wax crystals into a two-dimensional plane. The growth speed of the wax crystal in the direction perpendicular to the plane is accelerated, as well as the shape of the wax crystal is also changed. − Normally, the wax crystal morphology can be summarized as a needle-shaped one-dimensional structure, sheet-like or plate-like two-dimensional structure, and spherical or granular structure. , The addition of EVA changes the morphology of the precipitated wax crystal into large spherical or granular-like and decreases the specific surface area/surface energy of the wax crystal, thus making it difficult to aggregate into a network structure.…”

Influence of Monomer Ratio on the Performance of Poly(octadecyl acrylate-co-styrene) as Pour-Point Depressants

“…This illustrates that the process of paraffin wax crystal growth in crude oil can be influenced by POA and POA-S-3, the lower of onset crystallization temperatures were consistent with those reported elsewhere. 6,36 Meanwhile, part of the paraffin molecule cocrystallized with the PPDs molecule with alkyl side chains and the paraffin wax crystallization process can be disrupted by POA-S-3 significantly. The presence of styrene with polar groups can increase the adsorption of PPDs molecules attached to the surface of wax molecules.…”

“…Waxy crudes pose serious flow assurance issues to prevent wax deposition in oil exploitation, transportation, and refining. − There are several strategies to avoid wax problems downhole and in flowlines. Methods of chemical wax control (removal and prevention), especially pour-point depressants (PPDs), can be used to improve oil flowability, besides insulation, mechanical removal, heating, diluent, etc. − Among these chemicals, polymers with comb structures are widely used as wax inhibitors throughout the world. − Nonpolar moieties of comb polymers can cocrystallize with waxes via van der Waals interactions, while a moderate increase in some types of polar moieties lowers the crystallinity and aids solubility, which permits the avoidance of deposition of paraffin waxes as well as changes the wax crystal morphology. , Polyacrylate-type PPDs are typical comb polymers, as they can change the ratios of nonpolar and polar moieties to modify their architecture as well as improve the performance of wax PPDs and adaptability . Polyacrylate polymers with polar moieties, which are reported to interact with n -alkanes, can improve the crude oil low-temperature fluidity .…”

Phase boundaries for synthetic light oils and gas condensate mixtures using predictive equations of state with a solid solution model

“…The potential threat to the world economy is clearly enormous due to paraffin wax deposit and its repercussions. As a result, studying wax formation and mitigation has been continued for ages …”