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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.

Nanoparticles coated with poly(octadecyl acrylate) (POA) pour-point depressants are investigated, and the effect of the amount of coating material is investigated and compared with the effect of the coating material without nanomaterial. Pour point depressing performance is demonstrated using a model waxy oil system in order to isolate material performance. The present study focus on the effect of how the amount of coverage of the nanoparticles affects the performance of the nanoparticles. In order to access this information, the adsorption of the poly(octadecyl acrylate) (POA) on silica (the material of the nanoparticles) was determined using a quartz crystal microbalance with dissipation monitoring (QCM-D). Adsorption was performed from two different solvents, toluene and dodecane, because the nanoparticles were been prepared from toluene while the model system used is dodecane-based. Using the QCM-D data, it was possible to prepare nanoparticles with different amounts of poly(octadecyl acrylate), as de...

Introduction of nanomaterials constitutes a novel and efficient means to enhance the performance of polymeric pour point depressants (PPDs). Based on the specific layered structure and favorable cationic exchange characteristics of nano-clay particles in the presence of charged organic compounds, an original hydrophilic nano-clay is first modified by octadecyl trimethyl ammonium chloride (OTAC) and then by polyoctadecylacrylate (POA). The modified nano-clay serves as an effective nanocomposite PPD. Compared to an identical content of POA, addition of POA/clay nanocomposite PPD to Changqing waxy crude oil improves the rheological properties while elevating the wax appearance temperature of the oil. Polarized microscope observation shows that POA/clay nanocomposites provide wax nucleation sites upon which wax molecules assemble and precipitate. Addition of POA/clay nanocomposite PPD results in larger and more compact crystal morphology, thus inhibiting the formation of a network structure, and further improving rheological properties of waxy crude oil.

Rheological measurement of wax–oil gel breakage is highly susceptible to the phenomenon of adhesive breakage, hindering instrument-scale replication of cohesive breakage processes. Adhesive breakage measurements are notoriously irreproducible due to strongly nonaffine gel deformation. Efforts to ensure mechanical fixation give rise to spatially inhomogeneous deformation fields in the measuring geometry, particularly with respect to azimuthal and radial location. To elucidate the functional role of mechanically fixating geometries during gel breakage processes, three model solutions were prepared containing 5, 7.5, and 10 wt % macrocrystalline wax in dodecane. Rheograms were acquired in controlled deformation mode at imposed shear rates in the range of 0.1–1.0 s–1 using a vane or a cone and plate geometry. Yield stress values, nominally ascribed to primary peak height, were established based on 95% confidence intervals. Yielding trends confirm that adhesive breakage is particularly pronounced in high solid-fraction gels. A solid-fraction threshold delineates cohesive breakage in low solid-fraction gels from inherent adhesive breakage in high solid-fraction gels. Mechanical fixation in a vane geometry precludes wall slippage, ensuring cohesive breakage; resultant yield stress values follow a modified power-law dependency on the total wax content, characterized by a power-law exponent of ∼1.25. Nonuniform deformation within the vane geometry confers a modest (artificial) reduction in apparent yield stress value as a consequence of azimuthal integration of the torque signal. Nonuniform deformation also confers a distinct (artificial) broadening of the breakage peak and is accompanied by the appearance of a new shoulder peak located at a deformation value of ∼5. Conversely, in the cone and plate geometry, adhesive breakage occurs inherently for high solid-fraction gels and is manifested by a substantial reduction in measured yield stress, albeit without a concomitant peak broadening. Hence, the practical utility of the cone and plate geometry is limited to low solid-fraction gels that inherently exhibit cohesive breakage behavior. Mechanical fixation afforded by the vane geometry effectively precludes wall slippage, enhancing measurement reproducibility while ensuring a cohesive breakage of high solid-fraction wax-gels that otherwise rupture in adhesive mode. Locked until 22.1.2020 due to copyright restrictions. This document is the Accepted Manuscript version of a Published Work that appeared in final form in [Energy & Fuels], copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.energyfuels.8b02725

A new class of hybrid pour point depressants (PPDs) are developed on the basis of poly(octadecyl acrylate) (POA) functionality and POA/nanosilica hybrid particles. Activity performance is demonstra...

Wax crystallization processes are investigated using differential scanning calorimetry, near-infrared spectroscopy, and nuclear magnetic resonance spectroscopy. The performance of a chemical additive is assessed using calorimetry and NMR. Heat flows of model waxy oils are obtained using differential scanning calorimetry, providing the wax appearance temperature and crystallization profiles. The effect of cooling rate, wax content, asphaltene, and chemical additive on the wax appearance temperature is investigated. The wax appearance temperature increases with increasing wax contents. The wax appearance temperature decreases in the presence of chemical additive, effectively increasing the instantaneous supersaturation. Furthermore, near-infrared spectroscopy and nuclear magnetic resonance spectroscopy are utilized to determine wax appearance temperature. The NMR experiments quantify liquid and solid fractions at thermal equilibrium conditions, effectively circumventing the need for dynamic thermal techniques.

The influence of microcrystalline wax addition upon the rheological properties of model wax-oil gels is investigated. Addition of less than 1 wt % microcrystalline wax to a model oil consisting of 5 wt % macrocrystalline wax in dodecane shows no significant impact on the WAT and gelation temperature. Beyond 1 wt % added microcrystalline wax, increases in WAT and gelation temperature are observed and are attributable to the higher crystallization temperature of the microcrystalline wax. The effect of microcrystalline wax addition upon the WAT and gelation temperature is shown to be attributed to merely overlapping compositions of macro- and microcrystalline wax. However, a substantive effect of microcrystalline wax addition is observed on the yield stress. Addition of 0.13 wt % microcrystalline wax reduces the yield stress of the waxy oil model from 238.0 to 22.5 Pa. Addition of 0.5 wt % microcrystalline wax decreases the yield stress to 5.4 Pa, which is close in value to the yield stress of neat 5 wt % microcrystalline wax gel. Microscopic images reveal two mechanisms leading to formation of weak mixed wax gels. At low to medium addition of microcrystalline wax, microcrystalline crystallites formed during cooling provide nucleation sites for subsequent precipitation of macrocrystalline wax. Macrocrystalline wax crystals formed in contact with microcrystalline crystallites are smaller in size and the growth is localized, in comparison to neat macrocrystalline wax. Modified macrocrystalline wax precipitation leads to uneven dispersion of the macrocrystalline crystals in the liquid phase. At high concentration, microcrystals form throughout the sample prior to precipitation of macrocrystalline wax. Hence, only a small and discrete space remains for macrocrystalline crystals to grow, forming small crystals. Interlocking among macrocrystals is spatially hindered by the presence of microcrystalline crystallites. In this condition, the system completely behaves as a microcrystalline gel. This investigation provides a plausible mechanistic account for the known gel weakening activity of microcrystalline wax. © American Chemical Society 2018. This is the authors accepted and refereed manuscript to the article. Locked until 23.04.2019 due to copyright restrictions.

Paraffin precipitation during pipeline transport of waxy crude oils gives rise to several challenges, including wax deposition, flow reduction, and gel formation, which adversely impacts pipeline performance. Small dosages of polymeric wax inhibitors or pour point depressants comprise an effective preventative measure. In this article, the structural character, functionality, and mechanisms of the polymeric additives targeting paraffin wax are reviewed, and factors influencing product efficacy are summarized. Most polymeric additives contain a nonpolar moiety as well as a polar moiety, with the exception of crystalline-amorphous copolymers. Via nucleation, adsorption, co-crystallization and solubilization interactions, polymeric additives alter the morphology and interface of precipitated wax crystals, inhibiting wax deposition, improving flow, and impeding gel formation. The presence of asphaltenes significantly impacts wax crystal morphology and interfaces, thus influencing the mechanism of polymeric ad...

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.

Thermal behavior of waxy oils is investigated using the techniques of thermogravimetric (TG) analysis and differential scanning calorimetry (DSC). Model waxy oils and real waxy crude oils are utilized. Decomposition temperatures of waxy oils are obtained using TG analysis. The effects of thermal history, wax content, and additive on the gelation process of waxy oils are investigated using DSC. The DSC method provides a measure of wax solubility as well as solid fraction. An integration method and a computation method are utilized to predict solid fraction. In addition, wax crystallization onset points are obtained at the cooling rates ranging from 1 to 20 °C min−1. Similarly, wax dissolution endset points are obtained at heating rates ranging from 1 to 20 °C min−1. Extrapolated onset and endset points yield wax precipitation temperature and wax dissolution temperature, respectively. Subsequently, wax solubility curves are obtained using thermodynamic computations. A wax precipitation temperature method and a wax dissolution temperature method combine thermodynamic phase behavior with onset/endset points to predict solid fraction. Both the wax precipitation temperature method and the wax dissolution temperature method can predict solid fraction of waxy oil samples. The wax precipitation temperature method and the wax dissolution temperature method are accurate when the temperature is close to the wax appearance temperature. A heat-integration method provides accurate values of the solid fraction at temperatures significantly below the wax appearance temperature. Therefore, integration method and wax precipitation temperature/wax dissolution temperature method are combined to predict solid fraction. The effect of solid fraction on yield stress is also investigated using differential scanning calorimetry and rheometry. Finally, a new solid fraction dependent gel strength model is obtained for shut in and restart of waxy crude oil pipelines.

An experimental rheometric investigation is performed to assess the utility of various gelation point determination methodologies. Controlled shear stress and controlled shear rate methods are developed to investigate gelation processes in waxy oils. The nonoscillatory rheological method exhibits high reproducibility for model wax oils as well as for real crude oils. In addition, the nonoscillatory methods are in good agreement with standard oscillatory gel point determination methods. The effect of imposed shear stress, imposed shear rate, and cooling rate on gelation point is investigated with two types of model oils: 5 wt % macrocrystalline wax in Primol 352 and 5 wt % macrocrystalline wax in dodecane. In addition, the effect of wax content on gel temperature of macrocrystalline wax in dodecane is investigated. Moreover, the effect of additives (A3 and A4) on gelation point of a real crude oil UL-YS1 is investigated. Finally, the gelation temperatures of 5 wt % macrocrystalline wax in Primol 352, crude...

An experimental investigation of waxy oil gelation behavior is performed using the methods of rheometry, optical analysis, tensiometry, and microscopy. Thermal history, shear history, asphaltene content, and chemical additives influence the gelation process. Consequently, the final gel state is strongly correlated to the gelation conditions. Various model wax–oil systems are prepared, including 5 wt % microcrystalline wax or 5 wt % macrocrystalline wax in dodecane, as well as 5 wt % macrocrystalline wax in Primol 352. Real waxy crude oils UL-YS1 and Se-7-E06 are also investigated. A new yield stress model is developed on the basis of experimental results and a modified Eyring theory to provide gel strength predictions for petroleum transport pipelines. In the absence of shear during gelation, the yield stress can be correlated with the thermal history. However, for non-quiescent gelation conditions, the gel strength is also dependent upon the imposed shear history during the gelation process. The imposed ...

Gelation and breakage of model wax–oil systems is investigated using microscopy, densitometry, rheometry, and XRD. Various model waxy oils are prepared, including 1 to 20 wt % (w/w) macrocrystalline wax in dodecane, 1 to 20 wt % microcrystalline wax in dodecane, and 5 wt % macrocrystalline wax in Primol 352. The influence of shear history, thermal history, and fluid composition is ascertained. A novel gel breakage model is introduced which spans the entire mechanical response of wax gels from initial Hookean behavior at low strains to equilibrium slurry flow at the infinite strain limit. The local rheology model will benefit shut-in and restart processes of waxy crude pipelines via application of standard fluid mechanics relationships.

Fluid characterization is a key technology for success in process design for crude oil mixtures in the future offshore. In the present article modern methods have been developed and optimized for crude oil applications. The focus is on destabilization processes in w/o emulsions, such as creaming/sedimentation and flocculation/coalescence. In our work, the separation technology was based on improvement of current devices to promote coalescence of the emulsified systems. Stabilizing properties based on particles was given special attention. A variety of particles like silica nanoparticles (AEROSIL®), asphalthenes, wax (paraffin) were used. The behavior of these particles and corresponding emulsion systems was determined by use of modern analytical equipment, such as SARA fractionation, NIR, electro-coalescers (determine critical electric field), Langmuir technique, pedant drop technique, TG-QCM, AFM.

A near-infrared (NIR) scattering technique is used to measure the wax appearance temperature of several petroleum fluids under nonquiescent conditions. Within the Rayleigh scattering limit, NIR attenuation measurements at a wavelength of 1100 nm can theoretically detect wax crystallites

Paraffin wax deposition is a ubiquitous phenomenon in the petroleum production industry. Many types of internal pipe coating materials have previously been tested for preventing wax deposition, but none have demonstrated successful performance. It has become increasingly evident that an improved knowledge of the chemistry and physics of wax deposition will be required in order to develop new wax-repellent materials. In particular, it is important to understand the mechanisms used to inhibit similar deposition problems in outside industries. In order to achieve these objectives, a state-of-the-art literature survey was performed to identify the role and function of nonstick and anti-adhesive surfaces in the food, paint, marine, automotive, biomedical, tribological, optical, and petroleum industries. Information was derived from academic, industrial, and intellectual property sources. This review presents a comprehensive compilation of materials and surface modification techniques that show potential for in...

Paraffin gel formation in sub-sea petroleum transportation pipelines is a common problem encountered during operational and emergency production shut-down periods. Restart of a gelled oil pipeline usually requires the application of a large pressure drop across the pipeline length. In severe cases, permanent wax plugs have formed, resulting in the loss of production capacity. In this investigation, the structural breakdown of a quiescently-formed model wax-oil gel is measured at shear rates ranging from approximately 10−5 sec−1 to 1 sec−1. It is demonstrated that gel breakdown can be mathematically modeled using a time-dependent Bingham equation in which the yield stress follows third order degradation kinetics. The Bingham plastic viscosity term becomes significant at shear rates above ∼10−1 sec−1 and follows a similar third order decay profile with time. When the imposed shear rate is altered in a step-wise manner during the course of the gel breakage, transient non-linear viscoelastic effects are also ...