Elizabete F. Lucas

Poly(ethylene-co-vinyl acetate) (EVA) as wax inhibitor of a Brazilian crude oil: oil viscosity, pour point and phase behavior of organic solutions

Abstract Several techniques have been used to minimize the problems caused by the wax deposition, and the continuous addition of polymeric inhibitors is considered an attractive technological alternative. The addition of copolymers like polyacrylates, polymethacrylates or poly(ethylene-co-vinyl acetate) (EVA) permit to inhibit the deposition phenomenon; nonetheless, this effect is specific, i.e. similar copolymers present different performance depending on their physical–chemical properties in solution. In this work, the influence of the EVA vinyl acetate content on the viscosity and the pour point of a Brazilian crude oil were evaluated. A correlation between both results was also obtained. The phase behavior and the solubility parameter of EVA copolymers, with different vinyl acetate contents, were investigated in various solvents together with an evaluation of the efficiency of these copolymers as pour point depressants for two different samples of crude oil. EVA copolymers containing 20, 30, 40 and 80 wt.% of vinyl acetate were used and tests with the crude oil were carried out using 50, 500, 1000 and 5000 ppm of EVA as additive. The results obtained from viscosity measurements showed that only below the temperature at which wax crystals start forming did the copolymer exhibit a strong influence in the reduction of oil viscosity, at an optimum concentration. The pour point results revealed EVA 30 to be the most efficient. The results obtained from both experiments showed that the viscosity and the pour point behaviors do not show good correlation. Not only the solubility parameter and the vinyl acetate content, but also the molecular weight and polydispersity have an important influence on both phase behavior and pour point depression. Furthermore, it was confirmed that the additive must present a reduced solubility at a temperature close to the crude oil cloud point. This, however, is not the only factor that determines the efficiency of the additive as paraffin/wax deposition inhibitor.

Polymer science applied to petroleum production

The science of polymers, more specifically, synthesis, characterization, and physicochemical properties in solutions, has wide application in the petroleum industry, which uses polymers as components of fluids or additives to correct problems that affect oil production and/or increase production costs. Polymers are utilized during all phases, from drilling to treatment of oil and water. Research on the synthesis of polymers and their respective characterization aims to develop new molecules, with controlled structures, for various applications, having one or more objectives, namely: (1) to enhance operating efficiency; (2) to reduce costs; and (3) to elucidate mechanisms of action that can help in the development of new technologies. The evaluation of the physicochemical properties of a polymer in solution in many cases permits establishing useful correlations between its properties and performance in a specific application, besides providing insight into the mechanisms inherent in the production system, as is the case of stabilization of asphaltenes. Our research group has applied the knowledge of polymer science to the petroleum industry, focusing on the following functions: viscosification, inhibition of clay swelling, formation of filter cake, drag reduction, divergence, modification of wax crystals, stabilization of asphaltenes, emulsification, demulsification, and cleaning of solids systems contaminated with petroleum, among others.

Effect of the structure of commercial poly(ethylene oxide-b-propylene oxide) demulsifier bases on the demulsification of water-in-crude oil emulsions: elucidation of the demulsification mechanism

Water-in-crude oil emulsions are formed during petroleum production and asphaltenes play an important role in their stabilization. Demulsifiers are added to destabilize such emulsions,however the demulsification mechanism is not completely known. In this paper, the performances of commercial poly(ethylene oxide-b-propylene oxide) demulsifiers were studied using synthetic water-in-oil emulsions and model-systems (asphaltenes in organic solvent). No change in the asphaltene aggregate size induced by the demulsifier was observed. The demulsification performance decreased as the asphaltene aggregate size increased, so it can be suggested that the demulsification mechanism is correlated to the voids between the aggregates adsorbed on the water droplets surface.

Stabilization of asphaltenes by phenolic compounds extracted from cashew-nut shell liquid

The liquid extracted from cashew-nut shell is composed almost completely of phenolic compounds containing 15-carbon chains with variable unsaturation degrees, meta-substituted in the aromatic ring. The similarity of these compounds with the structures described as efficient peptizing agents for asphaltenes, the crude oil polar fraction, induced us to evaluate cashew-nut shell liquid (CNSL) and its derivatives, cardanol and polycardanol, as asphaltene stabilizing agents. The results confirm that CNSL and cardanol have a performance comparable to nonylphenol. Polycardanol was not only less efficient than its monomer, but, instead, enhanced the precipitation of asphaltenes. This effect may be ascribed to the large number of phenol groups present in the polymer that may flocculate the asphaltene particles or increase its polarity, reducing its solubility in aliphatic solvents.

THE INFLUENCE OF VINYL ACETATE CONTENT OF THE POLY(ETHYLENE-CO-VINYL ACETATE) (EVA) ADDITIVE ON THE VISCOSITY AND THE POUR POINT OF A BRAZILIAN CRUDE OIL

Petroleum companies have enhanced the offshore exploration, where the fields are located under deep water. In such cases, the low temperature of the water leads to the cooling of the oil and provokes wax deposition. Several techniques are used to reduce the problems caused by wax deposition. Polymeric additives, as ethylene-co-vinyl acetate co-polymers (EVA), are intensively used. In this work, the influence of the EVA vinyl acetate content on the viscosity and the pour point of a Brazilian crude oil was evaluated, and correlations for these properties as a function of the EVA co-polymer concentration were established. EVA copolymers were used containing 22,32,40 and 82 wt% of vinyl acetate and the tests with the crude oil were carried out using 50, 500, 1000 and 5000 ppm of EVA as additive. The results obtained from viscosity measurements showed that only below the temperature in which the wax crystals start forming the copolymer exhibited a strong influence on the oil viscosity reduction at an optimum concentration. The pour point results showed the best efficiency to EVA 32. The results obtained from both experiments showed that the viscosity and the pour point behaviors do not present good correlations to each other.

POLY(ETHYLENE-CO-VINYL ACETATE) (EVA) COPOLYMERS AS MODIFIERS OF OIL WAX CRYSTALLIZATION

ABSTRACT This work describes the performance of poly(ethylene-co-vinyl acetate) (EVA) copolymers as pour point reducer and organic deposits inhibitor. The molecular weight, molecular weight distribution and vinyl acetate content of the EVA copolymers were determined by gel permeation chromatography and thermogravimetric analyses, respectively. The copolymer with the highest vinyl acetate content (within the range analyzed, 28-41 wt %) exhibited the best performance as organic deposits inhibitor. Results from differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) suggest that the EVA copolymer acts modifying the morphology of the wax crystals.

The Effect of Asphaltenes, Naphthenic Acids, and Polymeric Inhibitors on the Pour Point of Paraffins Solutions

The influence of asphaltenes and naphthenic acids on wax appearance temperature (WAT), wax crystals morphology, and pour point was estimated for solutions of a commercial paraffin sample dissolved in a solvents mixture. In addition, the performance of copolymers obtained by modification of ethylene‐vinyl acetate copolymers as organic deposition inhibitors (ODI) also was studied. Asphaltenes reduced the pour point and this effect increased with the increase in the asphaltenes concentration, indicating that asphaltenes interact with the paraffins to form particles with a different interaction profile. The observation of the wax crystals using optical microscopy revealed that in the absence of additives the solid wax particles form a homogeneous mass, evenly distributed throughout the whole sample having a plane lamellar structure which favor aggregation. When asphaltenes were incorporated, the particles were smaller and less well defined. At higher asphaltenes concentrations, dark particles whose surface resembled asphaltenes also were observed. Naphthenic acids caused a small increase in the pour point and when both fractions, asphaltenes and naphthenic acids, were added together, the asphaltenes seem to have their pour point reduction effect depressed. The ODI presented some efficiency as pour point reducers but, in the presence of asphaltenes, this efficiency was largely enhanced suggesting that beside the alteration of the particles an efficient dispersion mechanism is also necessary to inhibit the aggregation of the wax particles.

Phase behavior of aqueous systems containing block copolymers of poly(ethylene oxide) and poly(propylene oxide)

Phase behavior of aqueous systems containing block copolymers of poly(ethylene oxide (PEO) and poly(propylene oxide) (PPO) was evaluated by building up temperature-concentration phase diagrams. We have studied bifunctional triblock copolymers (HO-PEO-PPO-PEO-OH) and monofunctional diblock copolymers (R-PEO-PPO-OH and R-PPO-PEO-OH, where R length is linear C 4 and C 12-14 ). The cloud points of the polymer solutions depended on EO/PO ratio, polarity, R length and position of the hydrophilic and hydrophobic segments along the molecule. Such factors influence on the solutions behavior was also analyzed in terms of critical micelle concentration (CMC), which was obtained from surface tension vs. concentration plots. Salts (NaCl and KCl) added into the polymer solutions change the solvent polarity decreasing the cloud points. On the other hand, the cloud points of the polymer solutions increased as a hydrotrope (sodium p-toluenesulfonate) was added.

THE INFLUENCE OF A HYDROTROPIC AGENT IN THE PROPERTIES OF AQUEOUS SOLUTIONS CONTAINING POLY(ETHYLENE OXIDE)-POLY( PROPYLENE OXIDE) SURFACTANTS

Abstract The aqueous solution behavior of diblock poly(ethylene oxide)–poly(propylene oxide) (PEO–PPO) copolymers coupled with hydrocarbon groups was studied in the presence of the hydrotropic agent sodium p-toluenesulfonate (NaPTS). The change in phase of the aqueous systems was evaluated by building up temperature–concentration phase diagrams. The critical micelle concentrations (CMC) of the copolymers and the aggregation points of NaPTS and NaPTS/copolymer mixtures were obtained by surface tension measurements, viscometry data and dye solubilization. The copolymers and NaPTS adsorb and reduce the surface tension of the solution until the surface becomes saturated: the CMC values are related to the solubility of the copolymers. Solutions containing NaPTS/copolymer mixtures exhibit the opposite behavior: at constant copolymer concentrations and with increasing NaPTS concentration, the surface tension remains constant until the aggregates of NaPTS start to form. Above this concentration, the surface tension increases. The surface tension and the aggregation points of the NaPTS solutions are dependent on the structure of the copolymer. The influence of the length of the hydrocarbon groups and the PPO position segment in the structure of the copolymers were also studied. From viscometric data, a pronounced increase in solution viscosity was observed as aggregates began to form. The results obtained from dye solubilization are in good agreement with the surface tension and viscometric measurements.

CHARACTERIZATION OF ASPHALTENE PARTICLES BY LIGHT SCATTERING AND ELECTROPHORESIS

The solubility of asphaltenes in heptane/toluene mixtures was studied at several temperatures. A significant increment in asphaltene solubility was observed when the temperature increases from 0°C to 20°C and a moderate increase when the temperature rose from 20°C to 50°C. These results indicate that asphaltenes behave as a higher consulate temperature system, similar to nonpolar waxes. Examined by photon correlation spectroscopy, diameters from the particles formed a range between 125 and 400 nm, depending on the amount of non-solvent (n-heptane) used for the precipitation process and the initial concentration of asphaltenes. The particles presented a small positive surface potential that was not altered by the addition of resins.