Claudia R. E. Mansur

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.

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.

Separation and characterization of asphaltenic subfractions

The structure of the various asphaltenic subfractions found in crude oil was evaluated. For this purpose, C5 asphaltenes were extracted from an asphaltic residue using n-pentane as the flocculant solvent. The different subfractions were isolated from the C5 asphaltenes by the difference in solubility in different solvents. These were characterized by infrared spectroscopy, nuclear magnetic resonance, X-ray fluorescence, elementary analysis and mass spectrometry. The results confirmed that the subfractions extracted with higher alkanes had greater aromaticity and molar mass. However, small solubility variations between the subfractions were attributed mainly to the variation in the concentrations of cyclical hydrocarbon compounds and metals.

Behavior of aqueous solutions of poly(ethylene oxide‐b‐propylene oxide) copolymers containing a hydrotropic agent

The effect of the hydrotropic agent, sodium p-toluenesulfonate (NaPTS), was evaluated on the micelle formation process and on phase behavior of aqueous solutions containing poly(ethylene oxide-b-propylene oxide) (PEO–PPO) copolymers. We have studied monofunctional diblock copolymers coupled with hydrocarbons groups (R—PEO—PPO—OH and R—PPO—PEO—OH, where R length is linear C4 and C12–14). The critical micelle concentration (CMC) and critical micelle temperature (CMT) values of the aqueous copolymers solutions were obtained from both surface tension versus concentration plots and the dye solubilization method. The influence of the hydrocarbons groups length and PPO segment position in the structure of the copolymers were also analyzed. The same measures were obtained for the aqueous solutions of hydrotropic agent which, in turn, also presented molecular aggregation. The presence of the hydrotropic agent in the aqueous copolymers solutions altered the surface tension of these solutions and the occupied molecular area per copolymer molecule at air–water interface and CMC and CMT values of the copolymers. On the other hand, the aggregation points and the surface tension of the NaPTS solutions were dependent on the copolymer structure and composition.

A study of asphaltene-resin interactions

A study was carried out to investigate the interaction between asphaltenes (in toluene solutions) and resins (in n-heptane solutions). To better understand the type of interaction between these fractions, it was quantified the resin uptake when asphaltenes (dissolved in toluene) were precipitated by a resin-containing n-heptane solution. These results indicated the asphaltene precipitation occurs together with a reduction in the resin concentration. The binding isotherm profiles indicated that saturation occurred in one case, while collective association following an initial plateau was observed for the other two samples. These results confirmed the hypothesis that resins can adsorb on asphaltenes but cannot prevent asphaltenes from flocculating and precipitating. Furthermore, microcalorimetric results suggested that the resin and asphaltene interact by weak van der Waals forces. These results are in stark contrast with the school of thought prevalent since the 1940s that resins can peptize and stabilize asphaltenes.

Determination of the Onset of Asphaltene Precipitation by Visible Ultraviolet Spectrometry and Spectrofluorimetry

Abstract Asphaltene deposition is a problem for the petroleum industry, affecting the production, transport, and storage of crude oil. The aim of this work is to develop and compare different methods to determine asphaltene precipitation. Two asphaltene fractions, one extracted from a Brazilian crude oil sample and the other from petroleum distillation residue, were evaluated by using model systems constituted of toluene/n-heptane in different compositions, using visible ultraviolet spectrometry and spectrofluorimetry. The results of the precipitation tests carried out by these two methods agreed, indicating they are effective to analyze asphaltene deposition and the performance of chemicals as asphaltene stabilizers.

Thermal analysis and NMR studies of methyl methacrylate (MMA)–methacrylic acid copolymers synthesized by an unusual polymerization of MMA

Methyl methacrylate-methacrylic acid (MMA-MAA) copolymers were pre- pared from the polymerization reaction of the methyl methacrylate (MMA) monomer with concentrated nitric acid (65% HNO3) at different reaction times in the absence of other reagents in the reaction mixture. The hydrolysis degrees of the MMA-MAA (sodium salts) copolymers estimated by thermogravimetry (TG) corroborated the data obtained by chemical titration. By calorimetry (DSC), a relationship between the glass transition temperature (Tg) and the hydrolysis degree was obtained. The results pre- sented a deviation from linear behavior and it was related to the strength of the interactions involved in the copolymer chains. The equation that relates the glass transition temperature to the interaction parameter, x, for miscible binary polymer blends was applied for the MMA-MAA copolymers and demonstrated the composition dependence of x. The molecular mobility was determined by nuclear magnetic reso- nance (NMR) in the solid state and through the proton spin-lattice relaxation time in the rotating frame. The NMR data were in a good agreement with the results obtained by calorimetry.

Characterization of methacrylic polymers by calorimetry and infrared analyses

Methyl methacrylate-methacrylic acid (MMA-MAA) copolymers, prepared by the action of concentrated nitric acid (65% HNO 3 ) on methyl methacrylate in absence of other reagents, were characterized using calorimetry (DSC) and infrared (FTIR) analyses. DSC curves of ester/acid copolymers suggested the anhydride formation at ∼200°C, which was corroborated by thermogravimetry (TG). This structure was assigned by FTIR spectra. The results obtained by DSC data are in good agreement with the hydrolysis degree of the MMA-MAA copolymers obtained from chemical titration. The molecular weight of the copolymers were estimated by viscometry.