Energy Fuels 2010, 24, 2312–2319 Published on Web 12/30/2009
: DOI:10.1021/ef900952y
Use of Microemulsion Systems in the Solubilization of Petroleum Heavy Fractions for the Prevention of Oil Sludge Waste Formation† )
Tereza Neuma de Castro Dantas,‡ Afonso Avelino Dantas Neto,§ ^ C atia Guaraciara F. T. Rossi,‡ Diego Angelo de Ara ujo Gomes,§ and Alexandre Gurgel*,
Department of Chemistry, and §Department of Chemical Engineering, Federal University of Rio Grande do Norte, Natal, 59072-970 RN, Brazil, and Department of Chemistry, Federal University of Vic- osa, Vic- osa, 36570-000 MG, Brazil )
‡
Received August 30, 2009. Revised Manuscript Received November 29, 2009
In this work, we investigate the use of microemulsions in the solubilization of heavy crude oil fractions, which are responsible for the formation of deposits in petroleum processing operations. Initially, the construction of phase diagrams was addressed, with the intention of determining the area within which microemulsions are formed. Unitol L 90 was used as a non-ionic surfactant. Butan-1-ol and butan-2-ol were tested as co-surfactants. Four different systems were studied: Unitol L 90 þ butan-1-ol þ water þ kerosene (system 1), Unitol L 90 þ butan-1-ol þ water þ xylene (system 2), Unitol L 90 þ butan-1-ol þ water þ 90% kerosene/10% xylene (system 3), and Unitol L 90 þ butan-2-ol þ water þ xylene (system 4). Physical adsorption experiments were carried out with the static method, aiming to simulate natural reservoir conditions. Crude oil samples from the Fazenda Belem field (Rio Grande do Norte State, Brazil) were used and dissolved in xylene. Arenite samples from the Assu (Rio Grande do Norte State) and Botucatu (Paran a State, Brazil) geological formations were tested as rock reservoirs. The adsorption curves featured the “S” profile. The solubilization process was accomplished via the batch method, by varying the stirring time, microemulsion composition, and the solid/solution ratio. The experiments showed that the microemulsions presented high efficiency in the solubilization of crude oil adsorbed on the arenites. In particular, system 2 presented an efficiency as high as 99% when tested on the Assu arenite and 97% on the Botucatu arenite. No significant differences were detected on the extent of solubilization of heavy fractions, by varying the surfactant concentration in the formulations used in this work. Therefore, for economical reasons, it could be suggested that systems containing only 20% in active matter (surfactant plus co-surfactant) are more suitable for applications involving the use of non-ionic microemulsions on the prevention of oil sludge waste formation.
Laboratory analyses and field interventions help producer avoid or remediate the deposition of asphaltenes. In many cases, these problems may be solved with a proper understanding of the multiphase behavior of the species that form the precipitates and also their interactions with the environment where phase segregation occurs.3 On the basis of this, novel technologies and methodologies are being continuously proposed to optimize the operation of reservoirs. Separation of petroleum heavy fractions is generally based on incompatibility among its constituents, such as resins and asphaltenes, depending upon the nature of the oil sample and the physicochemical conditions under which the tests are conducted.4 However, it is also known that asphaltenes may stabilize petroleum emulsions, because of their amphiphilic properties, although not so powerful as surfactants themselves. In the study of surfactant systems, microemulsions are renowned as excellent solvents for both polar and nonpolar compounds, with high solubilization capacity, enhancing the advantages of applications involving surfactants in solution. Microemulsions are also highly stable, single-phase chemical systems, exhibiting low viscosity and optical isotropy. Despite being very versatile components in many technological applications, microemulsions are still not widely used in activities involving the removal of petroleum heavy fractions, partly
1. Introduction Variations on fluid properties and parameters such as pressure, temperature, and composition normally occur during oil production and may induce the precipitation of asphaltenes. These compounds are found in crude oil and feature classical colloidal behavior,1 with strong tendencies to form agglomerates and modify interfacial properties. They have potential applications, for example, in road pavement and corrosion inhibition. However, during oil explotation, they may adhere onto the inner surfaces of pumps, pipelines, and safety valves, without disturbing the flow but ultimately impairing production because of the generation of thick deposit layers, causing problems associated with fluid transport and severe damages to storage tanks and process equipment.2 Downstream operations, as in oil refineries, where large amounts of petroleum heavy fractions are processed, are still susceptible to asphaltene clogging. In some cases, the deposits reduce the permeability of the reservoir rocks, further hindering oil production. † Presented at the 10th International Conference on Petroleum Phase Behavior and Fouling. *To whom correspondence should be addressed. Telephone: þ55-313899-3208. Fax: þ55-31-3899-3065. E-mail:
[email protected]. (1) Sheu, E. Y. Energy Fuels 2002, 16, 74–82. (2) Amin, A.; Riding, M.; Shepler, R.; Smedstad, E.; Ratulowski, J. Oilfield Rev. 2005, 17, 4–17.
r 2009 American Chemical Society
(3) Vazquez, D.; Mansoori, G. A. J. Pet. Sci. Eng. 2000, 26, 49–55. (4) Speight, J. G. J. Pet. Sci. Eng. 1999, 22, 3–15.
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Energy Fuels 2010, 24, 2312–2319
: DOI:10.1021/ef900952y
de Castro Dantas et al.
because of the complexity of the phase behavior of petroleum mixtures.5,6 Therefore, comprehensive investigations on both fundamentals and applications of surfactant systems in the petroleum industry are still required. Phenomena that affect the formation of emulsions or deposition of asphaltenes, when related to processes of exploration and stimulation of oil wells within the producing region, may represent a major problem in the optimization of the production yield. Experience indicates that, once formed, it is very difficult to destabilize emulsions and remove asphaltene aggregates from the well, which is necessary to reach the original production levels. For this reason, it is important to monitor the operation conditions, keeping them unfavorable to the generation of emulsions and deposits. In this work, we investigate the ability of microemulsion systems in satisfying this requirement and examine the influence of the surfactant concentration on the solubilization of petroleum heavy fractions by developing a novel methodology that enables the solution of problems associated with the phenomena mentioned above.
hence their characterization in equilateral triangular diagrams. The technique is based on volumetric titration of the proper components and involves visual investigation of the aspect of the chemical systems as composition is altered, for example, upon the addition of the aqueous phase to pseudo-binary mixtures of active matter (surfactant þ co-surfactant, at a predetermined mass ratio) and oil phase. Transitions between each Winsor equilibrium system may be detected as the titration procedure is carried out: Winsor IV (WIV) f Winsor II (WII) f Winsor III (WIII) f Winsor I (WI). These equilibrium systems are described in terms of the phases that are formed as composition is changed. Their denomination was proposed by Winsor in 1948 and is useful in the characterization of the phase behavior of microemulsion systems.8 2.3. Characterization of Microemulsion Systems. Surface tension, viscosity, and small-angle X-ray scattering (SAXS) measurements were performed to provide a thorough characterization of the microemulsion samples tested. Surface tension measurements were taken in a SensaDyne QC-6000 tensiometer (Chem-Dyne Research Corp.) by means of gaseous nitrogen flow. The SensaDyne tensiometer software, version 1.21, was available, and the results were expressed in dyn/cm or mN/m. Viscosity measurements were carried out at 25 °C with an Ostwald glass viscometer, and the results were referred to that of pure water. SAXS measurements were performed at the Brazilian Synchrotron Light Laboratory (LNLS), in the city of Campinas (Brazil), using the novel SAXS2 beamline. The sample-detector distance was set at 707.106 mm, and the amplitude of the scattering vector (q) ranged between 0.018 and 0.4756 A˚-1. The wavelength of the X-ray beams was 1.488 A˚, and the system operated under high vacuum (
