Adsorption of Native Resins on Asphaltene Particles: A Correlation between Adsorption and Activity Olga Leo ´n,* ,† Eliasara Contreras, † Estrella Rogel, † Gilberto Dambakli, ‡ So ´crates Acevedo, ‡ Lante Carbognani, † and Joussef Espidel † PDVSA-Intevep, Apdo. 76343, Caracas-1070A, Venezuela, and Escuela de Quı ´mica, Universidad Central de Venezuela, 47102, Caracas-1041, Venezuela Received September 4, 2001. In Final Form: March 7, 2002 Adsorption isotherms of two native resins on two different asphaltene surfaces were obtained using the UV spectrophotometric technique. The shape of the curves obtained can be attributed both to multilayer adsorption and to penetration of resins in the microporous structure of the asphaltenes. The relationship between adsorption behavior and activity of the native resins as asphaltene stabilizers indicates that their effectiveness is related to their adsorbed amount on asphaltene particles and also to their capacity to dissolve asphaltenes. The results obtained support a model for asphaltene stabilization where the resins are incorporated into the bulk asphaltenes helping them to diffuse in the solvent. Significant differences in the behavior of native resins and alkylbenzene-derived amphiphiles as asphaltene stabilizers were observed. At the same equilibrium concentration, the adsorbed amount of native resins is lower than the adsorbed amount of amphiphiles. However, the native resins exhibit a higher asphaltene dissolution power than amphiphiles and a comparable effectiveness as asphaltene stabilizers. Introduction The success of crude oil production operations depends on the colloidal stability of crude oils. During production of crude oils, changes in pressure, temperature, and composition can significantly disrupt the colloidal stability inducing asphaltene precipitation. 1 The consequences of this phenomenon are economically devastating. Reservoir damage, reduction of well productivity, and clogging of tubing and production facilities are some of them. An- nually, the oil industry spends significant amounts of money in well cleaning operations and treatments to avoid asphaltene precipitation. 1-3 Despite this, the main causes of asphaltene deposition are not completely understood at the present. It is currently accepted that crude oils are colloidal systems where asphaltenes and resins compose the disperse phase and maltenes are the continuous phase. 4 The precipitation of asphaltenes depends on the colloidal stability of this complex system. 5 Among the causes that originate this phenomenon, it has been found that composition plays a major role. 6-10 In particular, the characteristics of the disperse phase 6-8 and the peptizing power of the resins 10,11 are considered fundamental factors for the stabilization of asphaltenes in crude oil. In fact, the separation of the resins from crude oil originates the precipitation of asphaltenes. 11 The resins seem to provide a transition between the most polar (asphaltenes) and the relatively nonpolar (maltenes) fractions in petroleum, making it possible to maintain asphaltenes in solution. 4 It has been proposed that resins attach to asphaltene aggregates to form a steric stabilization layer around them. 12 The strong interactions between asphaltenes and resins have been proved qualitatively using spectroscopic techniques. However, severe difficulties in using these techniques for quantification of asphaltene-resin inter- actions have limited their use. 13 For this reason, the interactions between asphaltenes and resins have been studied using alkylbenzene-derived amphiphiles as model systems of native resins. From these earlier studies, it has been shown that the strength of the asphaltene- amphiphile interactions and the capacity of the am- phiphiles to form a steric stabilization layer are the key factors in the effectiveness of amphiphiles as asphaltene stabilizers. 13 Even more, it has been shown that the activity of the amphiphiles is related to the maximum amount of amphiphile adsorbed on the asphaltene surface. 14,15 There seems to be no doubt regarding the important role of resins in stabilizing asphaltene colloids in crude oil and organic solvents. However, the mechanism for such stabilization is not yet completely clear. A steric mech- anism and desorption of resins after dilution with the precipitating solvent has been suggested. 12 However, adsorption of resin solutions of n-heptane on an asphaltene surface leading to multilayer formation has been re- ported. 16 This finding is not clearly consistent with a steric * To whom correspondence should be addressed. E-mail: leono@pdvsa.com. Phone: 58-212-908-7804. Fax: 58-212-908-7524. † PDVSA-Intevep. ‡ Universidad Central de Venezuela. (1) Leontariris, K. J. Oil Gas J. 1998, Sept 01, 122. (2) Taylor, S. E. Fuel 1992, 71, 1338. (3) Galoppini, M.; Tambini, M. SPE European Production Operations Conference and Exhibition, Aberdeen, U.K., 1994; SPE 27622. (4) Andersen, S. I.; Birdi, K. S. J. Colloid Interface Sci. 1991, 142, 497. (5) Laux, H.; Rahimian, I.; Butz, T. Fuel Process. Technol. 1997, 53, 69. (6) von Hatke, A.; Rahimian, I.; Neumann, H. J. Erdo ¨ el Erdgas Kohle 1993, 109, 73. (7) Leo ´ n, O.; Rogel, E.; Espidel, J.; Torres, G. Energy Fuels 2000, 14, 6. (8) Rogel, E.; Leo ´n, O.; Espidel, J.; Gonza ´lez, J. SPE Prod. Facil. 2001, May, SPE72050. (9) Loeber, L.; Muller, G.; Morel, J.; Sutton, O. Fuel 1998, 77, 1443. (10) Taylor, S. E. Fuel 1998, 77, 821. (11) Koots, J. A.; Speight, J. G. Fuel 1975, 54, 179. (12) Leontaritis, K. J.; Mansoori, G. A. 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