Adsorption of Asphaltenes at the Toluene-Silica Interface: A Kinetic Study Sócrates Acevedo,*·t María A. Ranaudo,t Corornoto García,t Jirnrny Castillo.* and Alberto Fernández··; Laboratorio de FisicoquÍmica de Hidrocarburos and Laboratorio de Espectroscopia Laser, Universidad Central de Venezuela, Facultad de Ciendas, Escuela de Química. 47102. Caracas 1041. Venezuela Rece/ved May 8. 2002 The adsorption kinetics of asphaltenes at the toluene - silica interface has been measured for nine solutlon concentratlons Cs (from 5 to 3000 mgL -1) Results could be adjusted to an Irreversible second-order adsorption kinetlcs. where the adsorptlon rate k was strongly dependent on concentratlon. Thus a large reduction in k was observed when Cs was Increased in the studied concentration range. This rate reductlon was accounted for In terms of adsorption of aggregates formed in solution. The step - wise trends observed for too adsorptlon lsotherms of asphaltenes on mineral surfaces. could be reproduced uslng the aboye k values. lntroduction As a result of too possible lmpact on reservoir wet- tability. change in crude composition during migration. envlronmental damage. and asphaltene precipitatlon durlng production. asphaltene adsorption has been the subjeet of studies in the pasto Measurements of large quantities of pOOnol adsorbed on precipltated aspha1tene suggested a loose structure for this solid.! Adsorptlon of toluene solutions of asphaltenes under difTerent clay minerals afTorded Langmulr-type lsotherms and two- stage adsorptlon was observed when a toluene-heptane mixture was used as the solvent. 2 Changes In crude oH compositlon durlng mlgratlon have been studied. 3 Ad- sorption of petroleum acids and phenols on argillaceous and sandy rocks were reported. 4 The impact of emul- slo05 stablllzed by asphaltenes adsorbed on solld par- ticles such as goethite has been studled. 5 Large aggregates of asphaltenes have been observed by atomic force microscopy (AFM) when toluene solu- tions were contacted with mica surfaces. 6 The authors reported fractal-like objects with lengths of a few micrometers. 6 According to a report,7 the adsorption of toluene solutlons of reslns and asphaltenes on quartz and feldspar do not change the eletrophoretic moblllty • Corresponlfing authors. , laboratorio de Flsicoquimlca de Hidrocarburos. 1 Laboratorio de Espectroscopia Laser. (1) Jaqul. M.; Achant. C.; Hasnaool. N.; Rogalskl. M. Rev. lnsc. Fr. 1998. 53. 35-40. (2) Pernyeszl. T.; Patzl<o. A.; Berkesl. O.; Dékány. 1. CoIJo/ds Sur!'.. A 1991. 137,373-384. (3) Vandenbrouke. M. Scudy of Primary Migradon: Change in romposldon of rock extraccs passing through parenc rock/reservolr. Advances in Organ/c Geoc:hem/stry. Gaerner. H. R. Wehner. H.. Eds.; Pergamon Press: Oxford. 1977; p 547. (4) Manakova. R. A.; Savlnykh. Yu. V. Pec. Chem. 1996. 36. 24-30. (5) Jeon. Y. W.; YI. S. H.; Chol. S. J. Fue1 Sel. Techno1.lnt. 1995. 13. 195-214. (6) Toulhoat. H.; Prayer. C.; Rouquet. G. Collo/ds Sur!'.. A 1994. 91. 267-283. (7) Gonzalez. G.; Mlddea. A. J D/s. ScJ. Technol. 1987. 8.525-548. of these mlnerals. suggesting that the surface sites responsible for surface charge were not afTected by the adsorptlon. although the adsorptlon turned the minerals hydrophobic. Between 20 and 30 mglg of asphaltene were adsorbed when toluene soluUo05 were contacted wlth several cl ays8 and wlth slllca. 9 Langmuir type I IsotOOrms were found In these cases. and wettability studles showed that water was capable of reduclng but not elíminatlng asphaltene adsorpUon. 8 As expected. adsorbed asphalt- ene changed the surface from hydrophillc to hydropho- blc. 8 Most of the aboye work describes changes in mineral surfaces related to wettabUity and otOOr phenomena requlrlng a low coverage of surface. In this regard.just a monolayer of organlc matter would be enough to change the mineral surface from hydrophillc to hydro- phobic. and hence only dilute solutlons of asphaltenes are needed. In this case, simple L-type lsotherms are usually found. For studles on the lnfluence of aggregate formatlon on adsorpUon hlgher solution concentratio05 are re· qulred. However. higher concentrations of asphaltene complicate the problem due to multilayer formaUon. time dependence. aggregate formaUon. and preclpita- tlon. These pOOnomena. such as mulUlayer formation and time dependence J o- 12 as well as precipitation!3 have been studled previously In our laboratorles. (8) Colllns. S. H.; Melrose. J. C. SPE 11800 (Soclety oC Petroleum Engineers) 1913. 249-256. (9) Frltachy. G.; Papler. E. Fue11978. 57, 701-704. (10) Acevedo. S.; Ranaudo. M. A.; Escobar. G.; Gutlerrez. L.; Ortega. P. Fue11995. 74. 595-598. (11) Acevedo. S.; Castillo, J.; Fernéndez, A.: Goncalvez. S.; Ranaudo. M. Energy Fue1s 1998, 12.386-390. (12) Acevedo. s.; Ranaudo. M. A.; Garda. C.; Castillo. J.; Fernández. A.; Caetano, M.; GoncaJvez, S. Collo/ds Sur!'.. A ZOClO. 166. 145-142. (13) Castillo. J.; Fernández. A.; Ranaudo, M. A.; Acevedo. S. AN. Sel. Techno1. 2001. 19. 79-110. IO.I021/etu20104q CCC; $25.00 () xxxx American Chemlcal Society Published on Web PACE EST: 4.7