Aggregation-dissociation studies of asphaltene solutions in resins performed using the combined freeze fracture-transmission electron microscopy technique

TY - JOUR

T1 - Aggregation-dissociation studies of asphaltene solutions in resins performed using the combined freeze fracture-transmission electron microscopy technique

AU - Acevedo, Socrates

AU - Zuloaga, Clara

AU - Rodríguez, Pedro

PY - 2008/7

Y1 - 2008/7

N2 - Solutions of asphaltenes in resins (3%) were studied combining the freeze fracture and transmission electron microscopy techniques (FF-TEM). These studies were performed by analyzing samples prepared at different temperatures (7) from 25 up to 250 °C. In this temperature range, mean particle diameters (Dp) were found to drop from about 5 to about 3.5 nm. The smallest diameter measured at each temperature (Ds) reached a constant value equal to 2.5 nm in the range between 100 and 250 °C. Frequencies f(D) of all but Ds values were found to decrease at some temperatures reveling that diameters D > Ds correspond to aggregates (Ag). Moreover, during this heating, we found that whereas for big (B) and smallest diameters frequencies f(D) either decrease (big) or increase (Ds) continuously, maxima were found for intermediate (1) diameters. This suggests that under the conditions of this experiment (temperature and time) conversion from intermediate to smallest diameter meets some energy barrier high enough for the accumulation of intermediate size diameters. These results were interpreted in terms of the consecutive process Ag(B) k1→T Ag(I) k1→T A1M where A1M stand for A1-type molecules and k1 > k2; consequently, because of the low solubility of A1M, conversion from intermediate aggregates to molecules is a difficult step. The above results and many others in the literature are in agreement with the colloidal, solubility, and aggregates hypothesis related to A1 and A2 fractions of asphaltenes.

AB - Solutions of asphaltenes in resins (3%) were studied combining the freeze fracture and transmission electron microscopy techniques (FF-TEM). These studies were performed by analyzing samples prepared at different temperatures (7) from 25 up to 250 °C. In this temperature range, mean particle diameters (Dp) were found to drop from about 5 to about 3.5 nm. The smallest diameter measured at each temperature (Ds) reached a constant value equal to 2.5 nm in the range between 100 and 250 °C. Frequencies f(D) of all but Ds values were found to decrease at some temperatures reveling that diameters D > Ds correspond to aggregates (Ag). Moreover, during this heating, we found that whereas for big (B) and smallest diameters frequencies f(D) either decrease (big) or increase (Ds) continuously, maxima were found for intermediate (1) diameters. This suggests that under the conditions of this experiment (temperature and time) conversion from intermediate to smallest diameter meets some energy barrier high enough for the accumulation of intermediate size diameters. These results were interpreted in terms of the consecutive process Ag(B) k1→T Ag(I) k1→T A1M where A1M stand for A1-type molecules and k1 > k2; consequently, because of the low solubility of A1M, conversion from intermediate aggregates to molecules is a difficult step. The above results and many others in the literature are in agreement with the colloidal, solubility, and aggregates hypothesis related to A1 and A2 fractions of asphaltenes.

UR - http://www.scopus.com/inward/record.url?scp=49649098209&partnerID=8YFLogxK

U2 - 10.1021/ef800108p

DO - 10.1021/ef800108p

M3 - 文章

AN - SCOPUS:49649098209

SN - 0887-0624

VL - 22

SP - 2332

EP - 2340

JO - Energy and Fuels

JF - Energy and Fuels

IS - 4

ER -