Study Of Very High Molecular Weight Cluster Presence In Thf Solution Of Asphaltenes And Subfractions A1 And A2, By Gel Permeation Chromatography With Inductively Coupled Plasma Mass Spectrometry

Super high-molecular-weight (SHMW) asphaltene aggregates, hereafter called asphaltene clusters, have been observed for the first-time using gel permeation chromatography with inductively coupled plasma mass spectrometry (GPC-ICP HR MS). Presumably these clusters are composed by nanoaggregates joined by physical interactions such as polar and dispersion forces. These clusters were observed for three asphaltenes samples (Hamaca, Cerro Negro and Boscan) and in their corresponding subfractions, A1 (insoluble in toluene) and A2 (soluble in toluene). Under the present conditions, dilution experiments showed no significant change of these profiles suggesting that these clusters, as well as the other lower molecular weight (LMW) aggregates and molecules are not in equilibrium with each other and behave as independent units. This is supported by the presence of trapped compounds within asphaltenes (TC) which are released after the p-nitrophenol treatment. A temperature cycle was implemented to monitor possible changes of GPC-ICP HR MS profiles with temperature. Here Boscan samples were heated from 25 to 200 degrees C, left standing by for 24 h and then cooled back to 25 degrees C before measurement. Whereas we found small changes for Boscan asphaltenes (As-Bo), vast changes in the profiles were detected for A1-Bo and A2-Bo subfractions, and these disclose interchange of material between the cluster and the other components of the solution. These results are discussed in terms of different arrays that may result when asphaltenes are separated in the two subfractions, and nanoaggregates are relocated within the cluster before and after heating. Preliminary molecular dynamics calculation afforded intensity-size distribution coherent with the usual experimental GPC chromatography profiles.