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

Abstract

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 °C, left standing by for 24 h and then cooled back to 25 °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.

Asphaltenes, Subfractions A1 and A2 Aggregation and Adsorption Onto Rh-Sio2 Nanoparticles: Solvent Effect on the Aggregate Size

“…As reported in previous studies [18,27,28], GPC-ICP HR MS analyses were performed using a Thermo Scientific Element XR sector field ICP HR MS instrument that operates at a resolution of 4000 (medium resolution) to access spectrally interfered isotopes of 58 Ni, 32 S, and 51 V. The spectrometer was equipped with a Fassel-type quartz torch shielded with a grounded Pt electrode and a quartz injector (1.0 mm i.d.). A Pt sampler (1.1-mm orifice diameter) and a Pt skimmer (0.8-mm orifice diameter) were used.…”

Molecular Cartography of A1 and A2 Asphaltene Subfractions from Classical Molecular Dynamics Simulations

“…To go further and complete this study, future simulations may investigate solvent effects by considering a solvent such as THF. Indeed, a recent study 41 suggests the formation and characterizes very high molecular weight clusters of asphaltene from subfractions A1 and A2.…”

SiO2 Biogenic Nanoparticles and Asphaltenes: Interactions and Their Consequences Investigated by QCR and GPC-ICP-HR-MS

“…The complex nature of asphaltenes has been extensively researched, and their characterization has been the subject of many studies using different techniques. After early work on gel permeation chromatography (GPC) inductively coupled plasma atomic emission spectroscopy by Reynolds et al that have shown a trimodal distribution of vanadium compounds in asphaltene, recent results with the same separation technique but hyphenated with inductively coupled plasma high-resolution mass spectrometry (GPC-ICP-HR-MS) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) demonstrate that asphaltenes are composed of low- to medium-, medium-, high- and superhigh-molecular-weight fractions, meaning that, by nature, asphaltenes form families of aggregates of different hydrodynamic volumes in solution. − This result can have an important impact on the understanding of asphaltene adsorption processes and may be the key to discerning the dynamics of the process.…”