Two-Step Laser Mass Spectrometry of Asphaltenes

Citations Over TimeTop 1% of 2008 papers

Abstract

Defined by their solubility in toluene and insolubility in n-heptane, asphaltenes are a highly aromatic, polydisperse mixture consisting of the heaviest and most polar fraction of crude oil. Although asphaltenes are critically important to the exploitation of conventional oil and are poised to rise in significance along with the exploitation of heavy oil, even as fundamental a quantity as their molecular weight distribution is unknown to within an order of magnitude. Laser desorption/ionization (LDI) mass spectra vary greatly with experimental parameters so are difficult to interpret: some groups favor high laser pulse energy measurements (yielding heavy molecular weights), arguing that high pulse energy is required to detect the heaviest components of this mixture; other groups favor low pulse energy measurements (yielding light molecular weights), arguing that low pulse energy is required to avoid aggregation in the plasma plume. Here we report asphaltene mass spectra recorded with two-step laser mass spectrometry (L2MS), in which desorption and ionization are decoupled and no plasma is produced. L2MS mass spectra of asphaltenes are insensitive to laser pulse energy and other parameters, demonstrating that the asphaltene molecular weight distribution can be measured without limitation from insufficient laser pulse energy or plasma-phase aggregation. These data resolve the controversy from LDI, showing that the asphaltene molecular weight distribution peaks near 600 Da and previous measurements reporting much heavier species suffered from aggregation effects.

Related Papers

• → Effect of Chemical Composition on Asphaltenes Aggregation(2010)122 cited
• → Toward Separation and Characterization of Asphaltene Acid and Base Fractions(2021)16 cited
• → Asphaltene Gradients and Connectivity Analysis in Reservoirs, Asphaltene Onset Pressure, Bitumen and Tar Mats All Treated Within a Simple, Unified Chemistry Treatment(2018)2 cited
• → Products of thermal degradation of asphaltenes of heavy oil from the Ashalchinskoye oilfield in supercritical hexane(2020)