Effect of Thermal Treatment on Acidic Organic Species from Athabasca Bitumen Heavy Vacuum Gas Oil, Analyzed by Negative-Ion Electrospray Fourier Transform Ion Cyclotron Resonance (FT-ICR) Mass Spectrometry

Abstract

We examine suspected molecular transformations of thermally treated Athabasca bitumen heavy vacuum gas oil (HVGO) by ultrahigh-resolution negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Liquid products from HVGOs treated under an inert N2 atmosphere at temperatures of 300, 325, 350, and 400 °C were each characterized by class (heteroatom content), type (double-bond equivalents = number of rings plus double bonds to carbon), and carbon number distribution. In addition, the inert N2 sweep gas of the autoclave was collected, condensed, and analyzed. The total acid number (TAN) of the HVGO liquid products decreases with an increasing treatment temperature (from 4.13 at 300 °C to 1.46 at 400 °C), indicative of potential carboxylic acid decomposition. The highly abundant O2 class contains species with DBE = 3; however, no compositional changes occur with increased treatment temperature. A bimodal DBE distribution is observed for the S1O2 class, suggesting two possible stable core structures. Only low relative abundance classes show slight changes with thermal treatment. Condensed nitrogen sweep gas obtained at 350 and 400 °C contains highly abundant O2 species with DBE of 3 and but at lower carbon number. Similarly, the condenser product S1O2 classes display the same bimodal DBE distributions as the HVGO liquid products but with lower carbon number (∼18−27 for condenser versus ∼25−35 for the liquid products). The similarity of the O2 speciation in the HVGO liquid products after thermal treatment combined with the detailed analysis of the condenser products suggests that the gross decrease in total acid number (TAN) at higher temperature is due to global (class, DBE, and carbon number indiscriminant) decomposition of the naphthenic acids as well as a small contribution from the loss of the lower boiling, lower carbon number acids by simple distillation.