Upgrading Heavy Crude Oils and Extra Heavy Fractions in Supercritical Methanol

Herein, we report a method of upgrading unconventional crude oils and extra heavy fractions using supercritical methanol (scMeOH) and compare it to supercritical water (scH₂O)-based and pyrolytic upgrading. The yields and properties of upgraded oil are explored as functions of operating parameters (temperature, pressure, and concentration) and feedstocks for high-acid crude oils (Laguna and Bachaquero-13), a heavy crude oil (Rubiales), and a vacuum tower bottom (VTB). As a result, scMeOH upgrading of unconventional crude oils at 400 °C and 30 MPa effectively reduced their asphaltene content to ∼0 wt % and increased that of naphtha–diesel fractions to 30–40 wt %. Conversely, a considerable amount of asphaltenes (8.8–10.0 wt %) was present in oil upgraded using scH₂O and pyrolysis. Additionally, scMeOH upgrading resulted in a more effective reduction of the total acid number (TAN) of high-acid crude oils (<0.5 mg of KOH/g of oil) compared to values achieved by scH₂O and pyrolysis methods. Finally, scMeOH treatment significantly reduced the metal (Ni, V, and Fe) content of the upgraded oil. The effective asphaltene content and TAN reduction realized in scMeOH was attributed to its hydrogen donation and esterification ability, with plausible mechanisms of scMeOH, scH₂O, and pyrolytic upgrading presented and discussed in detail.