Abstract
Heavy oil will likely dominate the future energy market. Nevertheless, processing heavy oils using conventional technologies has to face the problems of high hydrogen partial pressure and catalyst deactivation. Our previous work reported a novel method to upgrade heavy oil using hydrogen non-thermal plasma under atmospheric pressure without a catalyst. However, the plasma-driven catalytic hydrogenation mechanism is still ambiguous. In this work, we investigated the intrinsic mechanism of hydrogenating heavy oil in a plasma-driven catalytic system based on density functional theory (DFT) calculations. Two model compounds, toluene and 4-ethyltoluene have been chosen to represent heavy oil, respectively; a hydrogen atom and ethyl radical have been chosen to represent the high reactivity species generated by plasma, respectively. DFT study results indicate that toluene is easily hydrogenated by hydrogen atoms, but hard to hydrocrack into benzene and methane; small radicals, like ethyl radicals, are prone to attach to the carbon atoms in aromatic rings, which is interpreted as the reason for the increased substitution index of trap oil. The present work investigated the hydrogenation mechanism of heavy oil in a plasma-driven catalytic system, both thermodynamically and kinetically.
Highlights
Heavy oil, including heavy, extra heavy crude and refinery residue, will likely dominate the future energy market because high-quality light crude is becoming depleted and more expensive.heavy oil has a low H/C atomic ratio and a high content of heteroatoms compared to light crude [1], which is a challenge for processing heavy oils using conventional technologies.Carbon rejection and hydrogenation are two general routes for upgrading heavy oil [2].Carbon rejection processes extract the light products from heavy oil by thermal cracking, which usually leads to the quality of light products being poor
density functional theory (DFT) study results indicate that toluene is hydrogenated by hydrogen atoms, but hard to hydrocrack into benzene and methane; small radicals, like ethyl radicals, are prone to attach to the carbon atoms in aromatic rings, which is interpreted as the reason for the increased substitution index of trap oil
Heavy oils mainly consist of aromatic-kind compounds, which account for more than 70% [7]
Summary
Heavy oil, including heavy, extra heavy crude and refinery residue, will likely dominate the future energy market because high-quality light crude is becoming depleted and more expensive. In our previous work [7], it has been demonstrated that non-thermal plasma could increase light oil yield significantly and add hydrogen to heavy oil under atmospheric pressure without a catalyst, the plasma-driven catalytic hydrogenation mechanism is still ambiguous, especially the reason for the increased substitution index of trap oil. The density functional theory (DFT) has been used to study the thermodynamics associated with steam reforming of small organic molecules (e.g., DiMethyl Ether and Ethanol) under cold plasma conditions [19,20]. This study attempts to reveal the plasma-driven catalytic hydrogenating mechanism of heavy oil using DFT calculation. Toluene and 4-ethyltoluene have been chosen as the heavy oil model compounds, respectively; a hydrogen atom and ethyl radical have been chosen as the high reactivity species generated in a plasma-driven catalytic reaction system. It shows that small radicals, like ethyl radicals, are prone to attach to the carbon atoms in the 4-ethyltoluene ring, which is interpreted as the reason for the increased substitution index of trap oil
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