Development of a simple and efficient oil-soluble nanocatalytic system for aquathermolysis upgrading of heavy crude oil

Catalytic aquathermolysis is one of the key and cost-effective chemical method for recovering heavy oil. This process transforms the asphaltene and resin compounds of the oil into lighter fractions. Oil-soluble transition metal-based catalysts have been reported as efficient catalysts that improve the viscosity reduction efficiency of the aquathermolysis process. Previous studies have mainly focused on using long alkyl chains as oil-soluble ligands to prepare the catalysts. However, aromatic ligands that effectively interact with asphaltene and resin fractions have not been extensively studied. In other words, the molecular structure of ligand used in the catalyst synthesis significantly changes its activity in aquathermolysis. This study aims to fill this gap using catechol as a novel ligand to develop oil-soluble catalyst (Ni-OSC), which can interact with heavy oil fractions during aquathermolysis. Ni-OSC decreased the content of resin and asphaltene by 32.1% and 26.5%, respectively, and increased the amounts of saturated and aromatic hydrocarbons by 19.6% and 22.9%, respectively, compared to heavy oil. Moreover, a GC–MS study indicated that low molecular weight hydrocarbons in the composition of heavy oil increased, and the relative content of alkanes raised to 79% in the presence of Ni-OSC. The catalyst also increased the concentration of alkylbenzenes and naphthalenes in the composition of aromatic compounds, improving the quality and recovery of heavy oil. Furthermore, the viscosity of heavy oil was considerably reduced, and a maximum hydrogen to carbon ratio of 2.03 was observed in Ni-OSC system. To the best of our knowledge, this is the highest reported hydrogen-to-carbon ratio for catalytic aquathermolysis of heavy oil using oil-soluble catalysts.