Hydrogen donating capacity of water in catalytic and non-catalytic aquathermolysis of extra-heavy oil: Deuterium tracing study

Abstract

The goal of this work is to try to figure out the role of water in catalytic and non-catalytic aquathermolysis by using isotope tracing techniques. For this purpose, heavy water (deuterium oxide, D2O) was used to replace the ordinary water (H2O) for catalytic and non-catalytic aquathermolysis processes of extra-heavy oil with high sulfur content in autoclave. The donating and upgrading performance of D2O were deeply investigated by analyzing the upgraded (deuterated) oil and their SARA (saturates, aromatics, resins and asphaltenes) fractions using different tracing techniques (FTIR, isotope and elemental analysis), evolved gases by GC, and change in physical-chemical properties of upgraded (deuterated) oils by viscosity measurement, SARA analysis, elemental analysis and GC, etc. The results proved the chemical role of water as a green and environmental hydrogen-donor solvent during aquathermolysis process, verified by considerable deuterium substitution (deuteration) obtained from isotope analysis both in upgraded oil and SARA fractions. The results are further supported by significant deuterium exchanges (deuteration) of aliphatic and aromatics parts in the initial and deuterated oil samples and their individual SARA fractions in FTIR spectra. Simultaneously, introducing Ni-tallate as an oil-soluble catalyst promoted the donating capacity of water, thus significantly improving the upgrading performance. The important finding about the role of water in catalytic and non-catalytic aquathermolysis not only enriches the theoretical basis in this area, but also provides a strong support for the use of catalysts in aquathermolysis for improving in-situ heavy oil upgrading performance.