Reaction pathways and kinetics for hydrogen production by oilfield wastewater gasification in supercritical water

Supercritical multi-component thermal fluid (SMTF) generation technology is vastly promising for the application of offshore heavy oil recovery. The first step of the novel technology is hydrogen production by supercritical water gasification (SCWG). And oilfield wastewater can be used directly for SMTF generation as a toxic waste of heavy oil recovery. In this paper, crude oil was used as a model compound for oilfield wastewater. Experiments were conducted at a pressure of 25 MPa, the temperature of 600–700 °C, the residence time of 2–30 min, the feedstock concentration of 2–8 wt%, and with Na₂CO₃ as a catalyst. The results showed that the gas yield and carbon gasification efficiency (CE) were improved under the catalysis of Na₂CO₃. The increased reaction temperature and prolonged residence time were both beneficial for high CE. The most abundant gaseous product was H₂ and the maximum CE was 96.12%. The intermediate products from SCWG were analyzed using the lumped parameter method to establish the reaction pathways and kinetics model. This quantitative kinetics model was developed to describe the gaseous products, which consist of H₂, CO, CH₄, and CO₂. The model turned out to be robust by the experimental results. This work would be of great value to reveal the mechanism of SMTF generation technology.