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 degrees 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 H-2 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 H-2, 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.

Automated summary

Supercritical multi-component thermal fluid (SMTF) generation technology shows great promise for offshore heavy oil recovery. The first step involves hydrogen production through supercritical water gasification (SCWG), while oilfield wastewater can be used as a toxic waste for SMTF generation. The study conducted experiments to analyze the effects of Na2CO3 catalyst, temperature, and residence time on gas yield and carbon gasification efficiency (CE). The results showed that Na2CO3 catalysis improved gas yield and CE, with higher temperatures and longer residence times being beneficial. The research provides insights into the mechanism of SMTF generation technology.