Efficiency and energetic analysis of the production of gaseous green fuels from the compressed steam and supercritical water gasification of waste lube oils

•H2 and CH4 are obtained from steam reforming and supercritical water gasification of waste lube oils.•More than 70% of the energy contained in the waste lube oil can be recovered as H2 and CH4.•The valorization is energetically more efficient when H2 and CH4 are the main products obtained.•H2 and CH4 production are promoted at high temperatures and long reaction times.•Diverse influence of pressure on kinetics, H2 and CH4 production, and energy efficiency are analyzed. [Display omitted] The gasification of a waste lube oil (WLO), using water under vapor and supercritical states leads to its valorization into green fuels with high energetic power like H2 and CH4. This work investigates how the most important variables of a flow continuous gasification process, temperature, pressure and reaction time, influence the efficiency of gasification and the amounts and characteristics of the gases produced. The study of the influence of these variables on the energetic efficiency of the process was also completed. The highest production yields, 2.4 10−2 molH2goil−1 and 3.0 10−2 molCH4goil−1, were registered at supercritical water conditions (750°C, 250 bar and 1.87 min). The energetic study revealed that the energetic efficiency increased as the reaction time was lengthened. Gasification kinetics were slower as pressure increased but the reaction times inside the flow reactor were longer. A pressure range from 150 bar, steam region, to 250 bar, supercritical region, was identified as optimal since allowed the most suitable balance between kinetics and the reaction times achieved.