Supercritical Water\nGasification of Ethanol as Biomass\nModel Compound in Tandem with Steam Reforming: Kinetic Modeling of\nthe Reforming Step and Techno-Economic Analysis of the Integrated\nConcept

The integration of “biomass gasification with\nsupercritical\nwater ”, “steam reforming of hydrocarbons”, and\n“water–gas shift reaction” is a promising process\nconcept for the conversion of moist biomass to “green hydrogen”.\nThis process concept was investigated in this work, considering ethanol\nas a biomass model compound. The gasification of ethanol with supercritical\nwater can be accurately simulated, allowing a very good prediction\nof the gaseous product that will undergo steam reforming. A multidisciplinary\nstudy is presented, in which a comprehensive kinetic model for steam\nreforming of the gasification product gas was developed and validated\nwith experimental data and then employed in a simulation of the whole\nprocess chain. Finally, a techno-economic and sensitivity analysis\nwas applied. In the kinetic model, the high steam content overshadowed\nthe influence of other substances in the sites balance on the catalyst\nsurface, except for methane. After investigating the effect of ethanol\nconcentration and feed flow rate, and considering the technical constraints\nimposed by the high organic matter content and the availability of\nactual waste biomass, the optimal values of the ethanol concentration\nand feed flow rate were 50 t h<sup>–1</sup> and 15 wt % ethanol,\nreaching a hydrogen break-even price of 6.8 $ kg<sub>H<sub>2</sub></sub><sup>–1</sup>. The sensitivity analysis identified the\nethanol price as the primary cost driver. Exploring waste biomass\nfeedstocks, such as sewage sludge, demonstrated potential break-even\nprices as low as 0–1.8 $ kg<sub>H<sub>2</sub></sub><sup>–1</sup>, which can compete with conventional technologies.