Conversion of biomass into hydrogen by supercritical water gasification: a review

The rising issues of global warming due to the rapid use of fossil fuels are calling for sustainable energies such as dihydrogen, thereafter named ‘hydrogen’. The hydrogen demand has quadrupled in the past 45 years from 18 million tons in 1975 to 90 million tons in 2020 with a projected increase to 180 million tons by 2030. Here, we review the conversion of biomass into hydrogen by supercritical water gasification into hydrogen-rich syngas, with focus on thermophysical properties of supercritical water, parameters influencing water gasification and supercritical water gasification of cellulose, hemicellulose, lignin, biomass and model compounds. Parameters influencing water gasification include temperature, pressure, feedstock concentration and reaction time. Processes influencing products distribution comprise hydrolysis, water–gas shift, methanation, hydrogenation and reforming.