Hydrothermal gasification of sorbitol: H2 optimisation at high carbon gasification efficiencies

Using both experiments and modelling, hydrothermal gasification of sorbitol (SB) aiming at maximal carbon to gas conversion and H2 production was investigated over a wide temperature range (270-350 °C). Kinetics were studied in a continuous tubular reactor using a Pt/γ-Al2O3 catalyst. The addition of N2, resulting in lower H2 concentrations in the liquid phase, was found to have a beneficial effect in terms of higher H2 yield without compromising on the carbon gasification. The highest H2 yield obtained in this work was 4 mol H2/mol SB. Existing reaction schemes for sorbitol gasification were used to derive a path-lumped scheme. A multi-phase reactor model including a path-lumped scheme and gas-liquid-solid mass transfer was developed and parameterized based on datasets with varying temperature, space velocity, inlet gas composition (N2 or H2) and gas-liquid flow ratio. The developed model was used to provide guidelines for the design of an industrial reactor for the gasification of 10 tons/h of 10 wt% aqueous sorbitol. The effect of N2 stripping and industrially attainable kLa values were found to boost the H2 yield from 4 to 12 mol H2/mol SB making it an attractive process for further consideration.