Synthetic natural gas from biomass by catalytic conversion in supercritical water

Biomass can be effectively converted to synthetic natural gas (Bio-SNG) in water near or above its critical point (374 °C, 22.1 MPa). If an active and selective catalyst is used, no tars or char are formed. The onset of the gasification reaction was visualized in sealed quartz capillaries as high pressure batch reactors, by using an optical microscope. By pressure differential analysis of batch experiments, the onset temperature was found around 250 °C, which is much lower than conventional atmospheric gasification processes operating at 800–900 °C. The temporal evolution of the gaseous products in the batch experiments was consistent with a sequential gasification–methanation mechanism, where methane is formed from CO₂ and H₂. A Ru on carbon catalyst exhibiting excellent long-term stability was tested at 400–500 °C and space velocities up to 33 G_HC G_cat.⁻¹ h⁻¹ in a continuous test rig at 30 MPa.