Reaction kinetics analysis of hydrogen production by biomass gasification in supercritical water

The reaction kinetics of sodium carboxymethylcellulose (CMC) and sawdust/CMC gasification in supercritical water was studied. The results indicate that the reaction is of pseudo-first-order kinetics. The activation energy of CMC is 160 kJ/mol at 20 MPa and 97-81 kJ/mol at 25-35 MPa, respectively. The activation energy decreases with the increasing pressure. The activation volume can reach the order of magnitude of 10³ at near-critical state of water and decrease rapidly away from the critical point of water. The curves of solubility parameter, dielectric constant, and supercritical water density versus reaction rate constant have the similar tendency of linear relation. The reaction rate decreases with the increase of these parameters. The value of activation volume at the near-critical state of water is larger than that of leaving away from the critical point of water when sawdust/CMC is gasified in supercritical water at 923 K. The curves of solubility parameter, dielectric constant, and supercritical water density versus reaction rate have the similar trends.