Catalytic steam gasification of biomass surrogates: Thermodynamics and effect of operating conditions

Abstract

Thermodynamic chemical equilibrium of biomass steam gasification is considered using both stoichiometric and non-stoichiometric analyses. These thermodynamic analyses include gaseous products, tars and coke, as well as consider a wide range of operating conditions. It is shown that both stoichiometric and non-stoichiometric approaches provide close results. Catalytic steam gasification of biomass surrogate species (glucose and 2-methoxy-4-methylphenol) is developed in a CREC Riser Simulator under the expected conditions of a circulating fluidized bed gasifier. A highly active and stable fluidizable Ni/La2O3-γ-Al2O3 catalyst is employed in this study, to investigate the effects of gasifier operating conditions. This catalyst yields 98% carbon conversion of glucose to permanent gases with no tar formation and negligible coke deposition at 700°C. Catalytic gasification results with the variation of temperature and steam/biomass ratio show limited deviation from equilibrium predictions. The deviation between experimental results and equilibrium predictions can be attributed to the relatively shorter reaction time (20s). As the reaction time is increased, experimental results approach chemical equilibrium. For 2-methoxy-4-methylphenol gasification, 90% carbon conversion is obtained with only 5.7wt% tar formation and 3.3wt% coke deposition. Again chemical equilibrium predictions are close. The only exceptions are: (a) coke and methane being overestimated and (b) tars being underestimated. Regarding synthesis gas from glucose and 2-methoxy-4-methylphenol gasification, the Ni/La2O3-γ-Al2O3 catalyst yields a H2/CO ratio greater than 2.0.