Thermodynamic Equilibrium Modeling and Optimization of Glycerol Air–Steam Gasification for Syngas Production

Biodiesel production generates ~10% crude glycerol as a byproduct, and its oversupply has depressed its value; the air–steam gasification of crude glycerol remains underexplored. This study models the equilibrium of that route through Gibbs minimization in Cantera, with solid carbon as a condensed phase. The model is verified against published equilibrium results and validated with 27 independent experimental points (RMSE of the H2 fraction of 0.027 for T ≥ 500 °C). The effects of temperature and of the S/G and A/G ratios on composition and heating value are evaluated, and an efficiency that accounts for the external heat and the steam enthalpy is optimized under two Q conventions. The efficiency exhibits an interior maximum at ≈433 °C (91.3%, nearly autothermal) where solid carbon formation is substantial (1.02 mol/mol), and the carbon-free boundary crosses S/G = 1 at T* = 685.1 °C. The constrained optimization places the practical optimum at T ≈ 686 °C, S/G = 1, A/G = 0.5 (η = 88.6%, C(s) = 0, LHV = 14.6 MJ/kg). Crude glycerol impurities modulate carbon formation: water reduces it (0.77 versus 1.02 mol/mol with 10 wt%) while methanol and MONG increase it (1.07 and 1.26 mol/mol with 5 wt%); for an 80/10/5/5 wt% crude, the crude-basis efficiency is ~90%. These results delimit the carbon-free conditions for valorizing crude glycerol.