Supercritical water gasification of glycerol and methanol mixtures as model waste residues from biodiesel refinery

Abstract

The eco-friendly processing in biodiesel refineries is feasible with effective utilization of the byproducts and waste residues. The motive of this research is to convert the model byproducts of biodiesel refineries to H2. In this study, different glycerol⿿methanol mixtures were gasified in supercritical water at variable temperatures (450⿿600°C) and pressures (23⿿25MPa) for 45s in a continuous-flow tubular reactor. Glycerol and methanol concentrations were varied from 5 to 20wt% individually in the mixtures, and their impacts on gas yields were investigated both experimentally and thermodynamically. The thermodynamic simulations were performed using Aspen Plus based on Gibbs free energy minimization method. The thermodynamic yield (25.3mmol/g) of H2 was higher compared to experimental yields (19mmol/g) at 600°C, 25MPa and 1:1 glycerol-to-methanol feed solution. To enhance the gas yields, the effects of four alkali catalysts such as KOH, NaOH, K2CO3 and Na2CO3 at 0.5wt% concentration were examined. Among all the catalyst, 0.5wt% K2CO3 resulted in highest H2 yields (24.8mmol/g), total gas yields (1.24g/L) and carbon gasification efficiency (96.7%) at 600°C and 25MPa with 1:1 glycerol-to-methanol feed solution. The results suggest that effluents from biodiesel refineries can be used as potential feedstock for waste-to-energy conversion.