Catalytic subcritical and supercritical water gasification as a resource recovery approach from waste tires for hydrogen-rich syngas production
Abstract Massive amounts of waste tires are generated globally posing disposal and recycling challenges. Waste tires were gasified in subcritical and supercritical water to study their degradation behavior during syngas production. The process parameters including temperature (325 °C to 625 °C), reaction time (15 min to 60 min) and feed concentration (5 wt% to 20 wt%) were optimized to maximize gas yields from waste tires. The highest total gas yields (34 mmol/g), hydrogen yields (14.4 mmol/g) and carbon gasification efficiency (42.6%) were achieved at optimal temperature (625 °C), reaction time (60 min) and feed concentration (5 wt%). The application of homogeneous and heterogeneous catalysts improved hydrogen yields from waste tires in the order: Ni/SiO2-Al2O3 (19.7 mmol/g) > Ru/Al2O3 (17.9 mmol/g) > Ba(OH)2 (16.9 mmol/g) > Ca(OH)2 (16.7 mmol/g) > Mg(OH)2 (15.4 mmol/g). The results suggest waste tires as a potential resource for recovery of hydrogen-rich fuel gas through hydrothermal gasification.