Co-gasification of plastic wastes and soda lignin in supercritical water

In this study, the co-gasification of soda lignin produced from black liquor and various plastics in supercritical water was investigated experimentally. The effect of the mixing ratio of soda lignin/PE, temperature, reaction time, total concentration and plastic types was studied. A synergetic effect was found in co-gasification of PE and soda lignin, and the maximum influence was obtained at a mixing ratio of 50:50. Increasing the temperature and reaction time, and reducing the concentration improved the gasification efficiency and hydrogen production from co-gasification of PE/soda lignin (50:50). The H₂ yield increased over 5 times to 57.0 mol/kg with temperature increasing from 500 °C to 750 °C, and the highest H₂ yield of 63.3 mol/kg was obtained at 700 °C when the concentration was reduced to 5 wt%. The gasification efficiencies of different plastics were distinct and the order is: PE > PC ≈ PP > ABS, and the addition of soda lignin improved all the gasification efficiencies. The alkali salts in soda lignin also catalyzed the reforming of CH₄ and C₂H₆ that generated from the depolymerization of plastics, especially PE and PP and improved the hydrogen production.