A comparison study on pyrolysis, gasification, and gasification-catalytic reforming characteristics of waste sewage sludge for co-production of bio-oil and H2-rich gas

Thermochemical treatment of waste sewage sludge into valuable products such as bio-oil and syngas is a promising way to mitigate the solid waste problems. Pyrolysis, gasification, and gasification-catalytic reforming of sewage sludge were performed and compared in a two-stage fixed bed reactor. The effect of reaction temperature and steam space velocity was taken into consideration and comparatively analyzed. Steam, as a gasification agent, plays a vital role in removing fixed carbon and the cracking of heavy aromatic hydrocarbons and oxygen-containing compounds, while have no impact on the yield of gaseous products during sludge gasification. A novel high-entropy oxide (Mg0.2Co0.2Ni0.2Cu0.2Mn0.2)Al2O4 catalyst was synthesized and applied in the gasification-catalytic reforming tandem process. It contributes to the tar removal and regulating of the fuel gas with the assistant of steam by cracking large molecules and catalytic reforming of gaseous products. The highest H2/CO ratio of 3.61 after the gasification-catalytic reforming tandem process is obtained, compared to 0.83 of pyrolysis and 0.85 of gasification. The synergistic effect of the active sites of high-entropy oxide catalyst and steam promotes the cracking and conversion of tar and the modulation of gas components, which is beneficial for improving the quality and calorific value of the produced bio-oil and H2-rich gas by thermochemical treatment of sewage sludge.