Catalytic reforming of volatiles and nitrogen compounds from sewage sludge pyrolysis to clean hydrogen and synthetic gas over a nickel catalyst

• Volatiles and nitrogen compounds from SS pyrolysis were catalytically reformed.
• Syngas and H2-rich gas were produced under inert and steam reforming conditions.
• Steam improved tar reforming and inhibited carbon deposition on Ni/Al2O3.
• Almost all the NOx precursors were converted to N2 over Ni/Al2O3 at 650 oC.

Low-temperature catalytic reforming of volatiles and nitrogen compounds from sewage sludge (SS) pyrolysis was performed in a two-stage fixed-bed reactor over Ni/Al2O3 under inert and steam-reforming conditions. The results show that the reforming of SS volatiles significantly depended on temperature, space velocity, steam partial pressure, and feedstock type. Catalytic cracking of SS volatiles at 650 °C under inert atmosphere produced a tar-free synthetic gas with a H2/CO ratio of 2:1 in a high yield, which is preferred for maximum conversion efficiency for methanol synthesis. Steam as the gasifying agent gave a H2-rich gas (H2 content 68.0 vol.%) with a high yield of 82.5 mmol · g-1 (daf) at 650 °C, while the H2 yield is twice as that from non-steam gasification. Ni/Al2O3 effectively improved tar reforming and showed great resistance to coke deposition in the presence of steam. NH3, HCN, and nitrogen in tar are the main volatile nitrogen species in SS pyrolysis. Almost all the NOx precursors were converted to N2 by catalytic reforming at 650 °C both in the presence and absence of steam. Such an approach may lead to the development of a clean SS utilization technology and also H2/synthetic gas production technology from SS.