Catalytic Methanation of CO2-Lean Gas from Sorption-Enhanced Pyrolysis of Sewage Sludge

CO2-lean pyrolysis streams from processing industrial or municipal by-products, such as sewage sludge, were tested for catalytic methanation in a bench-scale laboratory plant over a temperature range of 300–450 °C and atmospheric pressure. Two home-made Ni-based catalysts supported on both cordierite and activated vegetable carbon were tested against a commercial Ni catalyst formulation, at a space velocity variable between 250 and 1000 h−1. Quantitative CO conversions were detected at 350 and 400 °C for the Ni catalysts supported on cordierite and activated carbon, despite CO2 conversion values being averagely low. Methane selectivity approached values up to 90%, accounting for a relative content up to 80 mol% in the outlet methanation mixture. Overall, the cascade integration of a pyrolysis step for processing sewage sludge into a CO2-lean gaseous stream feeding a catalytic methanation reactor was successfully demonstrated, with the whole chain representing a viable strategy to dispose of by-products and produce bio-synthetic natural gas.