Effect of sulfur on catalytic gasification of lignin in supercritical water

Gasification of lignin in supercritical water was investigated over ruthenium catalysts in the presence of various sulfur contaminants. In the absence of sulfur, lignin was gasified over supported ruthenium catalysts completely to methane, carbon dioxide, and hydrogen. In the presence of sulfur, the gas yield decreased with the amount of sulfur added. The carbon dioxide composition in the presence of sulfur was lager than that in the absence of sulfur, and the methane composition was lower. From X-ray photoelectron spectroscopy characterization of catalysts used for gasification, the sulfur species which poisoned the ruthenium sites were found to be ruthenium sulfide, ruthenium sulfite, and ruthenium sulfate. The gas yield increased with an increase in water density. In addition, the amount of sulfur that remained on the catalyst surface after gasification decreased with increasing water density.