Continuous Sulfur Sorption in Supercritical Water by Carbon-supported Zinc Oxide Materials

Sulfur (S) capturing materials working at supercritical water (SCW) conditions need to be designed and developed to overcome issues related with catalyst poisoning during the hydrothermal gasification of wet biomass, an efficient and sustainable technology for alternative fuels production. Sorbent materials of zinc oxide (ZnO) deposited on porous carbon (C) support were prepared by an innovative continuous flow SCW impregnation method. Their S-adsorption performance was tested under the same supercritical conditions in the presence of sodium hydrosulfide (NaHS), as model inorganic sulfur compound. During sulfidation experiments, ZnS replaced ZnO indicating an efficient chemisorption of S with the formation of the sulfide particles by a pseudomorphic replacement mechanism. The S adsorption capacity of the ZnO/C composites reaches 1.55 molS/molZn at relatively low temperature, which is much higher than those of other reported S capturing materials employed in SCW processes. The results reported here confirm that S sorbents can be both generated and used under the continuous flow SCW conditions relevant for technological applications towards the production of hydrogen and methane from biomass wastes and residues.