Manganese and ceria sorbents for high temperature sulfur removal from biomass-derived syngas - The impact of steam on capacity and sorption mode

Syngas derived from biomass and coal gasification for fuel synthesis or electricity generation contains sulfur species that are detrimental to downstream catalysts or turbine operation. Sulfur removal in high temperature, high steam conditions has been known to be challenging, but experimental reports on methods to tackle the problem are not often reported. We have developed sorbents that can remove hydrogen sulfide from syngas at high temperature (700°C), both in dry and high steam conditions. The syngas composition chosen for our experiments is derived from statistical analysis of the gasification products of wood under a large variety of conditions. The two sorbents, Cu-ceria and manganese-based, were tested in a variety of conditions. In syngas containing steam, the capacity of the sorbents is much lower, and the impact of the sorbent in lowering H ₂S levels is only evident in low space velocities. Spectroscopic characterization and thermodynamic consideration of the experimental results suggest that in syngas containing 45% steam, the removal of H ₂S is primarily via surface chemisorptions. For the Cu-ceria sorbent, analysis of the amount of H ₂S retained by the sorbent in dry syngas suggests both copper and ceria play a role in H ₂S removal. For the manganese-based sorbent, in dry conditions, there is a solid state transformation of the sorbent, primarily into the sulfide form.