Perovskite Adsorbents for Warm-Gas Removal of Sulfur
DOE Phase I SBIR Contract DE-FG02-07ER84666
New materials and processes are required to remove trace impurities including sulfurs and metals from hydrogen. The DOE is seeking advanced processes, materials and devices for producing ultra-pure hydrogen from coal-derived synthesis gas; processes that remove all impurities are the goal.
Currently, oxides based on zinc are commonly used to remove sulfur from industrial gas streams. However, in the presence of steam and under warm-gas clean-up conditions (250 - 450°C), standard industrial adsorbents (based on zinc) are not adequate for reducing sulfur to levels in the part per billion by volume range, which prevents poisoning of many types of catalysts used in the production of synthetic fuels derived from coal or in fuel cells utilizing hydrogen produced from coal.
Thermodynamic analysis at Eltron indicates that a number of elements will form much more stable sulfides (relative to those of zinc) and therefore could be used to form better adsorbents for removing sulfur in the presence of steam. Eltron’s research is focused on developing materials with the perovskite crystal structure, containing elements with high binding energy for sulfur, as improved adsorbents for the warm-gas removal of sulfur.
Removing sulfur from process streams will become more important as coal and high-sulfur petroleum feedstocks are increasingly utilized. It is highly desirable that sulfur levels are reduced to the part-per-billion by volume range, in the presence of steam and at warm-gas temperatures ranging from 250-450°C. Sulfur must be reduced to such low levels to protect many catalysts, including those used in Fischer-Tropsch synthesis, from poisoning. Warm-gas clean-up would save energy and costs, compared to processes that require cooling and reheating of gas streams and the condensation and re-introduction of steam. Combining the adsorbents for sulfur reduction with Eltron’s hydrogen transport membranes would essentially remove all impurities from hydrogen gas streams.