Removal of hydrogen sulfide from landfill gas using a solar regenerable adsorbent

Abstract

Landfill gas is a complex mix of gases, containing methane, carbon dioxide, nitrogen and hydrogen sulfide, created by the action of microorganisms within the landfill. The gas can be collected and flared off or used to produce electricity. However, the hydrogen sulfide content, which may vary from 10's to 1000's of ppm, can cause irreversible damage to equipment, and when combusted creates sulfur dioxide, a precursor of acid rain. It is also a toxic eye and lung irritant, so that prolonged exposure must be kept below a few ppm. Therefore, hydrogen sulfide must be removed before landfill gas can be utilized. Our approach is to scrub hydrogen sulfide into aqueous media and then use an adsorbent to sequester it. The adsorbent is then regenerated in a photocatalytic reaction potentially using sunlight. The adsorbents are metal sulfides such as Copper sulfide, Molybdenum sulfide, tungsten sulfide, and silver sulfide. The expected reaction is the oxidation of sulfide in hydrogen sulfide to elemental sulfur, and the reduction of water to hydrogen gas. The volume of hydrogen obtained during photoreaction and the potentiometric shift of a sulfide ion-selective electrode were taken as measures of the extent of sulfide uptake and subsequent oxidation. Of the various sulfides examined, molybdenum sulfide with platinum co-catalyst displayed the optimum in terms of toxicity, stability and photocatalytic activity. Using a xenon arc lamp as illumination source and adding a surfactant or low surface energy material such as Teflon® to promote bubble formation, gas evolution rates on the order of 5 mL/g-hour were achieved.