Pelletization of Iron Oxide Based Sorbents for Hydrogen Sulfide Removal

Biogas derived from anaerobic digestion of biological wastes has been extensively used for heating purposes and/or electricity generation. Presence of hydrogen sulfide (H2S) in biogas affects engine performance adversely, thus reducing H2S content is a valuable part in practical application before utilizing biogas. Adsorptive separation is very appealing due to being an economical and effective method including the use of iron oxide based adsorbents. Pelletization of iron oxide adsorbents has never been reported among the adsorbents described to date. Therefore, H2S capture in two iron oxides (ferric oxide (Fe2O3) and magnetite (Fe3O4)) was experimentally investigated to determine technical feasibility of shaping pellets based on active iron oxide sorbent in removing H2S from a simulated gas stream (0.35 vol.% H2S balanced in N2). Many factors affecting the behavior of gas adsorption such as gas in-flow rate, adsorption temperature, binder loadings and textural characteristics were considered. The pellet strengths were also undertaken using a bulk crushing strength analyzer. The results indicated that higher temperature favors the diffusion of H2S molecules from the surface into the bulk of iron oxides. The H2S-sorption capacity of Fe3O4 sorbent was higher than that of Fe2O3 sorbent corresponding with the different pore volume and surface area in each adsorbent. With the same active Fe3O4, the extruded pellet produced with starch binder showed the excellent H2S uptake and crushing resistance. The higher gas in-flow rate had positive impact to contacting efficiency and mass transfer of solid and gas phase. The adsorbed H2S gas can be readily desorbed from the pellets with the desorption temperature below 60°C and the H2S-sorption capacity was consistent over repeated cycles. The pellets can be reused several times for consecutive adsorption/desorption cycles, without loss of performance in a large-scale reactor and therefore represent serious candidates for use in commercial absorbers.