Low-cost biomass ash-based adsorbent for removal of hydrogen sulfide gas

This research aims to use boiler-biomass ash to produce low-cost and efficient adsorbent for removing hydrogen sulfide (H₂S) in biogas from small scale biogas plant. To reduce pressure drop across adsorbent bed during the practical adsorption, clay was selected as a binder to perform the extruded adsorbent. 15 different adsorbents using different proportion of ash to clay (70–90 %) together with the an amount of NH₄HCO₃ as pore-forming reagent (0–6 %), and baking temperature (100–500 °C) were prepared. From the breakthrough cure studies using fixed-bed column fed by 0.1 L/min synthetic H₂S containing gas, it was found that quadratic equation with R² 0.75 can be used to optimize adsorption preparation and predict H₂S adsorption capacity. The optimized adsorbent prepared using 79 % ash, and 2.5 % NH₄HCO₃ at 293 °C was validated and had achieved H₂S adsorption capacity of 3.67–3.88 mg/g. The characterization results, including BET surface area analysis and SEM imaging, show significant pore formation due to the presence of NH₄HCO₃. CHNS/O SEM-EDX, and XRF analyses confirmed that there wasan increase in sulfur content of the post-adsorbent. The decrease in surface area and change of functional groups in FTIR spectrum of the spent adsorbent, and presence of metal elements supporting the chemisorption mechanism were also discovered. The best fitted breakthrough curve operated at 200–10,000 ppm H₂S containing gas to Thomas model which could be implemented for further scaling up are also proposed. This is a successful attempt to use an abundance industrial waste, eco-friendly local material and novel pore forming agent in order to create an eco-efficient adsorbent for H₂S removal.