H2S removal from syngas using wastes pyrolysis chars

Abstract

Pyrolysis chars from wastes were investigated as sorbents for H2S removal from syngas. The H2S removal tests were performed at ambient temperature in various dry gas matrices (N2, Air, Syngas) to study the effect of the gas composition on the adsorption efficiency. Two chars were produced by the pyrolysis of: used wood pallets (UWP), and a 50/50% mixture of food waste (FW) and coagulation-flocculation sludge (CFS). The chars were functionalized by low-cost processes without chemicals: gas phase oxygenation and steam activation. Activated chars were the most efficient materials due to their large specific surface area, alkaline pH, basic O-containing groups and structural defects in graphene-like sheets. Raman analysis evidenced that inherent mineral species (especially Ca and Fe) increased the H2S removal efficiency by promoting the formation of metal sulfide and metal sulphate species at the char surface. Mesopores lower than 70 Å were revealed to be important adsorption sites. Under dry Syngas matrix, the chars remained efficient and selective toward H2S removal despite the presence of CO2, while O2 in the Air matrix decreased their removal capacity due to the formation of sulfur acid species. The most efficient material was the steam activated char from FW/CFS, with a removal capacity of 65 mgH2S.g−1 under dry syngas. This char was proved to be completely regenerated with a thermal treatment under N2 at 750 °C. This study demonstrated that activated chars from food waste and sludge could be used as eco-friendly, affordable, and selective materials for syngas desulfurization even under dry atmosphere.