Preparation of Straw Porous Biochars by Microwave-Assisted KOH Activation for Removal of Gaseous H2S

Two types of straw porous biochars were prepared from agricultural waste (i.e., rice straw and wheat straw) using microwave-assisted KOH activation to eliminate H2S in the gas phase. Influences of sorption temperatures and KOH/biochar mass ratios on the performance of the adsorbent for H2S removal were studied. Several characterization methods were used to analyze the changes in physical structures and the changes of chemical sorption sites of the samples before/after activation and H2S removal experiment. H2S adsorbing kinetics was explored, and the sorption capacities for gaseous Hg0 of the spent adsorbents were also tested. The results exhibited that the physical structures of straw porous biochars were evidently improved, and the contents of the oxygen-containing functional group were also raised via the activation of microwave-assisted KOH. The largest specific surface areas of rice straw/wheat straw porous biochars are, respectively, up to 1999.96 m2/g (WKRS4) and 877.16 m2/g (WKWS4), resulting in the best performance for eliminating H2S. The equilibrium adsorption capacities of WKRS4/WKWS4 to H2S are 57.91 and 61.47 mg/g, respectively. Both temperature and KOH/biochar mass ratio achieve dual effects on H2S sorption. In the sorption processes of H2S over two types of porous materials, both of the rate-determining steps are the external mass transfers. The deactivated porous biochars after adsorbing H2S showed good capturing capabilities for Hg0 in the gas phase.