Performance evaluation of zero-valent iron nanoparticles (NZVI) for high-concentration H₂S removal from biogas at different temperatures

The removal performance of high-concentration H₂S (ca. 10000 ppm) from simulated biogas by zero-valent iron nanoparticles (NZVI), with the majority of the particles in the size range of 60-150 nm, at different reaction temperatures (room temperature, 100 °C, 200 °C and 250 °C) were evaluated using a custom-designed quartz fixed-bed reactor. The results showed that the H₂S removal capacities of NZVI were quite limited at room temperature and 100 °C, being 12.56 and 14.77 mg H₂S gNZVI^-1, respectively. However, these values increased significantly to 391.02 (200 °C) and 488.95 (250 °C) mg H₂S gNZVI^-1. Scanning electron microscopy analysis showed that the products of the NZVI-H₂S reaction aggregated to form irregular polygonal-shaped structures. The main X-ray diffraction pattern peaks of the product matched well with troilite, and no pyrite was observed. The deconvolution of the X-ray photoelectron spectrometry peaks showed the presence of monosulphide (S^2-) and disulphide (S₂^2-) in the product, in which 36% of the sulphur existed as monosulphide and 64% as disulphide. It is proposed that the effective removal of hydrogen sulphide by NZVI at elevated temperatures can be attributed to the combination of nano-constituents, oxide shell and underlying Fe core to produce FeS similar to troilite and amorphous FeS₂.