Regenerable α-MnO2 nanotubes for elemental mercury removal from natural gas

Abstract

The elemental mercury (Hg0) vapor removal ability of α-MnO2 nanotubes (NTs), nanorods (NRs) and nanowires (NWs) was evaluated in simulated natural gas mixtures. It was shown that NTs exhibited superior efficiency (~100%) at the temperature range of interest (25–100 °C). The Hg0 breakthrough (corresponding to 99.5% Hg0 removal efficiency) at ambient conditions and Hg0in = 870 μg∙m−3, occurred after 48 h, reflecting a Hg0 uptake of >10 mg∙g−1 (1 wt%). Most importantly, the developed nanosorbent was repeatedly, sufficiently regenerated at the relatively low temperature of 250 °C in a series of seven successive sorption-desorption tests, maintaining its capacity to remove all incoming Hg0in in each cycle. Interestingly, kinetic studies showed that at least 85% of total adhered Hg0 could be recovered within the first hour of a 3-h regeneration process. Moreover, the presence of CO2 and H2S did not affect its activity. The thermogravimetric analysis indicated significantly higher dehydration for NTs due to the loss of bound water inside its tunnels, likely indicating the presence of abundant surface adsorbed oxygen species which are believed to facilitate Hg0 adsorption. This was also confirmed by X-ray spectroscopy, possibly explaining the enhanced activity of NTs.