Carbon consumption and regeneration of oxygen-containing functional groups on activated carbon for flue gas purification.

High carbon consumption is an important factor restricting the wide application of activated carbon technology for flue gas purification. A fixed-bed reactor combined with a Fourier transform infrared (FTIR) spectrometer was used to explore the source of carbon consumption at various SO2 concentrations and cyclic adsorption-regeneration times. The results demonstrate that carbon consumption originates from two sources and is mainly determined by the reaction of H2SO4 and C at high SO2 concentrations and by the thermal decomposition of oxygen-containing functional groups at low SO2 concentrations. An interesting observed phenomenon is that carbon consumption does not increase as the SO2 concentration increases. The conversion mechanism reveals that carboxylic and anhydride groups are converted to phenol and quinone groups, which do not easily decompose with increasing SO2 concentration. In the process of cyclic adsorption-regeneration, it is discovered that the carbon consumption in the first cycle is several times higher than that in the following cycles due to the decomposition of functional groups from the activated carbon itself. The regeneration mechanism of functional groups has been elucidated. The carboxylic acid and the phenolic hydroxyl on the surface of activated carbon are consumed in the regeneration process and formed again from the conversion of carbonyl groups in the next adsorption process under the roles of O2 and H2O. It is proposed that the functional groups are regenerated in the adsorption process rather than in the regeneration process.