Adsorption of SO2 by typical carbonaceous material: a comparative study of carbon nanotubes and activated carbons

Applying activated carbons for SO2 adsorption and conversion to H2SO4, as a dry process, has been considered the development direction of desulfurization technology. Coal-based activated carbon, coconut shell activated carbon, single wall carbon nanotube and multi-wall carbon nanotubes were used as typical carbonaceous materials to study the SO2 adsorption mechanism. SEM, N-2 adsorption, XPS and fixed-bed reaction system were employed to study the morphology, pore structure, surface functional groups and SO2 adsorption behaviors of the four adsorbents. The fixed-bed experiment was carried out at normal pressure and SO2 concentration was set 1,000 ppm. According to SEM and N-2 adsorption results, hierarchical pore structure was an important characteristic of activated carbon. Aggregation was an important characteristic of CNTs. Mesopores and macropores took the dominance of pore structure in CNTs. According the SO2 adsorption data and correlation analysis, it can be concluded that the dominant adsorption type on activated carbons does not alter with adsorption temperature changing. However, the adsorption type of SO2 adsorption on CNTs changes with adsorption temperature varying. With adsorption temperature increasing, the dominant adsorption type transforms to chemisorption by physisorption. Higher-density pi-pi* in carbon nanotubes may be the active sites for the SO2 chemical adsorption. Micropores with the diameter smaller than 0.7 nm were the best SO2 adsorption place for both activated carbons and carbon nanotubes. The results provided a profound insight into the microstructure and SO2 adsorption mechanism of the two kinds of carbonaceous materials.