Effect of activation agents on the surface chemical properties and desulphurization performance of activated carbon

Abstract

Flue gas pollution is a serious environmental problem that needs to be solved for the sustainable development of China. The surface chemical properties of carbon have great influence on its desulphurization performance. A series of activated carbons (ACs) were prepared using HNO3, H2O2, NH3·H2O and steam as activation agents with the aim to introduce functional groups to carbon surface in the ACs preparation process. The ACs were physically and chemically characterized by iodine and SO2 adsorption, ultimate analysis, Boehm titration, and temperature-programmed reduction (TPR). Results showed that the iodine number and desulphurization capacity of NH3·H2O activated carbon (AC-NH3) increase with both activation time, and its desulphurization capacity also increases with the concentration of activation agent. However, HNO3 activated carbon (AC-HNO3) and H2O2 activated carbon (AC-H2O2) exhibit more complex behavior. Only their iodine numbers increase monotonously with activation time. Compared with steam activated AC (AC-H2O), the nitrogen content increases 0.232% in AC-NH3 and 0.077% in AC-HNO3. The amount of total basic site on AC-HNO3 is 0.19 mmol·g−1 higher than that on AC-H2O. H2O2 activation introduces an additional 0.08 mmol·g−1 carboxyl groups to AC surface than that introduced by steam activation. The desulphurization capacity of ACs in simulate flue gas desulphurization decreases as follows: AC-NH3 > AC-HNO3 > AC-H2O2 > AC-H2O. This sequence is in accord with the SO2 catalytic oxidation/oxidation ratio in the absence of oxygen and the oxidation property reflected by TPR. In the presence of oxygen, all adsorbed SO2 on ACs can be oxidized into SO3. The desulphurization capacity increases differently according to the activation agents; the desulphurization capacity of AC-NH3 and AC-HNO3 improves by 4.8 times, yet AC-H2O increases only by 2.62 as compared with the desulphurization of corresponding ACs in absence of oxygen.