Preparation and regeneration performance of modified semi-carbon for flue gas SO₂ adsorbent

The use of adsorbents such as activated coke to separate pollutants from flue gas is an effective flue gas treatment method. As a cheap carbon material, semi-carbon is a potential porous alternative material to the existing commercial activated coke. In this work, the effects of the carbonization time, carbonization temperature, and binder addition on the properties of prepared adsorbents from Shanxi semi-coke were studied. The microstructure changes were investigated, and the changes in the surface functional groups in the adsorption and desorption process were explored via X-ray photoelectron spectroscopy (XPS). The results show that the carbonization temperature has a significant effect on the wear resistance and compressive strength index, and the carbonization time has a significant effect on the saturated desulfurization value and the breakthrough desulfurization value. In addition, under the conditions of 50% coal tar addition ratio, 700 ℃ carbonization for 20 min, and 900 ℃ activation for 60 min, the modified semi-coke parameters were as follows: abrasion resistance 95.81%, compressive strength 536.1 N·cm⁻¹, saturated desulfurization value per g of semi-carbon is 45.71 mg, and breakthrough desulfurization value per g of semi-carbon is 23.45 mg. When the first failure occurred in the adsorbents after 10 thermal regeneration processes, the activated carbon surface was etched over a large area with severe changes in the surface morphology under the above conditions. Some large granular activated carbons were etched and pulverized into small particles. The activated carbon surface structure was also etched out of pores, which may be caused by the C consumption resulting from the interaction of C and H₂SO₄. The results also show that the secondary activation could increase the adsorption capacity in a short time, but the activated carbon performance degradation is also significant. The amount and composition ratio of the oxygen-containing groups on the surface of the modified semi-coke affected the adsorption performance. The ratio of oxygen to carbon groups corresponded to the adsorption performance: the higher the proportion of oxygen-containing groups, the worse the adsorption performance. The proportion of oxygen-containing groups was changed by the second activation regeneration, and C=O decreased significantly, O−C=O increased significantly, while C−O changed slightly. Although the O−C=O functional group contains oxygen, it may not significantly inhibit adsorption. This study provides a new adsorbent-preparation method for industrial flue gas treatment and also provides a reference for the research on the surface modification of semi-coke and the adsorption and desorption mechanisms of sulfur dioxide.