Preparation and evaluation of adsorbents from waste carbonaceous materials for SOx and NOx removal

Abstract

AbstractThis paper presents studies of a new integrated process for simultaneous SOx and NOx removal and utilization of waste carbonaceous materials. It is mainly centered on some fundamental aspects of preparing microporous adsorbents from solid wastes such as coal reject, sewage sludge and sawdust. Surface area and pore structural evolution are investigated to illustrate the importance of processing parameters such as pyrolysis temperature and hold time, activation methods and carbon burn‐off, etc. It is shown that pyrolysis temperature, activation chemicals used and carbon burn‐off have significant effects on the surface area development and pore structure evolution. There exist an optimal pyrolysis temperature and hold time for maximum surface area development for all precursor materials. Physical activation of coal reject char after pyrolysis can improve the surface area of the derived chars, while chemical treatment in ZnCl2 can enhance the microporosity of sewage sludge char. In physical activation, carbon burn‐off or hold time is a critical factor in determining the surface area. Concentration of the activating agent is an important factor in chemical treatment of sewage sludge. Adsorption characteristics of the wastes‐derived adsorbents with respect to SO2, H2S, and NOx are also studied in this work. It is shown that solid wastes such as sawdust and coal mining wastes can be converted into effective adsorbents for SO2 and NOx removal from the flue gases, whilst activated chars derived from sewage sludge have been shown to be promising adsorbents for H2S removal. The significance of using waste solids is two‐fold: on one hand the waste materials are utilized or minimized; on the other, they can replace or partially substitute the expensive activated carbons for the removal of SOx and NOx.