Feasibility Study on Preparation Activated Carbon from Sewage Sludge Exploiting Low Oxygen Flue Gas

Abstract

This study focused on the feasibility of exploiting low oxygen flue gas to prepare activated carbon from sludge to improve the economic efficiency. Base on the physical (steam as activated agent) and chemical (ZnCl2 as activated agent) activation method, the effect of the operation parameters such as activation temperature, time, steam content, the ratio of sludge to ZnCl2 and oxygen content on the performance of sludge-derived activated carbon was investigated. The performance of the activated carbon was characterized by BET surface area, methylene blue adsorption value and methyl orange adsorption value. The results show that the optimal operational parameters of activation temperature, time and steam content are 800°C, 90min and 34.8% respectively for the physical activation method. However, the products are not so good. The specific surface area, yield, adsorption value of methylene blue and methyl orange are only 246.3m2·g-1, 46%, 18.1mg·g-1, 14.8mg·g-1 respectively. The flue gas is not enough for physical activation to produce activated carbon due to its low vapor content and high operation cost to satisfy demands of high activation temperature. Considering the chemical activation method, the existence of oxygen can promote the formation and development of micro pore of activated carbon. The optimal oxygen content is about 2%~4% for ZnCl2 as activated agent. Under the optimal condition of activation temperature 550°C, activation time 90min and oxygen content 2%, the specific surface area and methylene blue adsorption value are the largest, which are 516.1m2·g-1 and 129.8mg·g-1. The pore volume, micro pore volume and average pore size are 0.29cm3·g-1, 0.16cm3·g-1 and 3.95nm respectively. All the data demonstrate that combination with chemical activation, the flue gas with high temperature and low oxygen content can be used as heat resource, shielding gas and activation gas to produce activated carbon from dewatered sludge with moisture content higher than 80% directly. This study can provide a theoretical basis to low the cost of production sludge-derived activated carbon and realize recycling of sludge.