Preparation of activated coke by carbonization, activation, ammonization and thermal treatment of sewage sludge and waste biomass for SO2 absorption applications

Abstract

Flue gas desulfurization of coal-burning power plants is imperative to mitigate pollution and acid rain. Use of activated coke as a sulfur dioxide adsorbent is a promising technology, particularly since activated coke can also effectively remove other emissions, such as mercury. In this manuscript, a modified method of ammonia water was used to prepare activated coke for flue gas desulfurization. The feedstock is a blend of sewage sludge and waste biomass, at a mass ratio of 2:1. This material was carbonized prior to activation and ammonization; in some cases, additional thermal treatment was applied. The products were successfully tested for sulfur dioxide adsorption. A graphene model incorporating nitrogen-containing functional groups was used to simulate the sulfur dioxide adsorption process. Thereby, the effects of different ammonia modification concentrations on the physical and chemical properties of activated coke were studied, and the sulfur dioxide adsorption process of nitrogen-containing functional groups (such as pyridine and pyrrole) in activated coke, during flue gas desulfurization, was simulated. This study confirmed that the method of ammonization and heating can introduce nitrogen-containing functional groups on the surface of the activated coke. This greatly improves its chemical properties and, as a result, it markedly improves its SO2 adsorption capacity. It was found through simulation that the doping of nitrogen atoms changes the uniform electrostatic potential distribution and changes the surface polarity. H2O, pyridine functional groups and pyrrole functional groups can promote the adsorption of SO2 on the graphene surface. The pyrrole functional group showed selective adsorption for both SO2 and H2O, but it was predicted to be more effective in adsorbing SO2 than in adsorbing H2O. The pyridine functional group showed no selective adsorption for SO2 and H2O, and it was predicted to be more active in adsorbing SO2 when compared with the pyrrole functional group. The O2 had no effect on the physical adsorption of SO2 on the graphene.