Adsorption Characteristics of Polycyclic Aromatic Hydrocarbons by Biomass-Activated Carbon in Flue Gas

Activated carbon (AC) injection is a well-proven end-of-pipe control technique for reducing polycyclic aromatic hydrocarbon (PAH) emission from flue gas. This paper introduces an effective and economical adsorption material making from wheat straw via water vapor activation. The adsorption performance of wheat straw-based activated carbon on PAHs in simulated flue gas was studied on an entrained flow adsorption reactor. Meanwhile, the effects of the AC pore structure, flue gas temperature, and initial PAH concentration on the removal efficiencies of PAHs were also investigated. After that, AC was submitted to PAH adsorption exploratory testing by using a fixed bed adsorption reactor to analyze the mechanism of the PAH adsorption process from the perspective of kinetics. The results revealed that the adsorption capacity of AC for PAHs improved with the increase of mass fraction and aromatic ring number. Among all the pore structure parameters, the Brunauer–Emmett–Teller specific surface area had the greatest influence on PAH adsorption, and the adsorption of low-molecular weight PAHs with two to three aromatic rings was dependent on the micropore volume, while middle-molecular weight PAHs with four aromatic rings were more dependent on the mesopore volume. Furthermore, the total removal efficiency of PAHs decreased from 51.0 to 29.4% when the temperature of the flue gas rose from 90 to 150 °C. Most importantly, the results of mechanism analysis indicated that the pseudo-first-order kinetic model could be used to describe the adsorption process of PAHs on AC. External mass transfer had a significant impact on the adsorption process.