Pyrolyzed tannery sludge as adsorbent of volatile organic compounds from tannery air emissions

The tanning industry has a great impact on the environment for the large consumption of water, the huge amount of waste generated, and the high emissions of volatile organic compounds (VOCs), used in leather finishing operations. In this study, pyrolyzed tannery sludge (PTS) was investigated, after further pyrolysis at high temperature, as a sorbent of VOCs. Pyrolysis experiments were performed at various temperatures (750–850 °C) and times (6–60 min) to evaluate the optimal operating conditions in terms of developed BET specific surface area. Fixed bed adsorption experiments were performed to determine the breakthrough curves at room temperature using an air stream containing n-butyl acetate, a VOC largely used in leather finishing products. By pyrolysis at 850 °C for 6 min the BET of PTS increased from 72 to 127 m2/g, improving its sorption capacity. The effects of superficial velocity, inlet VOC concentration, and bed height on the sorption behaviour of PTS after further pyrolysis (PPTS) were investigated. Breakthrough curves were well fitted by the Bohart-Adams model (R2 = 0.92) and the adsorption isotherms with Freundlich equation (R2 = 0.97). Preliminary sorbent desorption tests were carried out by hot air in the temperature range 100–180 °C, demonstrating the feasibility of thermally regenerating this material. Multiple adsorption/desorption cycles on the PPTS will be performed on lab scale in a future study to investigate the real sorbent recyclability.