Anion exchange resins are being used by the drinking water industry to remove per-and polyfluoroalkyl substances (PFAS) including perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFSAs) from water, and spent resins are commonly incinerated by the industry. By conducting thermogravimetric analysis (TGA) studies, this investigation is aimed at filling some of the knowledge gaps that currently exists in the incineration of PFAS-laden resins. This work is aimed at understanding the impact of characteristics (i.e., carbon chain length and acid functionality) of nine PFAS compounds, in the presence or absence of a calcium oxide (CaO) additive, on the decomposition and burning characteristics of PFAS-laden resins. The TGA profiles of selected pure PFAS compounds confirmed the near-complete evaporation of these compounds below their boiling points, whereas PFAS-laden resin profiles exhibited the partial holding of PFAS compounds by resin well above their boiling points. Resins laden with PFCAs exhibited TGA profiles similar to those of the blank resins, whereas resins laden with PFSAs showed a drastic weight loss from 400 to 500 °C. These results suggested that decomposition and oxidation reactions were accelerated by sulfonic acid functionalities, and the impact of sulfonic acid groups appears to increase with the increase in the chain length of PFSAs. The presence of the CaO additive resulted in similar TGA profiles for all tested PFCA-laden resins, where all exhibited a relatively flat profile in the∼470−700 °C range as a result of the simultaneous burning of carbon char and the reaction of CO 2 with CaO, followed by a rapid weight loss at 700−800 °C from the decomposition of the formed CaCO 3 to CaO. The TGA profiles of PFSA-laden resins in the presence of CaO exhibited a similar impact of sulfonic acid functionalities accelerating the decomposition and oxidation of the resin without any clear correlation with the PFSA chain length.
Nitric oxide can be removed from flue gas by catalytic oxidation of NO to NO 2 , followed by dissolution of NO 2 in water. The work presented here includes catalytic NO oxidation by activated carbons (ACs) at atmospheric and elevated pressures under dry and wet conditions at ambient temperature. The AC samples had different physicochemical characteristics including surface areas of ∼400–1600 m 2 /g and micropore volumes of ∼0.2–0.6 cm 3 /g while having different surface chemistries. Dry tests indicated that introducing nitrogen functionalities or coating with pyrolytic carbon could enhance the catalytic activity of AC for NO oxidation. Nitric oxide concentration profiles from the oxidation experiments under dry conditions showed maximum values after 5–15.5 h of testing and a steady-state condition after ∼12–30 h and that a major release of NO 2 began after reaching the maximum values in the NO concentration. Adsorption profiles showed a high rate of NO x adsorption during the early hours of these experiments, and this rate decreased almost exponentially to a near-zero value. A near-complete catalytic conversion was achieved for NO oxidation at 120 psig under dry conditions, substantially higher than the 62% value of the noncatalytic NO oxidation at 217 psig. The wet trickle-bed experiments revealed that an inert packing material with a high external surface was a more suitable option than the ACs for NO oxidation in a wet trickle-bed system, even for ACs that exhibited high catalytic reactivity under dry conditions. Noncatalytic NO oxidation in the trickle-bed system was enhanced by the higher gas–liquid contact surface of the packing material for NO 2 dissolution in water. Complete wetting of the hydrophilic AC or the presence of water vapor in the gas in contact with the surface of the superhydrophobic AC could eliminate or drastically reduce the catalytic activity of the AC for NO oxidation.
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