Activation energy for utilizing peroxy-acid for treating polycyclic aromatic hydrocarbons (PAHs)

Tentori, Egidio F.
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Nyman, Marianne
Kilduff, James
Zimmie, T. F.
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Environmental engineering
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Polycyclic aromatic hydrocarbons (PAHs) are a group of hydrophobic organic contaminants (HOCs) of importance due their environmental and human health effects, their widespread occurrence and persistence in the environment. Advanced oxidation processes (AOPs) are a set of treatment methods that have been proven to be successful in degrading organic contaminants in water, soils and sediments. AOPs usually rely on the oxidative potential of the hydroxyl radical (HO*) to degrade organic contaminants, like PAHs. The peroxy-acid process, an advanced oxidation process (AOP) proven to degrade PAHs, which utilizes a mixture of organic acids, like acetic acid, and hydrogen peroxide to oxidize organic compounds. Peracetic acid (PAA) is produced from the combination of acetic acid and hydrogen peroxide. The peroxy-acid process was used to investigate the degradation process of four PAHs: anthracene, benzo[a]pyrene, phenanthrene and pyrene.
Once the reaction rate constants were obtained from the degradation for each of the four selected PAHs at the three selected temperatures, the activation energy (Ea) was calculated for anthracene, benzo[a]pyrene, phenanthrene and pyrene using the Arrhenius equation. The findings of the peroxy-acid degradation process at temperatures of 25, 32, and 40 °C after 24 hours were as follows: [i] anthracene mass % amount reductions of 30.5 %, 44.6 %, and 98.1 %, with reaction rate constants of 0.0107, 0.0182 and 0.1536 hr-1, respectively; [ii] benzo[a]pyrene mass % amount reductions of 20.1 %, 38.1 %, and 92.4 %, with reaction rate constants of 0.0080, 0.0133 and 0.1027 hr-1, respectively; [iii] phenanthrene mass % amount reductions of 17.9 %, 27.7 %, and 61.3 %, with reaction rate constants of 0.0068, 0.0112 and 0.0336 hr-1, respectively; and [iv] pyrene mass % amount reductions of 19.8 %, 39.7 % and 89.6 %, with reaction rate constants of 0.0074, 0.0194 and 0.0852 hr-1, respectively. The Eas calculated from these reaction rates were found to be: 138.96 kJ mol-1 for anthracene, 133.13 kJ mol-1 for benzo[a]pyrene, 83.07 kJ mol-1 for phenanthrene and 126.76 kJ mol-1 for pyrene. These obtained reaction rate and Ea findings could prove to be a valuable asset in helping determine the exact reaction mechanism of the peroxy-acid process with PAHs and be potentially useful in the treatment of PAHs and other organic contaminants in the environment.
Peroxy-acid PAH degradation experiments were conducted to determine the peroxy-acid process reaction rate constants (k) of the four selected compounds: anthracene, benzo[a]pyrene, phenanthrene and pyrene. Three different temperatures (e.g., 25, 32, and 40 °C) were investigated over a 24-hour time period. Reactions took place in 35 mL centrifuge tubes with volume ratios of 3:3:9 (v/v/v) acetic acid : 50% hydrogen peroxide : DI water with a total volume of 15 mL in each reaction vessel. Controls were also implemented for each of the reagents separately.
Previous work done on PAHs found a correlation between the presence of PAA in solution and the degradation of PAHs undergoing the peroxy-acid process. A study was conducted to investigate the effects of varying amounts of hydrogen peroxide, acetic acid and an acid catalyst, sulfuric acid, would have on PAA concentrations in solution. Titrations were performed to determine the % amounts of hydrogen peroxide and PAA in solution. It was found that amount of hydrogen peroxide decreased over time while the amount of PAA in solution increased over time. In addition, the addition of the acid catalyst, sulfuric acid, increased significantly the amount of PAA present while decreasing the amount of hydrogen peroxide present in solution.
May 2013
School of Engineering
Dept. of Civil and Environmental Engineering
Rensselaer Polytechnic Institute, Troy, NY
Rensselaer Theses and Dissertations Online Collection
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