Targeted degradation of polycyclic aromatic hydrocarbons: a potential strategy for coal tar remediation

Al-Shra'ah, Ahmad Qublan (2018) Targeted degradation of polycyclic aromatic hydrocarbons: a potential strategy for coal tar remediation. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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The presence and degradation of coal tar deposits is of a great environmental concern due to the toxicity of many of its components especially polycyclic aromatic hydrocarbons (PAHs) on the health of humans and animals. In this work, the chemical degradation of PAHs in coal tar was investigated by using several approaches: a) chemical reduction using an acidified Mg/EtOH system; b) chemical oxidation using Fenton’s reagent or peroxyacetic acid; c) thermal removal using microwave-assisted heating; and d) PAH bromination. The reductive degradation of anthracene as a model PAH compound using Mg/EtOH in the presence of glacial acetic acid was achieved in which anthracene was converted to 9,10-dihydroanthracene. The reaction was optimized by investigating the effect of Mg concentration, co-solvent, volume of glacial acetic acid, and time on conversion yield. Experimental design methodology was used for optimizing the anthracene reduction conditions and these optimum conditions were then used for PAH reduction in coal tar. The main advantage of this approach is that the hydrogenated PAHs formed are less toxic than the parent compounds. Selective reduction of anthracene and fluoranthene in coal tar was achieved with high conversion (>90%) at room temperature within a short time (0.5 h) as determined by GC/MS and GC/FID. Fenton’s reagent (Fe²⁺ + H₂O₂) was used to convert anthracene to 9,10-anthraquinone. The reaction was optimized by investigating the effect of the concentration of Fe2+, and H2O2, temperature and time on the conversion % of anthracene. In addition, anthracene oxidation using peroxyacetic acid in acetic acid and H2SO4 was also investigated. The reaction conditions were optimized by studying the influence of temperature and time on removal % of anthracene. Experimental design methodology was used for optimizing the anthracene oxidation using Fenton’s reagent or peroxyacetic acid. Fenton’s reagent showed more efficiency in removal of PAHs compared to peroxyacetic acid. Microwave-assisted thermal removal of pyrene and PAHs in coal tar was achieved using both closed and open microwave systems at low temperatures (<300 °C). The effect of microwave absorbers such as biochar, activated carbon, and TiO₂ on pyrene and coal tar was investigated. The volatile and non-volatile fractions from microwave heating were individually collected and dissolved in dichloromethane (DCM) then analyzed by GC-MS and GC-FID. In addition, TGA analysis of coal tar with and without additives (e.g., biochar, activated carbon, and TiO2) was investigated for additive influence. Bromination of pyrene was achieved using hydrobromic acid/H₂O₂ and a binary solvent, diethyl ether and methanol (1:1, v/v), 12 h. The reaction was selective, where 1-bromopyrene was formed with high yield (>95%). This reaction was also used for PAH bromination in the coal tar. The removal percentages of PAHs from coal tar increased with increasing the molar equivalents (0.25–4.00 equiv.) of the brominating reagent (HBr/H₂O₂), but the resulting products could not be ascertained possibly due to side reactions occurring in the coal tar mixture during the bromination reaction.

Item Type: Thesis (Doctoral (PhD))
Item ID: 13174
Additional Information: Includes bibliographical references. -- Restricted until 9/1/2018.
Keywords: Coal tar, PAHs, Fenton oxidation, Magnesium/Ethanol, Microwave heating, PAH bromination
Department(s): Science, Faculty of > Chemistry
Date: February 2018
Date Type: Submission
Library of Congress Subject Heading: Polycyclic aromatic hydrocarbons -- Biodegradation; Coal-tar -- Biodegradation

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