Oxidation Of Pentachlorophenol Research Articles

A Kinetic Study on Oxidation of Pentachlorophenol by Ozone

ABSTRACT The kinetics of pentachlorophenol (PCP) ozonation in terms of the gaseous O3 and dissolved PCP concentrations has been investigated. When the O3 concentration in the gas phase was in the range of 10 to 40 g O3/m3, the O3 dissolved for a short time period was proportional to the gaseous O3 concentration. In this range, the ozonation reaction was first order for each reactant and the overall reaction was second order. At 25 °C, in an aqueous solution, the reaction rate constant was estimated to be 10.048 L/mol-sec. The reaction rate was much greater than the mass-transfer rate, indicating that the reaction of O3 and PCP was an interface reaction on the surface of gaseous O3 bubbles. The final product of the PCP ozonation was oxalic acid, with the carbon yield of the reaction being 59.4%. The ozonation of PCP in the aqueous solution was not a radical reaction but a direct reaction between O3 and PCP molecules under the conditions investigated in this study, since O3 has a high selectivity toward PCP. The reaction rate increased with the reaction temperature up to 35 °C but decreased at temperatures greater than 35 °C due to the decreased solubility of O3. The addition of H2O2 did not increase the reaction rate significantly.

The Anodic Electrochemistry of Pentachlorophenol

The aqueous‐phase electrochemical oxidation of pentachlorophenol (PCP) was studied. The oxidation was carried out at pyrolytic carbon, glassy carbon, gold, and platinum anodes in pH 6‐7 solutions with phosphate and in some cases acetate electrolyte. The potential range studied was from the onset of PCP oxidation to the onset of oxygen evolution. For most of the potential range the reaction was a one‐electron oxidation resulting in 2,3,4,5,6‐pentachloro‐4‐pentachlorophenoxy‐2,5‐cyclohexadienone. The product is essentially insoluble and precipitated on the electrode surface. Various thicknesses, crystallinities, and patterns of deposit were observed to form, giving rise to different current‐time or potential‐time responses depending on factors including electrode material, current density, electrolyte, PCP concentration, and reaction time. At very low overpotentials the reaction product became complex and the reaction took place with less than one electron per molecule and with the appearance of some chloride. Under these conditions the reaction is felt to be an electrochemically initiated, chain reaction polymerization. This involves the electrochemical formation of a radical which attacks the pentachlorophenoxalate substrate, forming a radical anion intermediate. This intermediate decomposes, yielding a chloride ion and reforming a neutral radical (though now of higher molecular weight), thus continuing the reaction. The application of such electrochemically initiated condensation reactions for removal of PCP and some other phenols from wastewater is discussed. © 1999 The Electrochemical Society. All rights reserved.

Microbially Driven Fenton Reaction for Transformation of Pentachlorophenol

A microbially driven transformation system was developed for the oxidative degradation of pentachlorophenol (PCP). The system was based on a free radical-generating Fenton reaction between bacterially produced Fe(II) and H{sub 2}O{sub 2}. The Fe(III)-reducing, facultative anaerobe Shewanella putrefaciens strain 200 was used as a catalyst for both Fe(III) reduction and H{sub 2}O{sub 2} production by alternating between anaerobic and aerobic conditions in liquid batch cultures supplemented with Fe(III). The highest observed PCP degradation rate was approximately 0.31 {micro}M h{sup {minus}1}. Tetrachlorohydroquinone (TCHQ) and tetrachlorocatechol (TCC) were formed as the principal PCP transformation products, indicating that PCP oxidation proceeded via hydroxyl radical ({sup {sm_bullet}}OH) attack on the ortho and para positions of the aromatic ring. PCP was degraded, and TCHQ and TCC were produced in a chemically driven (biomimetic) system where H{sub 2}O{sub 2} and Fe(II) were supplied at concentrations comparable to those detected in the microbially driven system. PCP was not degraded (and PCP transformation products were not produced) in a set of control experiments that included (1) the presence of Fe(II)-chelating agents or radical scavenging compounds, (2) strict aerobic or anaerobic conditions, (3) the substitution of NO{sub 3}{sup {minus}} for Fe(III) as anaerobic electron acceptor, and (4) the omissionmore » of S. putrefaciens. The microbially driven Fenton reaction system operated at neutral pH and required neither addition of exogenous H{sub 2}O{sub 2} nor UV irradiation to regenerate Fe(II). The newly developed system may provide the basis for novel Fenton-type bioremediation strategies.« less

Primary Product of the Horseradish Peroxidase-Catalyzed Oxidation of Pentachlorophenol

Peroxidases are a class of enzymes that catalyze the oxidation of various phenolic substrates by hydrogen peroxide. They are common enzymes in soil and are also available commercially, so that they have been proposed as agents of phenolic pollutant transformation both in the environment and in engineered systems. Previous research on the peroxidase-catalyzed oxidation of pentachlorophenol (PCP) has suggested that tetrachloro-p-benzoquinone (chloranil) is the principal product and that a considerable fraction of the PCP added to reaction mixtures appears to be resistant to oxidation. In experiments employing alternative methods of product separation and analysis, the authors found that both of these observations are artifacts of extraction and analytical methods used in previous studies. The major product of the horseradish peroxidase-catalyzed oxidation of pentachlorophenol from pH 4--7 was 2,3,4,5,6-pentachloro-4-pentachlorophenoxy-2,5-cyclohexadienone (PPCHD), which is formed by the coupling of two pentachlorophenoxyl radicals.

Steady-state oxidation model by horseradish peroxidase for the estimation of the non-inactivation zone in the enzymatic removal of pentachlorophenol

A theoretical model for the rate of oxidation of pentachlorophenol (PCP) catalyzed by horseradish peroxidase (HRP), was investigated to account for the influence of hydrogen peroxide (H 2O 2) concentration on the catalytic activity. To evaluate the maximum allowable H 2O 2 concentration, a relatively simple steady-state model was developed based on the Ping-Pong Bi-Bi mechanism considering the effect of excess H 2O 2. Several sets of experimental data obtained from batch reactions using an equimolar concentration of H 2O 2 and PCP were used to estimate the kinetic parameters by a nonlinear regression method. The model profiles acquired using the estimated parameters were in good agreement with experimental data at different initial enzyme and substrate concentrations. The best-fitted parameters were used to predict the initial rate of the enzyme reaction. The model prediction was coincident with the experimental results of other studies, indicating that the proposed model could be used for the optimization of reaction conditions. The maximum allowable H 2O 2 concentration to prevent H 2O 2 inhibition was calculated from the proposed model equation: [H 2O 2] 0,max = K m H 2O 2 K i [ PCP] 0 K m PCP +[ PCP] 0 . Using this equation, a curve depicting the non-inactivation zone for the two substrates (hydrogen peroxide and PCP) was plotted and it could be used for experimental design and optimal process operation. To minimize enzyme inactivation by H 2O 2, it was determined that the concentration of H 2O 2 should be lower than 2.78 mM, regardless of the stoichiometric ratio.

Fenton-Like Soil Remediation Catalyzed by Naturally Occurring Iron Minerals

The ability of the iron minerals hematite and magnetite to catalyze the decomposition of hydrogen peroxide (H2O2) and initiate the Fenton-like oxidation of pentachlorophenol (PCP) was investigated in batch, bench-scale systems in which PCP was spiked onto silica sand. Pentachlorophenol degradation was documented in silica sand–mineral–H2O2 systems by the release of chloride and the loss of total organic carbon. The most efficient oxidation stoichiometry was the magnetite-catalyzed reaction over the first 8 h with 490 mol H2O2 consumed/mol PCP degraded. After 8 h, the peroxide efficiency decreased significantly; amorphous iron hydroxide formation on the magnetite surface may have catalyzed the decomposition of H2O2 to oxygen species other than hydroxyl radicals. Mineral-catalyzed Fenton-like treatment in two natural soils was demonstrated after spiking the soils with PCP; the contaminant was degraded with no iron addition. The oxidation stoichiometry in the two soils was 1,100 and 2,930 mol H2O2 consumed/mol PCP degraded. Key words: Advanced oxidation processes; Fenton's reagent; hydrogen peroxide; iron oxyhydroxides; pentachlorophenol; soil remediation

Rapid Analytical Methods To Measure Pentachlorophenol in Wood

Pentachlorophenol (PCP) was measured in wood following extraction with methanol:0.1% acetic acid. The extract was derivatized with acetic anhydride in a biphasic solvent containing toluene and 0.1 M Na2CO3 (pH 11.4), and pentachlorophenyl acetate was quantitated by gas chromatography−mass spectrometry (GC−MS) using [13C6]PCP as an internal standard. A second detection method employed thin layer chromatography (TLC) after nitric acid-mediated oxidation of PCP to tetrachloro-1,4-benzoquinone. The third method was by colorimetry and required a liquid−liquid partitioning of PCP under acidic and alkaline pH against toluene. Then, PCP was coupled to 4-aminoantipyrine in the presence of sodium persulfate to form a dye which was measured at 580 nm. The limit of detection approached 50 ppb by GC−MS and 1 ppm by TLC when 100 mg of wood was used for analysis and 1 ppm for the colorimetric method when 1 g of wood was used for detection. The estimates of PCP were comparable for all three methods. Keywords: Chlorophenols; pentachlorophenol; contamination; off-flavor; rapid detection; wood

Oxidative Degradation of Polychlorinated Phenols Catalyzed by Metallosulfophthalocyanines

Abstract2,4,6‐trichlorophenol (TCP) is oxidized by potassium monopersulfate or hydrogen peroxide in the presence of iron or manganese tetrasulfonatophthalocyanines (FePcS or MnPcS) to yield not only the corresponding 2,6‐dichloro‐1,4‐benzoquinone but also ring‐cleavage products. Catalytic oxidation of the TCP ring by hydrogen peroxide is more efficient than by potassium monopersulfate, despite a slower substrate conversion, suggesting that different mechanisms are involved for these two catalytic systems: a metal‐oxo mechanism for FePcS/KHSO5 and a metal‐peroxo mechanism for FePcS/H2O2. Eight different final oxidation products and four quinone intermediates have been identified in the oxidation of TCP by the FePcS/H2O2 catalytic system. Chloromaleic acid is the main product of the oxidative ring cleavage. An iron‐peroxo complex PcS‐FeOOH is probably the active species responsible for the epoxidation of 2,6‐dichloro‐1,4‐benzoquinone and the C–C bond cleavage of 3,5‐dichloro‐2‐hydroxy‐1,4‐benzoquinone ring, both intermediates generated during the catalytic TCP degradation. The oxidation of pentachlorophenol (PCP) is also catalyzed by FePcS or MnPcS with KHSO5 or H2O2.

Two-phase ozonation of hazardous organics in single and multicomponent systems

The destruction of pentachlorophenol (PCP), oxalic acid, chlorendic acid, and a mixture of pentachlorophenol, 1,3-dichlorobenzene (DCB), and trichloroethylene (TCE) were studied using a two-phase ozonation system. A two-phase ozonation system consists of water containing the pollutant and a second solvent phase which houses the ozone. The solvent phase is an inert fluorinated hydrocarbon (FC40) that is nonpolar and reusable. The solvent phase is desirable because it has a high ozone stability ( k = 0.0033 min −1) and an ozone solubility of 120 mg/L at 25°C, 10 times that of water. In addition to an enhanced oxidation rate of PCP, less ozone was utilized. At high pH (10.3), a first-order rate constant of 200 min −1 in the two-phase system was found for PCP degradation compared to k app = 0.154 min −1 in a single aqueous-phase system. Within 15 s, the concentration of PCP (100 mg/L initially) was degraded more than 90%, and 100% dechlorination was obtained with longer reaction times. This system also demonstrated the ability to selectively oxidize PCP while in the presence of free radical scavengers existing in the water phase. PCP was also successfully oxidized using actual wastwater which contained alkalinity, hardness, many inorganics, and trace hazardous organics. Oxalic acid, an intermediate formed during the degradation of PCP, was also degraded by two-phase ozonation. Preliminary work with chlorendic acid showed that two-phase ozonation was faster than single aqueous-phase ozonation at dechlorinating the compound. TCE and DCB degraded slightly faster when PCP was added to the mxture, possibly due to the production of other radicals during the oxidation of PCP.

Veratryl Alcohol-Mediated Indirect Oxidation of Pentachlorophenol by Lignin Peroxidase

The oxidation of pentachlorophenol (PCP) by lignin peroxidase (LiP) is characterized by a rapid loss of activity during which time the enzyme is quickly converted to compound III, an inactive form of the enzyme. We investigated the indirect oxidation of PCP by LiP using veratryl alcohol (VA) as a mediator. The oxidation of VA to veratryl aldehyde by LiP was inhibited by PCP. Inhibition was characterized by lag period followed by the same rate of VA oxidation. The lag period before VA oxidation was increased by increasing concentrations of PCP. During the lag period, PCP was oxidized and the extent of PCP oxidation increased with increasing concentrations of VA. The enzyme stayed as compound II during PCP oxidation in the presence of VA, suggesting that VA has a protective role in the LiP catalysis. The kinetics of PCP oxidation in the presence of VA were similar to those of VA oxidation. All these results suggest that PCP is oxidized indirectly via the veratryl alcohol cation radical. 2,3,5,6-Tetrachloro- p-benzoquinone was a stoichiometric product during PCP oxidation in both the presence and the absence of VA. An equivalent amount of inorganic chloride was formed by oxidative 4-dechlorination during PCP oxidation in the presence of VA. The increase in the rate and extent of PCP oxidation by VA results from mediation of PCP oxidation and reversion of inactive compound III to native enzyme, both by the veratryl alcohol cation radical.

Destructive Oxidation of Chlorophenols

The destructive oxidation of pentachlorophenol in alkaline aqueous solution has been attempted with tetraoxoruthenium species as catalysts and hypochlorite as the terminal oxidant. The product solution contained no pentachlorophenol. Only traces of chlorinated compounds which could be extracted with dichloromethane were present. Measurements of the quantity of base and of hypochlorite added to the reaction mixture indicated that the oxidation did not proceed to completely to carbonate, but rather to unidentified compounds with an average carbon oxidation state of about three. Oxidation with peroxodisulfate indicated that only two-thirds of the chlorine was present as ionic chloride in the product solution. In contrast, oxidation with permanganate, in the absence of ruthenium, led to the complete oxidation of pentachlorophenol and to release of all of the chlorine as ionic chloride. Qualitative rate measurements were made with the pH-stat technique. Some experiments were also conducted with 2,4,6-trichlorophenol, p- chlorophenol and phenol. Attempts to oxidize both phenol and pentachlorophenol at various ruthenium-containing electrodes in either basic or acidic solutions were unsuccessful.

Photocatalytic degradation of pentachlorophenol on titanium dioxide particles: identification of intermediates and mechanism of reaction

The photoassisted oxidation of pentachlorophenol (PCP) in TiO_2 particle suspensions was investigated. Complete dechlorination of 47 µM PCP was achieved after 3 h of illumination at high intensity with apparent quantum efficiencies (ΦPCP, ΦCI, ΦH+, ΦH_2O_2) ranging from 1 to 3%. p-Chloranil, tetrachlorohydroquinone, H_2O_2, and o-chloranil were formed as the principal intermediates. Formate and acetate were formed as products during the latter stages of photooxidation. The mechanism for photooxidation of PCP proceeds via hydroxyl radical attack on the para position of the PCP ring to form a semiquinone radical which in turn disproportionates to yield p-chloranil and tetrachlorohydroquinone. Under high-intensity illumination, the reaction intermediates are attacked further by •OH to yield HCO_2^-, CH_3CO_2^-, CO_2, H^+, and Cl^-.

Biodegradation of pentachlorophenol by the white rot fungus Phanerochaete chrysosporium.

Extensive biodegradation of pentachlorophenol (PCP) by the white rot fungus Phanerochaete chrysosporium was demonstrated by the disappearance and mineralization of [14C]PCP in nutrient nitrogen-limited culture. Mass balance analyses demonstrated the formation of water-soluble metabolites of [14C]PCP during degradation. Involvement of the lignin-degrading system of this fungus was suggested by the fact the time of onset, time course, and eventual decline in the rate of PCP mineralization were similar to those observed for [14C]lignin degradation. Also, a purified ligninase was shown to be able to catalyze the initial oxidation of PCP. Although biodegradation of PCP was decreased in nutrient nitrogen-sufficient (i.e., nonligninolytic) cultures of P. chrysosporium, substantial biodegradation of PCP did occur, suggesting that in addition to the lignin-degrading system, another degradation system may also be responsible for some of the PCP degradation observed. Toxicity studies showed that PCP concentrations above 4 mg/liter (15 microM) prevented growth when fungal cultures were initiated by inoculation with spores. The lethal effects of PCP could, however, be circumvented by allowing the fungus to establish a mycelial mat before adding PCP. With this procedure, the fungus was able to grow and mineralize [14C]PCP at concentrations as high as 500 mg/liter (1.9 mM).

Voltammetric determination of pentachlorophenol at a glassy carbon electrode.

An electroanalytical study of the pentachlorophenol oxidation process at a glassy carbon electrode in aqueous solution using different voltammetric techniques has been carried out. The results obtained by differential-pulse voltammetry allowed a method to be developed for the determination of pentachlorophenol in the ranges 1.0 × 10–5–10.0 × 10–5 and 2.0 × 10–6–10.0 × 10–6 mol l–1, using ΔE= 50 mV. The coefficient of variation is 2.3% for a concentration of 5.0 × 10–5, mol l–1, with a limit of determination of 1.5 × 10–6 mol l–1 and a limit of detection of 4.5 × 10–7 mol l–1. The effect of other chlorophenols has been studied. Good results were obtained by applying the proposed differential-pulse voltammetric method to the determination of pentachlorophenol in a commercial fungicide.

The microsomal metabolism of hexachlorobenzene: Origin of the covalent binding to protein

The musomal metabolism of hexachlorobenzene is studied, with special attention to the covalent binding to protein. The metabolites formed are pentachlorophenol and tetrachlorohy-droquinone. In addition, a considerable amount of covalent binding to protein is detected (250 pmoles pentachlorophenol, 17 pmoles tetrachlorohydroquinone and 11 pmoles covalent binding in an incubation containing 50 μmoles of hexachlorobenzene). In order to establish the potential role of reductive dechlorination in the covalent binding, the anaerobic metabolism of hexachlorobenzene was investigated. At low oxygen concentrations no pentachlorobenzene was detected, and only very small amounts of pentachlorophenol as well as covalent binding, indicating a relationship between covalent binding and the musomal oxidation of hexachlorobenzene. Incubations with 14C-pentachlorophenol at low concentrations showed that a conversion-dependent covalent binding occurs to the extent of 75 pmole binding per nmole pentachlorophenol. This is almost enough to account for the amount of label bound to protein observed in hexachlorobenzene incubations. This indicates that less than 10% of the covalent binding occurs during conversion of hexachlorobenzene to pentachlorophenol, and the remainder is produced during conversion of pentachlorophenol. The major product of musomal oxidation of pentachlorophenol is tetrachlorohydroquinone, which is in redox-equilibrium with the corresponding semiquinone and quinone (chloranil). The covalent binding is inhibited by addition of ascorbic acid or glutathione to the hexachlorobenze incubations. Ascorbic acid decreases the covalent binding with a simultaneous increase in formation of tetrachlorohydroquinone, probably due to a shift in the redox-equilibrium to the reduced side. Glutathione does not act as a reducing agent, since the inhibition of covalent binding is not accompanied by an increase in tetrachlorohydroquinone formation. Instead, glutathione reacts with chloranil, producing at least three stable products, probably in a Michael-type reaction. These results strongly indicate the involvement of chloranil or the semiquinone radical in the covalent binding during musomal hexachlorobenzene metabolism.