Showing papers on "Phenol published in 2001"

TIO2-photocatalyzed degradation of phenol and ortho-substituted phenolic compounds

Abstract: The photocatalytic degradation of phenol, guaiacol, 2-chlorophenol and catechol in aqueous suspensions of TiO 2 under different experimental conditions has been investigated. The photodegradation of the different organics follows a Langmuir–Hinshelwood kinetics, showing rate constants that decrease in the order: guaiacol>2-chlorophenol≅phenol>catechol. A similar trend is also observed, except for catechol, for the stability of the σ-complexes that may be formed between the aromatic ring and the OH radical. From different analytical techniques (HPLC, GC/MS and HPLC/MS), various hydroxylated intermediate compounds have been reported and different mechanisms of degradation of the starting compounds have been proposed. From experiments performed using aqueous solutions containing the four organics, it is observed that the competitive Langmuir–Hinshelwood kinetics for the degradation of each one of the phenolic compounds is obeyed.

Partial degradation of phenol by advanced electrochemical oxidation process.

Abstract: The partial electrocatalytic degradation of phenol to organic acids has been investigated using an undivided electrolytic reactor with a beta-PbO2 anode containing fluorine resin. It was found that the decrease of benzoquinone (BQ) formed during phenol degradation and the acceleration of the process from phenol to organic acids are possible under an optimized operating condition. A possible pathway for phenol degradation was proposed, and a mathematical model for phenol and BQ evolution was developed. Operating parameters such as initial pH, current density, and temperature of the reaction were found to greatly impact the degradation rate of the phenol and even the pathway. Higher removal rate of phenol and BQ can be achieved at an appropriate temperature and higher current density in acidic medium preferably at pH 4. Under these conditions, phenol would be more likely degraded in the pathway from phenol to organic acids rather than through the BQ. When phenol is completely removed, the toxicity of the wastewater would be lessened suitable for biological process treatment. Accounting for the decrease of instantaneous current efficiency (ICE) during degradation, partial degradation would be highly economical for wastewater treatment, which would be an alternative process in practical application.

Ferrate(VI) Oxidation of Aqueous Phenol: Kinetics and Mechanism

Abstract: Kinetic and thermodynamic parameters for ferrate(VI) oxidation of phenol have been measured in isotopic solvents, H2O and D2O, using ambient and high-pressure stopped-flow UV−visible spectroscopy. An increase (fast stage) and then a decrease (slow stage) in absorbance at 400 nm are observed when potassium ferrate (K2FeO4) and aqueous phenol solutions are mixed rapidly. This suggests that small amounts of unstable intermediate 4,4‘-biphenoquinone are produced during this redox process. An electron paramagnetic resonance signal for the reaction mixture of ferrate and phenol trapped by spin-trap α-(4-pyridyl-1-oxide)-N-tert-butylnitrone indicates a radical reaction pathway. Gas chromatographic/mass spectrometric measurements show p-benzoquinone is a major organic product, and the red ferric thiocyanate complex formed from addition of potassium thiocyanate to the spent reaction solution indicates that Fe(VI) is reduced to Fe(III). Activation enthalpy, entropy, and volume changes have been determined. There is...

Liquid-phase oxidation of benzene to phenol by CuO–Al2O3 catalysts prepared by co-precipitation method

Abstract: The liquid-phase catalytic oxidation of benzene to directly produce phenol was attempted under mild reaction conditions using supported Cu catalysts in aqueous acetic acid solvent. Gaseous oxygen and ascorbic acid were used as an oxidant and a reductant, respectively. Among the supported Cu catalysts studied, the Cu catalysts prepared by the impregnation method, irrespective of the oxide supports, the Cu species were considerably leached during the benzene oxidation. A supported Cu catalyst (CuO–Al 2 O 3 ) prepared by co-precipitation of Cu(NO 3 ) 2 ·3H 2 O and Al(NO 3 ) 3 ·9H 2 O inhibited the leaching of Cu species in comparison with the Cu catalysts supported by the impregnation method on Al 2 O 3 , SiO 2 , MCM-41, etc. The influences of the amount of supported Cu, the partial pressure of O 2 , the amount of ascorbic acid, the concentration of acetic acid in the solvent, and the reaction temperature on the phenol yield were investigated using the CuO–Al 2 O 3 catalyst. The aqueous solvent including high concentration of acetic acid (around 80 vol.%) dramatically inhibited the leaching of Cu species in the CuO–Al 2 O 3 catalyst. H 2 O 2 , which is considered to play an important role in phenol formation, was detected during the benzene oxidation catalyzed by CuO–Al 2 O 3 .

Gas-phase reaction of phenol with NO3

Abstract: The fast gas-phase reaction of NO3 radicals with phenol was found to yield 2-nitrophenol as the only relevant nitration product. The yield of this product was high and independent of the concentration of NO2 at the concentrations applied. In the presence of ozone, also significant amounts of 4-nitrophenol and p-benzoquinone were formed. The rate constant of the reaction between NO3 radicals and phenol was determined to be 5.8 x 10(-12) cm3 molecule-1 s-1. The selective formation of 2-nitrophenol (2) is suggested to derive from either the concerted keto-enol tautomerism in the reaction of a phenoxy radical with NO2 or the concerted elimination of nitric acid from a cyclohexa-3,5-diene intermediate.

Oxidation of several chlorophenolic derivatives by UV irradiation and hydroxyl radicals

Abstract: The oxidation of some chlorophenols: 4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, tetrachlorocatechol (3,4,5,6-tetrachloro-2-hydroxy phenol) and 4-chloroguaiacol (4-chloro-2-methoxy phenol) has been studied via single photodecomposition produced by polychromatic UV irradiation, oxidation by hydroxyl radicals generated by Fenton's reagent (hydrogen peroxide plus ferrous ions), and degradation by hydroxyl radicals produced by combinations of UV irradiation plus hydrogen peroxide, and UV irradiation plus hydrogen peroxide and ferrous ions (photo-Fenton system). These organics have been selected as models of chloro-phenolic derivative pollutants present in wastewaters and groundwaters. The degradation levels obtained in each process are reported. The quantum yields in the single photodecomposition reaction and the rate constants between the chlorophenols and the hydroxyl radicals in the reaction with Fenton's reagent are determined. Finally, the additional contributions to the photodecomposition promoted by the radical reaction in the combined UV/H2O2 and photo-Fenton systems are also evaluated. © 2001 Society of Chemical Industry

Anaerobic degradation of aromatic compounds coupled to Fe(III) reduction by Ferroglobus placidus.

Abstract: Aromatic compounds are an important component of the organic matter in some of the anaerobic environments that hyperthermophilic microorganisms inhabit, but the potential for hyperthermophilic microorganisms to metabolize aromatic compounds has not been described previously. In this study, aromatic metabolism was investigated in the hyperthermophile Ferroglobus placidus. F. placidus grew at 85 degrees C in anaerobic medium with a variety of aromatic compounds as the sole electron donor and poorly crystalline Fe(III) oxide as the electron acceptor. Growth coincided with Fe(III) reduction. Aromatic compounds supporting growth included benzoate, phenol, 4-hydroxybenzoate, benzaldehyde, p-hydroxybenzaldehyde and t-cinnamic acid (3-phenyl-2-propenoic acid). These aromatic compounds did not support growth when nitrate was provided as the electron acceptor, even though nitrate supports the growth of this organism with Fe(II) or H2 as the electron donor. The stoichiometry of benzoate and phenol uptake and Fe(III) reduction indicated that F. placidus completely oxidized these aromatic compounds to carbon dioxide, with Fe(III) serving as the sole electron acceptor. This is the first example of an Archaea that can anaerobically oxidize an aromatic compound. These results also demonstrate for the first time that hyperthermophilic microorganisms can anaerobically oxidize aromatic compounds and suggest that hyperthermophiles may metabolize aromatic compounds in hot environments such as the deep hot subsurface and in marine and terrestrial hydrothermal zones in which Fe(III) is available as an electron acceptor.

Liquefaction Mechanism of β-O-4 Lignin Model Compound in the Presence of Phenol under Acid Catalysis. Part 1. Identification of the Reaction Products

Abstract: Guaiacylglycerol-β--guaiacyl ether (GG) was used as a lignin model compound to study the liquefaction reaction mechanism of lignin in the presence of phenol under the catalysis of several typical acids such as sulfuric, phosphoric and oxalic acids. The reaction products were isolated by silicagel column chromatography and high performance liquid chromatography (HPLC). The structures of the obtained compounds were identified by means of GC-MS, 1 H-NMR, 13 C-NMR, 1 H- 1 H COSY, HMBC and HMQC. As a result, about 30 compounds were obtained as the main reaction products. It was found that their structural characteristics were significantly different from those yielded at the non-catalyzed liquefaction (Lin et al. 1997a), and independent on the acid species. The dominant products were guaiacylglycerol-α-phenyl-β-guaiacyl ethers, followed by guaiacol, triphenylethanes, diphenylmethanes, benzocyclobutanes and phenylcoumarans. The structural characteristics and yields of these main reaction products indicated that condensation between phenol and GG in its C-u and further cleavages in both the β-O-4 linkage and C β -C γ bonding could be the dominant reaction pathways.

Enzymatic modification of kraft lignin through oxidative coupling with water-soluble phenols.

Abstract: The aromatic polymer lignin can be modified through promotion of oxidative coupling between phenolic groups on lignin and various phenols. The reaction is initiated by an oxidation of both components, e.g., by using the oxidoreductases laccase or peroxidase. Coupling between phenolic monomers and lignin has previously been studied by the use of radio-labeled phenols. In this study, incorporation of water-soluble phenols into kraft lignin, using laccase as catalyst, was investigated. Several phenols with carboxylic or sulfonic acid groups were used as markers for the incorporation. The modified lignin was isolated and the amount of phenol incorporated was characterized by means of titration, quantitative 1H-NMR, and quantitative 31P-NMR after modification with 2-chloro-4,4,5,5-tetramethyl-1,2,3-dioxaphospholane. Only a few of the phenols studied were found to be incorporated into lignin. When the phenol guaiacol sulfonate was incorporated into kraft lignin, the lignin became water-soluble at pH 2.4 and a low ionic strength due to the introduction of sulfonic acid groups. The content of sulfonic acid groups in the product was 0.5–0.6 mmol/g lignin. A lower amount of 4-hydroxyphenylacetic acid was incorporated under similar conditions.

Process for producing bisphenol A

Abstract: There is disclosed a process for producing bisphenol A by subjecting phenol and acetone to condensation reaction in the presence of a catalyst composed of an acid type ion exchange resin which is modified in part with a sulfur-containing amine compound, wherein the ion exchange resin having a modification rate of 10 to less than 20 mol % is used for a methanol concentration in acetone of lower than 250 ppm by weight, and the ion exchange resin having a modification rate of 20 to 65 mol % is used for a methanol concentration in acetone of 250 to 8000 ppm by weight. The above process is capable of producing bisphenol A at high conversion and selectivity by suppressing deterioration of catalytic activity due to methanol as an impurity in acetone.

Characterization and activity of Fe-ZSM-5 catalysts for the total oxidation of phenol in aqueous solutions

Abstract: Fe-ZSM-5 zeolites with of Si/Fe ratios varying from 40 to 200 were synthesized and characterized by IR, XRD, SEM, ESR and ion-exchange techniques. From the obtained results, it is possible to conclude that, these zeolites have a good crystallinity and that the incorporation of Fe 3+ ions into the MFI-structure depends on the Si/Fe ratios in the gel: the higher the Si/Fe ratio, the more the percentage of Fe 3+ ions is incorporated into the MFI lattice. Catalytic properties of Fe-ZSM-5 were studied in the oxidation of phenol. The reaction was performed in a static system, at the atmospheric pressure, 343 K, and with H 2 O 2 concentration, which exceeds stoichiometric concentration for complete oxidation of phenol to carbon dioxide and water. From the catalytic results, it can be concluded that framework Fe can catalyze more completely phenol oxidation than the extra-framework Fe does.

Phenol hydrogenation over palladium supported on magnesia: Relationship between catalyst structure and performance

Abstract: A series of magnesia-supported palladium catalysts (Pd loading in the range 0.5–7.0 wt.%) has been prepared by impregnation from aqueous solutions of PdCl2 , Pd(NH3)4Cl2 and Pd(CH3COO)2 and characterised by X-ray diffraction (XRD), CO chemisorption and high resolution transmission electron microscopy (HRTEM). The gas-phase hydrogenation of phenol was employed as a model reaction to probe the dependence of catalytic activity/selectivity on changes in Pd particle size and surface acid–base properties. The catalyst prepared from the acetate precursor exhibited the greatest Pd dispersion when compared with the chloride and amine precursors. The surface mobility of the metal chloride resulted in larger Pd particles from the Cl-containing precursors while the presence of residual Cl in the activated catalysts lowered the hydrogenation rate and was responsible for a decline in activity with time-on-stream. The effects of varying such process variables as temperature, hydrogen/phenol mol ratio and inlet molar phenol feed rate are presented and discussed while the question of structure sensitivity is addressed. The reaction exhibited a negative dependence on phenol partial pressure up to 503 K but a positive dependence was evident at higher temperatures. The order of the reaction with respect to hydrogen remained positive and was close to unity at 563 K; an apparent activation energy of 63 kJ mol−1 was recorded. The effect of doping the support with calcium and fluoride has shown that modifications to the acid–base properties of magnesia can be used to control catalytic activity/selectivity.

A novel catalyst of copper hydroxyphosphate with high activity in wet oxidation of aromatics

Abstract: A novel catalyst of copper hydroxyphosphate (Cu2(OH)PO4) that has neither microporous nor mesoporous pores was successfully synthesized by a hydrothermal method. Catalytic data in the hydroxylation of phenol, benzene and naphthol by hydrogen peroxide showed that copper hydroxyphosphate is a very active catalyst. Comparison of various catalysts on phenol hydroxylation suggests that the unusual catalytic activity on the Cu2(OH)PO4 catalyst may be dependent on the unique structure of as-synthesized Cu2(OH)PO4. Characterization of catalytic phenol hydroxylation over Cu2(OH)PO4 catalyst by electron spin resonance (ESR) gives very strong signals assigned to hydroxyl radical (•OH) species, the intensities of which are linearly related to the catalytic conversion, suggesting that hydroxyl radicals are important intermediates in the catalysis.

Enzyme-catalyzed removal of phenol from refinery wastewater: feasibility studies.

Abstract: Phenols are present in petroleum refining wastewater. An enzymatic method for removing phenols from industrial aqueous effluent has been developed in the past several years. In this method, a peroxidase enzyme catalyzes the oxidation of phenol by hydrogen peroxide generation of phenoxyl radicals. These radicals diffuse from the active center of the enzyme into solution and react nonenzymatically to eventually form higher oligomers and polymers, which can be removed from wastewater by conventional coagulation and sedimentation or filtration. In this study, Arthromyces ramosus peroxidase (ARP) was applied to treat a petroleum refining wastewater containing 2 mM (188 mg/L) phenol in a batch and continuous-flow system. The latter consisted of a plug-flow reactor (PFR) where the reaction took place between phenol and hydrogen peroxide catalyzed by the enzyme in the presence of polyethylene glycol (PEG). A flocculation tank followed the PFR where alum and sodium hydroxide were added and then the polymers formed were settled in a sedimentation tank and removed from the system. Most (95 to 99%) of the phenol was removed by the same dose of ARP required for the treatment of synthetic wastewater containing an equal amount of phenol. Polyethylene glycol, as an additive, reduced enzyme inactivation and consequently reduced the enzyme dose and the cost of the treatment process. Step feeding of hydrogen peroxide was not effective in reducing the enzyme requirement. A significant removal of chemical oxygen demand was achieved when using PEG to reduce the enzyme dose.

Method for producing aromatic alcohols, especially phenol

Abstract: The invention relates to a method for the production of phenol derivatives by performing catalytic oxidation of an aromatic hydrocarbon to obtain a hydroperoxide and subsequently cleaving the hydroperoxide into a phenol derivative and a ketone in the presence of a radical starter, wherein a compound of formula (I) is used as oxidation catalyst, wherein R1, R2 = H, an aliphatic or aromatic alkoxy radical, a carboxyl radical, an alkoxycarbonyl radical or a hydrocarbon radical, with 1 to 20 carbon atoms, SO?3?H, NH2, OH, F, Cl, Br, I and/or NO2, wherein R?1 and R2? represent identical or different radicals or R?1 and R2? may be linked to one another by a covalent bond, wherein X, Z = C, S, CH?2;? Y = O, OH; k = 0, 1, 2; l = 0, 1, 2 and m = 1 to 3; wherein the molar ratio between the catalyst and the aromatic hydrocarbon is less than 10 mol %.