Anodic oxidation of phenol for waste water treatment

The electrochemical oxidation of phenol for waste water treatment applications was investigated on lead dioxide packedbed anodes. Cells were operated in both batch and continuous modes with feed streams up to 1100 mg/l phenol dissolved in aqueous solutions of Na₂SO₄ and H₂SO₄ or NaOH. All the phenol in solution could be readily oxidized but complete total organic carbon (T.O.C.) removal was more difficult. The percent phenol oxidized increased with increasing current density, and decreased as initial phenol concentration, electrolyte flow rate, pH and anode particle size were increased. Results are compared to simple mathematical models.     

Electrocatalytic production of OH radicals and their oxidative addition to benzene

The feasibility of the electrochemical generation of Fenton's reagent is demonstrated and the subsequent reaction of produced OH radical with benzene studied. Under the proposed working conditions, phenol is obtained as the main product, with current yield as high as 60% (on the basis of 3 F/mole of phenol) and with only traces of other higher oxidized compounds. At fixed H₂SO₄ concentration and with suitable [Fe³⁺]/[O₂] ratio, a maximum in current yield is obtained; this yield may presumably be increased if continuous removal of phenol is employed during the electrolysis.     

Alkylation of phenol with tert-butyl alcohol over zirconium incorporated mesoporous molecular sieves with enhanced acidity

Several SO₄^2?/Zr-MCM-41 and SO₄^2?/Zr-MCM-48 solid acid catalysts were prepared by wet impregnation method and were characterized by FT-IR, XRD, NH₃-TPD and N₂ physical adsorption, respectively. The catalytic activities of these catalysts were evaluated in alkylation reaction of phenol and tert-butyl alcohol. Experimental results reveal that the four solid acid catalysts still maintained a typical mesoporous framework. Under comparable condition, the SO₄^2?/Zr-MCM-48-25 catalyst exhibits much high catalytic activity and gives the highest phenol conversion as compared with the other catalysts. A maximum phenol conversion of 91.6% with 81.8% selectivity to 4-tert-butylphenol (4-TBP) was achieved at the reaction temperature of 140 °C.     

Impact of dissolved wastewater constituents on peroxidase‐catalyzed treatment of phenol

The impact of dissolved wastewater constituents on the treatment of synthetic phenol solutions using horseradish peroxidase (HRP) and hydrogen peroxide was investigated under a variety of reaction conditions. The constituents studied included various inorganic salts, organic compounds and heavy metals. Higher H₂O₂ doses were required to treat phenol in the presence of sodium sulfite, thiosulfate and sulfide; however, enhanced levels of phenol conversion were achieved once sufficient H₂O₂ was supplied. Sulfide and cyanide inhibited phenol transformation. The inhibition of sulfide was overcome by supplying sufficient H₂O₂ to oxidize the sulfide to sulfur. However, increasing the H₂O₂ dose was ineffective in attempting to overcome the strong inhibiting effect of cyanide. Among the heavy metal ions tested, only Mn(II) substantially inhibited phenol removal when it was present at a concentration of 1 mmol dm^?3. The presence of inorganic salts including NaCl, CaCl₂, MgCl₂, NH₄Cl and (NH₄)₂SO₄ reduced phenol conversion as compared with the treatment in distilled‐deionized water. This can be attributed to the increased ionic strength of the solution. © 2002 Society of Chemical Industry     

Modification of dry‐spun Suplon polyimide fibers by mixed‐acid oxidation and their effects on the properties of polypropylene‐resin‐based composites

In this study, the effects of mixed‐acid oxidation on the contents of surface elements, morphology, fiber fineness, mechanical properties, mass change rate, chemical structure, and microaggregate structure of dry‐spun Suplon polyimide (PI) fibers were systematically investigated with wet chemical treatment with HNO₃/H₂SO₄. Experiments investigating both the improvement in the O/C ratio of the fiber surface elements and the changes in other performance features were conducted through the functional modification of the fibers. Meanwhile, the causes of specific changes in the mechanical properties of the oxidized PI‐fiber‐reinforced polypropylene‐resin‐based composites were studied and are discussed. The results of this study demonstrate that the treatment of the fibers with HNO₃/H₂SO₄ mixed‐acid oxidation resulted in significant changes in the properties of the fibers; these changes included an uneven surface, increased specific surface area and surface roughness, a locally etched surface, increased surface energy and O/C ratio, an enhanced wettability, an increased fiber fineness, reduced mechanical properties, and a mass gain in the fibers. Although the chemical structures of the fibers treated by oxidized HNO₃/H₂SO₄ were not significantly changed compared to those of the untreated fibers, the microscopic aggregation of the treated fibers changed to some degree, and the ratio of the amorphous regions significantly increased. Taken together, the functional modification of the PI fiber surface was achieved efficiently through the use of a suitable HNO₃/H₂SO₄ oxidation process and with other performance features of the fibers taken into account. This was favorable for the enhancement of the interfacial properties of the polypropylene fibers and the matrix resins, and thus, the modification improved the mechanical properties of the composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44932.     

Ab initio study of the selective alkylation of m-cresol with tert-butanol catalyzed by SO3H-functionalized ionic liquids

Our previous work showed that for catalytic alkylation of m-cresol with tert-butanol (TBA) SO₃H-functionalized ionic liquids exhibited several characteristic advantages over conventional catalysts. This work investigated the reaction mechanism of the alkylation of m-cresol with tert-butanol catalyzed by the SO₃H-functionalized ionic liquid (IL) through quantum chemical calculation in combination with the experimental studies. The experimental results showed that 2-tert-butyl-5-methyl phenol (2-TBC), 4-tert-butyl-3-methyl phenol (4-TBC) and tert-butyl-m-cresol ether (TBMCE) products were all primary products, while 2,6-di-tert-butyl-3-methyl phenol (2,6-DTBC) was a secondary product. The calculation results indicated that the selectivities of the products depended on the fundamental natures of the reactive sites, including the orbital overlap, the Coulomb and the steric effect in the interaction between the tert-butyl ion ([t-C₄H₉]⁺) and the m-cresol; the TBMCE was dynamically favored but not thermodynamically stable, while the C-alkylated products, especially 2-TBC, were the thermodynamically preferred products; the IL played an important role in generating the [t-C₄H₉]⁺ from the TBA and the final products from the intermediates.     

Crosslinked phenol-formaldehyde sulphonates as cation exchangers

The suspension polycondensation of phenol sulphonic acid and its homologues with formaldehyde, to produce a satisfactory cation exchanger in the bead form in the presence of sulphuric acid catalyst, was investigated. The various reaction conditions for bead formation, using an organic liquid suspending medium in the presence of a suspension stabiliser, such as the nature and quantity of the suspension stabilisers, the quantity of water added, the nature and quantity of the organic suspending medium and the rate of mixing, were studied. o-Dichlorobenzene was the best organic suspending liquid and a chemically peptised colloidal kaolin suspension was a good suspension stabiliser in the presence of a wetting agent. The optimum reaction conditions were given. The best exchangers were obtained in good yields using a molar ratio of phenol: HCHO:H₂SO₄ of 1·0:2·5:1·5 or a mixture of equimolecular amounts of phenol and resorcinol in a molar ratio of mixed phenols: HCHO: H₂SO₄ of 1·0:1·0:1·5. The efficiency of all the products obtained was measured by determination of their total exchange capacity.     

Deactivation and regeneration of Pt anodes for the electro-oxidation of phenol

Electro-oxidation tests with different electrolytes (Na₂SO₄, NaCl, H₂SO₄) and anode types (Pt, Ti lined with Ir and Ta oxides, PbO₂, activated carbon) were performed on aqueous solutions containing phenol to assess the mechanism and nature of electrode deactivation phenomena. For the Pt electrode, the nature of the electro-deposited organic species was investigated by ATR-FTIR and FESEM-EDS analyses, which showed adsorption of intermediate oxidation products (e.g. benzoquinone, hydroquinone) is likely responsible for the early deactivation stages. Conversely, in the longer term, formation of polymeric films is promoted. Potentiostatic tests showed that anode regeneration can be achieved by anodic polarisation above 1.1 V (vs Hg/Hg₂SO₄). This reactivation was found to be easier in the presence of significant amounts of chloride ions. Conversely, the deactivated state is maintained for the Ti/IrO₂/Ta₂O₅ electrode even though anodic polarisation at high positive potentials is applied. Cyclic voltammetric curves on PbO₂ electrodes did not provide satisfactory results as the intensity of the lead-dioxide reduction peak was so high that peaks for phenol oxidation were hardly detectable. Finally, the activated carbon based electrode was found to be promising as it enables simultaneous adsorption of the organic pollutant and oxidation of the pollutant itself to constitute a sort of self-regenerating adsorber unit.     

Study of SO2 adsorption and thermal regeneration over activated carbon-supported copper oxide catalysts

The mechanisms of SO₂ adsorption and regeneration over activated carbon-supported copper oxide sorbent/catalysts were analyzed. Studies were carried out in a fixed-bed reactor equipped with a non-dispersive infrared gas analyzer to detect the reaction products and by using X-ray powder diffraction (XRPD) and temperature-programmed desorption (TPD) experiments to characterize the nature of the sulfate species and surface oxygen complexes. The results indicate that SO₂ was catalytically oxidized to SO₃ over a copper phase in the presence of gaseous oxygen, and then reacted with a copper site to form a sulfate linked to copper without desorption into the gas phase. The activated carbon support did not participate in this sulfation reaction. After the adsorption of SO₂, the exhausted sorbent/catalysts could be regenerated by direct heat treatment in inert gas at temperatures between 260 and 480 °C, while the neighboring surface oxygen complexes on the carbon surface were acting as the reducing agents to reduce CuSO₄ to Cu. During the subsequent adsorption process, the copper is rapidly oxidized by oxygen in the flue gas.     

Performance and Mechanism on Degradation of Estriol Using O3/PS Process

In this study, enhanced ozonation of estriol (E3) with persulfate (PS) was investigated in aqueous solution. Simultaneous generation of hydroxyl radical (?OH) and sulfate radical (?SO₄^?) by O₃/PS process was proposed and experimentally verified. Kinetic results revealed that the degradation of E3 was affected by the solution pH, PS concentration, O₃ dosage and E3 initial concentration. The optimal reaction rate was observed in alkaline solutions. The mechanism for the synergistic effect was preliminarily explored by the addition of hydroxyl and sulfate radical scavengers. The enhanced degradation of E3 by O₃/PS was also observed in actual water samples, which provided impetus for practical applications. The degradation intermediates were detected using LC/MS. Results showed that the phenol structures of the estrogens were mostly oxidized to cyclohexenone moieties and quinone-like structures.     

Electrochemical oscillations of the system Hg,HSO−4, BrO−3 and phenol

The electrochemical oscillations of the system Hg, HSO^?₄, BrO^?₃ and phenol are described. These oscillations arise at the dme in the range of potentials from +0.06 V to +0.01 V against a potential of a 1.5 mol dm^?3 Hg/Hg₂SO₄ electrode in a solution of sulphuric acid, sodium bromate and phenol. The temporal change of the limiting current and that of surface-tension of mercury oscillate in an anodic, anodic—cathodic or cathodic range depending on the concentration of phenol and on the value of the dme potential. The probable mechanism is also discussed. This is based on the simultaneous electroreduction of bromate ions and the electro-oxidation of mercury as the surface-tension changes, produced by the film of Hg₂SO₄ and Hg₂Br₂ formation and by the adsorption of phenol and/or its oxidation products.     

Flattening of oxidized diamond (111) surfaces with H2SO4/H2O2 solutions

Changes in the topography of a diamond (111) surface with atomically flat and wide terraces, caused by immersion in HNO₃/H₂SO₄ and H₂SO₄/H₂O₂ solutions were investigated by atomic force microscopy. We observed surface roughening from the HNO₃/H₂SO₄ treatment, and flattening of the HNO₃/H₂SO₄ treated surface from the H₂SO₄/H₂O₂ treatment. This suggests that the H₂SO₄/H₂O₂ treatment is an effective wet-process for preparing atomically flat oxidized diamond (111) surfaces.     

Effect of rice cultivars and fertilizer management on methane emission in a rice paddy in Beijing

Experiments were conducted during April-Oct. 1994 in a Beijing rice field. Four types of rice varieties have been tested. Large cultivar differences in methane emission flux have been found. Variety 93812 emitted about fivefold more CH₄ than did the Qiuguang variety. An organic amendment plus (NH₄)₂SO₄as the base fertilizer and (NH₄)₂SO₄as the topdressing applied in different amounts and growth stages, compared with no topdressing, reduced methane emission about 58% and increased rice yield about 31.7%. Emission peaks of CH₄ in the tillering stage and reproductive stage were suppressed. A comprehensive strategy could meet both the goal for sustainable rice productivity and methane reduction. Such a strategy includes: 1. Selection of cultivars which have reduced root exudate and litter but increased root mass most of which growing in the oxidized soil layer, cultivars also need an effective number of tillers for optimum yield but with less CH₄transportation ability; 2. Application of organic manure combined with chemical fertilizers, that reduce CH₄ emissions. Fertilizers such as SO₄ ² -or other inhibitors can be maintained for a long period in soil; 3. Adoption of scientific irrigation mode such as flooding-drainage- intermittent irrigation ,that can both increase the rice yield and decrease the CH₄ emission, etc.. This revised version was published online in August 2006 with corrections to the Cover Date.     

Preparation of SO42−/Fe2O3?MoO3 and its catalytic activity in the electrolytic reaction of phenol with methanol

BACKGROUND: Environmentally friendly solid catalysts are important in many processes from an industrial point of view and are applied widely in the study of alkylation of phenol with methanol in gas phase. However, liquid‐phase reactions have not been well studied. This paper deals with an assessment of liquid‐phase electrolytic alkylation in the presence of SO₄^2?/Fe₂O₃? MoO₃. RESULTS: A bidentate structure was formed between the SO₄^2? and metal. A catalyst with an amorphous structure delivered lower catalytic activity even at a higher Mo content. The highest activity was obtained at an Mo content of 16% (molar composition), which delivered a phenol conversion of up to 70.5%. Experiments also showed that the catalyst can be reused at least for three times. CONCLUSION: Application of solid catalyst in the liquid‐phase reaction assisted by electrolysis alkylation was found to be viable. The main products were methoxyphenols, in contrast to that associated with gas‐phase operation. A possible mechanism of product formation has been proposed. Copyright © 2008 Society of Chemical Industry     

Ion exchange resins from phenol/formaldehyde resin‐modified lignin

Phenol/formaldehyde resin, commonly sulfonated, is used as ion exchanger. Lignin, which is the phenolic polymer matrix in wood, was isolated from olive stone biomass by alkaline hydrolysis of weak ether bonds (Kraft lignin, KRL). It was then hydroxymethylated (KRLH) with an aqueous solution of formaldehyde. Novolac resin (N) was synthesized from phenol and formaldehyde under acidic conditions. KRL or KRLH was incorporated into phenol/formaldehyde during polymerization (N‐KRL, N‐KRLH). The products of polymerization (N, N‐KRL and N‐KRLH) were sulfonated with concentrated H₂SO₄ (1:3 w/w as typical proportion according to literature or 1:6 w/w as an excess of H₂SO₄) and then cross‐linked with formaldehyde. The different products were characterized by IR spectroscopy, swelling in ethanol, acetone and in an aqueous solution of 1 N NaOH. The ion‐exchange capacity, the moisture retention capacity and the titration curves of the sulfonated and cured products were determined. The ion‐exchange capacity and the uptake of metal ions (mainly Co²⁺ and Cu²⁺) detected by atomic absorption spectroscopy, on the sulfonated materials, prepared in an excess of H₂SO₄, is higher for N‐KRL and N‐KRLH than for N and it takes place at the same rate or faster. The latter shows a medium acidic behaviour according to the titration curves, in contrast with the sulfonated N‐KRLH and N‐KRL which show a strongly acidic behaviour. © 2001 Society of Chemical Industry     

Anodic Oxidation of Norcamphor in Aqueous Electrolytes

Norcamphor ( 1 ) was anodically oxidized at Pb/PbO₂ anodes in 1 M · H₂SO₄, MeCN/H₂O (V/V = 1/1). 3-Oxocyclopentaneacetic acid ( 3 ) and oxabicyclo[3.3.0]octan-3-one ( 4 ) were obtained with material yields up to 76% and 42%, respectively. The effects of electrode materials, current densities and concentrations were studied. A possible anodic oxidation mechanism was proposed.     

Direct oxidation of hydrogen sulphide to sulphur using impregnated activated carbon catalysts

Low concentrations of H₂S were directly oxidized to sulphur and small quantities of SO₂, over seven different activated carbons with or without impregnation. The effectiveness of virgin activated carbon was tested at 175°C, 700 kPa, and O₂/H₂S ratio with 5% greater than stoichiometry. The conversion of H₂S was 99.9 mol% with SO₂ production of 3–6%, for 360 min runtime for Fisher coconut shell activated carbon and 648 min for Envirotrol bituminous (EB) activated carbon. Then the activated carbons became deactivated due to deposition of sulphur on the surface. Under these conditions mesoporous activated carbons such as EB and Hydrodarco had the longest breakthrough time. The addition of 5.5 wt% ammonium iodide, potassium iodide and potassium carbonate individually to EB decreased the production of SO₂ while having minimal effect on the overall H₂S conversion. The addition of 5.5 wt% NH₄I decreased the average SO₂ production from 2.5% to 0.9%. The activation energy for the H₂S oxidation on the 5.5 wt% NH₄I on EB activated carbon was determined to be 40 kJ/mol.     

Polyaniline salt containing dual dopants,pyrelenediimide tetracarboxylic acid,and sulfuric acid: Fluorescence and supercapacitor

Storage of energy is considered as the most germane technologies to address the future sustainability. In this study, aniline was chemically oxidized with a controlled concentration of pyrelenediimide tetracarboxylic acid (PDITCA) by ammonium persulfate to polyaniline salt (PANI‐H₂SO₄‐PDITCA), with nanorods morphologies, having a sensibly decent conductivity of 0.8 S cm^?1, wherein H₂SO₄ was generated from ammonium persulfate during polymerization. PANI‐H₂SO₄‐PDITCA salt showed bathochromic fluorescence shift (595 nm) compared to PDITCA (546 nm). The Brunauer–Emmett–Teller surface area of the PANI‐H₂SO₄‐PDITCA‐25 and PANI‐H₂SO₄‐PDITCA‐50 were 18.3 and 21.4 m² g^?1, respectively. Furthermore, its energy storage efficiency was evaluated by supercapacitor cell configuration. The composite PANI‐H₂SO₄‐PDITCA‐50 showed capacitance 460 F g^?1 at 0.3 A g^?1 and large cycle life 85,000 cycles with less retention of 77% to its original capacitance (200 F g^?1) even at a better discharge rate of 3.3 A g^?1. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45456.     

Methods for measuring the concentrations of SO2, and of gaseous reduced sulphur compounds in the combustion chamber of a circulating fluidized bed boiler

The present work was aimed at developing and improving methods for measurement of gaseous sulphur compounds in the combustion chamber of a fluidized bed boiler (FBB). The sampling of SO₂ was improved by removing NH₃ and H₂O with a sorbent immediately after the probe. The concentration of reduced sulphur species was determined by means of two conventional SO₂ analyzers and an intermediate converter, where the reduced species are oxidized to SO₂. Gas phase sulphides were also sampled with a gas quenching probe by means of a basic solution which was subsequently analysed by wet chemistry. The methods were tested during coal combustion in a 12 MW circulating FBB without limestone for two cases of air‐staging.     

The identity of the sulfur‐containing phases present in cement clinker manufactured using a high sulfur petroleum coke fuel

Cement clinker produced using a high sulfur petroleum coke fuel has been analysed to determine the identity of the sulfate‐containing phases. Quantitative X‐ray diffraction methods were used in conjunction with extraction procedures to concentrate or extract the sulfate phases. The minerals of interest were anhydrite (CaSO₄), aphthitalite (3K₂SO₄·Na₂SO₄), arcanite (K₂SO₄), calcium langbeinite (K₂SO₄·2CaSO₄) and thenardite (Na₂SO₄). Overall sulfur content of the clinker increased in proportion with the amount of sulfur in the fuel. The clinker produced using the high sulfur fuel was found to contain a significantly increased concentration of aphthitalite but a reduced amount of thenardite. Comparison of the experimental results with theoretical predictions based on the Bogue formulae shows differences in respect of calcium langbeinite, which is not detected in the clinker, and thenardite, which is detected. Copyright © 2004 Society of Chemical Industry