Showing papers on "Phenol published in 2011"

Highly selective hydrogenation of phenol and derivatives over a Pd@carbon nitride catalyst in aqueous media

Abstract: Cyclohexanone is an important intermediate in the manufacture of polyamides in chemical industry, but direct selective hydrogenation of phenol to cyclohexanone under mild conditions is a challenge....

An easily recyclable Co/SBA-15 catalyst: Heterogeneous activation of peroxymonosulfate for the degradation of phenol in water

Abstract: A powder Co/SBA-15 catalyst for the activation of peroxymonosulfate (PMS) and the subsequent degradation of phenol was prepared through an incipient wetness impregnation technique using SBA-15 as the support, Co(NO 3 ) 2 ·6H 2 O as the precursor. A facile way to make a recyclable Co/SBA-15 catalyst was tested. The samples synthesized were characterized by X-ray diffraction (XRD), N 2 adsorption–desorption, high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) techniques. Effects of Co loading, calcination temperature and time on the performance of the powder catalyst were investigated. The results show that Co 3 O 4 was the main cobalt species present both inside and outside the support. Heat treatment led to the formation of Co–O–Si species during the calcinations and significantly inhibited Co leaching. The 10 wt%Co/SBA-15 calcined at 400 °C for 5 h had the best performance, with the phenol removal of more than 98% and total organic carbon (TOC) reduction of approximately 98%. The complete mineralization of phenol degradation was demonstrated, and the degradation mechanism was analyzed. Moreover, effects of PMS dosages and phenol concentrations on phenol degradation were also investigated. The results show that the appropriately high PMS dosage and the low phenol concentration were favorable to phenol removal. During 25 runs of recycling tests, the powder Co/SBA-15 wrapped with polytetrafluoroethylene (PTFE) membranes always maintained high catalytic activity with the phenol removal more than 90% in 2 h and Co leaching of less than 85 μg/L. Consequently, it is an easily recyclable catalyst.

Synthesis of polymers from organic solvent liquefied biomass: A review

Abstract: Biomass liquefaction with organic solvents is a unique thermochemical conversion process for biomass utilizations. It combines the useful functional groups from both biomass and organic solvents used in liquefaction, thus obtaining a large variety of polymers. This review is focused on the resin products synthesized from organic solvent liquefied biomass, including phenolic, polyurethane, epoxy, polyesters, etc. Many biomass species, such as wood, corn stover, waste paper, and wood bark, have been investigated as the feedstocks for liquefied biomass-based resin products. Phenol liquefied biomass was studied the most mainly based on expectation to utilize the aromatic structures of lignin in biomass as the substitute for phenol in phenolic resin synthesis. Further condensation reaction of phenol liquefied biomass with formaldehyde to synthesize novolac or resol phenolic resins was proven to be an efficient route to convert the un-reacted phenol from liquefaction to resins and improve the physical mechanical properties of the resulting resins. Except for phenolic resins, most other polymers from liquefied biomass were synthesized based on the utilization of hydroxyl groups in liquefied biomass. Polyhydric alcohols liquefied biomass was used as polyols to synthesize polyurethanes, epoxy, and polyesters. To achieve comparable mechanical strength of resulting resin products, the common liquefaction solvent to biomass ratio was 3/1, which indicates a biomass substitution around 25% to petroleum raw materials. A few cases could reach 50% substitution with biomass pretreatment before liquefaction. Three main concerns with the liquefied biomass-based resins were their relatively higher viscosities, highly hydrophilic characters, and relatively lower cross-linking density in cured resins.

Electrochemical oxidation of phenol on boron-doped diamond electrode

Abstract: The process of phenol oxidation on a boron-doped diamond electrode (BDD) is studied in acidic electrolytes under different conditions of generation of active oxygen forms (AOFs). The scheme of phenol oxidation known from the literature for other electrode materials is confirmed. Phenol is oxidized through a number of intermediates (benzoquinone, carboxylic acids) to carbon dioxide and water. Comparative analysis of phenol oxidation rate constants is performed as dependent on the electrolysis conditions: direct anodic oxidation, with oxygen bubbling, and addition of H2O2. A scheme is confirmed according to which active radicals (OH·, HO2·, HO2−) are formed on a BDD anode that can oxidize the substrate which leads to formation of organic radicals interacting with each other and forming condensation products. Processes with participation of free radicals (chain-radical mechanism) play an important role in electrochemical oxidation on BDD. Intermediates and polymeric substances (polyphenols, quinone structures, and resins) are formed. An excess of the oxidant (H2O2) promotes a more effective oxidation of organic radicals and accordingly inhibition of the condensation process.

Evolution of Aromatic Tar Composition in Relation to Methane and Ethylene from Biomass Pyrolysis-Gasification

Abstract: Tar reduction and monitoring is the major stake for gasification processes. Pyrolysis is the precursor mechanism of the gasification of solid fuels and tar production. The evolution of gas and tar composition produced from wood chips pyrolysis was investigated in a tubular reactor as a function of its wall temperature (700–1000 °C, with gas mean residence times of 1.1–2.7 s). High thermal severities lead to the “gasification” regime, promoting gas production from tar conversion. Tar (benzene, toluene, o- and m-xylenes, phenol, indene, o-, m-, and p-cresols, naphthalene, 1- and 2-methylnaphthalenes, acenaphthylene, and phenanthrene) were quantified by gas chromatography/mass spectrometry (GC/MS) analysis using deuterated internal standards. Closed mass balances were obtained. A simplified chemical scheme of secondary tar conversion is proposed. Under the investigated range of thermal severity, CH4 production is mainly controlled by aromatic tar demethylation. Linear relations were observed between the mola...

Selective phenol hydrogenation in aqueous phase on Pd-based catalysts supported on hybrid TiO2-carbon materials

Abstract: TiO2-C materials have been prepared by solvothermal and slurry synthesis and the influence of carbon properties upon the catalytic activity and selectivity of Pd-based catalysts on phenol hydrogenation in aqueous phase under mild reaction conditions has been studied. The nature of the catalysts can be modified to direct the reaction either to cyclohexanol (∼100% yield) or to cyclohexanone (∼96% yield). High selectivity to cyclohexanone is obtained with Pd on more polar TiO2-C supports, while when these are transformed into hydrophobic TiO2-C supports the resultant catalyst becomes selective to cyclohexanol. Thus, product distribution during the selective phenol hydrogenation in aqueous phase is easily controlled by controlling the functionalization of the hybrid support.

Sewage sludge based catalysts for catalytic wet air oxidation of phenol: Preparation, characterisation and catalytic performance

Abstract: In this study the use of novel CWAO catalysts, namely potentially low cost, sewage sludge derived activated carbons was explored. Two types of municipal sludge were used: dewatered raw filter cake and dewatered mesophilic anaerobically digested sludge. The carbons were produced by: carbonisation; physical activation (steam or CO2) and chemical activation (K2CO3). Hydrochloric acid washing of some of the carbons was also investigated. The carbons were characterised in terms of their surface area, contact pH, propensity towards metal leaching, surface chemistry (via FTIR), ash content and inorganic elemental composition. Their CWAO performance was assessed at 160 °C and a partial oxygen pressure of 4.2 bar (25 bar of air) within a stirred batch reactor containing a 5 g/L phenol solution. All the carbons exhibited catalytic activity, with the K2CO3 activated and HCl washed carbons attaining a phenol and TOC removal that matched the performance of an activated carbon specifically manufactured for oxidative wastewater treatment applications. A strong correlation was found between surface area and phenol or TOC conversion, suggesting that surface area is a primary requisite for their performance in the first batch cycle. Thus, the oxidation of phenol is thought to proceed via a free radical driven mechanism. The active sites necessary to facilitate this mechanism, whether present as surface functional groups or active metals (e.g., Fe), were detected on all of the sludge based activated carbons. However, no clear correlation between phenol conversion and these active sites could be established.

Mesoporous zirconium phosphate: An efficient catalyst for the synthesis of coumarin derivatives through Pechmann condensation reaction

Abstract: Mesoporous zirconium phosphate (m-ZrP) is used as a solid acid catalyst for the synthesis of coumarins via Pechmann condensation reaction and gave high catalytic activity for the condensation of phenols and ethyl acetoacetate in both conventional heating as well as microwave assisted method. The condensation reaction is studied in detail by varying the reaction parameters like effect of solvent, molar ratio of the reactants, temperature, and catalyst loading. Among the substituted phenols, m -amino phenol is more reactive and 100% yield is obtained in very short time at low temperature due to the presence of ring activating amine group in meta position. The m-ZrP is also active even for simple phenol and 57% yield of 4-methyl coumarin is obtained in conventional heating method. Microwave assisted synthetic method is found to be advantageous over conventional heating for the synthesis of coumarins, as it provides improved yield in very less time.

Highly stable Fe/γ‐Al2O3 catalyst for catalytic wet peroxide oxidation

Abstract: BACKGROUND: A highly stable Fe/γ-Al2O3 catalyst for catalytic wet peroxide oxidation has been studied using phenol as target pollutant. The catalyst was prepared by incipient wetness impregnation of γ-Al2O3 with an aqueous solution of Fe(NO3)3· 9H2O. The influence of pH, temperature, catalyst and H2O2 doses, as well as the initial phenol concentration has been analyzed. RESULTS: The reaction temperature and initial pH significantly affect both phenol conversion and total organic carbon removal. Working at 50 °C, an initial pH of 3, 100 mg L−1 of phenol, a dose of H2O2 corresponding to the stoichiometric amount and 1250 mg L−1 of catalyst, complete phenol conversion and a total organic carbon removal efficiency close to 80% were achieved. When the initial phenol concentration was increased to 1500 mg L−1, a decreased efficiency in total organic carbon removal was observed with increased leaching of iron that can be related to a higher concentration of oxalic acid, as by-product from catalytic wet peroxide oxidation of phenol. CONCLUSION: A laboratory synthesized γ-Al2O3 supported Fe has shown potential application in catalytic wet peroxide oxidation of phenolic wastewaters. The catalyst showed remarkable stability in long-term continuous experiments with limited Fe leaching, < 3% of the initial loading. Copyright © 2010 Society of Chemical Industry

Adsorption of phenol onto activated carbon from seaweed: Determination of the optimal experimental parameters using factorial design

Abstract: Brown seaweed biomass was used as a precursor for the preparation of activated carbon employing zinc chloride activation. The activated carbon was characterized and employed as an adsorbent for the removal of phenol from aqueous solution. In order to reduce the number of experiments to achieve better phenol removal efficiency, two independent sets of full 23 factorial design experiments were carried out. The results showed that all the factors were significant, besides several interactions among the factors were also significant. Using this statistical tool, the best conditions for phenol removal by the seaweed based activated carbon was established as pH 3.0; initial concentration of phenol 150 mg/L; adsorbent dosage 10 g/L; time 4 h; experimental temperature 50 °C and an agitation speed of 75 strokes/min. The maximum phenol uptake under these experimental conditions was 98.31%.