Phenol Oxidation In Supercritical Water Research Articles

Supercritical hydrothermal combustion and enhanced degradation characteristics of phenol

Supercritical hydrothermal combustion is a green combustion technology that produces flames in supercritical water (SCW), which can realize efficient disposal of aqueous wastes. In this study, the typical pollutant phenol is investigated through tubular reactor experiments and mechanism analysis to explore its hydrothermal combustion properties and enhanced degradation effects on refractory species. The results show that 3.06 and 3.41 wt% phenol can be self-ignited in the tubular reactor with a critical preheating temperature of 460 °C. Methanol could improve the ignition and burnout characteristics of phenol. As the COD ratio of methanol was greater than 0.35, the ignition temperature of phenol was reduced to 420 °C, with TOC removal rate achieving 99.9%. At 460 °C, phenol positively influenced the heat release during combustion of phenol/methanol. In oxidation of phenol/ammonia, 1.61 wt% phenol resulted in the reaction temperature rising by around 62.0 °C, allowing a NH4-N removal rate of 92.8% through its synergistic kinetic and thermal effects. Whereas, the nitrogen-containing intermediates from ammonia inhibited phenol oxidation. Finally, a mechanism-based kinetics model for oxidation of phenol in SCW was developed by means of real gas properties and sensitive reaction step modifications, which was viable for simulating the ring-opening path of phenol.

Experimental and kinetics study on oxidation of three‐component in supercritical water

ABSTRACTThe supercritical water oxidation of a methanol, acetic acid, and phenol mixture was investigated in this study. The experimental design was accomplished by means of response surface methodology. 16 experimental runs were performed in a continuous tubular reactor. Quadratic polynomial equations with a satisfactory data fit and accuracy were established on the basis of the experimental results. The calculation results demonstrate the promotion behaviour of methanol, the inhibition behaviour of acetic acid, and the positive effect of phenol on the supercritical water oxidation of the ternary mixture. The interactive effect of the mechanism was characterized by means of the computational simulation with the mechanism‐based kinetic model. It seems that the positive influence of methanol was derived from the co‐oxidation effect of the methanol in the destruction of both acetic acid and phenol. The oxidation of acetic acid was restrained in the mixture system, which is attributed to the more favourable radical capture for phenol, and, thus, the overall disappearance kinetics was retarded with the addition of acetic acid. Finally, the co‐oxidation enhancement of both methanol and acetic acid related to phenol oxidation in supercritical water contributed to the positive effect of phenol on mixture oxidation efficiencies.

Phenol oxidation in supercritical water in a well-stirred continuous reactor

A well-stirred reactor for phenol and acetic acid oxidation in supercritical water is considered. A mathematical model of an adiabatic reactor is formulated. A numerical algorithm for solving the model equations using the homotopy method is developed. The model takes into account specific features of processes under supercritical conditions, namely, the changes in the thermodynamic properties (enthalpy, heat capacity, and critical parameters) of mixtures with a change in pressure and temperature. The thermodynamic properties are calculated by methods of nonideal thermodynamics. It is shown that there is a multiplicity of steady-state solutions at various reactor performances. The results of numerical analysis of the effect of the inlet flow temperature, the amount of methanol (fuel) fed, and the total pressure on the reactor performance are presented.

Reaction Engineering Model for Supercritical Water Oxidation of Phenol Catalyzed by Activated Carbon

Supercritical water oxidation is an efficient technology for the ultimate destruction of organic waste materials. We previously reported that the addition of activated carbon catalyst promoted the oxidation of phenol in supercritical water and that yield of tarry materials was remarkably suppressed at 400 °C and 25 MPa. In this study, reaction kinetics of the carbon-catalyzed phenol oxidation in supercritical water was studied, and especially, the influence of mass-transfer limitation inside and outside of the catalyst particles was investigated. Experimental results indicated that mass-transfer limitation between bulk fluid and the catalyst surface was negligible whereas mass transfer within the pores of the activated carbon catalyst limited the overall reaction rate. This was in agreement with the result of the calculation of Mears' and Weisz-Prater's criteria. We then developed model equations considering the influence of mass transfer to investigate the intrinsic reaction rate and to describe the temporal change of reaction kinetics. In the model, three reactions were taken into account: homogeneous phenol oxidation, heterogeneous phenol oxidation on the catalyst surface, and combustion of carbon catalyst. The parameter values were determined by curve fitting with the experimental data. By this model, temporal changes of the mass-transfer effect and the reaction rate profile in the packed bed were determined.

Water‐density effects on phenol oxidation in supercritical water

AbstractSupercritical water oxidation (SCWO) experiments were performed in a tubular flow reactor at 420–465°C and 141–241 bar. Phenol was the organic reactant. Both pure water and a helium (1/3 by mol)–water mixture served as reaction media. Adding helium to the reaction medium permitted variation of the water concentration and system pressure independently. By decoupling the water concentration from the system pressure, it was shown that the rate of phenol disappearance during SCWO is influenced by the water concentration and not the system pressure. The experiments consistently revealed that adding helium, and thereby decreasing the water concentration at a fixed system pressure, increased the phenol conversion. In addition, experiments showed that lowering the water concentration using pure water as the solvent also increased the phenol conversion. The results suggest that dilution with helium (and perhaps other inert gases) may be a new way to control SCWO reaction rates.

Modeling of supercritical water oxidation of phenol catalyzed by activated carbon

Model equations were developed to describe the reactions of phenol oxidation in supercritical water catalyzed by activated carbon (AC) at 400°C, 25 MPa . In the model, three reactions were considered with assuming power-law kinetics: homogeneous phenol oxidation, heterogeneous phenol oxidation, and combustion of an AC catalyst. The parameter values were determined experimentally and by the fitting with experimental results. As a result, the model expressed the reaction characteristics well with respect to the temporal changes of phenol conversion, amount of AC catalyst, and oxygen concentration in the effluent. Also, a good agreement was obtained between the experimental results and the model prediction under the condition of changing initial oxygen concentration. Temporal changes of concentration profile and reaction rate profile in the packed-bed reactor were calculated by the model.

Catalytic Oxidation of Phenol over MnO2in Supercritical Water

Bulk MnO2 was used as a catalyst for phenol oxidation in supercritical water at 380−420 °C and 219−300 atm in a flow reactor. The bulk MnO2 catalyst enhances both the phenol disappearance and CO2 formation rates during supercritical water oxidation (SCWO), but it does not affect the selectivity to CO2 or to the phenol dimers at a given phenol conversion. The role of the catalyst appears to be accelerating the rate of formation of phenoxy radicals, which then react in the fluid phase by the same mechanism operative for noncatalytic SCWO of phenol. The rates of phenol disappearance and CO2 formation are sensitive to the phenol and O2 concentrations but independent of the water density. Both power-law and dual site Langmuir−Hinshelwood−Hougen−Watson (LHHW) rate laws were developed to correlate the catalytic kinetics. Our results show that SCWO reactor volumes can be reduced by an order of magnitude if bulk MnO2 is used as the catalyst and by yet another order of magnitude if a supported oxidation catalyst is used.

Phenol oxidation kinetics in supercritical water

Phenol oxidation in supercritical water was carried out in a flow reactor at a temperature range from 370°C to 430°C, and about 100 data were taken under various conditions in order to determine the kinetic parameters. Experimental results showed that the global rate of phenol disappearance was proportional to the phenol concentration, and to the 0.48 power of O 2 concentration, which were in good accordance with the reported values. Our results also showed a negative dependence of the global reaction rate on the H 2O density in a certain range. The kinetic parameters obtained in the present work always gave higher rates than those of previous research, though the reason for this difference has not yet been clarified.

On the kinetics of phenol oxidation in supercritical water

AbstractPhenol oxidation in supercritical water was carried out in a tubular laboratory‐scale reactor operated at a temperature range of 380°C to 450°C and pressures between 230 and 265 bar. The phenol feed concentrations were between 500 and 1,000 mg/L, while oxygen was fed into the reactor at 50 to 1,000% of the stoichiometric amount needed to oxidize phenol completely to carbon dioxide. Phenol conversions from 16 to 96% were attained as the reactor residence times varied from 15 to 203 s. The oxidation obeys a parallel‐consecutive reaction scheme that involves multiring, intermediate products such as phenoxy‐phenol, biphenol, dibenzo‐dioxin, maleic acid, and succinic acid. Experimental results showed that the phenol disappearance rate is represented well by a power‐law kinetic model in which the rate is proportional to the 0.4 power of the oxygen mole fraction and roughly linearly proportional to the phenol mole fraction. The pressure effect on the disappearance rate was appropriately accounted for by introducing the molar volume of the reaction mixture, which was readily calculated by an equation of state. Total organic carbon reduction can be estimated by a lumped kinetic equation. In the P‐T region the activation energy of the phenol disappearance was 124.7 kJ/mol.

A reaction network model for phenol oxidation in supercritical water

AbstractDilute aqueous solutions of phenol were oxidized in a flow reactor at 420, 440, 460 and 480°C at 250 atm. Phenol disappearance kinetics followed the trends exhibited by previously published data obtained at T < 420°C. By merging the two sets of data, a global rate low for phenol disappearance kinetics valid between 380 and 480°C was determined to be rate = 102.34 exp( −12.4/RT) [ϕOH]0.85 [O2]0.50 [H2O]0.42. Undesired multiring products, whose formation was reported previously at the lower temperatures, continued to form in high selectivities at these higher temperatures. Reaction products were classified into three categories: dimers, gases, and a remainder that included products from ring‐opening reactions. A global reaction network that describes the transformation of phenol into these product groups was developed. Steps in the network are: parallel oxidation paths for phenol that from dimers and ring‐opening and other products, secondary decomposition of dimers of ring‐opening and other products, and oxidation of the ring‐opening and other products to carbon oxides. The experimental products yields were used to determine optimal values for the reaction orders and rate constants for each step in the network. This quantitative reaction model shows that dimerization is the dominant primary path for phenol consumption. High temperatures and long residence times reduce the concentration of dimers in the reactor effluent and maximize the gas yield. High oxygen concentrations also increase the gas yield. The quantitative reaction network model is consistent with previously published product yields for T = 380 – 420°C.

Reaction Mechanism for Phenol Oxidation in Supercritical Water

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTReaction Mechanism for Phenol Oxidation in Supercritical WaterSudhama Gopalan and Phillip E. SavageCite this: J. Phys. Chem. 1994, 98, 48, 12646–12652Publication Date (Print):December 1, 1994Publication History Published online1 May 2002Published inissue 1 December 1994https://doi.org/10.1021/j100099a031RIGHTS & PERMISSIONSArticle Views913Altmetric-Citations101LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (762 KB) Get e-Alerts

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Kinetics of phenol oxidation in supercritical water

AbstractAqueous solutions of phenol were oxidized in a flow reactor at temperatures between 300 and 420°C (0.89 ⩽ Tr ⩽ 1.07) and pressures from 188 to 278 atm (0.86 ⩽ Pr ⩽ 1.27). These conditions included oxidations in both near‐critical and supercritical water. Reactor residence times ranged from 1.2 to 111 s. The initial phenol concentrations were between 50 and 330 ppm by mass, and the initial oxygen concentrations ranged from 0 to 1,100% excess. The oxidation experiments covered essentially the entire range of phenol conversions. Analysis of the kinetics data for phenol disappearance using a combination of the integral method and the method of excess revealed that the reaction was first order in phenol and 1/2 order in oxygen, and influenced by pressure. The global reaction order for water was taken to be nonzero, and the global rate constant was assumed to be independent of pressure so that the only effect of pressure was to alter the water concentration and hence the reaction rate. This approach led to a global reaction rate law that was 0.7 order in water and had a rate constant with an activation energy of 12.4 kcal/mol. The implications of these rate laws to the design of a commercial supercritical water oxidation reactor are also explored.

Phenol oxidation in supercritical water: formation of dibenzofuran, dibenzo-p-dioxin, and related compounds

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPhenol oxidation in supercritical water: formation of dibenzofuran, dibenzo-p-dioxin, and related compoundsThomas D. Thornton, Douglas E. LaDue III, and Phillip E. SavageCite this: Environ. Sci. Technol. 1991, 25, 8, 1507–1510Publication Date (Print):August 1, 1991Publication History Published online1 May 2002Published inissue 1 August 1991https://doi.org/10.1021/es00020a023RIGHTS & PERMISSIONSArticle Views238Altmetric-Citations57LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (485 KB) Get e-Alerts Get e-Alerts

Phenol oxidation in supercritical water

The oxidation of phenol has been accomplished in subcritical and supercritical water. Seventy experiments were performed in an isothermal, plug-flow reactor at temperature from 300 to 420°C, pressures from 188 to 278 atm, and residence times from 4 to 111 seconds. The initial phenol concentrations ranged from 2.8 × 10 −4 to 5.3 × 10 −3 M, and the oxygen concentrations were between 6.5 × 10 −5 and 6.4 × 10 −2 M at reaction conditions. The oxidation experiments covered essentially the entire range of phenol conversions. The experimental results were consistent with the global reaction order for phenol being in the range of1/2and 1, and with the global reaction order for oxygen being greater than zero. The conversion increased with increasing pressure, which may either suggest that the reaction order with respect to water was greater than zero, or that the apparent activation volume was less than zero. A variety of reaction products were detected, including mono- and di-car☐ylic acids, dihydroxybenzenes, phenoxyphenols, and dibenzofuran, indicating that the oxidation of phenol in supercritical water may involve a complex set of multiple reactions. The concentrations of metals in the reactor effluent were very low, indicating that corrosion effects were likely not a complicating factor in this study. No metals were detected in the solid material collected in the reaction product filter, also indicating an absence of corrosion effects.