Catalytic Wet Oxidation Of Phenol Research Articles

Kinetics study of catalytic wet oxidation of phenol over novel ceria promoted mesoporous silica supported Ru-Fe3O4 catalyst

A novel catalyst was synthesized via excess solution impregnation (ESI) of Ru and Fe3O4 nanoparticles (NPs) on ceria-loaded mesoporous SiO2 and mesoporous SiO2 was synthesized using sol-gel method. Degradation of phenol and effluent containing phenol from resin industry was performed over Ru-Fe3O4/CeOx-SiO2 (Ce3+/Ce4+, x = 1.64) catalyst in an autoclave reactor at 423 K and 14 bar oxygen pressure. Effective phenol degradation of 95% for the model aqueous solution of phenol and 92% for industrial effluent containing phenol were achieved when the both ruthenium and iron loadings were 0.25 wt% under optimized reaction conditions. The close contact between ruthenium and Fe3O4 nanoparticles facilitated the oxidation of phenol at very low temperature, whereas ceria NPs act as a promoter for oxidation reaction. The kinetics insights of oxidation reaction were studied and the catalysts were characterized thoroughly using BET, TPD, XRD, SEM, HR- TEM, ICP-AES, XPS and CO chemisorptions techniques. High surface area and large mesopores of silica facilitated the fine dispersion of the active catalytic sites and oxygen vacancy as supported by the DFT study for catalytic activity. Optimal process conditions could render much higher phenol degradation efficacy in comparison with previous scientific investigations.

Synthesis of highly active and stable Al/Zr pillared clay as catalyst for catalytic wet oxidation of phenol

Natural bentonite clay was used in the synthesis of single and mixed oxide Al/Zr pillared clay catalysts by means of ultrasonic treatment during the aging and intercalation steps. The raw bentonite and pillared clay catalysts were characterized using high resolution scanning electron microscopy with energy dispersive system (HRSEM-EDS), powder X-ray diffraction (PXRD), N2 adsorption/desorption, Fourier transform infrared spectroscopy, thermogravimetric analysis, cation exchange capacity, zeta potential and all the catalysts evaluated in the catalytic wet air oxidation (CWAO) of phenol. Calcination of the synthesized Al/Zr-PILCs at 500 °C for 120 min yielded optimum physical properties with BET surface area of 230 m2/g, pore volume of 0.115 cm3/g and basal spacing of 1.92 nm and with good thermal stability. Complete removal of phenol was obtained after 120 min and 88% TOC was removed after 180 min in aqueous solution under mild reaction conditions of 100 °C and 10 bar after. Catalyst reusability studies showed that the Al/Zr-PILCs catalyst demonstrated excellent chemical and structural stability with insignificant leaching of Zr4+ after six consecutive catalytic runs. The Al/Zr-PILCs catalyst therefore demonstrated excellent catalytic properties in the CWAO of phenol in aqueous solution.

Effect of nitrogen doping on the catalytic activity of activated carbon and distribution of oxidation products in catalytic wet oxidation of phenol

AbstractNitrogen‐containing functional groups were introduced into activated carbon (AC) by amination at high temperatures to investigate their effects on the catalytic activity and distribution of products in the catalytic wet air oxidation (CWAO) of phenol at 120 and 160 °C. The results show that the catalytic activity of the nitrogen‐doped AC increases with amination temperature from 250 to 850 °C. The linear relationship between the quantity of nitrogen‐containing functional groups and the catalytic activity indicates that the enhanced activities are closely related to the amount of pyridinic and pyrrolic nitrogen groups on the surface of the AC. The parent and aminated AC exhibit distinct distributions of oxidation products. Oxalic acid is favourably degraded on the aminated AC, whereas the all‐carbon AC shows a similar ability for the removal of acetic acid.

Catalytic wet oxidation of phenol with Fe–ZSM-5 catalysts

Systematic study of catalytic wet oxidation of phenol over Fe–ZSM-5 and Fe2O3/ZSM-5 catalysts.

Catalytic wet oxidation of phenol under mild operating conditions: development of reaction pathway and sludge characterization

Several process industries discharge wastewater with enormous amount of toxic phenolic compounds. Wet oxidation (WO) is considered among the potential cleaner treatment methods for such waste streams. The present study demonstrates the effectiveness of two homogeneous copper salts (nitrate and sulfate) as catalysts during batch WO process conducted under mild temperature and pressures (i.e., 120 °C and oxygen pressure = 0.5 MPa). The catalytic oxidation showed around 90 % reduction of phenol, chemical oxygen demand and total organic carbon from the wastewater within 2 h. The oxidation reaction pathway at mild conditions is also proposed based on the presence of intermediates/by-products. Fourier transform infrared spectroscopy confirmed the formation of polymerized compounds containing alcoholic/phenolic species. The inductively coupled plasma-atomic emission spectroscopy analysis revealed the presence of ~40 % of the total copper in sludge. The copper recovery from the treated wastewater and sludge and its reuse in the oxidation process should be studied in future.

The effect of reaction conditions on the apparent deactivation of Ce–Zr mixed oxides for the catalytic wet oxidation of phenol

A series of Ce–Zr mixed oxides with different composition have been characterized and used as catalysts in the catalytic wet oxidation (CWO) of phenol. The addition of Zr significantly enhanced the redox and catalytic activity of ceria. However, a catalytic activity drop occurred for zirconium contents higher than 80%, which is related with a ZrO 2 segregation observed in Zr-rich oxides. The effects of the temperature of reaction, the oxygen partial pressure and the phenol/catalyst ratio on the activity for the oxidation of phenol and the selectivity to CO 2 were also investigated. The values for CO 2 selectivities were greatly influenced by the formation of a carbonaceous deposit adsorbed on the catalyst surface. The results indicated that these C-deposits can be totally oxidized by selecting appropriate operating conditions, thus obtaining catalytic systems with a very promising performance for phenol abatement. A mechanism is proposed to interpret the role of the carbonaceous deposits in the oxidation of phenol as a function of the reaction conditions.

Deactivation of Pt/MnO x–CeO 2 catalysts for the catalytic wet oxidation of phenol: Formation of carbonaceous deposits and leaching of manganese

MnO x –CeO 2 and Pt(2%)/MnO x –CeO 2 catalysts were prepared and investigated in the catalytic wet oxidation (CWO) of phenol. The reaction was carried out in a high-pressure autoclave reactor operating at 140 °C and oxygen partial pressure of 2 MPa. The effect of a reduction pre-treatment at 350 °C on the catalytic performance of both, the platinum catalyst and the bare oxide was studied. Higher activities were found for the reduced catalysts, independently of the presence or absence of Pt. Formation of carbonaceous deposits on the catalytic surface and leaching of manganese was confirmed as the two major deactivation mechanisms occurring in CWO of phenol. The amounts of deposits formed and manganese leached were higher in the case of reduced samples. Different techniques (XRD, HREM, HAADF, EDS, ICP) were used to characterise the chemical and structural changes experimented by the catalysts during reaction. The behaviour of reduced catalysts was found to be associated to the presence of MnO. The formation of this manganese oxide phase during the reduction pre-treatment significantly influenced the catalytic performance and stability of the catalysts under operation conditions.

Fenton Pretreatment in the Catalytic Wet Oxidation of Phenol

Catalytic wet oxidation (CWO) of 1000 mg/L of phenol (PhOH) aqueous solutions has been carried out using a commercial activated carbon as catalyst, placed in a continuous three-phase reactor at 16 bar, and temperature was changed in the interval 127−160 °C. Pure oxygen was fed as gaseous phase. Pollutant conversion, mineralization, intermediate distribution, and toxicity were measured at the reactor exit. The catalyst weight (W) to liquid flow rate (QL) ratio was varied from 0.3 to 17.5 gACmin/mL. Fenton reagent (FR) has been applied to the same phenolic aqueous samples using different amounts of H2O2 (between 10 and 100% of the stoichiometric dose) and 10 mg/L of Fe2+, in a batch way at 50 °C. An integrated process has been proposed that combines FR as pretreatment of the CWO process. In the FR step, 10% of H2O2, 10 mg/L of Fe2+, and reaction times shorter than 40 min are used. Efluent from FR step is fed to the CWO reactor at 127 °C. High mineralization (80−90%) and total detoxification of the effluent ...

Catalytic wet oxidation of phenol using membrane reactors: A comparative study with slurry-type reactors

The wet air oxidation of phenol over cerium mixed oxides has been carried in autoclave slurry-type reactor and also in a contactor type membrane reactor to assist about the benefits provided by the employment of the mesoporous top layer of a ceramic tubular membrane as catalyst (Ce mixed oxides) support. The effect of mixed oxide composition and use of Pt as dopant onto the phenol removal rate and selectivity towards mineralization have been studied on both types of reactor. For slurry-type reactors, two different autoclave reactors were used: one mechanically stirred highly pressurized, and the other magnetically stirred containing a porous stainless steel membrane as gas diffuser in an attempt to attain higher gas–liquid interfacial area. The performances of these reactors have been compared under similar reaction conditions (i.e. catalyst loading/liquid volume, temperature, phenol concentration) although the way in which reactants are fed to the reaction vessel (different among each other configuration) is clearly affecting the CWO phenol degradation route. From the catalytic systems studied, Pt doped Ce–Zr mixed oxides exhibit the best reaction performance in spite of the achieved phenol conversion levels are below 50%. For autoclave reactors, the gas feeding to the liquid volume by a membrane diffuser has almost no effect on phenol removal for the reaction conditions tested; whereas the catalytic membrane contactor type reactor clearly outperform autoclave reactor provided with membrane diffuser.

Total catalytic wet oxidation of phenol and its chlorinated derivates with MnO2/CeO2 catalyst in a slurry

In the present work, a synthetic effluent of phenol was treated by means of a total oxidation process-Catalyzed Wet Oxidation (CWO). A mixed oxide of Mn-Ce (7:3), the catalyst, was synthesized by co-precipitation from an aqueous solution of MnCl2 and CeCl3 in a basic medium. The mixed oxide, MnO2/CeO2, was characterized and used in the oxidation of phenol in a slurry reactor in the temperature range of 80-130ºC and pressure of 2.04-4.76 MPa. A phenol solution containing 2.4-dichlorophenol and 2.4-dichlorophenoxyacetic acid was also degraded with good results. A lumped kinetic model, with two parallel reaction steps, fits precisely with the integrated equation and the experimental data. The kinetic parameters obtained are in agreement with the Arrhenius equation. The activation energies were determined to be 38.4 for the total oxidation and 53.4 kJ/mol for the organic acids formed.

Fe-MCM-41 with highly ordered mesoporous structure and high Fe content: synthesis and application in heterogeneous catalytic wet oxidation of phenol

Iron-substituted MCM-41 materials (Fe-MCM-41) have been synthesized via a hydrothermal method with in situ incorporation of Fe(III) oxalate complex under various basic conditions. The resulting Fe-MCM-41 samples were characterized by X-ray diffraction, N2 adsorption measurement, and UV–Vis spectrometry. By controlling initial synthesized pH, the Fe-MCM-41 with highly ordered hexagonal mesoporous structures and high iron content (Si/Fe = 20) could be obtained. The iron species in Fe-MCM-41 samples mainly coexisted in isolated iron and highly dispersed iron oxide nanoclusters. Activity and stability of the obtained catalyst were evaluated on the wet peroxide oxidation of phenol under mild reaction conditions (<80 °C, ambient pressure). The Fe-MCM-41 with highly ordered mesoporous structure and high Fe content appeared to be the most interesting catalysts for phenol degradation owing to its high organic mineralization, low sensitivity to leaching Fe out and good oxidant efficiency.

Catalytic wet oxidation of phenol: The role of promoter and ceramic support

Complete mineralization of phenol has been achieved over a cerium–manganese catalyst, doped with potassium, supported on a modified zeolite with a high surface area, under very mild conditions (110 °C, PO2 = 0.5 MPa). This newly developed supported catalyst restricts the formation of bulk polymeric species on the surface, thus increasing the lifetime of the catalyst. It demonstrates superior textural, structural and surface oxygen properties compared with the reference cerium–manganese oxide catalyst. The supported catalyst maintains not only the high surface area but also the nanoparticle size during the catalytic run, thereby providing the full availability of the surface for reacting molecules. The geometry of the catalyst is modified electronically by the addition of potassium, and the zeolite addition restricts the conversion of Ce, Mn and K to higher oxidation states, thereby maintaining the geometry of catalytic active sites. The performance measured with this novel catalyst indicates a major improvement in the efficient application of the catalytic wet oxidation process for complete purification of a complex waste stream.

Efficient catalytic wet oxidation of phenol using iron acetylacetonate complexes anchored on carbon nanofibres

Iron acetylacetonate complexes anchored on oxidized carbon nanofibres (CNFs) were prepared by a three steps procedure: (i) oxidation of commercial CNFs by treatment with HNO 3, (ii) synthesis of acetylacetonate (acac) functional groups on the oxidized CNFs surfaces (acac/CNFs) and (iii) iron ions complexation on the acac sites of the CNFs (Fe-acac/CNFs). The surface groups exposed on the functionalized CNFs were characterized by using attenuated total reflectance Fourier transform infrared spectroscopy, temperature programmed desorption, thermogravimetric analysis and X-ray photoelectron spectroscopy. The functionalized CNFs and the iron complexes anchored on the CNFs were tested as heterogeneous catalysts for the wet oxidation of phenol with pure oxygen. Complete phenol conversion and high mineralization values were achieved with fresh and reused Fe-acac/CNFs catalysts, which demonstrate the improved stability of the catalysts under the phenol degradation reaction conditions. Furthermore these conditions are comparatively mild, typically 413 K of reaction temperature and 2.0 MPa of oxygen pressure.

Optimization of the MnCeOx system for the catalytic wet oxidation of phenol with oxygen (CWAO)

A class of MnCeOx catalysts has been synthesized via the new redox-precipitation route in alternative to the conventional co-precipitation technique. The effects of preparation method, composition and calcination temperature on catalyst texture, dispersion and reduction pattern properties have been addressed. Redox-precipitated systems exhibit high surface area (SA, 120–170m2/g), large pore volume (PV, 0.4–0.5cm3/g) and a “narrow” pore size distribution (PSD) in a wide range of the Mn/Ce ratio (1/3–3/1). A quasi-molecular dispersion markedly improves oxide-support interactions and reducibility of the active phase. Redox-precipitated systems show a superior performance in the catalytic wet oxidation of phenol with oxygen (CWAO) at 373K in terms of substrate and total organic carbon (TOC) elimination and mineralization (i.e., CO2 formation) selectivity. Carbon mass-balance from TG-DSC data of used catalysts and CO2 selectivity values signal that the CWAO of phenol proceeds via a L–H reaction path, the oxidation of C-containing species being the rate limiting step (r.l.s.). Then, an optimum average pore diameter (APD, 10–15nm) enhances the rate of the adsorption step, while a straight relation between CO2 selectivity and reducibility prove that dispersion and redox properties of the active phase control the mineralization activity of the MnCeOx system.

Activity and leaching features of zinc–aluminum ferrites in catalytic wet oxidation of phenol

A series of ZnFe 2− x Al x O 4 spinel type catalysts prepared by sol–gel method have been characterized and tested for catalytic wet oxidation (CWO) of phenol with pure oxygen. The iron species existed in these materials as aggregated iron oxide clusters and Fe 3+ species in octahedral sites. With a decrease in iron content the concentration of the first iron species decreased and the latter increased. Complete phenol conversions and high chemical oxygen demand (COD) removals were obtained for all catalysts during phenol degradation at mild reaction conditions (160 °C and 1.0 MPa of oxygen pressure). Increasing with the concentration of Fe 3+ species in octahedral sites, induction period became significantly shortened. After phenol was completely degraded, the concomitant recycling of the leaching Fe 3+ ions back to the catalyst surface was observed, and in this case it is possible to perform successful CWO reactions with some cycles. It is also suggested that during the reaction the Fe 3+ cations coordinated in octahedral sites in the ZnFe 2− x Al x O 4 catalysts are resistant to acid leaching, but the reduced Fe 2+ cations become much more labile, leading to increased Fe leaching.

Influence of partial replacement of Cu by Fe on the CWO of phenol in the Cu 0.5− xFe xZn 0.5Al 2O 4 spinel catalysts

The activity and stability of the Cu 0.5− x Fe x Zn 0.5Al 2O 4 spinel type catalysts prepared by sol–gel method were studied in the catalytic wet oxidation of phenol. All catalysts showed high catalytic activity and leach-proof ability. The loss of activity for the catalysts ( x ⩽ 0.25) can be attributed to the elution of the active phase. The cation distribution of the spinel was calculated from XRD and it has been found that the amount of Cu leached ions in CWO reaction decreases with the fraction of Cu ions occupied in the octahedral sites decreasing.

Modeling Catalytic Trickle-Bed and Upflow Packed-Bed Reactors for Wet Air Oxidation of Phenol with Phase Change

In this study, to simulate the steady-state behavior of packed-bed reactors for catalytic wet oxidation of phenol, one-dimensional (1D) axial dispersion model for the liquid phase is coupled with a cell stack model for the gas phase, providing considerable phase change under the selected operating conditions. The reactor scale governing equations, reaction kinetics involved, and solution strategy are discussed. The computational approach accounts for the observed catalyst activities, combined with local transport and catalyst wetting effects. The approach selected is shown to be suitable and efficient in dealing with the problem in question. Comparisons of simulated model predictions and lab scale experimental data are presented. Reasonably simulating the concentration profiles in the reactor at steady-state operation, the model allows designers to determine the effects of catalyst activity and operating and feed conditions on reactor performance. The model also clearly demonstrates the importance of including the phase change effect in the reactor scale flow distribution.

Study of the copper leaching in the wet oxidation of phenol with CuO-based catalysts: Causes and effects

Catalytic wet oxidation of phenol as a model pollutant has been performed in a three phase fixed-bed reactor (FBR) by using a commercial catalyst based on copper oxide in order to analyze the variables affecting significantly the copper leaching. It has been found that temperature has an almost negligible influence in the range studied (70–160°C). On the contrary, an important effect of the pH value was noticed. The copper leaching reduces when the pH of the solution fed to the reactor increases, being almost negligible at pH≥5. Moreover, the composition of the reaction media also influences the leaching. Higher copper concentrations than those expected by the effect of the acid aqueous media have been measured in the reactor effluent when phenol, catechol, hydroquinone, p-benzoquinone and maleic acid are present in the reaction media. On the contrary, oxalic acid has a negative influence on the leaching, since it captures the copper in solution to form copper oxalate which precipitates on the catalyst surface. For a previously acidified medium, the acetic and formic acids do not have any other effect on the copper leaching. It has been also demonstrated that as copper in solution decreases, so does phenol conversion, because the homogeneous catalysis contributes significantly to the oxidation reactions even in fixed-bed reactors.

Kinetic model of wet oxidation of phenol at basic pH using a copper catalyst

Catalytic wet oxidation of phenol employing a commercial copper catalyst has been studied. The pH of the media was maintained in the range 7–8 by using 500 mg/L of sodium bicarbonate as buffer solution. The use of this chemical avoids the copper leaching from the solid catalyst and presents another additional advantage since the organic oxidation intermediates obtained at these basic conditions are far less toxic than phenol. Thus, detoxification of phenolic wastewater is directly linked to the phenol conversion achieved. The kinetic model of the phenol disappearance rate has been discriminated by fitting experimental data. These data have been obtained by feeding a phenol solution of 1000 mg/L to a three phase fixed bed reactor at different catalyst weights to liquid flow rates ratios. Temperature and oxygen pressure were changed in the range from 127 ∘ C to 160 ∘ C and from 8 to 16 bar, respectively. The kinetic model proposed is based on a heterogeneous free radical mechanism which takes into account the scavenger effect of the bicarbonate on the phenoxy radicals formed on the catalyst surface by reduction of the active copper sites. A slight positive influence of the temperature, but no effect of the oxygen pressure has been found on the kinetic equation for phenol oxidation, at least in the ranges studied. These facts can be explained by the free radical mechanism proposed. Besides, a linear relationship was found between phenol and TOC disappearance that allows quite an accurate prediction of the mineralization achieved.

Catalytic wet oxidation of phenol with homogeneous iron salts

AbstractThe catalytic wet oxidation of phenol has been investigated in a 1 L semi‐batch reactor in the presence of both ferrous and ferric salts. Oxidation reactions follow first‐order kinetics with respect to phenol and half‐order kinetics with respect to dissolved oxygen. The activation energy for the reaction was 44.5 and 48.3 kJ mol−1 for runs employing Fe3+ and Fe2+, respectively. Rate constants and induction periods were also similar for both catalysts. This result could be explained by analysing the evolution of iron during the oxidation process. For pH &gt; 2, Fe2+ was rapidly oxidized under reaction conditions to Fe3+, resulting in a unique catalytic redox system Fe2+/Fe3+. It was also shown that if pH &lt; 2 the dissolved oxygen was unable to oxidize ferrous ion, resulting in a much slower oxidation rate of phenol. The absence of a redox pair resulted in a complete lack of catalytic activity of the dissolved iron salt. Copyright © 2005 Society of Chemical Industry