Catalytic wet air oxidation of phenol in concurrent downflow and upflow packed-bed reactors over pillared clay catalyst

Synthesis, Characterization of Magnetic Composites and Testing of Their Activity in Liquid-Phase Oxidation of Phenol with Oxygen

The development and improvement of methods for the synthesis of environmentally friendly catalysts based on base metals is currently an urgent and promising task of modern catalysis. Catalysts based on nanoscale magnetite and maghemite have fast adsorption–desorption kinetics and high chemical activity. The purpose of this work is to obtain magnetic composites, determine their physicochemical characteristics and verify their activity in the process of liquid-phase oxidation of phenol with oxygen. Magnetic nanocomposites were obtained by chemical co-deposition of salts of ferrous and trivalent iron. The synthesized magnetic composites were studied by X-ray diffractometry, energy dispersive X-ray fluorescence and Mössbauer spectroscopy, IR-Fourier spectroscopy and elemental analysis. To increase the catalytic activity in oxidative processes, the magnetite surfaces were modified using cobalt nitrate salt. Further, CoFe2O4 was stabilized by adding polyethylenimine (PEI) as a surfactant. Preliminary studies of the oxidation of phenol with oxygen, as the most typical environmental pollutant were carried out on the obtained Fe3O4, CoFe2O4, CoFe2O4/PEI catalysts. The spectrum of the reaction product shows the presence of CH in the aromatic ring and double C=C bonds, stretching vibrations of the C=O groups of carbonyl compounds; the band at 3059 cm−1 corresponds to the presence of double C=C bonds and the band at 3424 cm−1 to hydroquinone compounds. The band at 1678 cm−1 and the intense band at 1646 cm−1 refer to vibrations of the C=O bonds of the carbonyl group of benzoquinone. Peaks at 1366 cm−1 and 1310 cm−1 can be related to the vibrations of C–H and C–C bonds of the quinone ring. Thus, it was demonstrated that produced magnetic composites based on iron oxide are quite effective in the oxidation of phenol with oxygen.

Comparative evaluation of synthesis routes of Cu/zeolite Y catalysts for catalytic wet peroxide oxidation of quinoline in fixed-bed reactor

In order to find a better alternative of conventional aqueous ion-exchange method, several Cu/zeolite Y samples were synthesized by different routes and examined for the catalytic wet peroxide oxidation of quinoline aqueous solution in continuous fixed-bed reactor. The characterization of catalysts using ICPMS, XRD, N₂ sorption, UV-vis DRS, FESEM and XPS techniques reveals the profound influence of preparation methods on synergy between copper-support interfaces. Aqueous ion-exchange (CuY_AIE) and wet-impregnation (CuY_IMP) methods promoted isolated Cu^1+/2+ species; however, large crystallites of CuO were present on the external surface of precipitation-impregnation (CuY_PI) catalyst. Interestingly, CuY_PI showed hierarchical porosity and increase of surface area from 567 to 909 m² g^-1. The generation of mesoporosity in CuY_PI was result of higher desilication from zeolite framework due to synergetic effect of copper and NaOH. Almost comparable mineralization (61-65%) and H₂O₂ stoichiometric efficiencies (44.2-45.7%) were observed for CuY_AIE and CuY_IMP samples. Higher catalytic activities of both catalysts in comparison to CuY_PI suggest that isolated sites are the most redox-active sites for H₂O₂ activation and play more important role than high surface area, i.e., for CuY_PI. Wet-impregnation was found better than aqueous ion-exchange method. CuY_IMP exhibited high operation stability with >60% mineralization at LHSV = 4 h^-1, particle size = 1.2-1.7 mm, H₂O₂/quinoline = 48 and T = 80 °C. Copper leaching was majorly influenced by LHSV and particle size. The system was following Eley-Rideal mechanism and kinetic parameters were calculated using model based on this mechanism.

Removal of organic phosphorus and formaldehyde in glyphosate wastewater by CWO and the lime-catalyzed formose reaction

Glyphosate (PMG) wastewater with 40-600 mg/L organic phosphorus (OP) and 1-4% CH2O was treated by catalytic wet oxidation (CWO) and the lime-catalyzed formose reaction to remove total phosphorus (TP) and improve biodegradability. Activated carbons (ACs) modified by H2O2 oxidation and thermal treatment with melamine were used as CWO catalysts and characterized by N2 adsorption/desorption and XPS. The CWO experiments were performed in an autoclave reactor at 110-130 °C and 1.0 MPa. The modified AC showed higher catalytic activity than the parent AC due to the introduction of nitrogen-containing functional groups, exhibited over 90% OP removal for various real PMG wastewaters, and had good stability for 20 consecutive CWO runs. The CWO effluents were further treated by lime at 80 °C to remove TP and CH2O. The treated effluents, containing 0.5-12 mg/L TP and 20-60 mg/L CH2O, showed good biodegradability with a BOD5/COD ratio of 0.31-0.41. The combination of CWO and lime is an effective treatment method prior to biological treatment for solving the problems of OP and CH2O encountered by the glyphosate industry.

Applicability of fluidized bed reactor in recalcitrant compound degradation through advanced oxidation processes: a review

Treatment of industrial waste water (e.g. textile waste water, phenol waste water, pharmaceutical etc) faces limitation in conventional treatment procedures. Advanced oxidation processes (AOPs) do not suffer from the limits of conventional treatment processes and consequently degrade toxic pollutants more efficiently. Complexity is faced in eradicating the restrictions of AOPs such as sludge formation, toxic intermediates formation and high requirement for oxidants. Increased mass-transfer in AOPs is an alternate solution to this problem. AOPs combined with Fluidized bed reactor (FBR) can be a potential choice compared to fixed bed or moving bed reactor, as AOP catalysts life-span last for only maximum of 5-10 cycles. Hence, FBR-AOPs require lesser operational and maintenance cost by reducing material resources. The time required for AOP can be minimized using FBR and also treatable working volume can be increased. FBR-AOP can process from 1 to 10 L of volume which is 10 times more than simple batch reaction. The mass transfer is higher thus the reaction time is lesser. For having increased mass transfer sludge production can be successfully avoided. The review study suggests that, optimum particle size, catalyst to reactor volume ratio, catalyst diameter and liquid or gas velocity is required for efficient FBR-AOP systems. However, FBR-AOPs are still under lab-scale investigation and for industrial application cost study is needed. Cost of FBR-AOPs highly depends on energy density needed and the mechanism of degradation of the pollutant. The cost of waste water treatment containing azo dyes was found to be US$ 50 to US$ 500 per 1000 gallons where, the cost for treating phenol water was US$ 50 to US$ 800 per 1000 gallons. The analysis for FBR-AOP costs has been found to depend on the targeted pollutant, degradation mechanism (zero order, 1st order and 2nd order) and energy consumptions by the AOPs.

Novel Na₂Mo₄O₁₃/α-MoO₃ hybrid material as highly efficient CWAO catalyst for dye degradation at ambient conditions

We report a novel hybrid material Na2Mo4O13/α-MoO3 as highly efficient catalytic wet air oxidation (CWAO) catalyst, which showed the highest ever activity at room temperature and atmosphere pressure for the degradation of cationic red GTL. SEM and TEM analyses indicated that this hybrid catalyst has bamboo-shaped nanofiber morphology. In view of practical applications, the influence of some key parameters including operation temperature, catalyst calcination temperature, and the volume of dye wastewater have been optimized. The mechanism for the superior catalytic performance was investigated. XRD, XPS, and ESR suggested the Na2Mo4O13/α-MoO3 hybrid catalyst possesses more O(2-) ions in the oxygen deficient regions than neat α-MoO3, promoting the formation of active ·OH radicals and resulting in a higher activity. Considering the facile preparation and its superior activity, this novel catalyst is promising for practical dye wastewater treatment.

CuO impregnated activated carbon for catalytic wet peroxide oxidation of phenol

This paper presents an original approach to the removal of phenol in synthetic wastewater by catalytic wet peroxide oxidation with copper binding activated carbon (CuAC) catalysts. The characteristics and oxidation performance of CuAC in the wet hydrogen peroxide catalytic oxidation of phenol were studied in a batch reactor at 80 degrees C. Complete conversion of the oxidant, hydrogen peroxide, was observed with CuAC catalyst in 20 min oxidation, and a highly efficient phenol removal and chemical oxygen demand (COD) abatement were achieved in the first 30 min. The good oxidation performance of CuAC catalyst was contributed to the activity enhancement of copper oxide, which was binding in the carbon matrix. It can be concluded that the efficiency of oxidation dominated by the residual H2O2 in this study. An over 90% COD removal was achieved by using the multiple-step addition in this catalytic oxidation.

Elimination of phenol and aromatic compounds by zero valent iron and EDTA at low temperature and atmospheric pressure

This work deals with a new abiotic oxidation process designed as a suitable pre-treatment step within a biological depuration of wastewater containing phenol or its derivatives (o-cresol, 2-chlorophenol and p-nitrophenol) or aniline. The reaction was carried out in a stirred tank reactor at 20 degrees C and atmospheric pressure in presence of the organic compound, 150mgl(-1), zero valent iron particles (10g), ethylenediamine tetraacetic acid (EDTA, 101mgl(-1)) and air. The experimental results show that 85% of phenol conversion can be achieved after 360min. 2-Chlorophenol was found to be more easily degradable and it is completely eliminated after 300min. The oxidation of o-cresol and aniline behaved more closely to phenol obtaining after 360min 70% and 68% of conversion respectively. p-Nitrophenol was a very refractory compound, giving only 28% of conversion after 360min. Moreover, the influence of some operating variables was studied over the following ranges: temperature from 20 to 50 degrees C, initial phenol concentration from 150 to 1000mgl(-1), EDTA concentration from 50 to 200mgl(-1) and iron particles from 5 to 20g. As expected, temperature strongly enhances phenol conversion. Also, an increase of the catalyst to phenol ratio or the iron or EDTA to phenol ratio improves the reaction rate. A preliminary kinetic analysis of the data shown that the rate of phenol disappearance is not first order with respect to the phenol.