Treatment of dyehouse waste‐water by supercritical water oxidation: a case study

BACKGROUND: Supercritical water oxidation (SCWO) of dyehouse waste‐water containing several organic pollutants has been studied. The removal of these organic components with unknown proportions is considered in terms of total organic carbon concentration (TOC), with an initial value of 856.9 mg L^?1. Oxidation reactions were performed using diluted hydrogen peroxide. The reaction conditions ranged between temperatures of 400–600 °C and residence times of 8–16 s under 25 MPa of pressure. RESULTS: TOC removal efficiencies using SCWO and hydrothermal decomposition were between 92.0 and 100% and 6.6 and 93.8%, respectively. An overall reaction rate, which consists of hydrothermal decomposition and the oxidation reaction, was determined for the hydrothermal decomposition of the waste‐water with an activation energy of 104.12 ( ± 2.6) kJ mol^?1 and a pre‐exponential factor of 1.59( ± 0.5) × 10⁵ s^?1. The oxidation reaction rate orders for the TOC and the oxidant were 1.169 ( ± 0.3) and 0.075 ( ± 0.04) with activation energies of 18.194 ( ± 1.09) kJ mol^?1, and pre‐exponential factor of 5.181 ( ± 1.3) L^0.244 mmol^?0.244 s^?1 at the 95% confidence level. CONCLUSION: Results demonstrate that the SCWO process decreased TOC content by up to 100% in residence times between 8 and 16 s under various reaction conditions. The treatment efficiency increased remarkably with increasing temperature and the presence of excess oxygen in the reaction medium. Color of the waste‐water was removed completely at temperatures of 450 °C and above. Copyright © 2010 Society of Chemical Industry     

Removal of C.I. Basic Blue 41 from aqueous solution by supercritical water oxidation in continuous-flow reactor

Oxidation of aqueous solution of C.I. Basic Blue 41 (BB41), which is model azo dye pollutants, was studied in a continuous-flow reactor that was operated between 400 and 650 °C at a fixed pressure of 25 MPa. The total organic carbon (TOC) concentration of BB41 was in the range of 30.60 and 152.97 mmol/L in the feed stock solution. Hydrogen peroxide (H₂O₂) was used as an oxygen source and the oxidant concentrations were between 73.53 and 489.64 mmol/L in the feed stock solution. The results demonstrated that supercritical water oxidation (SCWO) process decreases the TOC up to 99.87% in very short reaction times (at residence times of 9–19 s). According to the wastewater and oxidant concentrations, the global rate expression was regressed from the complete set of data for each dye solution. As a result of regression analysis, the reaction rate expression for the oxidation of BB41 was determined with the activation energy of 18.88 (±0.9) kJ/mol and the pre-exponential factor of 2.8 (±0.5) mmol^?0.16 L^0.16 s^?1; and the reaction orders for BB41 (based on TOC) and the oxidant were 0.84 (±0.03) and 0.32 (±0.05) in a 95% confidence level.     

Kinetic analysis for decomposition of 2,4-dichlorophenol by supercritical water oxidation

2,4-Dichlorophenol (2,4-DCP), as a halogenated model pollutant, was decomposed by using supercritical water oxidation (SCWO) in a batch reactor made of Hastelloy C-276. SCWO experiments for 2,4-DCP decomposition were performed in the range of 380–420 °C, 230–280 bar and 0.074-0.221 mol/L H₂O₂. The effect of oxidant concentration on decomposition rate and efficiency was significant near the critical temperature of 380 °C. However, the role of the oxidant concentration in the SCWO process decreased with an increase in temperature; also, excess oxidant played a key role in quite significantly decreasing the activation energy of 2,4-DCP oxidation. Variation of the reaction rate by the change of pressure was negligible even at a near critical temperature. The kinetic rate for the decomposition of 2,4-DCP in the SCWO process was well described by a simple first-order kinetic and global reaction rate model. From the SCWO experiments, the various intermediates identified with a GC/MS implied that the first reaction pathway for 2,4-DCP decomposition led to dimers such as dichlorophenoxyphenols, and the second led to single-ring and ring-opening products.     

Supercritical water oxidation of coal: Investigation of operating parameters' effects, reaction kinetics and mechanism

Supercritical water oxidation (SCWO) of coal was conducted in a continuous tubular reactor under various reaction conditions. Our experimental results show that the removal rate of chemical oxygen demand (COD) had no significant dependence on the temperature variations. Effect of residence time was less significant as exceeded fixed values. Free radical mechanism of SCWO reaction may be a possible explanation for the relative low conversion rate of coal at the range of tested oxygen excess. Compared with other parameters, effect of pressure was less significant. A global power-law rate expression was regressed from experimental data. The reaction orders for coal slurry and oxidant were 1.79 and 0.28 respectively. The reaction activation energy E_a was determined to be 112.3 kJ mol⁻¹, and the pre-exponential factor k₀ was 412 (mol/L)^−1.07 s⁻¹. The deviation between the model and experimental data was within ± 9%. Free radical mechanism, oxidation and hydrolysis mechanisms and phenolic hydroxyl oxidation mechanism were considered to be the possible mechanisms for the SCWO process of coal.     

Transformation of propane and CO to carboxylic acid and ester by highly active CaCl2 catalyst

The functionalization reaction of propane with CO to afford carboxylic acids and an ester by CaCl₂ catalyst in the presence of K₂S₂O₈ and CF₃COOH has been studied. The reaction gave isobutyric acid as the main product and n-butyric acid and isopropyl trifluoroacetate as by-products. Atmospheric pressure of propane underwent the reaction with 30 atm of CO pressure at 80 °C for 24 h, giving about 95% total yield based on propane. The activation and thermodynamic parameters have been determined to be E_a = 130.3, 138.0 and 153.8 kJ/mol; A = 7.14 × 10¹³, 5.83 × 10¹⁴ and 5.80 × 10¹⁶ 1/s; ΔH ^‡ = 128.0, 134.7 and 150.5 kJ/mol; ΔS ^‡ = 10.3, 28.6 and 66.8 J/mol K and ΔG^‡ ₂₅₃ = 124.4, 123.9 and 126.9 kJ/mol for the products of isobutyric acid, n-butyric acid and isopropyl trifluoroacetate, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

TNT在超临界水中的氧化反应动力学

利用超临界水氧化(SCWO)实验装置,氧气为氧化剂,对废水中的TNT在超临界水中的氧化反应进行了研究,用幂函数法则建立了COD去除率宏观动力学方程。结果表明,SCWO技术可有效消除废水中的TNT,随着反应温度的升高和停留时间的延长,TNT模拟废水的COD去除率显著增大。在温度为673~823K、压力24MPa、300%过氧量、TNT浓度为5.7×10-4mol/L的实验条件下,有机物的反应级数为1.18,活化能Ea为96.85kJ/mol,指前因子A为4.87×103s-1。     

Kinetics of oxidation of food wastes with H2O2 in supercritical water

In this study, supercritical water oxidation (SCWO) of carrots and beef suet was carried out in a batch reactor system with an H₂O₂ oxidant, at a temperature between 400 and 450°C and reaction times from 10 s to 10 min. The results showed that the oxidative decomposition of carrots and beef suet proceeded rapidly and a high total organic carbon (TOC) decomposition of up to 97.5% was obtained within 3 min at 420°C for carrots and within 5 min at 450°C for beef suet when there was a sufficient supply of oxygen. It was also found that the oxidation reaction for both carrots and beef suet might be separated into a fast reaction at the early stage and a slow reaction at the later stage. In the later stage following the early stage reaction, acetic acid, which is a fairly stable product of the early stage reaction, is the reactant and the rate of overall oxidation reaction for complete decomposition is dominated by the later stage reaction. Global kinetic analysis based on the model described above showed that the early stage oxidative reaction of beef suet could be considered as a first-order reaction with respect to the concentration of organic carbon. The activation energy was 37.3 kJ mol⁻¹. Oxidation of acetic acid could also be expressed as a first-order reaction, and the activation energy was 106.5 kJ mol⁻¹. The early stage oxidation reaction of carrots was too fast to be analyzed. On the basis of intermediate products identified, reaction pathways were discussed. For carrots, polysaccharides may first be hydrolyzed to glucose and then oxidation of the glucose may take place. For beef suet, glyceride is first hydrolyzed to glycerin and carboxylic acids corresponding to the components of glyceride, followed by consecutive reactions for oxidative decomposition.     

Oxidation of a coal particle in flow of a supercritical aqueous fluid

A study was made of the conversion of single spherical coal particles of diameter 1–5 mm in a supercritical H₂O/O₂ fluid with an oxygen mass fraction of 0–6.6% in a semibatch reactor at a pressure of 30 MPa and a temperature of 673–1023 K. A decrease in the particle mass was observed in two parallel processes: gasification of coal with water and oxidation of coal with oxygen. An activation energy 19 ± 7 kJ/mole and a pre-exponential factor 10^−2±0.4 sec⁻¹ were obtained under the assumption of zero order for the concentration H₂O and an Arrhenius dependence for the rate of gasification with water. The oxidation with oxygen at a temperature above 780 K was found to be limited by the rate of O₂ diffusion to the coal organic matter. Below 780 K, the rate of heterogeneous oxidation with oxygen is described by a first-order reaction for the concentration of O₂ and a zero-order reaction for the concentration of H₂O with an activation energy of 150 ± 27 kJ/mole and a pre-exponential factor of 10^7.6±1.9 cm³/(g · sec). __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 23–31, March–April, 2008.     

Thermodynamic features of the Cu-ZSM-5 catalyzed NO decomposition reaction

Over a Cu-ZSM-5 catalyst with a quantified amount of the active Cu²⁺-dimers (Cu²⁺-O^2--Cu²⁺), the kinetics of the catalytic NO decomposition to N₂ and O₂ was derived on the basis of the proposed reaction mechanism, and such thermodynamic data as adsorption enthalpies of NO and O₂ onto the Cu ion dimer sites were evaluated. It was revealed that the enthalpy of the adsorption of NO (δH=-34.1 kcal/mol) onto a reduced Cu⁺-dimer, as the initiating step of NO decomposition catalysis, was higher than that (δH=-27.8 kcal/mol) onto an oxidized Cu²⁺-dimer, or that (δH=-27.4 kcal/mol) of the dissociative adsorption of O₂ onto the two reduced Cu⁺-dimers in neighbor. The strong inhibition effect of gas phase oxygen on the kinetic rate of NO decomposition at 400–600 ‡C could be explained by the thermodynamic predominance of the oxidized Cu²⁺-dimers against the active reduced Cu⁺-dimers on the catalyst even at high temperature and under the low partial pressure of oxygen. It was also found that the maximum catalytic activity at temperatures around 500 ‡C, which was commonly observed in the Cu-ZSM-5 catalyzed NO decomposition reaction, was attributed to the relatively large enthalpy of NO adsorption onto the reduced Cu⁺-dimers as compared to that of the reaction activation energy (=19.5 kcal/mol), resulting in less favored NO adsorption at the higher temperatures than 500 ‡C.     

Synthesis,crystal structure and dehydration kinetics of NaB(OH)<Subscript>4</Subscript>·2H<Subscript>2</Subscript>O

Sodium metaborate tetrahydrate (NaB(OH)₄·2H₂O) was synthesized by reaction of anhydrous borax (Na₂O·2B₂O₃) with sodium hydroxide (NaOH) under conditions at 90 °C for 150 min. The structure was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscope (SEM) and Thermogravimetric (TG) analyses. Moreover, dehydration kinetics of NaB(OH)₄·2H₂O was carried out under non-isothermal conditions and the Coats-Redfern method was applied to analyze the TG data for calculation of activation energies (E _a ) and pre-exponential factors (k _o ) for different heating rates. It was determined that dehydration of sodium metaborate tetrahydrate occurred in five steps. According to the Coats-Redfern non-isothermal model, E _a and k _o were calculated as 50.89 kJ/mol and 26×10⁴ min⁻¹ for region I, 18.51 kJ/mol and 0.87×10³ min⁻¹ for region II, 15.72 kJ/mol and 0.52×10³ min⁻¹ for region III, 4.37 kJ/mol and 0.04×10³ min⁻¹ for region IV and 37.42 kJ/mol and 8.56×10³ min⁻¹ for region V, respectively.     

Sintering Rates for Pristine and Doped Titanium Dioxide Determined Using a Tandem Differential Mobility Analyzer System

Sintering rates of pristine and V-doped TiO ₂ were obtained using a tandem DMA system. A range of experiments were conducted to first map out the variation of mobility size of a monodisperse (by mobility) agglomerate with time at three fixed temperatures. Using relationships of the surface area to the mobility size, the sintering equation was solved to determine the activation energy and pre-exponential factor. The value of the activation energy was 236 (± 46) kJ/mol for pristine TiO ₂ and 363 (± 1) kJ/mol for V-doped TiO ₂ . The corresponding pre-exponential factors were 7.22 × 10 ¹⁹ and 2.22 × 10 ¹² s/m ⁴ K, respectively. These values were then used to predict changes in mobility diameter at different temperatures, and good agreement was obtained with measurements. Possible reasons for faster sintering rates of V-TiO ₂ relative to pristine TiO ₂ were conjectured.     

Intrinsic kinetics of low-temperature oxidation of oil shale kerogen

The kinetics of oxidation of kerogen in the Colorado oil shale were measured using a thermogravimetric analysis technique in a continuously increasing temperature mode. The rate data were analysed based on the assumption that, at the relatively low temperatures at which the kinetics were measured, the oxidation reaction takes place on the surface of solid kerogen and that the decomposition of kerogen is not significant. The oxidation rate was determined to be of first order with respect to oxygen partial pressure. The activation energy of reaction was 11.0 ± 2.3 kJ mol⁻¹, and the pre-exponential factor was (6.8 ± 2.5) × 10⁻⁶ m(kPa · s)⁻¹.     

A DSC study of the polymerization of 2-Vinylpyridine in dimethylformamide

The polymerization of 2-vinylpyridine (2VP) in dimethylformamide (DMF) with azobisisobutyronitrile (AIBN) as initiator was studied with a differential scanning calorimeter. By taking an appropriate amount of AIBN and after correction for its decomposition, the following values could be obtained: Heat of polymerization ΔH_p,o = ?68 ± 4 kJ/mol; overall Arrhenius activation parameters E_a = 90.0 ± 4 kJ/mol and ln A = 24 ± 1.0 (A = 2.6 × 10¹⁰ dm^3/2/mol^1/2. s).     

Thermal decomposition of precursor of SmBiO3 buffer layer for YBCO high-temperature superconducting tape

In order to explore the rapid preparation process of the buffer layer of the high-temperature superconducting tape, the thermal decomposition and the phase formation kinetics of buffer layer precursor were studied. The precursor solution was prepared by using lactic acid as solvent, and nitrates as solutes. The synthesis mechanism of SmBiO₃ phase was determined by the combination of universal integral method, differential method and multi-rate scanning Kissinger method, and the related kinetic parameters were solved. The results show that the thermal decomposition processes of the precursor is divided into two stages from room temperature to 800 °C. The second stage of SmBiO₃ phase synthesis reaction obeys the second order chemical reaction model. The average apparent activation energy and the pre-exponential factor of the synthesis reaction calculated by the integration and the differential methods are 73 kJ/mol and 3.24 × 10⁴/min, respectively.     

Pyrolysis kinetics and characteristics of the mixtures of waste ship lubricating oil and waste fishing rope

Kinetic investigations on the pyrolysis of a mixture of waste ship lubricating oil (WSLO) and waste fishing rope (WFR) were carried out using a thermogravimetric analyzer (TGA) at a heating rate of 0.5 ‡C/min, 1.0 ‡C/min and 2.0 ‡C/min. WSLO and WFR were mainly decomposed at the temperature of range of 400 ‡C to 455 ‡C and 370 ‡C to 410 ‡C, respectively. The WSLO/WFR mixture was mainly decomposed at the temperature range of 300 ‡C and 450 ‡C, which is a lower temperature than that for the WSLO or the WFR alone at each heating rate. The ranges of apparent activation energies of the WALO/WFR mixture were between 137 kJ mol^-1 and 197 kJ mol^-1 at conversions in the range of 10–95%. The mixture of WSLO and WFR was pyrolyzed in a micro-scale tubing reactor at 440 ‡C for 60 min and 80 min. The yield of pyrolyzed gases increased from 2.13 wt% to2.29 wt% with reaction time. The selectivity to C₇ hydrocarbons was shown in the pyrolyzed oil of the mixture.     

NH3 Decomposition Kinetics on Supported Ru Clusters: Morphology and Particle Size Effect

The supported Ru clusters with mean sizes ranging from 1.9 to 4.6 nm showed a high activity towards the NH₃ decomposition reaction. The structural properties of catalysts were characterized by N₂ adsorption/desorption, X-ray diffraction (XRD) and transmission electron micrograph (TEM). Steady-state reaction kinetics revealed that the apparent activation energy increased with a decrease in Ru particle size and ranged from 79 kJ mol⁻¹ to 122 kJ mol⁻¹. The decomposition rate over Ru nanoparticles showed a strong dependency on mean crystallite size and the optimum appeared at d _Ru = 2.2 nm. The dependencies of reaction rate on partial pressures of NH₃ and H₂ were also sensitive to the varying Ru particle size. Experimental data could be well fitted by the Temkin–Pyzhev equation, indicating that the recombinative desorption of surface nitrogen atom acts as the rate-determining step. A compensation effect between the pre-exponential factor (k ₀) and activation energy (E _a ) was quantified.     

Supercritical water oxidation of quinoline in a continuous plug flow reactor—part 1: effect of key operating parameters

This work presents the supercritical water oxidation (SCWO) of quinoline, a nitrogen‐containing organic compound found in pharmaceutical wastewaters, to products that are more readily biodegradable. The effects of the operating variables, namely process temperature, stoichiometric ratio of oxidant to organic, residence time and system pressure were studied in order to optimise quinoline removal efficiency and to investigate the fate of carbon and nitrogen after oxidation. Hydrolysis experiments undertaken in the range 480–650 °C showed no significant degradation of quinoline. The present study confirmed that, as an alternative to incineration, the process is fast and effective in treating quinoline in water, converting it into primarily carbon dioxide (CO₂), water (H₂O) and nitrogen gas (N₂) and to a lesser extent ammonium ions (NH₄⁺). Temperature was shown to be the primary variable in the complete destruction of quinoline and TOC reduction, upon operating at around 250 bars. Essentially, complete quinoline removal was observed above 575 °C and complete TOC removal was obtained at 650 °C, where CO₂ was the main reaction product. Copyright © 2006 Society of Chemical Industry     

Kinetics of the hydroformylation of soybean oil by ligand-modified homogeneous rhodium catalysis

The kinetics and mechanism of the hydroformylation of soybean oil by homogeneous ligand-modified rhodium catalysts were investigated at 70–130°C and 4000–11,000 kPa. The effects of reaction rates on systematic variations in reaction parameters were evaluated in order to develop an industrial process to convert vegetable oils to polyaldehydes. The activation energies in the presence of triphenylphosphine (Ph₃P) (61.1±0.8 kJ/mol) (mean±SD) and triphenyl phosphite [(PhO)₃P] (77.4±5.0 kJ/mol) were determined. The catalyst was deactivated at temperatures higher than 100°C. An evaluation of the effects of the reaction parameters on initial rates yielded the rate laws for Ph₃P {rate=k [olefin][Rh(CO)₂Acac]^1.1 [Ph₃P]^−0.5 (pH₂+pCO)^1.4, where Rh(CO)₂Acac is (acetylacetonato)dicarbonylrhodium (I)} and (PhO)₃P {rate=[olefin] [Rh(CO)₂Acac]^1.2 [(PhO)₃P]^−0.8 (pH₂+pCO)^0.9 at total pressures lower than 7000 kPa, and rate =[olefin] [Rh(CO)₂Acac]^1.2 [(PhO)₃P]^−0.8(pH₂+pCO)^1.7 at total pressures higher than 7000 kPa}.     

A kinetic study of in situ polyaniline–gold composite film formation

Chloroaurate acid (HAuCl₄) was used as an oxidant and aniline (ANI) was used as a reducing agent to prepare a polyaniline–gold (PANI-Au) composite film by in situ polymerization. The formation of the composite film was monitored using a quartz crystal microbalance (QCM). The effects of the concentrations of HAuCl₄ and ANI as well as the reaction temperature on the formation of the PANI-Au composite film are discussed. The kinetics of the reaction were investigated by the QCM technique. The results indicate that the kinetics of the reaction are of order 0.5 with respect to HAuCl₄ and 1.5 with respect to aniline. The film growth rate increased with increasing ANI, HAuCl₄ concentration and reaction temperature. The activation energy calculated from the temperature dependence of the growth rate was 40.32 ± 0.15 kJ/mol. In situ UV-visible spectra of the reaction process were obtained and compared to the reaction process using the QCM technique.     

Decomposition of ozone on Ag/SiO2 catalyst for abatement of waste gases emissions

A silica-supported Ag system made by the incipient wetness impregnation method was investigated in the reaction of heterogeneous catalytic decomposition of ozone. It was established that the catalytic ozone decomposition on Ag/SiO₂ proceeded in the temperature interval −40 °C to 25 °C as a first order reaction with activation energy of 65 kJ/mol (pre-exponential factor 5.0 × 10¹⁴ s⁻¹). Based on the results from the instrumental methods (SEM, XRD, XPS, EPR, TPD) it can be concluded that in presence of ozone the silver is oxidized to a complicated mixture of Ag₂O₃ and AgO. Due to the high activity and stability of the Ag/SiO₂ catalyst, it is promising for neutralization of waste gases containing ozone.