Hydroxyl Radical Oxidation Processes For The Removal Of Triazine From Natural Water

The purpose of this study was to point out processes that can provide triazine oxidation via hydroxyl radical production in a water treatment line. We focus our attention on:

- oxido-flocculation, using Fe²⁺, H₂O₂

- inter-oxidation, using O₃, H₂O₂ and eventually an heterogeneous catalyst.

- disinfection, using UV, O₃ and H₂O₂ combinations.

Results show that triazines can be removed by all these processes with different efficiencies. At full scale, the O₃/H₂O₂ process presents the best performances from an economical and technical point of view.     

Efficient separation scheme for binary mixture of CO2 and H2S using aromatic components

Separating a mixture of CO₂ and H₂S into two products through distillation is both difficult and complicated because of similar relative volatility between the two gasses, particularly when a CO₂ concentration exceeds 80%. Therefore, the separation process can involve many separating stages. However, adding a solvent (agent) to the distillation column during the separation process makes this procedure easier.

In this study, different solvents (ethylbenzene, o-xylene, m-xylene, and toluene) and operating conditions (temperature, pressure, and reflux ratio) for separating CO₂ from H₂S have been simulated through distillation using Aspen HYSYS software. Furthermore, four different aromatic compounds (solvents) for different concentrations (from 0 to 40 mol%) have been evaluated to increase the CO₂/H₂S relative volatility, reducing the quantity of the solvent required and energy consumption.

m-xylene was found to be the best solvent for separating CO₂ from H₂S because of the significant effect on relative volatility, the low quantity required for high CO₂ recovery, and the low energy for generating the solvent.     

SELECTIVE GAS ABSORPTION UNDER PRESSURE

For selective removal of H2S from much larger quantities of CO₂ under pressure, an industrial prototype spray column has been constructed. Sodium hydroxide solution was atomized by a pressure nozzle of special design and entered the scrubber as fine spray to contact the sour gases.

Several operating variables were examined in order to indicate optimal operating conditions for maximum selectivity of H₂S over CO₂. Fine mist and short contact time favor this selective absorption process. An optimum inlet reactant concentration was found dependent upon the H₂S content relative to CO₂ in the inlet sour gas mixture. A special nozzle/shield configuration to avoid contact of sour gas with highly turbulent liquid during droplet formation significantly improved the selectivity.     

CORRELATION FOR DROP SIZE IN LIQUID/LIQUID SPRAY COLUMNS

A single equation is presented which predicts the drop size in liquid/liquid spray columns up to the critical nozzle velocity:

with an average deviation of 9.7%. This can be reduced to 7.3% if two regions are considered separated by a critical nozzle diameter:     

Oxidation of 1,3,5‐trichlorobenzene using advanced oxidation processes

The oxidation of 1,3,5‐trichlorobenzene (TCB) by ozone, ozone/UV, ozone/H₂O₂ and ozone/UV/H₂O₂ was studied. All studies were conducted in a continuously‐flowing completely mixed reactor (CFCMR), operated at steady‐state conditions using a hydraulic retention time of 10 minutes. The greatest removal of TCB using ozone/H₂O₂ treatment was achieved using a H₂O₂ concentration of 60 μM. At low pH values (approx. 2) ozone/UV performed significantly better than either ozone alone or ozone/H₂O₂. However, at circumneutral pH, the removal efficiencies of TCB by ozone/UV and ozone/H₂O₂ and ozone/UV/H₂O₂ were essentially equal (～ 97% for TCB). The removal efficiency of ozone alone was ～93% for TCB. At high pH (> 9) there was no advantage in supplementing ozone with either UV or H₂O₂ as the removal efficiencies for all processes studied were essentially equal.

The effect of humic acid and bicarbonate on the removal of TCB was studied. At 1.6 mg/L humic acid, 92–95% of the TCB was oxidized by the processes studied. The removal of TCB by ozone alone was significantly affected by the presence of bicarbonate ion. For the other processes at 10 mM bicarbonate, approximately 80% of the TCB was oxidized.     

Reactions of ketene dithioacetal for a new versatile synthesis of 4,5-substituted 3-aminothiophene-2-carboxylate derivatives

Poly substituted 3-aminothiophenes were successfully synthesized in good yields by using a one-pot protocol via ketene S,S-acetal as an intermediate in basic medium (K₂CO₃/N,N-dimethylformamide) followed by Dieckmann condensation with ethyl bromoacetate. Further, chemistry of thiophenes was explored using active functional groups such as C₃–NH₂, C₄–CN and C₅–SCH₃ on the thiophene nucleus.

Synthesis of ethyl 3-acetamido-4-cyano-5-(methylthio)thiophene-2-carboxylate derivatives and ethyl 3-amino-4-carbamoyl-5-(methylthio)thiophene-2-carboxylate derivatives.     

Synthesis of Porous Submicron Gd0.1Ce0.9O1.95 Particles by Carbon Nanoparticle-Addition Ultrasonic Spray Pyrolysis (CNA-USP) and Nanoparticle Preparation by Ball Milling

A new ultrasonic spray pyrolysis method, called carbon nanoparticle-addition ultrasonic spray pyrolysis (CNA-USP), is developed to synthesize nanoparticles of electrolyte material for solid oxide fuel cell applications. In CNA-USP, carbon nanoparticles are added in a precursor solution. First, Gd_0.1Ce_0.9O_1.95 (GDC) particles were synthesized from an aqueous solution of Ce(NO₃)₃ 6H₂O and Gd(NO₃)₃ 6H₂O by using the CNA-USP method. The resulting synthesized GDC particles were agglomerated, porous, primary particles on the order of 10 nm in diameter. EDX images revealed uniform distributions of Ce, Gd, and O in these porous particles. Then, these agglomerated, porous submicron GDC particles were ground into primary nanoparticles by ball milling for 24 h. The average diameter of the ground GDC nanoparticles was about double of their average crystallite size.

Copyright 2014 American Association for Aerosol Research     

CHLORINATION KINETICS OF Nb2O5

The reaction of single sintered pellets of α-Nb₂O₅ with chlorine and carbon monoxide was studied in the temperature range from 773 K to 1073 K using a thermogravimetric apparatus. The rate controlling step of the reaction was determined from experiments carried out at variable gas flow rates, gas composition, surface geometry, pellet porosity and temperature. The vapor phase transport reaction can be written as:

Nb₂O₅(s) + 3Cl₂ (g) + 3CO(g) = 2NbOCl₃ (g) + 3CO₂(g).

Up to 60% conversion, the amount of volatilized product was found to be directly proportional to the time of reaction. The external surface area of the pellets remains unchanged up to this stage while the intergranular morphology changes.

These results were compared with reaction rates of commercial pyrochlore concentrate in order to establish the fundamental reaction stages of the process of extraction of Nb₂O₅ from pyrochlore.     

Use Of Static Mixer For Oxidation And Disinfection By Ozone

Ozone is used in drinking water treatment as a biocide, as an oxidant and as a pretreatment in order to improve the performance of subsequent processes. Increasing concern over the quality of drinking water has led to a number of new stringent regulations in the control of chemical and microbiological contaminants. Disinfection deals with the concept of “CT”, which is the need to maintain a certain minimum concentration for a given time. Under ideal laboratory conditions, it is 0.4 mg O₃/L for 4 min. In practice, since the method for the CT determination has not been finalized by the EPA, “T” can be the minimum detention time of 90% of total flow, and “C” can be a measured ozone residual at the outlet of cells of the contactor. New standards for micropollutants in drinking water imply an optimization of the ozonation step, by improving the ozone transfer from gas to water, and the control of the detention time as well as ozone residual within the contactor.

All these considerations have led us to use static mixers to transfer ozone into water. This process enables us to control the ozone concentration in water and detention time. It is a very simple system, with very low maintenance requirements due to the lack of moving parts. Civil engineering is minimized. A pilot scale study is presented here. It took place at the Méry-sur-Oise water treatment plant, on a pilot plant working at 8-12 m³/h. It is composed of a static mixer for the transfer of ozone from gas to liquid, linked to an air lift to separate gas from liquid, providing ozonated water.

The optimization of transfer was achieved by studying the impact of water flow, gas flow and ozone concentration in the gas. It is possible to reach 90% of transfer in less than 15 s. Headloss (ΔP) across the mixer is a function of gas and water flows and remains economically very acceptable as 0.15 bar for 12 m³/h.

Atrazine removal was studied using a static mixer, an air lift and a contact pipe 80-m long, providing an optimum contact time phase, working as a plug flow reactor. Ozone and H₂O₂/O₃ treatments were compared. The maximum reduction of atrazine concentrations (e.g., for an infinite contact time) is a function of the amount of transferred ozone, but H₂O₂ influences the kinetics of the reaction. In the presence of H₂O₂ with a ratio of H₂O₂ to O₃ of 0.4 w/w, maximum elimination is reached in 2 min 30 s.

The effect of such treatments on environmental bacteria also was followed. A counting of total germs at 20°C showed a decrease of 1- to 3-logs 10 after 1 min 30 s of contact time for about 2 mg/L of transferred ozone. No significant difference between treatments with or without H₂O₂ was shown. The same conclusions were obtained from heterotrophic plate counts (37°C) and epifluorescence countings.     

Effect of a Horizontal Inlet on the Collection Efficiency of a Rectangular-Slit-Nozzle Impactor

A horizontal inlet was employed to improve the collection efficiency of a rectangular-slit-nozzle impactor. A numerical and experimental study of the collection efficiency of rectangular-slit-nozzle impactors, with either typical inlets or horizontal inlets, was conducted. In the comparison of typical inlet impactors and horizontal-inlet impactors, parameters such as the nozzle width, impaction plate width, nozzle-to-plate distance, and aerosol flow rate were held constant, and only the inlet shape was changed. A parametric study was conducted to examine the effects of the horizontal inlet dimensions on the collection efficiency of rectangular-slit-nozzle impactors. It was found that a horizontal inlet could reduce the square root of the Stokes number corresponding to the cutoff size from 0.77 to 0.60, compared with a typical inlet.

Copyright 2014 American Association for Aerosol Research     

Comparison of Ozone and Hydroxyl Radical-Induced Oxidation of Chlorinated Hydrocarbons in Water

The efficiency of ozonation and advanced oxidation processes such as ozone/UV, ozone/H₂O₂ and H₂O₂/UV was assessed for chlorinated hydrocarbons using a closed batch-type system. 1,1-Dichloropropene (DCPE), trichloroethylene (TCE), 1-chloropentane (CPA), and 1,2-dichloroethane (DCA) were used as model compounds.

The direct reaction between substrates and ozone predominated at lower pH, which resulted in the efficient oxidation of the olefin, DCPE. At higher pH, ozonation resulted in more efficient oxidation of the chlorinated alkanes, with a corresponding decrease in the efficiency of DCPE oxidation. Consistent results were observed for ozone/H₂O₂ and ozone/UV treatment. Due to slow UV-induced decomposition of H₂O₂, the process using H₂O₂/UV (254 nm) resulted in very slow oxidation of all four compounds.

The total ozone requirement to achieve a given degree of elimination (to 37% of the original concentration), δ0.37, was used to assess the combined effects of the direct and indirect reactions for different types of waters.     

Dynamic Changes in Reactive Oxygen Species in the Shoot Apex Contribute to Stem Cell Death in Arabidopsis thaliana

In monocarpic plants, stem cells are fated to die. However, the potential mechanism of stem cell death has remained elusive. Here, we reveal that the levels of two forms of reactive oxygen species (ROS), superoxide anion free radical (O2·−) and hydrogen peroxide (H₂O₂), show dynamic changes in the shoot apex during the plant life cycle of Arabidopsis thaliana. We found that the level of O2·− decreased and disappeared at four weeks after bolting (WAB), while H₂O₂ appeared at 3 WAB and showed a burst at 5 WAB. The timing of dynamic changes in O2·− and H₂O₂ was delayed for approximately three weeks in clv3-2, which has a longer lifespan. Moreover, exogenous application of H₂O₂ inhibited the expression of the stem cell determinant WUSCHEL (WUS) and promoted the expression of the developmentally programmed cell death (dPCD) marker gene ORESARA 1 (ORE1). These results indicate that H₂O₂ triggers an important signal inducing dPCD in stem cells. Given that O2·− plays roles in maintaining WUS expression and stem cell activity, we speculate that the dynamic shift from O2·− to H₂O₂ in the shoot apex results in stem cell death. Our findings provide novel insights for understanding ROS-mediated regulation during plant stem cell death.     

EFFECT OF CONTAMINANTS ON CRITICAL HEAT FLUX AT LOW PRESSURES

Critical heat flux (CHF) tests were performed to evaluate the effect of dissolved, nonreactive contaminants on low-pressure industrial boilers. These tests were conducted on a 2.38-inch (60.5 mm) I.D. vertical smooth bore tube with nonuniform circumferential heating at pressures between 100 and 500 psia (0.69 and 3.45 MPa). Tests were performed under two water chemistry conditions: clean (less than 1.6 ppm total dissolved solids) and contaminated (greater than 2000 ppm TDS). With all other operating parameters held constant, the following effects of contamination on the steam quality (X) at CHF were determined at the pressures indicated:

At 100 psia (0.69 MPa) X_clean < X_cont

At 300 psia (2.1 MPa) X_clean?X_cont

At 500 psia (3.5 MPa) X_clean > X_cont

The effect of contamination on CHF was found to be a function of pressure, initial contaminant concentration, and the relative steam quality at which CHF conditions occur. These results are compared to data available in the open literature where X_clean is always greater than X_cont. A method for correlating these data is also illustrated.     

IN SITU LEACHING OF URANIUM USING DILUTE SULFURIC ACID AND MOLECULAR OXYGEN

The technical feasibility of in situ uranium leaching using dilute sulfuric acid and molecular oxygen has been assessed and the important process parameters examined by use of laboratory high pressure leaching columns.

The dilute H₂SO₄/O₂ lixiviant was effective in leaching uranium from the ore samples tested. The leaching process was chemical reaction rate limited and can be represented using pseudo first-order kinetics. The leaching rate constant is proportional to the proton concentration of the lixiviant.

Much of the uranium was leached from the ore before decomposition of carbonate minerals by the acid was complete. Acid consumption per pound of U₃O₈ increased sharply as the uranium recovery level exceeded 70%. There appears to be a minimum oxygen pressure for effective uranium leaching. A pressure of 2758 KPa was adequate for the ore samples tested     

Reactivity Studies In The Ozonolysis Of Pollutants Using A Perforated Spinning Disc Reactor To Enhance Mass Transfer

A perforated spinning disc ozone contactor is described with reference to its use as an absorber with simultaneous chemical reaction.

Greatly enhanced mass transfer coefficients k_L are measured whilst simultaneously maintaining low ozone loss. Comparisons of k_L and volumetric coefficient, k_L a values, are made with more conventional packed or bubble columns.

Acetic acid, 2-propanol and 4-nitrophenol, representing a wide reactivity range, are used to elucidate the applicability of rotating contactors in effluent treatment. It has been possible to study the effects of surface activity on mass transfer with subsequent reaction and to generate design data for the next generation of rotating contactors.     

Simulation Of Ozone Transfer In Water. Comparison With A Pilot Unit

A computer simulation of a bubble column is established to determine the residual ozone concentration in the air and the dissolved ozone residual in the water. This study is aimed to improve the control of ozonation systems, both technically and economically.

The program is based on mass balances along the contact column, which take into account the ozone consumption due to both the self-decomposition and the reactions with organic compounds contained in the water. The experimental measurements allow quantification of the ozone concentration in the air at the inlet and outlet of the pilot unit, as well as the dissolved ozone concentration at different heights along the column. A relation between the transfer coefficient, k_La, and the superficial velocity of the ozonated air is established. It is specific to the diffusion characteristics of the pilot unit. The k_La then is reintroduced in the program.

The calculated and the measured values are shown to be similar regarding the transfer yields, the dissolved ozone concentrations at the pilot unit outlet and the profiles of dissolved ozone concentrations along the contact column. Using the program, the influence of the most important parameters of ozonation on the transfer (treatment rates, initial ozone concentration in the air, pH and organic content of the water, k_La values) have been simulated.     

TiO2 nanoparticles prepared by mechanical reduction technique for superior DMFC nanocomposite PVA membranes

TiO₂ nanoparticles (50–80 nm) are produced by simple nanomilling by stirred media mill. Reasonably high purity TiO₂ nanoparticles are observed by inductively coupled plasma atomic emission spectroscopy. Thus, the prepared TiO₂ nanoparticles are applied as inorganic nanofillers for direct methanol fuel cell nanocomposite proton-exchange membranes. Cross-linked sulphonated polyvinyl alcohol is used for membrane preparation. Water uptake and ion exchange capacity of membranes are observed to be enhanced due to increase in concentration of nanoparticles. Very high proton conductivity and extremely diminutive methanol permeability are achieved. In addition, the durability and lifetime is observed to be exceptionally good (>2000 h).

Abbreviations: DW: Deionised water; DLS: Dynamic light scattering; DMFC: Direct methanol fuel cell; DMSO: Dimethyl sufoxide; DSDSBA: 4-formylbenzene-1,3-disulphonic acid disodium salt hydrate; GA: Glutaraldehyde; FTIR: Fourier transform infrared spectroscopy; ICP-AES: Inductively coupled plasma atomic emission spectroscopy; IEC: Ion exchange capacity; MCO: Methanol crossover; MO₂: Metallic oxides; Na-PAA: Sodium-polyacrylic acid; PEM: Proton exchange membrane; PEMFC: Proton-exchange membrane fuel cells; PSD: Particle size distribution; PVA: Poly vinyl alcohol; RH: Relative humidity; SEM: Scanning electron microscopy; SPEEK: Sulphonated poly (ether ether ketone); SPVA: Sulphonated polyvinyl alcohol; SPVA (5%): composite polymer membrane with 5% TiO₂; SPVA (10%): composite polymer membrane with 10% TiO₂; SPVA (15%): composite polymer membrane with 15% TiO₂; TEM: Transmission electron microscope; TG-DSC: Thermo gravimetric differential scanning     

RADIAL FLOW HOLLOW FIBERREVERSE OSMOSIS: EXPERIMENTS AND THEORY

The performance of a hollow fiber reverse osmosis system is studied both theoretically and experimentally. Experiments were carried out for applied pressure ranging from 200 to 400 psig, feed rates varying from 75 to 380 cc/sec and for feed concentrations up to 34,000 ppm of sodium chloride.

A mathematical model is proposed to predict productivity, ?, and product concentration, θ_p. The model involves solving membrane transport equations simultaneously with the hydrodynamic equations. The solubility-diffusion-imperfection, or pore diffusion model, is used to describe solute and solvent transport across the membrane. The axial gradients of shell side concentration, neglected in previous investigations, are taken into account. The differential equations are solved numerically by the 4th Order Runge-Kutta method.

Predicted values of ? and θ_p agree within 8% and 17% respectively, with experimental data over the entire range of operating conditions. However, membrane transport coefficients were found to be concentration dependent.

An approximate analysis shows that the concentration polarization is negligible in present day hollow fiber systems.     

Comparative study: Correlating extraction efficiency for Hg(II), Cd(II), and Pb(II) metal ions with the chelate stability and total hardness in simple nitrogen donors

Four N-donors (PHDA, ATPH, APHO, and MTAN) containing NH₂ were used to extract Hg(II), Cd(II), and Pb(II). Their extraction capacity was determined by measurement of percentage extraction.

The chelates extract these metals differently: for example, efficiency of ATPH was the highest for Hg(II) compared to PHDA, APHO, and MTAN.

The extraction efficiency was found to depend on: donor atom hardness, chelate total hardness, metal: chelate mole ratio and substituent’s electronic effects. Among all, total hardness and chelate stability are key factors and molecule of small (E_HOMO – E_LUMO) is more reactive, where extraction efficiency increases as molecular stability decreases.     

Online Characterization of Syngas Particulates Using Aerosol Mass Spectrometry in Entrained-Flow Biomass Gasification

Entrained flow gasification is a promising technique where biomass is converted to a synthesis gas (syngas) under fuel-rich conditions. In contrast to combustion, where the fuel is converted to heat, CO₂, and H₂O, the syngas from gasification is rich in energetic gases such as CO and H₂. These compounds (CO and H₂) represent the building blocks for further catalytic synthesis to chemicals or biofuels. Impurities in the syngas, such as particulates, need to be reduced to different levels depending on the syngas application. The objective of this work was to evaluate the amount of particulates; the particle size distribution and the particle composition from entrained flow gasification of pine stem wood at different operating conditions of the gasifier. For this purpose, online time resolved measurements were performed with a soot particle aerosol mass spectrometer (SP-AMS) and a scanning mobility particle sizer (SMPS). The main advantage of SP-AMS compared to other techniques is that the particle composition (soot, PAH, organics, and ash forming elements) can be obtained with high time resolution and thus studied as a direct effect of the gasifier-operating conditions. The results suggest that syngas particulates were essentially composed of soot at these tested process temperatures in the reactor (1200–1400°C). Furthermore, the AMS analysis showed a clear correlation between the amounts of polycyclic aromatic hydrocarbons (PAH) and soot in the raw syngas. Minimization of soot and PAH yields from entrained flow gasification of wood proved to be possible by further increasing the O₂ addition.

Copyright 2014 American Association for Aerosol Research