Reaction Kinetics Of Degradation Research Articles

Gas phase photocatalysis and liquid phase photocatalysis: Interdependence and influence of substrate concentration and photon flow on degradation reaction kinetics

The photocatalytic degradation of metolachlor in water and butyric acid in air on coated TiO2 has been investigated to study the interdependency on the degradation rate of the UV photon flux and the concentration of the organic compound. Experimental results clearly showed that the kinetic change of order with respect to light intensity depended on the value of the concentration of organic compound. The fitting of experimental results with the Langmuir–Hinshelwood (L-H) model emphasized that the corresponding “apparent adsorption constant”, KR, could not be considered as an equilibrium constant in the dark since the value of KR varied with regard to the photon flow. The assumption of a pseudo-steady-state for the concentration of hydroxyl radicals associated either with L-H model (under certain conditions) or Eley–Rideal model explains consistently the dependence of the apparent kinetic parameter, kobs, and KR with the light intensity. A rate expression taking into account the interdependency of the degradation rate on the UV photon flux and the initial concentration of the organic compound is proposed and validated for a liquid and a gas phase reaction. The constants of this correlation are independent of the initial concentration and light intensity.

Degradation of environmental endocrine disruptor di-2-ethylhexyl phthalate by a newly discovered bacterium, Microbacterium sp. strain CQ0110Y

In this study di-2-ethylhexyl phthalate (DEHP)-degradation strain CQ0110Y was isolated from activated sludge. According to the biophysical/biochemical characteristics and analysis of 16S rDNA, the strain was identified as Microbacterium sp. The results of this study showed the optimal pH value and optimal temperature which influenced the degradation rate in wastewater: pH 6.5-7.5, 25-35 degrees C. Kinetics of degradation reaction had been performed at different initial concentrations and different time. Analyzed with SPSS10.0 software, the DEHP degradation can be described as the same exponential model when the initial DEHP concentration was lower than 1,350 mg/l. The kinetics equation was ln C = -0.4087t + A, with the degradation half life of DEHP in wastewater (1.59 days). To the best of our knowledge, this is the first reported case of DEHP degradation by Microbacterium sp. strain.

Formaldehyde degradation by UV/TiO 2/O 3 process using continuous flow mode

The degradation of formaldehyde gas was studied using UV/TiO 2/O 3 process under the condition of continuous flow mode. The effects of humidity, initial formaldehyde concentration, residence time and ozone adding amount on degradation of formaldehyde gas were investigated. The experimental results indicated that the combination of ozonation with photocatalytic oxidation on the degradation of formaldehyde showed a synergetic action, e.g., it could considerably increase decomposing of formaldehyde. The degradation efficiency of formaldehyde was between 73.6% and 79.4% while the initial concentration in the range of 1.84–24 mg/m 3 by O 3/TiO 2/UV process. The optimal humidity was about 50% in UV/TiO 2/O 3 processs and degradation of formaldehyde increases from 39.0% to 94.1% when the ozone content increased from 0 to 141 mg/m 3. Furthermore, the kinetics of formaldehyde degradation reaction could be described by Langmuir-Hinshelwood model. The rate constant k of 46.72 mg/(m 3-min) and Langmuir adsorption coefficient K of 0.0268 m 3/mg were obtained.

A novel method for producing hydrogen based on the Ca–Br cycle

The Ca–Br cycle is a promising method for efficiently producing hydrogen from water; however, it suffers from limitations inherent to gas–solid reactions. The cycle depends on the repeatable transformation of calcium bromide to calcium oxide and back to calcium bromide. The use of pure solids for these reactions would lead to rapid particle degradation and slow reaction kinetics. To circumvent these problems, a new reactor concept based on molten calcium bromide with dissolved calcium oxide has been proposed and developed. Preliminary experimental results indicate that the solubility of calcium oxide in calcium bromide at 800 °C is at least 1.2 wt%, a level that is expected to be high enough to make the proposed process work as designed. Early attempts to hydrolyze molten calcium bromide indicated that solid calcium oxide formation may inhibit reactivity, and thus injection of the moisture into the salt must be optimized.

Bioremediation of environmental endocrine disruptor di- n-butyl phthalate ester by Rhodococcus ruber

In this study DBP-degradation strain CQ0301 was isolated from rubbish landfill soil. According to the biophysical, biochemical characteristics and analysis of 16S rRNA, the strain was identified as Rhodococcus ruber. Three new protein bands could be fractioned after DBP-inducing, which were suspected to participate the process of DBP-degrading. Catechol was suspected to be an intermediate product of DBP and cleaving the benzene ring was catalyzed by catechol 1,2-dioxygenase, because a highly activity of catechol 1,2-dioxygenase could be detected after DBP-inducing. The results of this study also showed the optimal pH value, optimal temperature which influenced the degradation rate in soil: pH 7.0–8.0, 30–35 °C. Kinetics of degradation reaction had been performed at different initial concentration and different time. Analyzed with SPSS10.0 software, the DBP degradation can be described as the same exponential model when the initial DBP concentration was lower than 50 mg/kg. The kinetics equation was ln C = −0.1332 t + A, with the degradation half-life of DBP in soil (5.20 d). Inoculating CQ0301 could relieve DBP content in plant. We also found that adding nutrient materials into soil was useful for decreasing the DBP content in plant. In summary, we isolated a bacterium capable of degrading DBP and decreasing DBP content in plant. We also explored the mechanism of biodegradation and characterized the environmental factors influencing the degradation process in contaminated soil. Based on this work, we hope that these findings can provide some information for applying of bioremediation of DBP contaminated soil.

Retention of Ascorbic Acid during Drying of Tomato Halves and Tomato Pulp

The objective of this study was to determine a mathematical model for the reaction kinetics of ascorbic acid degradation to describe the rate of vitamin C loss in a drying process of tomato halves or tomato pulp. Tomato samples with different moisture contents were heated at specified temperatures for different time periods. The kinetics of ascorbic acid degradation followed a first-order reaction with a reaction rate constant dependent on product moisture content, in addition to temperature. Furthermore, there was a maximum rate constant when the moisture content of tomato samples was between 65 and 70%. These effects were expressed by a linear relationship between temperature, moisture content, and natural logarithm of rate constant. The model was used to simulate the vitamin C loss during drying of tomato halves and two drying processes of tomato pulp—evaporative concentration and spray drying. It was concluded that there was a close agreement between the experimental and predicted values of ascorbic acid loss during the tomato pulp concentration, confirming the validity of the proposed model for this process. However, for the spray-drying process and the tomato halves drying a correction coefficient was introduced in the model due to more intense exposure of the product surface to air.

Kinetics of MB degradation and effect of pH on the photocatalytic activity of MIn2O4 (M = Ca, Sr, Ba) under visible light irradiation

Degradation of Methylene Blue (MB) on MIn2O4 (M = Ca, Sr, Ba) semiconductors was observed and the analysis of the products confirmed that MB was decomposed other than simply bleached on these photocatalysts under visible light irradiation. The activity order under visible light irradiation was CaIn2O4 > SrIn2O4 > BaIn2O4. The reaction kinetics of MB degradation on MIn2O4 was investigated, suggesting that these reactions followed approximately first-order kinetics. Furthermore, the effects of pH value of the solution on the photocatalytic properties of these materials were observed in detail, which indicated that the decomposition efficiency of MB was the highest in the alkaline solution and the lowest in the acidic solution on all of the photocatalysts.

Reusable adsorbents for dilute solution separation. 6. Batch and continuous reactors for the adsorption and degradation of 1,2-dichlorobenzene from dilute wastewater streams using titania as a photocatalyst

Two types of external lamp reactors were investigated for the titania catalyzed photodegradation of 1,2-dichlorobenzene (DCB) from a dilute water stream. The first one was a batch mixed slurry reactor and the second one was a semi-batch reactor with continuous feed recycle with titania immobilized on inert supports (quartz and low density polyethylene, LDPE). The batch reactor was used to study the intermediates and reaction kinetics of DCB degradation. Four intermediate products were observed in the degradation of DCB; these being 2-chlorophenol (CP), 2,3-dichlorophenol (DCP), 1,2-dihydroxybenzene (catechol) and, o-benzoquinone. A mechanism based on these observations is proposed. Increasing the pH of the solution increased the intial rate of photodegradation of DCB. Added oxidant (hydrogen peroxide) did not have any appreciable effect on the degradation of DCB. The Langmuir–Hinshelwood kinetic parameters for DCB, DCP and CP were obtained. The steady state removals and apparent rate constants were obtained for the plug-flow reactor with different supports and compared under similar conditions. The titania supported on LDPE showed a better rate of photocatalysis than titania supported on quartz, although the titania film thickness on LDPE was five times lower than on quartz. The modification of titania surface by adsorption of a non-photodegradable polyfluorinated surfactant vastly improved the rate of DCB degradation on both LDPE and quartz. The rate of photodegradation in the immobilized tubular reactor was mass transfer controlled for the flow regimes investigated, viz., Reynolds numbers, Re<550. The steady state removal was directly proportional to the radiant flux within the range 4–16 mW cm−2.

Comparison of Ozone-based and other (VUV and TiO2/UV) Radical Generation Methods in Phenol Decomposition

The degradation reaction kinetics and chemical mechanism of phenol decomposition by ozonation, TiO2-photocatalysis and vacuum ultraviolet (VUV) photolysis were investigated. The concentration dependences of the aromatic and aliphatic intermediates and the TOC content were compared as a function of the phenol conversion. The concentration profiles and the TOC curves obtained with each method were very similar. The results suggest a similar chemical mechanism for the transformation of phenol irrespective of the starting active component (a positive hole on the surface of the catalysts, a VUV photon, ozone or the hydroxyl radical).

Sonochemical degradation for toxic halogenated organic compounds

This paper describes the degradation of p-chlorophenol using three different ultrasonic devices. The dissipated power in the reaction matrix was measured based on calorimetric method. The study showed that hydrogen peroxide can improve the sonochemical reaction and gases dissolved in reaction matrix can affect the process to a small extent. The reaction mechanism and kinetics of degradation were also investigated.

Reaction kinetics and X‐ray Absorption Spectroscopy Studies of Yttrium‐Containing Metal Hydride Electrodes

This is a study of electrode degradation mechanisms and reaction kinetics of , ( x = 0.1, 0.2, and 0.3) and metal hydride electrodes. Alloy characterization included X‐ray diffraction, X‐ray absorption (XAS), hydrogen absorption in a Sieverts apparatus, and electrochemical cycling of alloy electrodes. The atomic volume of H was determined for two of the alloys. Electrochemical kinetic measurements were made using steady‐state galvanostatic measurements, galvanodynamic sweeep, and electrochemical impedance techniques. XAS was used to examine the degree of corrosion of the alloys with cycling. Alloying with Y decreased the corrosion rate. The results are consistent with corrosion inhibition by a Y‐containing passive film. The increase in the exchange current density of the hydrogen oxidation reaction with increasing depth of discharge was much greater on the Y‐containing alloys. This may be due to the dehydriding of the catalytic species on the surface of the metal hydride particles. © 1999 The Electrochemical Society. All rights reserved.

Alteration in sewage characteristics upon aging

To improve the understanding of the nature of sewage changes upon aging during transport or storage, simulation experiments were conducted using batch reactors under a number of well defined conditions, i.e. anaerobic, aerobic and micro-aerophilic at 10°C, 20°C and 30°C. Important characteristics of the studied sewage were the visual appearance, various chemical properties and odour. The effect of temperature on the degradation processes and reaction kinetics of different polluting fractions of the sewage is studied under mainly micro-aerophilic and anaerobic conditions. The results of non-inoculated batch simulating experiments reveal that micro-aerophilic conditions are suitable for both pre- and post-treatment of sewage, while anaerobic conditions will suffice for pre-treatment. At low temperatures, anaerobic conditions mainly serve for pre-acidification. On the basis of the results obtained, we recommend putting emphasis on further research dealing with on-site and on-line treatment systems, combined with a central wastewater treatment plant. Such processes look attractive in improving the organic removal efficiency and in reduction of operating cost and capital outlay of wastewater treatment systems.

Alteration in sewage characteristics upon aging

To improve the understanding of the nature of sewage changes upon aging during transport or storage, simulation experiments were conducted using batch reactors under a number of well defined conditions, i.e. anaerobic, aerobic and micro-aerophilic at 10°C, 20°C and 30°C. Important characteristics of the studied sewage were the visual appearance, various chemical properties and odour. The effect of temperature on the degradation processes and reaction kinetics of different polluting fractions of the sewage is studied under mainly micro-aerophdic and anaerobic conditions.The results of non-inoculated batch simulating experiments reveal that micro-aerophilic conditions are suitable for both pre- and post-treatment of sewage, while anaerobic conditions will suffice for pre-treatment. At low temperatures, anaerobic conditions mainly serve for pre-acidification. On the basis of the results obtained, we recommend putting emphasis on further research dealing with on-site and on-fine treatment systems, combined with a central wastewater treatment plant. Such processes look attractive in improving the organic removal efficiency and to reduction of operating cost and capital outlay of wastewater treatment systems.

A fibre-optic oil condition monitor based on chromatic modulation

A novel optical fibre sensor has been developed for on-line monitoring of oil quality within industrial equipment. The monitoring is based on chromatic modulation because of the inherent self-referencing demonstrated by this technique. The sensor is shown to exhibit long-term stability and is capable of operating up to a temperature of 120 degrees C. Several industrial oils have been examined using the sensor, and typical modulation depths of 20% were obtained with resolution in the range of 0.1%. This is sufficient to record some interesting physical and chemical changes related to the reaction kinetics of oil degradation. The sensor is also capable of detecting oil leaks within a system since it can distinguish between the chromaticities of oil and air.

Effects of pH and Temperature on Reaction Kinetics of Catechins in Green Tea Infusion

Stability of tea catechins during heat processing was examined. Effects of pH and temperature on reaction kinetics of degradation of tea catechins were investigated. Reaction of – EC was accelerated at pH higher than 6.0, inhibited at those lower than 5.0. A dominant reaction of – EC in slightly acidic media was isomerization. The apparent first order reaction proceeded in slightly acidic media under sterilization conditions. A similar reaction proceeded for – EC, – EGC, – ECg, and – EGCg in green tea infusion at temperatures below 95°C. A turning point temperature on an Arrhenius plot was observed at 82°C. A great difference of apparent activation energies was observed lower and higher than 82°C. The reaction rate constant of catechins in slightly acidified tea infusion was less than half as much as the constant in the original infusion. The stability of catechins in green tea infusion was subject to the turning point temperature.

Parameters affecting process efficiency of peroxide‐initiated controlled degradation of polypropylene

AbstractParameters affecting the process efficiency of the peroxide‐initiated controlled degradation of polypropylene, such as concentration of peroxide, reaction temperature, and reaction time, are investigated under in situ uniform, microsegregation, and macrosegregation conditions. Reactions were carried out under static (no mixing) and dynamic conditions on model samples and samples processed in batch mixers, respectively. As expected, MW and MWD decrease with increasing peroxide concentration. Low‐ and mid‐MW fractions increase at the expense of the high‐MW fractions. Localization of peroxide occurs under macrosegregation conditions and causes overall loss of peroxide efficiency and side reactions. MW and MWD undergo no further change after three to four times the half‐life of the peroxide. A kinetic model developed using the quasisteady‐state approximation on free radicals successfully simulates the degradation reaction kinetics for peroxide uniformly mixed. The method of moments is used to calculate the molecular weight averages. The results of this work confirm the importance of mixing uniformity as a parameter controlling the product characteristics in reactive processing.

KINETICS of METHYLMETHIONINE SULFONIUM IN BUFFER SOLUTIONS FOR ESTIMATING THERMAL TREATMENT of LIQUID FOODS

Reaction kinetics of MMS degradation in sodium citrate buffer solutions followed a first order reaction kinetics in the temperature range of 121.1°C-132.2°C and the pH range of 4 to 6. Reaction rate constant ranged from 0.1260 to 1.1003 min−1 and the corresponding D-values varied from 18.28 min to 2.09 min depending on the pH and temperature. Activation energy (117.1 - 135.4 kJ/mole or Z-values (22.8 - 20.0°C) were slightly dependent on pH. the kinetic data was used for estimating potential decimal reduction in B. Stearothermophilus spores.

Electrochemistry of Conductive Polymers: VI . Degradation Reaction Kinetics of Polyaniline Studied by Rotating Ring‐Disk Electrode Techniques

The degradation reaction kinetics of oxidized polyaniline has been studied employing rotating ring‐disk electrode techniques. Polyaniline films were grown on the disk electrode and were then oxidized at a potential more positive than 0.90V vs. , while the degradation product (benzoquinone) was monitored at the ring electrode at an applied potential of 0.05V. The product was monitored either with the disk potential maintained at >0.90V (closed‐circuit experiment) or with the disk circuit disconnected after the polyaniline film was oxidized for some time (open‐circuit experiment). The results of closed‐circuit experiments indicate that electrochemical generation of oxidized polyaniline was a limiting step and its rate decayed for a given amount of polyaniline film according to the zeroth order. The rate of hydrolysis for the oxidized polyaniline in quinonoid forms was determined to be consecutive first order from open‐circuit experiments. The dependencies of the hydrolysis reaction on the acidity of the degradation medium and sulfate concentrations have also been studied; the results are consistent with the Schiff base hydrolysis mechanism.

Chromatographic study of reaction kinetics of formation and degradation of polyamido acid

1. The kinetics of the formation and aging of poly(4,4′-hydroxydiphenylene)pyrromellitamido aeid were studied by chromatography. 2. The rate constants of the basic reactions comprising the process, determined from the kinetic data, agree with the values obtained by other methods.

Contribution au Probleme de la Corrosion et du Vieillissement des Plastiques

AbstractWith frequent reference to the recent Russian book by M. B. Neiman, Aging and Stabilization of Polymers, the authors show that the important advances made in the field are based upon knowledge of the reaction kinetics of degradation by heat, oxidation, photooxidation, hydrolysis, and mechanochemical action. The synergy in the effects of these factors and in the search for economical mixtures of stabilizers and anti‐oxygens is illustrated by numerous examples. Bell‐shaped curves are considered, showing the rise from zero to a maximum and the subsequent return to zero, concerning the daily variation of total radiation and its seasonal variations at various latitudes. The energy distributions between ultraviolet, visible, and infrared are also given. The standardization of a radiation hydrothermal cycle, taking into account the extremes of temperature and of relative humidity encountered in moderate and tropical climates, is considered. Special cycles are suggested for arctic and desert climates. The authors give an example of a cycle and a prototype of climatizer, using a triphare or xenon source capable of establishing such cycles, with the possibility of applying a mechanical stress under various conditions. The correlation between natural and artificial aging is discussed.