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Kinetics Study (kinetics + study)
Selected AbstractsFormation Mechanism of Hydrous Zirconia Particles Produced by the Hydrolysis of ZrOCl2 Solutions: III, Kinetics Study for the Nucleation and Crystal-Growth Processes of Primary ParticlesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2001Koji Matsui The formation rate and primary particle size of monoclinic, hydrous zirconia particles produced by the hydrolysis of various ZrOCl2 solutions (with and without the addition of HCl, NH4OH, NaCl, CaCl2, or AlCl3) were measured to clarify the effects of the H+ and Cl, ion concentrations on the nucleation and crystal-growth processes of primary particles of hydrous zirconia. Chemical-kinetic analyses, to which Avrami,Erofeev's equation was applied, and XRD measurements revealed that both the rate constant and the primary particle size of the hydrous zirconia decreased as the concentrations of H+ and/or Cl, ions produced by hydrolysis increased. The nucleation rate per unit of ZrOCl2 concentration and the crystal-growth rate of the primary particles of the hydrous zirconia were determined by analyzing the relationships between the rate constant and primary particle size. The nucleation rate per unit of ZrOCl2 concentration revealed almost no change and remained constant as the H+ and/or Cl, ion concentrations increased, except in the case of a slight increase for ZrOCl2 solutions with added HCl. The crystal-growth rate decreased as the H+ and/or Cl, ion concentration increased. The present kinetic analyses revealed that the decrease in rate constant with increasing H+ and/or Cl, ion concentrations resulted from the decrease in the crystal-growth rate. The decreasing tendency of the crystal-growth rate was attributed to interference with crystal growth by the Cl, ions attracted onto the particle surface through the formation of an electric double layer. The formation mechanisms for the primary particles of hydrous zirconia were determined based on the present experimental results. [source] Ultrasound-facilitated electro-oxidation for treating cyan ink effluentTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2008Chee-Yong Chua Abstract The feasibility of using ultrasonication in combination with the Fenton's reaction was investigated for treating cyan ink effluent. A two-step treatment process was developed,the first step was an ultrasound-assisted electro-oxidation, while the second was chemical oxidation through the addition of hydrogen peroxide. The use of electro-oxidation in the first step significantly reduced the amount of iron needed compared with the conventional Fenton's reaction, resulting in a 98% reduction in the amount of sludge produced. A simple technique based on refractive index measurements was introduced as a rapid way to quantify the amount of sludge produced. It was postulated that ultrasonication in the presence of iron (from electrolysis) in the first step converted the ink components into reaction intermediates which were more amenable to peroxide oxidation in the second step. These intermediates were quantified by ultra-violet absorption at wavelengths of 275,400 nm. The two-step treatment process was able to reduce the COD and copper contents in the ink waste water to within the discharge limit, which conventional Fenton's reaction was unable to meet for copper discharge. The same COD removal was also achieved in about half the time. Kinetics study performed to further understand the reaction mechanisms show second-order kinetics for both steps with activation energies of 18.2 and 20.4 kJ/mol for steps 1 and 2, respectively. On a étudié la possibilité de recourir à l'ultrasonification combinée à la réaction de Fenton pour traiter l'effluent d'encre de cyan. Un procédé de traitement en deux étapes a été mis au point: la première étape consiste en une électro-oxydation assistée par ultrasons, tandis que la seconde consiste en une oxydation chimique par ajout de peroxyde d'hydrogène. Le recours à l'électro-oxydation dans la première étape réduit significativement la quantité de fer requis comparé à la réaction de Fenton classique, entraînant une réduction de 98% de la quantité de suspension produite. Une technique simple basée sur des mesures d'indice de réfraction a été introduite comme une façon rapide d'établir la quantité de suspension produite. On a posé comme postulat que l'ultrasonification en présence de fer (de l'électrolyse) dans la première étape convertit les composantes de l'encre en des intermédiaires de réaction qui étaient plus propices à l'oxydation du peroxyde dans la seconde étape. Ces intermédiaires ont été quantifiés par l'absorption des ultraviolets à des longueurs d'ondes de 275 nm à 400 nm. Ce procédé de traitement en deux étapes a permis de réduire la DCO et les teneurs en cuivre dans l'eau usée de l'encre pour les amener à la limite des normes de rejet, ce que la réaction de Fenton classique n'a pu permettre de réaliser pour le cuivre. Le même retrait de DCO a été également réalisé dans un temps inférieur de 50%. L'étude de cinétique effectuée pour mieux comprendre les mécanismes de réaction montre une cinétique de second ordre pour les deux étapes avec des énergies de désactivation de 18,2 et 20,4 kJ/mol pour les étapes 1 et 2, respectivement. [source] Kinetics and mechanism of the reaction between maleic anhydride and fatty acid esters and the structure of the productsEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 5 2008Florina Stefanoiu Abstract Alkenyl succinic anhydrides (ASA) were obtained by reaction between maleic anhydride and high-oleic sunflower oil (HOSO) esters. A kinetics study of the maleinization of alkyl esters indicated that the maleinization reaction was second order overall and first order with respect to the individual reactants, and the activation energy was 77.2,±,3.3,kJ/mol in the investigated temperature range (185,225,°C). These results showed that the cis configuration and the central position of the double bond in HOSO esters facilitate the maleinization of the latter. On the contrary, the length of the linear ester moiety had no influence on the course of the maleinization reaction. Moreover, new evidence demonstrates that there are two different reaction mechanisms: ene-reaction and addition in allylic position with a 2,:,1 ratio, respectively. This ratio was constant throughout the reaction, thus indicating that these mechanisms are independent. [source] A temperature-dependent kinetics study of the reaction of O(3PJ) with (CH3)2SOINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2002F. D. Pope A laser flash photolysis,resonance fluorescence technique has been employed to investigate the kinetics of the reaction of ground state oxygen atoms, O(3PJ), with (CH3)2SO (dimethylsulfoxide) as a function of temperature (266,383 K) and pressure (20,100 Torr N2). The rate coefficient (kR1) for the O(3PJ) + (CH3)2SO reaction is found to be independent of pressure and to increase with decreasing temperature. The following Arrhenius expression adequately describes the observed temperature dependence: kR1(T) = (1.68 ± 0.76) × 10,12 exp[(445 ± 141)/T] cm3 molecule,1 s,1, where the uncertainties in Arrhenius parameters are 2, and represent precision only. The absolute accuracy of each measured rate coefficient is estimated to be ±30%, and is limited predominantly by the uncertainties in measured (CH3)2SO concentrations. The observed temperature and pressure dependencies suggest that, as in the case of O(3PJ) reactions with CH3SH and (CH3)2S, reaction occurs by addition of O(3PJ) to the sulfur atom followed by rapid fragmentation of the energized adduct to products. The O(3PJ) + (CH3)2SO reaction is fast enough so that it could be a useful laboratory source of the CH3SO2 radical if this species is produced in significant yield. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 156,161, 2002; DOI 10.1002/kin.10040 [source] Direct kinetics study of the temperature dependence of the CH2O branching channel for the CH3O2 + HO2 reactionINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2001Matthew J. Elrod A direct kinetics study of the temperature dependence of the CH2O branching channel for the CH3O2 + HO2 reaction has been performed using the turbulent flow technique with high-pressure chemical ionization mass spectrometry for the detection of reactants and products. The temperature dependence of the CH2O-producing channel rate constant was investigated between 298 and 218 K at a pressure of 100 Torr, and the data were fitted to the following Arrhenius expression: 1.6 × 10,15 × exp[(1730 ± 130)/T] cm3 molecule,1 s,1. Using the Arrhenius expression for the overall rate of the CH3O2 + HO2 reaction and this result, the 298 K branching ratio for the CH2O producing channel is measured to be 0.11, and the branching ratio is calculated to increase to a value of 0.31 at 218 K, the lowest temperature accessed in this study. The results are compared to the analogous CH3O2 + CH3O2 reaction and the potential atmospheric ramifications of significant CH2O production from the CH3O2 + HO2 reaction are discussed. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 363,376, 2001 [source] | ||||||||||