Kinetics Of Various Reactions Research Articles

A quantified nitrogen metabolic network by reaction kinetics and mathematical model in a single-stage microaerobic system treating low COD/TN wastewater

A single-stage intermittent aeration microaerobic reactor (IAMR) has been developed for the cost-effective nitrogen removal from piggery wastewater with a low ratio of chemical oxygen demand (COD) to total nitrogen (TN). In this study, a quantified nitrogen metabolic network was constructed based on the metagenomics, reaction kinetics and mathematical model to provide a revealing insight into the nitrogen removal mechanism in the IAMR. Metagenomics revealed that a complex nitrogen metabolic network, including aerobic ammonia and nitrite oxidation, anammox, denitrification via nitrate and nitrite, and nitrate respiration, existed in the IAMR. A novel method for solving kinetic parameters with high stability was developed based on a genetic algorithm. Use this method to calculate the kinetics of various reactions involved in nitrogen metabolism. Kinetics revealed that simultaneous partial nitritation-anammox (PN/A) and partial denitrification-anammox (PDN/A) were the dominant approaches to nitrogen removal in the IAMR. Finally, a kinetics-based model was proposed for quantitatively describing the nitrogen metabolic network under the limitation of COD. 58% ∼ 67% of nitrogen was removed via the anammox-based processes (PN/A and PDN/A), but only 7% ∼ 12% and 1% ∼ 2% of nitrogen were removed via heterotrophic denitrification of nitrite and nitrate, respectively. The half-inhibition constant of dissolved oxygen (DO) on anammox was simulated as 0.37 ∼ 0.60 mg L−1, filling the gap in quantifying DO inhibition on anammox. High-frequency intermittent aeration was identified as the crucial measure to suppress nitrite-oxidizing bacteria, although it has a high affinity for DO and NO2−-N. In continuous aeration mode, the simulated NO3−-N in the IAMR would rise by 39.6%. The research provides a novel insight into the nitrogen removal mechanism in single-stage microaerobic systems and provides a reliable approach to practicing PN/A and PDN/A for cost-effective nitrogen removal.

Thermodynamic study of evolution of sinter phases at different alumina level

Though sintering is controlled by kinetics of various reactions and is far from equilibrium, a thermodynamic analysis can provide useful inputs on melt formation and helps understand deviation from actual process conditions. The thermodynamic software ‘FACTSAGE™’ was used for this study. The general sequence of reactions during the heating cycle is as follows: decomposition of calcium carbonate to calcined lime; formation of calcium ferrites/silicates; decomposition of calcium ferrites, reduction of haematite to magnetite and formation of spinel and silicates; assimilation of ferrites, silicates, spinel and magnetite into the melt. During the cooling stage, the amount of melt decreased with subsequent precipitation of phases such as magnetite, ferrites, silicates, spinel and formation of haematite. It is very much clear that the sinter made by using higher alumina levels generate fewer amounts of oxides and more slag phase compared to its low alumina counterpart.

Streptokinase and Staphylokinase: Differences in the Kinetics and Mechanism of Their Interaction with Plasminogen, Inhibitors and Fibrin

Comparative in vitro study of the kinetics of various reactions involved in the process of thrombolysis initiated by streptokinase (SK) and staphylokinase (STA) was carried out. It was shown that at the interaction of an equimolar ratio of plasminogen (Pg) with SK or STA the rate of formation and the specific esterase activity of the complex plasmin (Pm) · SK are higher than those of the complex Pm · STA. The catalytic efficiency (kcat/Km) of hydrolysis of the chromogenic plasmin substrates by Pm · SK complex was 2 times higher than by Pm · STA complex. In the absence of fibrin catalytic efficiency (kPg/K(Pg)) of activation of Glu-plasminogen and Lys-plasminogen glycoform II by Pm · SK complex was higher than by Pm · STA complex, but the pres- ence of fibrin increased kPg/K(Pg)) activation of both plasminogens by Pm · STA complex significantly stronger than by Pm · SK complex due to the decrease in K(Pg)). In contrast to STA (15.5 kDa), SK molecule (47 kDa) creates significant steric hindrances for the interaction of plasmin in Pm · SK complex with protein inhibi- tors. In addition, SK caused greater fibrinogen degradation than STA. It is shown that Pm · SK and Pm · STA complexes lyse fibrin clots in buffer with similar rates, while the rate of lysis of plasma clots, immersed in plas- ma, by Pm · STA complex are significantly higher than those by Pm · SK complex. It was revealed that the species specificity of STA and S K is determined mainly by the rate of formation and the efficiency of Pm · SK and Pm · STA complexes in the activation of autologous plasminogen. The lysis efficiency of plasma clots of mammals fell in the series: human > dog > rabbit for SK and the dog > human > rabbit for STA. The results show that in the purified system SK is a more effective activator of plasminogen than STA. In the system con- taining fibrin and α2-AP, the activator and fibrinolytic activities of STA are higher than those of SK, due to the increased stability in plasma and fibrin specificity of STA, the fast reaction of the complex Pm · STA with α2AP and the ability of the STA to recyclization in the presence of α2AP.

Morphology-dependent activity of Pt nanocatalysts for ethanol oxidation in acidic media: Nanowires versus nanoparticles

The morphology of nanostructured Pt catalysts is known to affect significantly the kinetics of various reactions. Herein, we report on a pronounced morphology effect in the electrooxidation of ethanol and carbon monoxide (CO) on Pt nanowires and nanoparticles in an acidic solution. The high resolution transmission electron microscopy analysis showed the inherent morphology difference between these two nanostructured catalysts. Voltammetric and chronoamperometric studies of the ethanol electrooxidation revealed that these nanowires had a higher catalytic activity by a factor of two relative to these nanoparticles. The rate for CO monolayer oxidation exhibits similar morphology-dependent behavior with a markedly enhanced rate on the Pt nanowires. In situ infrared reflection–absorption spectroscopy measurements revealed a different trend for chemisorbed CO formation and CO2-to-acetic acid reaction product ratios on these two nanostructures. The morphology-induced change in catalytic activity and selectivity in ethanol electrocatalysis is discussed in detail.

Observation of Chemical Reactions at the Solid−Water Interface by Quick XAFS Combined with a Column Reactor

A simple method for the observation of the kinetics of the reactions at the solid-water interface was developed using quick X-ray absorption fine structure combined with a column reactor. We applied the method to the oxidation reaction of As(III) by manganese oxide, a strong oxidizer in natural systems. A reliable reaction rate constant k', 3.9 x 10(-4) %(-1) min(-1) at pH 7.1, was obtained, where the effect of photooxidation under X-ray beam can be eliminated. Considering the average Mn/As molar ratio in the system, the value is reasonable compared with other reported values. Since this method is very simple, we can apply it to various elements and reaction systems at the solid-water interface as a tool to understand the kinetics of various reactions in detail.

Review: Effect of thermal processing on soymilk

SummaryHeating conditions are the most important variables in the processing of soymilk. the heat treatments given to soymilk during extraction, cooking, and subsequent pasteurization or sterilization, principally influence (1) the yields and nutritive quality of solids and proteins, (2) destruction of spoilage microorganisms, and (3) the colour and the flavour of the milk. the qualities of other soy products derived from soymilk, e.g. the texture of tofu and the suitability for lactic acid fermentation, may also be affected by the net heat treatment received by the milk. Excess heating generally leads to the destruction of amino acids and vitamins, browning and the development of cooked flavour. Considerable research efforts have been devoted to establish the effects of heat on the elimination of off‐flavours, inactivation of antinutritional factors such as trypsin inhibitors, and the recovery of solids and proteins in soymilk. Other heat‐induced chemical changes such as loss of vitamins, Maillard reaction and protein denaturation have not been studied as extensively. Published studies show that higher temperature heating and UHT treatment may have beneficial effects on the yields of solids and proteins, retention of the nutrients, and minimizing chemical changes in soymilk, provided that optimum processing conditions are used. Process optimization is only possible if data on the kinetics of various chemical reactions involved are available. However, such data are lacking, especially in the UHT range.The principal objective of this review article is to compile a comprehensive description of heat‐induced changes occurring in soymilk. Attention has been given to the analysis of published data relating to the kinetics of various reactions. Such an analysis would permit the evaluation of kinetic parameters (such as rate constants and activation energies), and would form the basis for reaction engineering studies leading to the design of optimum heat exchangers for the processes.

Evaluation of the Thermodynamics and Kinetics of Catalytic Steam Reforming Over SOFC Anode Materials

The purpose of this investigation is to study the catalytic effect of SOFC anode material on steam reforming of methane and coking. The thermodynamics and kinetics of various reactions taking place at the anode of the solid oxide fuel cell when methane is used as fuel have been investigated at various steam/methane ratios at 1,000 C. An analysis of the residual gas from the SOFC under open circuit condition showed the extent of steam reforming in the presence and absence of the anode. The carbon deposition, when different steam/methane ratios were used, has been studied after running the cell under open circuit conditions. The structure of the cermet after exposure to different conditions has also been analyzed using optical microscope and AES.

Quelques Aspects de la Chimie Theorique Contemporaine

AbstractIn this paper we make a survey of various aspects of theoretical chemistry to which we have made some contribution. Our Localized Molecular Orbital (LHO) approach to the electronic structure and reactivity of chemical species allowed us not only to generalize the Lewis and Linnett theories of valence but also to determine the mechanism of a wide variety of organic reactions. We have also proposed a general definition of the concept of stabilization energy applying to any compound. Using this concept, we have been able to elaborate a table of standard bond energy terms, to unify various notions such as hyperconjugation, resonance, ring strain and steric repulsion energy and to carry out a critical analysis of former definitions of the stabilization energy of olefines and free radicals. Furthermore, we have shown that the enthalpy changes and, eventually, the rate constants of any physical or chemical process involving paramagnetic or charged species could be rationalized in terms of their stabilization energies. In this prospect, we have proposed an original interpretation of the persistence of some free radicals and we have made interesting predictions concerning the thermochemistry and the kinetics of various reactions involving neutral or charged reactive intermediates. Moreover we have devised a semi‐empirical method for estimating the barrier heights of atom transfer reactions. So, we have been able to systematically determine the kinetic parameters of these processes using the transition state theory with an Eckart tunnelling correction. Finally, our barrier height modelling allowed us to interpret the effect of substituents on the activation barriers of hydrogen transfer reactions leading to carbon centred free radicals. On the whole, we have tried to demonstrate the promising role theory is presumably led to play in the development of modern chemistry, owing to the joint utilization of its own tools ‐ concepts, models and formalism ‐ and the information provided as much by experimental techniques as by the ab initio methods of quantum chemistry.

A continuous micro-reactor system with gas chromatograph for studying combustion of hydrocarbons

Pulsed and continuous micro-reactors have been used, along with gas chromatography, by several workers to determine the kinetics of various reactions involving gaseous hydrocarbons. Pulsed micro-reactors have been reported to overcome the difficulties of pre-ignition and non-isothermality in exothermic reactions. However, in situation where diffusional resistance is present and a one-step analysis of the reaction products is difficult, e.g. in the combustion of liquefied petroleum gas (LPG) at higher temperatures, data from a continuous micro-reactor which is amenable to simple kinetic analysis are preferred. This paper reports the development of a continuous micro-reactor system in which the problems of pre-ignition and non-isothermality are successfully resolved. The system was tested up to a temperature of 700 °C for the combustion of LPG and can be used to study the conversion of other hydrocarbons.