Mass-transfer kinetics

Oxidation processes may rely on pH adjustment to enhance the chemical reaction. Figure 16 illustrates the typical configuration of a chemical oxidation process. The m or engineering considerations for chemical oxidation include reaction kinetics, mass transfer, by-products, temperature, oxidant concentration, pH and vent gas scrubbing. 

Romanainen, J.J and Salmi T (1992) The Effect of Reaction Kinetics, Mass Transfer and Flow Pattern on Noncatalytic and Homogeneously Catalyzed Gas-Liquid Reactions in Bubble Columns, Chem Eng Sci, 47 2493. 

These components of scale-up manifest themselves through the effects of chemical kinetics, mass transfer, and heat transfer. As an example of the way these factors interrelate to scale-up, the general process of commercial scale reactor design is shown inFigure 3.19, which is similar to presentations in [204, 205]. 

Many wastewater flows in industry can not be treated by standard aerobic or anaerobic treatment methods due to the presence of relatively low concentration of toxic pollutants. Ozone can be used as a pretreatment step for the selective oxidation of these toxic pollutants. Due to the high costs of ozone it is important to minimise the loss of ozone due to reaction of ozone with non-toxic easily biodegradable compounds, ozone decay and discharge of ozone with the effluent from the ozone reactor. By means of a mathematical model, set up for a plug flow reactor and a continuos flow stirred tank reactor, it is possible to calculate more quantitatively the efficiency of the ozone use, independent of reaction kinetics, mass transfer rates of ozone and reactor type. The model predicts that the oxidation process is most efficiently realised by application of a plug flow reactor instead of a continuous flow stirred tank reactor. 

The characteristic shape of i-E curve depends on the nature of the redox couple in the condensed phase, its thermodynamics, kinetics, mass transfer, and on the voltage-time profile (E—t). In this section we will discuss various voltammetric techniques and their applications in modern chemistry. 

Poly(Ethylene Terephthalate) Polymerization - Mechanism, Catalysis, Kinetics, Mass Transfer and Reactor Design... 

Alkylation Reactor Model Kinetics, Mass Transfer and Dynamics... 

Combustion processes are fast and exothermic reactions that proceed by free-radical chain reactions. Combustion processes release large amounts of energy, and they have many applications in the production of power and heat and in incineration. These processes combine many of the complexities of the previous chapters complex kinetics, mass transfer control, and large temperature variations. They also frequently involve multiple phases because the oxidant is usually air while fuels are frequently liquids or solids such as coal, wood, and oil drops. 

It is clear that in addition to thermodynamic models, kinetic mass transfer models can bring about some additional information that is required for a better definition of the system. In this context, natural analogues provide some of the required scale and time-frames necessary for the testing of kinetic mass transfer models and the Cigar Lake ore deposit is probably the better constrained for such an exercise. 

The kinetic mass transfer model developed to take into consideration the geochemical evolution of the Cigar Lake ore deposit was mainly done by simulating the evolution of the Al-Si system in the Cigar Lake ore deposit system. To this aim the system formed by kaoli-nite, gibbsite and illite as main aluminosilicate solid phases was considered and kinetics for the dissolution-precipitation processes were taken from the open scientific literature (Nagy et al. 

Bruno, J., Casas, I., Cera, E. Duro, L. 1997. Development and application of a model for the long-term alteration of U02 spent nuclear fuel. Test of equilibrium and kinetic mass transfer models in the Cigar Lake ore deposit. Journal of Contaminant Hydrology, 26, 19-26. 

Apart from the analysis of kinetics, mass transfer, and equilibrium of the processes at a fundamental level, the analysis of material, and in fixed beds energy balances in the reactors, as well as a number of analytical solutions of the reactors models are presented. Furthermore, the hydraulic behavior of the reactors is presented in detail. Hydraulic analysis is basically... 

In the following pages we shall see that reactor design involves all the basic principles of chemical engineering with the addition of chemical kinetics. Mass transfer, heat transfer and fluid flow are all concerned and complications arise when, as so often is the case, interaction occurs between these transfer processes and the reaction itself. In designing a reactor it is essential to weigh up all the... 

In industrial practice, the laboratory equipment used in chemical synthesis can influence reaction selection. As issues relating to kinetics, mass transfer, heat transfer, and thermodynamics are addressed, reactor design evolves to commercially viable equipment. Often, more than one type of reactor may be suitable for a given reaction. For example, in the partial oxidation of butane to maleic anhydride over a vanadium pyrophosphate catalyst, heat-transfer considerations dictate reactor selection and choices may include fluidized beds or multitubular reactors. Both types of reactors have been commercialized. Often, experience with a particular type of reactor within the organization can play an important part in selection. 

The operating conditions needed for adsorption rate measurements differ considerably from the requirements of the preparative packed bed operation mode. Kinetic mass transfer effects will increase as the flow rate is increased and the column capacity decreased. Furthermore, the major problem is to differentiate between a diffusion rate-limited process and the kinetic-limited one. The contribution of the diffusional mass transfer to the overall adsorption process will be reduced by using an immunoadsorbent with a low density of binding sites immobilized on a nonporous support. 

Bencala K. E. (1983) Simulation of solute transport in a mountain pool-and-riffle stream with a kinetic mass transfer model for sorption. Water Resour. Res. 19, 732—738. 

This part demonstrates how deterministic models of impedance response can be developed from physical and kinetic descriptions. When possible, correspondence is drawn between hypothesized models and electrical circuit analogues. The treatment includes electrode kinetics, mass transfer, solid-state systems, time-constant dispersion, models accounting for two- and three-dimensional interfaces, generalized transfer functions, and a more specific example of a transfer-function tech-nique.in which the rotation speed of a disk electrode is modulated. 

To simulate the effects of reaction kinetics, mass transfer, and flow pattern on homogeneously catalyzed gas-liquid reactions, a bubble column model is described [29, 30], Numerical solutions for the description of mass transfer accompanied by single or parallel reversible chemical reactions are known [31]. Engineering aspects of dispersion, mass transfer, and chemical reaction in multiphase contactors [32], and detailed analyses of the reaction kinetics of some new homogeneously catalyzed reactions have been recently presented, for instance, for polybutadiene functionalization by hydroformylation in the liquid phase [33], car-bonylation of 1,4-butanediol diacetate [34] and hydrogenation of cw-1,4-polybutadiene and acrylonitrile-butadiene copolymers, respectively [10], which can be used to develop design equations for different reactors. 

Using reversed micellar phase as a liquid membrane, Armstrong and Li (66) could perform continuous extraction from and stripping to aqueous solutions in either side of the membrane. However, improvements of kinetic mass transfer parameters, as influenced by membrane thickness and stability in conditions of appropriate hydrodynamics, remain necessary. 

Studies have been made on the mechanism of separation, process kinetics, mass transfer modehng, and engineering evaluation with metals hke copper, zinc, cadmium, cobalt, nickel, mercury, uranium, chromium, rhenium, and several others, including noble metals hke gold and silver, lanthanides and rare earths. Table 4.2 presents some examples. 

Catalyst supports such as silica and alumina have low thermal conductivities so that temperature gradients within catalyst particles are likely in all but the finely ground powders used for infrinsic kinetic studies. There may also be a film resisfance fo heaf fransfer af fhe exfemal surface of the catalyst. Thus the internal temperatures in a catalyst pellet may be substantially different than the bulk gas temperature. The definition of the effectiveness factor, Equation 10.23, is unchanged, but an exothermic reaction can have reaction rates inside the pellet that are higher than would be predicted using the bulk gas temperature. In the absence of a diffusion limitation, rj > 1 would be expected for an exothermic reaction. (The case > 1 is also possible for some isothermal reactions with weird kinetics.) Mass transfer limitations may have a larger... 

The three-phase nonequilibriimi model developed in our laboratory which includes kinetics, mass transfer and heat transfer models [6] is used to predict the yield and selectivity of EGME from the reaction of ethanol and EO. The model predicts fliat die conversion of EO would reach 94 % and 99 % selectivity to EGME at an operating pressure of 235 kPa and a reflux ratio of 2. The model predictions are in excellent agreement with experimental data (Table 2). This result shows that our three-phase non-equilibrium model could be used for the prediction of yield and selectivity in a CD process. 

Before evaluating Eq. [30], the parameters of kinetics, mass transfer, and thermodynamic equilibrium must be established. The aim of this work is to evaluate the equilibrium and extraction of a quaternary salt in an organic solvent/aqueous solution. The studies on distribution equilibrium of the quaternary salts enable one to clarify the true mechanism through which the reactant anion is transferred. 

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