Homogeneous reactions in the

A second source of difficulty is caused by the unavoidable empty space in recycle reactors. This limits their usefulness in some studies. Homogeneous reactions in the empty gas volume may interfere with heterogeneous catalytic measurements. Transient experiments could reveal much more information on various steps in the reaction mechanism but material in the empty space can obscure sharp changes. 

The concentrations of reactants are of little significance in the theoretical treatment of the kinetics of solid phase reactions, since this parameter does not usually vary in a manner which is readily related to changes in the quantity of undecomposed reactant remaining. The inhomogeneity inherent in solid state rate processes makes it necessary to consider always both numbers and local spatial distributions of the participants in a chemical change, rather than the total numbers present in the volume of reactant studied. This is in sharp contrast with methods used to analyse rate data for homogeneous reactions in the liquid or gas phases. 

S.4. Guidelines for scale-up of semibatch reactors for fast homogeneous reactions in the absence of data on chemical kinetics and on the distribution of energy dissipation in the reaction zone... 

Model flame studies in hydrogen-oxygen flames show that vaporized Mg, Cr, Mn, Sn or U salts are active as radical recombination catalysts at about 1 ppm (4). It was not determined whether this effect was produced by homogeneous reactions in the vapor phase or by the presence of Gne particles. 

Chemical reactions can be involved in the overall electrode process. They can be homogeneous reactions in the solution and heterogeneous reactions at the surface. The rate constant of chemical reactions is independent of potential. However, chemical reactions can be hindered, and thus the reaction overpotential rj can hinder the current flow. 

Figure 1(1-14 Concentration profiles around a burning carbon particle, either with or without homogeneous reaction in the boundaiy layer around the particle.

There is homogeneous reaction in the process tube as well as heterogeneous reaction on the inside of the tube wall. Assume that the net rates of homogeneous and surface reaction of the steam may be represented as... 

In all of these situations, homogeneous reactions in the gas phase provide source and sink terms in the species continuity equation. In addition the creation and destruction of species can be an important heat source or sink term in the energy equation. Therefore it is important to understand the factors that govern gas-phase chemical kinetics. 

C.T. Goralski and L.D. Schmidt. Modeling Heterogeneous and Homogeneous Reactions in the High-Temperature Catalytic Combustion of Methane. Chem. Eng. Sci., 54 5791-5807,1999. 

Equations (5.46) and (5.47) are referred to as steam methane reforming (SMR) reaction and Water Gas Shift (WGS) reaction respectively. These reactions are homogenous reactions that occur everywhere inside the anode, whereas Equations (5.48) and (5.49) only occur at the active triple phase boundary. Treatment of source terms due to electrochemical oxidation of H2 (Equation 5.49) is already covered in the previous sections and the treatment is similar for electrochemical oxidation of CO (Equation 5.48). Specie source terms due to homogenous reactions in the mechanism are given by ... 

The approximation of Eq. (Bl) allows one to reduce Eqs. (A10) and (A11) to a linearized boundary-value problem (183,184,186). The latter can then be solved analytically and yields a compact matrix-form solution for the concentration profiles in the film region [58], Such a solution gives simple analytical expressions for the component fluxes with regard to the homogeneous reaction in the fluid films (see Ref. 135), which can be of particular value when large industrial reactive separation units are considered and designed. 

With this general basis we consider the development of specific expressions for different types of chemical reactions. We first consider a homogenous reaction in the gas phase, and use the virial equation of state accurate to the second virial coefficient. The chemical potential of the fcth substance is given by Equation (7.72)... 

However, the intercept of the straightline d/dt (In [CIO]) = f ([DMS]) -, which was found to be (80 5)s indicates a substantial wall reactivity of ClO in the presence of DMS. Some dependence of CIO wall loss with DMS concentration can exist if the reactor wall is not saturated with DMS in the range of DMS concentration used to derive kj from the plots - d In [QO] /dt = f([DMS]). In such a case k2 is an upper limit of the rate constant of the homogeneous reaction. In the absence of any indication of the saturation degree of the reactor wall in this study, k should be considered as an upper limit for the rate constant. Such complications have not been observed for the reaction BrO + DMS —> products (3). For DMS and BrO concentrations ranging from 15 x 1014 to 7.9 x 1014 molecules cm 3 and from 1.33 x 1013 to 1.55 x 1013 molecules cm 3, respectively, die following rate constant was determined at 298 K and 1.4 Tom... 

A non-linear mathematical model, which is a set of ordinary differential equations, for the process in the SPBER was developed.19 The model accounts for the heterogeneous electrochemical reaction and homogeneous reaction in the bulk solution. The lateral distributions of potential, current density and concentration in the reactor were studied. The potential distribution in the lateral dimension, x, of the packed bed was described by a one dimensional Poisson equation as ... 

As is shown in Figure 2, in the two-phase model the fluid bed reactor is assumed to be divided into two phases with mass transfer across the phase boundary. The mass transfer between the two phases and the subsequent reaction in the suspension phase are described in analogy to gas/liquid reactors, i.e. as an absorption of the reactants from the bubble phase with pseudo-homogeneous reaction in the suspension phase. Mass transfer from the bubble surface into the bulk of the suspension phase is described by the film theory with 6 being the thickness of the film. D is the diffusion coefficient of the gas and a denotes the mass transfer coefficient based on unit of transfer area between the two phases. 6 is given by 6 = D/a. 

The continuity equation in the washcoat concerns axial and radial diffusion, and net production due to homogeneous reactions in the pores and catalytic reactions, that ultimately result from the difference between adsorption and desorption rates ... 

The overall reaction, Eq. (1), may take place in a number of steps or partial reactions. There are four possible partial reactions charge transfer, mass transport, chemical reaction, and crystallization. Charge-transfer reactions involve the transfer of charge carriers (ions or electrons) across the double layer. This is the basic deposition reaction. The charge-transfer reaction is the only partial reaction directly affected by the electrode potential. In mass transport processes, the substances consumed or formed during the electrode reaction are transported from the bulk solution to the interphase (double layer) and from the interphase to the bulk solution. This mass transport takes place by diffusion. Chemical reactions involved in the overall deposition process can be homogeneous reactions in the solution and heterogeneous reactions at the surface. The rate constants of chemical reactions are independent of the potential. In crystallization partial reactions, atoms are either incorporated into or removed from the crystal lattice. 

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