Reactant mixing

Instead of shifting the detector position, as indicated in figure B2.5.1 one often varies the location of the reactant mixing region using moveable injectors. This allows complex, possibly slow, but powerfril, analytical teclmiques to be used for monitoring gas-phase reactions. In combination with mass-spectrometric detection. 

A quite different approach was introduced in the early 1980s [44-46], in which a dense solid electrode is fabricated which has a composite microstructure in which particles of the reactant phase are finely dispersed within a solid, electronically conducting matrix in which the electroactive species is also mobile. There is thus a large internal reactant/mixed-conductor matrix interfacial area. The electroactive species is transported through the solid matrix to this interfacial region, where it undergoes the chemical part of the electrode reaction. Since the matrix material is also an electronic conductor, it can also act as the electrode s current collector. The electrochemical part of the reaction takes place on the outer surface of the composite electrode. 

We first explain the setting of reactors for all CFD simulations. We used Fluent 6.2 as a CFD code. Each reactant fluid is split into laminated fluid segments at the reactor inlet. The flow in reactors was assumed to be laminar flow. Thus, the reactants mix only by molecular diffusion, and reactions take place fi om the interface between each reactant fluid. The reaction formulas and the rate equations of multiple reactions proceeding in reactors were as follows A + B R, ri = A iCaCb B + R S, t2 = CbCr, where R was the desired product and S was the by-product. The other assumptions were as follows the diffusion coefficient of every component was 10" m /s the reactants reacted isothermally, that is, k was fixed at... 

A second type of polythermal path traces temperature as reactants mix into the... 

A flame could begin with the reactants mixed (premixed) or reactants that might diffuse together (diffusion flame). Generally, a flame is thought of with the reactants in the gas phase. Variations in this viewpoint for a flame or fire process might occur and are defined in special terminology. Indeed, while flame applies to a gas phase reaction, fire,... 

Reactant Mixing Catalyst Reaction Zone-Zone (cooled) Single Winding Channel (Heated)... 

A rapid mixing device, introduced nearly eighty years ago by Hartridge and Roughton, to mix two or more reactants (mixing time 10-50 jusec) and to utilize a constant flow rate through a loop that then passes... 

EFFECT OF THE DEGREE OF REACTANT MIXING ON THE REACTION RATE... 

All reactants mixed in cold premixed Fe(acac) + PhSH solutions allowed to stand before adding indene ... 

Standard chemical kinetics systems with complete reactant mixing... 

All local concentrations C of particles entering the non-linear functions F in equation (2.1.40) are taken at the same space points, in other words, the chemical reaction is treated as a local one. Taking into account that for extended systems we shouldn t consider distances greater than the distinctive microscopic scale Ao, the choice of equation (2.1.40) means that inside infinitesimal volumes vo particles are well mixed and their reaction could be described by the phenomenological reaction rates earlier used for systems with complete reactant mixing. This means that Ao value must exceed such distinctive scales of the reaction as contact recombination radius, effective radius of a dynamical interaction and the particle hop length, which imposes quite natural limits on the choice of volumes v0 used for averaging. 

Chemical reactions are classified usually as diffusion-controlled, whose rate is limited by a reactant spatial approach to each other, and reaction-controlled (kinetic stage), whose rate is limited by a reaction elementary event. For systems with ideal reactant mixing considered in Section 2.1.1, there is no mechanism of reactant mutual approach. On the other hand, the kinetic equations (2.1.40) distinguish between reaction in physically infinitesimal volumes and the distant reactant motion in a whole reaction volume. In the absence of reaction particle diffusion is described by equation... 

There are two main process categories for the direct hydration of ethylene to ethanol. Vapor-phase processes contact a solid or liquid catalyst with gaseous reactants. Mixed-phase processes contact a solid or liquid catalyst with liquid and gaseous reactants. Generally, ethanol is produced by a vapor-phase process mixed-phase processes are used for the analogous hydration of propylene to 2-propanol. Important exceptions to these two generalizations exist, but the discussion that follows emphasizes technology associated with the commercially important vapor-phase direct hydration of ethylene. 

Basic alumina (18 g) was added to the solution of ethyl bromoacetate 2 (0.01 mol) in dichloromethane (20 mL) and to the solution of potassium thiocarbamate 1 (0.01 mol) in hot acetone (5 mL) at room temperature in two separate beakers. Adsorbed material was dried and the two reactants mixed properly using a mortar and pestle. The reaction mixture was kept inside an alumina bath and irradiated in a microwave oven for 100-110 s. The mixture was cooled and the product was extracted into CH2C12 (5x4 mL). The product was collected by evaporating the solvent and recrystallizing from a mixture of methanol and CH2C12. 

Let us consider the application of this technique to a Calvet differential calorimeter. According to the standard procedure an ampoule with the reactant mix is placed in the measuring chamber. If the wall thicknesses of the measuring chamber and the ampoule are sufficiently small, the heat flux q passing through a unit wall area with a stepwise change in temperature is described by the expression ... 

A reaction has to be performed at 80 °C. Two thermograms were recorded (Figure 11.21). The upper thermogram was obtained with the reactants mixed at room temperature. The lower thermogram was obtained with a sample of the final... 

Figu re 11.21 DSC thermograms of the reactants mixed at room temperature (upper) and of the final reaction mass (lower). 

Stoichiometric quantities quantities of reactants mixed in exactly the correct amounts so that all are used up at the same time. (3.9)... 

In most practical systems, e.g., combustors or furnaces, the combustion process is much more comphcated because of two important factors. First, to a large extent the fuel and oxidant are mixed within the quarl of a burner or within the combustion chamber itself. The mechanism of the reactant mixing therefore plays an important role. Second, the flow aerodynamics are complicated by the flow recirculation and turbulence and frequently cannot be represented by simplifled models. 

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