Stirred flow

Multiphase Reactors. The overwhelming majority of industrial reactors are multiphase reactors. Some important reactor configurations are illustrated in Figures 3 and 4. The names presented are often employed, but are not the only ones used. The presence of more than one phase, whether or not it is flowing, confounds analyses of reactors and increases the multiplicity of reactor configurations. Gases, Hquids, and soHds each flow in characteristic fashions, either dispersed in other phases or separately. Flow patterns in these reactors are complex and phases rarely exhibit idealized plug-flow or weU-stirred flow behavior. 

Integration of the Ergim equation for well stirred flow gives... 

Houser and Lee studied the pyrolysis of ethly nitrate using a stirred flow reaetor. They proposed the following meehanism for the reaetion ... 

Continuous isothermal perfeetly stirred flow reaetor (the reaetion mixture is at equilibrium with the heat transfer medium). 

Continuous adiabatie perfeetly stirred flow reaetor. 

The interpretation of the above data on iodination has been questioned by Buss and Taylor217, and by Grovenstein et a/.218,219. The former workers studied the iodination of 2,4-dichlorophenol at about 25 °C using a stirred flow reactor, the advantages of which are that once a steady state has been reached there is no change in the concentration of the reactive species in the reactor with time and the rate of reaction is simply a product of extent of reaction multiplied by the reciprocal ol the contact time hence it is possible to use unbuffered solutions and low iodide ion concentrations. They found general catalysis by the base component of added phosphate buffers and the observed rate coefficients varied with [H+ ] according to... 

Table 13 Influence of Stirring Flow Rate on the Permeability of [14C] Testosterone Across Caco-2 Cell Monolayer/Filter Support in 02/C02 Gas Lift Side-by-Side Diffusion at 37°C...

Houser and Lee [J. Phys. Chem., 71 (3422), 1967] have studied the pyrolysis of ethyl nitrate using a stirred flow reactor. They iiave proposed the following mechanism for the reaction. 

Young and Hammett [J. Am. Chem. Soc., 72 (286), 1950] have studied the alkaline bromi-nation of acetone in a stirred flow reactor (VR = 118 cm3). The stoichiometric equation for the bromination is usually considered to be ... 

Keairns and Manning AIChE J., 15 (660), 1969] have used the reaction between sodium thiosulfate and hydrogen peroxide in a well-stirred flow reactor to check a computer simulation of adiabatic CSTR operation. Data on their experimental conditions and the reaction parameters are listed below. The reaction may be considered second-order in sodium thiosulfate. 

The flow systems are generally of two types, viz. (i) plug flow (Fig. 7.1), in which there is no stirring in the reactor and (ii) stirred flow, in which there is stirring in the reactor to effect complete mixing within the reactor. 

The complete mixing in a stirred flow reactor has been discussed by Denbigh. In stirred flow, the composition becomes uniform throughout the entire volume of the reactor as a result of efficient stirring. 

In the steady-state approach to determining the rate law, solutions containing reactants are pumped separately at a constant flow rate into a vessel ( reactor ), the contents of which are vigorously stirred. After a while, produets and some reactants will flow from the reactor at the same total rate of inflow and a steady state will be attained, in which the reaction will take place in the reactor with a constant concentration of reactants, and therefore a constant rate. This is the basis of the stirred-flow reactor, or capacity-flow method. Although the method has been little used, it has the advantage of a simplified kinetic treatment even for complex systems. 

Reactor type Stirred flow Stirred How and batch Batch Flow Batch Batch... 

A condition achieved in a multistep process when the rate of formation of unstable intermediates is time-invariant, or nearly so. 2. In stirred flow systems, the steady-state condition refers to the procedure in which the concentration of all components is kept constant, via additions to and withdrawals from the system. 

In chapters 2-5 two models of oscillatory reaction in closed vessels were considered one based on chemical feedback (autocatalysis), the other on thermal coupling under non-isothermal reaction conditions. To begin this chapter, we again return to non-isothermal systems, now in a well-stirred flow reactor (CSTR) such as that considered in chapter 6. 

Following Jorgensen and Aris (1983), we take a well-stirred flow reactor fed by a stream of reactant A. This reactant is successively converted to an... 

Taylor, T. W. and Geiseler, W., 1986, Periodic operation of a stirred flow reaction with limit cycle oscillations. Ber. Bunsenges Phys. Chem. (submitted). 

If one desires to make meaningful use of small changes in entropies of activation, for example of AA values as might be caused by small structural changes in a reactant, then one must insist on kinetic measurements of really high precision. For well-behaved reactions the necessary precision can be obtained even with conventional techniques. Special techniques such as the stirred flow-reactor, first applied by Denbigh et al. (1948), and later modified by Hammett ef al. (1950), are occasionally helpful. 

Eick, M.J., A. Bar-Tal, D.L. Sparks, and S. Feigenbaum. 1990. Analyses of adsorption kinetics using a stirred-flow chamber II. Potassium-calcium exchange on clay minerals. Soil Sci. Soc. Am. J. 54 1278-1282. 

Su, P.-H. 1994. Sorption studies of atrazine using continuous stirred-flow and batch techniques. Master s thesis. Utah State University, Logan, UT. 

Advantages and Disadvantages 41 Specific Batch Techniques 42 Data Analysis 46 Flow and Stirred-Flow Methods 46 Advantages and Disadvantages 46 Continuous Flow Method 48 Fluidized Bed Reactors 50 Stirred-Flow Technique 51... 

Data Analyses Using Continuous Flow and Stirred-Flow Methods 53 Comparison of Kinetic Methods 57 Conclusions 59 Supplementary Reading 60... 

FLOW AND STIRRED-FLOW METHODS Advantages and Disadvantages... 

Stirred-flow reactors have been studied and used by chemical engineers for many years, but their application to chemical research is more recent, first by Denbigh (1944), and then by Hammett (1960). Stirred-flow reactors have recently been used by soil chemists to study soil chemical reaction... 

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