Stirred-flow method

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... 

Data Analyses Using Continuous Flow and Stirred-Flow Methods... 

Since continuous flow and stirred-flow methods include a physical parameter, flow rate, data analyses used for batch techniques are inappropriate. 

In the original stirred-flow method (Denbigh, 1944), there were two or more openings for the flow of reactants and one opening for the flow of effluent. The effluent is a complex of reactants and products. With time, a steady state is established representing a balance between reactant additions in the influent and loss of reactant through reaction occurrence in the effluent. This steady state simplifies the mathematical treatment such that,... 

Equation (7.12) can be extended to more complex rate equations. Some of the advantages of the stirred flow method are (i) complicated rate expressions can be handled without integration, (ii) reaction can be carried out under constant conditions of solvent composition, ionic strength and transient intermediate can be built up in concentration, detected and measured. 

The rates of ion exchange for heterogeneous mixtures of ion exchanger may also be investigated in a stirred-flow cell. For a better understanding of the characteristics of the stirred-flow method, however, the results obtained for homogeneous systems are discussed briefly first [28]. This... 

The stirred-flow method is an integration of the best characteristics of continuous-how methods with the ability of batch methods to overcome diffusion effects. The system consists of a reaction chamber that can be stirred magnetically and is ported such that experimental solution can be howed thorough the reaction volume and hltered upon exiting the cell. Therefore, the system does not lose any particulate material and the experimental solution can be fraction collected for analysis. The only drawback with this method is the restricted data collection time (Sparks et al., 1996 Sparks, 1999, 2002). 

Stirred-flow methods have long been used by chemical engineers and chemists to obtain kinetic data in homogeneous sytems. They have only recently been used to obtain kinetic data in heterogeneous soil systems (Carski und Sparks, 1985 Randle and Hartmann, 1987 Miller et al., 1988 Seyfried Cl al., 1989). 

Seyfried et al. (1989) showed that the Carski and Sparks (1985) stirred-flow reactor is a well-mixed system in the flow velocity range of 0.28 to 2.20 mL min . A requirement of the stirred-flow method is that (he time-... 

As with the batch reactor method, radiotracers are an excellent means of following the extent of kinetic reactions in flow methods. Flow methods using radiotracers are identical to those where other analytical methods are used to determine the solute of interest except that a radiolabeled solute is used. Radiotracers have been used numerous times in column transport studies but apparently have not as yet been used with thin-disk and stirred-flow methods. 

In the stirred-flow method, time-dependent concentration curves for reactions must be distinguishable from the instantaneous reaction case and from the dilution curve obtained with no solid phase present. 

---