Real reactors mean conversions

Segregated Flow A real example is bead polymerization of styrene and some other materials. The reactant is in the form of individual small beads suspended in a fluid and retarded from agglomeration by colloids on their surfaces. Accordingly, they go through the reactor as independent bodies and attain conversions under batch conditions with their individual residence times. This is called segregated flow. With a particular RTD, conversion is a maximum with this flow pattern. The mean conversion of all the segregated elements then is given by... 

Example 13-6 Mean Conversion Calculations in a Real Reactor... 

From Eq. (2), the measured diffusivities may be used to determine the mean lifetime of the reactant and product molecules within the individual crystallites under the assumption that the molecular exchange is exclusively controlled by intracrystalline diffusion. These values, being of the order of 30 ms, are found to agree with the real intracrystalline mean lifetime directly determined by NMR tracer desorption studies (208], so that any influence of crystallite surface barriers may be excluded. From an analysis of the time dependence of the intracrystalline concentration of the reactant and product molecules, the intrinsic reaction time constant is found to be on the order of 10 s. This value is much larger than the intracrystalline mean lifetimes determined by PFG NMR, and thus any limiting influence of mass transfer for the considered reaction may be excluded. In agreement with this conclusion, the size of the applied crystallites was found to have no influence on the conversion rates in measurements with a flow reactor (208]. 

Following the model of parallel arranged plug flow reactors, the mean conversion in a real reactor can be estimated with Equation 3.64... 

Calculation of the conversion in a real isothermal reactor by means of the tanks-in-series model is straightforward. Based on a step or pulse input experiment, we get directly either the F or the E function of a real reactor. We just have to compare the measured function with the solutions given in Figures 4.10.49-4.10.52, and determine the hypothetical number N of CSTRs of our real system by the best fit of... 

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