Flow regime Differential reactor

Unlike porous pellets, it is mathematically feasible to account for chemical reaction on the well-defined catalytic surfaces that bound the flow regime in regular polygon duct reactors. A qualitative description of the boundary conditions is based on a steady-state mass balance over a differential surface element. Since convective transport vanishes on the stationary catalytic surface, the following contributions from diffusion and chemical reaction are equated, with units of moI/(areatime) ... 

CPBR behavior under pseudo-steady-state and plug-flow regime is described by the resolution of the system of differential Eqs. 5.76 and 5.79. This model was experimentally validated in a laboratory packed-bed reactor with chitin-immobilized... 

To determine the kinetic parameters, we use the differential reactor. In this continuous flow system, the variation in concentration between the inlet and outlet of the reactor should be small and finite. The conversions should be around 5-10%. Under these conditions, the diffusive and mass transfer effects are avoided, assuring a kinetic regime for the determination of the kinetic parameters. Unlike the case of the batch system, the spatial time and consequently, the inlet flow and the mass or volume of the reactor are varied. Therefore, the reaction rate is directly determined. 

From Figure 23.12, we can see that in spite of using a high space velocity and catalyst bed diluted, the sample showed a very high conversion in the first hour and drops considerably after some time of reaction, stabilizing it at around 10%. After 48 h of reaction, the flow was increased and the conversion decreased proportionally. This suggests that the system operated in the kinetic regime, i.e., in the absence of diffusion effects in a differential reactor. 

In principle, epi reactors that operate in the diffusion-controlled regime could be designed by solving the partial differential equations governing the fluid dynamics16 17 so that deposition rates could be predicted. In fact, such a procedure is generally not followed, since experimental evaluation of the flow behavior seems to be preferred.18... 

The concentration and therefore the molar flows and reaction rate vary along the reactor. The differential balance is performed, starting from Equation 4. Considering a permanent regime for simplification, as in the previous case, we obtain Scheme 4.2 ... 

In the case of transient operation, an accumulation term, that is, a differential term with respect to time, has to be added to equations 79 and 80 for being able to describe the observations. A batch reactor with uniform concentrations throughout the entire reactor but without continuous feed addition and effluent removal, is inherently operating in a transient regime. The corresponding reactor model equation is analogous to that of a plug flow reactor with the derivative taken with respect to time rather than with respect to position ... 

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