Plug-Flow Reactors: Species Balances, RTD, and Axial Dispersion

All flashcards

What is an ideal plug flow reactor (PFR)?

A continuous-flow model with perfect radial mixing, no axial mixing, and fluid progressing through the reactor in sequence.

What differential equation describes the steady-state concentration of species $i$ in a PFR?

$u\frac{dC_i}{dx}=\nu_i r$, where $u$ is linear velocity, $\nu_i$ is the stoichiometric coefficient, and $r$ is the volumetric reaction-rate term.

How does concentration vary with residence time for an isothermal, irreversible first-order reaction?

For the stated assumptions, $C_A=C_{A0}e^{-k\tau}$.

What does the E-curve represent in a tracer experiment?

The normalized distribution of fluid exit times; its area is one.

What does the Peclet number compare in the axial dispersion model?

Convective transport with axial dispersion; $P_e=LU/D_L$.

Quiz questions

1. In a PFR species balance, what does the sign of a stoichiometric coefficient indicate?Answer: Whether the species is consumed or produced by the reaction.
2. For an isothermal, irreversible first-order reaction with constant velocity, what is the reactant concentration at position $x$?Answer: $C_A(x)=C_{A0}e^{-kx/u}$
3. What is the total area under a normalized E-curve, $E(t)$?Answer: One, since the curve is normalized as an exit-time distribution.
4. For an axial dispersion model, which expression defines the Peclet number?Answer: $P_e=LU/D_L$
5. What is channeling in a non-ideal reactor?Answer: Preferential flow of fluid along some paths through the reactor.