Reactor Engineering Flashcards
Design equation for batch reactor
dNa/dt = -ra .V
Where the negative sign is indictive of a reactant and dNa can be written as the differential of conversion (dNa = -Na0 . xa)
Under what conditions is the volume constant and if not how is it calculated?
When it is a liquid reaction it is considered constant volume. In cases where it is constant pressure, the volume is not constant. To calculate this volume you need the expansion factor ε = (-moles of reactants + moles of product)/(moles of reactant). Once this value is obtained the volume can be calculated as V = V0(1+εxa). Take into consideration that it affects the formula for concentration.
Design equation for CSTR reactor
ra =Fa0-Fa/V where the molar flowrate term can be replaced with concentration using volumetric flowrate.
Design equation for PFR
-dFa/dV = ra where the molar flowrate term can be replaced with concentration using volumetric flowrate. The negative sign is used as its a reactant.
How to calculate selectivity and use it to determine the maximum rate?
Instant selectivity = rate of desired product/rate of other products
Overall selectivity = molar flowrate of desired product/molar flowrate of other product
d/dCr (selectivity of p) = 0 allows us to determine the max production of p (by finding the conc of reactant needed). This doesn’t work for STR/PFR.
How to calculate yield
moles of reactant (r) reacted to form product (p)/total moles fed into system
Fp/Fr0
Equation for space time (Tau)
τ = V/v
where the curly v is the volumetric flowrate (v0 is a thing)
Effect of temperature in reaction
K = K0 × e-(E/RT)
Where K0 (A) is the pre-exponential rate factor.
Effect of temperature on heat of reaction
Multiple reactor design equations (CSTR + PFR) using a two reactor example
CSTR: V = (Fa1 - Fa2)/ra = Fa0(x2-x1)/ra
PFR: V = Fa0 x1∫x2 dxa/ra
Re-writting Fa in terms of conversion (differrential form included)
xa = (Fa0 - Fa)/Fa0
dFa = -Fa0 dxa
