Details

The pressure decreases down the length of the reactor, and thus the volumetric flow rate increases. As a result, the concentration of the reactant decreases (in addition to the decrease due to conversion), which lowers the rate of reaction.

The Ergun equation for pressure drop in a packed bed reactor (PBR) is:

,

,

,

where is pressure, is PBR length, is void fraction, is volumetric flow rate, is viscosity, is the diameter of catalyst particles, is cross sectional area of the PBR, is mass flow rate, is a laminar flow term, and is the turbulent flow term.

Material balance on reactant for a first-order reaction:

,

where is the molar concentration of reactant , is the molar flow rate of , is a rate constant, and is the inlet molar flow rate of .

Since the reaction is , and only is fed to the reactor, the total molar flow rate .

Volumetric flow rate in reactor (from the ideal gas law):

,

where is the ideal gas constant, and is absolute temperature.

Conversion of reactant:

.