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Lecture 11 : Isothermal Reactor Design

Analytical solution

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The second order isothermal reaction in a PBR

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Analytical so lution

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Example: Effect of Pressure Drop on theConversion Profile

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Cont’d

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Solution

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Cont’d

(b)

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Cont’d

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(c)

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Example: Calculating X in a Reactor with PressureDrop

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We want to calculate the catalyst weight necessary to achieve 60%conversion when ethylene oxide is to be made by the vapor-phasecatalytic oxidati on of ethylene with air.

Ethylene and oxygen are fed in stoichiometric proportions to a packed-bedreactor operated isothermally at 160 C. Ethylene is fed at a rate of 0.30 Ibmol/s at a pressur e of 10 atm. It is propos ed to use 10 banks of 1.5 in diameter schedule 40 tubes packed with catalyst with 100 tubes per bank.Consequently, the molar fl ow to each tube i s 3 X 10 -4 lb mol/s. The propertiesof the reacting fluid are to be considered identical to those of air at thistemperature and pressure. The density of the 0.25 in catalyst particles is 120lb/ft 3 and the bed void fr action i s 0.45. The rate law is:

Solution

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X=60% W=44.5 lb

Mole Balance in terms of Concentration and

Molar Flow Rates

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Membrane reactors and multiple reactions in gasphase: Molar flow rates are preferred .

Concentration for liquids and molar flow rate for gases as dependent variable

In molar flow rate/concentration algorithm, we

need to write mole balance for each and everyspecies.

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Step 1: Mole balance on all species

Step 2: Rate law

Step 3: Relate mole balances to one another

Steps 4 and 5: Relate the concentrations to the

molar flow rates

Step 6: Combine all steps by ODE solver

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0

0

0

0T

T

P

P

F

F

T

T

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Mole Balances on CSTRs, PFRs, PBRs, and BatchReactors

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L iqu id Phase: no volume change.Concentration is the preferred variable.

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For a plug flow reactor:

Gas Phase: The molar flow rates are preferred.

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Example: Gas-Phase Reaction in aMicroreactor

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Solution

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