Question 2 : Consider the following gas phase reactions: (flow reactor) Rxn 1 :

Question

Question 2 :

Consider the following gas phase reactions: (flow reactor)

Rxn 1 : A X

k1 = 0.004 (mol/dm3)1/2.min-1

Rxn 2 : A B - k2 = 0.3 min-1.

Rxn 3 : A Y

k3 = 0.25 dm3/mol/min

B is the desired product and X and Y are the foul pollutants that are expensive to get rid of. The

specific reaction rates are at 27 oC ( 300K).

The reaction system is to be operated at 27 oC and 4 atm.

Pure A enters the system at a volumetric flow rate of 10 dm3/min.

[a] Sketch the instantaneous selectivity ( SB/X and SB/Y and SB/(X+Y)) as a function of the

concentration in a CSTR.

The activation energy data for each reaction :-

E1 = 20000 cal/mol

E2 = 10000 cal/mol

E3 = 30000 cal/mol

[b] What temperature would you recommend for a single CSTR with a space time of 10

mints and an entering concentration of A, CAO = 0.1 mol/dm3.

Explanation / Answer

A ) The rate of nth order reaction can be represented as

This can be written as

Where           = Concentration of the reactant

n             = order of the reaction

k              = rate constant of the reaction

the units of rate constant can be found by rearranging the terms.

Hence the units of rate constant are

Given data

Reaction 1:

with rate constant

From the above generalized equation, the units of rate constant can compared to determine the order of the reaction

On comparing units of rate constant,

Hence the order of Reaction 1 is

Reaction can be written as

Reaction 2:

with rate constant

On comparing units of concentration,

1-n = 0

n = 1

Hence the order of reaction 2 is one and reaction can be represented as

Reaction 3

with rate constant

On comparing units of concentration,

1-n = -1

n = 1+1

n=2

Hence the order of reaction 3 is two and the reaction can be represented as

Now Instantaneous selectivity of the each of the terms can be calculated as per the definition.

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