Chapter 3 Example

Stoichiometric Table - Conversion

Let’s consider the production of ethyl benzene

The gas feed consists of 25% toluene and 75% ethylene. Set up a stoichiometric table to determine the concentrations of each of the reacting species and then to write the rate of reaction solely as a function of conversion. Assume the reaction is elementary with . The entering pressure is 8.2 atm and the entering temperature is 227°C and the reaction takes place isothermally with no pressure drop.

Hint 1: What is your basis of calculation?

Hint 2: What are the entering concentrations of ethylene and toluene?

Hint 3: What are e and d?

Hint 4: Write the row in the stoichiometric table for toluene.

Hint 5: Write the row in the stoichiometric table for ethylene.

Hint 6: Write the complete stoichiometric table including total molar flow rates.

Hint 7: Write the volumetric flow rate in terms of conversion.

Hint 8: Write the concentration of toluene and ethylene in terms of conversion

Hint 9: Write the rate of disappearance of A, –r_A solely as a function of conversion

Hint 10: What are the relative rates of reaction of A and B?

The stoichiometric ratio is one toluene to two ethylene (1/2). However, the feed is one toluene to three ethylene (1/3) and there is not sufficient toluene to consume all the ethylene. Therefore toluene is the limiting reactant and thus the basis of calculation.

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Let A = toluene,  B = ethylene, C = ethyl benzene and D = propylene

Ethylene:     

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Since toluene, i.e. A, is the limiting reactant and has a stoichiometric coefficient of 1

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                                                        Leaving F_B =

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Complete the stoichiometric table including coolant flow rates

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Write the volumetric flow rate in terms of conversion

                                                                P = P₀ and T = T₀

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In terms of conversion

For a flow system at constant T and P

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In terms of conversion

We now have –r_A solely as a function of X and can use the methods in Ch.2 to design reactors.

                                                       at

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