Elements of
Chemical Reaction Engineering
6th Edition



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Essentials of
Chemical Reaction Engineering
Second Edition

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Chapter 9: Reaction Mechanisms, Pathways, Bioreactions and Bioreactors

Example 9.6: Reasons for "f" less than 1.0

1. Chain transfer to initiator

However, even though a radical is generated, this reaction does result in a wastage of initiator, there is no increase in the number of radicals or the amount of monomer being converted to polymer.

2. Side reactions

Cage effects

                      [     ]

Most significant reaction in the cage is

[        ] = cage where radicals are held for some time before they diffuse out. Once outside the cage the radicals can react with monomer [2 f COO•] 2 f COO•

Other reactions

of secondary importance

Average lifetime of neighboring radicals is 10–10 to 10–9 seconds with kf = 107 dm3/mol/s

In the cage:

The concentration of radicals in the solvent cage ~ 10 mol/dm3

Out of cage:

CMonomer = 0.1 to 10 mol/dm3

CR1 = 10–9 to 10–7 mol/dm3

3. Recombination of primary radicals has no effect on initiator efficiency



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