Problem
A semi-batch stirred tank reactor produced an excess of polymeric by-products. The client thought this was due to their own poor scale up.

Objective
Provide consultancy to reduce by-product formation.

Approach
The client provided a reaction scheme with the chemical names replaced by letters to ensure complete confidentiality. Properties of the reactants (density and viscosity) were also provided, along with details of the reactor geometry and operation. The reaction scheme, reactor design and mixing in the vessel were thoroughly studied.

Results
The client's scaling was found to be correct Mixing of a low density feed to the liquid surface was found to be the problem The feed arrangement was modified such that:

• Problem feed was fed to impeller region
• No back-mixing, and hence by-product formation, was possible in the dip-pipe
• Results were successfully implemented by the client.

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