Production Units for Azo Pigment Manufacture by Batch Operation

The particle size of the resulting pigment can only be influenced to a limited extent by adjusting the reaction parameters, because the decisive factor is the ratio of the rate of formation of the crystal nucleus to the rate of crystal growth. 

Another variety of the continuous-coupling technique operates by transporting the coupling component suspension as a laminar flow upwards inside a vertical reaction tube. Portions of the diazonium compound, dissolved in an acidic aqueous medium, are added through appropriately located inlets in the walls of the reaction tube. The concentration of the added solution decreases as the reaction mixture flows upward and is designed to synchronize the uppermost inlet for the diazonium salt solution with the stoichiometric end point of the coupling reaction. 

Reliable measuring techniques [9] and appropriate process control are the basic elements of successful azo pigment synthesis by the continuous process. These are the parameters which are responsible for maintaining constant reaction conditions flow rate, pH, temperature, and the concentrations of the reactants, before and after the point of mixing itself. 

The dominant role of the batch operation over the continuous process throughout the pigment industry is somewhat in contrast to the patent literature, which includes numerous proposals for complete azo pigment manufacture by the continuous process as well as descriptions of the partial steps, such as the diazotization or the coupling reaction. 

6 Production Units for Azo Pigment Manufacture by Batch Operation 

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