Solid Processing

The options described next can prevent pollution generated in solid processing.

Optimizing Crystallization Conditions

A company should optimize crystallization conditions to (1) reduce the amount of product lost to the mother liquor and cake wash and (2) obtain the necessary crystal size. A crystal size that is too small needs recrystallization; a crystal size that is too large needs milling. A common practice is to add small crystals known as seeds into the solution immediately before incipient crystallization.

Using Multiprocessors

New reactor-filter-dryer systems can handle more than one operation in the same vessel, thus minimizing transfer losses.

Coupling the Centrifuge and Dryer

With this option, the solid is separated, washed, and dropped into the dryer to minimize transfer losses. A company can also use an easily emptied, bottom-discharge centrifuge.

Using Bag Filters

A company should consider the use of bag filters instead of cartridge filters. Products can be recovered, and the bags can be washed and reused, while used filter cartridges must be disposed.

Installing a Dedicated Vacuum System

This option can be used to clean spilled powders for companies producing dry formulations.

Minimizing Wetting Losses

To minimize wetting losses, a company can modify the tank and vessel dimensions to reduce contact (e.g., the use of conical vessels).

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