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Washing and Purification of Nitrated Aromatics

NORAM expertise in nitration technology extends to washing and purification of crude nitro-compounds. These treatments involve both standard and proprietary equipment and procedures. Today, more than half of the world's mononitrobenzene (MNB) supply is washed and purified using NORAM's technology. This success is a result of in-depth knowledge of the system chemistry and hydraulics, and attention to the engineering details of the process.

Process Description
The NORAM process for washing and purification of nitration products uses a combination of acid washers, alkaline washers, stripping columns, and a distillation column. The combination of the unit operations is dependent on the product specifications.

In the particular case of MNB, washing and purification consist of four steps, all of which are classical mass transfer operations. Firstly, the entrained mineral acids from the nitration process are removed from the crude MNB by extraction with water. This
washing stage combines both mixing, in a compact static mixer, and phase separation by gravity in a decanter.

Secondly, nitrophenols are removed from the MNB by reaction and extraction in a weak alkaline solution. This step may require
one or two washing stages depending on the product specifications. As is the case in the acidic washing stage, this step
combines both mixing, in a compact static mixer, and phase separation in a decanter.

Thirdly, the washed MNB is rinsed with water to remove residual traces of impurities. Subsequently, the MNB is introduced
to either a distillation column or a stripping column.

In a stripping column, the excess benzene is stripped and recycled back to the process. Product MNB, saturated
with water, is the end product.

In a distillation column, the excess benzene and soluble water are removed to produce a dry MNB product.

Key Features and Benefits of the NORAM Process
•  Mixing energy input has been optimized to meet mass transfer and gravity separation requirements.
•  Separation residence time has been optimized to minimize organic inventory within the plant.
•  An acid washer is used to segregate mineral acids from the nitrophenols in order to give maximum
   flexibility in effluent treatment options.
•  Inventory transfer is controlled through weir arrangement to increase maximum reliability