Acrylonitrile Application Note

Acrylonitrile is an important precursor in many plastic end-products. During its storage the pH value should be kept below 7.5 at all times. If the pH increases to higher values, acidification with acetic acid is immediately recommended to not risk explosions.

This application note explains the process of producing and storing acrylonitrile and how a continuous in-line pH measurement system from METTLER TOLEDO for monitoring storage is recommended to prevent explosions or combustion.

Acrylonitrile is produced through the ammoxidation process. Propylene, ammonia and air are brought into contact with a solid powder catalyst in constant mixing at high temperatures. This is accomplished in a fluidized-bed reactor, which keeps the mixture in a continual 'fluid' state to provide a large surface area for the catalyst. The product then goes through numerous separation steps involving absorbers and distillation columns to remove by-products such as hydrogen cyanide (HCN) and acetonitrile.

The final product is either stored as a bulk chemical or delivered to further bulk storage via pipeline, railcar, truck or ship. When in storage, the risk of polymerization and explosion or flammability risks must be considered. Certain conditions have to be controlled and action immediately taken if changes are observed. pH is one of the most important conditions when storing acrylonitrile. For this, METTLER TOLEDO has a monitoring system that consists of a pH sensor, an automatic cleaning and calibration system, a transmitter and a retractable housing.

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