|Analysis Point||Analyte||Typ. Range||Suitable Analyzer|
|Polymerization Inhibitor||MEHQ||0-100 ppm||OMA Process Analyzer|
Polymerization inhibitors are chemicals which stabilize reactive monomers and prevent spontaneous polymerization. If too little inhibitor is added to a reactive monomer, polymerization can occur in pipes or vessels and require mechanical removal. On the other hand, if too much inhibtor is added, the final product may have difficulty polymerizing at the intended stage.
MeHQ is usually added as an inhibitor to acyrolinitrile (a precursor to polyacrylonitrile fibers for the textile industry). The concentration of MeHQ in the monomer needs to be regulated at approximately 100 ppm to avoid spontaneous polymerization (to polyacrylonitrile) as well as waste of MeHQ.
MeHQ has a distinct UV absorbance curve which allows the OMA system to easily monitor its real-time concentration. The full-spectrum analysis is critical for differentiating MeHQ absorbance from other absorbing impurities in the sample.
The OMA continuously outputs the MeHQ reading to the plant's main computer, providing new measurements at a 1 second interval for extremely tight process control.
Zeroing the system on pure acrylonitrile is highly impractical due to storage difficulty. Since water mixing with acrylonitrile leads to coating and miscibility effects, water is also not a zeroing option. Air has proven to be an effective and practical zeroing fluid when used with a proper sampling system that minimizes bubble formation.