Introduction

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.

Measuring MeHQ (Polymerization Inhibitor)

Application Summary

Analytes hydroquinone monomethyl ether (MeHQ)
Detector OMA-300 Process Analyzer
Process Stream acrylonitrile
Zeroing Fluid air
Typical Measurement Range 0-100 ppm

Monitoring hydroquinone monomethyl ether (MeHQ) in Acrylonitrile

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 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 1-5 second intervals 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.

Absorbance Spectra of MeHQ in Acrylonitrile

These spectra were taken by the OMA-300 on calibration standard mixtures of MeHQ in Acrylonitrile:

Absorbance Spectrum of MeHQ in Acrylontrile

Absorbance Spectrum of MeHQ in Acrylontrile



1st Derivative of Absorbance Spectrum of MeHQ in Acrylontrile

1st Derivative of Absorbance Spectrum of MeHQ in Acrylontrile



The OMA readings on calibration standards correlate extremely well with lab readings:

The OMA readings on calibration standards correlate extremely well with lab readings

Application Data

The specifications below represent performance/build of the OMA-300 Process Analyzer in a typical MeHQ application.

For technical details about the OMA-300 Process Analyzer, see the data sheet:
DS-001A: OMA-300 Process Analyzer

All performance specifications are subject to the assumption that the sample conditioning system and unit installation are approved by Applied Analytics. For any other arrangement, please inquire directly with Sales.

Performance Specifications
Accuracy hydroquinone monomethyl ether
0-100 ppm: ±0.22 ppm

Note: Subject to modifications. Specified product characteristics and technical data do not serve as guarantee declarations.

Measuring TBC (Polymerization Inhibitor)

Application Summary

Analytes tert-butyl catechol (TBC)
Detector OMA-300 Process Analyzer
Process Stream Butadiene
Zeroing Fluid Pure isopropanol
Typical Measurement Range 0-200 ppm

Monitoring tert-Butyl Catechol (TBC) in Butadiene

TBC is usually added as a polymerization inhibitor to monomers like butadiene. The concentration of TBC in the monomer needs to be regulated at approximately 100 ppm to avoid spontaneous polymerization as well as waste.

TBC 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 TBC absorbance from other absorbing impurities like toluene.

Since pure liquid butadiene is very difficult to prepare for system blanking purposes (i.e. at normal temperatures and pressures), pure isopropanol is used to zero the instrument. The full-spectrum analysis allows for normalization of the discrepancy between the butadiene spectrum and the isopropanol spectrum.

The OMA continuously outputs the TBC reading to the plant’s main computer, providing new measurements at a 1-5 second interval — much faster than the traditional HPLC used for this application (15 minute interval). Response time is critical in order to respond quickly to sudden changes in TBC concentration.

Absorbance Spectra of TBC in Isopropanol

These spectra were taken on calibration standard mixtures of TBC in isopropanol.

spectra TBC

Application Data

The specifications below represent performance/build of the OMA-300 Process Analyzer in a typical TBC application.

For technical details about the OMA-300 Process Analyzer, see the data sheet:
DS-001A: OMA-300 Process Analyzer

All performance specifications are subject to the assumption that the sample conditioning system and unit installation are approved by Applied Analytics. For any other arrangement, please inquire directly with Sales.

Performance Specifications
Accuracy tert-butyl catechol 0-200 ppm: ±1 ppm

Note: Subject to modifications. Specified product characteristics and technical data do not serve as guarantee declarations.

Installation and Product Photos

Further Reading