Generated as a by-product of acrylonitrile manufacture, acetonitrile is used as a solvent in butadiene purification and as a component in batteries. The purity of acetonitrile must be verified to ensure suitability for these industrial uses.
The traditional offline method for acetonitrile quality control relies on pulling samples for lab analysis. The lab system compares the sample’s UV transmittance at a few wavelengths (220 nm, 240 nm, 275 nm, 350 nm) to that of demineralized water at the same wavelengths. Since pure acetonitrile has zero absorbance in the UV range, a simple principle applies: higher transmittance = higher purity.
The OMA system applies the same principle but with enormous advantages, including: (1) continuous analysis updating every 1-5 seconds, as opposed to slow sample transport for discrete lab measurements; (2) fast response for immediately pinpointing changes in stream purity; (3) totally automated sampling system normalizes measurement by Auto Zero; (4) installation of system close to sampling point for convenience of process adjustment.
The transmittance at 220 nm of various acetonitrile samples is shown below in spectra and table form.
Some applications call for purity in the 99-100% transmittance range. Verification requires extremely accurate measurement.
Transmittance measurement requires extremely stable wavelength accuracy. If the diode drifts wavelength assignment, significant measurement error is introduced. Mechanical scanning instruments with filters have moving parts that wear over time and lose wavelength assignment. The solid state OMA uses a photodiode array for extremely stable accuracy.
Since the OMA performs continuous analysis of acetonitrile purity, trend data is available to the operator with easily configured data storage to view process history.
The specifications below represent performance of the OMA-300 Process Analyzer in a typical acetonitrile purity 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.
|Accuracy||Acetonitrile Transmittance at 220 nm
@ 80-100 %T measurement range: ±0.3 %T
Note: Subject to modifications. Specified product characteristics and technical data do not serve as guarantee declarations.