NIR spectroscopy for monitoring of industrial manufacturing processes

When it comes to monitoring industrial manufacturing processes, near-infrared spectroscopy (NIRS) offers a rapid and reliable supplement to conventional titration methods. With NIRS, important process parameters can be determined directly and continuously, enabling comprehensive in-process control.

The determination of chemical indices is crucial in many chemical production processes, e.g., in the manufacture of polyols, resins, fats, oils, polymers, etc. Chemical indices such as

• Hydroxyl number
• Acid number
• Amine value
• Iodine value
• Peroxide value

are used for incoming goods inspections and final product testing. Random sample checks are made, primarily during production, and traditional wet chemistry analysis methods are used. Sample preparation is usually tedious, and the analyses require the use of expensive and sometimes hazardous reagents.

NIRS detects functional groups in the molecules, e.g., the OH bonds for determining the hydroxyl number. Absorption characteristics vary depending on the particular chemical index. NIRS provides this information immediately, enabling the monitoring of the production process in real time. NIRS provides reliable results even under extreme production process conditions, with no need for sample preparation or the use of reagents.

The analysis system is linked to the process via fiber optic cable and an in situ probe. Light in the near-infrared region (800-2,200 nm) interacts with the product, and this is measured; different probes can be selected depending on the process requirements. Up to nine sample streams can be monitored by a single system.

NIRS is a multi-component method, which means that several parameters can be monitored simultaneously in a single measurement. In addition to determining the oxygen number, for example, the water content and hydroxyl number can also be quantified.

Because NIRS is a secondary analytical method, customer-specific calibrations for the parameters to be analyzed are required. Metrohm provides both, NIRS as well as the wet chemistry instrumentation and methods to perform such calibrations. Moreover, Metrohm offers a host of applications enabling the determination of single or multiple chemical indices in very different products, e.g.: