Inline process monitoring of moisture content in tetrahydrofuran

Significance of Topic

The use of recovered solvents is crucial to reduce costs and environmental impact in chemical and pharmaceutical production processes.
Maintaining low moisture levels in tetrahydrofuran (THF) is critical because water impurities can disrupt chemical reactions and degrade product quality.

Objectives and Study Overview

The study aims to implement and validate a near-infrared spectroscopy (NIRS) method for inline, real-time monitoring of trace moisture in THF streams.
It compares NIRS predictions against traditional Karl Fischer titration over a moisture range of 20–500 mg/L.

Methodology and Used Instrumentation

The analytical setup employs a 2060 The NIR-REx Analyzer capable of explosion-proof operation in ATEX environments.
Key features include:

• Five independent probe channels for in-situ measurements via fiber optics or flow cells
• Purge/pressurization system to prevent ingress of hazardous vapors
• Remote human interface module separated by optical fibers

THF samples were circulated through a 10 mm Hellma flow cell in transmission mode. Spectra were acquired from 1000 to 2250 nm with data processed in OMNIS software.
A partial least squares (PLS) calibration model with two factors was developed using 28 calibration samples and validated with 10 external samples.

Main Results and Discussion

The NIRS model achieved an R2 of 0.999, indicating excellent correlation with Karl Fischer titration.
Performance metrics included a standard error of calibration (SEC) of 3.79 mg/L, cross-validation error (SECV) of 4.01 mg/L, and prediction error (SEP) of 5.19 mg/L.
This level of precision demonstrates that inline NIRS can detect moisture in the low ppm range, matching laboratory-based reference methods while providing immediate feedback.

Benefits and Practical Applications

• Non-destructive, reagent-free analysis that eliminates sample handling
• Continuous, real-time monitoring reduces downtime and prevents out-of-spec batches
• Enhanced process control improves product consistency and shelf life
• Streamlined operations lower hazardous waste disposal costs and operator exposure

Future Trends and Potential Applications

• Expansion of NIRS models to multi-component streams, tracking additional impurities simultaneously
• Integration with process control systems for automated feedback loops and adaptive process adjustments
• Development of portable or miniaturized NIR probe designs for decentralized monitoring
• Application of advanced chemometric methods, such as machine learning, to further refine prediction accuracy

Conclusion

Inline NIRS on the 2060 The NIR-REx Analyzer provides a robust, accurate, and rapid solution for measuring low levels of moisture in THF.
It bridges the gap between time-consuming laboratory titration and modern process analytical technology, enabling cost savings, improved safety, and superior quality control.

References

• 1. Tetrahydrofuran (THF) Market; CH 6125; Markets and Markets, 2018.