On-line moisture detection for a microwave vacuum dryer

Area of Science:

• Analytical Chemistry
• Process Engineering
• Spectroscopy

Background:

• Accurate determination of moisture content is crucial for optimizing drying processes.
• Traditional methods for moisture analysis can be time-consuming and may not be suitable for real-time monitoring.
• Microwave vacuum drying offers efficient water removal but requires precise endpoint detection.

Purpose of the Study:

• To develop and validate a near-infrared spectroscopy (NIR) method for real-time moisture endpoint determination in microwave vacuum dryers.
• To correlate NIR moisture measurements with established methods like Karl Fischer titration.
• To assess the capability of NIR spectroscopy in evaluating water homogeneity during the drying process.

Main Methods:

• Utilized a NIRSystems Model 5000 Analyzer with a fiber-optic probe for on-line spectral data collection.
• Developed a calibration equation based on absorbance measurements at 1410, 1930, and 1630 nm.
• Conducted drying studies in T.K. Fielder Spectrum 65 and Spectrum 1200 microwave vacuum dryers.

Main Results:

• NIR moisture determination correlated within 1% of Karl Fischer results for samples below 6% moisture (absolute SEP 0.6%, average residual -0.2%).
• Above 6% moisture, NIR results showed less correlation with Karl Fischer but effectively indicated water homogeneity.
• The developed NIR method enabled consistent prediction of the moisture endpoint.

Conclusions:

• Near-infrared spectroscopy is a viable tool for on-line moisture monitoring and endpoint prediction in microwave vacuum drying.
• The NIR method provides both quantitative moisture data and qualitative insights into water distribution, enhancing process control.
• This spectroscopic approach offers a significant advancement for optimizing industrial drying operations.