Drying end-point

Given that the introduction of solvent obviously produces wet granules, the wet granulation process includes a drying step. Drying typically occurs in a fluid bed dryer. But there are other options, such as microwave vacuum dryers. In 1994, White applied on-line NIRS to monitor moisture content and predict drying end point in two TK Fielder microwave dryers. The NIR spectral data were correlated to off-line Karl Fischer measurements which resulted in a standard error of prediction equal to 0.6% when the samples... 

Gieseler et al. utilized tunable diode laser absorption spectroscopy to detect water vapor concentrations, gas velocities and mass flow during freeze-drying of pure water at different pressure and shelf temperature settings and of a 5%w/w mannitol solution. The analyzer was interfaced to the spool that connected the dryer chamber to the condenser. The reported method was advantageous in that primary and secondary drying end-point control based upon mass flow rate was independent of freeze-dryer size and configuration. ... 

Based on these data try to fix a drying end point of the process (e.g., correlation between moisture content of the product and the product bed temperature). 

Andersson M, Folestad S, Gottfires J, Johansson MO, Josefson M, Wahlund KG. Quantitative analysis of film coating in a fluidized-bed process by in-line NIR spectroscopy and multivariate batch calibration. Anal Chem 2000 72 2099-2108. Vazquz Elizabeth Rivera Master of Science Thesis, Optimization of Drying-end-points. Measurements for the automation of a fluidized-bed dryer using FT-NIR Spectroscopy, Univ of Puerto Rico, 2004. 

This modeling becomes important as a soft-gel product is being developed and a drying end point needs to be established and reproduced. 

Vazquz ER. Optimization of Drying-End-Points Measurements for the Automation of a Fluidized-Bed Dryer Using FT-NIR Spectroscopy. M.S. Thesis, University of Puerto Rico, 2004. 

When microwave processors were first introduced, there was the expectation that E-lield would be a reliable indicator of the drying end point. With experience, users found that the E-lield tends to be too variable, and now view it primarily as a safety feature monitoring the microwave field within the drying cavity. Most microwave driers on the market today do not even include E-field monitoring any more, because of the difficulties with validation of this system. 

Product temperature, time, cumulative forward power, and reflected power are proving to be more reliable indicators of drying end point with verification by some... 

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