Inline Real-Time Near-Infrared Granule Moisture Measurements of a Continuous Granulation–Drying–Milling Process

The purpose of this research was to use inline real-time near-infrared (NIR) to measure the moisture content of granules manufactured using a commercial production scale continuous twin-screw granulator fluid-bed dryer milling process. A central composite response surface statistical design was used to study the effect of inlet air temperature and dew point on granule moisture content. The NIR moisture content was compared to Karl Fischer (KF) and loss on drying (LOD) moisture determinations. Using multivariate analysis, the data showed a statistically significant correlation between the conventional methods and NIR. The R2 values for predicted moisture content by NIR versus KF and predicted moisture values by NIR versus LOD were 0.94 (p < 0.00001) and 0.85 (p < 0.0002), respectively. The adjusted R2 for KF versus LOD correlation was 0.85 (p < 0.0001). Analysis of the response surface design data showed that inlet air temperature over a range of 35–55°C had a significant linear impact on granule moisture content as measured by predicted NIR (adjusted R2 = 0.84, p < 0.02), KF (adjusted R2 = 0.91, p < 0.0001), and LOD (adjusted R2 = 0.85, p < 0.0006). The inlet air dew point range of 10–20°C did not have a significant impact on any of the moisture measurements.