In-line moisture monitoring in fluidized bed granulation using a novel multi-resonance microwave sensor

Microwave resonance technology (MRT) is known as a process analytical technology (PAT) tool for moisture measurements in fluid-bed granulation. It offers a great potential for wet granulation processes even where the suitability of near-infrared (NIR) spectroscopy is limited, e.g. colored granules, large variations in bulk density. However, previous sensor systems operating around a single resonance frequency showed limitations above approx. 7.5% granule moisture. This paper describes the application of a novel sensor working with four resonance frequencies. In-line data of all four resonance frequencies were collected and further processed. Based on calculation of density-independent microwave moisture values multiple linear regression (MLR) models using Karl-Fischer titration (KF) as well as loss on drying (LOD) as reference methods were build. Rapid, reliable in-process moisture control (RMSEP≤0.5%) even at higher moisture contents was achieved. [Display omitted] •Novel multi-resonance microwave sensor was used for determination of granule moisture.•In-line moisture determination above former limit of 7.5% and up to 14% residual moisture by MRT was feasible.•MRT method was correlated with conventional LOD and KF measurements.•A lean quantitative calibration by MLR could be established.•Novel, non-destructive moisture determination method is fast and independent from temperature and bulk density.