Archimedes tube crystallizer: Design and characterization for small-scale continuous crystallization

Various continuous crystallizer concepts have been developed for the small-scale production (V˙≤100 mL min−1) of APIs and fine chemicals. The existing concepts differ in terms of achievable residence times and residence time distribution (RTD) width and can be classified qualitatively in a portfolio on the basis of these characteristics. The classification demonstrates, that it is still challenging to achieve long, flexible residence times in combination with narrow RTD width leading to narrow particle size distributions. Thus, an air-segmented coiled tube crystallizer was developed based on the Archimedes screw principle: The Archimedes tube crystallizer (ATC). In this device, coiled tubing is employed to convey individual fluid batches by rotation. Thereby, the air-segmented flow is generated by a specifically designed inlet tank mounted on the rotational axis. As a first step towards the implementation of the ATC concept in industry, characterization experiments were focused in this work. In a Design of Experiment, liquid phase RTD with tracer sodium chloride/water and solid phase RTD with material system L-alanine/water were investigated. The experimental results proved narrow RTD close to ideal plug flow for both liquid and solid phase over the complete operating window. Hence, the ATC represents a reasonable expansion of the continuous crystallizer portfolio.