Continuous Crystallization Using Ultrasound Assisted Nucleation, Cubic Cooling Profiles and Oscillatory Flow

Continuous tubular crystallizers have the potential to reduce manufacturing costs and increase product quality. However, designing tubular crystallizers is a complex and challenging task as crystallization is a complex, multiphase process with a propensity for fouling and clogging. While several designs have been proposed to overcome these issues, these designs are either unproven or poorly scalable and complex. In this work a continuous crystallizer is designed and evaluated to mitigate these issues. The tubular crystallizer combines a novel method to obtain a cubic cooling profile to control the supersaturation, ultrasound to induce nucleation and oscillatory flow to improve mixing and minimize fouling and sedimentation. The results show that the crystallizer was able to operate for more than 4 h without clogging, with high yields and a narrow particle size distribution. The design proposed here is therefore considered a viable approach for continuous crystallizers.

Nucleation in continuous flow cooling sonocrystallization for coiled capillary crystallizers

Nucleation in continuously operated capillary coiled cooling crystallizers is experimentally investigated under the influence of ultrasound. It was found that there is no sharp boundary but rather a transition zone for nucleation under sonication. For this purpose, a tube with an inner diameter of 1.6 mm and a length of 6 m was winded in a coiled flow inverter (CFI) design and immersed into a cooled ultrasonic bath (37 kHz). The CFI design was chosen for improved radial mixing and narrow residence time distribution, which is also investigated. Amino acid l-alanine dissolved in deionized water is employed in a supersaturation range of 1.10 to 1.46 under quiet and sonicated conditions. Nucleation is non-invasive detected using a flow cell equipped with a microscope and camera. Graphical abstract Since the interest and demand for small-scale, continuous crystallization increases, seed crystals were generated in a coiled tube via sonication and optically investigated and characterized. No distinct threshold for nucleation could be determined in a wide range of supersaturations of l-alanine in water