Solid hollow fiber cooling crystallization

Solid hollow fiber cooling crystallization (SHFCC) is a new technique suitable for crystal size distribution (CSD) control of aqueous/organic systems from bench to industrial scale. Solid hollow fiber devices possessing good temperature control and operational flexibility can serve as seed/nuclei generators, stand-alone crystallizers, or supersaturation creation devices. Operating schemes implemented include feed recycling, once-through, and solid hollow fiber crystallizer-completely stirred tank (SHFC-CST) in-series operation mode. The performance of SHFCC of aqueous ICNOs solutions was assessed against mixed suspension mixed product removal (MSMPR) crystallizer data. Feed recycling and the once-through operation modes were similar and characterized by broader CSDs and lower reproducibility due to generation of a large number of fines causing slow filtration and localized growth on the filters. SHFC-CST in-series operation proved successful yielding narrow and reproducible CSDs with mean sizes between 100 and 150 μm, 3-4 times lower than those of MSMPR crystallizers. Also, 90% of the crystals were smaller than 370 μm compared to 550-600 μm for MSMPR crystallizers. Further, the number of crystals generated per unit volume was 2-3 orders of magnitude higher. SHFC-CST in-series crystallization of salicylic acid from ethanol solutions clearly showed that, unlike other membrane hollow fiber based crystallization techniques, SHFCC does not suffer any performance loss for organic systems.