Oiling-out crystallization of Beta-Alanine on solid surfaces controlled by solvent exchange

© 2020 Wiley-VCH GmbH In this work, the solvent-exchange crystallization processes of beta-alanine in mixture of isopropanol and water on solid surfaces are reported. As the antisolvent isopropanol displaces the alanine solution pre-filled in a microchamber, liquid–liquid phase separation occurs at the mixing front. The alanine-rich subphase forms surface microdroplets that subsequently crystallize with during the solvent exchange. It is found that the flow rates and solid surfaces have significant influence on the droplet size, growth rate, and crystal size and morphology. At fast flow rates, the droplets solidify rapidly, forming spherical-cap structures resembling the shape of droplets, in contrast to crystal microdomains or thin films formed at slow flow rates. On a highly hydrophilic surface, the crystals form thin film without droplets formation. It is further demonstrated that by the solvent exchange, the crystals, generated by using a stock solution with a very low concentration of the precursor, can be used as seeds to facilitate crystallization in bulk solution. The results suggest that the solvent exchange has the potential to be an effective approach for controlling oiling-out crystallization, and to be wider applied in, such as, separation and purification of many food, medical, and therapeutic ingredients.