Limits of operation for the integration of water removal by membranes and crystallization of L-phenylalanine

Integration of crystallization and water removal using membrane technology is being used as a means to improve control over supersaturation generation and, consequently, to improve crystal quality. However, it is not clear yet how water removal, which has a limited window of operation, can be combined with crystallization in case of occurrence of several crystal forms (and, therefore, also a limited window of operation). In this work we evaluated the use of nanofiltration and reverse osmosis for water removal to achieve selective crystallization of L-phenylalanine anhydrate from aqueous solution. Water removal and crystallization were first studied separately, and models were used to define the limits of operation for the coupled system so that the target crystal form and production rate could be achieved. A narrow window of operation was obtained, and it was shown that practical implementation can be difficult due to operation near the limits of the window of operation. Possibilities for widening the window of operation are briefly discussed.