Use of Continuous MSMPR Crystallization with Integrated Nanofiltration Membrane Recycle for Enhanced Yield and Purity in API Crystallization

If continuous processing is to be employed in pharmaceutical production, it is essential that continuous crystallization techniques can meet the purity and yield achievable in current batch crystallization processes. Recycling of mother liquor in steady state MSMPR crystallizations allows the yield in the equivalent equilibrium batch process to be met or exceeded. However, the extent to which yield can be increased is limited by the buildup of impurities within the system. In this study, an organic solvent nanofiltration membrane was used to preferentially concentrate an API (deferasirox, M.W. = 373 Da) and purge the limiting impurity 4-hydrazinobenzoic acid (MW = 152 Da) from the mother liquor recycle stream in a mixed solvent (THF:ethanol) antisolvent (water) system. Incorporation of the membrane recycle allowed yields of 98.0% and 98.7% to be achieved. This compares to the following; a control MSMPR run without a membrane (70.3%), an equivalent batch process (89.2%), and the current commercial batch process (92%). Comparable product impurity levels were measured for the following: the MSMPR membrane recycle experiments (0.15 ppm and 0.22 ppm), the MSMPR control (0.13 ppm), and batch (0.32 ppm) control experiments. All processes met the regulatory specifications of a maximum of 3 ppm of the impurity 4-hydrainobenzoic acid.