Impact of Mother Liquor Recycle on the Impurity Buildup in Crystallization Processes

Abstract

Reusing the mother liquor fraction in crystallization processes significantly increases the product yield but also leads to an accumulation of impurities. In this work, we investigated how a mother liquor recycle operation affects the crystallization of paracetamol as a result of the gradual buildup of the impurity 4-nitrophenol. The results show that the rate of impurity buildup decreases with increasing number of cycles until the amount of the impurity remains the same. The number of cycles required to reach the steady state increases when larger fractions of mother liquor are reused. A simple model was used to describe the impurity buildup and to estimate the largest possible mother liquor recycle fraction required to obtain the maximum achievable product yield while still maintaining the desired product specifications. The presented work shows how to optimize mother liquor recycle conditions that will lead to enhanced process efficiency by reducing product and solvent waste.