A mathematical model based parametric sensitivity analysis of an evaporative crystallizer for lactose monohydrate

• We model an evaporative crystallizer producing lactose monohydrate.
• We study the sensitivity of the crystallizer to different operating and kinetic parameters.
• Secondary nucleation most affected the crystal size produced by the crystallizer.
• The model was validated using industrial data.
• Design and operational guidelines for evaporative crystallizer were laid down.

Lactose is produced from whey by crystallization after a series of concentration steps. Evaporative crystallization is the process where both concentration and crystallization occur simultaneously. There is no current literature on an industrial scale evaporative crystallizer producing lactose monohydrate. Crystal size is the most important output parameter for the lactose crystallization process. In order to understand the effect of various operational and kinetic parameters on the final crystal size coming out of the crystallizer, a mathematical model was developed to mimic the operation of the industrial unit. The model includes mass and crystal population balances along with mutarotation and nucleation kinetics for lactose. A sensitivity analysis was conducted by simulating the developed model for a range of values for parameters like residence time, evaporation rate, crystallizer temperature and growth and nucleation kinetics. It was found that the secondary nucleation rate was the factor most affecting the crystal size. The crystal size and dissolved lactose data from the industrial unit were collected and fitted to the model predictions to estimate the crystallization kinetics of lactose in the industrial unit. Based on the simulation results, operational and design guidelines for an evaporative crystallizer were laid down.