  We present a mathematical model for solvated crystallization of alpha
-lactose monohydrate in semi-batch mode. The process dynamics are governed by
conservation laws including population, molar and energy balance equations. We
present and discuss the model and then control the process with the goal to
privilege the production of small particles in specific the range. We compare
several specific and unspecific cost functions leading to optimal strategies
with significantly different effects on product quality. Control inputs are
temperature, feed rate, and the choice of an appropriate crystal seed.
