Continuous Membrane Crystallization
Membrane processes meet the requirements of Process Intensification since they have the potential to replace conventional energy-intensive techniques, to accomplish the selective and efficient transport of specific components, and to improve the performance of reactive processes. In this framework, the innovative concept of Membrane Crystallization – integrating the principles of diffusive mass transfer through microporous hydrophobic membranes and the theory of heterogeneous nucleation promoted by foreign interfaces – offers unprecedented opportunities to overcome the limits of traditional crystallization devices. Many variants of Membrane Crystallization technology exist; in the most investigated and promising configurations, microporous hydrophobic membranes are used to precisely control the evaporation rate of volatile solvent from the crystallizing solution and, ultimately, the supersaturation level. In addition, physico-chemical characteristics of the membranes such as porosity, roughness, surface energy and chemistry of the surface influence significantly the kinetics of crystallization, leading to interesting advantages such as polymorph selection, reduced induction time in protein crystallization, modulation of crystal morphology and narrow crystal size distribution. This chapter provides a general overview of Membrane Crystallization principles, including mass transfer and nucleation phenomena, and reviews the main applications so far explored.