
Crystallization
Crystallization processes play a role in many industries, and are applied for manufacture of commodities (e.g. inorganic salts) and fine chemicals, as pharmaceuticals, food and agrochemicals. The two general objectives of crystallization processes are, first, separation and purification of substances, and, second, production of particles of desired properties, as for example a definite particle size distribution. Often both objectives are combined and the crystallization step within the industrial (synthesis – separation –formulation) process chain has to fulfill several tasks simultaneously.
On that basis the goal of the projects in the crystallization team are directed to deeper understand, design and optimize crystallization-based processes aiming to isolate pure target compounds from mixtures while keeping control of the particulate properties of the compounds as well. Those mixtures might be composed of only two very similar components, as enantiomers in a racemic mixture, or contain a multitude of constituents, as it is the case in plant extracts or synthesis mixtures (Figure below).

To address such separation tasks the underlying phase equilibria and crystallization kinetics need to be determined. Based on this key information, separation processes are derived and their applicability and performance verified. In the work we focus on developing novel and advanced variants of separation processes that facilitate to produce pure compounds at desired target properties as well as process characteristics (yield, productivity) considering batch, semi-continuous and continuous operation modes. Model and industrially-relevant example systems investigated range from enantiomers, over inorganic salts to the isolation of fine chemicals from plant- based extracts and particulate lignin from wood-based black liquors.
Various batchwise and continuously operated crystallization facilities from a couple of mL’s up to 20 L reactor volume are applied. The reactors can be equipped with various in- and online measurement techniques to follow separation progress and particle evolution by analyzing temperature, solution concentration (supersaturation), enantiomeric excess, particle size etc.
Three selected subjects will be described in more detail in the following:
- Separation process design
- Coupling reaction and crystallization
- Natural products separation and valorization
These tasks are handled interdisciplinary in different research groups of the Max Planck Institute and in cooperation with companies and universities.