Solvent-aided layer crystallization-Case study glycerol-water

Solid-layer melt crystallization with an additional assisting liquid medium, just like an extraction solvent, is introduced. A case study of the purification of glycerol from mixtures containing 1-10 wt% water and the use of 1-butanol as additional solvent assisting to control crystallization kinetics is presented. Cold finger experiments were carried out. It was found that in regular melt crystallization without the use of 1-butanol, water concentration could be reduced to 30-80 wt% in comparison to the residual melt at growth rates between 4×10−8 and 1.4×10−7 m/s, with lower growth rates resulting in lower water concentrations. No post-treatment like sweating or washing was applied. The dependence between purification success and growth rate could not be changed by initial water content or duration of the experiment and only little by agitation of the melt. The use of 1-butanol allowed an improvement of the process in terms of higher product purities and higher growth rates. Distribution coefficients improved by a factor of 2-4 without a loss in the growth rate or growth rates could be increased by a factor 5 without harming the separation quality. The influence of 1-butanol on the crystallization in comparison to that of water is further investigated. An understanding of how to use additional assisting solvents to control crystallization kinetics and to improve the separation is interesting for the purification of other components, especially high-viscous ones such as tocopherols or phytosterols as well.