Mathematical modeling and experimental coupling of solution layer crystallization on a vertically cold surface

Solution static layer crystallization is an effective technique that promises to overcome the challenges for the isolation, separation and purification of phenolic compounds that remained in treated Olive Mill Wastewater, after the application of a combination of other physicochemical separation processes. Crystallization in unstirred solutions is based on supercooling gradients of the different components in a liquid mixture. Due to the large number of experimental variables involved, a theoretical model was developed for the description of the system with the least possible variables. The mathematical model was compared with laboratory-scale experiments for the separation of a common phenolic compound, ferulic acid (FA), from aqueous solutions. Τhe transient profiles of the solution temperature and solute concentration were calculated numerically, solving a system of coupled partial differential equations, taking into consideration the mass and heat transfer and the crystallization kinetics. The determination of the crystal growth parameters was done by comparison of the experimental data with the values predicted by the model, for two different operational conditions. Knowledge of the solution temperature distribution allowed the determination of the solution saturation with respect to FA, which affects the crystal growth rate, the yield and the purity of the final product. The model can be further used to assist the optimization of the process design with respect to the product recovery and the duration of the process. Furthermore, despite the fact that the proposed methodology is validated at a preliminary level, focusing on the recovery of a single component from an aqueous solution, it could be served as the first step for the development of a more realistic model to predict the behaviour of a multi-component system.