The influence of solvent composition and process parameters on the particle properties of phytosterols in batch cooling crystallization

Phytosterols, which are utilized in the food, pharmaceutical, and cosmetics industries, are typically produced via a solvent cooling crystallization process from a variety of different vegetable oil and tall oil based feedstocks. When designing an industrial crystallization process, the chosen solvent system needs to generate a product within the targeted specifications (e.g., current focus on total phytosterol purity and profile) in addition to the process being techno-economically viable. The solvent system impacts the particle properties produced, which are important aspects for downstream processing. The current research focused on identifying the role of each solvent in the chosen solvent combination (ethyl acetate/methanol/water) in terms of the properties of the crystallized phytosterol products. The obtained products were analyzed by GC, SEM and laser diffraction. For the selected products crystallized using a ternary solvent system, the powder-XRD and TGA analyses were performed. The results showed that particles with different properties can be produced from the same commercial starting material using different solvent combinations. Crystal nucleation and growth occur through different mechanisms, following either a one-step or two-step crystallization. The solvent concentrations, especially the methanol and water ratios, as well as the kinetics, play an important role in modifying the crystal formation mechanism. Particle size distribution can be controlled further both by means of the cooling rate strategy and mixing. The ternary solvent system of ethyl acetate/methanol/water seems to be the preferred alternative in respect to the obtained product and mixing behavior.