Crystallization of lysozyme using different polymeric hydrophobic membranes

Membrane crystallization has been recently proposed as one of the most promising extension of the membrane distillation technology. This innovative technique makes use of the evaporative mass transfer of volatile solvents through microporous hydrophobic membranes in order to concentrate aqueous feed solutions above the saturation limit, thus attaining a supersaturated environment where crystals may nucleate and grow. In addition, the presence of a polymeric membrane increases the probability of nucleation with respect to other locations in the system (heterogeneous nucleation). Two different methodologies can be employed, depending on the strategy used to activate the driving force (a partial pressure gradient) for the selective extraction of the solvent. In osmotic membrane crystallization, the difference in activity of the two solutions induces a vapour pressure difference that generates the mass transfer from the dilute solution (containing the molecules of interest) towards the stripping solution. In thermal membrane crystallization, the membrane is in contact with the warm crystallizing solution at the retentate side and with a cold condensing solution at the distillate side, so that the driving force is generated by a temperature difference. The performance of membrane crystallization strongly depends on the properties of the microporous hydrophobic membranes used. A high hydrophobicity is required in order to prevent wetting and mixing between contacting phases, elevated porosity leads to high fluxes, low thickness decreases the membrane resistance. In this work, flat sheet membranes have been used in osmotic membrane crystallization for the crystallization of lysozyme. The effect of membrane hydrophobicity and membrane morphology on heterogeneous nucleation, evaporation rate, and morphology of lysozyme crystals, has been investigated